Abstract:
The invention relates to a multi-stage reduction gear by which at least seven speeds can be shifted. Apart from the input shaft ( 1 ) and the output shaft ( 2 ), the gear consists of a non-engageable upstream gear and an engageable downstream gear in the form of a gear with two fixed links and four shafts. The upstream gear consists of a first planetary gear ( 3 ) which, next to the input RPM of the input shaft ( 1 ), also provides a second RPM which can be shifted alternatively via a downstream gear. The downstream gear consists of two engageable planetary gears ( 4, 5 ) which, with of six shift elements (A to F), can generate a minimum of seven forward speeds, whereby two output paths are formed (P, Q). Thereby, series shifts are always avoided for each shift action.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a multi-stage reduction gear, which is able to shift into eight forward speeds. 
   BACKGROUND OF THE INVENTION 
   Such a gear is known from DE 690 10 472 T2. This gear essentially consists of an input shaft and an output shaft, which are arranged coaxially to each other, a double planetary gear which is arranged concentrically with the output shaft, and five shift elements in the form of three clutches and two brakes, whose alternative actuation, which occurs always in pairs, determines the various speed transmissions between the input shaft and the output shaft. 
   The known gear consists of two output paths whereby a first element of the double planetary gear is connected to the first output paths by means of a first clutch, a second element of the double planetary gear has a fixed connection with the output shaft, a third element is connected to the second output path by means of a third clutch and is locked by a first brake, and a fourth element of the double planetary gear is connected to the first output path by means of a second clutch and is reduced by a second brake, so that the alternative shifting, which always occurs in pairs between the shifting element is guaranteed in such a way that six forward speeds are created. Thereby, a first speed is shifted by means of the first clutch and the first brake, a second speed by means of the first clutch and the second brake, a third speed by the first and second clutches, a fourth speed by means of the first and third clutches, a fifth speed by means of the second and third clutches, and a sixth speed by means of the third clutch and the second brake. Finally, the reverse gear is shifted by means of the second clutch and the first brake. 
   The invention is based on the task of creating a multi-stage reduction gear which can shift to eight forward speeds and provides a favorable speed grading as well as, at the same time, a large spread of gear ratios. 
   SUMMARY OF THE INVENTION 
   The gear according to the invention essentially consists of an input shaft, an output shaft and three planetary gears, whereby one of the planetary gears can be engaged and two other planetary gears cannot be engaged. The first planetary gear forms an upstream gear and the two engageable planetary gears together form a downstream gear in the form of a gear consisting of two fixed links and four shafts. 
   The gear has two output paths. In the first output shaft, the input speed is geared with a second speed via the first planetary gear by means of a fixed transmission. In the second output path, the input speed is directly transmitted into the two planetary gears of the downstream gear. 
   The downstream gear consist of two planetary gears which, in turn, consist of 4 shafts, whereby the first shaft is connected to the first output path by means of the first clutch, the second shaft with the first output path by means of a second clutch, and by means of a third clutch with the second output path, and which is also stopped by a first brake; whereby the third shaft is connected with the second output path by means of a fourth clutch and is stopped by means of a second brake, and whereby the fourth shaft has a fixed link with the output shaft. Hereby a first speed is shifted by means of the first clutch and the second brake, a second speed by means of the first clutch and the first brake, a third speed by means of the first and second clutches, a fourth speed by means of the first and the third clutches, a fifth speed by means of the first and fourth clutches, a sixth speed by means of the third and the fourth clutches, a seventh speed by means of the second the fourth clutches, and an eighth speed by means of the fourth clutch and first brake, the first reverse gear by means of the second clutch and the second brake, as well as a second reverse gear by means of the third clutch and the second brake. 
   An essential advantage consists of the fact, that the multi-stage reduction gear, according to the invention, has eight forward speeds with a smaller number of gears and shift elements. Thereby in each shifted gear, only two shift elements are shifted each. When shifting from one speed to the next, only one shift element is disengaged and another shift element is engaged. Thus, shifting series, in which several shift elements simultaneously have to be put into gear, and which can be critical for the shift quality, can be avoided. 
   The following applies to the RPMs at the shafts and the shift elements:
     1. The RPM at the input shaft and at the shift elements E and B is n=“one” (as a normed size);   2. The RPM at the shift elements A and F is equal and is in the range of &gt;“zero” and &lt;“one”.   3. The RPM at the shift elements C and D equals “zero”;   

   The following description relates to preferred implementations of the invention, which relate to multi-stage reduction gears, which can be produced cost-efficiently. In these, as many speeds as possible are shifted into gear with the smallest possible number of shift elements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
       FIG. 1  is a gear diagram of a first implementation of a multi-stage reduction gear with eight forward speeds and two reverse gears; 
       FIG. 2  is a gear diagram of another implementation of a multi-stage reduction gear with eight forward speeds and two reverse gears; 
       FIG. 3  is a table with the shift logic regarding FIG.  1  and  FIG. 2 , with the exemplary transmission of the individual speeds, of the spread of the gear ratios, and the park transmission of the individual planetary gears; 
       FIG. 4  is a gear diagram of another implementation of a multi-stage reduction gear with eight forward speeds and two reverse speeds; and 
       FIG. 5  is a table with the shift logic regarding  FIG. 4  with the exemplary transmission of the individual speeds, the spread of the gear ratios and the park transmission of the individual planetary gears. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  provides a schematic illustration of a first example of an implementation of the solution according to the invention. A first planetary gear  3  has a fixed connection with an input shaft  1  by means of a sun wheel  10 . The planetary gear consists of inner and outer planet wheels  11 ,  12 . The inner planet wheels  11  are supported by a fixed link  14  and engage with the sun wheel  10  and with the outer planet wheels  12 . The outer planet wheels  12  are supported by a fixed link  15  and engage with the inner planet wheels  11 , as well as with a ring gear  13 , which is connected to a first and a second clutch A, F. Furthermore, the two fixed links  14 ,  15  as well as a first brake C are tightly coupled to each other and have a fixed connection with the housing. The first planetary gear  3  has a fixed gear ratio which is &gt;zero. 
   The downstream gear consists of two simple planetary gears  4 ,  5 . Planetary wheels  17  are supported by a fixed link  19 , and these gears as well as a sun wheel  16  and a ring gear  18  are part of the planetary gear  4 . Planetary wheels  21  are supported by a fixed link  23 , and these gears along with a sun wheel  20  and a ring gear  22 , are part of the planetary gear  5 . The ring gear  18  of the second planetary gear  4  hereby has a fixed connection with the fixed link  23  and the third planetary gear  5 . 
   The first shaft  6  of the downstream gear encompasses the sun wheel  16  of the second planetary gear  4  and is connected with the first clutch A. A second shaft  7  consists of a sun wheel  20  of the third planetary gear  5 , which is connected with the second clutch F, a third clutch B and the first brake C. A third shaft  8  is a coupler shaft and consists of a ring gear  18  of the second planetary gear  4  and a fixed link  23  of the third planetary gear  5  and is connected to a fourth clutch E, as well as the second brake D. A fourth shaft  9  is also a coupler shaft and consists of a ring gear  22  of the third planetary gear  5  and a fixed link  19  of the second planetary gear  4  and has a fixed connection with the output shaft  2 . 
     FIG. 2  shows an alternative version of the first example of an implementation whereby, as opposed to  FIG. 1 , clutch B is arranged between brake C and the upstream gear. All elements common to FIG.  1  and  FIG. 2 , or performing the same functions, are designated with the same reference numerals. This arrangement may result in advantages with respect to the oil supply to clutch B and the total space requirement of the transmission, in comparison to the first example of the implementation. Of course, clutch E can, for example, be arranged underneath brake D or also between brake D and the third planetary gear  5 , just as well as the clutch assembly A and F may be arranged via the clutch B and the brake C or between the clutch B and the brake C and the second planetary gear  4 . 
     FIG. 3  shows the shift logic pertaining to the first two examples of implementation, as well as exemplary transmission of the individual speeds, speed gradation, spread of gear ratios and park transmission of the individual planetary gears. 
     FIG. 4  illustrates a further example of an implementation of a gear according to the invention. The upstream gear corresponds to the first planetary gear  3  from FIG.  1 . The planetary gear  3  has a fixed connection to the input shaft  1  by means of a sun wheel  10 . The planetary gear  3  has inner and outer planet wheels  11 ,  12 . The inner planet wheels are supported by a fixed link  14 , and engage with the outer planet wheels  12  and with the sun wheel  10 . The outer planet wheels  12  are supported by a fixed link  15  and engage with the inner planet wheels  11 , as well as a ring gear  13 , which is connected with the first and the second clutch A, F. Furthermore the two fixed links  14 ,  15 , as well as a first brake C, are firmly coupled to each other and have a fixed connection with the housing. A first output path P can be connected with the downstream gear by means of planetary gear  3  and the first two clutches A, F. 
   The downstream gear consists of two simple planetary gears  4 ,  5 . Hereby the planetary gear  4  encompasses planet wheels  17 , which are supported by a fixed link  19  and engage with a sun wheel  16  and a ring gear  18 . The planetary gear  5  encompasses the planet wheels  21 , which are supported by a fixed link  23  and which engage with a sun wheel  20  and a ring gear  22 . The sun wheels  16  and  20  have a fixed connection with each other, just as the fixed link  19  has a fixed connection with the ring gear  22 . 
   A first shaft  6  of the downstream gear consists of a ring gear  18  of the second planetary gear  4  and is connected with a first clutch A. A second shaft  7  consists of a coupler shaft between the sun wheels  16  and  20  is connected with the second and third clutch F, B, as well as a first brake C. A third shaft  8  consists of the fixed link  23  of the third planetary gear  5  and is connected to the fourth clutch E. A fourth shaft  9  consists of a coupler clutch between the fixed link  19  of the second planetary gear  4  and the ring gear  22  of the third planetary gear  5  and has a fixed connection with the output shaft  2 . 
   The advantage of the third example of implementation according to the invention, in comparison to the first two, consists in that the sun wheels  16  and  20  are arranged next to each other on the shaft  2 . Herewith, the two sun wheels  16 ,  20  can be produced in just one production cycle which may reduce the production costs. Furthermore, the sun wheels  16 ,  20  can be arranged closer to each other, than with the separate way of construction, which saves construction space. Furthermore, the two planetary gears  4 ,  5  can be produced with the same gear ratios, which again can save production costs. 
     FIG. 5  shows the shift logic pertaining to the third example of implementation, as well as exemplary transmissions of the individual speeds, speed gradation, spread of gear ratio and park transmissions of the individual planetary gears. 
   In all three examples of implementation,  FIGS. 1 ,  2  and  4 , the first speed is shifted by means of the first clutch A and the second brake D, the second speed by means of the first clutch A and the first brake C, the third speed by means of the first clutch A and the second clutch F, the fourth speed by means of the first clutch A and the third clutch B, the fifth speed by means of the first clutch A and the fourth clutch E, the sixth speed by means of the third clutch B and the fourth clutch E, the seventh speed by means of the fourth clutch E and the second clutch F, the eighth speed by means of the first brake C and the fourth clutch E, the first reverse gear by means of the second brake D and the second clutch F, and the second reverse gear by means of the third clutch B and the second brake D. 
   Furthermore, the possibility is given in all three examples of an implementation according to the invention, to shift eight forward speeds and two reverse gears by means of only six shift elements. In comparison hereto, a maximum of six forward speeds are shifted with five shift elements according to the mentioned state of the art. Thus, with just one additional shift element, two more forward speeds are obtained. This means, that with very few constructional requirements, a large increase in engageable speeds is made possible. 
   In the three examples of implementation according to the invention, the RPM feed may also occur from the opposite side. 
   Reference Numbers 
   
       
       A first clutch 
       B third clutch 
       C first brake 
       D second brake 
       E fourth clutch 
       F second clutch 
       P first output path 
       Q second output path 
         1  input shaft 
         2  output shaft 
         3  first planetary gear 
         4  second planetary gear 
         5  third planetary gear 
         6  first shaft 
         7  second shaft 
         8  third shaft 
         9  fourth shaft 
         10  sun wheel 
         11  inner planet wheels 
         12  out planet wheels 
         13  ring gear 
         14  fixed link 
         15  fixed link 
         16  sun wheel 
         17  planet wheel 
         18  ring gear 
         19  fixed link 
         20  sun wheel 
         21  planet gear 
         22  ring gear 
         23  fixed link