Abstract:
A chassis actuator adjusting a movably mounted component of a chassis, which has a first actuator component connected to the movably mounted component and a second actuator component connected to a fixed chassis component. The actuator components are adjustable axially by a ball screw that has a threaded spindle and a nut which runs on spindle. The nut is driveable by a drive motor that has a rotor coupled to the nut and a fixed stator arranged axially symmetrically with respect to the nut. The rotor is coupled to the nut by a wrap spring which radially surrounds the nut and via which the nut is rotated during rotation of the rotor and which forms a brake device. The brake device can be actuated by an external chassis force which acts on and rotates the nut and builds up a friction moment that counteracts the rotation of the nut.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of DE 10 2010 052 920.6 filed Nov. 30, 2010 and this application is incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention relates to a chassis actuator for adjusting a movably mounted component of a vehicle chassis. 
     BACKGROUND OF THE INVENTION 
     Chassis actuators of said type are being increasingly used in so-called “active” chassis. There, said chassis actuators serve for example for toe or camber adjustment or for adjusting the vehicle ride height. Said adjustment is made possible in that the actuator has two actuator components which are movable relative to one another, one of which actuator components is arranged on a first chassis part and the other of which is arranged on a second chassis part. The two actuator components are connected by means of a ball screw which in turn can be driven by means of an electric motor which can be actuated by means of a suitable control device. When the electric motor is in operation, the nut is rotated relative to the spindle by means of the electric motor, which spindle is, as a result, displaced axially, thereby effecting the axial adjustment of the actuator components and, as a result, the adjustment of the chassis. 
     A problem with such chassis actuators is that forces acting externally on the chassis actuator, that is to say forces which are introduced into the actuator via the chassis itself, can lead to an unintentional adjustment of the actuator and therefore of the selected chassis setting, for which reason said forces must be absorbed or the actuator must be fixed in the selected adjustment position. This may be realized directly by means of the electric motor itself, that is to say said electric motor is provided with a continuous supply of electrical current in order to hold the actuator in the desired position. This however involves a large amount of expenditure in terms of control and also with regard to energy balance. 
     DE 38 36 255 C2 discloses a chassis actuator of the type mentioned in the introduction, in which, aside from a planetary gear set which couples the rotor in terms of movement to the nut and which is of complex design, an electromagnetic jaw clutch is provided for blocking the spindle nut when the electric motor is not supplied with electrical current. Said jaw clutch comprises a clutch disk which is arranged in an axially movable but non-rotatable manner on a collar, which faces away from the electric motor, of a spindle nut flange. The clutch disk is preloaded in the direction of the end wall of the actuator housing by means of a spring. By means of in each case one spur toothing on the clutch disk and the inner side of the end wall, it is possible in the engaged state of the clutch disk to obtain a positively locking connection of the clutch disk to the end wall, and to thereby obtain blocking of the spindle nut and of the threaded spindle. For decoupling of the claw clutch, an annular magnet is provided on the side of the spring, which annular magnet, when excited, pulls the clutch disk out of the spur toothing counter to the force of the spring, and consequently eliminates the blocking action. It is thus possible by means of said blocking device for the actuator to be fixed in position by purely mechanical means when the electric motor is not actuated. However, firstly, the design involves a high level of expenditure from both a structural and also a functional aspect, and secondly, a simultaneous supply of electrical current is always necessary both to the electric motor and to the annular magnet which opens the jaw clutch. If a supply of electrical current to the annular magnet is not possible on account of a fault, an adjustment of the actuator is not possible. 
     SUMMARY OF THE INVENTION 
     The invention is therefore based on the problem of specifying a chassis actuator which is of relatively simple construction and which has a high level of functional reliability. 
     To solve said problem, in a chassis actuator comprising a first actuator component for connecting to the movably mounted component and a second actuator component for connecting to a positionally fixed chassis component, wherein the two actuator components can be adjusted axially by means of a ball screw comprising a threaded spindle and comprising a nut which runs on said threaded spindle, and wherein the nut can be driven by means of a drive motor, which is designed as an electric motor comprising a rotor coupled in terms of movement to the nut and comprising a positionally fixed stator arranged axially symmetrically with respect to the nut, for the axial adjustment of the threaded spindle, it is provided that the rotor, which is rotatably mounted on the nut by means of two bearings axially spaced apart from one another, is coupled in terms of movement to the nut by means of a wrap spring which radially surrounds the nut and via which the nut is rotated during rotation of the rotor and which forms a brake device, which brake device can be actuated by means of an external chassis force which acts on and rotates the nut and which brake device builds up a friction moment which counteracts the rotation of the nut. 
     In the actuator according to the invention, firstly, the rotor is rotatably mounted exclusively on the nut of the ball screw, which is advantageous not least from an assembly aspect. In the chassis actuator according to the invention, for movement coupling and also for blocking of the ball screw, only a wrap spring is provided via which the rotor is connected to the nut. If the rotor rotates, then after the rotor has rotated relative to the nut by a defined angular increment, the nut is driven by the wrap spring, such that an axial adjustment of the spindle takes place. The movement coupling between the rotor and nut via the coil wrap spring is self-evidently configured such that driving of the nut and, as a result, a spindle adjustment is possible in both rotor rotational directions. This is however the case only when the movement or the force which acts on the actuator or the ball screw is actively introduced via the rotor. In contrast, if an external force is introduced into the system via the chassis, which force is introduced via the spindle, a very small, defined relative movement takes place between the nut and rotor, that is to say the nut is rotated relative to the stationary rotor by a small angular increment. Said rotation has the result that the coil wrap spring, depending on its design, is expanded or contracted, such that in any case, a friction moment is built up which counteracts the further rotation of the nut. The ball screw is blocked, and the external force, no matter how large, cannot lead to a further rotation of the nut because the friction moment built up by means of the wrap spring counteracts said force. 
     As is evident, the structural design of the chassis actuator according to the invention is significantly simpler than that of the actuator known from the prior art. Neither a movement-coupling planetary gear set nor a cumbersome coupling mechanism using a magnet element, which itself must be actively actuated, is used. In fact, purely mechanical movement coupling and movement blocking is realized in the chassis actuator according to the invention. Also, on account of the radially and axially optimized construction in the region of the movement coupling and of the blocking, that is to say in the region between the rotor and nut, a design is obtained which is optimized in terms of installation space. 
     As described, the mounting of the rotor is realized by means of two bearings by means of which the sleeve-shaped rotor is mounted in the region of its two ends on the nut. One bearing is expediently a fixed bearing while the other bearing is a floating bearing. As a floating bearing of said type, use may be made for example of a needle-roller bearing or a plain bearing. This is directly possible here because, in the event of an actuation of the chassis actuator, the nut and the rotor rotate at different rotational speeds only for a very short moment. When the movement coupling by means of the wrap spring takes effect, the rotor and the nut rotate at the same speed, such that simply-designed bearings, such as exactly the described needle-roller bearing or a plain bearing, can be directly used in the actuator according to the invention. 
     For assembly reasons, it is particularly advantageous for the floating bearing to be arranged in the region of that end of the rotor which is connected to the wrap spring. The floating bearing, that is to say for example the needle-roller bearing, is pressed into the rotor before the insertion of the latter and is pushed together with the rotor onto the nut, which considerably simplifies assembly. 
     The fixed bearing itself may be any desired bearing; use is preferably made here of a ball bearing or a four-point bearing. According to one refinement of the invention, for secure fixing, the fixed bearing may be fixed with its inner ring to the nut by means of two circlips and to the rotor by means of contact with its outer ring against an annular collar with a further circlip. The fitting of the circlips and, as a result, the fixing of the bearing, is also very simple and facilitates assembly. 
     In a refinement of the invention, the nut may additionally be mounted by means of a floating bearing on a housing component, in particular a housing cover, which permits an increase in the stiffness of the nut-rotor unit. In this case, the nut is also mounted on the housing by means of two hearings, specifically a hearing which is designed preferably as a fixed bearing and by means of which the nut is mounted in the region of one end thereof on a housing component, whereas the other end of said nut is mounted on another housing component, preferably on the described housing cover, by means of the described floating bearing. The rotor mounting and also the wrap spring coupling are situated between said two bearings. 
     The rotor itself is formed preferably in the manner of a sleeve, that is to say is a simply designed component which may also have a small wall thickness, because it ultimately serves merely to transmit the torque to the wrap spring and, via the latter, to the nut. 
     The inner diameter of the stator is slightly larger, over a length overlapping the rotor, than the outer diameter, such that a small air gap is formed. In particular in conjunction with the sleeve-like design of the rotor, this results overall in an advantageously low construction as viewed radially. 
     The nut, too, is preferably of hollow cylindrical and sleeve-like design. Closing elements, for example driver shoes and the like, which interact with the wrap spring are arranged on, in particular pressed onto, the outer side of said nut, interact with a correspondingly guided, for example angled end of the wrap spring. The rotor self-evidently also has corresponding closing elements which interact with the other end of the wrap spring and which drive the wrap spring. Said closing elements may be integrally formed on or likewise pressed onto or into the rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the invention is illustrated in the drawings and will be described in more detail below. In the drawings: 
         FIG. 1  shows a sectional view through a chassis actuator according to the invention in a first embodiment; 
         FIG. 2  shows an exploded illustration of the main individual parts of the chassis actuator from  FIG. 1 ; 
         FIG. 3  shows an exploded illustration of a module of the chassis actuator, comprising the ball screw, the wrap spring and a bearing which serves for mounting the nut of the ball screw; 
         FIG. 4  shows a further exploded illustration of a further module of the chassis actuator, comprising the assembled module from  FIG. 3  and additionally the rotor together with its bearings; and 
         FIG. 5  shows a sectional view through a chassis actuator of a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a sectional view through a chassis actuator  1  according to the invention, which is shown in even greater detail in the exploded illustrations of  FIGS. 2-4 . The chassis actuator  1  comprises a housing  2 , composed of a first, relatively large  5  housing component  3  and a second, relatively small housing component  4 . On the housing component  3 , there is arranged an actuator component  5  which closes off the housing to one side, and on the opposite side there is situated a second actuator component  6 , which is connected to a threaded spindle of a ball screw yet to be described below. The two actuator components  5 ,  6  can be adjusted axially relative to one another  10  by means of the ball screw yet to be described. The actuator component  5  should be fastened to a first chassis component  50 , whereas the actuator component  6  should be attached to a second chassis component  55  which is to be moved relative to the first chassis component  50  of a vehicle chassis  40 . It should be appreciated that in an alternate embodiment the actuator component  5  is fastened to the second chassis component  55  (the movably mounted component) and the actuator component  6  is fastened to the first chassis component (the positionally fixed chassis component). In other words, it should be understood that the actuator component  5  could be either fixed to a positionally fixed chassis component  50  or a movably mounted component  55 . Depending on which component the actuator component  5  is fastened, the actuator component  6  is fastened to the other component so that one actuator component is movable with respect to the other. 
     As described, a ball screw  7  is provided, comprising a threaded spindle  8  which has an external thread  9 . A sleeve-like nut  11  runs, mounted by means of balls  10 , on the threaded spindle  8 , which nut has an internal thread  12  in which the balls  10  run. Whereas the nut is mounted in a positionally fixed manner in the housing  2 , the threaded spindle  8  is axially movable, resulting in the axial adjustability of the actuator components  5 ,  6  relative to one another. 
     To drive the nut  10  in rotation, an electric motor  13  is provided, comprising a stator  14  and a sleeve-shaped rotor  15  which are spaced apart from one another by means of an air gap  16  in a manner known per se. The rotor  15  is mounted directly on the outside of the sleeve-shaped nut  11  by means of a first bearing, in this case a floating bearing  17  in the form of a needle-roller bearing which is pressed into the sleeve-shaped rotor  15 . At the other end, the sleeve-shaped rotor  15  is mounted likewise directly on the nut  11  by means of a second bearing, in this case a fixed bearing  18 . Said fixed bearing  18  is fixed with its inner ring  21  to the nut  11  by means of a first circlip  19 , which is arranged on the nut in a groove, and a second circlip  20 , which is likewise arranged on the nut. The outer ring  22  of the fixed bearing  18  bears against a stop collar  23  of the rotor, and the other side of the outer ring is retained by means of a third circlip  24  which is fixed in a corresponding groove on the rotor. 
     The rotor  15  rotates when the electric motor  13  is operated, that is to say when the stator  14  is supplied with electrical current. As a result, the nut  11  is rotated, which in the exemplary embodiment shown in  FIG. 1  is rotatably mounted on the housing  2  by means of a fixed bearing  25 . The outer ring  26  of the fixed bearing is held in a corresponding housing groove, whereas the inner ring  27  of the fixed bearing  25  bears against a stop collar  28  of the nut  11  and is fixed in position at the opposite side by means of a further circlip  29 . To be able to rotate the nut  11 , movement coupling between the rotor  15  and nut  11  is required, which movement coupling is realized here by means of a wrap spring  30 . The wrap spring  30  has respective drivers  31  at its two ends, which drivers interact with corresponding closing elements  32  on the nut and  33  on the rotor, respectively, in a manner known per se. In the assembled position, the respective closing elements  32 ,  33  engage into the wrap spring  30 , such that in the event of a rotation of the rotor, the respective closing element  33  which is active depending on the rotational direction engages on the respective driver side of the driver  31  and thereby twists the wrap spring. Said torsional or rotational movement is transmitted via the other driver side, or the other driver  31  respectively, to the corresponding closing element  32  of the nut  11 , such that the latter is rotated. Said rotation results, in turn, in the axial movement of the spindle  8  which runs in the nut  11 . Because in each case two closing elements  32 ,  33  are provided, an active actuating movement in both directions is evidently obtained. 
     The wrap spring  30  however serves not only to couple the rotor  15  and nut  11  to one another in terms of movement but rather also to block the ball screw  7  in order to prevent the latter from being inadvertently adjusted. If an external force acts on the threaded spindle for example via the actuator component, this causes a slight rotational movement of the nut  11 . Said rotational movement results in one of the closing elements  32  in turn engaging on the driver  31 . As a result, the wrap spring  30  is expanded, in contrast to normal active actuating operation when the rotational movement is introduced via the rotor  15 , during which the wrap spring  30  is contracted. As a result of the expansion of the wrap spring which however occurs in this operating situation, the outer side of the wrap spring  30  bears against the inner side of the cylindrical extension section  34  of the outer ring  26  of the fixed bearing  25 . In this way, a friction moment is built up which becomes ever greater with increasing acting force and resulting rotation of the nut  11 , until complete blockage occurs. The angular rotation of the nut before said blocking takes effect is relatively small, and amounts to only a few degrees, such that ultimately no actuator adjustment occurs. That is to say, the wrap spring here performs a double function, specifically firstly that of the movement coupling of the rotor  15  and nut  16 , and secondly that of the formation of a blocking or arresting element. 
       FIG. 2  shows the main components in an exploded illustration, wherein the main part component comprising the ball screw  7  and the rotor  15  is shown already in the assembled position. 
       FIG. 3  shows, in the form of an exploded illustration, the ball screw drive  7  together with the spindle  8  and nut  11 , onto which have been pressed the two closing elements  32  which are fixed to a carrier ring  35 . For assembly, firstly the wrap spring  30  is placed onto the ball screw drive  7 , such that the driver  31  engages between the two closing elements  32 . The fixed bearing  25  is subsequently placed on and subsequently fixed by means of the circlip  29 . 
     The module formed in this way is shown in  FIG. 4 . The rotor  15  is then to be mounted on said module. The floating bearing  17 , in this case in the form of a needle-roller bearing, is firstly pressed into the rotor at the inside. The rotor  15  together with the floating bearing  17  is then pushed onto the nut  11 , and the rotatable mounting on the nut  11  is realized by means of the floating bearing  17 . In the next step, the circlip  19  is snapped into the groove  36  on the nut  11 , whereupon the fixed bearing  18  is pushed onto the nut  11  or into the rotor  15 . The outer ring and the inner ring of the fixed bearing  18  are then fixed by means of the circlip  20 , which is inserted into the groove  37  on the nut, and by means of the further circlip  24 , which is inserted into a groove (not shown) on the inner wall of the rotor  15 . Said module, which is then fully assembled, is shown in the middle in  FIG. 2 . Said module is then inserted into the housing part  3 , whereupon the housing part  4  is placed on and the actuator components  5 ,  6  are subsequently fixed with the interposition of suitable sealing rings and the like. 
       FIG. 5  finally shows a further embodiment of a chassis actuator  1  according to the invention, the design of which is in this respect similar to that of the actuator  1  from  FIGS. 1 to 4 . The same reference numerals have therefore also been used for identical parts. Provided again are a ball screw  7  with spindle  8  and nut  11 , and an electric motor  13  comprising a stator  14  and a rotor  15 . The movement coupling and also the position blocking are realized again by means of a wrap spring  30  in the same way as described above. 
     Here, too, the rotor  15  is mounted on the nut  11  by means of a floating bearing  17  and a fixed bearing  18 . Here, however, the nut  11  is additionally mounted at its second end on a housing component, in this case a housing cover  39 , by means of a further floating bearing  38 . The stiffness of the nut-rotor unit can be increased in this way. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Chassis Actuator 
           2  Housing 
           3  Relatively Large Housing Component 
           4  Relatively Small Housing Component 
           5  Actuator Component 
           6  Second Actuator Component 
           7  Ball Screw 
           8  Threaded Spindle 
           9  External Thread 
           10  Balls 
           11  Nut 
           12  Internal Thread 
           13  Electric Motor 
           14  Stator 
           15  Rotor 
           16  Air Gap 
           17  Floating Bearing 
           18  Fixed Bearing 
           19  Circlip 
           20  Circlip 
           21  Inner Ring 
           22  Outer Ring 
           23  Stop Collar 
           24  Circlip 
           25  Fixed Bearing 
           26  Outer Ring 
           27  Inner Ring 
           28  Stop Collar 
           29  Circlip 
           30  Wrap Spring 
           31  Driver 
           32  Closing Element 
           33  Closing Element 
           34  Extension Section 
           35  Carrier Ring 
           36  Groove 
           37  Groove on the Nut 
           38  Floating Bearing 
           39  Housing Cover 
           40  Vehicle chassis 
           50  Positionally fixed chassis component 
           55  Movably mounted component