Note: Descriptions are shown in the official language in which they were submitted.
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TTTT~ OF T~ lNv~r-~lON
Ceramic adjusting shim
FT~Tn OF T~ ~Nv~:r-.lON
This invention relates to an adjusting shim
used in a valve train for an internal combustion
engine.
D~CRIPTION OF TU~ PRIOR ART
The adjusting shim is used to regulate a
valve clearance. Although a conventional adjusting
shim consists usually of a metal, there is known an
adjusting shim formed out of a ceramic material for the
purpose of reducing the weight thereof and improving
the wear resistance thereof.
However, even when the weight of a ceramic
adjusting shim is reduced, a decrease in a power loss
caused thereby is not substantially recognized in
practice since the percentage of the inertial weight of
the adjusting shim with respect to the whole inertial
weight of the valve train is extremely small.
Moreover, the offensiveness of the shim with respect to
the parts with which the shim contacts, so that these
two parts wear greatly.
SUMM~RY OF TH~ lNv~ ON
Therefore, an object of the present invention
is to provide a ceramic adjusting shim having a smooth
surface in which the above-mentioned problems are
eliminated.
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According to the present invention, there is
provided a ceramic adjusting shim comprising a ceramic
material the surface roughness of which is not more
than 2.0 ~m in ten-point average roughness (Rz).
As the ceramic material for the ceramic
adjusting shim, silicon nitride is mainly used. The
surface roughness of the adjusting shim is preferably
not more than 0.8 ~m and more preferably not more than
0.2 ~m, in ten-point average roughness (Rz).
BRI~F DESCRIPTION OF TH~ DRAWINGS
FIG. 1 is a longitudinal section of an
adjusting shim.
FIG. 2 is a longitudinal section of an
adjusting shim and a valve lifter.
FIG. 3 is a longitudinal section of a valve
train for an engine.
FIG. 4 is a longitudinal section of an
apparatus for testing a product according to the
present invention.
D~T~IT.~n D~-~CRIPTION OF TH~ pR~F~RR~n ~MRODTM~NTS
The present invention will be now described
in detail hereinbelow.
Referring first to FIG. 3, a reference
numeral 1 denotes a cylinder head of an engine, 2 a
cam, 3 a valve lifter, 4 an adjusting shim, 5 an intake
or exhaust valve, 6 a valve seat and 7 a valve spring.
In the valve train shown in FIG. 3, the valve lifter 3
is driven by the cam 2, and the displacement of the cam
2 is transmitted to the intake or exhaust valve 5. As
may be understood from FIG. 3, an adjusting shim 4 is
disposed between the valve lifter 3 and cam 2. A
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longitudinal section of the adjusting shim 4 is shown
in FIG. 1.
When a ceramic adjusting shim having a smooth
surface is used, a frictional loss occurring between
the cam and the ceramic adjusting shim can be reduced,
so that a power loss of the internal combustion engine
can be minimized. Moreover, the offensiveness of the
ceramic adjusting shim with respect to the cam 2 and
valve lifter 3 shown in FIG. 3 decreases, and the wear
of these two parts can therefore be reduced.
In this case, the roughness of the surface
(designated by a reference numeral 8 in FIG. 1), which
the cam contacts of the ceramic adjusting shim is not
more than 0.2 ~m in ten-point average roughness (Rz),
and a torque loss caused thereby becomes smaller than
that in a case where a conventional metal adjusting
shim is used. When the ten-point average roughness
(Rz) is up to 0.2 ~m, a torque loss decreases in
accordance with a decrease in the surface roughness.
In a region in which the ten-point average roughness is
(Rz) of the contact surface is less than 0.2 ~m, a
torque loss caused thereby is substantially equal to
that in a case where the ten-point average roughness is
0.2 ~m.
In a region in which the roughness of the
surfaces (designated by reference numerals 9 and 10 in
FIG. 1), which the valve lifter contacts, of the
ceramic adjusting shim is not more than 0.8 ~m in ten-
point average roughness, a wear loss of the
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'~
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valve lifter decreases sharply in accordance with a
decrease in the surface roughness of the ceramic
adjusting shim, and, in a region in which the surface
roughness of the same shim is less than 0.2 ~m, a wear
loss of the valve lifter becomes
substantially constant.
The present invention will now be described
concretely on the basis of its embodiments.
Example 1
The same adjusting shims as shown in FIG. 1 were
produced out of a silicon nitride ceramic sintered
body having a relative density of not less than 98%.
The surface, which a cam contacts, i.e. the surface
designated by a reference numeral 8 shown in FIG. 1,
of each of the adjusting shims was finished under
various conditions by a diamond wheel to set the
roughness of the surfaces of these adjustin~ shims to
levels shown in Table 1. Each of the adjusting shims
thus produced was subjected to the evaluation of power
loss with respect to the power consumption of a motor
rotated at a predetermined number of revolutions per
minute (2000 RPM and 4000 RPM in terms of number of
revolutions per minute of engine), by using a motoring
system shown in FIG. 4 and simulating an over head
camshaft type valve train. Table 1
shows the results of the above with the results of
similar evaluation of power loss caused by
conventional steel adjusting shims which constitute
comparative examples.
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Table 1
No. Material for Surface roughness Power consumption
adjusting Rz of contact of motor (kW )
shim surface (~m) 2000 RPM 4000 RPM
1 Silicon 1.5 1.13 1.24
nitride
2 Silicon 1.2 1.11 1.22
nitride
3 Silicon 1.0 1.08 1.18
nitride
4 Silicon 0.7 1.00 1.10
nitride
Silicon 0.5 0.94 1.03
nitride
6 Silicon 0.2 0.90 0.99
nitride
7 Silicon 0.05 0.89 0.98
nitride
*8 Silicon 2.5 1.20 1.32
nitride
*9 Silicon 5.0 1.32 1.45
nitride (not processed)
*10 Cr-Mo steel 5.0 1.17 1.28
* comparative example
Example 2:
The adjusting shims produced out of various
kinds of ceramic materials were subjected to the
evaluation of power loss caused thereby by a method
identical with that used in Example 1, and the results
are shown in Table 2.
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Table 2
No. Material for Surface roughness Power consumption
adjusting Rz of contact of motor (kW)
shim surface (~m) 2000 RPM 4000 RPM
11 Zirconia 0.05 0.91 1.00
12 Zirconia 1.0 1.11 1.22
13 Composite 1.0 1.09 1.19
material of
SiC-Si3N4
14 Composite 0.2 0.92 1.01
material of
SiC-Si3N4
*15 Zirconia 5.0 1.34 1.47
*16 Composite 8.0
material of (not processed)1.36 1.49
SiC-Si3N4
*10 Cr-Mo steel 5.0 1.17 1.28
* comparative examples
Example 3:
Each of the adjusting shims produced under the
same conditions as in Example 1 was subjected to a
200-hour.continuous operation test with a motor
rotated at a predetermined number of revolutions per
minute (6000 RPM in terms of number of revolutions per
minute of engine), by using the motoring system used
in Example 1, and the wear loss, which was
determined after the tests had been completed, of the
valve lifter was evaluated. The evaluating of the
wear loss of the valve lifter was done by
measuring the inner diameter, which is shown by a
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reference numeral 11 in FIG. 2, of the valve lifter
before and after each test was conducted, and
determining the quantity of variation thereof. The
results of the evaluation are shown in Table 3.
Table 3
No. Material for Surface Roughness Rz Wear
adjusting shim of contact surface loss**
(~m) (~m)
17 Silicon nitride 1.5 12
lO18 Silicon nitride 1.2 11
19 Silicon nitride 1.0 10
20 Silicon nitride 0.7 5
21 Silicon nitride 0.5 3
22 Silicon nitride 0.2
1523 Silicon nitride 0.05 <1
*24 Silicon nitride 2.5 18
*25 Silicon nitride 5.0 20
(not processed)
- * comparative example
** Wear loss: Difference between the inner
diameter of valve lifter measured before test was
conduct~d and that thereof measured after test was
conducted.
The present invention is not limited to these
embodiments. The surfaces of the adjusting shims were
smoothed by being processed with a diamond wheel.
Even if these surfaces are smoothed by being subjected
to chemical and physical surface treatments (etching
and coating), or a chemical applying treatment which
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is conducted before and after the sintering of a
ceramic material, obtaining the same effect as those
in the embodiments can be expected. The same effect
can also be expected even if the roughness of the
surfaces designated by the reference numerals 8, 9 and
10 in FIG. 1 is set to different levels according to
different purposes.
The adjusting shim according to the present
invention enables a power loss and wear resistance of
a valve train to be reduced and increased
respectively, and the fuel consumption, performance
and durability of an internal combustion engine to be
improved.
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