The patent's assignee for patent number 8613687 is ZF Friedrichshafen AG (Friedrichshafen, DE).
News editors obtained the following quote from the background information supplied by the inventors: "Automatic transmissions for motor vehicles having gearboxes comprising nested planetary gear stages are known, wherein the gearboxes' power can be transferred between one inner lying sun gear, two planetary stages and one outer lying ring gear. The planetary stages can be disposed offset to each other in the axial direction due to the tight construction space in this automatic transmission.
"The document U.S. Pat. No. 5,503,605 A discloses such a planetary gearbox for an automatic transmission in which planetary gears of a first stage are engaged with an inner lying sun gear and with an inner gearing of a first ring gear. This ring gear of the first planetary gear stage has a further gearing at its outer circumference by means of which it is in effective engagement with planetary gears of a second planetary gear stage, which in turn mesh with an outer lying ring gear. The planetary gears of both planetary stages are disposed aligned behind one another in the radial direction guided by a common planet carrier, where the planetary gears of the first stage are disposed offset in the axial direction to the planetary gears of the second stage due to the prevailing conditions of the construction space. In addition, the planet carrier is composed of two individual pieces, each of which accommodate the planetary gears of a stage and are joined together in the area of the first planetary gear stage.
"Furthermore, a planet carrier of a planetary gearbox can be produced by means of a primary shaping manufacturing process, as is generally known.
"The two piece design of the planet carrier has the problem that the planet carrier must be joined together in an additional assembly step, which increases the expense, and reduces the load capacity of the carrier in this region. However, manufacturing such a planet carrier as one piece would make the production process much more difficult because the arrangement of the planetary gears forms an undercut. Therefore, it is necessary either to use an expensive casting procedure in which the undercut pockets of the first stage are formed using a melt-out core, or to machine cut the pockets after the casting. Both variants significantly increase the cost of production."
As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "Therefore, the problem addressed by the current invention is to create a planetary gearbox having nested planetary stages for an automatic transmission, in which a planet carrier guiding the planetary gears is implemented as one piece, while at the same time reducing the production costs for producing this planet carrier.
"The invention comprises the technical teaching that the planet carrier is implemented as one piece so that each of the pockets in the planet carrier for accommodating the planetary gears of the first stage are disposed at an angle offset in the circumferential direction to the pockets for accommodating the planetary gears of the second stage, so that it is possible to form the pockets during casting using slides. The pockets of each planetary gear can be demolded using radial slides due to this design of the relative offset of the planetary gears of the two stages to each other. Consequently, it is possible to manufacture the planet carrier of the planetary gearbox according to the invention using a conventional casting process and at low cost.
"The offset angle is the angle enclosed between lines connecting adjacent receiving bores for bolts of the planetary gears with a center point of the planet carrier.
"According to one embodiment of the invention, the offset angle lies in the range of 20.degree. to 70.degree.. Selecting an offset angle in this range between the respective pockets of the first and second stage has the advantage that a pocket of the first stage can be formed together with a pocket of the second planetary gear stage using a radial slide. As a result, the number of slides that are required during casting is reduced.
"In a further development of the invention, every pocket can be formed by means of an individual slide. This advantageously results in each pocket being optimally shaped with respect to its contour and therefore, with respect to strength, and an optimal shape and smooth running of the planet carrier.
"In one embodiment of the present invention, there are webs in the circumferential direction, in each case between the pockets for accommodating the planetary gears of the second stage and the openings for manufacturing the pockets of the first stage. This has the advantage that the stiffness of the planet carrier can be significantly increased by the formed webs in this region.
"Correspondingly, in a further advantageous embodiment of the invention, the first and second stage comprise different numbers of planetary gears. As a result, each planetary stage can be individually adapted to the torques to be transmitted by selecting an appropriate number of planetary gears, whereby the number of planetary gears can be reduced, thereby reducing the production costs of the planetary gearbox.
"The planet carrier is expediently designed as a high pressure die casting. This means that the planet carrier can be produced with greater precision."
For additional information on this patent, see: Dopfert, Hagen; Bucher, Alexander; Ziemer, Peter; Hantke, Ulrich. Planetary Gearbox Having Nested Planetary Gear Stages. U.S. Patent Number 8613687, filed May 19, 2010, and published online on December 24, 2013