The present invention relates to a tapered roller bearing.
A tapered roller bearing which is used for supporting a pinion shaft in a differential gear of an automobile is lubricated by a large quantity of high-viscosity gear oil. For this reason, friction (dynamic friction) torque ascribable to rolling viscous resistance and the agitation resistance of oil is large, which constitutes one factor deteriorating the fuel consumption of the automobile. Accordingly, to promote further low fuel consumption, it is desirable to reduce the friction torque as practically as possible. To reduce the friction torque, it is known that it suffices if, for example, the number of tapered rollers is reduced, their length is shortened, or their diameter is made small. However, the reduction of the friction torque in such a manner leads to a substantial decline in the load carrying capacity as the bearing, so that it is not expedient to do so.
In view of the above-described conventional problems, the object of the invention is to reduce the friction torque while suppressing a decline in the load carrying capacity of the tapered roller bearing.
The tapered roller is characterized by including an outer ring whose outside diameter is D, an inner ring whose inside diameter is d, and a plurality of tapered rollers which are interposed between the outer ring and the inner ring and whose pitch circle diameter is dm, wherein a PCD parameter expressed by 2 dm/(D+d) is a value which falls within a range of 0.96 to 0.985.
The friction torque of the above-described tapered roller bearing changes with a correlation with the PCD parameter, and by setting the PCD parameter in the aforementioned range, it is possible to reduce the friction torque while suppressing a decline in the load carrying capacity.
In addition, in the above-described tapered roller bearing, a contact angle α of the outer ring is preferably set such that 22°≦α≦26°.
In this case, it is possible to reduce the friction torque without causing rigidity and the load carrying capacity to decline.
The results shown in Table 1 below were obtained by conducting the following examination: By using as a PCD parameter a numerical value expressed by ε=2 dm/(D+d), with respect to 13 kinds of samples whose PCD parameters ε and contact angles α differed, an examination was made as to what values the rated value C and the total displacement δ assumed and what value the friction torque T assumed in a state in which the aforementioned motor was rotated at a predetermined speed.
It should be noted that Sample 1 was a tapered roller bearing based on a conventional design, and the torque ratio was calculated by using the torque ratio of that tapered roller bearing as being 1.
It should be noted that, of the plotted points in the aforementioned optimum range, as for Samples 3 to 5whose contact angle α was 20°, since the total displacement δ (the root mean square of the radial displacement and the axial displacement) increased more than that of Sample 1 as shown in Table 1, it is considered that rigidity declined slightly. However, since the rated load C was equal to or increased over that of Sample 1, it is considered that Samples 3 to 5 are capable of withstanding practical use. In addition, of the plotted points in the aforementioned optimum range, as for Sample 13 whose contact angle α was 28°, the rated load C, i.e., the load carrying capacity, was lower than that of Sample 1, but its decline rate was 5% or thereabouts, so that it is considered that Sample 13 is barely at a permissible level. It should be noted, however, that it is preferable to avoid the contact angle α from being set to 20° or 28° and to set it such that 22°≦α≦26°.
Next, with respect to two kinds of tapered roller bearings having different sizes, Examples 1 and 2 of the invention in which the PCD parameter ε was in the range of 0.96 to 0.985 were respectively compared with Comparative Examples (conventional examples) 1 and 2 in which the PCD parameter ε was not in that range. A comparison was made in the change of the friction torque with respect to the rotational speed, the rated load ratio, the total displacement ratio, and the calculated service life ratio. Comparative data are shown in Tables 2 and 3 below. Table 2 shows the comparative data with respect to tapered roller bearings in which d=35 mm, D=80 mm, and axial width=32.75 mm. Table 3 shows the comparative data with respect to tapered roller bearings in which d=40 mm, D=85 mm, and axial width=24.75 mm.
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In accordance with the tapered roller bearing according to the present invention, the friction torque changes with a correlation with the PCD parameter, and by setting the PCD parameter in the range of 0.96to 0.985, it is possible to provide a tapered roller bearing in which the friction torque is reduced while suppressing a decline in the load carrying capacity.
Further, in accordance with the tapered roller bearing according to the present invention, it is possible to reduce the friction torque without causing rigidity and the load carrying capacity to decline.
Number | Date | Country | Kind |
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P.2002-152528 | May 2002 | JP | national |
Number | Name | Date | Kind |
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6086261 | Nakagawa et al. | Jul 2000 | A |
6464398 | Takehara et al. | Oct 2002 | B2 |
Number | Date | Country |
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0 756 095 | Jan 1997 | EP |
1 158 192 | Nov 2001 | EP |
09-096352 | Apr 1997 | JP |
11-210765 | Aug 1999 | JP |
Number | Date | Country | |
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20040017957 A1 | Jan 2004 | US |