Friction gear transmission systems or components – With lubrication
Reexamination Certificate
2001-03-22
2003-02-25
Lavinder, Jack (Department: 3683)
Friction gear transmission systems or components
With lubrication
C476S040000, C476S073000
Reexamination Certificate
active
06524212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission (CVT) for automobiles, which is used to continuously control change gear ratio, and more specifically to a surface roughness structure of rolling elements of the toroidal-type CVT, such as an input disk, an output disk and a power roller.
U.S. Pat. No. 5,676,618 discloses one example of the toroidal-type CVT, which is incorporated herein by reference.
FIG. 1
shows the basic structure of the toroidal-type CVT. The toroidal-type CVT includes a plurality of metal rolling elements contacting one another through a traction oil film. The rolling elements include input disk
3
connected with input shaft
1
, output disk
5
connected with output shaft
2
, and power rollers
6
,
6
interposed between input disk
3
and output disk
5
and rotatable to transmit rotational force from input disk
3
to output disk
5
. Each power roller
6
has a tiltable roller shaft such that power roller
6
is inclined relative to input and output disks
3
and
5
when the roller shaft tilts. Power roller
6
is contacted with input disk
3
and output disk
5
through a traction oil. When power roller
6
is inclined, the contact between power roller
6
and input and output disks
3
and
5
shifts. This changes the ratio of the torque radius of input disk
3
to that of output disk
5
to thereby continuously change the transmission ratio.
Table 1 shows one example of the results of measurement of a surface structure or texture, specifically, a surface roughness, of the mutually contact surfaces of input and output disks
3
and
5
and power roller
6
of the toroidal-type CVT, which surfaces are hereinafter referred to as traction surfaces.
TABLE 1
Surface structure
Measurement results
Ra (JIS B0601)
0.018 &mgr;m
Rq
0.022 &mgr;m
Mr2 (DIN4776)
86.67%
Rk (DIN4776)
0.055 &mgr;m
Rvk (DIN4776)
0.027 &mgr;m
Vo
1.8 × 10
−6
mm
3
/mm
2
K
0.54
Generally, the traction surfaces of the rolling elements of the toroidal-type CVT in the earlier technique have the surface structure in which arithmetical mean roughness Ra prescribed by JIS B0601-1994 is not more than 0.05 &mgr;m, root-mean-square roughness Rq is not more than 0.07 &mgr;m, oil retention volume Vo is not more than 1.3×10
−5
mm
3
/mm
2
, and oil retention depth ratio K is less than 0.9.
If the surface roughness of the traction surfaces of the rolling elements exceeds a certain value relative to a thickness of the traction oil film formed between input and output disks
3
and
5
and power roller
6
, rolling-fatigue lives of input and output disks
3
and
5
and power roller
6
are deteriorated so that durability of the CVT decreases. Therefore, the traction surfaces are subjected to grinding and super-finishing such that the surface roughness is limited to a sufficiently small level in height, that is, arithmetical mean roughness Ra of not more than 0.05 &mgr;m. Here, as prescribed in JIS B 0601, arithmetical mean roughness Ra is determined as the value obtained by the following formula and expressed in micrometer (&mgr;m) when sampling only the reference length L from the roughness curve in the direction of mean line, taking X-axis in the direction of mean line and Y-axis in the direction of longitudinal magnification of this sampled part and the roughness curve is expressed by y=f(x):
Ra
=
1
L
∫
0
L
&LeftBracketingBar;
f
(
x
)
&RightBracketingBar;
ⅆ
(
x
)
(
1
)
where L is reference length.
Namely, arithmetical mean roughness Ra means the mean deviation obtained by dividing the area defined by the roughness curve f(x) and the mean line, i.e., X-axis, as shown in
FIG. 2A
, by the reference length L.
Root-mean-square roughness Rq is determined as the value obtained by the following formula and expressed in micrometer (&mgr;m) when sampling only the reference length L from the roughness curve in the direction of mean line, taking X-axis in the direction of mean line and Z-axis in the direction of longitudinal magnification of this sampled part and the roughness curve is expressed by z=f(x):
Rq
=
1
L
∫
0
L
f
2
(
x
)
ⅆ
(
x
)
(
2
)
where L is reference length.
Namely, root-mean-square roughness Rq means the square root of the mean deviation obtained by dividing the area defined by the mean line (X-axis) and the curve obtained by squaring the distance between the roughness curve f(x) and the mean line (X-axis), as shown in
FIG. 2B
, by the reference length L.
DIN4776 defines parameters Mr
1
, Mr
2
, Rpk, Rvk and Rk for evaluation of lubricating characteristic of a surface structure, based on an initial wear part, a substantial contact part, and an oil retention part, which are separated from a bearing curve (material ratio curve). Parameters Mr
1
, Mr
2
, Rpk, Rvk and Rk are determined as follows.
(1) Mr
1
: Material Portion
1
Level, in percent, determined for the intersection line which separates peaks from roughness profile and cooperates with Mr
2
described later to determine the roughness core profile which is roughness profile excluding the peaks and deep valleys (see FIG.
3
). Mr
1
is calculated as follows. As shown in the right part of
FIG. 3
, slope line SLsg includes the secant line of material ratio curve MrC over 40% of the material ratio which shows the smallest gradient. This is determined by moving the secant line for &Dgr;Mr=40% along material ratio curve MrC. Intersection of a lower limit line at Mr=0% and slope line SLsg with the smallest gradient is indicated at a. Intersection of material ratio curve MrC and a horizontal line passing through intersection a is indicated at c. Material ratio at intersection c is expressed by Mr
1
(%). Mr
1
indicates the material portion after initial wear.
(2) Mr
2
: Material Portion
2
Level, in percent, determined for the intersection line which separates deep valleys from the roughness profile (see FIG.
3
). Mr
2
is calculated as follows. As illustrated in
FIG. 3
, intersection of an upper limit line at Mr=100% and slope line SLsg with the smallest gradient is indicated at b. Intersection of material ratio curve MrC and a horizontal line passing through intersection b is indicated at d. Material ratio at intersection d is represented by Mr
2
(%). Mr
2
indicates the material portion after long-period wear.
(3) Rpk: Reduced Peak Height
Average height of the peaks above the roughness core profile. In
FIG. 3
, if an area of a right triangle formed by base ac and a side lying on the lower limit line Mr=0% is equal to an area defined by the lower limit line Mr=0%, base ac and material ratio curve MrC, the height of the right triangle is expressed as Rpk (&mgr;m). In other words, the distance between intersection a and a vertex of the right triangle which is located on the lower limit line Mr=0% is represented by Rpk (&mgr;m). Rpk indicates a height of initial wear.
(4) Rvk: Reduced Valley Depth
Average depth of the profile valleys projecting through the roughness core profile. In
FIG. 3
, if an area of a right triangle formed by base bd and a side lying on the upper limit line Mr=100% is equal to an area defined by the upper limit line Mr=100%, base bd and material ratio curve MrC, the height of the right triangle, namely, the distance between intersection b and a vertex of the right triangle which is located on the upper limit line Mr=100%, is represented by Rvk (&mgr;m). Rvk indicates a depth of oil retention valley.
(5) Rk: Core Roughness Depth
Height difference between intersections c and d is represented by Rk (&mgr;m). Rk indicates a height of long-period wear which is reduced by wear during a long period until the surface is worn out to unuseable state.
Vo and K are determined as follows.
Vo: oil retention volume
Vo is represented by the following formula:
Vo=[(100−Mr
2
)×Rvk]/200000(mm
3
/mm
2
) (3)
Vo indicates a volume of oil retain
Chiba Nobutaka
Nanbu Toshikazu
Ushijima Kenshi
Watanabe Jun
Foley & Lardner
Nissan Motor Co,. Ltd.
Pezzlo Benjamin A
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