Abstract:
A damped ball joint includes a socket bush ( 30 ) having an outer wall, a ball socket ( 14 ) arranged in the socket bush ( 30 ), a ball pin ( 16 ) held in the ball socket ( 14 ), a casing bush ( 32 ) having an inner wall and being arranged concentrically outside the socket bush ( 30 ), and an elastomer body ( 34 ) provided between the socket bush ( 30 ) and the casing bush ( 32 ). The elastomer body ( 34 ) has at least one stop section (38) which, in an unstressed state of the ball joint, does not lie simultaneously against the outer wall of the socket bush ( 30 ) and the inner wall of the casing bush ( 32 ).

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a damped ball joint.  
         [0002]     Damped ball joints are used in vehicles, in particular in chassis components of motor vehicles such as track rods and stabilizer coupling struts. In travelling operation the joints are exposed to alternating stresses in axial and radial direction. In order to counteract these stresses, currently dampers are used which are made of cylindrical rubber/metal combinations. The dampers, which are stressed in alternating load applications with regard to thrust, are arranged substantially in axial direction of the corresponding vehicle components, the axial direction corresponding to the axial direction of the pin shaft of the ball joint or of an axial joint coupled to the ball joint. In order to include such dampers structurally, the shafts are constructed so as to be quite bulky. This may lead to problems with surrounding components. A further disadvantage is the considerable increase in weight of the joint.  
         [0003]     German utility model DE 93 18 586 U1 shows a ball joint comprising a socket bush, a ball socket arranged in the socket bush, a ball pin held in the ball socket, and a casing bush arranged concentrically outside the socket bush. An elastomer sleeve is arranged between the socket bush and the casing bush of the ball joint. To improve the radial damping, the elastomer sleeve is provided with notches at several points.  
         [0004]     It is an object of the invention to provide a ball joint enabling an improved absorbing or reducing of introduced stresses.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     The ball joint according to the invention comprises a socket bush having an outer wall, a ball socket arranged in the socket bush, a ball pin held in the ball socket, a casing bush having an inner wall and being arranged concentrically outside the socket bush, and an elastomer body provided between the socket bush and the casing bush. The elastomer body has at least one stop section which, in an unstressed state of the ball joint, does not lie simultaneously against the outer wall of the socket bush and the inner wall of the casing bush. Thus, in particular, radially acting forces introduced via the socket bush of the ball joint can be effectively damped. If the ball joint according to the invention is used in a vehicle steering system, the oscillation and shock stresses introduced via the wheels during travelling operation can be reduced. This contributes to a reduction in wear of the intercalated components, to a gentler response behaviour of the steering and therefore to an increase in steering comfort.  
         [0006]     In order to achieve an initially linear and, with increasing stress of the socket bush of the ball joint, a progressive damping characteristics, the stop section lies against the outer wall of the socket bush and is spaced apart from the inner wall of the casing bush.  
         [0007]     To improve the damping behaviour upon tensile and compressive stresses, provision is made that the elastomer body has at least two opposite stop sections.  
         [0008]     On introduction of stresses via a joint shaft of the ball joint, optimum damping results are achieved in that the stop section is aligned to the longitudinal axis of the joint shaft.  
         [0009]     The damping in the axial direction of the ball joint, as defined by the orientation of the ball pin, can be improved by an encircling elastomer layer provided on at least one of the two end faces of the socket bush.  
         [0010]     The construction of the ball joint can be simplified in that the socket bush, the casing bush and the elastomer body are part of a pre-assembled damper bearing which is inserted into a joint head of the ball joint. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  shows a sectional side view of the individual parts of a ball joint according to the invention;  
         [0012]      FIG. 2  shows an enlarged top view of the damper bearing of the ball joint;  
         [0013]      FIG. 3  shows a top view of the joint head and the joint shaft of the ball joint;  
         [0014]      FIG. 4  shows a side view, partially in section, of the composed ball joint connected with an axial joint; and  
         [0015]      FIG. 5  shows a diagram to illustrate the damping behaviour of the ball joint with tensile and compressive stress. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     The ball joint described below consists substantially of the following components illustrated in  FIG. 1 : a closure cover  10 ; a plate spring  12 ; a ball socket  14 ; a ball pin  16  held in the ball socket  14  and having a ball head  18  and a pin shaft  20 ; a damper bearing  22 ; a joint head  24  with formed-on joint shaft  26 ; and a sealing element  28 .  
         [0017]     The damper bearing  22  is made up of a socket bush  30  and a concentrically spaced apart outer casing bush  32  (in relation to the longitudinal axis X of the ball joint defined by the longitudinal axis of the pin shaft  20 ). Between the socket bush  30  and the casing bush  32  an elastomer body  34  is arranged. The elastomer body  34  is firmly connected via two opposite holding sections  36  both to the outer wall of the socket bush  30  and the inner wall of the casing bush  32  (see  FIG. 2 ). Viewed in peripheral direction of the bushes  30 ,  32 , the elastomer body  34  has two opposite, bead-like stop sections  38 . The staggered stop sections  38  are offset with respect to the holding sections  36 , which are spaced apart from the inner wall of the casing bush  32 . The elastomer-free intermediate spaces  40  thus formed in peripheral direction between the holding sections  36  represent functional zones, the mode of operation of which will be explained later.  
         [0018]     The socket bush  30  has a substantially cylindrical interior space which changes at one end face into a ball shape having an opening  41  for the pin shaft  20  of the ball pin  16 . At the other end face of the socket bush  30 , an encircling radial bearing groove  42  is formed. On both of the end faces of the socket bush  30  an encircling elastomer layer  44  is provided.  
         [0019]     The interior space of the joint head  24  is defined by a multi-stepped bore. The interior space is composed of a first section  46  with a larger diameter and a second section  48  with a smaller diameter which changes into an end-face passage opening  49  for the pin shaft  20  of the ball pin  16 .  
         [0020]     On assembly of the ball joint, at first a structural unit consisting of the ball socket  14 , the ball pin  16  and a grease filling is inserted into the interior space of the socket bush  30 . By means of the preformed plate spring  12 , the arm ends of which are fixed under prestress in the bearing groove  42 , an axial pressure is exerted onto the ball socket  14  via the convex central cross-piece of the plate spring  12 . Thus, the rotational and tilting moments are controlled, and an adjustment of the ball socket  14  in the case of wear is provided for.  
         [0021]     The damper bearing  22  is inserted into the joint head  24  onto the radial shoulder of the stepped bore formed between the second section  48  and the passage opening  49 , so that the stop sections  38  of the elastomer body  34  are aligned parallel to the longitudinal axis Y of the joint shaft  26  (see  FIG. 2 ). By means of suitable measures, the damper bearing  22  is secured axially and radially. A relative small gap dimension is kept between the shoulder of the stepped bore and the elastomer layer  44  encircling the end face of the socket bush  30 . The passage opening  49  of the stepped bore is constructed parallel to the longitudinal direction Y of the joint shaft as an elongated hole (see  FIG. 3 ) with a steel covering towards the socket bush  30  as security against so-called misuse forces in extraction direction (directed downwards in  FIG. 1 ).  
         [0022]     The sealing element  28  is supported on the one hand in an external radial groove  50  of the joint head  24  and on the other hand on the pin shaft  20  of the ball pin  16  by means of suitable clamping elements, and thus protects the ball joint from external influences.  
         [0023]     Above the damper bearing  22 , the cap-shaped closure cover  10  is inserted into the first section  46  of the interior space of the joint head  24 . The closure cover  10  is fixed, for example, by bending over the edge of the joint head  24  surrounding the first section  46 . The closure cover  10  seals the ball joint off against external influences and serves as security against misuse forces in the pressing-out direction (directed upwards in  FIG. 1 ). Here also, a small gap dimension is kept between the base of the closure cover  10  and the elastomer layer  44  encircling the end face of the socket bush  30 .  
         [0024]     The ball joint can be used, for example, in a steering system of a motor vehicle for coupling the track link steering arm to the steering gear. For this, the ball joint is fastened via a thread of the pin shaft  20  on the track link steering arm. The connecting to the steering gear is undertaken by an axial joint  52  (see  FIG. 4 ). The axial joint  52  comprises an axial housing pin  54 , which represents the connection to the steering rack of the steering system, and a threaded pin  56 . By means of the external thread of the threaded pin  56 , matching the internal thread of the joint shaft  26 , the axial joint  52  and the ball joint are connected with each other so as to be longitudinally adjustable. The connection is secured by means of a hexagonal nut  58 .  
         [0025]     The hysteresis-type behaviour of the “elastic rigidity” of the ball joint as a function of an introduced tensile or compressive stress onto the socket bush  30  in axial direction of the track rod is illustrated in  FIG. 5 . By means of the socket bush  30 , the elastomer body  34  is acted upon radially by a combined thrust/pressure force. In the first phase of the traction or pressure action, owing to the elastomer-free function zones  40 , the ball joint firstly shows a defined, linearly rising elastic rigidity. As soon as the corresponding stop section  38  of the elastomer body  34  comes into abutment with the inner wall of the casing bush  32 , the stop section  38  then takes up the further deformation work and therefore represents a damped stop with a progressive elastic rigidity.  
         [0026]     By means of an increase/reduction of the elastomer component of the elastomer body  34  and/or different Shore hardnesses, various rigidities of the damping can be realized. Furthermore, the damping behaviour can be influenced by means of the shaping, in particular by the extent of the stop sections  38 . Different shapes of the two stop sections  38  are also conceivable. A different number of stop sections  38  and/or holding sections  36  and/or a different arrangement in peripheral direction can also be provided.  
         [0027]     With a stress application of the ball pin  16  in the direction of the longitudinal axis X, the ball joint is stressed with regard to thrust. In this case the elastomer layers  44  encircling the end face of the socket bush  30 , bring about a damped stop.