High ratio planetary type traction roller transmission

Abstract: In a traction roller transmission which has disposed in a housing (1) two planetary type transmission structures (9, 15) each having traction rollers (11, 17) disposed between spaced concentric sun rollers (8, 14) and traction rings (10, 16) and supported by support members (13, 18) of which one (13) which is associated with one (9) of the transmission structures (9, 15) carries the sun (14) of the other transmission structure (15) and the other (18) is connected to the transmission output shaft (4) while the input shaft (3) carries the sun (8) of the one transmission structure (9), the planetary rollers (11, 17) are supported in an inclined position, and the traction rings (10, 16) are axially curved and forced toward one another so as to engage therebetween the planetary rollers (11, 17) which are supported at predetermined angles (α, β ) selected such that their engagement forces with the sun rollers (8, 14) and traction rings (10, 16) correspond to the torque to which they are subjected during operation.

Description: The invention relates to a high ratio planetary type traction roller transmission utilizing two planetary transmission stages. Such high ratio transmissions are needed in large numbers for converting rotary motion from a high speed motor, for example, for low speed, high torque applications. However, various machines utilize various speeds and torques so that, for different applications, different transmissions are required with different sun rollers, different planetary rollers and different traction rings. The motion transmitting traction surfaces of such transmissions need to be engaged with one another with forces sufficient to transmit the respective torque and, as the torque changes within a transmission from stage to stage, so do the engagement force requirements. One could of course provide for maximum engagement forces for all the traction surfaces but then all the traction surfaces would be exposed to full loads at all times which not only reduces their lives but also reduces transmission efficiency and would require the use of relatively expensive materials for the traction surface areas. In the arrangement according to the generic U.S. Patent No. 4,060,010, for example, the traction roller engagement forces are the same for all the stages although the torque at the drive shaft end of the transmission is by far lower than at the output shaft end. The same can be said for the arrangement shown in U.S. Patent No. 3,490,311 in which a single engagement cam structure is provided for both main planetary drive structures providing for both the same engagement forces. It is the principal object of the present invention to provide a two stage planetary type traction roller transmission in which the traction surfaces are subjected essentially only to the forces needed for the transmission of the appropriate torque and wherein, with the same transmission housing and traction ring structures, various transmission ratio planetary and sun rollers may be utilized, thereby providing for easy changeover to different transmission ratios or for a relatively large variety of different ratio transmissions with relatively few parts. With this object in view, the present invention resides in a traction roller transmission as defined in claim 1. With such an arrangement the traction surfaces are not subjected to unnecessarily large contact forces and structure with various ratios and correspondingly various angles may be utilized in connection with one type or even the same housing and traction rings. The invention will become more readily apparent from the following description of a preferred embodiment thereof shown, by way of example, in the accompanying drawings, wherein: Figure 1 is a cross-sectional view of the transmission according to the invention; and Fig. 2 shows an embodiment with concentric input and output shafts. As shown in Fig. 1 the transmission includes a housing 1 which receives the transmission structure and is provided with a cover 2. Coaxial input and output shafts 3 and 4 are rotatably supported in the housing end wall 5 and the cover 2 by antifriction bearings 6 and 7. The input shaft 3 is provided at its inner end with a sun roller structure 8 which forms the center roller of a first planetary traction roller structure 9 having a first traction ring 10 supported in the housing 1 in spaced relationship from the sun roller structure 8 and a first set of planetary type traction rollers 11 disposed in the space between the ring 10 and the sun roller 8 and in engagement with both of them. The traction rollers 11 are rotatably supported on a first planetary roller support structure 12 which is part of an intermediate transmission member 13 supporting the traction rollers 11 at a predetermined angle α with respect to the axis of the input shaft 3. The intermediate transmission member 13 is further provided with a roller structure 14 which forms the sun roller of a second planetary type traction roller transmission 15 having a second traction ring 16 supported with housing 1 in spaced relationship from the sun roller 14 and a second set of planetary type traction rollers 17 disposed in the space between, and in engagement with, the sun roller 14 and the traction ring 16. The traction rollers 17 are rotatably supported on a second planetary roller support structure 18 so as to be disposed at a predetermined angle β with respect to the axis of the output shaft 4. The second planetary roller support structure 15 is mounted on, or part of, the output shaft 4. The second sun roller structure 14 has a slightly conical surface defined by a cone having an apex preferably coinciding with the axes of the traction rollers 17 on the axis of the output shaft 4. The sun roller 8 of the first planetary type transmission structure is shown in Fig. 1 with a cylindrical surface, an arrangement wherein the apex of the cone defined by the conical surface of the traction rollers 11 is disposed on the cylindrical envelope of the sun roller 8. Both traction rings 10 and 16 have inner traction surfaces 19 and 20 which are curved in axial direction such that the planetary traction rollers 11 and 17 engage them properly along a circular line independently of the angular inclination α or β of the planetary traction rollers. The surface areas 19 and 20 are shown in the drawings as being symmetrical but need to extend only from the innermost point only far enough to accommodate the largest angles α or β utilized in connection with a particular transmission design. It is noted however that preferably the rings 10, 16 are provided with symmetrical surface areas as shown in the drawings since this permits their reversal when worn on one side thereof. One of the traction rings, that is, traction ring 10, is mounted so that it is not rotatable whereas the other, that is, ring 16, is rotatably supported but has an axial cam structure 21 associated therewith which forces the ring 16 axially toward the ring 10 with a force that depends on the torque transmitted thereto by the rollers 17, thereby causing firm engagement of the traction rollers with their respective sun and ring structures. Cam springs 22 extend between the traction rings 10 and 16 in order to insure return of the ring 16 when the reaction torque forces thereon diminish. A spacer ring or a set of rings 23 is disposed between the traction ring 10 and the housing 1, the rings 23 being so selected as to insure a slight preload of all the traction surfaces. The planetary traction rollers 17 are rotatably supported on shaft members 24 which are mounted at one of their ends to the support structure 18 and carry at their opposite ends a connecting ring 25 which interconnects all the shaft members 24 and which is adapted to transmit the axial thrust forces generated by the loading cam structure 21 to the intermediate transmission member 13 by way of an axial thrust bearing 26 arranged therebetween. Axial thrust bearings 27 and 28 are also arranged between the traction rollers 17 and the connecting ring 25 and between the traction rollers 11 and their support structure 12 for the transmission of the axial engagement forces. The input shaft sun structure as shown in Fig. 1 is essentially cylindrical since cylindrical structures are easy to manufacture and since, because of the relatively high speed of the input shaft, the torque and the required surface contact forces are relatively low. Slight spin on its surface is therefore not damaging particularly if the surfaces of the traction rollers 11 are slightly curved as they may be because of the relatively low torque to be transmitted. The slight curvature of the traction rollers and the angles α and β of their inclination are so selected as to provide the appropriate contact forces. A larger angle α, for example, provides for smaller contact forces in the planetary transmission structure 9 relative to those applied in the planetary transmission structure 15 since the axial forces applied to the traction rings are the same for both transmission structures. The value for the relative engagement forces can be selected as desired depending on the selected transmission ratios. Various roller and sun sizes may be used in the same size housing simply by using different traction roller and sun structures. The housing and the traction rings 10 and 16 which are relatively expensive need not be different. They can accommodate any suitable roller size and inclination. As mentioned earlier the arrangement permits to make different ratio transmissions with a single housing and a relatively small number of different internal parts. Depending on the selection of sizes for the rollers and sun structures a plurality of different ratio transmissions can be provided. With, for example, components for four ratios of 4,6,9 and 12, depending on their combination, twelve different transmissions with various ratios of 16,24,36,48,54,72,81 and 108 can be provided. Fig. 2 shows an embodiment similar to that of Fig. 1 and therefore the same reference numerals are used where appropriate. However, as shown the input shaft 3' extends concentrically through the output shaft 4' and through a central bore 30 in the intermediate transmission member 13' and carries at its end a sun roller structure 8' which, in this case, is slightly conical for spin-free motion transmitting engagement with the planetary traction rollers 11. The shaft 3' is supported in the output shaft by a bearing 31 which is capable of taking up also the axial component of the engagement forces applied by the inclined planetary rollers 11 to the sun roller structure 8' As mentioned earlier, the inclination angles α and β for the planetary rollers 11 and 25 are selected such that the engagement forces generated by their engagement with the traction rings 10 and 16 are appropriate to transmit the torques to be transmitted at the various engagement locations. For example, the inclination angle _ of the traction rollers 11 is larger than the inclination angle β of the traction rollers 25 since the torque to be transmitted by the rollers 11 is smaller than that to be transmitted by the rollers 25. To determine the appropriate angles a computer program was developed which supplies the transmission design parameters when given the basic design features such as transmission ratio and maximum input or output torque.

Claims: A traction roller transmission comprising a housing (1), two planetary type transmission structures (9, 15) arranged in tandem in said housing (1), each including a sun roller (8, 14), a traction ring (10, 16) having a traction surface (19, 20) spaced from said sun roller (8, 14) and planetary traction rollers (11, 17) disposed in the space between, and in engagement with, said sun roller (8, 14) and traction ring (10, 16), and a planetary traction roller support member (13, 18) rotatably supporting said traction rollers (11, 17), an input shaft (3) connected to or forming the sun roller (8) of one of said planetary type transmission structures (9), and an output shaft (4) associated with the planetary traction roller support structure (18) of the other planetary type transmission structure (15), the planetary traction roller support member (13) of one (9) of said planetary type transmission structures (9, 15) having the sun roller (14) of the other planetary type transmission structure (15) associated for rotation therewith, and means (21) provided for forcing said traction rings (10, 16) toward one another, one of said traction ring (10) being non-rotatable mounted in the housing 1, characterized in that said means (21) forcing said traction rings (10, 16) toward one another are adapted to force the other traction ring (16) toward the one traction ring (10) and in engagement with the planetary traction rollers (11, 17) with a force which depends on the torque transmitted through the transmission; and in that the traction surfaces (19, 20) of said traction rings (10, 16) are axially curved and said planetary type traction rollers (11, 17) are supported such that their axes are inclined and intersect the transmission axis at spaced points outside the traction roller transmission and at acute angles (α, β) selected so as to provide radial engagement forces for the planetary type traction rollers (11, 17) with the respective sun rollers (8, 14) and traction rings (10, 16) sufficient to accommodate the different relative torque values transmitted through the two planetary type transmission structures (9, 15). A traction roller transmission according to claim 1, characterized in that said one traction ring (10) is fixed in said housing (1) and said other traction ring (16) is provided with an axial cam structure (21) adapted to force the latter toward said one traction ring (10) and in engagement with the planetary traction rollers (11, 17) with said force which depends on the torque transmitted through the transmission. A traction roller transmission according to claim 1 or 2, characterized in that springs (22) are disposed between the traction rings (10, 16) to insure reduction of their engagement with the traction rollers (11, 17) when the torque transmitted through the transmission decreases. A traction roller transmission according to claim 1, 2 or 3, characterized in that the surfaces of the sun (14) and of the planetary traction rollers (17) of at least said other planetary type transmission structure (15) are conical and any axial tangent on the traction rollers and the sun (14) intersect on the transmission axis. A traction roller transmission according to claim 4, characterized in that the surfaces of the sun (8) and of the planetary traction rollers (11) of said one planetary type transmission structure (9) are conical and any axial tangents on said surfaces intersect on the transmission axis. A traction roller transmission according to claim 4, characterized in that the surface of the sun (8) of said one planetary type transmission structure (9) is essentially straight cylindrical and the surfaces of the planetary traction rollers (11) of said one planetary type transmission structure (9) are conical and the axial tangents of the planetary traction rollers (11) intersect the axes of the respective rollers (11) on the cylinder envelope of the cylindrical sun roller (8). A traction roller transmission according to any one of claims 1 to 6, characterized in that the planetary traction rollers (17) are supported on the other (18) of said support members (13, 18) by shaft members (24) extending through said traction rollers (17) and being interconnected at their free ends by a connecting ring (25) and that an axial thrust bearing (26) is arranged between said connecting ring (25) and the support member (13) of said one planetary type transmission structure (9) adapted to transmit the axial transmission engagement forces therebetween. A traction roller transmission according to claim 7, characterized in that axial thrust bearings (28) are arranged between the planetary traction rollers (11) and the support member (13) of said one planetary type transmission structure (9).

Inventors: KRAUS CHARLES E, KRAUS, CHARLES E.
Applicants: EXCELERMATIC, EXCELERMATIC INC.
Application year: 1991
Main classification: F16H13
IPC codes: F16H13