Mechanical variable-speed drive

Abstract: In a mechanical variable-speed drive, an epicyclic gear (4) has a sun gear (8) connected to an input shaft (3), a planet carrier (13) connected to an output shaft (2), an outer ring gear (24), and a number of planet gears (17) connected frictionally to the sun gear (8) and the ring gear (24); the ring gear (24) being defined by a movable ring (26) movable to and from a fixed ring (25) so as to control the radial position of the planet gears (17) with respect to the sun gear (8) and so vary the velocity ratio of the input shaft (3) and output shaft (2); the movable ring (26) being connected to a further fixed ring (6) by a screw coupling (27) for enabling the movable ring (26) to rotate about and translate along a longitudinal axis (5) of the variable-speed drive.

Description: The present invention relates to a mechanical variable-speed drive. More specifically, the present invention relates to a mechanical variable-speed drive of the type disclosed, for example, in EP-A-0 311 734, which shows the features of the preamble of claim 1, shown in Figure 1, and comprising an epicyclic gear A interposed between an input shaft B and an output shaft C mounted to rotate about a given longitudinal first axis D at a first and second angular velocity respectively. Epicyclic gear A comprises a sun gear E connected in angularly-fixed manner to input shaft B; a planet carrier F connected in angularly-fixed manner to output shaft C; an outer ring gear G substantially coaxial with first axis D; and a number of planet gears H, each having a respective longitudinal second axis I substantially parallel to first axis D. Planet gears H are connected frictionally to sun gear E and ring gear G to rotate about respective second axes I and simultaneously about first axis D, so as to rotate planet carrier F, and hence output shaft C, about first axis D. Ring gear G normally comprises an angularly- and axially-fixed first ring L; and a second ring M movable to and from first ring L to control the radial position of second axes I with respect to first axis D and vary the velocity ratio of input shaft B and output shaft C. The variable-speed drive also comprises an angularly- and axially-fixed third ring N on the opposite side of second ring M with respect to first ring L; and connecting means for connecting second ring M to third ring N, and which enable second ring M to move along first axis D as it rotates about first axis D. The connecting means normally comprise an annular member O interposed between second and third ring M, N and supporting for rotation a number of balls P, which are distributed about first axis D and simultaneously engage two annular tracks of two cams Q, formed on second and third ring M, N respectively, so as to move second ring M axially as it rotates about first axis D. The connecting means are therefore relatively complex and expensive by comprising cams Q and annular member O supporting balls P, and on account of the difficulty in both forming cams Q on respective rings M, N, and assembling annular member O, i.e. positioning balls P between cams Q. It is an object of the present invention to provide a variable-speed drive designed to eliminate the aforementioned drawbacks. According to the present invention, there is provided a variable-speed drive as claimed in Claim 1. A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 2 shows a longitudinal section of a preferred embodiment of the mechanical variable-speed drive according to the present invention; Figure 3 shows a view in perspective of a detail of the Figure 2 variable-speed drive. Number 1 in Figure 2 indicates as a whole a variable-speed drive for selectively varying the angular velocity of an output shaft 2 with respect to a constant angular velocity of an input shaft 3 by means of an epicyclic gear 4 interposed between shafts 2 and 3. Shaft 3 has a longitudinal axis 5 and is rotated about axis 5, and with respect to an outer tubular casing 6 coaxial with axis 5, by a known actuating device not shown; and shaft 2 is positioned substantially facing and coaxial with shaft 3, and is rotated about axis 5, and with respect to casing 6, by gear 4 and with the support of two ball bearings 7. Gear 4 comprises a sun gear 8 in turn comprising a tubular body 9, which is connected in angularly- and axially-fixed manner to shaft 3 and has, at one end, an annular flange 10 extending radially outwards from the outer surface of body 9. Sun gear 8 also comprises an annular plate 11, which is connected in axially-sliding manner to body 9 and is normally kept pressed against flange 10 by a spring 12 fitted to body 9 and coaxial with axis 5. Gear 4 also comprises a planet carrier 13 in turn comprising a disk 14, which is connected in angularly-and axially-fixed manner to shaft 2, has a substantially cylindrical outer surface 15, and comprises a number of grooves 16 (four in the example shown) equally spaced about axis 5 and extending radially inwards from surface 15. Gear 4 also comprises a number of planet gears 17 equal in number to grooves 16 and each comprising a respective disk 18, which has a longitudinal axis 19 substantially parallel to axis 5, is defined axially by two substantially truncated-cone-shaped surfaces 20, and has a pin 21 coaxial with axis 19. Pin 21 is fitted in rotary and axially-fixed manner inside a bush 22, which is substantially parallelepiped-shaped so as to engage in sliding manner a respective groove 16. Finally, gear 4 comprises an outer ring gear 24 in turn comprising a ring 25 coaxial with axis 5 and connected in angularly- and axially-fixed manner to casing 6, and a ring 26 which is coaxial with axis 5, is positioned facing ring 25, and is connected to casing 6 by a recirculating-ball coupling 27 so as to move axially to and from ring 25 when rotated by a control pawl 28 projecting radially outwards from the lateral surface of ring 26 itself. Coupling 27 comprises two tracks 29 coiling along and about axis 5, one on the outer surface of ring 26 and the other on the inner surface of casing 6, and which have respective substantially arc-shaped cross sections and are positioned facing each other to define a channel 30 along which are distributed and travel a number of balls 31. Coupling 27 also comprises a block 32 having a channel 33 facing the outer surface of ring 26 and for recirculating balls 31 along channel 30. In actual use, planet gears 17 are connected frictionally to both sun gear 8 and ring gear 24. More specifically, each planet gear 17 is gripped between flange 10 and plate 11 and between rings 25 and 26 so as to rotate about respective axis 19 and simultaneously about axis 5 and so rotate planet carrier 13 about axis 5. The ratio between the angular velocities of shafts 2 and 3 is varied by adjusting the radial position of planet gears 17 with respect to sun gear 8, i.e. by adjusting the distance between axes 19 and axis 5. More specifically, when axes 19 of planet gears 17 are located a maximum distance (Figure 2) from axis 5, the angular velocity of planet carrier 13, and therefore of shaft 2, is minimum. Conversely, when axes 19 of planet gears 17 are located a minimum distance (not shown) from axis 5, the angular velocity of planet carrier 13, and therefore of shaft 2, is maximum. The radial position of planet gears 17 with respect to sun gear 8 is varied by means of pawl 28 and recirculating-ball coupling 27, so that: when ring 26 is moved towards ring 25, the grip exerted by rings 25 and 26 on truncated-cone-shaped surfaces 20 moves planet gears 17 radially towards axis 5 in opposition to spring 12; and when ring 26 is moved away from ring 25, the grip exerted on truncated-cone-shaped surfaces 20 by flange 10 and plate 11 of sun gear 8, with the aid of spring 12, moves planet gears 17 radially towards outer ring gear 24. Variable-speed drive 1 has several advantages, foremost of which are that recirculating-ball coupling 27 is relatively cheap and easy to produce, and provides for relatively little friction between ring 26 and outer tubular casing 6. Moreover, by virtue of channel 30 having a substantially circular cross section and being engaged by a relatively large number of balls 31, the contact pressures between channel 30 and each ball 31 are relatively small, thus enabling casing 6 to be made using materials which are relatively cheap and/or require no surface treatment.

Claims: A mechanical variable-speed drive comprising an epicyclic gear (4) interposed between an input shaft (3) and an output shaft (2) mounted to rotate about a given longitudinal first axis (5) at a first and second angular velocity respectively, the epicyclic gear (4) comprising a sun gear (8) connected in angularly-fixed manner to said input shaft (3), a planet carrier (13) connected in angularly-fixed manner to said output shaft (2), a number of planet gears (17), each having a respective longitudinal second axis (19) substantially parallel to said first axis (5), and an outer ring gear (24) substantially coaxial with the first axis (5), said planet gears (17) being connected frictionally to said sun gear (8) and to said ring gear (24) to rotate about the respective said second axes (19) and about said first axis (5) so as to rotate said planet carrier (13) about the first axis (5), and said ring gear (24) comprising an angularly- and axially-fixed first ring (25), and a second ring (26) movable to and from said first ring (25) to control the radial position of said second axes (19) with respect to said first axis (5) and so vary the velocity ratio of said input shaft (3) and said output shaft (2); a body (6) extending at least partly about said second ring (26); and connecting means (27) for connecting said second ring (26) to said body (6) and enabling the second ring (26) to move along said first axis (5) when the second ring (26) is rotated about the first axis (5); characterized in that said connecting means (27) are recirculating-ball connecting means comprising two tracks (29) coiling along and about said first axis (5), said tracks (29) being formed respectively on an inner surface of said body (6) and on an outer surface of said second ring (26), and being positioned facing each other to define a channel (30); and a number of balls (31) distributed along said channel (30). A variable-speed drive as claimed in Claim 1, wherein said connecting means (27) also comprise a further channel (33) for recirculating said balls (31) along said channel (30). A variable-speed drive as claimed in any one of the foregoing Claims and also comprising an outer tubular casing (6); said body (6) being formed in one piece with said casing (6). A variable-speed drive as claimed in any one of Claims 1 to 3 and also comprising an outer tubular casing (6); said body (6) being connected in axially- and angularly-fixed manner to said casing (6).

Inventors: COGNIGNI ENZO, DEPIETRI PIETRO, PERNI FEDERICO, PIZZONI LUCIANO, PORZI CARLO, COGNIGNI, ENZO, DEPIETRI, PIETRO, PERNI, FEDERICO, PIZZONI, LUCIANO, PORZI, CARLO
Applicants: BONFIGLIOLI RIDUTTORI SPA, UMBRA CUSCINETTI S P A, BONFIGLIOLI RIDUTTORI S.P.A., UMBRA CUSCINETTI S.P.A.
Application year: 2000
Main classification: F16H15
IPC codes: F16H15