Abstract:
The present invention refers to a mechanism for mechanical speed reducer or in some cases for speed increase, in which for each reducing stage there are two sprockets disposed laterally and in parallel position between themselves, moreover one of them in orbital motion provided by a eccentric cam reciprocal to the reducer input element and the other sprocket disposed concentric with the input element and the torque transmission between the sprockets is done through a chain.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a planetary gear mechanism used for speed reduction or overdrive and, in particular, to the use of one sprocket drivingly connected by a chain to another sprocket, where one of the sprocket is concentric with the input shaft and been laterally and parallel with the other sprocket which one has orbital motion provided by a eccentric cam reciprocal to the reducer input shaft. 
       BACKGROUND OF THE INVENTION 
       [0002]    Planetary or epicyclic gear systems for use in speed reducers are a long time known. One example of such system is described in U.S Pat No. 276,776, issued to George F. Clemons on May 1, 1883. There are known mechanisms of epicyclic speed reduction, which typically include a pinion gear in orbit coupled to an internally toothed gear. These transmissions make possible great speed reduction however there is the limiting factor, which is the precise aspect of the complicated teeth and the transmitted torque limitation due to the small contact area between the teeth of the gears. In other aspect mechanical speed reductions or overdrive by chain and sprockets are widely used in machines, bicycles, household devices, etc. The constraint in the use of such transmissions performed by chain and sprockets for great transmission rates is in the relative size between the sprockets, what in some cases, leads to the various transmission stages. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention provides other possibility to use the idea of the planetary gear mechanism in a reduction or an overdrive transmission, using sprockets and chain. The great advantage of this type of sprocket for reducer or overdrive is the great transmission ratio reached in just one reduction or overdrive stage besides the very simple structure. The present invention uses sprockets in which one of them has orbital motion in relation to the rotating center of the other. The sprockets are disposed laterally and in parallel position between themselves, and the chain (single strand) is wide enough to embrace simultaneously both of sprockets, or one double chain (double strand) is doing the torque transference between the sprockets. The invention allows a variety of transmission ratios in compact sets with very few parts in a single stage or multiple stages for big reductions or overdrive. 
         [0004]    These and others aspects of the present invention are herein described in particularized detail with reference to the accompanying Figures, as non-limited examples. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0005]      FIG. 1  presents a frontal view in a schematic representation of a didactic reducer model with one of the sprockets fixed to the reducer structure and the other sprocket with orbital motion. 
           [0006]      FIG. 2  presents the  FIG. 1  model with the orbital motion sprocket added of four pulling pins fixed to it. 
           [0007]      FIG. 3  presents an overview in longitudinal cross-section of a reducer assembled on an engine according to  FIG. 2  model. 
           [0008]      FIG. 4  presents a second reducer construction modality in which the orbital motion sprocket has four cavities, which are inserted in the four pins fixed in the structure and the other sprocket is the reducer output element. 
           [0009]      FIG. 5  illustrates an overview in longitudinal cross-section of a construction possibility for the reducer model of  FIG. 4  assembled on an engine. 
           [0010]      FIG. 6  presents an overview in longitudinal cross-section of a reducer with double stage, using the two constructions modalities, double strand chain and the output shaft is supported on the reducer case. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    The functioning principle of such a reducer can be seen in  FIG. 1  which is the first constructive modality where the rotational motion of the input element  1  makes the eccentric cam  2  moves in orbital motion which is reciprocal to input element  1  and moving, the eccentric cam  2  transmits the orbital motion to the sprocket  3 . The sprocket  3  rotates on the eccentric cam  2 . The chain  4  makes the drivingly coupling between the sprocket  3  and the sprocket  5 . In this case, the sprocket  5  is reciprocal to the reducer structure. 
         [0012]    As represented in  FIG. 1 , the rotary motion of the input element  1  makes the sprocket  3  drivingly coupled to the sprocket  5  rotates. The transmission relation between the rotation of the input element  1  and the sprocket  3  is given by the number of teeth of the sprocket  3  divided by the difference between the number of teeth of the sprocket  3  and the number of teeth of the sprocket  5 . One negative result means different rotation direction between input and output shaft. The lower difference between the number of teeth of the sprocket  5  and the sprocket  3 , higher the reduction. 
         [0013]    There are two constructive modalities for this reducer. In a first modality as represented in  FIG. 1 and 2  with the sprocket  5  reciprocal to the reducer case and placed concentric with the input element  1 . In this modality as there are orbital and rotational motion in the sprocket  3 , set on the eccentric cam  2 , it is necessary a special coupling to transfer only rotational motion to the reducer output, since normally the orbital motion is not desirable. On a second constructive modality represented in  FIG. 4 , the sprocket  3  is activated by the eccentric cam  2  motion and coupled to the case reducer in a way that the coupling allows only the orbital motion and not the rotary motion on the sprocket  3 . In this constructive modality the sprocket  3  in orbital motion coupled to the case, makes through the chain  4  the rotational motion of the sprocket  5  which is placed on the same center of the input element  1  so the sprocket  5  serve as a reducer output element. 
         [0014]    In  FIG. 2  we have the first constructive modality in which case the sprocket  5  is reciprocal to the reducer structure and concentrically placed with the input element  1 , and the sprocket  3  is set on the eccentric cam  2  and it has, as an example, four pins  7  fixed to it, which make part of the coupling to transmit only rotational motion from the sprocket  3 , and not orbital motion, to an output element not shown, which rotates concentrically with the input element  1 . 
         [0015]    We have in  FIG. 3  a longitudinal cross-section of a reducer assembled on an engine  8 . This is a constructive possibility to the model of  FIG. 2 . In this construction the sprocket  5  is reciprocal to the engine  8  case which also serves as reducer structure and the output of the reducer is done through the shaft  14  which belongs to the rotating element  13  which is coupled to the sprocket  3  through the fitting of its four cavities  9  in the four fixed pins  7  of the sprocket  3 . Through this coupling of the four pins  7  of sprocket  3  with the four cavities  9  of the rotating element  13  is transmitted from the rotational and orbital motion of the sprocket  3  only a rotational motion to the rotating element  13 . The cavities  9  have bigger diameter than the pins  7 , the diameter of the cavity  9  is equal the diameter of the pins  7  more twofold the eccentricity of the eccentric cam  2 . Therefore the power input in the reducer is done through the input element  1  of the engine  8  it has its output in the shaft  14  of the reducer. 
         [0016]    We have in  FIG. 4  the second constructive modality of the reducer where the sprocket  5  rotates. The sprocket  3  is coupled to the reducer structured, which in this example is done through the fitting of its four cavities  9  in the four pins  7  fixed in the reducer structure. In this case as in the former one, the cavity  9  diameter is the sum of the pin  7  diameter added twofold the eccentricity of the eccentric cam  2  in relation with the input element  1 . This coupling of the sprocket  3  with the reducer structure only allows the orbital motion and eliminates the possibility of sprocket  3  rotation around the same center of the input element  1 . The rotary motion of the input element  1  and consequently the eccentric cam  2  reciprocal to it, produce an orbital motion on the sprocket  3  which under the restriction of the rotation imposed by the four pins  7  fitted in the four cavities  9  and in contact with the chain  4 , rotates the sprocket  5 . The rotation direction of the sprocket  5  is opposite to the direction of the rotation of the input element  1  if its number of teeth is smaller than the number of teeth of the sprocket  3 . The transmission relation for this second modality between the input element  1  and the external ring  5  is given by the number of teeth of the sprocket  5  divided by the difference of the number of teeth of the sprocket  5  and the sprocket  3 . One negative result means different rotation direction between input and output shaft. 
         [0017]    We have in  FIG. 5  a longitudinal cross-section of reducer assembled on an engine  8 . This reducer is the model of  FIG. 4 , where to improve the slipping between the eccentric cam  2  surfaces and the sprocket  3  it was used a bearing  10 . It was also used two bearings  11  between the input element  1  and the sprocket  5 , which in this case also has a pulley  12  as an integral part. The pulley  12  of the sprocket  5  is only an example of a possibility of the reducer output power. In this example the sprocket  3  is coupled to the engine  8  case, which also works as a reducer structure, being the coupling done through the suiting of the four pins  7  in the four cavities  9  of the sprocket  3 . The four pins  7  are fixed on the engine case. 
         [0018]    Generally these reducers are suitable for great transmission rates due to be necessary a bigger difference of teeth between the sprockets and than a bigger eccentricity for the eccentric can  2  for smaller ratios, considering for small transmission rates it may be an advantage to apply sprockets and chain in a conventional way. 
         [0019]      FIG. 6  presents a constructive possibility for the reducer using the two constructive modalities in one double stage reducer. This kind of double stage reducer increases the transmission ratios possibilities and avoids the coupling to the orbital sprocket. As an example, the entrance element  1  has a flange  6  for the power input connection. The first constructive modality is represented by the sprocket  5 A reciprocal with the reducer case and the sprocket  3 A has orbital motion and transfer his motion to the sprocket  3 B which is reciprocal to it and the second constructive modality where the sprocket  3 B has orbital motion and the sprocket  5 B concentric with the input element  1  serves as output power. The sprocket  5 B rotates on the bearings  11 , which bearings  11  are supported on the case  16  and the reducer output power is done through the shaft  14 , which is an integral part of the sprocket  5 B. In this example, the sprocket  3 A has number of teeth different from the sprocket  3 B. Due to the sprockets  3 A and  3 B are been set at the same eccentric cam  2 , consequently each stage have the same eccentricity, the two reduction stages must have the same difference between the primitive diameter of each pair of sprockets, that is the difference of the primitive diameter of the sprockets  3 A and  5 A must be the same of the difference of the primitive diameter of the sprockets  3 B and  5 B. This way the rotation of the input element  1  moves the eccentric cam  2 , which is reciprocal to it, which the eccentric cam  2  moves in orbital motion the sprockets  3 A and  3 B through the two bearings  10 . The orbital motion of the sprocket  3 A brings rotation motion too for the sprocket  3 A due to be coupled with the sprocket  5 A by the chain  4 A and transmit torque to the sprocket  3 B which is reciprocal to it and the sprocket  3 B with orbital and rotation motion too, transmit torque to the sprocket  5 B by the chain  4 B making the sprocket  5 B to rotate. In this example of  FIG. 6 , the relief hole  18  in the eccentric cam  2  serve to minimize the unbalanced power raised by the orbital motion, therefore avoiding vibrations, which normally are undesirable. In some other cases, such holes for mass relief are not enough to balance the eccentric set, so it is necessary the use of, for example, a reciprocal counter-weight to the eccentric cam  2 . The kind of chain used in this example is the two strand chain, been each sprocket in meshes with one different strand of the chain. 
         [0020]    This double stage reducer construction has infinite possibilities of transmission rates, depending of the primitive diameter of the sprockets. In many cases it can work to increase speed if the transmission rate is not so big. The rotation direction of the output shaft depends of the primitive diameter of the sprockets too. For example, if the sprockets  5 A,  3 A,  5 B,  3 B have respectively number of teeth  52 ,  53 ,  53 ,  52  the reducer will work as speed overdrive too and the transmission rate will be 1: 26.75. If we change just the number of teeth of the sprocket  5 B to  51  teeth, it will make the inversion of the rotation direction of the output shaft and the reducer will work just as speed reducer with transmission rate of 1: 2703. Generally this speed reducer or overdrive is extremely compact compared to traditional chain transmissions. 
         [0021]    All the shown examples herein, of such a reducer, can be set sequentially in various reducing stages through coupling of reducers or performed by a construction of a reducer with various reducing stages on the same case.