Patent Publication Number: US-2023159087-A1

Title: Steering drive for a steering axle of a steerable vehicle, steering axle, and industrial truck

Description:
RELATED APPLICATIONS 
     This application claims the benefit of and right of priority under 35 U.S.C. § 119 to German Patent Application no. 10 2021 213 067.4, filed on 22 Nov. 2021, the contents of which are incorporated herein by reference in its entirety. 
     FIELD OF THE DISCLOSURE 
     The invention relates to a steering drive for a steering axle of a steerable vehicle, to a corresponding steering axle, and to a corresponding industrial truck. 
     BACKGROUND 
     The prior art has disclosed various embodiments of servo steering units which either assist a manual steering input by a driver or automatically set a desired steering angle in response to an electrical signal. Here, a hydraulic cylinder or an electric motor is commonly used as an actuator. In addition to the actuator, these steering units generally comprise a steering gear of concentric construction and have a shaft as an output. The steering units are of column-like construction with a pedestal in the lower region, which pedestal serves for fastening to a chassis of the vehicle. The upper region of the steering unit is rotatable relative to the lower region in order to set a steering angle at the steerable wheels. 
     In this context, DE 10 2019 116 644 A1 has disclosed a servo steering unit for vehicles, which servo steering unit comprises a steering column with a pedestal and comprises an electrically assisted steering apparatus with a housing and electric motor, the housing being movable relative to the pedestal with one degree of freedom. The steering column itself furthermore comprises a lower spindle which is rotatably connected to, and partially contained within, the pedestal. The electric motor is configured such that it can set the lower spindle in rotation via an output shaft. 
     SUMMARY 
     Known servo steering units however have the disadvantage that, owing to their column-like structural form, they have a large space requirement and are subject to unfavourable mechanical loads, which can in turn lead to increased wear and failure of the servo steering units. 
     It is an object of the present invention to propose an improved steering drive for a steering axle of a steerable vehicle. 
     Said object is achieved according to the invention by means of the steering drive for a steering axle of a steerable vehicle according to the present disclosure. Advantageous embodiments and refinements of the invention will emerge from the present disclosure. 
     The invention relates to a steering drive for a steering axle of a steerable vehicle, comprising an electric motor with a motor shaft, comprising a first planetary stage with a first sun gear, first planet gears and a first planet carrier, comprising a second planetary stage with a second sun gear, second planet gears and a second planet carrier, and comprising a steering lever, the steering drive being configured such that a force flow runs from the first sun gear via the first planet gears to the first planet carrier, such that the force flow furthermore runs via the second sun gear and via the second planet gears to the second planet carrier, and such that the force flow furthermore runs to the steering lever, and the steering lever being supported so as to be rotatable about a pivot axis. The steering drive according to the invention is distinguished by the fact that the steering drive furthermore comprises a spur gear stage, wherein the electric motor is arranged parallel to the pivot axis, and wherein the steering drive is configured such that a force flow from the motor shaft to the first sun gear runs via the spur gear stage. 
     Thus, an electric steering drive is provided, which is intended for actuating the steerable wheels of a steering axle of a steerable vehicle. The vehicle is preferably a utility vehicle, such as an agricultural machine, a work machine or an industrial truck. 
     The steering drive comprises an electric motor with a motor shaft. The electric motor is preferably a three-phase brushless electric motor. Here, in accordance with an actuation, the electric motor respectively provides the required torque and the required rotational speed. The steering drive furthermore comprises a first and a second planetary stage, having a first and a second sun gear respectively, first and second planet gears respectively and a first and a second planet carrier respectively, and comprises a steering lever. 
     The first and the second planetary stage are arranged such that the force flow runs from the first sun gear via the first planet gears to the first planet carrier, at least two first planet gears being provided, and the first planet gears meshing with the first sun gear and being held by the first planet carrier. Torques and rotational speeds can thus be transmitted from the first sun gear to the first planet carrier. 
     From the first planet carrier, the force flow furthermore runs to the second sun gear, the first planet carrier and the second sun gear being connected rotationally conjointly to one another, for example by means of a spline toothing or via a welded connection, and in particular being formed as a single piece. The second sun gear meshes with the second planet gears, such that the force flow runs from the second sun gear to the second planet gears. It is advantageous for at least two planet gears to be provided. From the second planet gears, the force flow runs to the second planet carrier, which holds the second planet gears. Torques and rotational speeds can correspondingly also be transmitted from the second sun gear to the second planet carrier. 
     The force flow finally runs onward from the second planet carrier to the steering lever, the steering lever being supported so as to be rotatable about a pivot axis. The second planet carrier and the steering lever are advantageously connected rotationally conjointly to one another, for example by means of a spline toothing. A rotational movement of the second planet carrier can thus be easily converted into a steering movement of the steerable wheels of the steering axle. For example, the steering lever may actuate a steering linkage of the steering axle. Here, the pivot axis is preferably the axis of rotation of the second planet carrier. 
     A rotation of the first sun gear thus results in a pivoting movement of the steering lever. A rotational movement of the motor shaft is thus ultimately converted into a rotational movement of the steering lever. 
     In other words, a rotation of the motor shaft thus results in a rotational movement of the final planet carrier, whereas the ring gear is held fixed. 
     The first and the second planet stage are advantageously arranged coaxially, such that the pivot axis is simultaneously the axis of rotation of the first and of the second planetary stage. 
     According to the invention, provision is now made whereby the steering drive furthermore comprises a spur gear stage, wherein the electric motor is arranged parallel to the pivot axis, and wherein the steering drive is configured such that a force flow from the motor shaft to the first sun gear runs via the spur gear stage. 
     By virtue of the electric motor being arranged parallel to the pivot axis - and not coaxially as is conventional in the prior art - an advantageously short structural height of the steering drive according to the invention is advantageously realized, such that the steering drive according to the invention can also be used for steering axles or vehicles which are relatively compact and which can thus provide only little structural space. An advantage is achieved here in particular in the case of relatively compact vehicles such as industrial trucks. 
     The use of the spur gear stage for guiding the force flow from the motor shaft of the electric motor to the first sun gear furthermore offers the advantage here that a speed reduction of the rotational speed of the motor shaft can advantageously be achieved already by means of the spur gear mechanism. The spur gear stage is accordingly preferably configured as a speed reduction stage. It is thus advantageously possible to omit a third planetary stage, because the required overall speed reduction can also be achieved by means of the first planetary stage, the second planetary stage and the spur gear stage. It is however at least possible for the first and the second spur gear stage to be made more compact, because they each need to provide only a relatively small speed reduction. 
     The invention accordingly leads to a synergistic effect owing to the spur gear stage that is preferably configured as a speed reduction stage, because, by means of the spur gear stage, not only can the electric motor be offset in parallel with respect to the pivot axis, whereby the structural height of the steering drive is significantly reduced, but it is also possible for the first planetary stage and the second planetary stage to be of compact and structural-space-saving form, and in particular, no third planetary stage is required. 
     The spur gear stage advantageously comprises at least two spur gears. 
     This yields the advantage that the steering drive has a very short structural form in relation to the prior art, and the steering axle is accordingly of relatively space-saving form. 
     In one preferred embodiment of the invention, provision is made whereby the steering drive comprises a housing, a partial region of the housing constituting a front end shield of the electric motor. Here, the housing of the steering drive makes it possible for all components of the steering drive to be arranged in their respectively required position in or on the housing, and thus for the steering drive to be functional. The housing preferably furthermore has a protective action for the steering drive, in that it keeps in particular contaminants, moisture and other corrosive substances away from those components of the steering drive which are arranged in the housing. By virtue of the fact that the partial region of the housing constitutes the front end shield of the electric motor, a separate end shield that would otherwise be required can advantageously be omitted. The steering drive is thus relatively lightweight, compact and inexpensive. 
     In a further preferred embodiment of the invention, provision is made whereby the motor shaft has a toothing that meshes with an intermediate gear of the spur gear stage. The motor shaft, by means of its toothing, thus already has a first gear of the spur gear stage. The toothing may be formed on the motor shaft by milling, for example. Since the motor shaft commonly has a relatively small diameter, a relatively large speed reduction can thus be easily achieved already in the force flow from the motor shaft to the intermediate gear. 
     In one particularly preferred embodiment of the invention, provision is made whereby the intermediate gear is supported by means of a bolt that can be screwed into the housing. Here, the bolt also constitutes the axis about which the intermediate gear is rotatable. In order that it can be screwed into the housing, the bolt advantageously has an external thread, and the housing has a corresponding internal thread for receiving the bolt. The intermediate gear can thus be easily and inexpensively arranged at the required position in the housing. 
     In a further particularly preferred embodiment of the invention, provision is made whereby the intermediate gear meshes with a further spur gear that is connected rotationally conjointly to the first sun gear. The further spur gear constitutes the output of the spur gear stage and guides the force flow from the electric motor to the first spur gear stage, specifically to the first sun gear. 
     The further spur gear and the first sun gear are preferably both arranged on a common shaft, to which they are each connected rotationally conjointly, for example by means of a spline toothing. 
     The first sun gear and the shaft may preferably also be formed as a single piece, or else the further spur gear and the shaft are formed as a single piece. 
     In a further preferred embodiment of the invention, provision is made whereby the further spur gear is supported on a first cover that closes the first spur gear stage and the second spur gear stage in a partial region of the housing. The first cover thus performs two mutually independent functions in that it firstly closes that partial region of the housing in which the spur gear stages are arranged, and thus holds the spur gear stages in place, and secondly supports the further spur gear. The first cover advantageously supports the further spur gear via the shaft that rotationally conjointly connects the further spur gear to the first sun gear. 
     In a further preferred embodiment of the invention, provision is made whereby the steering lever has a conical receptacle for the arrangement of a bearing assembly. Via the conical region, force can be introduced for example into a linkage, for example coupling or tie rods, for the actuation of the steerable wheels. Here, the conical region of the steering lever is advantageously arranged at the same level as a bearing assembly of the steering lever, such that forces can be transmitted into the steering lever, and forces can be transmitted out of the steering lever, without tilting. 
     In a further preferred embodiment of the invention, provision is made whereby the steering lever and the second planet carrier are supported on a second cover by a common bearing assembly. Since the second planet carrier and the steering lever are connected rotationally conjointly to one another, they can advantageously also be jointly supported. Here, in particular from an opposite direction in relation to the first cover, the second cover likewise closes that partial region of the housing in which the first spur gear stage and the second spur gear stage are arranged. 
     In a further preferred embodiment of the invention, provision is made whereby the steering drive comprises a ring gear, the ring gear meshing with the first planet gears and the second planet gears and being arranged rotationally fixedly with respect to the housing. The ring gear thus radially encloses the first planetary stage and the second planetary stage and supports the first and the second planet gears on the housing. By virtue of the ring gear being rotationally fixed with respect to the housing, it is furthermore possible for the force flow to be guided entirely into the second planet carrier and led onward from there to the steering lever. 
     Provision may preferably be made whereby the ring gear is composed of a multiplicity of individual ring gears that are arranged concentrically with respect to one another. 
     In one particularly preferred embodiment of the invention, provision is made whereby the ring gear is held between the first and the second cover. This has the result that the first and the second planetary stage can be installed particularly easily, because both the first cover and the second cover can be removed, such that the further elements of the first and of the second planetary stage can be arranged within the ring gear. 
     The invention also relates to a steering axle comprising a steering drive according to the invention. The advantages already described in conjunction with the steering drive according to the invention are thus also realized for the steering axle according to the invention. 
     The steering axle furthermore preferably comprises an axle body and two steerable wheels. 
     The invention furthermore relates to an industrial truck comprising a steering axle according to the invention. The advantages already described in conjunction with the steering axle according to the invention are thus also realized for the industrial truck according to the invention. 
     The invention will be discussed by way of example below on the basis of embodiments illustrated in the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In the drawings: 
         FIG.  1    shows, by way of example and schematically, a possible embodiment of a steering drive according to the invention for a steering axle of a steerable vehicle. 
     
    
    
     Identical objects, functional units and similar components are denoted by the same reference designations throughout the figures. These objects, functional units and similar components are of identical design in terms of their technical features unless explicitly or implicitly stated otherwise in the description. 
     DETAILED DESCRIPTION 
       FIG.  1    shows, by way of example and schematically, a possible embodiment of a steering drive  27  according to the invention for a steering axle (not illustrated) of a steerable vehicle. 
     The steering drive  27  comprises an electric motor  1  with a motor shaft  2 . The electric motor  1  and the motor shaft  2  are in this case concentric with respect to an axis  3 , which also constitutes the axis of rotation of the motor shaft  2 . As can be seen, the motor shaft  2  is supported in a housing  4  of the steering drive by means of a bearing assembly  28 . The housing  4  thus, in the region of the bearing assembly  28 , constitutes a front end shield of the electric motor  1 . 
     The steering drive  27  furthermore comprises a first planetary stage  29  with a first sun gear  31 , first planet gears  16  and a first planet carrier  17  and comprises a second planetary stage  30  with a second sun gear  18 , second planet gears  19  and a second planet carrier  20 . The first sun gear  31  meshes with the first planet gears  19 , which are held by the first planet carrier  17 . The first planet carrier  17  is connected rotationally conjointly to the second sun gear  18 , which in turn meshes with the second planet gears  19 . The second planet gears  19  are held by the second planet carrier  20 . 
     The first planetary stage  29  and the second planetary stage  30  are furthermore enclosed radially by a ring gear  22 . Both the first planet gears  16  and the second planet gears  19  mesh with the ring gear  22 . Here, the ring gear  22  is held rotationally fixedly between a first cover  26  and a second cover  21 . The first cover  26  and the second cover  21  axially enclose the first planetary stage  29  and the second planetary stage  30  and thus enclose a partial region of the housing  4  which houses the first planetary stage  29  and the second planetary stage  30 . 
     Furthermore, the steering drive  27  also comprises a steering lever  25 , which is connected rotationally conjointly to the second planet carrier  20 . The steering lever  25  itself has a conical receptacle  24  for the arrangement of the bearing assembly (not illustrated). As can be seen, the receptacle  24  is situated at the same level as the bearing assembly  23  which supports the second planet carrier  20  and the steering lever  25 . The bearing assembly  32  can thus be kept free of tilting forces. 
     The steering drive  27  finally also comprises a spur gear stage  33  which, in the example, comprises a toothing  5  of the motor shaft  2 , an intermediate gear  6 , and a further spur gear  13 . The intermediate gear  6  is supported on a bolt  11  via a bearing assembly  9 . The bolt  11  has, at its lower end, a threaded region  7  by means of which it is screwed into a corresponding mating thread  12  of the housing  4 . An inner ring of the bearing assembly  9  is clamped axially by means of a planar contact surface  10  and a ring  8 , which is planar on both sides. The further spur gear  13  is supported, via a bearing assembly  32 , on a shaft  14  on which the first sun gear  31  is also supported. The shaft  14 , the first sun gear  31  and the further spur gear are rotatable about the pivot axis  15 , in the same way as the steering lever  25  is pivotable about the pivot axis  15 . The toothing  5  of the motor shaft  2  meshes with the intermediate gear  6 , and the intermediate gear  6  meshes with the further spur gear  13 . 
     In  FIG.  1   , a force flow in the steering drive runs from the electric motor  1  via the motor shaft  2 , and the toothing  5  of the motor shaft  2 , to the intermediate gear  6 . A first speed reduction of the rotational speed occurs here. The force flow runs onward to the further spur gear  13  and via the shaft  14  to the first sun gear  31 . From there, the force flow runs via the first planet gears  16  to the first planet carrier  17 , and onward via the second sun gear  18  and via the second planet gears  19  to the second planet carrier  20 . Since the ring gear  22  is held rotationally fixed with respect to the housing  4 , the force flow runs onward from the second planet carrier  20  to the steering lever  25 , such that the steering lever  25  can actuate a steering system of the steering axle. 
     
       
         
           
               
               
             
               
                 Reference signs 
               
             
            
               
                 
                   1 
                 
                 Electric motor 
               
               
                 
                   2 
                 
                 Motor shaft 
               
               
                 
                   3 
                 
                 Axis 
               
               
                 
                   4 
                 
                 Housing 
               
               
                 
                   5 
                 
                 Toothing of the motor shaft 
               
               
                 
                   6 
                 
                 Intermediate gear 
               
               
                 
                   7 
                 
                 Thread region 
               
               
                 
                   8 
                 
                 Ring 
               
               
                 
                   9 
                 
                 Bearing assembly 
               
               
                 
                   10 
                 
                 Contact surface 
               
               
                 
                   11 
                 
                 Bolt 
               
               
                 
                   12 
                 
                 Mating thread 
               
               
                 
                   13 
                 
                 Further spur gear 
               
               
                 
                   14 
                 
                 Shaft 
               
               
                 
                   15 
                 
                 Axis 
               
               
                 
                   16 
                 
                 First planet gear 
               
               
                 
                   17 
                 
                 First planet carrier 
               
               
                 
                   18 
                 
                 Second sun gear 
               
               
                 
                   19 
                 
                 Second planet gear 
               
               
                 
                   20 
                 
                 Second planet carrier 
               
               
                 
                   21 
                 
                 Second cover 
               
               
                 
                   22 
                 
                 Ring gear 
               
               
                 
                   23 
                 
                 Bearing assembly 
               
               
                 
                   24 
                 
                 Receptacle 
               
               
                 
                   25 
                 
                 Steering lever 
               
               
                 
                   26 
                 
                 First cover 
               
               
                 
                   27 
                 
                 Steering drive 
               
               
                 
                   28 
                 
                 Bearing assembly 
               
               
                 
                   29 
                 
                 First planetary stage 
               
               
                 
                   30 
                 
                 Second planetary stage 
               
               
                 
                   31 
                 
                 First sun gear 
               
               
                 
                   32 
                 
                 Bearing assembly 
               
               
                 
                   33 
                 
                 Spur gear stage