The present invention relates to a coil retainer in use for an engine valve, and further a process of manufacturing the coil retainer. The coil retainer has a specific composition of aluminum based alloy, and can be manufactured only by the specific process comprising special treatments.
A conventionally used coil retainer in use for an internal engine valve is as shown in FIG. 1 (prior art).
Referring to FIG. 1, there is shown a partial view in partial section of an internal engine valve 1 of which the end is mounted through a pair of cotters 3, 3 on a coil retainer 2, on which a spring coil 4 is stemmed within a hollow of the valve 1 against a cylinder head (not shown).
The valve 1 is driven by movement of a cam 7 pressing the upper surface of a shim 6 embedded in a tappet 5 of the valve 1.
Such engine provided with a direct movement type valve has smaller numbers of members therefor, and therefore the allowable number of revolution of the engine can be improved so as to raise a power performance of the engine.
One of the obstacles for the allowable number of revolution of the engine to raise is a weight of a moving valve assembly. When the weight of the valve assembly increases, the inertial mass of the valve will be increased so as to lose a follow-up character to the movement of the cam, thereby affecting efficiency of suction and exhaust valve to lower the power of the engine.
Recently, there has been used an aluminum alloy in place of iron, for a retainer 2 to be mounted on a tappet 5 and a valve spring coil 4, thereby reducing the inertial mass of the valve assembly.
However, the retainer 2 must be exposed to repetition of high weight loading at the contact portion with the end of the coil 4, and therefore, the retainer made of the aluminum based alloy which has less abrasion resistance than that of iron will be more abraded at the contact portion 2 with the coil 4, to cause some trouble on durability of the engine.
There have been proposed the use of an aluminum alloy for a light- weighted retainer; and the use of a titanium alloy is described in Japanese (Unexamined) Patent Laid-open application No. 4-171206/1992, and the use of other light metal alloy for a retainer. However, there has been found several disadvantages such as lack of abrasion durability and lack of permanent set in fatigue.
In order to overcome such disadvantages, the prior art aluminum alloy retainer uses a metal lining embeded in the contact portion with the coil (e.g. Japanese (Unexamined) Patent Laid-open application No. 63-50613/1988, Japanese (Unexamined) Utility Model Laid-open application No. 63-34312/1988), and further, there is proposed use of a fiber reinforced aluminum alloy with a plated coating layer on the surface thereof (Japanese (Unexamined) Patent Laid-open application No.62-45915/1987) to improve the abrasion resistance of the contact portion with the coil, and further alumitization (making alumite surface layer) of surface layer, i.e. surface treatment of the aluminum alloy to improve abrasion resistance, and dispersion of hard material such as ceramic powder in the aluminum alloy to impart abrasion proof. Such improvement or rearrangement of the surface of the alloy will raise the cost of manufacture of the retainer.
It is an object of the present invention to provide a coil retainer for an engine valve with highly competitive performance at a substantial cost saving.
It is other object of the present invention to provide an aluminum based alloy with highly competitive performance without need of additional reinforcing fibers to be incorporated.
It is another object of the present invention to provide an aluminum based alloy with light weight as well as high abrasion durability.
It is other object of the present invention to provide an aluminum based alloy composition without need of additional plating step, which comprises only relatively uncostly ingredients.
The further object of the present invention will be understood from the below description.
A more detailed description of the invention is facilitated by reference to the drawings which form a part of this specification and wherein:
The prior art retainer needs a different metal member such as a surface hard layer, and an additional step of binding such metal member to the retainer, to increase a manufacturing cost. Further, the weight of the retainer will raise because of the different metal member.
In accordance with the present invention, a coil retainer for an engine valve to be mounted thereon can be manufactured from an aluminum based alloy composition consisting essentially of
Such aluminum based alloy has not been known. An aluminum base alloy of JIS standard No. 4032 comprises 11 to 13.5 weight percent of silicon, 0.50 to 1.5 weight percent of copper, 0.8 to 1.3 weight percent of magnesium, 0 weight percent of manganese. An aluminum alloy moulding and die casting respectively of JIS standard No. AC 8B and AC 8C comprise 8.5 to 10.5 weight percent of silicon, 1.0 weight percent of iron, 2.0 to 4.0 weight percent of copper, 0.50 weight percent of manganese, 0.50 to 1.5 weight percent of magnesium, 0.50 weight percent of zinc.
What is critically important is that the aluminum based alloy for the coil retainer formed for an engine valve spring coil thereon contain the following ingredients in the proportion below:
The blank of the retainer having the above aluminum based alloy composition is forged especially at a cold temperature.
Therefore, the retainer of the present invention has significant economy, because of saving cost of starting material (not use of costly metals), and of saving steps (without need of additional steps).
The reasons for the limitation of each ingredient in the aluminum based alloy composition in use for the preparation of the coil retainer are as follows:
Silicon is added so as to ensure hardness and abrasion resistance of the prepared retainer at the desired levels.
The content of silicon ranges from 8 % by weight to 17 % by weight. The hardness and the abrasion resistance cannot be afforded enough to be used as a coil retainer, when the content of silicone is less than 8 % by weight. Further, when the content of silicon exceed 17 % by weight, the workability ( work limit of the material) is dramatically reduced, and thereby, the strength and fatigue limit are significantly decreased.
The content of copper ranges from 2 to 5 % by weight. When the content of copper is up to 2 % by weight, the strength of the retainer cannot be afforded at the desired sufficient level. Further, when the content of copper exceeds 5 % by weight, the strength of the aluminum alloy will drop.
The content of magnesium ranges from 0.2 to 2.5 % by weight. When the content of magnesium is higher than 0.2 % by weight, the initiation of Si crystallization is restrained to improve the strength, but when the content of magnesium exceeds 2.5 % by weight, the workability of the aluminum alloy will be lowered.
The content of manganese is less than 1.5 % be weight. Within such range, manganese can be effective to maintain the strength high even at high temperature.
Preferably, the DAS (dendrite arm spacing) value of the aluminum alloy should be less than 15 micrometer. When the DAS value exceeds 15 micrometer, the forging workability will drastically drop until it is difficult to forge into a desired shape.
The aluminum based alloy is used to forge into the retainer blank, and then, the blank is exerted to the following specific thermal treatment to impart practical performance of a retainer for an engine valve.
The retainer blank as forged is heated at the temperature ranging 450 to 540 °C to melt partially, and then maintained at the temperature of 150 to 200 °C for one to six hours for aging.
Further, the blank is heated to melt partially, thereby homogenizing the structure of the aluminum alloy. This heating temperature should be 480 to 540 °C. When the temperature is up to 450°C, the heating to melt partially is not sufficient, and when the temperature is above 540°C, the blank is excessively heated. The partially melting means melting partially, especially at the margin or the boundary or the inner surface of the grains in the aluminium based alloy being used as a blank for the coil retainer.
The treated blank is further heated at a certain temperature for aging treatment. The optical condition for this aging is at the temperature of 150 to 200 °C, and for the period of 1 to 6 hours.
When the the aging temperature is up to 150 °C, the necessary period will be longer. When the aging temperature is above 200 °C, the aging will be excessive. Further, the aging temperature is more preferably 170 to 190 °C.
The aging period depending on the aging temperature is preferably 1 to 6 hours. When the aging period is up to 1 hour, the aging is not enough. When the aging period exceeds 6 hours, the aging will be excessive.
The retainer blank after forged and treated at high temperature and aged is finished into a desired shape. The retainer is worked by tumbling, and further treated to impart rust prevention.
When the DAS value of the aluminum alloy blank is above 15 micrometer, the forging limit workability will be significantly decreased to lower the forging workability of the blank. The DAS value of the aluminum alloy is preferably less than 15 micrometer.
When the content of silicon increases, the ratio of the area of eutectic phase to the whole area will increase, thereby decreasing a forging workability to reduce the workability limit.
The present invention is further illustrated by the following example to show the coil retainer of the present invention, but should not be interpreted for the limitation of the invention.
Retainer blanks formed from the following aluminum based alloy compositions, and measuring 30 mm in outer diameter were prepared by a cold forging method.
The prepared retainer blanks were heated at the temperature of 490 °C, and maintained at the temperature of 180 °C for two hours for aging treatment. The treated retainers were used in an internal engine for testing, and the results are shown in Table 1. The specimen nos. 1 to 3 shown in the table use the composition of the present invention, and the other specimen nos. 4 to 5 are not within the composition specified by the present invention.
The table 1 shows the following:
The increase of the silicon content will reduce the abrasion, while the other contents will effect somehow.
When the silicon content is higher than 8 % by weight, the abrasion will be reduced to one tenth. Further, the other specific data was measured if necessary for a coil retainer.
When the contents of silicone is changed, the workability limit (%) will change as shown in FIG. 2. The workability limit will keep constant when the silicon content changes from 8 weight % to 17 weight %, but the work rate limit will decrease drastically when the silicone content becomes more than 17 weight %.
A coil retainer can be manufactured in accordance with the present invention, as follows: An aluminum based alloy bar of the above mentioned composition is cut into a blank of a coil retainer and the blank is worked together with a lubricating agent coated at a cold temperature, and treated at high temperature as the above.
After the blank of the retainer is treated at high temperature to cause partial melting, the retainer is maintained at high temperature for aging. Then, it is finished by tumbling, and is treated to have rust preventive control.
Accordingly, the coil retainer of the present invention, having a specific composition of aluminum based alloy can reduce a cost of manufacture as well as light weight of the product.
Further, the inventive coil retainer does not need any additional metal layer, neither any plating layer, and improve abrasion durability.
It is clear from these test results that the coil retainer of the present invention is quite competitive in terms of wear and abrasion resistance, under the test conditions described, to the substantially more expensive structure of the prior art.