Abstract:
A torsion spring system for a wheel suspension of a motor vehicle includes an actuator that is provided on the vehicle body and variably maintains the torsion spring system under tension, and which acts, via a torsion bar and an output lever, with a biasing force on a wheel suspension element of the wheel suspension. The torsion bar is configured in two parts between the actuator and the output lever and has a first bar part and a second bar part coupled thereto with a spring element connected in between the first and second bar parts.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2014/000103,filed Jan. 16, 2014,which designated the United States and has been published as International Publication No. WO 2014/124722and which claims the priority of German Patent Application, Ser. No. 10 2013 002 714.4,filed Feb. 16, 2013,pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a torsion spring system for a wheel suspension of a motor vehicle. 
     An example of such a suspension assembly is known from DE 10 2009 005 899A1. The suspension assembly includes a torsion spring bar which is actuatable by an actuator and extending in the vehicle transverse direction to about the vehicle transverse center and which on the wheel side acts on a driven lever that, in turn, is articulated to a wheel suspension element of the wheel suspension. The torsion spring bar is configured in the DE 10 2009 005 899A1 of several parts and in an interlaced arrangement in which two radially outer hollow bars and a radially inner solid bar are provided from spring steel, which are connected to one another in a force-transmitting manner via splines, for example. 
     In the torsion spring bar system known from DE 10 2009 005 899 A1, spring work is picked up and released during interplay of a wheel compression and wheel rebound motion. At the same time, it is possible that the actuator superimposes moments, i.e., to tighten or relax the torsion spring bars depending on need. The presence of the support spring as a primary spring, renders it possible for the rotary actuator to proportionally provide actuating forces to change the wheel load. A superimposition of the spring forces of the primary spring and the torsion spring bar continuously takes place, depending on the requirement of the driving situation and the corresponding command from the control. At the output of the torsion spring bar system is a rocker having an end to which a coupler is articulated. The coupler connects the rocker to the trapezoidal link, which is connected to the vehicle wheel. Thus, the torques generated in the rotary actuator can be transmitted via the load path motor/gear/torsion spring bar/rocker/coupler/trapezoidal link/vehicle wheel ultimately as linear actuating forces upon the vehicle wheel. 
     In the afore-described torsion spring bar system, the torsion spring bar is comprised of only two components, namely tube spring and solid bar spring. In contrast thereto, the remaining components are dimensioned absolutely rigid in the afore-mentioned load path without affecting the overall spring constant of the system. If there is need for example for realization of a softer torsion spring bar, as first measure the diameter of tube spring and/or solid bar spring would have to be reduced. However, by reducing the diameter, the operational capability of the torsion spring bar would decrease and at the same time stress would increase disproportionately, so that the tube spring and bar spring would have to be extended. Such a change in length is, however, not feasible in view of the extremely critical space conditions in the area of the wheel suspension. As a consequence, especially when smaller vehicle models are involved, which require a reduction in the total spring stiffness, such a rotary actuator cannot be installed because of the high packing tightness. 
     EP 2 01 1674 A1 discloses a two-part stabilizer for a motor vehicle, having stabilizer sections which are able to execute a rotational relative movement and to apply in the presence of a twisting load in opposite directions a restoring force which is adjustable by an actuator in conjunction with a gear. A torsion damper is provided in the gear. With the assistance of the torsion damper, gear noise can be avoided that otherwise would develop as a result of a tooth gap between the gear elements. The torsion damper reduces such mechanical noise within the gear, with the torsion damper being dimensioned such that the spring rate of the stabilizer assembly remains unaffected. This means that the spring rate of the stabilizer assembly is not lowered by the torsion damper, 
     SUMMARY OF THE INVENTION 
     The object of the invention is to propose a suspension assembly of the generic type, which enables additional influence of the spring rate of the torsion spring bars in a structurally and constructively simple manner. 
     The solution of this object is set forth by a torsion spring system for a wheel suspension of a motor vehicle, including an actuator which variably maintains the torsion spring system under tension and is arranged on the vehicle body and which acts on a wheel suspension element of the wheel suspension with a biasing force via a torsion bar and an output lever, wherein the torsion bar is configured between the actuator and the output lever in two parts with a first bar part and a second bar part coupled thereto, with interposition of a spring element. 
     Advantageous and particularly appropriate configurations of the invention are set forth in the dependent claims. 
     In accordance with the present invention, the torsion bar is not formed from same material and/or in one piece between the actuator and the output lever, but rather of two parts with a first bar part and a second bar part coupled thereto. A spring element is placed between the first and second bar parts. In this way, there is no longer any need for the torsion bar to be provided with a predefined sufficiently large torsion length to lower the spring rate to a predefined value. Rather, the spring rate is defined solely by the interposed spring element. The torsion motion is therefore provided in a space-efficient manner by the spring element interposed between the first and second bar parts of the torsion bar. 
     Preferably, the first bar part and the second bar part are arranged for rotation relative to each other from an initial position by a free movement range about a torsion angle. The rotation movement from the initial position is realized while building up a restoring force of the spring element. 
     The first bar part and the second bar part may, preferably, be arranged in coaxial relationship and/or between the actuator and the output lever behind one another in series. Correspondingly, the coupling point of both bar parts is arranged between the output lever and the actuator. 
     In one embodiment, the first bar part and the second bar part have at the coupling point support elements, which overlap each other in the axial direction. The at least one spring element may be arranged between the support elements of the first and second bar parts which support elements are nested within one another in the axial direction. 
     In a further embodiment, the first bar part and the second bar part can be coupled with one another at the coupling point via a ball-ramp system. The ball-ramp system includes ramp-like guideways respectively extending in circumferential direction on the first bar part and the second bar part and at an incline to a rotation plane. Balls are provided between the guideways of the first and second bar parts to respectively roll thereon. The two bar parts can be moved apart by an axial stroke as they are rotated relative to one another. The axial stroke is established while the spring element builds up a restoring force. 
     The particular advantage of the invention resides, compared to the prior art, in a much simpler construction of the motor-gear unit of the actuator in conjunction with a simplified design of the torsion spring bar that can be configured especially shorter. The required spring travel and the spring stiffness or spring rate is determined by the spring element arranged between the two bar parts. 
     In order to achieve a structurally simple construction, it is advantageous when the first bar part and/or the second bar part are configured as solid bars. The actuator may, preferably, be supported with its housing rigidly and/or in fixed rotative engagement on the vehicle body. 
     According to a particularly preferred arrangement on an axle of the motor vehicle, two torsion spring systems are provided which are aligned transversely to the vehicle longitudinal direction, with their motor-gear units of the actuators being rotatably supported in the area of the vertical vehicle longitudinal center plane. The torsion bars with the output levers can be positioned relative thereto on the outside. 
     The advantageous configurations and/or refinements of the invention, as described above and set forth in the dependent claims, can—except for example in the cases of clear dependencies or incompatible alternatives—be used individually or also in any combination with each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention and its advantageous configurations and refinements and their advantages are explained in more detail with reference to drawings. 
       It is shown in: 
         FIG. 1  a plan view upon the lower plane of a left-side wheel suspension of a rear axle of a motor vehicle, with a lower transverse link, a shock absorber, and a torsion spring bar system; 
         FIG. 2  an equivalent diagram of the suspension assembly according to  FIG. 1  with illustration of individual spring rates c 1  and c 2 , which substantially determine an overall spring rate; 
         FIG. 3  an enlarged sectional view of the coupling point between the two bar parts of the torsion spring bar; and 
         FIG. 4  a planar illustration of the primary part of the first bar part and the secondary part of the second bar part of a torsion spring bar system according to a further exemplary embodiment, with the primary and secondary parts assuming a rest position; 
         FIG. 5  a view corresponding to  FIG. 4 , in which the primary and secondary parts are rotated from the rest position to a tightened state; and 
         FIG. 6  a plan view of the guideway of the primary part of the first bar part of the torsion spring bar system. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In  FIG. 1, 10  designates the lower plane of a left-hand side wheel suspension for a motor vehicle, including a lower transverse link  12  which is articulated on one hand to an only partially illustrated subframe  14  and on the other hand to a not shown wheel carrier for a rear wheel  17 . The upper transverse link or control arm, guiding the wheel carrier, is not visible. 
     The wheel suspension shown in  FIG. 1  on the left-hand side has a shock absorber  24  and a separate support spring  20  (only indicated in  FIG. 2 ). The suspension assembly according to the invention is comprised according to  FIG. 1  of a torsion spring bar  22 , extending in the vehicle transverse direction y, as a storage spring of a construction still to be described. 
     The shock absorber  24  is supported on the lower transverse link  12  and in a manner not shown at the top to the body  26  of the motor vehicle on which also the subframe  14  is mounted via vibration-isolating bearings. 
     The torsion spring bar  22  is shown in  FIG. 1  formed in two parts comprised of a first bar part  23  and a second bar part  25 . The bar parts  23 ,  25  are made of solid material and joined to one another at a coupling point K. The coupling point K is comprised of a first primary part  27  of greater diameter, which is connected in fixed rotative engagement to the first bar part  23 , and a secondary part  32 , which is connected in fixed rotative engagement to the second bar part  25 . A spring element  16  is connected between the primary part  27  and secondary part  32 , as will be described further below. The torsion spring bar  22  extends, as shown in  FIG. 1 , from a cylindrical actuator  28 , mounted to the subframe  14 , axially toward the vehicle outer side. 
     The housing  31  of the actuator  28  is supported rigidly and/or in fixed rotative engagement at a bearing point  33  ( FIG. 1 ) to a vehicle-body-side subframe  14 . 
     The second bar part  25  of the torsion spring bar  22  is extended at a bearing point  39  out of the actuator  28 , whereas the first bar part  23  has an outer end which carries an output lever  38  which projects forward in radial relation to the transverse link  12  in the travel direction F of the vehicle and which is hinged via bearing points  42  and a substantially vertically oriented connecting rod  40  to the transverse link  12 . 
     The actuator  28  is a motor-gear unit, which is composed of a powering electric motor and a high ratio gear (for example, a harmonic drive or a cycloidal drive), indicated only roughly with reference numeral  29 , with the output member of the gear being in driving relationship with the second bar part  25  of the torsion spring bar  22 . The overall spring rate c F  ( FIG. 2 ) of the torsion spring bar  22  is determined solely by the spring rate of the spring element  16 , but not by the rigid bar parts  23 ,  25  and the other components which are arranged in the force path between the actuator  28  and the wheel suspension element  12 . 
       FIG. 3  shows the primary part  27  of the first bar part  23 . The primary part  27  of the bar part  23  is configured as a hollow cylinder with support elements  34  which project inwards in radial direction and are dispersed about the circumference of the inner wall of the primary part  27 . Support elements  35  of the secondary part  32  are directed in a star shape outwards and project between the support elements  34  of the primary part  27 , so that the support elements  34 ,  35  of the primary and secondary parts  27 ,  32  overlap in axial direction. 
       FIG. 3  shows the support elements  34 ,  35  of the first bar part  23  and the second bar part  25  in an initial position I. Starting from the initial position I, the two bar parts  23 ,  25  can be rotated in opposition to one another in circumferential direction by a free movement range s, i.e. about a predefined torsion angle. Such a rotation is accompanied by a buildup of a restoring force of the spring element  16 . In  FIG. 3 , the spring element  16  has a plurality of helical compression springs which are respectively arranged between the support elements  34 ,  35  of the primary and secondary parts  27 ,  32 . 
       FIGS. 4 to 6  merely roughly indicate a further exemplary embodiment of the invention. Accordingly, the primary part  27  of the first bar part  23  is coupled in  FIG. 4  via a ball-ramp system  40  to the secondary part  32  of the second bar part  25 . The ball-ramp system  40  illustrated in  FIG. 4  in a rest position I is shown for sake of clarity by way of a planar view. 
     Provision is made for guideways  36  at the confronting sides of the primary and secondary parts  27 ,  32 , as indicated in  FIGS. 4 to 6 . The guideways  36  extend undulated in circumferential direction, i.e. with axially projecting wave peaks and intermediate recessed valleys. Balls  38  respectively run there along between the guideways  36  of the primary part  27  and the secondary part  32 . 
     As the two bar parts  23 ,  25  are rotated in opposite directions, the balls  38  roll on the flanks of the undulated guideways  36 . Both bar parts  23 ,  25  are thereby moved apart from the rest position I ( FIG. 4 ) by an axial stroke Δh to a tightened state II ( FIG. 5 ), accompanied by a buildup of a restoring force which is effected by the spring element  16 . The spring element  16  is formed, according to  FIGS. 4 and 5 , by two helical springs, with which the primary part  27  and the secondary part  32  are pressed against each other. 
       FIG. 2  shows, by way of an equivalent diagram, the interaction of the spring assembly of a wheel suspension  10 , using the same reference signs. 
     As is apparent, the parallel spring systems c 2  (support spring  20 ) and c 1  (the spring element  16  of the torsion spring bar  22 ) are effective between the body  26  of the motor vehicle and the wheel  17  or transverse link  12  and determine the overall spring rate (for sake of completeness, also the spring rate c Rei  of the wheel  17  or tire thereof is identified). 
     As a result of the spring element  16 , the spring rate c 1 , controlled by the actuator  28  as a storage spring and thus the associated overall spring rate c total  (c 1 +c 2 ) can be reduced or advantageously suited to structural conditions at hand.