Abstract:
The present invention relates to an actuator for generating a rotational positioning movement, wherein the actuator comprises an electric motor ( 1 ) and a reduction gear ( 2 ) which consists of two assemblies ( 4, 5 ). The first assembly ( 4 ) is formed by a gear of the harmonic, cycloid or wobble, type and the second assembly ( 5 ) by a gear of the single-step or multistep planetary or Wolfrom type, whereby both assemblies ( 4, 5 ) are so tuned to each other, that the reduction gear ( 2 ) is not self-locking.

Description:
[0001]    This application is a National Stage completion of PCT/EP2007/063112 filed Dec. 3, 2007, which claims priority from German patent application serial no. 10 2006 058 133.4 filed Dec. 9, 2006. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an actuator for generating rotational positioning movement. 
       BACKGROUND OF THE INVENTION 
       [0003]    Actuators are frequently used in vehicles for generating positioning movements which are controlled by the system or the driver. Actuators may, for example, adjust a vehicle seat, support the steering force or adjust the ride height of the chassis to the driving speed. The energy required for this purpose is normally provided in electric, hydraulic or pneumatic form, whereby electric actuators may be cost-effectively positioned in nearly any place in the vehicle because of the easy transfer of the electric energy from the energy source to the actuator. Moreover, nearly all types of vehicles have an electric energy source, like a generator or battery, by means of which, compared to pneumatic or hydraulic actuators, electric actuators are easier to integrate in existing vehicle systems. 
         [0004]    Besides an electric motor, electric actuators for generating rotational positioning movement mostly comprise a reduction gear which reduces the speed at the output shaft of the electric motor to a desirable level or increases the torque generated by the electric motor. In this respect, EP 1 627 757 A1 discloses an electric actuator for generating rotational positioning movement between halves of a vehicle stabilizer bar, the actuator consisting of a brushless electric motor, a reduction gear and a case surrounding the electric motor and the reduction gear. A two-step planetary gear or a single-step well gear (also known as harmonic gear) is disclosed as reduction gear. Since the voltage in the power system of a vehicle, as well as the maximum current that can be tapped, is usually very limited, the electric motor can only generate a low torque for which reason the reduction gear increases the torque generated by the electric motor to the required level by means of a high gear ratio. For this purpose, single-step or multistep planetary gears comprise multiple rotating elements which increase the price of the reduction gear because of its complexity and reduce the positioning speed because of the mass inertia. For this purpose, a harmonic drive is, in fact, less complex and, because of the lower mass inertia, has a high positioning speed for accomplishing the required high gear ratios with higher efficiency and high transmission capacity, but its installation space compared to the consecutively arranged planetary gears is less compact, i.e. it has a comparatively large outer diameter. Therefore, a single-step harmonic gear may be disadvantageous, considering the cramped installation conditions available in a vehicle. 
       SUMMARY OF THE INVENTION 
       [0005]    The object of the present invention is therefore to create an actuator for generating rotational positioning movements which is suitable for the cramped installation conditions of a vehicle and has a high positioning speed. 
         [0006]    Accordingly, an actuator for generating rotational positioning movement comprises an electric motor and a reduction gear connected to an output element of the motor. 
         [0007]    In order to achieve an increase in the positioning speed of the actuator considering the installation conditions prevailing in a vehicle, like limited voltage, current and installation space, the masses mobilized in the reduction gear have to be reduced and the efficiency of the reduction gear has to be increased, and the positioning forces acting against the actuator have to be utilized for which reason the reduction gear according to the present invention is designed such, that it is not self-locking. Since a single reduction gear of the harmonic, cycloidal or wobble type has a comparatively large diameter for the gear ratio required for generating the required torque, has no acceptable efficiency and is self-locking from experience, and unadulterated stepped, planetary or Wolfrom gears have too-large a mass inertia, the reduction gear of the actuator according to the present invention comprises two component assemblies. The first assembly comprises a single-step harmonic, cycloidal or wobble gear, and the second assembly comprises a single-step or multistep planetary, stepped or Wolfrom gear. Both assemblies are interconnected such, that the required total gear ratio results from a high efficiency and a compact installation space, and the reduction gear is simultaneously not self-locking. Compared to an unadulterated planetary, stepped or Wolfrom gear, the reduction gear has low complexity and inertia, resulting in a drop in the peak current consumption of the electric motor. As a result, it may be designed with a smaller size which allows a further reduction in the required installation space. 
         [0008]    An embodiment of the present invention provides, that the first assembly is arranged between the electric motor and the second assembly, whereby the first assembly, i.e. the harmonic, cycloidal of wobble gear, is arranged on the side of the reduction gear having the lower torque. Since the torque placed on the first assembly is consequently reduced, it can be designed more compact, i.e. the diameter of the first assembly may be considerably reduced. It is especially advantageous, if the gear ratio of the first assembly is below 1:40, as higher gear ratios in practice cause unfavorable efficiency and self-locking. In addition, it is advantageous, if the second assembly comprises at least one planet carrier, at least one sun gear and, if necessary, at least one ring gear, whereby one of the planet carriers or one of the ring gears serves as a preferred output element of the reduction gear, from which the rotational movements can be tapped. 
         [0009]    A preferred application of the actuator according to the present invention provides, that it is used as part of a vehicle stabilizer bar which is divided in two parts and electromechanically adjustable for roll stabilization or ride height control. For roll stabilization, a single actuator according to the present invention is inserted between both parts of the vehicle stabilizer bar, as a result of which in case of rolling movement, both parts may rotate against one another such that they generate movement in the opposite direction of the rolling movement thus attenuating or eliminating the rolling movement. In an especially preferred embodiment of the present invention a first part of the vehicle stabilizer bar is connected stationary to the output element of the reduction gear of the actuator, and a second part of the vehicle stabilizer bar is connected to the actuator case. 
         [0010]    For controlling the ride height of the vehicle, an actuator according to the present invention is connected in a rotationally fixed manner to a vehicle body, as well as to at least one of the parts of the vehicle stabilizer bar, as a result in case of a rotational positioning movement the actuator may lift the vehicle body on both sides and/or on the vehicle side that is operatively connected to the part of the stabilizer bar. Thus, two actuators according to the present invention may each be connected to a part of the vehicle stabilizer bar and coupled to one another electronically or mechanically, such that for controlling the ride height the actuators generate rotational movement of both parts of the stabilizer bar that is aligned with the vehicle body. Or an actuator according to the present invention may also be connected to both parts of the stabilizer bar such, that it twists both parts relative to the vehicle body by means of a rotational positioning movement. 
         [0011]    In another preferred embodiment, the actuator according to the present invention is used for reinforcing the steering force generated by the driver for changing the driving direction. For this purpose, the output element of the actuator is mechanically coupled to a push rod of the steering mechanism, for example a steering rod or a tie rod, and applies a force on the push rode in the direction of the steering movement, when the driver makes a steering movement. The conversion of the rotational positioning movement of the actuator to a linear movement of the push rod required for this purpose may, for example, be accomplished by means of a lever or a spindle nut and a spindle. The force applied by the actuator may additionally be adjusted to the momentary vehicle speed or to the steering force applied by the driver by controlling the output of the electric motor of the actuator by means of sensors. 
         [0012]    Besides the described examples, the actuator according to the present invention may be used in multiple applications, where rotational positioning movement is required. By way of example the use of the actuator in a winch could still be mentioned, where the actuator is used as a compact motor gear unit for retracting or extending a tensioned winch rope. In this case it is especially advantageous, that the reduction gear of the actuator is not self-locking, while featuring a high gear ratio and good efficiency at the same time, as a result of which, on the one hand, the tensioned winch rope may be wound off the winch without the electric motor having to generate kinetic energy and, on the other hand, heavy loads may be moved even at a low motor output. In cases where the actuator according to the present invention is used in technical areas, where low actuating forces develop, for example, using the actuator for adjusting a vehicle seat or for adjusting the ventilation flaps of a ventilation system in a vehicle, the reduction gear may be made in part or completely of plastic for weight and cost saving reasons. In case it is necessary that the rotational positioning movement of the actuator should be executed very accurately or measured very accurately, it may additionally comprise an angle sensor which can be disposed directly on the electric motor, between the electric motor and the reduction gear, in the reduction gear, or at the output element of the reduction gear. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will hereafter be explained in more detail by means of examples and drawings from which further advantageous embodiments will become apparent. Schematic diagrams respectively show in 
           [0014]      FIG. 1  an actuator according to the present invention having a harmonic gear and a two-step planetary gear; 
           [0015]      FIG. 2  an actuator according to the present invention having a harmonic gear and a single-step Wolfrom gear in modular design; and 
           [0016]      FIG. 3  an actuator according to the present invention of an electromechanically adjustable vehicle stabilizer bar with a harmonic gear and a sing-step Wolfrom gear. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    The actuator shown in  FIG. 1  for generating rotational positioning movements comprises an electric motor  1  and a reduction gear  2  which are mounted in a common housing  3 . The reduction gear  2  consists of two assemblies  4 ,  5 , the first assembly  4  consisting of a well-known harmonic gear having a wave generator  6 , an elastic wheel  7  and a rigid wheel  8 , and the second assembly  5  consisting of a well-known two-step planetary gear having two sun gears  9 ,  10 , two planet carriers  11 ,  12 , two ring gears  13 ,  14  and at least two planetary gears  15 ,  16 . For the generation of rotational positioning movement, the motor output shaft  18  attached to the rotor  17  of the electric motor  1  actuates the wave generator  6  of the harmonic gear, generating the rotation of the elastic wheel  7  against the rotational direction of the wave generator  6  owing to the difference in the number of teeth between the elastic wheel  7  and the rigid wheel  8 . The elastic wheel  7  forms the output element of the harmonic gear which in turn acts upon the first sun gear  9  of the two-step planetary gear. The planetary gear  9  moves the first planetary gears carried by the first planet carrier  11  along the first ring gear  13 , consequently setting the first planet carrier  11  in rotation. It is In turn used as an output element of the first planetary gear and actuates the second sun gear  10  which moves the second planetary gear  16  along the second ring gear  14 . The movements of the second planetary gears  16  generate the rotational movement of the second planet carrier  12  used as output element of the reduction gear, the second planet carrier  12  being connected in a rotationally fixed manner to a lever  19  protruding from the actuator. The rotational positioning movement may be tapped from there, whereby the output element of the reduction gear may alternatively also be connected to a ball nut or pinion which may also be used for converting the rotational positioning movement to linear positioning movement. 
         [0018]    Besides the electric motor  1 , the actuator illustrated in  FIG. 2  comprises a reduction gear  2  consisting of a harmonic gear and a one-step Wolfrom gear. The entire actuator is configured in modular design, whereby the electric motor  1 , the first assembly  4  consisting of the harmonic gear, and the second assembly  5  consisting of the Wolfrom gear, as well as the output element of the actuator, respectively form one module. Therefore, the actuator may be adjusted in a modular manner to the specific operating conditions, for example, by means of a more powerful electric motor  1  or a second assembly with a higher gear ratio or higher stability. In addition, defective or damaged modules may be easily replaced. The individual assemblies  4 ,  5  are connected to one another via claw clutches, for example, which allow any consecutive alignment of the assemblies, especially the modules of the assemblies  4 ,  5 . According to the present invention, the gear types of the assemblies  4 ,  5  may be freely varied by consecutively aligning the modules of the assemblies  4 ,  5  in any order, for example, the first assembly may consist of a module with a harmonic, cycloidal or wobble gear and the second assembly of a consecutively arranged first module with a single-step planetary gear and a second module with a two-step planetary gear. In theory, it would also be possible to arrange two or more modules consecutively with a harmonic, cycloidal or wobble gear each which, however, has no technical advantages compared to a single, slightly larger harmonic, cycloidal or wobble gear and therefore is not the subject matter of the present invention. 
         [0019]    In conjunction with the first assembly of  FIG. 1 , the first assembly  4  shown in  FIG. 2  consists of a wave generator  6  as input element, a rigid wheel  8  and an elastic wheel  7  as output element. The wave generator  6  is connected to the motor output shaft  18  via the clutch  20 . The elastic wheel  7  is in turn connected to a sun gear  21  used as input element of the Wolfrom gear via another clutch  20 , where the sun gear  21  drives at least one planetary gear  22  along a first stationary ring gear  23  during rotational movement. The planetary gear  22  in turn rotates on the planet carrier  24  that is mounted so as to rotate on the sun gear  21  and actuates a second ring gear  25  that is mounted so as to rotate in the housing  3 , whereby the rotational movement of the planetary gear  22  around its own axis and the rotational movement of the planet carrier  24  around the axis of the sun gear  21  superimpose on the rotation of the second ring gear  25 . The second ring gear  25  is used as output element of the reduction gear  2  and is connected to the output element of the actuator by means of a third clutch  20 , the output element being configured, for example, as a lever  26  mounted in a case  3 . 
         [0020]      FIG. 3  shows a variation of the actuator according to the present invention illustrated in  FIG. 2  which is suitable for use in an adjustable vehicle stabilizer bar. The gear lay out of the reduction gear  2  fully corresponds to the actuator of  FIG. 2 . In order not to have a negative effect on the springiness of a vehicle having an adjustable vehicle stabilizer bar divided in two parts  27 ,  28 , both parts  27 ,  28  of the stabilizer bar together should have the same or similar springiness as a one-piece nonadjustable vehicle stabilizer bar for which reason they should be arranged as close to one another as possible. The second ring gear  25  forms the output element of the actuator of the Wolfrom gear which is connected stationary to the first part  27  of the stabilizer bar. It is directed out of the housing  3  along the longitudinal axis of the actuator through both assemblies  4 ,  5 , the clutches  20  and the output shaft  18 , as well as through the rotor  17  of the electric motor  1 . The second part  28  of the stabilizer bar is, on the other hand, connected in a fixed manner with the side of the housing  3  opposite the point where the first part  27  of the stabilizer bar emerges from housing, whereby the ends of the parts  27 ,  28  of the stabilizer bar are close to one another and thus the common length of the parts  27 ,  28  of the stabilizer bar corresponds to the approximate length of a one-piece stabilizer bar. 
       REFERENCE NUMERALS 
       [0000]    
       
           1  Electric motor 
           2  Reduction gear 
           3  Housing 
           4  First assembly 
           5  Second assembly 
           6  Wave generator 
           7  Elastic wheel 
           8  Rigid wheel 
           9  First sun gear 
           10  Second sun gear 
           11  First planetary carrier 
           12  Second planetary carrier 
           13  First ring gear 
           14  Second gear ring 
           15  First planetary gear 
           16  Second planetary gear 
           17  Rotor of the electric motor 
           18  Motor output shaft 
           19  Lever 
           20  Clutch 
           21  Sun gear of the Wolfrom gear 
           22  Planetary gear of the Wolfrom gear 
           23  First ring gear of the Wolfrom gear 
           24  Planet carrier of the Wolfrom gear 
           25  Second ring gear of the Wolfrom gear 
           26  Lever 
           27  First part of the stabilizer bar 
           28  Second part of the stabilizer bar