Abstract:
A steering drive for a steeled wheel of an industrial truck, particularly a rear wheel of a three-wheeled industrial truck, comprising a steering bolster supporting the rear wheel which is supported to be pivotable about a vertical steering axle inside the flame of the industrial truck, a steeling motor coaxial with the steering axle, a bearing assembly between the flame of the industrial truck and the bolster, and a steering transmission between the steering motor and bolster, wherein the steering transmission has a single-stage or multi-stage stepped planetary mechanism or planetary coupler mechanism which is coaxial with the steering axle and the bearing assembly for the bolster is arranged within the steering transmission.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    Electrically driven counterweight-type trucks including a three-wheeled chassis mostly have a steered, non-driven rear wheel. The real wheel mostly is designed as a twin wheel and is rotatably mounted on the vehicle frame by means of a body bolster. The steering motion is transferred to the rotary bolster by means of a steering rack or transmission. 
         [0004]    From DE 101 13 775 A1, the entire contents of which is incorporated herein by reference, a steering transmission has become known where the steering motor acts on the steering bolster via an eccentric drive. The steering bolster is supported on the vehicle frame by means of a four-point support. 
         [0005]    It is the object of the invention to provide a steering drive for a steered wheel of a three-wheeled industrial truck which exhibits an improved efficiency for the steering transmission, allows for a smaller construction size of the steering motor and steering transmission, and reduces the effort for a support of the steeling bolster. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    In the inventive steering drive, the steering transmission has a single-stage or multi-stage stepped planetary mechanism or planetary couplet mechanism which is coaxial with the steering axle and the bearing assembly for the bolster is arranged within the steering transmission. 
         [0007]    The stepped planetary mechanism or planetary coupler mechanism may be preceded by another planetary transmission. 
         [0008]    The inventive steering transmission allows for an improved efficiency. Both the steering motor and steering transmission exhibit a smaller construction size. The arrangement of the steering bolster bearing inside the planetary transmission allows using less expensive bearings. The formation of assembly units for the steering bolster and steering drive makes possible a reduction of assembly efforts. 
         [0009]    An aspect of the invention provides that the inner race of at least one antifriction bearing is supported on a central bearing component coupled to the bolster while the outer race is supported on a transmission case portion. It is preferred to provide two axially-spaced antifriction bearings, which preferably are tapered roller bearings. 
         [0010]    If a planetary coupler mechanism is provided the bearing component also serves as a planet pinion carrier, the driven wheel of the transmission being defined by an internal gear provided on the bolster. According to another aspect of the invention, the internal gear may be formed integrally with the bolster. 
         [0011]    According to another aspect of the invention, the motor case portion and disc-like transmission case portions stacked on top of each other define a closed drive case. The bolster may have disposed thereon a contacting gasket which sealingly interacts with a sealing surface of the case portion facing it. This protects the entire steering drive unit from dirt, moisture, etc. 
         [0012]    Further advantageous aspects of the invention are set forth in further dependent claims. 
         [0013]    The drive case may have disposed therein sensors and assembly units for the control of the steering motor. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Embodiments of the invention will be described in detail below with reference to the drawings. 
           [0015]      FIG. 1  shows a section through a first embodiment of a steering drive according to the invention which has a planetary coupler mechanism. 
           [0016]      FIG. 2  shows a section through a second embodiment of a steering drive according to the invention which has a two-stage stepped planetary mechanism. 
           [0017]      FIG. 3  shows an enlarged view of a modified detail of the representation of  FIG. 1 . 
           [0018]      FIG. 4  shows a modified detail of the representation of  FIG. 1 . 
           [0019]      FIG. 5  shows a section through the representation of  FIG. 4  along line  5 - 5 . 
           [0020]      FIG. 6  shows a steering drive having a rotation angle sensor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    While this invention may be embodied in many different forms, there are described in detail herein a specific preferred embodiment of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated. 
         [0022]    Referring to  FIG. 1 , a frame of an industrial truck is outlined at  40  where the three-wheeled industrial truck has a steered, non-driven rear wheel. In  FIG. 1 , the rear wheel is a so-called twin wheel  42  which is supported by a steering bolster  8 . A drive case generally designated  44  is composed of a cup-like motor case portion  46  and two disc-like superimposed transmission case portions  11 ,  3  with the latter being attached to the frame  40 , which is not shown, however. The steering bolster  8  is of a shell-like shape in the upper portion where a contacting gasket  11   a  is accommodated in the border and interacts with a level lower surface of the case portion  3  that faces it in order to prevent dust and moisture from entering the drive case  44 . 
         [0023]    An electric motor  10  with a motor shaft  9 , which has an axle  48 , is located inside the motor case portion  46 . A pinion  6  is disposed on the motor shaft  9  or is formed integrally therewith. The motor shaft  9  and steering bolster  8  are coaxial. The motor shaft  9  is supported by the case portion  11  by means of an antifriction bearing  50 . 
         [0024]    A planetary coupler mechanism is arranged within the transmission case and has stepped planetary gears  4   a  and  4   b  which are coupled to each other via a coupler shaft  5 . Firmly connected coaxially to the steering bolster  8  is a bearing component  1  which also is a planet pinion carrier for the stepped planetary gears  4 b. The planet carrier for the stepped planetary gears  4   a  is constituted by the transmission case portion  3 . The lower step of the stepped planetary gears  4   a  interacts with a tooth system  7  of an internal gear which is defined by the steering bolster  8 . The pinion  6  interacts with the larger stage of the stepped planetary gears  4   b  while the smaller stage interacts with the coupler shaft  5 . Hence, the output of the steering transmission is defined by the bearing component  1  attached to the steering bolster (planet carrier), on one hand, and the internal gear coupled to the steering bolster  8 , on the other. 
         [0025]    In the representation of  FIG. 1 , two tapered roller bearings  2   a ,  2   b  further can be recognized which are axially spaced and the inner rings of which are supported each on the bearing component  1  (planet carrier). The outer ring of the lower tapered roller bearing  2   a  is supported on the transmission case portion  3  and the outer ring of the upper tapered roller bearing  2   b  is supported on the transmission case portion  11 . Thus, the bearing of the steering bolster  8  is within the steering transmission shown. 
         [0026]    As far as the representation of  FIG. 2  uses the same components as the representation of  FIG. 1  it is largely provided with the same reference characters. A drive case  44   a  is constituted by the motor case portion  46 , in which a motor  30  is arranged with a motor shaft  33  and transmission case portions  24  and  21 , which latter ones are disposed in a disc-like relationship on top of each other. The drive case  44   a  is fixedly coupled to the flame  40  via the transmission case portion  21 , which fact is not shown in detail. A contacting gasket  11  of the steering bolster  31 , which shape is relatively similar to that of the steering bolster of  FIG. 1 , sealingly interacts with the level surface of the transmission case portion  21  facing it in order to guard the drive case  44   a  from the ingression of dirt and moisture. 
         [0027]    The motor shaft  33  has a pinion  32  which interacts with the larger stage of first stepped planet gears  26 . The planet gears  26  are mounted by the case portion  24  which, thus, is a planet carrier. The smaller stage of the stepped planet gears  26  is coupled to the larger stage of second stepped planet gears  22  via a connecting shaft  25 . The stepped planet gears  22  are mounted by the case portion  21  which, thus, is a planet carrier. The smaller stage of the stepped planet gears  22  is meshes with an internal gear  27  which is formed in the interior of the steering bolster  31 . Coaxially connected to the steering bolster  31  is a trunnion  20  which has a portion larger in diameter near the steering bolster  31  and a portion smaller in diameter near the pinion  32 . A first antifriction bearing is formed as a tapered roller bearing and is supported by the trunnion  20  in the portion larger in diameter and a second antifiiction bearing  29  is supported by the smaller-diameter portion of the trunnion  20  with the two tapered roller bearings  28 ,  29  being at an axial spacing. The trunnion  20 , the motor shaft  33 , and the steering bolster  31  are coaxial as is the two-stage stepped planetary mechanism shown. The output of the steering transmission is performed via the internal gear  27 . 
         [0028]    Referring to  FIG. 3 , a particularity modified as compared to  FIG. 1  is illustrated. The transmission case portion of  FIG. 1  is formed by two superimposed portions  35 ,  36  there, the antifriction bearing  50  being disposed between the motor shaft  9  and case portion  35  while the antifriction bearing  2   b  is disposed between the case portion  36  and the associated portion of the carrier component  1  or planet carrier. To this end, the case portion  36  has a shoulder  52  on which the outer ring of the tapered roller bearing  2   b  is supported while a spring washer  54  provides an axial safety device on the plant carrier  1 . 
         [0029]    In another modified embodiment of  FIGS. 4 and 5 , the case portion  37  which corresponds to the case portion  11  of  FIG. 1  has disposed thereon a bearing ring  38  which is seated in a recess of the case portion  37 . At this time, the bearing ring assumes the supporting function for the tapered roller bearing  2   b , which is taken by the case portion  36  in  FIG. 3 , Thus, the bearing ring  38  also has a shoulder  60  which axially secures the antifriction bearing  2   b.    
         [0030]    As can be seen in  FIG. 5  the bearing ring  38  is secured by tangentially disposed pins  62 ,  64 . This way allows mounting the bearing ring  38  on the case portion  37  dismounting it therefrom in an easy manner. 
         [0031]    In  FIG. 6 , a steering drive similar to that of  FIG. 1 , for example, is illustrated where only a single wheel is steered, however. Therefore, particular reference is not made to the structure of the transmission and its interaction with the steering motor. The particularity in  FIG. 6  is that a shaft  123  of the steering motor is of a hollow construction and a sensor shaft  122  is passed therethrough. The sensor shaft  122  is firmly coupled to the planet carrier  1  for rotation at its lower end ( FIG. 1 ). At its upper end, the sensor shaft  122  interacts with a rotation angle sensor  120  which is mounted on the case  46  of the steering motor. The steering angle sensor  120  measures the steering angle redundantly with respect to the steering angle detection in the steering motor. A redundant steering angle sensing is also possible via an incremental sensor  124  which traces a contour on a component joined to the steering bolster  8 , e.g. a tooth system  125 . 
         [0032]    The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims. 
         [0033]    Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim  1  should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below. 
         [0034]    This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.