Planetary gear transmission systems or components – Planet pinion is friction gear
Reexamination Certificate
2000-08-15
2002-10-08
Estremsky, Sherry (Department: 3681)
Planetary gear transmission systems or components
Planet pinion is friction gear
C475S186000, C475S189000, C475S195000
Reexamination Certificate
active
06461268
ABSTRACT:
The present invention relates generally to a continuously variable transmission device, and particularly to such a device in which forces are transmitted by rolling traction.
One known type of continuously variable transmission, which has been put into commercial use in the drive train of a motor vehicle comprises a transmission belt of trapezoidal section passing around two split pulleys the opposite halves of which have facing inclined conical surfaces and are urged towards one another such that the effective transmission ratio between one pulley and the next is determined by the relative separation of the two parts of the pulleys. On being moved apart, the two parts of a pulley allow the belt to contact the conical faces at a radially inner position thereby changing the transmission ratio.
In this case the resilient forces exerted on the two parts of the other pulley cause them to move together to compensate for the reduction in tension in the belt thereby increasing the radius of the contact between the belt and the pulleys. Such transmission devices are, however, relatively large as they comprise two substantially spaced shafts, and moreover are not capable of rapid ratio change. They also tend to have low efficiency under part load operation. Versions having rubber belts can also be subject to large amounts of wear largely because of the sliding friction which takes place between the belt and the pulleys as the gear “ratios” are changed. It does have the advantage over conventional gear boxes of providing a continuous or stepless variation in drive transmission from a minimum to a maximum drive ratio. It is not, however, capable of providing a reverse ratio without further structural complications.
Other forms of continuously variable transmission are known, for example from U.S. Pat. No. 1,800,388. The present invention seeks to provide a continuously variable transmission in which the forces are transmitted between the members in motion by rolling contact. This minimises the amount of wear to which the members are subject upon changing the transmission ratio, and allows a continuously variable transmission to be made which is easy to control, requires low maintenance and offers a durable mechanism with a long service life.
According to one aspect of the present invention, therefore, there is provided a continuously variable transmission device of the type having planet members in rolling contact with radially inner and outer races each comprising two axially spaced parts, with control means for selectively varing the axial separation of the two parts of one race and thus the radial position of the planet members in rolling contact therewith, in which there are provided means sensitive to the torque applied to a drive-transmitting member of the transmission operable both to determine the compensating variation in the separation of the two parts of the other race and thus the transmission ratio of the device and to vary the forces exchanged between the planets and the races normal to the interface between them.
In a preferred embodiment of the invention the planet members are substantially spherical bodies. They may be right circular, oblate or prolate spheroids. Alternatively, the planet members may have respective first and second surface portions comprising surfaces of revolution about the same axis (for each member) the surface portions being inclined with respect to one another in opposite directions about the axes of revolution. The planet members may have a convex or concave surface of revolution defined by a curved generatrix which may be a regular or irregular curve or a part-circular curve. In the case of a part-circular generatrix this may be a semi-circle, in which case the surface of revolution of the planet member is spherical.
In such a structure the inner and outer races preferably comprises two parts, one in contact with each of the first and second portions respectively, and each having a respective surface constituted by a surface of revolution about a common axis and inclined in opposite directions with respect to the said axis. The two parts of one of the inner or outer races may be supported in such a way as to be relatively displaceable towards or away from one another whereby to vary the radius of the point or line of contact between the said one race and the planet members.
Embodiments of the invention may be provided with torque-sensitive mechanical coupling means interposed between an input drive member and one of the races whereby to balance the torque transmission and the contact pressures between the two parts of that race and the planet members.
In practice, it is preferred that the planet members are substantially spherical and captive between the radially inner races and the radially outer races, there being roller follower members circumferentially intercalated between adjacent pairs of planet members for transmitting drive to or from the said planet members. In such an arrangement it is particularly convenient if the roller follower members are carried on a planet carrier member to which drive to or from the planet members is transmitted in operation of the device.
In general terms, the present invention provides a drive transmission device as defined above, in which the axes of rotation of the planet members about their own axis are substantially parallel to the axis of rotation of the planets about the radially inner race. In such a drive transmission device it is a particular feature that the axis of rotation of the radially inner race is substantially parallel to the axis of the means defining the radially outer race defining the planetary path of the planet members.
In any event it is convenient if the means for selectively varying the axial separation of the two parts of the radially inner race or the means defining the radially outer race include two adjustment members interconnected by a helical interengagement such that relative turning motion of one of the adjustment members results in relative axial displacement of the other. In such a device the helical interengagement of the two adjustment members comprises a screw threaded engagement of the members themselves, the said one of the two adjustment members being turnable through at least a limited arc of movement about a first axis and the said other of the adjustment members being restrained against rotary motion at least about an axis substantially parallel to the said first axis. The helix angle may be constant over the entire length of the helix although for certain applications it may be found to be useful if the helix angle of the said helical interengagement varies over the circumferential extent of the helix.
In general, it is convenient if the said other of the two adjustment members is or is carried by or on the said means defining the radially outer track. The two parts of the radially inner race may be carried on a drive or driven shaft, and the means for allowing relative separation of the two parts of the radially inner race comprise at least one inclined surface acting to react the forces exerted by the transmission of drive forces between the radially inner race and the planet members. The said inclined surface may be part of a helical interengagement between the parts of the radially inner race and the drive shaft. The helix angle may be constant or may vary over the length of the helix.
Whether the helix is constant or varying its form and helix angle should preferably be such that the circumferential component of the axial force reacted by the helix is substantially equal to and opposite in sign from the direct circumferential force reacted by the helix such that the force required to be applied to the said selective adjustment means to maintain or change a transmission ratio is minimised.
The present invention also comprehends an infinitely variable transmission device comprising a continuously variable transmission as defined above together with a further epicyclic transmission train of fixed ratio gears or rolling traction members the dimensions of which
Estremsky Sherry
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
Lewis Tisha D.
Orbital Traction Ltd.
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