Abstract:
A motor vehicle lock for a trunk lid or a tailgate of a motor vehicle. In this motor vehicle lock, two driver elements are provided on a disk-shaped driving element and they implement different speed reduction ratios with respect to the ratchet. In this way, an optimum, staggered starting characteristic is produced; moreover, construction effort and costs are minimized.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a motor vehicle lock, and, more specifically to a motor vehicle door lock for a trunk lid or a tailgate of a motor vehicle. 
   2. Description of Related Art 
   Known motor vehicle locks, designed and suitable for a trunk lid or the tailgate of a motor vehicle as described in German Patent Application DE 195 05 779 A1 (which corresponds to U.S. Pat. No. 5,938,253) are advantageous because an electric motor drive can be controlled without a reset spring by a driving element which rotates in one rotational direction in blocking operation, and thus, without microswitches. 
   The known motor vehicle lock noted above is made such that, when the electric motor drive fails, emergency actuation by hand enables the ratchet to be moved, at any time, into the lifted position. Overall, for the mechanical background of motor vehicle locks of the type under consideration, and for the particulars in motor vehicle locks for trunk lids or tailgates, reference should be made to U.S. Pat. No. 5,938,253, the contents of which are incorporated by reference in their entirety. 
   In the above-described known motor vehicle lock, a driver element is described as a cylindrical component. For the purposes of this application, however, a crank-like component or a component with some other shape, such as an elliptical shape, can also be regarded as the driver element. As in the prior art, the drive is provided with a degressive starting characteristic. This means that, upon starting, a large torque can be applied in order to release the ratchet from the engagement position on the latch. As the lifting motion of the ratchet continues, this torque is continuously reduced by the shape of the driver element. In particular, a control crank in the shape of a helical cam as a driver element has come into use as shown in German Patent Application DE 101 00 008 A1 (which corresponds to U.S. Pat. No. 6,698,805). In this respect, implementation of stepped reduction of the torque by lever action arms of different length is also known as shown in German Patent DE 41 19 703 C1. This is not implemented with the driving element of an electric motor drive in which the driving element rotates in one direction. However, in a motor vehicle lock with manual actuation, it is implemented via a gradually acting coupling of the opening handle to the ratchet. 
   SUMMARY OF THE INVENTION 
   A primary object of the present invention is to optimize the opening function of a motor vehicle lock by consideration of the particulars of an electric motor drive with a driving element which rotates in one direction and with implementation of block operation for driving. 
   The aforementioned object is achieved in a motor vehicle lock where a driving element of the electric motor drive, embodied as a drive wheel, is provided with two driver elements, i.e. driver journals. The journals are located in different positions, especially in a different radial position on the driving element. The second driver element is preferably a control crank which is shaped like a helical cam and executes the actual lifting of the ratchet with a great force on the ratchet, therefore has a large reduction ratio. The first driver element is relieved of its function of lifting of the ratchet and implements overtravel motion of the ratchet and a block operation only with little force on the ratchet, but with a comparatively higher speed. 
   Thus, it is possible, in a manner which is especially suitable for an electric motor drive with a driving element which rotates in one direction, to implement a two-stage opening motion of the ratchet without the need to introduce additional levers. This means that a large force for lifting the ratchet is available, but it is then gradually reduced to the benefit of the path which is to be quickly traversed. With the type of speed reduction on the driving element provided by the present invention, large holding forces on the latch can be overcome with a comparative small electric drive motor, as is normally used for centralized locking system drives. 
   The present invention is explained in detail below using the drawings with reference to one preferred embodiment or preferred embodiments. In the course of these explanations other embodiments and developments and other features, properties, aspects and advantages of the invention are explained at the same time. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic perspective of a motor vehicle with a motor vehicle locking system; 
       FIG. 2  shows an embodiment of a motor vehicle lock as provided by the present invention, made as a lock for a tailgate, with the latch in the main locked position and the ratchet engaged; 
       FIG. 3  shows the embodiment of  FIG. 2 , with the ratchet in the lifted position; and 
       FIG. 4  shows the embodiment of  FIG. 2 , with the drive turned off by a blocking operation. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the figures, the same reference numbers are used for the same or similar parts. Thus, it should be indicated that the corresponding or comparable properties and advantages are achieved, even if a repeated description of these parts is omitted. 
     FIG. 1  shows in a schematic a motor vehicle  1  with a motor vehicle locking system  2  which is indicated only in part. The system can include several motor vehicle locks  3 , specifically those for side doors  4 , for a trunk lid  5 , optionally for a rear hatch or tailgate, but also for a glove box, a fuel tank cover or the like. In accordance with the present invention, the installation positions of the motor vehicle locks  3  are schematically indicated by the arrows in  FIG. 1 . 
   In this embodiment, the motor vehicle locks  3  can be actuated by a motor, which also can be locked and unlocked by an electric motor, and/or which can be opened by an electric motor. 
     FIGS. 2 to 4  show a motor vehicle lock, in accordance with an exemplary embodiment of the present invention, which can be employed with a trunk lid or a tailgate of a motor vehicle.  FIG. 2  shows the closed position of the motor vehicle lock.  FIG. 3  shows the lifted position and  FIG. 4  shows the block disengagement for the motor vehicle lock. 
   The illustrated motor vehicle lock includes a latch  6  which, in this embodiment and according to the most common version, is a rotary latch. On the latch  6 , which is pivotally supported on a swivelling axle  7 , there is a main catch  8  which is used in a main locking position of the latch  6  and a preliminary catch  9  which is used in a preliminary locking position of this latch  6 . The latch  6  could also be employed without the preliminary catch  9 . 
   The latch  6  is kept in the main locking position and, in this embodiment, also in the preliminary locking position by a ratchet  10 . The ratchet  10  is pivotally supported on a pivot axis  11  and locks with the main catch  8  or the preliminary catch  9  of the latch  6  by means of a corresponding catch projection  12 . The locking elements of the motor vehicle lock, in this embodiment, are jacketed with plastic or are made partially as plastic parts, the power transmission areas which engage being exposed in the metal. 
   The illustrated embodiment shows that the ratchet  10  is an integral part. However, fundamentally, the ratchet  10  can also be coupled to another catch lever which then transfers the movements to the ratchet  10 . 
   On the ratchet  10 , or even on a catch lever which is coupled to the ratchet, there is an actuating surface  13  at a distance from the engagement point to the latch  6 , and at a distance from the catch projection  12 . Furthermore, there is an electric motor drive  14  with a driving element  15 , which is preferably a driving wheel as illustrated, and which rotates in one direction (in this embodiment counterclockwise). A driver element  16  is arranged eccentrically on this driving element  15 . Other driving elements, for example, have a lobe shape or elliptical shape or also simply the shape of a one-armed pivot lever. 
   By turning the driving element  15 , the driver element  16  strikes the actuating surface  13 , moves the ratchet  10  into an overtravel position beyond a lifted position, and afterwards runs past the actuating surface  13 . This movement transitions from the state in  FIG. 3  to the state in  FIG. 4  in a counterclockwise direction. The lifted position of the ratchet  10  is the position in which the catch projection  12  does not engage the main catch  8  or the preliminary catch  9  of the latch  6 . The latch  6  can therefore easily swivel out around its swivelling axle  7  in a counterclockwise direction to the open position. 
   For the latch  6  and the ratchet  10 , there are spring elements which pretension them into the respective set position; the latch  6  into the open position, and the ratchet  10  into the engagement position. The springs can also be replaced by a single spring which acts on both locking elements. In this regard, reference should be made to the prior art which was explained at the beginning. 
   On the ratchet  10 , a catch lever which is coupled to the ratchet  10 , or also on a blocking lever which is separate from the ratchet  10 , but dynamically coupled to it, a driver stop surface  17  is provided at a distance beyond the actuating surface  13  viewed in the direction of rotation of the driving element  15 . The driver stop surface  17 , when the ratchet  10  is in the lifted position, is in the path of motion of the driver element  16  (shown in  FIG. 4 ). However, when the ratchet  10  is in the engagement position, the driver stop surface  17  is outside of the path of motion of the driver element  16  (illustrated in  FIG. 2 ). 
   When the latch  6  is in the open position, the latch  6  keeps the ratchet  10  in the lifted position ( FIG. 4 ). In this way, it is possible for the driver element  16 , after running past the actuating surface  13  when the ratchet  10  is in the lifted position, to strike the stop surface  17 . In this way, the electric motor drive is turned off in a blocking operation. The ratchet  10  and the catch lever or the separate blocking lever are fixed by the latch  6  so that the necessary resistance force against the starting of the driver element  16 , which can be used for the blocking operation, arises. 
   The blocking operation means disengagement by monitoring the torque, monitoring the current, monitoring the time or a combination of difference types of monitoring. Reference should also be made to the prior art for further details. 
   In accordance with an exemplary embodiment of the invention, the driver element  16  does not perform the actual lifting of the ratchet  10  out of the engagement position on the latch  6 . On the driving element  15 , there is a second eccentrically arranged driver element  18  and, on the ratchet  10  or the catch lever, there is an opening control surface  19  which interacts with the second driver element  18 . When the drive  14  starts to lift the ratchet  10  out of the main locking position, the second driver element  18  first engages the opening control surface  19  and only afterwards does the first driver element  16  engage the actuating surface  13 . The effective speed reduction ratio with respect to the second driver element  18  is larger than with respect to the first driver element  16 . By this division into the first driver element  16  and the second driver element  18 , optimum application of torque to the ratchet  10  at the start of the lifting motion is combined with fast motion of the ratchet  10  at the end of the lifting motion, especially in overtravel. This graduated starting characteristic, which is implemented by double lever action in the prior art, is implemented in the present invention by using another driver element  18  on the driving element  15 . The implementation of another driver element in accordance with the present invention is feasible and economical. 
   The illustrated embodiment which is preferred in this respect, otherwise shows that the ratchet  10  or the catch lever is arranged overlapping with the driving element  15  and that the first driver element  16  is located radially farther to the outside on the driving element  15  than the second driver element  18 . The different lever arm ratios can be employed and they lead to the desired different speed reducing action. 
   Furthermore, in this embodiment, it is provided that the opening control surface  19  is farther away from the engagement point to the latch  6  than the stop surface  17 . In fact, the stop surface  17  is near the lower reversal point of the first driver element  16 , if the ratchet  10  is in the lifted position ( FIG. 4 ). In this way, the stop surface  17  acts on the ratchet  10  with the shortest possible lever arm with respect to the pivot axis  11 , so that, in this respect, the blocking action of the stop surface  17  is accompanied by the smallest possible action of force between the latch  6  and the ratchet  10 , so that the entire bending stress on the ratchet  10  is kept as small as possible. 
   The illustrated and preferred embodiment furthermore shows a crank-like configuration of the second driver element  18  such that the second driver element  18  proceeds from one point near the center point of the driving element  15 . Here, it is provided that the second driver element  18  is a control crank with the shape of a helical cam. 
   The illustrated and preferred embodiment has another aspect where the two driver elements  16 ,  18  lie on one side of the driving element  15 , and can also be in one plane with respect to the ratchet  10  or the catch lever or the blocking lever. Because the two driver elements  16 ,  18  lie in one plane, the force is applied to the ratchet  10  or the catch lever or the blocking lever very effectively. 
   Finally,  FIG. 3  shows one particular aspect of the illustrated embodiment of a motor vehicle lock as provided in the present invention which is established in that the first driver element  16  only engages the actuating surface  13  after the lifting of the ratchet  10  has been completed by the second driver element  18 . Here, transfer from one driver element to the other therefore takes place. Basically, it would also be possible to make the influencing action overlapping, of course its having to be considered that no static matching occurs.