Friction gear transmission systems or components – Friction gear includes idler engaging facing concave surfaces – Toroidal
Reexamination Certificate
1998-10-29
2002-04-23
Footland, Lenard A. (Department: 3682)
Friction gear transmission systems or components
Friction gear includes idler engaging facing concave surfaces
Toroidal
C384S492000
Reexamination Certificate
active
06375593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved power roller bearing for use in a toroidal type continuously variable transmission system which is used, for example, as a transmission system of an automobile.
2. Description of the Related Prior Art
In a conventional toroidal type continuously variable transmission system used as a transmission system of an automobile, the rotation of an input disk is transmitted to an output disk in a continuously variable manner through a plurality of power rollers which are respectively included in their corresponding power roller bearings and swingably interposed between the input and output disks.
Here, the power roller bearing comprises: an inner race including a power roller which has a traction portion to be contacted with the above-mentioned input and output disks and also which, due to its rotational movement, can transmit the rotation of the input disk to the output disk; an outer race disposed opposed to the inner race so as to hold the power roller in a freely rotatable manner; and, a rolling ball body which is interposed between the inner and outer races in such a manner as to be held by and between ring-shaped race grooves respectively formed in the mutually opposing surfaces of the inner and outer races, and also which not only transmits a thrust load, which is applied to the inner race from the power roller, to the outer race, but also can be rolled on the race grooves to thereby reduce resistance produced between the inner and outer races during the relative rotation thereof.
As described above, the structure of the power roller bearing, except for the power roller which is provided in the inner race, is almost similar in appearance to that of a thrust ball bearing used to bear a rotary shaft to which a thrust load is to be applied.
In view of this, persons skilled in the art have studied a method for producing the power roller for use in a toroidal type continuously variable transmission system at low costs by diverting parts, which are designed for an existing thrust ball bearing, to the power roller bearing.
However, although the power roller bearing is quite similar in the appearance of the component parts thereof to the thrust ball bearing, the function of the inner race of the power roller bearing is entirely different from that of an ordinary thrust ball bearing. Because of such functional difference of the inner race, the distribution of loads acting on the inner race itself, contact behaviors between the rolling ball bodies, which are interposed between the inner and outer races, and the inner and outer races, and the like are greatly different from those of the ordinary thrust ball bearing. Therefore, in the above component diverting method, there are still left various points to be improved with these differences taken into consideration.
For example, an inner race used in the ordinary thrust bearing serves as a support member for supporting a shaft, whereas a power roller, which is employed in the power roller bearing and can be rotated integrally with its associated inner race, serves as a power transmission member for transmitting the rotation of the input disk to an output disk, that is, it corresponds to a speed change gear in a multistage transmission system of a gear type. And, since such a power roller is rotated at high speeds while it receives a strong pressure from the input and output disks, it generates a great amount of heat; and, such heat generated by the power roller in turn heats the inner race and rolling ball body.
For this reason, as a lubrication oil to be supplied between the inner and outer races, it is indispensable to use a high-viscosity traction oil which has been developed exclusively for the purpose of power transmission.
Also, the traction portion of the power roller to be contacted with the input and output disks provided mutually opposing positions which are located on the outer peripheral edge of the power roller and are spaced 180° apart from each other; and, the strong pressures given from the input and output disks are concentrated onto these mutually opposing positions (of the traction portion) as a total force of thrust and radial loads. Therefore, in the traction portion of the power roller to be contacted with the input and output disks, there is generated a very high contact surface pressure.
For example, an ordinary bearing is used at a contact surface pressure of 2 to 3 Gpa or less. On the other hand, in the case of a power roller bearing used in a toroidal type continuously variable transmission system for a vehicle, at a normal decelerating time, the contact surface pressure thereof provides 2.5 to 3.5 Gpa and, at the maximum decelerating time, the contact surface pressure thereof can sometime reach even 4 Gpa.
Further, the strong pressures given from the input and output disks are concentrated onto the 180°-spaced-apart mutually opposing positions of the traction portion of the power roller as the radial loads, thereby causing the power roller and the inner race, in which the power roller is provided, to be compressed and deformed in the radial direction thereof. Such compression and deformation in turn causes the inner race to be curved. This makes it almost impossible that the thrust loads applied to the inner race from the power roller can be shared uniformly by a plurality of rolling ball bodies respectively interposed between the inner and outer races. That is, the thrust loads to which the rolling ball bodies are subjected become larger on parts of the rolling ball bodies that are situated at positions apart from the above-mentioned mutually opposing positions of the traction portion of the power roller by 90°. As a result of this, the contact surface pressures of the rolling ball bodies with respect to the race grooves are caused to vary, while part of the rolling ball bodies are caused to roll on the race grooves with a very high contact pressure.
Therefore, the traction portion of the power roller to be contacted with the input and output disks as well as the race grooves of the inner and outer races to be contacted by the rolling ball bodies must be specially adjusted in the material thereof, the hardness of the surfaces thereof, and the surface roughness thereof, in order to prevent the lives thereof from being shortened due to the localized application of the high contact surface pressures.
In view of the above-mentioned background, the present applicants have proposed a technology in which the rolling ball bodies are respectively formed of medium or high carbon steel and the hardness and strength of the surfaces of the rolling ball bodies are adjusted by a carbonitriding treatment or by a quenching and tempering treatment, in order to enhance the durability of the rolling ball bodies against the localized application of the contact surface pressures thereto to thereby be able to improve the life of the bearing (see Japanese Patent Unexamined Publication No. Hei. 7-208568).
Also, the present applicants have further proposed a technology in which input and output disks as well as a power roller and an inner race to be contacted with the input and output disks are carburized and thereafter finished by grinding to thereby adjust the hardness of the surfaces of these components and the effective hardened layer depth thereof to a proper value (in the range of 2 mm to 4 mm) which allows the components to resist the localized application of the contact surface pressures (see Japanese Patent Unexamined Publication No. Hei. 7-71555).
However, the above-mentioned employment of the exclusive traction oil as the lubrication oil to be supplied between the inner and outer races, and the special proper adjustments of the hardness, effective hardened layer depth, and surface roughness of the power roller, inner race and rolling ball bodies through the selection of material and surface treatment, as such, are not sufficient.
In other words, since the original object of the power roller bearing is power transmission, it is i
Aramaki Hirotoshi
Imanishi Takashi
Itoh Hiroyuki
Miyata Shinji
Footland Lenard A.
NSK Ltd.
Sughrue & Mion, PLLC
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