Patent Publication Number: US-2015068360-A1

Title: Geared motor series

Description:
The present invention relates to a geared motor series having two pinions with different numbers of teeth, and a plurality of toothed wheels with different numbers of teeth, the pinions and the toothed wheels being designed such that each pinion, in a plurality of predetermined axial distances, can be paired with one of the toothed wheels in order to form a first gear stage. 
     Geared motor series of the type described above are already known in the prior art. They form an assembly kit of individual components from which different geared motors can be assembled which differ from each other with respect to the motor dimension, the transmissions achieved in the gear and the like. Very high variance in the transmissions of a gear is primarily achieved by way of a large number of different transmissions in the first motor-side transmission stage. Intermediate and end stages of a gear tend to have low variance on the other hand. The total number of toothed parts required is therefore principally shaped by the first stage. For cost reasons geared motor manufacturers are constantly striving to keep the number of individual components of a geared motor series as low as possible. 
     A reduction in the individual components of a geared motor series has previously been primarily achieved in it having been possible to use one pinion at as many different axial distances as possible, with one separate toothed wheel being provided per pinion for each axial distance. Therefore, two different transmissions can be achieved with two pinions and two toothed wheels for a first axial distance. Another two transmissions can be achieved for each additional axial distance using the same pinions and two additional toothed wheels. The variance in the pinions, and therefore the number of individual components, of a geared motor series could already be considerably reduced in this way. 
     Further geared motor series are disclosed in documents EP 1 215 417 A2, EP 0 452 739 A1 and DE 103 12 941 A1. 
     Starting from this prior art it is an object of the present invention to further reduce the number of individual components of a geared motor series of the type mentioned in the introduction without restricting the variance in the achievable transmissions in the process. 
     To achieve this object the present invention creates a geared motor series of the type mentioned in the introduction which is characterized in that one individual toothed wheel is provided for each predetermined axial distance, which is embodied such that it can be optionally paired with the one pinion or with the other pinion to form a first gear stage. As a result of this construction of the inventive geared motor series two different transmissions can be achieved with the two pinions and one individual toothed wheel in the case of a first axial distance. Another two transmissions can be achieved for each additional axial distance using the same pinions and one additional toothed wheel. In this way a large variance is achieved with a very low number of individual components, and this is associated with very low costs. 
     The number of teeth on the two pinions preferably differs from each other by one tooth, so the following applies: z 1   a =z 1   b +1. 
     According to one embodiment of the present invention the addendum modification coefficients of the two pinions are chosen in such a way that the respective difference between the backlash angles, which are adjusted in each case during cogging between the individual toothed wheel provided for each predetermined axial distance and the two pinions, satisfies previously defined acceptance criteria in the case of a plurality of predetermined axial distances, with the difference advantageously being minimal. The cogging components are optimally adjusted to each other accordingly. 
     According to one embodiment of the present invention the acceptance criteria include a backlash difference from the standard value close to zero and/or adherence to a desired transmission ratio and/or the attainment of required strength values. 
    
    
     
       Further advantages and features of the present invention will become clear with the aid of the following description of an embodiment of an inventive geared motor series which makes reference to the accompanying drawings, in which: 
         FIG. 1  shows a tabular view of individual parameters of a first gear stage of a known geared motor series that may be achieved with two pinions and various toothed wheels, and 
         FIG. 2  shows a tabular view of individual parameters of a first gear stage of a geared motor series according to an embodiment of the present invention that may be achieved with two pinions and various toothed wheels. 
     
    
    
     It will be explained by way of example below how the parameters, listed in  FIG. 1 , of the known geared motor series can be changed to achieve an inventive geared motor series. 
     According to  FIG. 1  a known geared motor series comprises a first gear stage which comprises two pinions with the numbers of teeth z 1   a  and z 1   b , where z 1   a =16 and z 1   b =17. Both pinions z 1   a  and z 1   b  have the same normal module mn, where mn=2 mm applies. 
     A toothed wheel with number of teeth z 2   a =44 is provided for the axial distance a=70 mm for the pinion with the number of teeth z 1   a . A further toothed wheel with the number of teeth z 2   b =43 is associated with the pinion with the number of teeth z 1   b  with the same axial distance a=70 mm. By pairing the pinion with the number of teeth z 1   a  with the toothed wheel with the number of teeth z 2   a  and by pairing the pinion with the number of teeth z 1   b  with the toothed wheel with the number of teeth z 2   b , two different transmissions accordingly can be achieved in the case of this axial distance. For the axial distance 80 mm there are two additional toothed wheels with numbers of teeth z 3   a =52 and z 3   b =51, and for the axial distance a=90 mm toothed wheels with the number of teeth z 4   a =61 and z 4   b =60 are provided. Overall, there are six different possible transmissions i therefore for the first gear stage. 
     With 
         x 2=( z 1 +z 2)*(inv(α w t)−inv(α t ))/(2*tan(α n ))− x 1
 
     and 
       α wt =arccos (mn*( z 1 +z 2)*cos(α t )/cos(β)/2/ a )
 
     and 
       α t =arctan(tan(α n )/cos(β))
 
     the addendum modification coefficients x 2   a , x 2   b , x 3   a , x 3   b , x 4   a  and x 4   b  listed in the table result in the case of the predetermined values for x 1 , αn, β, mn, z 1  and z 2 , where αwt is the operating pressure angle, αt the real pressure angle, αn the normal pressure angle, β the helix angle, mn the normal module and a the axial distance. 
     The tooth thickness dimensions Asn follow agreed specifications for a desired circumferential backlash and can be taken by way of example from appropriate standards such as DIN 3967. 
     With 
         v 2=2* jt/dw 2 
     and 
         jt =−(Asn1=Asn2)/cos(β)
 
     and 
         dw 2=2* a*z 2( z 1 +z 2) 
     the backlash angle v 2  is determined, where for the sake of clarity the displaying of additional, but in this case irrelevant, variables influencing the backlash, such as the axial distance tolerance, has been omitted. jt is the theoretical backlash, Asn the chosen tooth thickness dimension and dw 2  the pitch circle diameter of the wheel. The backlash angle shown here therefore applies in the case of measurement on the wheel. 
     The additional data, given in the table, for the two pinions and the six toothed wheels as well as the values for the backlash angle v 2  of the six transmissions i result by specifying the values for x 1 , αn, β, mn, z 1  and z 2  and appropriate choice of the tooth thickness dimensions Asn. 
     With a total of eight individual components, six different transmissions can be achieved with a geared motor series of this kind, as emerges from the last block of the table. 
     Analogously to  FIG. 1 ,  FIG. 2  shows a tabular view of the parameters described above, with the parameters having been modified in such a way however that a first gear stage of a geared motor series according to one embodiment of the present invention results. 
     The starting point is again two pinions with the numbers of teeth z 1   a =16 and z 1   b =17, which have the same normal module mn=2. In contrast to the table shown in  FIG. 1 , however, the addendum modification coefficients x 1   a  and x 1   b  are adjusted in such a way that across a plurality of wheels and axial distances there is simultaneously only a slight difference from the backlash illustrated earlier. For this purpose x 1   a  is chosen so as to be sufficiently large and x 1   b  sufficiently small for z 1   a &lt;z 1   b , as is the case at hand. In the present example x 1   a =0.6 and x 1   b =0.0029. For the axial distances a=70 mm, a=80 mm and a=90 mm only one individual toothed wheel respectively with the number of teeth z 2  is provided which can cog with the two pinions to achieve different transmissions i, where the following applies in the present case: z 2   a =z 2   b =44; z 3   a =z 3   b =52 and z 4   a =z 4   b =61. 
     The addendum modification coefficients x 2   a , x 2   b , x 3   a , x 3   b , x 4   a  and x 4   b  listed in the table result by way of calculation with the addendum modification coefficients x 1  of the two pinions and numbers of teeth z 2 , z 3 , z 4  of the three toothed wheels. The design should be such that the addendum modification coefficients x 2   a  and x 2   b  are approximately equal. The same applies to the addendum modification coefficients x 3   a  and x 3   b  and x 4   a  and x 4   b.    
     An altered circumferential backlash is produced by the remaining difference between x 2   a  and x 2   b , x 3   a  and x 3   b  and x 4   a  and x 4   b . This can be expressed as the change in the tooth thickness dimension at the wheel ΔAsn 2 , ΔAsn 3  and ΔAsn 4 . The value of the change in the tooth thickness dimension can be calculated as follows: 
       ΔAsn2=|( x 2 a−x 2 b )*mn*tan(α n )|
 
     The same applies to ΔAsn 3  and ΔAsn 4 . 
     If the design has produced acceptable differences in the circumferential backlash across all axial distances a considered, then the two toothed wheels for each axial distance a according to the table in  FIG. 1  can be replaced by one individual toothed wheel respectively, as can be seen in the table in  FIG. 2 . One individual toothed wheel with two pinions can therefore be paired for each axial distance a, whereby two transmissions i respectively can be achieved, as is shown in the last block of the table in  FIG. 2 . In addition to the purely geometric boundary conditions, by way of example the avoidance of jamming of the wheels, for which reason the total backlash must be greater than zero, acceptance criteria are the exceeding or falling below of a desired backlash, the attainment of a desired transmission range, the attainment of required strength values and the like. 
     If this procedure is applied over as many different pinions z 1   a  and z 1   b  and axial distances a of the first stage of a geared motor series as possible, then an accordingly increased saving potential results. Due to the high number of boundary conditions a numerical way of proceeding is recommended in each case for the selection of optimum values for x 1   a  and x 1   b , where it is assumed in the present case that the additional geometric data already exists. It is stated by way of example as a boundary condition in the table according to  FIG. 2  that the difference |v 2   a −v 2   b |should be ≦0.0255. 
     In the preferred iterative procedure described above values for x 1  have been chosen and values for x 2  calculated on the basis of this choice. Alternatively, values can of course analogously be chosen for x 2  and then the values calculated for x 1 . In this case the following then applies 
         X 1=( z 1+ z 2)*(inv(α wt )−inv(α t ))/(2*tan(α n ))− x 2
 
     The geared motor series according to the present invention is characterized in particular in that a large number of different transmissions can be achieved in the first gear stage with few individual components, so an inexpensive geared motor series is provided. 
     Although the invention has been illustrated and described in detail by the preferred exemplary embodiment, it is not limited by the disclosed examples and a person skilled in the art can derive other variations herefrom without departing from the scope of the invention.