Abstract:
A threaded spindle ( 11 ), having a drive part ( 20 ), which has a longitudinal axis (A) and is mounted in a first journal ( 70 ), and having a threaded part ( 30 ), which has a longitudinal axis (B), and having a threaded nut ( 50 ), which is mounted in a second journal ( 80   a;    80   b ) and in which the threaded part ( 30 ) is guided. The drive part ( 20 ) and the threaded part ( 30 ) are formed as separate parts and are each provided with at least one coupling element ( 25, 55 ), which are connected to each other in an articulated manner by plugging together. An offset of the longitudinal axes (A, B) can be compensated in this manner. The two-part threaded spindle ( 11 ) forms a threaded drive with the threaded nut ( 50 ) thereof, which can for example be used in a parking brake of a vehicle braking system.

Description:
BACKGROUND 
     The invention relates to a threaded spindle with a drive part, which has a longitudinal axis and is mounted by a first journal, and having a threaded part, which likewise has a longitudinal axis, and having a threaded nut, which is mounted to a second journal and in which the threaded part is guided. 
     Such a threaded spindle with a threaded nut is commonly embodied in prior art as a ball screw, which may be used in the field of flap and door opening systems and primarily in the field of vehicles. In vehicles it can be used, for example in the vehicle brakes. Here, the drive part is set in motion with the help of an electric motor. This results in a longitudinal motion of the threaded nut being generated, which operates a brake piston and this way acts as the locking device for a vehicle brake. The threaded part contacts via balls the threaded nut. In the spindle/ball journal arrangement known from the document DE 101 50 803 A1, thus in a ball screw drive, a jamming may occur of the threaded nut and the threaded spindle when the threaded nut is moved back. In order to prevent this it is known from the document WO 99/45292 A1 to provide the threaded nut with a projection at its face adjacent to the drive part, which can be made to contact a stop embodied at the drive part, acting in the circumferential direction, and thus can be brought to a certain alignment in reference to the thread of the threaded spindle. 
     Although in FIGS. 2 and 3 the document U.S. Pat. No. 5,711,709 shows a threaded spindle with a drive part, which has a longitudinal axis, and shows a threaded part, which also has a longitudinal axis, and with a threaded nut in which the threaded part is guided, with the drive part and the threaded part being embodied as separate parts, here, which are connected to each other in an articulate fashion by way of plugging together, so that a radial mutual off-set or an inclination of the longitudinal axes of the drive part and the threaded part can be compensated, in spite thereof it cannot be excluded here that the ball drive jams during operation. 
     The primary problem in such ball drives is namely given such that in a faulty alignment of the two journals or in case of a distortion of the threaded spindle, thus a radial mutual off-set or incline of the longitudinal axes of the drive part and the threaded part, the ball drive may jam during operation and thus may be hindered from fulfilling its intended purpose, they are subject to considerably higher wear and tear, and may show a worsened effectiveness. 
     SUMMARY 
     The objective of the invention is to provide a threaded spindle of the type mentioned at the outset such that the disadvantages connected to a distortion of the threaded spindle can be avoided or at least strongly reduced. 
     This objective is attained according to the invention in a threaded spindle of the type mentioned at the outset such that the drive part and the threaded part are embodied as separate parts, each respectively provided with at least one coupling element, which are connected or can be connected to each other in an articulate fashion by way of plugging together such that a mutual off-set of the longitudinal axes of the drive part and the threaded part can be compensated. 
     The two-part embodiment of the threaded spindle according to the invention avoids or at least reduces the severity and the disadvantageous effects of shearing forces, which may occur during a distortion of a one-part threaded spindle, by creating the option of a joint between the drive part and the threaded part of the threaded spindle. Shearing forces, occurring in prior art when the threaded spindle is distorted and may lead to the threaded spindle and the threaded nut to jam, are excluded right from the start in the threaded spindle according to the invention because the drive part and the threaded part are both independently capable to compensate shearing forces and this way prevent any jamming. Simultaneously, by the embodiment of the threaded spindle according to the invention as a two-part spindle its wear and tear is reduced. Additionally, higher effectiveness is yielded in the drive train between the electric motor, the drive part, the threaded part, and the threaded nut because losses due to friction or the like in the threaded spindle according to the invention is considerably lower than in threaded spindles embodied in the technology of prior art described above. 
     Advantageous embodiments of the invention form the objectives of the dependent claims. 
     In an embodiment of the threaded spindle according to the invention said threaded spindle comprises at least one axially effective stop element, which cooperates in a contact position with at least one axially effective stop element of the drive part. In this embodiment the axially effective stop elements of the threaded nut and the drive part are embodied in a particular relationship to the start of the thread and to the pitch. This way, the two directions of rotation between the threaded nut and the drive part always exhibit a distance preventing the above-described jamming between the threaded nut and the threaded spindle, even when the longitudinal axes of the drive part and the threaded part might form an angle in reference to each other. 
     In another embodiment of the threaded spindle according to the invention the stop elements contact each other even in case of a radial off-set of the two longitudinal axes in the stop position and at least a slight distance is given between the face of the threaded nut and the stop boss of the drive part. 
     In another embodiment of the threaded spindle according to the invention the stop elements are arranged in at least one annular ring, with both diameters being greater than the external diameter of the thread of the threaded part and/or smaller than the external diameter of the threaded nut. This way the stop elements are held in a circumferential area in which they can fulfill their optimal effectiveness with regards to upholding an axial distance in order to avoid jamming. 
     In another embodiment of the threaded spindle according to the invention the stop element at the drive part or the threaded part represents a cam or the like. This yields a simple embodiment for an axially effective stop element. 
     In another embodiment of the threaded spindle according to the invention the thread of the threaded part exhibits a pitch which is greater than the height of the cam. This additionally serves to ensure that no jamming can occur. 
     In another embodiment of the threaded spindle according to the invention the cam projects from the face of the drive part and has radially a stop area and a corresponding stop recess is provided at the threaded nut or vice versa. When the threaded nut is turned back here the cam of the drive part is accepted by the stop recess of the threaded nut, or vice versa, in order to form a stop effective in the circumferential direction. 
     In another embodiment of the threaded spindle according to the invention, the cam is provided such that in the plugged-together state 360° prior to the stop position an assembly distance is given between the drive part and the threaded nut which is slightly greater than the pitch of the thread of the threaded nut. By this embodiment it is ensured in a simple fashion that a minimum distance remains between the drive part and the threaded nut even when the drive part is turned back. 
     In another embodiment of the threaded spindle according to the invention a grid for several plug-in positions is provided for plugging together the drive part and the threaded part. By selecting an appropriate plug-in position the axial distance can be chosen which ultimately remains when the drive part and the threaded nut are turned back. 
     In another embodiment of the threaded spindle according to the invention the thread is a ball screw or another low-friction thread. This yields the desired advantage that the threaded nut engages the threaded part in a very smooth-running fashion. 
     In another embodiment of the threaded spindle according to the invention the coupling elements are designed with little play. This way, the axial distance between the threaded nut and the drive part resulting at the end is better predictable. 
     In another embodiment of the threaded spindle according to the invention the coupling element of the drive part has a circlip for loss prevention. This way it can be prevented in a simple fashion that the drive part and the threaded part separate from each other unintentionally. 
     A safety system with a threaded spindle according to the invention or one of the above-described embodiments shows a simple, proven, and reliable structure. 
     One embodiment of the safety system represents a brake system for a vehicle. In this case the drive train, which comprises an electric motor, a drive part, a threaded part, and a threaded nut, leads to the otherwise hydraulically operated brake piston, forming the so-called parking brake. 
     Another embodiment of the safety system represents a steering system of a vehicle. The design of the drive train for operating the steering is equivalent to the above-mentioned drive train. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following exemplary embodiments of the invention are described in greater detail with reference to the drawings. It shows: 
         FIG. 1  in a longitudinal cross-section a first exemplary embodiment of a threaded spindle according to the invention, 
         FIG. 2  a threaded spindle according to  FIG. 1  in a longitudinal side view, 
         FIG. 3  in a longitudinal side view a detail of the drive part of the threaded spindle according to  FIGS. 1 and 2 , 
         FIG. 4  the drive part according to  FIG. 3  in a view from the left in  FIG. 3 , 
         FIG. 5  in a longitudinal side view another embodiment of the drive part of the threaded spindle according to  FIGS. 1 and 2 , 
         FIG. 6  the drive part according to  FIG. 5  in a view from the left in  FIG. 5 , 
         FIG. 7  in a longitudinal side view the threaded part of the spindle nut according to  FIGS. 1 and 2  in a partially opened state in order to disclose a coupling element, with in  FIG. 7  the thread of the drive part only being indicated in a sketch, 
         FIG. 8  a view of the threaded part according to  FIG. 7  in a view from the right in  FIG. 7 , 
         FIG. 9  in a longitudinal side view another embodiment of the drive part of the spindle nut according to  FIGS. 1 and 2 , which again is shown in a partially opened state in order to disclose a coupling element, with the thread of the threaded part being shown, here, 
         FIG. 10  a view of the threaded part according to  FIG. 9  in a view from the right in  FIG. 9 , 
         FIG. 11  in a longitudinal cross-section a first embodiment of the threaded nut of the threaded spindle according to  FIGS. 1 and 2 , 
         FIG. 12  a threaded nut according to  FIG. 11  in a view from the right in  FIG. 11 , 
         FIG. 13  in a longitudinal cross-section a second embodiment of the threaded nut of the threaded spindle according to  FIGS. 1 and 2 , 
         FIG. 14  the threaded nut according to  FIG. 13  in a view from the right in  FIG. 13 , 
         FIG. 15  in a longitudinal side view a third embodiment of the threaded nut, 
         FIG. 16  the threaded nut according to  FIG. 15  in a view from the right in  FIG. 15 , 
         FIG. 17  in a longitudinal cross-section a second embodiment of the threaded spindle according to the invention, which differs from the embodiment according to  FIGS. 1 and 2  in the embodiment of the thread and a second journal, and 
         FIG. 18  a threaded spindle according to  FIG. 17  in a simplified longitudinal side view (without journal). 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows in a longitudinal cross-section a first embodiment of a threaded spindle according to the invention, which is marked  10  in its entirety. The threaded spindle  10  comprises a drive part  20 , which has a longitudinal axis A and is supported by a first journal  70 , and a threaded part  30 , which has a longitudinal axis B, as well as a threaded nut  50 , which is supported by a second journal  80   a  and with the threaded part  30  being guided therein. The second journal can show at least two optional embodiments, with the first embodiment being shown in  FIG. 1 , marked  80   a , and a second embodiment being shown in  FIG. 17 , marked  80   b . According to the illustration in  FIG. 1 , the threaded part  30  and the threaded nut  50  each comprise a thread  31  and  51 , respectively, which are mutually engaging. The thread  31  is an external thread, the thread  51  an internal thread. The drive part  20  and the threaded part  30  are embodied as separate parts, each respectively provided with one coupling element  25  ( FIGS. 3 and 4 ) and/or  55  ( FIGS. 7 and 9 ). The coupling elements  25 ,  55  can be connected in an articulate fashion by way of being plugged together so that a mutual radial off-set V develops ( FIG. 1 ) or a mutual incline a ( FIG. 17 ) of the longitudinal axes A, B of the drive part  20  and/or the threaded part  30  can be compensated. Shearing forces can be absorbed by the agility or joint motion possible by the drive part  20  and the threaded part  30  in the plugged-together state so that any mutual radial off-set V or inclination a can be compensated, which is described in greater detail in the following. If the drive part  20  and the threaded part  30  were arranged precisely aligned coaxially their mutual radial off-set V would be zero. The same applied for the inclination a, if the drive part  20  and the threaded part  30  were arranged precisely collinearly. 
     The coupling elements  25 ,  55  are each embodied similar to keyway gears. In the plugged-together state of the drive part  20  and the threaded part  30  both gears comb each other. In order for the drive part  20  and the threaded part to engage each other a grid is provided for several plugging positions. The drive part  20  and the threaded part  30  can also be plugged together in different, radially off-set positions. The coupling elements  25 ,  55  are designed with little mutual play. The coupling element  25  of the drive part  20  comprises a circlip  61  for loss prevention. The drive part  20  has a groove  40  ( FIGS. 3 and 5 ) to accept the circlip  61 . A corresponding groove  42  ( FIGS. 7 and 9 ) comprises a threaded part  30 . The assembly of the circlip  61  occurs here as follows: The circlip  61  is inserted into the groove  40  of the drive part  20 . The groove  40  has approximately the depth of the radial thickness of the circlip  61 . However, the circlip  61  inserted in the groove  40  projects in the relaxed state from the groove  40 . During the insertion of the drive part  20  into the threaded part  30  the circlip  61  in the groove  40  of the drive part  20  is compressed. Subsequently the circlip  61  expands again and additionally snaps into the groove  42  of the threaded part  30 . Now the circlip  61 , which once more shows its original diameter, is installed in both grooves  40 ,  42  and thus ensures loss prevention. 
     The journal  70  is commonly embodied as a roller bearing. This roller bearing could be embodied as a radial and an axial roller bearing. However, an axial journal may be inserted between the journal  70  and the stop boss  21  of the drive part  20 , which compensates axial forces and is axially supported on the journal  70  or a housing part carrying said journal  70 . The journal  80   a  at the threaded nut  50  is embodied as a guide bearing or friction bearing. The threaded nut  50  can perform a displacing motion only in the axial direction. At least one area  56  ( FIG. 2 ) formed at the threaded nut  50 , which cooperates with a complementary area at the journal  80   a , hinders the threaded nut  50  from any rotation. 
     The second journal  80   a  or  80   b  represents the guide for the threaded nut  50 . In the first embodiment of the second journal  80   a , shown in  FIG. 1 , the journal is embodied as a socket, which extends in  FIG. 1  at the left face over the adjacent face of the threaded nut  50 . The journal  80   a  in turn is supported in a displaceable fashion in a guide part  90 , which is embodied stationary. When the threaded spindle  10  is used in a vehicle brake, as shown in the document WO 99/45292 A1 mentioned at the outset, the threaded nut  50  would form, together with the journal  80   a , an actuator of the brake. In the threaded spindle  11  according to  FIG. 17  the threaded nut  50  would form the actuator alone, because the second journal  80   b  is embodied in a stationary fashion. 
     The stop boss  21  of the drive part  20  cooperates with an adjacent face  58  of the threaded nut  50  in a manner described in greater detail in the following. 
     When the drive part  20  is set in motion in one direction by an electric motor (not shown) or the like, the threaded nut  50  is moved towards the left in  FIG. 1  via the coupling elements  25 ,  55  engaged according to the illustration in  FIG. 1  until a part operated by the journal  80   a , e.g., the brake piston of a vehicle brake, has reached a desired position, in which the brake is activated. This desired position is not shown in  FIG. 1 . When the electric motor or the like is operated in the opposite direction the threaded nut  50  is moved back together with the journal  80   a  on the threaded part  30  into the position shown in  FIG. 1 . It is critical here that during the return motion between the drive part  20  and the threaded nut  50 , jamming can occur when the faces  57 ,  58  mutually contact, so that the position generated by operating the threaded part  30  via the drive part  20 , in which the faces  57 ,  58  contact each other, cannot be easily released. 
     In order to address this problem the threaded nut  50  comprises a stop element  53  at its face  57  in  FIG. 1  at the right side. There are different optional embodiments for the stop element  53 , with three of them being shown in FIGS.  12  and  14 - 16 , which are discussed in greater detail in the following. In the stop position the stop element  53  cooperates with a stop element  23  of the drive part  20  acting in the circumferential direction. There are several options for its embodiment, with two of them being shown in  FIGS. 4-6 , which are explained in greater detail in the following. 
     It is important that even in case of a radial off-set V of the longitudinal axes A and B of the drive part and the threaded part the stop elements  24 ,  53  contact each other and at least a slight distance is given between the faces  57  of the threaded nut  50  and the face  58  of the stop boss  21  of the drive part  20 . 
     The stop elements  23 ,  53  are arranged in an annular ring, with both of its diameters being greater than an external thread diameter D ga  of the threaded part  30  ( FIG. 18 ) and/or smaller than an external diameter D ma  of the threaded nut  50 . The stop element  23  or  53  at the drive part  20  and/or at the threaded nut  50  is a cam  24  or  53 ′. The cam  24  has a height H. The thread  12  of the threaded part  30  shows, a pitch P like the thread  51  of the threaded nut  50 , which is greater than the height H of the cam  24 . The cam  24  projects from a facial area of the drive part  20  and exhibits radially a stop area  26  ( FIG. 6 ). A corresponding stop recess  54  is provided at the threaded nut  50  ( FIGS. 11 and 13 ). The arrangement may also be vice versa, meaning the stop area and the cam can be mutually exchanged. The cam  24  is fastened such that in the inserted state between the drive part  20  and the threaded part  30 , 360° prior to the stop position, an assembly distance M ( FIG. 2 ) is given between the drive part  20  and the threaded nut  50 , which is slightly greater than the pitch P of the thread  12  of the threaded part  30  or the thread  51  of the threaded nut  50  ( FIGS. 9  and/or  13 ). By the assembly with the circlip  61  the position of the stop element  23  or  53  is defined in reference to the pitch P. 
     When the threaded nut  50  has been returned to the stop position shown in  FIG. 1  the threaded nut  50  and the drive part  20  may be mutually jammed, because their faces  57  and  58  tightly contact each other. The friction between the two faces  57 ,  58  may become so severe that the electric motor cannot release them from each other. Accordingly a projection is provided between the two faces  57 ,  58 , such as the above-mentioned cam  24 , which ensures a certain minimum distance in this position and this way prevents any jamming between the threaded spindle  10  and the threaded nut  50 . 
     The stop recess  54  is allocated to the cam  24 , formed in the face  57  of the threaded nut  50 . When the drive part  20  is turned back the cam  24  contacts a lateral area of the stop recess  54  before the face  57  contacts the face  58  of the stop boss  21 . This way a stop is formed in the circumferential direction, which prevents any jamming between the threaded nut  50  and the threaded spindle  10 . The stop boss  21  is formed at the drive part  20 , as discernible from  FIG. 1 . 
     The second embodiment of the threaded spindle according to the invention shown in  FIGS. 17 and 18  and marked  11  in its entirety differs from the first embodiment according to  FIGS. 1 and 2  primarily in that the internal thread  51  of the threaded nut  50  and the external thread  31  of the threaded part  30  are each embodied as ball screws and that the second journal  80   b  is embodied in a stationary fashion. The function and the structure of the ball screw is conventional and thus requires no description in greater detail. 
     The division of the threaded spindle  10  into a drive part  20  and a threaded part  30  yields the following advantages, once more summarized here:
         Higher efficiency   Longer life, due to less wear and tear   Compensation of shearing forces due to the optional motion between the drive part  20  and the threaded part  30     Reduction of shearing forces due to the joint function   Lower production costs   Longer life   Higher resilience       

     LIST OF REFERENCE CHARACTERS 
     
         
           10  Threaded spindle (1 st  embodiment) 
           11  Threaded spindle (2 nd  embodiment) 
           12  Thread 
           20  Drive part 
           21  Stop boss 
           23  Stop element 
           24  Cam 
           25  Coupling element 
           26  Stop area 
           30  Threaded part 
           31  External thread 
           40  Groove 
           42  Groove 
           50  Threaded nut 
           51  Thread of the threaded nut 
           53  Stop element 
           53 ′ Cam 
           54  Stop recess 
           55  Coupling element 
           56  Area 
           57  Face 
           58  Face 
           61  Circlip 
           70  First journal 
           80   a  Second journal (1 st  embodiment) 
           80   b  Second journal (2 nd  embodiment) 
           90  Guide part 
         A Longitudinal axis 
         B Longitudinal axis 
         H Height of cam 
         M Distance when assembled 
         P Pitch 
         α Inclination 
         D ma  External diameter of the threaded nut 
         D ga  External diameter of the threaded part 
         V Radial off-set