Abstract:
A torsion bar spring arrangement for a wheel suspension of a motor vehicle includes an actuator arranged on a vehicle body or on a subframe and constructed to variably pre-tension the torsion bar spring arrangement, a coaxial first torsion bar spring having an output side that is connected by way of an output lever to a wheel suspension element of the wheel suspension, and a housing of the actuator supported on the vehicle body in at least one bearing location for movement in a circumferential direction and resiliently yieldingly supported on the vehicle body in the direction of torsional moments acting on the torsion bar spring by way of at least one spring element.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application, Serial No. 10 2013 002 713.6, filed Feb. 16, 2013, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a torsion bar spring arrangement for a wheel suspension of a motor vehicle. 
     The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
     In conventional torsion bar spring arrangements, the torsion bar spring is composed of only two components, namely a tubular spring and solid bar spring. The remaining components in the load path are designed to be absolutely rigid without affecting the overall spring constant of the system. For example, when a softer torsion bar spring needs to be realized, a first measure would include a reduction of the diameter of tubular spring and/or of the solid bar spring. However, the working capacity of the torsion bar would decrease by reducing the diameter, and the stresses would simultaneously increase disproportionately, so that the tubular spring and solid bar spring would have to be lengthened. However, such a change in length is not feasible due to the extremely critical space situation in the area of the wheel suspension. As a result, especially with the smaller vehicle production runs, where a reduction of the total spring stiffness is essential, such a rotary actuator can not be installed due to the high packing density. 
     It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved torsion bar spring arrangement for a wheel suspension of, in particular, a two-track vehicle, wherein the spring rate of the torsion spring can be additionally influenced by simple structural designs. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a torsion bar spring arrangement for a wheel suspension of a motor vehicle includes an actuator arranged on a vehicle body or on a subframe and constructed to variably pre-tension the torsion bar spring arrangement, a coaxial first torsion bar spring having an output side that is connected by way of an output lever to a wheel suspension element of the wheel suspension, and a housing of the actuator supported on the vehicle body in at least one bearing location for movement in a circumferential direction and resiliently yieldingly supported on the vehicle body in the direction of torsional moments acting on the torsion bar spring by way of at least one spring element. 
     According to the invention, it is proposed that the housing of the actuator is no longer rigidly mounted on the vehicle body without having a resilient property, but is mounted resiliently yielding at a body-side bearing point of the vehicle with a defined spring rate. In this way, a resilient component is connected upstream in series with the torsion bar spring in a simple manner, or superimposed, which lowers the spring rate of the spring arrangement and reduces the torsional loads on the torsion bar springs. 
     Optionally, a nested torsion bar spring arrangement composed of a tubular spring and a solid bar spring may be augmented with the spring-elastic bearing of the motor-gear unit. Thereby, the total spring rate can be adjusted downward while maintaining the geometric dimensions, i.e. the length of the torsion bar spring arrangement. Accordingly, the rotary actuator can then also be installed with smaller vehicle production runs, where a reduction in the overall stiffness of the wheel suspension is required. 
     According to another advantageous feature of the present invention, the motor-gear unit may be mounted at the bearing point on the vehicle body so as to be movably in the circumferential direction and may be supported on the vehicle body by at least one spring element in the direction of the torsion moments acting on the rotary bar springs. This proposed arrangement quasi divides the torsion bar spring arrangement into the torsion bar and the additional spring element, namely with an interposed motor-gear unit. The motor-gear unit produces the variable pre-tension in a conventional manner, whereas the torsional moment is supported by the output lever and the torsion bar spring is supported on the actuator unit and on the vehicle body (or subframe) by the housing of the actuator unit via the spring element. This advantageously produces a simpler design of the motor-gear unit in conjunction with a simplified, in particular shorter torsion bar spring. 
     According to another advantageous feature of the present invention, at least one radially outwardly projecting lever, which is clamped between two opposing springs supported on the vehicle body, may be mounted on the motor-gear unit or on its housing. This produces a dynamically sensitive torsion bar spring arrangement having a defined central position, for example, in a design position of the wheel suspension, and high-frequency matching of the trim with the compression and/or rebound movements of the wheel suspension. 
     The springs may preferably be formed by coil compression springs and/or by rubber-elastic buffers. The buffers may at the same time also be designed as progressively acting spring stops. 
     According to another advantageous feature of the present invention, the spring element may be composed of at least one coil spring arranged around the motor-gear unit and acting in both rotation directions, with the spring ends being anchored on the vehicle body and the motor-gear unit. When little additional installation space surrounding the rotatable mounted motor-gear unit is available, the coil spring which also has a defined torsional rigidity may be designed so as to be able to absorb from a central position (design position) rebound and compression movements commensurate with the defined spring deflection. 
     Due to the additional spring element on the rotatably mounted motor-gear unit, the rotary bar spring may be designed as a single piece and drivingly connected at one end with the output lever and at its other end with the output element of the motor-gear unit. A simple, inexpensive torsion bar spring can then be employed and the motor-gear unit can have a simple design for easy production which need not be designed as a hollow-shaft assembly with an internal torsion bar spring. 
     The additional spring element may be an additional torsion bar spring supported on the housing of the motor-gear unit which is supported at its free end on the vehicle body. The torsion bar spring may be connected with one end to the actuator housing and supported with the other end on a torque support on the vehicle body. The first torsion bar spring extending to the output lever and the second torsion bar spring supported on the torque support and/or the cylindrical housing of the motor-gear unit of the actuator may be constructed coaxially with respect to each other. 
     The first torsion bar spring and the second torsion bar spring may also be arranged at the opposing end faces of the cylindrical housing of the motor-gear unit of the actuator. 
     Furthermore, to attain a structurally simple design, the first torsion bar spring may be made as a single piece, for example, of spring steel and may be drivingly connected at one of its ends to the output lever and at its other end to the output element of the motor-gear unit. 
     Lastly, two torsion bar spring arrangements oriented transversely to the vehicle&#39;s longitudinal direction may be provided on an axle of the vehicle (front and/or rear axle), wherein their motor-gear units are positioned (inside) in the area of the vehicle&#39;s vertical longitudinal center plane, whereas the torsion bar spring or the torsion bar spring with the output lever are positioned at the outside. Furthermore, the motor-gear unit may also be aligned in the longitudinal direction. 
     The aforedescribed advantageous embodiments and/or modifications of the invention, which are also recited in the dependent claims, can be employed either individually or in any combination with each other—except for example in cases of clear dependencies or incompatible alternatives. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
         FIG. 1  is a plan view on the lower plane of a left-side wheel suspension of a rear axle of a motor vehicle, with a lower transverse control arm, a shock absorber and a torsion bar spring arrangement according to the present invention; 
         FIG. 2  is an equivalent diagram of the suspension arrangement of  FIG. 1  illustrating individual spring constants c 1  and c 2 , which essentially determine the total spring rate; 
         FIG. 3  is the torsion bar spring arrangement according to the present invention in a side view; 
         FIG. 4  is another torsion bar spring arrangement according to the present invention in a view corresponding to  FIG. 3 , and 
         FIG. 5  is a torsion bar spring arrangement according to the present invention in a view corresponding to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
     Turning now to the drawing, and in particular to  FIG. 1 , there is shown a lower plane of a left-side wheel suspension for motor vehicles designated by  10 , with a lower transverse control arm  12  which is articulated, on the one hand, on an only partially shown subframe  14  and, on the other hand, on an only schematically indicated wheel carrier for a rear wheel  17 . The upper control arm guiding the wheel carrier is not shown. 
     The left-side wheel suspension shown in  FIG. 1  has a telescopic shock absorber  24  with a separate support spring  20 , which is shown only in the equivalent model of  FIG. 2 . The spring arrangement according to the invention is composed in accordance with  FIG. 1  of a torsion bar spring  22  extending in the vehicle&#39;s transverse direction and forming a storage spring of yet to be described construction. 
     The telescopic shock absorber  24  is supported on the lower transverse control arm  12  and at the top on the body  26  of the motor vehicle (not illustrated), on which the subframe  14  is also mounted on vibration-isolation bearings. 
     The torsion bar spring  22  is composed, as shown in  FIG. 1  by way of example, of a radially outer tubular spring  22   a , which extends—starting from an actuator  28  mounted on the subframe  14 —inwardly to proximate the depicted vehicle&#39;s perpendicular longitudinal center plane  18 , where it is drivingly connected to a solid bar  22   b  made of spring steel, for example by way of a plug-in connection  32 . 
     The solid bar  22   b  extends radially inward again to the outside of the vehicle, where it passes through the actuator  28  and is attached, also by way of a plug-in connection  36 , to a farther outward guide bushing  34 . 
     The guide bushing  34  is rotatably supported in the actuator  28  and has an output lever  38  that projects in relation to the control arm  12  radially forwardly in the direction of travel F of the motor vehicle, wherein the output lever  38  is pivotally connected to the control arm  12  via bearings  42  and an approximately vertically aligned coupling rod  40 . 
     The actuator  28  is a motor-gear unit composed, as only schematically indicated by the reference numeral  29 , of a driving electric motor and a high-gear-ratio gearbox (for example, a harmonic drive gearbox or a cycloid gearbox), wherein the output element of the transmission is drivingly connected to the tubular spring  22   a . The length of the effective torsion bar spring  22  which also determines the spring rate is thus determined cumulatively from the length of the tubular spring  22   a  from the actuator  28  to the plug-in connection  32  and the length of the solid bar  22   b  between the plug-in connections  32 ,  36 . 
     In addition, the housing  31  of the actuator  28  is supported in a slide bearing  33  for movement in a circumferential direction and supported on the vehicle body  26  and the subframe  14  by a spring element  16  ( FIGS. 2 to 5 ) in the direction of the torsional moments acting on the torsion bar spring  22 . The spring rate of the spring element  16  is superimposed on the spring rate of the torsion bar spring  22  in form of a serial connection. 
     A radially outwardly projecting lever  27  is formed on the slideably mounted housing  31  of the actuator  28 , as shown in  FIG. 3 , which is clamped at its free end between two coil compression springs  44 ,  46  as spring element  16 . The coil compression springs  44 ,  46  are in turn supported on the vehicle body  26  with a defined pre-tension. 
     Furthermore, two rubber-elastic buffers  35  are inserted between the vehicle body  26  and the lever  27  which acts as progressive end stops. Depending on the structural conditions, the lever  27  can be aligned on the vehicle body  26  or on the subframe  14  horizontally, vertically or inclined. 
     The length of the lever  27 , the design of the coil compression springs  44 ,  46  and the design of the torsion bar spring  22  determine the overall torsional stiffness or the spring rate of the torsion bar spring arrangement, which can be provided in the wheel suspension of the motor vehicle to operate as a storage spring for the support spring  20  and can be used both as a stabilizer as well as for adjusting the vehicle height and for pitch and roll stabilization of the body of the motor vehicle. 
     The motor-gear unit and/or the actuator  28  inserted in the force flow between the torsion bar spring  22  and the spring element  16  operates here due to the rotary support on both the torsion bar spring  22  and the spring element  16  and enables through appropriate adjustment by way of the actuator  28  a matched torsional stiffness of the torsion bar spring arrangement even at high-frequency suspension movements. 
       FIG. 2  shows in the equivalent diagram the interaction of the spring arrangement of a wheel suspension  10 , using the same reference symbols. 
     As can be seen, the parallel-connected spring systems c 2  (support spring  20 ) and c 1  (the torsion bar spring  22  and, connected in series, the spring element  16 ) are effective between the body  26  of the motor vehicle and the wheel  17  and the transverse control arm  12 , respectively, which determine the overall spring rate c tot  (shown for the sake of completeness is also the spring rate c tire  of the wheel  17  and the tire, respectively). 
     With the series connection of the torsion bar spring  22  and the spring element  16 , the spring rate c 1  controlled via the actuator  28  can be reduced as storage spring and thus also the overall spring rate c tot  and advantageously adapted to design conditions, as needed. 
       FIG. 4  shows an alternative embodiment of the invention, which is only described insofar as it differs significantly from the embodiment according to  FIG. 1 . Functionally identical parts are provided with the same reference symbols. 
     According to  FIG. 4 , the additional spring element  16  is formed as a coil spring which is arranged around the motor-gear unit of the actuator  28  and whose angled spring ends  16   a ,  16   b  are anchored on the vehicle body  26  and on the housing  31  under a defined pre-tension in the circumferential direction of the housing  31 . 
     The structure and operation of the torsion bar spring arrangement shown in  FIG. 5  are substantially identical to that of the torsion bar spring arrangement shown in the preceding figures. Therefore, reference is made to the description of  FIGS. 1 to 4 . 
     In contrast to  FIGS. 1 to 4 , the spring element  16  in  FIG. 5  is designed as a torsion bar spring. The housing  31  of the actuator  28  is supported on a torque support  32  of the subframe  14  by way of the torsion bar spring  16 . The second torsion bar spring  16  is rotation-locked both with respect to the housing  31  and the torque support  32  of the vehicle-body-side subframe  14 . The spring rate of the second torsion bar spring  16  is superimposed on the spring rate of the first torsion bar spring  22  in form of a serial connection. 
     The length l and the design (material, material thickness, etc.) of the first torsion bar spring  22  and of the second torsion bar spring  16  determine the overall torsional stiffness or the spring rate of the torsion bar spring arrangement which can be provided in the wheel suspension of the motor vehicle operating as a storage spring for the support spring  20 , serving both as a stabilizer and for adjusting the vehicle height and for stabilizing pitch and roll of the body of the motor vehicle. The motor-gear unit of the actuator  28  inserted the force flow between the torsion spring bars  22  and  16  operates due to its rotary support both on the first torsion bar spring  22  and on the second torsion bar spring  16  and enables with suitable adjustment by way of the motor-gear unit of the actuator  28  dynamically sensitive and appropriately adapted torsional stiffness of the torsion spring arrangement even at high-frequency suspension movements. 
     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.