Abstract:
In a flat sliding gear drive formed of flat panel-shaped sliding elements ( 1 ), ( 2 ), with a first sliding element ( 1 ) connected to a motor and a second sliding element ( 2 ) connected to a variable load, the first and second sliding elements ( 1 ), ( 2 ) have interacting wedge surfaces which are curved for providing a uniform torque loading of the driving motor.

Description:
BACKGROUND OF THE INVENTION 
     The present Invention is directed to a sliding gear drive with a first sliding element in connection with a motor and a second sliding element, engaged by a variable load, and in engagement with the first sliding element by a wedge-shaped transmission connection. 
     Sliding gear drives are generally used where, for spatial or other functional reasons, a direct and linear force flow deflection is desired. In addition, sliding gear drives offer the capability of a path reduction/power ratio, and in particular the advantage of being able to interrupt the gear connection after a shifting motion and locking of the driven sliding element, for example, in conjunction with a step function, the driving sliding element can be returned to its starting position. 
     As an example, a data card unit represents a typical application case. In a data card unit, a data card carrier, in a read/write position of the data card, must be shifted against the action of a spring into a removal position when the data card is to be removed. In this position, a locking of the data card carrier takes place. When inserting a data card in such an arrangement, the data card carrier is unlocked and displaced my means of a spring into the read/write position. Accordingly, in the read/write position, it lies against a stop under the action of the spring. 
     If, for example, the data card unit is used in a commercial vehicle, then it is necessary, to insure exact positioning or contacting of an inserted data card and to exclude the risk of positional changes due to operationally induced vibrations, that the data card carrier must be under a relatively large contacting pressure in the read/write position. As a result, the motor, moving the data carrier by means of the sliding gear drive, is acted upon by a relatively large initial load and by an additional transporting load, which increases with the shifting of the data card carrier. Further, the data card is to be removed in a relatively short time whereby an appropriately powerful motor must be used. The high costs resulting from such an arrangement are not acceptable, especially if it is located in the instrument area of a vehicle. This means that motors, suitable with respect to torque, cannot be used. In addition, as a result of various voltage drops, the full voltage of the vehicle battery is not available and the current consumption is limited for safety reasons as well as legal provisions. 
     Of course, the torque required by the motor can be reduced owing to the fact that a high transmission reduction is provided between the motor and the driving sliding element and/or that the wedge angle of the sliding gear drive is constructed relatively flat. In each of these cases, the waiting time for removing data cards is unacceptable. Moreover, additional space is required and, due to the transmission expansion, the costs are increased. 
     SUMMARY OF THE INVENTION 
     Therefore, a primary object of the present invention is to gain a sufficiently short actuation of the driven sliding element in geared connection and formed by a sliding gear drive and acted upon with a variable load even when the driving power is limited and to achieve the object at a cost which can be justified for continuous production. 
     In accordance with the present invention, a wedge gear connection is provided so that the motor is acted upon by a torque not proportional to the variable load. 
     In a preferred embodiment of the wedge gear connection, the wedge surfaces of the sliding elements, interacting during transmission, have a curved configuration in the sliding direction. 
     Further advantageous developments of the invention are evident from the dependent claims. 
     The advantage afforded by the invention is that a variable wedge angle between the sliding elements is particularly effected in that it can be accomplished without any additional technical effort, that is, without additional components and that only the basic or initial load has to be taken into consideration for the torque required to drive the motor. A suitable curved shape for the interacting wedge surfaces, a torque compensation and optionally, a constant torque requirement for the driving motor can be created even in the case of loads which do not increase linearly. Furthermore, the inventive arrangement can also be used for a case in which a constant load to be moved at different speeds and torque, required by the driving motor, is to be kept essentially constant. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by it use, references should be had to the drawings and description matter in which there are illustrated and described preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic showing of the manner in which the inventive sliding gear drive functions; 
     FIG. 2 is a plan view of a data card unit with transporting means embodying the present invention with the data card unit in the read/write mode; 
     FIG. 3 is also a plan view of the data card unit and provided with cut-outs illustrating the data card unit in an input mode; 
     FIG. 4 is a schematic showing another embodiment of the inventive sliding gear drive; 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown schematically in FIG. 1, a first sliding element  1 , mounted for displacement in the directions of arrow X, is in wedge gear engagement with a second sliding element  2  displaceable in the directions of the arrow Y. A driving force F A  acts on the sliding element  1 . A lifting force F H , resulting from the wedge gear engagement between the first sliding element  1  and the second sliding element  2 , acts counter to a path-dependent varying force Fz of a tension spring engaging the sliding element  2 . An adjustment so that F A  and with it the torque required by the motor remain essentially constant, is accomplished by constructing the wedge surfaces  3 ,  4  of the sliding elements  1 ,  2  disposed in a gear connection, as curved surfaces. The first and second sliding elements  1 ,  2  are flat, panel shaped components in the simplest case, the curved surfaces can be formed as arcs of a circle. The lengths of the designated radii are R 1  and R 2  and the positions of the respected middle points, which are not shown, can be freely selected within certain limits, but also optimized mathematically for the intended object of a variable torque relief of the driving motor. As shown in FIG. 1, it is essential that the wedge angle be variable and decreases from 45° in the starting position to 20° in the final or latched position of the driven component. In the embodiment described as follows, the driven component represents a carriage in the form of a data carrier. 
     In another embodiment, the first sliding element  1  can be in engagement with the second sliding element  48  by a pin  49 . 
     As shown in FIG. 2, a front wall  5  of a housing, for example a tachograph, is shown in which a data card unit  16  is arranged. A side wall  7  and a bottom  8  form a part of the housing. In the front wall  5 , usually containing at least different keys (one serves for producing a data card output signal) and a LC display are provided though not shown, because they are not essential to the invention. In the front wall  5  a slot  9  is arranged serving as front access to the data card unit  6 . The data card unit is formed of two side guide walls  10 ,  11  fastened in a suitable manner or integrally molded directly to a printed circuit  4  of the unit, along with a carriage  13 , displaceably supported in the side guide wall  10 ,  11 , and constructed as a data card carrier. Further, FIG. 2 illustrates a data card  14  provided with an arrow  15  indicating the correct input position and input direction, as well as a contact area  16 . A contact bank, assigned to the data card  15 , is fastened on the printed circuit board  12 , however, it cannot be seen in the cut-out of the printed circuit board  12  in FIG.  2 . One end of a tension spring  18 , effecting the transport of the carriage  13  into the read/write position shown in FIG. 2 is fixed at a stationary pin  17  or at another suitable element. In the illustrated position, a tab  19  integrally molded to the carriage  13  and a slide  20 , displaceably supported on the carriage  13  extend into the path of movement of the sliding element  21  guided transversely of the carriage  13 . The sliding element  21  supported in a suitable manner, has a gear tooth system  22  which is connected to a driving motor by a transmission chain, not shown. Two wedge surfaces  23 ,  24  on the sliding element  21  have a curved configuration. When the sliding element  21  is moved in the direction of the carriage  13 , wedge surfaces  25 ,  26  integrally molded on the tab  19  and the slide  20 , respectively, interact with the wedge surface  23 , 24 . Another tab  27  constructed symmetrically to the tab  19  on the carriage  13 , enables the data card unit  6  to be installed in such a manner that the carriage  13  can be triggered from the opposite direction shown in FIG.  2 . 
     If the tilting point of the tilting over-center device is exceeded when placing a data card  14  in the direction of the arrow Q, the carriage  13  is unlocked under the action of the compression spring, at the same time the data card  14  is held at the side and, under the action of the compression spring, at the same time the data card  14  is held at the side and, under the action of the tension spring  18 , one end of which is supported by a small post  46  attached to the carriage, transport of the carriage  13  into the read/write position takes place. In the reverse case, when the data cards  14  are removed, an operation must be triggered, for example, by actuating a key, and the sliding element  21  is shifted by the motor in the direction of the arrow T and, at the same time, the carriage with the wedge surfaces  24 ,  26  entered into a sliding connection, is shifted into a position where the fingers  37 ,  38  are opposite the recesses  34 .  35 . Upon further transport of the sliding element  21 , the wedge surfaces  23 ,  25  become drivingly connected with each other and, as a result the slide  20 , with the carriage  13  stationary, is shifted up to the tilting point of the tilting over-centered device. Subsequently, a component of the compression spring  45  and of the tension spring  42  conduct the slide  20  to a stop  47  with the connecting link being arranged so that the fingers  37 ,  38  and the recesses  34 ,  35  remain engaged. Advisable, the sliding element  21 , as shown in FIG. 3, is moved with an over-lift to actuate a switch reversing the direction of movement of the driving motor. Accordingly, it is returned to the starting position, permitting the input of a data card  14  and a shifting of the carriage into the read/write position. 
     In the operational position illustrated in FIG. 2, with the data card  14  in the read/write position, the fingers  37 ,  38  grasp the side of the data card  14  and hold the card at the opposite wall of a holder  39  formed in the carriage  13  and assigned to the data cards  14 . In this arrangement, the slides  20 , 36  are formed at the carriage  13  with H-shaped prismatic guides and end flush with the surface  40  (FIG. 3) of the holder  39  in the carriage  13 . Only a nose  41 , formed on the slide  20 , engages the holder which has at its edge holding-down devices arranged parallel to the surface  40 , but not shown, when the carriage  13  is in the insertion/removing position with the fingers  37 ,  38  of the T-shaped slide  36  disposed in working connection with the recesses  34 ,  35 . Accordingly, when data cards  14  are placed in the data card unit  6 , the slide  20  is shifted by the nose  41  opposite to the action of a tension spring  42  and, at the same time, a tilting over-center device is triggered provided between the slide  20  and the slide  36  and provides two stable positions of the slides  20 ,  36 . The tilting over-center device consists of a connecting link  43  formed in the slide  20  and provided with a tilting point, a pin  44  fastened at the slide  36  and in working connection with the connecting link  43  along with a compression spring  45  which on one hand engages the slide  36  and on the other supports the carriage  13 . In this connection, it is noted that the force of the compression spring  45  is considerably greater than that of the tension spring  42 . 
     If the tilting point of the tilting over-center device is exceeded when placing a data card  14  in the direction of the arrow Q, the carriage  13  is unlocked under the action of the compression spring, at the same time the data card  14  is held at the side and, under the action of the compression spring, at the same time the data card  14  is held at the side and, under the action of the tension spring  18 , one end of which is supported by a small post  46  attached to the carriage, transport of the carriage  13  into the read/write position takes place. In the reverse case, when the data cards  14  are removed, an operation must be triggered, for example, by actuating a key, and the sliding element  21  is shifted by the motor in the direction of the arrow T and, at the same time, the carriage with the wedge surfaces  24 ,  26  entered into a sliding connection, is shifted into a position where the fingers  37 ,  38  are opposite the recesses  34 ,  35 . Upon further transport of the sliding element  21 , the wedge surfaces  23 ,  25  enter into a gear connection and as a result the slide  20 , with the carriage  13  stationary, is shifted up to the tilting point of the tilting over-centered device. Subsequently, a component of the compression spring  45  and of the tension spring  42  conduct the slide  20  to a stop  47  with the connecting link being arranged so that the fingers  37 ,  38  and the recesses  34 ,  35  remain engaged. Advisably, the sliding element  21 , as shown in FIG. 3, is moved with an over-lift to actuate a switch reversing the direction of movement of the driving motor. Accordingly, it is returned to the starting position, permitting the input of a data card  14  and a shifting of the carriage into the read/write position. 
     What is claimed as new and desired to be protected by letters patent is set forth in the appended claims.