Patent EP-2960546-A1 (EP)
Inventor: BYDON STAWOMIR
IPC: F16H1/28
Filed: 2015-06-24
Abstract: The input element (11) in the gearbox takes the form of a roller whose end is eccentrically associated with the drive shaft (12) disposed via a bearing (8) in the external teeth rotary wheel (2), disposed eccentrically inside the internal teeth stationary wheel (1) fixed rigidly to the housing (10) or forming a monolith with the housing (10). The rotary wheel (2) is rigidly connected with the internal teeth rotary wheel (3), disposed eccentrically inside the internal teeth rotary wheel (4), which is rigidly connected to the output element (13). In any position the rotary wheel (2) is partially meshed with the stationary wheel (1) and the rotary wheel (3) is partially meshed with the rotary wheel (4) in any position. 
     The subject of the invention is a gearbox consisting of four gear wheels with parallel rotation axles. The first gear wheel has teeth directed inwardly, and is locked relative to the housing. The second gear wheel is meshed with the first one and its axis moves inside the first wheel with eccentric motion. The eccentric center of rotation is the rotation axis of the first wheel. The second and third wheels have a common axis of rotation and are mounted via a rotary bearing on the element which may move eccentrically. The third gear gear facing the outside is rigidly connected to a second wheel or the second and third wheels are formed as one piece. The third wheel is meshed with the fourth wheel, which has the teeth facing inward. The movement of the third wheel puts the fourth wheel in rotation. Pitch diameters of the wheels are selected so that the first and second wheel always mesh with each other and the third and fourth wheels also constantly mesh with each other. 
     There are solutions of gearboxes with the internal gear wheels, which are meshed with the external gear wheels, wherein the axis of the external gear wheel moves eccentrically with respect to the rotation axis of the internal gear wheel. In these structures, called cycloidal gearboxes, changing the movement of the gear wheels whose axles are moving eccentrically into the movement of the gearbox output elements moving with a rotational movement occurs via a number of eccentric rollers. The rotational movement of the eccentricity is caused by the rotation of the input shaft on which a gear wheel, engaged with the gear wheels mounted on the eccentric rollers (usually there are two or more rollers), is mounted, which requires very precise machining of all the elements of the kinematic chain in order to obtain a small clearance in the gearbox. Examples of such gearboxes are products by Nabtesco (www.nabtesco.pl). A gear wheel of such a gearbox, whose axis eccentrically has cycloidal teeth and rotates by one tooth at a full rotation of the elements putting its axis in the eccentric movement. In turn, in cycloidal gearboxes, such as products by Sumitomo (www.sumitomodrive.com), the transmission of the drive from the wheel moving eccentrically onto the output wheel of the gearbox occurs via a number of pins moved by appropriately shaped holes in the wheels, whose axles are moving eccentrically. 
     A gearbox according to the invention is characterized in that the input element of the gearbox causes direct eccentric movement of the axle of two gear wheels connected together, their axles of rotation are shared and move together eccentrically within two other internal gear wheels. One of the internal gears is locked relative to the housing. The axis of rotation of the eccentric coincides with the axis of the internal gear wheel. The movement of the fourth gear wheels is the output movement of the gearbox and due to that construction the rotational speed thereof is changed in relation to the rotational speed of the input element. Pitch diameters of the wheels must be selected so that the wheels placed inside are constantly meshed with the corresponding wheels located on the outside. The advantage of such a solution is a considerable simplification of the construction of the gearbox (no additional components which convert the rotational movement into the eccentric one) and the possibility of achieving very high gear ratios. 
     Racks, whose axles are moving eccentrically for one full revolution of the eccentric exercise a revolution by the number of teeth being the difference between the number of teeth and the number of teeth of the gear wheel meshing with it. 
     It is obvious that the gearbox can operate in other configurations than those described above; the housing  1  and element  13  can rotate, and the element  11  can be locked or element  13  can be locked and elements  1  and  11  can rotate. 
     The solution according to the invention is shown schematically in  Fig. 1  and in  Fig. 2 . The numbering of the elements in both figures is consistent. 
     The internal gear wheel 1 is fixedly mounted in the housing 10. The internal gear wheel 4 is rotatably mounted in the housing 10 via the bearing 9. The bearing 9 may be attached to a rack or another element to which the rack is attached (e.g. to element 13). The external gear wheel  2  is meshed with the gear wheel  1 . The external gear wheel  3  is meshed with the gear wheel  4 . Wheels  2  and  3  are rigidly connected together and are formed as one piece. Wheels  2  and  3  are mounted on the element  12  by means of the bearing  8 . The element 12 is eccentrically attached to the element 11. The element 11 is an input element of the gearbox. Rotation of the element 11 causes eccentric movement of element  12  and the eccentric movement of axis of the wheels  2  and  3 . The element 11 may not be present in the gear structure and the eccentric movement of the element 12 may be caused by the element belonging to another device, e.g. drive motor shaft. The movement of the wheel 2 is forced by the eccentric movement of the axis of rotation and its meshing with the wheel 1 locked relative to the housing 10. The movement of the gear wheel 3 is forced directly by the movement of the gear wheel 2 because they are rigidly connected and are formed as one piece. The axles of rotation of the wheels 2 and 3 overlap. Movement of the wheel 3 causes the rotation of the wheels 4 meshed therewith. Movement of the wheel 4 is transmitted to the output element 13 of the gearbox rigidly attached thereto, which may be the shaft or disk, or the element of another shape or may not exist at all. Due to the fact that the axles of gears 2 and 3 move eccentrically preferred, but not imperative due to the functionality of the transmission is to attach the weights 5 or 6 to the elements 11 or 12 in order to balance the gearbox. Balancing the gearbox can also be performed by attaching the additional external gear wheel moving eccentricity opposite to the eccentricity of the element 12 and meshed with the wheels 1 or 4 balancing in this way the weight of the wheels 2 and 3. The bearings 7, 8 and 9 may be rotary, slide, ball, roller, needle or others bearings and may be installed in other places than those shown in the figure. Pitch diameters of the wheels  1 ,  2,   3  and  4  are  d 1   , d   2   , d   3    and  d 4   , respectively and their number of teeth is  z 1   ,  z 2   ,  z 3    and  z 4   , respectively. Gear ratio i depends on the number of teeth in the wheels and is expressed by formula No 1:
       
     According to formula 1, depending on the number of teeth in the gear wheels, the gearbox can reduce the number of rotations or multiply it. It may also change the direction of rotation to the opposite. Moving e the axis of rotation of the eccentricity of the member  12  relative to the axis of the gear wheels  1  and  4  is expressed by formula No 2:
       
     According to formula 2 a condition for a proper operation of the gearbox is a fulfilled equation of pitch diameter differences of the wheels 1 and 2 and wheels 3 and 4, respectively. This is due to the fact that the wheels 2 and 3 are connected to each other and eccentric movement of their axles are equal while the wheels 2 and 3 must be permanently meshed with the wheels 1 and 4, respectively. The gearbox can also be operated with unfulfilled equation 2 but the condition of its operation is for the teeth of gear wheels 1 and 2, and 3 and 4 to mesh. It is easy to construct the element which would eccentrically move the axles of the second and third wheel e allowing any adjustment of the clearances between the gearbox wheels. 
     According to formula 1 the condition for changing the rotary speed of the gearbox 1 input element  11  relative to the input element of the gearbox is for the pair of wheels  1  and  2  and  3  and  4  to have different ratios relative to each other. So that the equation no. 3 could be fulfilled: