Abstract:
A linear actuator for driving an actuating member of an internal combustion engine of a motor vehicle, the linear actuator having two rolling bearings for scanning mutually opposing sides of a rib that is formed as a guide curve. The rib has a variable width, against which the two sensing bodies are biased to reduce or eliminate undesired reaction forces.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of PCT Application PCT/EP2015/075460, filed Nov. 2, 2015, which claims priority to German Application DE 10 2014 222 413.6, filed Nov. 3, 2014. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention concerns a linear actuator for driving an actuating member, in particular of an internal combustion engine of a motor vehicle, with a rotatable drive shaft and an axially displaceable ram for adjusting the actuating member, with a guide curve driven by the drive shaft about a rotary axis and with a guide member scanning the guide curve. The guide member has two sensing bodies, and the sensing bodies are pretensioned against opposite sides of the guide curve. 
       BACKGROUND OF THE INVENTION 
       [0003]    Such linear actuators are used for example by exhaust gas recirculation valves in internal combustion engines of modern motor vehicles. The pretensioning of two sensing bodies against opposite sides of the guide curve serves to guarantee a play-free drive of the ram. The advantage of the known linear actuator is that the guide curve may be configured almost arbitrarily, and for example allow non-linear characteristic curves between the rotary angle of the drive shaft and the travel of the ram. 
         [0004]    However, in particular for non-linear characteristic curves, the problem exists that undesirable reaction forces occur between the sensing bodies and the guide curve. These reaction forces must be absorbed by a spring element which pretensions the sensing bodies against the opposite sides of the guide curve. The reaction forces and the spring forces lead to mechanical loads and uneven force-travel curves of the linear actuator, and are therefore undesirable. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is based on the problem of refining a linear actuator of the type cited initially, so that it avoids undesirable reaction forces. 
         [0006]    This problem is solved according to the invention in that the width of the guide curve is configured so as to be variable. 
         [0007]    With this design, a play-free guidance of the ram may be achieved even for non-linear characteristic curves. An even force-travel curve is achieved by the corresponding design of the width of the guide curve. Thanks to the invention, the guide curve may have a different width close to the rotary axis than remote from the rotary axis. Thus, the linear actuator may have a progressive characteristic curve of the rotary angle of the rotary axis to the travel of the ram. The forces on the drive shaft remain constant over the rotary angle. The width of the guide curve is designed such that the spacing of the sensing bodies and hence also the pretension forces always remain constant over the entire rotary angle of the rotary axis. Thus undesirable reaction forces are avoided. 
         [0008]    According to another advantageous refinement of the invention, particularly even force-travel curves can easily be achieved if the width of the guide curve is configured so as to change continuously over the entire travel of the ram. 
         [0009]    According to another advantageous refinement of the invention, the force-travel curve is smoothed out further if the guide curve is narrower in a portion arranged close to the rotary axis than in a portion remote from the rotary axis. Preferably, the difference in width of the portions of the guide curve is around 0.1 to 0.2 mm. 
         [0010]    If a connecting line of the sensing bodies precisely aligns with the rotary axis, during driving of the drive shaft, transverse forces are generated which are transmitted to the ram. According to another advantageous refinement of the invention, such transverse forces can easily be avoided if a connecting line of the sensing bodies is offset relative to the rotary axis. Preferably, the offset of the connecting line is around 1 mm. 
         [0011]    According to another advantageous refinement of the invention, a play in the sensing bodies on the guide curve during drive of the ram, caused by temperature fluctuations for example, can easily be avoided if the guide member has a spring element for pretensioning the sensing bodies towards each other or away from each other. 
         [0012]    The guide curve could for example be configured as a groove, and the sensing bodies pretensioned against the wall of the groove. This however requires a particularly wide groove or very small sensing bodies. For actuating members for components of an internal combustion engine, however, the installation space is very limited. In particular, however, linear actuators provided for internal combustion engines of motor vehicles have a particularly high stability in a limited installation space if the guide curve has a protruding rib and the sensing bodies lie against opposite sides of the rib. 
         [0013]    According to another advantageous refinement of the invention, lateral loads and tipping moments in the linear actuator may be kept particularly low if the sensing bodies each comprise a roller bearing. 
         [0014]    According to another advantageous refinement of the invention, a proposed translation of the linear actuator may easily be set if the guide curve is arranged on a disc extending over a part circle, if the disc has a partial toothed rim on its periphery and a pinion driven by the drive shaft meshes with the partial toothed rim, and if the sensing bodies are connected to the ram of a valve body. 
         [0015]    According to another advantageous refinement of the invention, the linear actuator may be constructed particularly simply if the spring element is configured as a stirrup-shaped spring plate connecting the two sensing bodies together. 
         [0016]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention allows numerous embodiments. To further clarify its basic principle, one of these is depicted in the drawing and described below. The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0018]      FIG. 1  is a perspective view of a linear actuator with adjacent components of an actuating member, according to embodiments of the present invention; 
           [0019]      FIG. 2  is an enlarged, perspective view of a linear actuator, according to embodiments of the present invention; 
           [0020]      FIG. 3  is a partial sectional view taken through a guide member of a linear actuator, according to embodiments of the present invention; 
           [0021]      FIG. 4  is graph depicting a characteristic curve of the operation of a linear actuator, according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0023]      FIG. 1  shows an exhaust gas recirculation valve  1  of a motor vehicle, with an exhaust gas channel  2  and a recirculation channel  3 . The exhaust gas recirculation valve  1  has an actuating member  4  with a valve body  5  and a valve seat  6 . A linear actuator  8  driven by an electric motor  7  serves to drive the actuating member  4 . The linear actuator  8  has a fixed stop  9  and a second soft stop  10 . The second stop  10  is formed by the valve seat  6  against which the valve body  5  lies. 
         [0024]    The linear actuator  8  has a ram  11  for driving the valve body  5 . 
         [0025]      FIG. 2  shows a perspective, enlarged view of the linear actuator  8  from  FIG. 1 . It is noted here that the electric motor  7  drives a drive shaft  12  with a pinion  13 . The linear actuator  8  has a disc  14  extending over a partial circle, with a partial toothed rim  15  arranged on the periphery. The disc  14  is mounted rotatably about a rotary axis  24 . The pinion  13  drives the disc  14  via the partial toothed rim  15 . A guide curve  16  with a rib  17  is arranged on the disc  14 . A guide member  18  scanning the guide curve  16  has two mutually opposing sensing bodies  19 ,  20 . The sensing bodies  19 ,  20  each comprise a roller bearing  21 ,  22  configured as a ball bearing, and are connected together via a spring element  23 . The spring element  23  is formed stirrup-shaped and is made of spring steel. Furthermore, the spring element  23  is connected to the ram  11 . 
         [0026]    By rotation of the disc  14  about the rotary axis  24  by driving by the electric motor  7 , the roller bearings  21 ,  22  of the sensing bodies  19 ,  20  roll along the rib  17  of the guide curve  16 . The guide member  18  is moved up and down according to the form of the guide curve  16 . This movement is transmitted via the ram  11  to the valve body  5 , which finally opens or closes the exhaust gas recirculation valve  1 . 
         [0027]      FIG. 3  shows the linear actuator  8  in a cross-sectional depiction through the guide member  18 . Due to the cross-sectional depiction, the sensing bodies  19 ,  20  with the spring element  23  connecting the ram  11  from  FIG. 2 , are not shown. It is evident here that the ram  11  aligns with contact points of the two sensing bodies  19 ,  20  on the rib  17 . However, the contact points of the two sensing bodies  19 ,  20  on the rib  17  do not align with the rotary axis  24  of the disc  14  and hence the rotary axis  24  of the guide curve  16 . The rotary axis thus has an offset a to the connecting line of the sensing bodies  19 ,  20 . Thus the ram  11  also has the same offset a to the rotary axis  24  of the rib  17 . The width b of the rib  17  reduces continuously over the entire travel of the ram  11 . For this, the guide curve  16  has a portion c arranged close to the rotary axis  24 , and a portion d remote from the rotary axis  24 . The rib  17  is narrower in the portion c arranged close to the rotary axis  24  than in the portion d remote from the rotary axis  24 . 
         [0028]      FIG. 4  shows for clarification a progressive curve of the travel of the ram  11  over the rotary angle of the rotary axis  24 . 
         [0029]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.