In U.S. Pat. No. 5,106,352 A, there is made known a plurality of schematic drawings and descriptions for automatic transmissions with one non-shiftable primary gear set followed by one after gear set, with which, by selective closure of five shifting elements, six forward gear stages can be achieved without group shifting. The after gear set is designed as a shiftable two-spider, four shaft, gear train with two connected planetary gear sets. The non-shiftable primary gear set can be built as a single spider planetary gear set or alternately as a forward power transmission means with two spur-gear pairs of differently determined ratios, which operate as a reducing gear train. One element of the primary gear set is bound securely to the transmission housing. The primary gear set is driven at the input speed of rotation of the transmission and produces a reduced output rotational speed. This reduced output rotational speed is transferred by two shifting elements to two different elements of the after gear set. Additionally, a third element of the after gear set can be directly driven by an additional clutch at the transmission input speed of rotation.
A six-gear stage automatic transmission 6HP26, which is derived by the applicant according to a concept from U.S. Pat. No. 5,106,352 A is described in, Prof. Dr. P. Tenberg: E-Automat—Automatic Transmission with Esprit, VDI Report No. 1610, 2001, pages 455 to 479. Relying on the basis of this report, Prof. Dr. Tenberg proposes to design the sun gear of the originally non shiftable, primary planetary gear set, to be actually shiftable by means of an additional brake. When this is accomplished, then, the now shiftable primary planetary gear set is designed, unchanged, as a so-called “minus-gearing”, the internal gear of which is driven at the input drive shaft speed of rotation and the spider thereof forms its output element. In regard to the “minus transmission”, what is to be understood is a simple planetary gear set with a negative fixed gear ratio. The ratio of the speeds of rotation of the internal gear and the sun gear, when the planet gear holder is fixed, is negative. The additional brake can be employed as an integral startup shifting element in the transmission. In accordance with corresponding toothing design, even seven forward stages can be provided, with a gear spread equivalent to that of a basic transmission, disadvantaged however, with an unfavorable succession of gear stages.
U.S. Pat. No. 3,941,013 A discloses a gear train schematic of an automatic transmission, with six forward stages. This transmission has one primary gear set designed as a single spider planetary gear set and one drive gear train consisting of two single spider planetary gear sets coupled together. Two of the three input elements of the second drive gear sets are, in this arrangement, connected together. The primary gear set is designed as a so-called “plus gear drive” with double planetary gear sets, the spiders of which are connected together and operate up to the sixth stage, in which it then revolves as a piece, serving as a reducing gear set. As far as “plus gear drive” is concerned, what is meant thereby is a simple planetary transmission with a positive fixed gear ratio. Further, the ratio of the speed of rotation of the internal gear and the sun gear is also positive during the imagined fixed spider. The sun gear of the primary gear is immobilized by means of a brake abutting the transmission housing. This brake is set spatially between the primary gear set and the after gear train. The primary gear set is driven at the speed of rotation of the input drive shaft by means of its coupled spider, its output drive is executed by means of the internal gear. The output speed of rotation of the following gear set can be transmitted by two clutches onto two different input elements of the following gear set, whereby these two different input elements of the following gear set, together with an additional clutch can be directly connected to run at the transmission input drive shaft speed of rotation. This additional clutch is placed on that side of the primary gear set which is remote from the subsequent gear set. Because of spatial positioning of the brake, by means of which the sun gear of the primary gear set is fixed, and the spatial placement of the clutch, by means of which the transmission input speed of rotation can transferred to the following gear set, a guide for input drive and output drive of the primary gearing is created. In this way, the torque of the primary gear set is directed outwardly and radially by its internal gear. That is to say, the drive of the primary gear set completely encompasses it. Further, the output drive of the primary gear set is directed centrally through the sun gear of the primary gear set to the input elements which are constructed as external disk carriers of the two clutches. The gear set concept of the U.S. Pat. No. 3,941,013 A additionally requires several group shiftings for the shifting of the six forward stages.
Thus, the purpose of the invention is to develop further, from the cited state of the technology, a multistage transmission, with at least six forward gear stages, without group shifting, wherein, one shifting element of the multistage transmission is to be an integrated startup shifting element, wherein the whole is made without excessive expense in construction, with a favorable stage succession, and an increased gear spread.