Abstract:
Taught is motor vehicle door latch with at least one locking mechanism ( 1, 2 ) comprising a catch ( 1 ); a pawl ( 2 ); a friction brake device ( 10 ); an end stop ( 13 ); and at least one cam ( 14 ). The friction brake device ( 10 ) cooperates with the cam ( 14 ) during the closing movement of the locking mechanisms ( 1, 2 ) and shortly before said friction brake device ( 10 ) reaches the end stop ( 13 ). The cam ( 14 ) and the catch ( 1 ) each comprise means for reducing noise associated with the closing movement of the locking mechanisms ( 1, 2 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a National Stage Application of International Patent Application No. PCT/DE2006/000982, with an international filing date of Jun. 8, 2006, which is based on German Patent Application No. 10 2005 027 734.9, filed Jun. 16, 2005. The contents of both of these specifications are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a motor vehicle door latch with at least one locking mechanism comprising a catch and a pawl and a flexible friction brake device for the locking mechanism that, as part of a closing movement of the locking mechanism only becomes effective shortly before reaching a rigid end stop, in which the locking mechanism comprises at least one cam in reciprocal action with the friction brake device as it assumes its closing position. 
     2. Description of the Prior Art 
     In motor vehicle door latches, as described for instance in DE 44 20 185 A1, the friction brake device ensures that the impact noise of the catch when coming into contact with the end stop, is effectively reduced. For this purpose, DE 44 20 185 A1 provides a cam on the catch or forked catch, with the friction brake device being designed as a leaf spring protruding in the path of movement of the cam shortly before reaching the closing position of the forked catch. This leaf spring slows down the catch as desired. It can, however, be improved with regard to its acoustic behavior. At this point, noise can still be expected, as the steel forked catch comes into contact with the leaf spring made of the same material. 
     DE 196 52 012 A1 also uses a leaf spring as a friction brake device. In this case, the main objective is, however, the prevention of the opening noises and not of the closing noises. 
     Finally, DE 43 03 532 C2 discloses a motor vehicle door latch in which the catch contains a conical, oval recess forming the friction brake or friction brake device, into which a tapered, oval section of a cover plate of the door latch engages. This type of device is particularly difficult to produce from a manufacturing point of view. The produced noise is also at a level that is not advantageous. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention is based on the technical problem of further developing a motor vehicle door latch of the aforementioned design, which while being of a simple design, considerably reduces the produced noise relative to conventional designs. 
     In order to solve this technical problem, the invention suggests a generic motor vehicle door latch in which the cam is designed to be noise reducing. Preferably, the catch is also designed to be noise reducing, although such a design is not mandatory. 
     It has shown to be advantageous for the cam to be located on the catch and at the same time being a part of a coating of the catch. Consequently, the cam and the catch are automatically designed to be noise reducing. In this way, noises of the locking mechanism are reliably suppressed, in particular during the closing and the opening. This is because the cam acting upon the friction brake device is acoustically-uncoupled by its plastic coating. This applies in particular when the friction brake device is, for instance, made from steel or is generally made from metal. The same applies to the catch and the end stop, made for instance of steel. As catches in any case increasingly often contain a coating for acoustic reasons, the cam can be easily defined in this coating. This keeps production costs to a minimum, whilst keeping the construction simple. 
     The invention also embodies the option of producing the cam and the friction brake device in one and the same piece. In this context, it is also advantageous to design the friction brake device as a buffer pocket with a buffer lip and the connected cams, where applicable, which are also part of the plastic coating of the catch. Where the buffer pocket contains the cam which in turn is in reciprocal action with the end stop in the frame box, the cam and the friction brake device can be more or less produced as one part. 
     In an alternative embodiment, the cam and the friction brake device are, however, designed as separate units. In this case, the friction brake device on the latch housing and/or on the locking mechanism is arranged independently from the cam. The friction brake device can be designed as a single component together with the latch housing and/or the locking mechanism and/or a part of the latch housing and or the locking mechanism. Where the latch housing is made of plastic, it is recommended, in this context, to also use a plastic friction brake device and to form or spray it onto the latch housing. 
     It is also particularly advantageous to design the friction brake device as a spring lip in reciprocal action with the catch as part of its closing movement. This spring lip is therefore preferably made of plastic. It normally has a shape, surrounding the cam on the locking mechanism or the catch, and generally when the locking mechanism or the catch is in the closing position or in the so-called overtravel position. This overtravel position corresponds with the catch bolt engaging in a feed-in mouth of the catch, moving said catch past the primary position of the closing operation. This can occur manually by an operating person or by motorized means, by for instance an assisted door closing system. 
     Such an overtravel is generally required to ensure a reliable engagement of the pawl in the primary position of the catch, taking into consideration the tolerances required for the closing movement. The motor vehicle door latch contains an end stop for limiting the overtravel. As a result of the friction brake device surrounding the cam—in reciprocal action with said device—in the overtravel position or the cam generally not being effective in the overtravel position, e.g. the friction brake device is not acted upon, the catch is hardly or not at all slowed down by the friction brake device in this position. In this way, resetting forces created anyway with the overtravel due to elasticities inevitably present, such as a rubber door seal, ensure that the locking mechanism or the catch are pushed back into the primary position. During this process, the friction brake device is not active or is hardly active, or there is no reciprocal action, or only a weak reciprocal action, between the cam and the friction brake device. 
     Otherwise, the friction brake device generally increasingly builds up resetting forces as the closing distance increases. This is intentional in order to provide increased braking of the catch bolt engaging in the catch. In this context, the locking mechanism ensures that the friction brake device is increasingly deformed as it assumes its closing position. This is ensured by the cam in reciprocal action with the friction brake device, which with its eccentric shape increasingly acts upon the friction brake device up to the primary position, with the deformation forces, which act on the friction brake device in the connected overtravel area and which are produced by the cam, being reduced. 
     The result is a motor vehicle door latch that is advantageous because of its well-contrived noise characteristics and simple design. This is, first of all, achieved with the friction brake device, braking the locking mechanism and thus the catch bolt moving into the catch as it assumes its closing position (in most cases the primary position). The locking mechanism and its cam with its eccentric shape actually ensure that the friction brake device is increasingly acted upon during the closing operation, resulting in increasing mechanical friction and thus braking forces. 
     After passing the primary position and thus being present in the overtravel area, the cam and the friction brake device ensure that the frictional forces produced as a result are reduced to a minimum. As a result, the then effective resetting forces can easily return the locking mechanism into its primary position after the pawl has been perfectly engaged. All advantages can, of course, also be gained when the pawl engages in the intermediate closed position, or, also, when the cam is positioned on the pawl instead of on the catch, which in this case will be covered by a coating. Generally, this can, of course, be advantageous for any motor vehicle door latch, for instance not only those used on side doors but also for those used on tailgates, motor hoods, etc., also falling under the generic term of vehicle door latch as used in this application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, the invention is explained in more detail with reference to a drawing showing only one embodiment, in which: 
         FIGS. 1 and 2  show two different views of a first embodiment of the motor vehicle door latch according to the invention in an open position, 
         FIGS. 3 and 4  show the motor vehicle door latch according to  FIGS. 1 ,  2  on the way towards the primary position, 
         FIG. 5  shows the motor vehicle door latch according to  FIGS. 1 to 4  in the overtravel area, 
         FIG. 6  shows an alternative embodiment on the way towards the primary position, 
         FIG. 7  shows the object according to  FIG. 6  in the primary position, and 
         FIG. 8  shows the object according to  FIGS. 6 and 7  in the overtravel area. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The figures show a motor vehicle door latch whose general design consists of a locking mechanism  1 ,  2  comprising a catch  1  and pawl  2 . In this embodiment, the pawl  2  is located on an actuating lever  3  although the invention is not restricted to this arrangement. Any pulling movement on this actuating lever  3  in the direction shown in  FIG. 4  causes the pawl  2  to release the catch  1  from the shown primary position and the catch to be displaced counter-clockwise with the aid of a spring, as also shown by the arrow on the catch  2  in  FIG. 4 , with the catch  1  revolving around its axis  4 . Catch  1  and pawl  2  as well as the actuating lever  3  are accommodated together in a frame box  5 , which is only indicated. 
     In addition to the frame box  5 , a latch housing  6  is provided, of which only certain individual parts can be recognized in the figures, which will be explained below. The latch housing  6 , made of plastic, actually includes a feed-in mouth or feed-in mouth insert  7 , containing a stop absorber  8 . The stop absorber  8  restricts the movement of a catch bolt  9  when entering the feed-in mouth  7  and the catch  1 . The feed-in mouth  7  (or the feed-in mouth insert), and thus the latch housing  6 , contains a shaped friction brake device  10 , which in the first embodiment shown in  FIGS. 1 to 5  is designed as spring lip  11 . The friction brake device  10  as part of the embodiment shown in  FIGS. 6 to 8 , on the other hand, is designed as a buffer pocket  12  arranged on the locking mechanism  1 ,  2 . 
     The friction brake device  10  for the locking mechanism  1 ,  2  has a flexible design and only becomes effective shortly before reaching the rigid end stop  13  (see  FIGS. 5 and 8 ). In the embodiment, although not limiting to the invention, the friction brake device  10  becomes effective shortly before reaching the intermediate closed position as shown in  FIG. 3  and ending in the overtravel area as shown in  FIGS. 5 and 8 . At the same time, the friction brake device  10  acts reciprocally with the cam  14  on the locking mechanism  1 ,  2 . In other words, the friction brake device  10  and the cam  14  together form a functional unit  10 ,  14 , ensuring that the catch bolt  9  moving into the feed-in mouth  7  and with it the locking mechanism  1 ,  2  are slowed down en route to the primary position. 
     In comparison, the functional unit  10 ,  14  or the friction brake device  10  in combination with the cam  14  on the locking mechanism  1 ,  2  does not (does no longer) considerably influence the movement of the catch bolt  9  and thus of the locking mechanism  1 ,  2  in the overtravel area, as shown in  FIGS. 5 and 8 . Instead, considerable resetting forces are exerted in the reached overtravel area by, for instance, the surrounding rubber door seal, ensuring that the catch bolt  9  and the locking mechanism  1 ,  2  are pushed back into the primary position. In this case, additional braking forces generated by the friction brake device  10  in connection with the cam  14  would more than likely be a hindrance and are actually not, or are hardly, taken into consideration. 
     In order to achieve an effective noise muffling of the entire motor vehicle door latch, cam  14  has a noise-reducing design. Catch  1  is actually designed with a plastic coating  15 , also covering cam  14 . In other words, the cam  14  is formed in the plastic coating  15  during its manufacture. In this way, cam  15  is also automatically made of plastic or contains a coating and thus acts between the catch  1  made of steel and the friction brake device  10  as an acoustic decoupling means. 
     From the embodiments shown in  FIGS. 1 to 5 , it is apparent that cam  14  protrudes out of the locking mechanism&#39;s plane G created by catch  1  in connection with pawl  2  in the direction of the feed-in mouth  7  which is arranged behind it, as shown in  FIGS. 1 and 2 . As a result, cam  14  is positioned directly in the sphere of influence of the friction brake device  10 , arranged more or less on the same plane as the feed-in mouth  7  and, in this case, the spring lip  11  on the feed-in mouth  7 . As soon as catch  1  moves into its closing position, the cam  14  increasingly moves towards the friction brake device  10  or the spring lip  11 , reaching it shortly before the intermediate closed position, shown in  FIG. 3 , is taken up. As a result, the friction brake device  10  or the spring lip  11  is able to transfer mechanical frictional forces onto the locking mechanism  1 ,  2 , braking its movement. 
     As a result of the eccentric shape of the cam  14  with its rising flank  14   a , the friction brake device  10  or the spring lip  11  is increasingly deformed so that progressively increasing resetting forces or brake forces are generated by the friction brake device  10  as the closing operation progresses. Shortly before reaching the primary position, as shown in  FIGS. 4 and 6 , the maximum deformation of the friction brake device  10  is reached, corresponding in space to the plateau area  14   b  of the cam  14 . 
     When the locking mechanism  1 ,  2  is moved past the primary position, as shown in  FIGS. 4 and 6 , it reaches the overtravel area, as shown in  FIGS. 5 and 8 . In this overtravel area, the falling flank  14   c  of the cam  14  is in reciprocal action with the friction brake device  10  so that in this position only few or no frictional forces are created. Further movement of the locking mechanism  1 ,  2  is now limited by the end stop  13 . At the same time, the friction brake device  10  or the spring lip  11  has covered cam  14  in this position (see  FIG. 5 ), so that basically no brake forces are created and the locking mechanism  1 ,  2  can easily return to the primary position. For this purpose, the friction brake device  10  or spring lip  11  has a two-part contour with a contact area  11   a  and a by-pass area  11   b  for cam  14 . The desired reciprocal action between the spring lip  11  and the cam  14  is indeed produced in the contact area  11   a , whilst the by-pass area  11   b  basically separates the cam  14  from the spring lip  11 . 
     The alternative embodiment, shown in  FIGS. 6 to 8 , functions similarly to that described above. The only difference is that the cam  14  together with the friction brake device  10  constitutes a single part, while in the embodiment according to  FIGS. 1 to 5  the friction brake device  10  and the cam  14  constitute separate parts. The first embodiment also uses a friction brake device  10  on the housing side, while the alternative embodiment, shown in  FIGS. 6 to 8 , features a friction brake device  10  on the locking mechanism side. 
     The friction brake device  10  is indeed designed as a buffer pocket  12  in this case, as already explained above. This buffer pocket  12  comprises a buffer lip  16  and a buffer slot  17 , permitting movement of the buffer lip  16 . Buffer lip  16  has the same function as spring lip  11 . The only difference is that buffer lip  16  contains the integral cam  14 , which in turn acts upon the buffer lip  16  by means of a stop  18  fixed to the housing. 
     As soon as the locking mechanism  1 ,  2  moves towards the intermediate closed position, stop  18  is in reciprocal action with cam  14  on the buffer lip  16 , ensuring increasing braking forces. As a result, the buffer lip  16 —like the spring lip  11  before—is increasingly deformed. Upon reaching the primary position, as shown in  FIG. 7 , the plateau  14   b  of the cam  14  has passed the stop  18 , corresponding with the aforementioned maximum deformation of the buffer lip  16 . The falling flank  14   c  of the cam  14  is then in reciprocal action with stop  18 , so that hardly any braking forces are still exerted in the following overtravel area, as shown in  FIG. 8 , and catch  1  runs directly against the end stop  13 . 
     Finally, it is apparent that the spring pocket  20  and spring pocket  21  are assigned to the end stop  13  and the further open stop  19 , respectively, in order to prevent in any case a hard impact of the catch  1 . The spring pockets  20 ,  21  are in turn formed in the plastic coating  15  and contain a slot or slit, accommodating the deformation of an associated slit lip  21   a  or  20   a .