Patent Publication Number: US-2023145968-A1

Title: Drive Unit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related and claims priority to 102020203712.4 filed in the German Patent Office on Mar. 23, 2020 and is a U.S. national phase of PCT/EP2021/054259 filed in the European Patent Office on Feb. 22, 2021, both of which are incorporated by reference in their entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to a drive unit for a manually driven vehicle. 
     BACKGROUND 
     DE 10 2015 100 676 A1 discloses a drive assembly with a manual drive, an electric auxiliary drive, and a common driven element. The drive unit has a complex structure with a large number of individual components and bearing points. 
     EP 2 724 926 A1 discloses a central drive unit with a bottom bracket shaft for manual drive and an auxiliary drive with a downstream planetary transmission. This drive unit also has a relatively complex structure with a large number of individual components. 
     DE 10 2014 108 611 A1 discloses a bicycle drive device with a drive housing for receiving a bottom bracket shaft and a harmonic drive which is arranged inside the drive housing and can be connected in driving fashion to a traction means carrier. This bicycle drive device also has a complex structure. 
     SUMMARY OF THE INVENTION 
     Example aspects of the invention provide an improved drive unit. In particular, a compact structure, reliable functioning, and very quiet running are desirable. 
     The drive unit is configured for a manually driven vehicle, in particular a bicycle or an EPAC (Electrically Power Assisted Cycle), wherein a manually driven vehicle refers in particular to a vehicle operated by muscular force. The drive unit has a housing, an electric motor with a rotor, a bottom bracket shaft, a harmonic drive coupled to the rotor, and an output shaft. The harmonic drive has an outer bushing with internal teeth, wherein the outer bushing of the harmonic drive is coupled to the housing via a buffer, for example a rubber/metal bearing. 
     The outer bushing and the housing can in this way be advantageously acoustically decoupled. Independently thereof, it is possible to compensate eccentricities caused, for example, by axial misalignment and/or tilting. 
     The drive unit has an electric drive branch for an electric drive, wherein the rotor of the electric motor is coupled to the output shaft via the harmonic drive and a first freewheel clutch. The torque of the electric motor is transmitted to the output shaft via the harmonic drive and the first freewheel clutch. 
     The drive unit has a mechanical or manual drive branch for a manual drive, wherein the bottom bracket shaft is coupled to the output shaft by a further second freewheel clutch. The torque which is applied to the bottom bracket shaft is transmitted to the output shaft via the second freewheel clutch. 
     The harmonic drive can expediently have a wave generator and a deformable, for example, cylindrical inner bushing with external teeth (flex spine). As explained above, the harmonic drive additionally has a, for example, cylindrical and preferably rigid outer bushing with internal teeth. A compact transmission unit with relatively high transmission ratios is hereby created. This contributes to a strictly coaxial arrangement of the harmonic drive and the drive unit as a whole. 
     The outer bushing of the harmonic drive can advantageously be coupled non-rotatably to the housing. The outer bushing can thus serve as a torque support mechanism relative to the housing. By virtue of the non-rotatable outer bushing, there is no superimposition with the rotational movement of the flex spline. For example, the rotational movement of the flex spline may not be superimposed on the non-rotatable outer bushing. 
     The bottom bracket shaft and the harmonic drive can expediently each be coupled to the output shaft by a freewheel clutch, wherein the harmonic drive, the freewheel clutches, and the output shaft can be arranged coaxially with one another in the housing. By virtue of the design with a harmonic drive as a single-stage transmission unit, a coaxial and particularly compact transmission unit is provided, which in turn favors a compact and space-saving design of the drive assembly. A manual drive and an electrically assisted drive are provided by the coupling to the output shaft. Torque addition, i.e., addition of the torques of the bottom bracket shaft and the electric motor, takes place at the output shaft. The output shaft can be designed as a hollow shaft. 
     The outer bushing of the harmonic drive and the buffer, possibly with an inner ring, an elastomeric body, and/or an outer ring, can advantageously be formed as a premountable unit such that the premounted unit can be mounted en bloc in the housing of the drive unit. The mounting is favored as a result because components do not need to be mounted individually in the housing and instead can be inserted as a premounted unit, i.e., as an assembly. The time required for final mounting may be shortened as a result. 
     The buffer can expediently have a metal inner ring and a metal outer ring, wherein an elastomeric body, for example an annular elastomeric body, can be arranged radially between the inner ring and the outer ring. In addition to acoustic decoupling, damping of torque peaks imparted by the motor can thus also take place. The buffer can thus act as a torsion spring. The outer ring can bear against an inner circumferential surface of the housing with the outer circumferential surface of the outer ring. The outer bushing of the harmonic drive can bear against an inner circumferential surface of the inner ring of the buffer with the outer circumferential surface of the outer bush. It is likewise conceivable that the elastomeric body has a non-annular geometry. For example, geometry of the teeth with a defined intermediate space which is elastically connected by the buffer can be formed between the inner ring and the outer ring. The buffer can then be formed optionally such that the buffer has an acoustic damping effect and ensures tolerance compensation in terms of amount and installed position. 
     The outer bushing of the harmonic drive can advantageously be coupled to the inner ring of the buffer by a snug or interference fit. This allows a structurally simple and precise fastening of the outer bushing to the inner ring. Mounting of the components on one another, for example also of a premountable unit, is favored hereby. 
     The outer ring of the buffer can expediently be formed from the same material as the housing of the drive unit or from a material with the same coefficient of expansion as the housing of the drive unit. Expansion of the material can be compensated in this way. The outer ring is also coupled more securely to the housing when thermal influences occur. 
     The inner ring of the buffer can expediently be formed from the same material as the outer bushing of the harmonic drive or from a material with the same coefficient of expansion as the outer bushing of the harmonic drive. Expansion of the material can be compensated in this way. The inner ring and the outer bushing are also coupled more securely to each other when thermal influences occur. 
     The inner ring of the buffer can expediently be formed from steel and/or the outer ring of the buffer can be formed from aluminum. A stable structure with a relatively low weight is possible as a result. Particularly advantageous compensation of the expansion of the material results. The housing of the drive unit can be formed from aluminum. The outer bushing of the harmonic drive can be formed from steel. 
     The elastomeric body advantageously has a first front side and an opposite second front side, wherein a preferably annular circumferential recess is formed at least at one of the front sides, in particular at both front sides. The damping effect produced by the buffer can be influenced as a result. The bearing can be designed with optimal axial, radial, and/or rotational stiffness. The recesses formed at the front can have, for example, a triangular cross-section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example aspects of the invention are explained in detail below with the aid of the drawings, wherein the same elements or elements with the same function are provided with identical reference numerals. In the drawings: 
         FIG.  1    shows an example embodiment of a drive unit in a view in section; and 
         FIG.  2    shows the housing, the buffer, the outer bushing, and the flex spine of the harmonic drive of the drive unit from  FIG.  1    in a schematic view. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein. 
       FIG.  1    shows a drive unit for a manually driven vehicle, in particular a bicycle or an EPAC, wherein the drive unit as a whole is provided with the reference numeral  10 . 
     The drive unit  10  has a housing  12  on or in which the components of the drive unit  10  are arranged. The drive unit  10  has, for manual drive by muscular force, a bottom bracket shaft  14  which is rotatably mounted in the housing  12 . In addition, the drive unit  10  has an electric auxiliary drive  16  which has an electric motor  18  and a harmonic drive  20 , wherein the electric motor  18  is mechanically coupled to the harmonic drive  20 . The bottom bracket shaft  14  and the auxiliary drive  16  are coupled to an output shaft  22  on which a chain ring carrier or a chain ring can be fastened (not illustrated). 
     The bottom bracket shaft  14  is mounted on a housing cover  26 , which closes the housing  12  of the drive unit  10  on one side (on the left-hand side in  FIG.  1   ), by a first rolling bearing  24 . In addition, the bottom bracket shaft  14  is mounted rotatably on the output shaft  22  designed as a hollow shaft by a second rolling bearing  28 . The output shaft  22  is mounted rotatably relative to the housing  12  by a third rolling bearing  30  and a fourth rolling bearing  32 . 
     The harmonic drive  20  has a wave generator  34 , a deformable inner bushing  36  with external teeth (flex spine), and an outer bushing  38  with internal teeth. The harmonic drive  20  is coupled on the input side to the electric motor  18  and on the output side to the output shaft  22 , and to be precise by a first freewheel clutch  40 . 
     The bottom bracket shaft  14  is coupled to the output shaft  22  by a second freewheel clutch  42 . At this point, the bottom bracket shaft  14  can have a radially outward projecting shaft shoulder  43  which is in contact with the second freewheel clutch  42 . The harmonic drive  20 , the freewheel clutches  40 ,  42 , and the output shaft  22  are arranged coaxially with one another in the housing  12 . 
     The electric motor  18  has a stator  44  with stator coils  45  and a rotor  46 . The rotor  46  is coupled to the harmonic drive  20 , in particular to the flex spline  36 . The rolling bearing  39  of the flex spline  36  (flex bearing) is mounted on a, for example, sleeve-shaped connecting section of the rotor  46 . 
     The drive unit  10  furthermore has a stator carrier  48  and an electronic unit which can be designed as an electronic circuit board  50 . The stator carrier  48  has a, for example, sleeve-shaped carrying section  52  and a, for example, disk-shaped fastening section  54 . 
     The stator  44  is fastened to the carrying section  52  and the rotor  46  is mounted rotatably on the carrying section  52  by a rolling bearing  58 . The stator carrier  48  can be connected to the housing  12  of the drive unit  10  via the fastening section  54 . 
     The drive unit  10  has an electric drive branch  60  for an electric drive, wherein the rotor  46  of the electric motor  18  is coupled to the output shaft  22  via the harmonic drive  20  and the first freewheel clutch  40 . The torque of the electric motor  18  is transmitted to the output shaft  22  via the harmonic drive  20  and the first freewheel clutch  40 . 
     The drive unit  10  has a mechanical or manual drive branch  62 , wherein the bottom bracket shaft  14  is coupled to the output shaft  22  by the second freewheel clutch  42 . The torque, which is applied to the bottom bracket shaft  14 , is transmitted to the output shaft  22  via the second freewheel clutch  22 . 
     The outer bushing  38  of the harmonic drive  20  is coupled non-rotatably to the housing  12 . The outer bushing  38  can thus serve as a torque support mechanism relative to the housing  12 . The outer bushing  38  of the harmonic drive  20  is coupled to the housing  12  via a buffer  64 , for example a rubber/metal bearing, with a preferably multi-part design. 
     The outer bushing  38  of the harmonic drive  20  and the buffer  64  are formed as a premountable unit  66  ( FIG.  2   ) such that the premounted unit  66  can be mounted en bloc in the housing  12  of the drive unit  10  in the premounted state. 
     The buffer  64  has a metal inner ring  68  and a metal outer ring  70 , wherein a, for example, annular elastomeric body  72  is arranged radially between the inner ring  68  and the outer ring  70 . The outer ring  70  bears with the outer circumferential surface of the outer ring  70  against an inner circumferential surface of the housing  12 . The outer bushing  38  of the harmonic drive  20  bears with the outer circumferential surface of the outer bushing  38  against an inner circumferential surface of the inner ring  68 . 
     The outer bushing  38  of the harmonic drive  20  is coupled to the inner ring  68  of the buffer  64  by a snug or interference fit. 
     The outer ring  70  is formed from the same material as the housing  12  of the drive unit  10  or from a material with the same coefficient of expansion as the housing  12  of the drive unit  10 . The outer ring  70  and/or the housing  12  can be formed from aluminum. 
     The inner ring  68  is formed from the same material as the outer bushing  38  of the harmonic drive  20  or from a material with the same coefficient of expansion as the outer bushing  38  of the harmonic drive  20 . The inner ring  68  and/or the outer bushing  38  can be formed from steel. 
     The elastomeric body  72  has a first front side  74  and an opposite second front side  76 . A circumferential recess  78 ,  80  is in each case formed on the front sides  74 ,  76 . The recesses  78 ,  80  can have, for example, a triangular cross-section. 
     Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims. In the claims, reference characters corresponding to elements recited in the detailed description and the drawings may be recited. Such reference characters are enclosed within parentheses and are provided as an aid for reference to example embodiments described in the detailed description and the drawings. Such reference characters are provided for convenience only and have no effect on the scope of the claims. In particular, such reference characters are not intended to limit the claims to the particular example embodiments described in the detailed description and the drawings. 
     LIST OF REFERENCE NUMERALS 
     
         
           10  drive unit 
           12  housing 
           14  bottom bracket shaft 
           16  auxiliary drive, electric 
           18  electric motor 
           20  harmonic drive 
           22  output shaft 
           24  first rolling bearing 
           26  housing cover 
           28  second rolling bearing 
           30  third rolling bearing 
           32  fourth rolling bearing 
           34  wave generator 
           36  inner bushing 
           38  outer bushing 
           39  rolling bearing (flex bearing) 
           40  first freewheel clutch 
           42  second freewheel clutch 
           43  shaft shoulder 
           44  stator 
           46  rotor 
           48  stator carrier 
           50  electronic circuit board, unit 
           52  carrying section 
           54  fastening section 
           58  rolling bearing 
           60  electric drive branch 
           62  manual drive branch 
           64  buffer 
           66  premountable unit 
           68  inner ring 
           70  outer ring 
           72  elastomeric body 
           74  first front side 
           76  second front side 
           78  recess 
           80  recess