Ceramic adjusting shim

Abstract: The present invention provides a ceramic adjusting shim (4) capable of minimizing the abrasion of parts contacting the adjusting shim, for example, a cam (2) and a tappet or valve lifter (3). The ceramic adjusting shim is produced from a ceramic material and has a surface roughness of not more than 2.0 µm in ten-point average roughness (Rz).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a ceramic valve clearance adjusting shim used in a valve operating mechanism for an internal combustion engine. 2. Description of the Prior Art FIG. 3 is a longitudinal section of a valve operating mechanism for an engine. Referring 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 operating mechanism 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 longitudinal section of the adjusting shim 4 is shown in FIG. 1. The adjusting shim 4 is used to regulate a valve clearance. Although a conventional adjusting shim 4 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 from EP-A-0 209 697. This document is silent as regards surface roughness. Furthermore, DE-A-32 39 325 discloses a cam-contacting insert, the surface roughness of the cam-contacting surface being Ra < 0,2 µm. However, this insert is secured to a valve lifter thus being not applicable for valve clearance adjusting and having a rather high ten-point average roughness Rz (Rz = 5 Ra). 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 operating system is extremely small. Moreover, the offensiveness of the shim with respect to the parts with which the shim contacts, i.e., the cam 2 and valve lifter 3 shown in FIG. 3 increases, so that these two parts wear greatly. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a ceramic valve clearance adjusting shim having a smooth surface in which the above-mentioned problems are eliminated. According to the present invention, there is provided a ceramic valve clearance adjusting shim comprising a ceramic material, the adjusting shim contacting a cam and a valve lifter and being movably disposed on the valve lifter, whereby the surface roughness of surfaces of the adjusting shim contacting the cam and the valve lifter is not more than 0.2 µm in ten-point average roughness (Rz) according to Japanese industrial standard JIS B 0601. As the ceramic material for the ceramic valve clearance adjusting shim, silicon nitride is mainly used. BRIEF DESCRIPTION OF THE 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 operating mechanism for an engine. FIG. 4 is a longitudinal section of an apparatus for testing a product according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be now described in detail hereinbelow. 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 abrasion 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 µm 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. In a region in which the ten-point average roughness (Rz) of the contact surface is less than 0.2 µm, a torque loss caused thereby is substantially equal to that in a case where the ten-point average roughness is 0.2 µm. As to 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, an abrasion loss of the valve lifter decreases sharply in accordance with a decrease in the surface roughness of the ceramic adjusting shim. In a region in which the surface roughness of the same shim is less than 0.2 µm, an abrasion 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 valve clearance 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 adjusting 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 operating mechanism. 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. No. Material for adjusting shim Surface roughness Rz of contact surface (µm) Power consumption of motor (kW ) 2000 RPM 4000 RPM 1 Silicon nitride 1.5 1.13 1.24 2 Silicon nitride 1.2 1.11 1.22 3 Silicon nitride 1.0 1.08 1.18 4 Silicon nitride 0.7 1.00 1.10 5 Silicon nitride 0.5 0.94 1.03 6 Silicon nitride 0.2 0.90 0.99 7 Silicon nitride 0.05 0.89 0.98 8 Silicon nitride 2.5 1.20 1.32 9 Silicon nitride 5.0 (not processed) 1.32 1.45 10 Cr-Mo steel 5.0 1.17 1.28 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. No. Material for adjusting shim Surface roughness Rz of contact surface (µm) Power consumption of motor (kW) 2000 RPM 4000 RPM 11 Zirconia 0.05 0.91 1.00 12 Zirconia 1.0 1.11 1.22 13 Composite material of SiC-Si₃N₄ 1.0 1.09 1.19 14 Composite material of SiC-Si₃N₄ 0.2 0.92 1.01 15 Zirconia 5.0 1.34 1.47 16 Composite material of SiC-Si₃N₄ 8.0 (not processed) 1.36 1.49 10 Cr-Mo steel 5.0 1.17 1.28 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 abrasion loss, which was determined after the tests had been completed, of the valve lifter was evaluated. The evaluating of the abrasion loss of the valve lifter was done by measuring the inner diameter, which is shown by a 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. No. Material for adjusting shim Surface Roughness Rz of contact surface (µm) Abrasion loss (µm) 17 Silicon nitride 1.5 12 18 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 1 23 Silicon nitride 0.05 <1 24 Silicon nitride 2.5 18 25 Silicon nitride 5.0 (not processed) 20 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 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 operating system to be reduced and increased respectively, and the fuel consumption, performance and durability of an internal combustion engine to be improved.

Claims: A ceramic valve clearance adjusting shim (4) comprising a ceramic material, the adjusting shim (4) contacting a cam (2) and a valve lifter (3) and being movably disposed on the valve lifter (3) characterized in that the surface roughness of surfaces (8, 9 and 10) of the adjusting shim contacting the cam (2) and the valve lifter (3) is not more than 0.2 µm in ten-point average roughness (Rz) according to Japanese industrial standard JIS B 0601. The ceramic valve clearance adjusting shim according to claim 1, wherein said ceramic material consists mainly of silicon nitride. The ceramic valve clearance adjusting shim according to claim 1 or 2, wherein the roughness of the surface (8) which contacts the cam (2) is identical with the roughness of the surfaces (9, 10) which contact the valve lifter (3). The ceramic valve clearance adjusting shim according to claims 1 or 2, wherein the roughnesses of the surfaces (8, 9 and 10) are different.

Inventors: MATSUNUMA KENJI C O ITAMI WORK, NISHIOKA TAKAO C O ITAMI WORKS, YAMAKAWA AKIRA C O ITAMI WORKS, MATSUNUMA, KENJI, C/O ITAMI WORKS OF SUMITOMO, NISHIOKA, TAKAO, C/O ITAMI WORKS OF SUMITOMO, YAMAKAWA, AKIRA, C/O ITAMI WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1992
Main classification: F01L1
IPC codes: F01L1, C04B35