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(11) | EP 1 528 123 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
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| (54) | CHEMICAL SURFACE TREATMENT METHOD OF PISTON RING |
(57) A chemical process for treating the surface of a piston ring to reduce its surface
friction includes immersing piston ring in machine oil, heating to 220-250 °C, adding
the following components to form a mixture:
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TECHNICAL FIELD
[0001] This invention is related to a chemical process for treating the surface of a piston ring. This treated piston ring can evidently reduce the friction between the piston ring and the cylinder wall and reduce the friction between the piston ring and the piston ring groove. It leads to evidently improve the tightness of cylinder and prolong the operational life of the piston ring, the cylinder liner and the piston.
BACKGROUND ART
[0002] The basic structure of an internal-combustion engine is a piston-connecting rod mechanism. The high- temperature and high-pressure gas generated by combustion of fuel in the cylinder drives the piston to move downwards. Then the piston transfers the power to a crankshaft by a connecting rod to make the crankshaft rotate to apply work.
[0003] Piston ring grooves are formed on the piston in order to prevent gas leakage. There is a piston ring in piston ring groove. The said piston ring is a circular alloy cast-iron ring with a clearance space. The piston ring is formed by means of the following process: for example, circular rings are cut out according to proper thickness from an alloy cast-iron pipe with specified outer diameter and inner diameter and then they are molded. A specified clearance space is cut out on somewhere of the circular ring in random. And then it gets the flexibility by heat-treatment. The clearance space at a cold state of piston ring is generally designed to 0.3-0.5 per cent of the diameter of cylinder, which makes the piston ring has a radial flexibility. When the piston implements reciprocating motion, the piston ring clings to cylinder all along so as to prevent the high-temperature and high-pressure gas get across between the piston ring and the cylinder wall, which results in a sealing action. There are two kinds of piston rings. One of the piston rings is gas ring having the function of air-sealing and oil-scraping and the another is oil ring having the main function of oil-sealing and oil-scraping.
[0004] The disadvantages of the piston ring in prior art design is as follows:
The piston ring will be elongated if it is heated, which will decrease the clearance space of the piston ring in the cylinder. The prior art design is to avoid the vanishing of the clearance space of the piston ring at a hot state, or else the mutual rubbing at the ports of the piston rings will make great pressure on cylinder, which will break the piston and the cylinder owing to gripping. The clearance space of the piston ring at a cold state is generally limited to 0.3-0.5 per cent of the diameter of the cylinder. The clearance space will act following effects: 1. A part of gas leaks downwards when the gas compressed by the piston (the compressing stroke of an internal-combustion engine) flows upwards so that the compressive force of the cylinder is reduced, which leads to the decrease of the internal-combustion engine performance; 2. When the high-temperature and high-pressure gas is generated by combustion of fuel in the cylinder, it drives the piston to move downwards (the applying work stroke of the internal-combustion engine). The gas leaks downwards so as to break the oil-film of the cylinder wall, which is easy to cause the cylinder scratch (roughing and wearing between the piston and the cylinder or between piston rings); 3. The gas leaking downwards enters the sump (deposited lubricant), which leads to the accelerated aging of the lubricant. Then the abrasion of motive parts is increased and the oil drain period is decreased; 4. The lubricant is forced by the flowing upwards of the piston to enter the channel on the top of the cylinder, which leads to the increase of the consumption of the lubricant and of the exhaust of the internal-combustion engine.
In order to improve the wear resistance and mesh resistance of the piston ring and the piston, the piston ring are treated commonly as follows:
phosphatizing and nitriding the surface on the piston ring; porous chrome-plating and spraying of molybdenum on the parts clinging to the cylinder. All of above treatments can not change the attrition essential caused by the half-dry glide of the piston ring and the cylinder at relatively high speed and can not make the piston ring move in the cylinder with non-slot or microgap. Thus the treatments at prior arts can not overcome radically the above shortcomings all along.
CONTENTS OF THE INVENTION
[0005] The objective of this invention is to provide a chemical process for treating the surface of a piston ring. It can overcome radically the above said shortcomings. Said process can evidently reduce the friction between the piston and the cylinder wall and reduce the friction between the piston ring groove and the piston ring. It allows the clearance space of the piston ring to vanish at a hot state. The process improves obviously the seal of the cylinder and prolongs obviously the operational life of the cylinder because of the decrease of friction.
[0006] The present inventors have considered that the movement of the piston ring in the cylinder with non-slot or in the piston ring groove with microgap is impossible. The main reason is that the conventional surface treatment techniques can not evidently reduce the friction between the piston ring and the cylinder wall and the friction between the piston ring and the piston ring groove. According to lubrication theory, the lubrication mechanism of the lubricant is to form a layer of oil-film on the surface of two parts against each other. It leads to the change of the friction between the two parts from direct friction to sliding friction with the two layers of oil films. There are various additives in the lubricant, especially sold in the market as commodity at present. The additive having the functions of lubrication is a kind of chain hydrocarbon with a polar group on one end of its chain. This polar group can adsorb on the surface of metals and make the another end with non-polar group erect upwards, thus a thicker layer of oil film can be form to ensure the function of lubrication on the surface of metal parts. Whereas, the adsorption of the polar group on smooth surface of metals isn't quite firm even though the lubricant component having the polar group. The adsorption between the metal surface and lubricant component may be broken when two metal parts rub each other. In order to overcome the shortcoming, the reticular pattern for storing oil is honed on the cylinder wall to supply continuously the lubricant to the cylinder wall in prior art. But the reticular pattern should not be ground too large and dense to prevent from forming the concavo-convex surface. Thus most of surfaces of the cylinder wall and whole surfaces of the piston appear smooth, which can not keep the integrated oil-films in a cylinder strokes.
[0007] The present inventors think that when plentiful homogeneously distributed invisible micro cavities are formed on the surfaces of the two mutual-friction metallic parts, the cavities can not only reserve lubricants, but also they allow polar groups on one end of lubricant additive molecules to get into them and adsorb firmly. Thus integrated oil-films are kept in all of cylinder strokes. Furthermore, because the micro cavities are very small, they can not affect slip property of the metal surfaces and thus can not affect the free slip of metal parts. The homogeneously distributed micro cavities may be formed on the surface of alloy cast-iron as long as a micro inhomogeneous weaker corrosive is found. Moreover, the present inventors think that small rigid oil-absorbing particles may roll freely, have a function of rolling friction if existing in the cavities. A layer of lubricant will be adsorbed surround the particles at the time, which can further reduce the friction between the two metal parts. All of above said aren't reported at prior arts. The present inventors have found the micro inhomogeneous weaker corrosive suitable for chemical micro etching of surface on the alloy cast-iron of the piston ring after our proceeded the plentiful tests. And the present inventors have also found that Ce-containing rare-earth oxide powder (Cerium existing in general mixed rare-earth and the content of Cerium being up to 50%), especially the oxide particles made from Ce-containing metal powder through explosive oxidation reaction, have a rigid and porous structure. The powders can not only adsorb plentiful oil but also be not cracked during the rolling process, which has a function of freely rolling friction. Thus the friction between the metal parts is substantially decreased.
[0008] To achieve above said object, there is a chemical process for treating the surface of piston ring to reduce its surface friction. The process includes immersing whole piston ring in machine oil, heating gradually to 220-250°C (preferably, 230-240°C) under the condition that the machine oil is not spilt, adding the following components to form a mixture:
| alkali-metal carbonate(preferably, sodium carbonate) | 0.15-0.50wt% |
| alkali-metal nitrite(preferably, sodium nitrite) | 0.15-0.50wt% |
| alkali-metal chloride(preferably, sodium chloride) | 0.10-0.30wt% |
| alkali-metal nitrate(preferably, potassium nitrate) | 0.50-1.2wt% |
| acidic manganese phosphate | 0.40-1.1 wt% |
[0009] Ce-containing rare-earth metal powder (preferably, Ce metal powder) 0.30-0.90wt%
| machine oil | rest, |
[0010] The % contents of above said components are based on the total weight of the whole solid additives and machine oil.
[0011] The present invention is described in detail as follows:
The kinds of machine oil used in said process are not especially limited as long as it is not obviously volatilizing under the temperature between 220°C and 250°C. And the heat-up rate is not also especially limited. It just isn't too rapid lest oil is spilt owing to the volatilization of water or impurity in machine oil. The quantity of machine oil should be supplied to the original level when the oil is decreased to ensure that machine oil can immerse all parts and maintain the above said ratio of machine oil to each component. Thus it can be seen that the heat-up time is prolonged along with the increase of quantity of machine oil, which is the reason why not limit the heat-up time.
alkali-metal carbonate(such as sodium carbonate) and alkali-metal nitrite (such as sodium nitrite and potassium nitrite) and alkali-metal chloride(such as sodium chloride and potassium chloride) and alkali-metal nitrate(such as potassium nitrate) are all weaker corrosive materials. Their molecules are strong polar and yet the molecules of machine oil are non-polar so that the above weaker corrosive materials can not dissolve in machine oil. But they can suspend in machine oil homogeneously at a finely divided state and thereby micro inhomogeneous weaker corrosive materials are formed. It is the reason why the present inventors select machine oil rather than water medium as carrier medium of micro etching. Owing to the synergistic effect of these corrosives, many homogeneously distributed micro cavities are formed on the surface of alloy cast-iron in the piston ring. If the ratio of these corrosives is too low in machine oil, the minimal requirements of the micro etching can not be met. But if the ratio of the corrosive to machine oil is too high, the micro cavities will be too large so as to affect the slip property of the surface of the piston ring.
[0012] Furthermore, acidic manganese phosphate is a kind of phosphating agent that acts a phosphorization on the alloy-cast iron surface of piston ring, which can be used to form a phosphide protective-film so as to improve the wear resistance of alloy-cast iron surface. And acidic manganese phosphate may be partially decompose to manganese dioxide in hot oil-bath on the other hand. Said manganese dioxide can adsorb firmly on the surface of alloy cast-iron and adsorb plenty of lubricants, which can form thicker lubricant oil-film on the surface of the piston ring. If the content of acidic manganese phosphate is less than 0.40wt%, the minimum effect of phosphorization can not obtained. And if the content of acidic manganese phosphate is more than 1.1wt%, the excessive manganese dioxide will affect the etching for forming the micro cavities. So the content of acidic manganese phosphate is limited to between 0.40wt% and 1.1wt%.
[0013] Moreover, rare-earth metals are active metals. They are prone to react with oxygen in air and then change to rare-earth oxide. Cerium dioxide is a kind of rigid particle so that it can be used as polishing compound. Cerium dioxide powder made by Cerium metal powder through explosive oxidation reaction has a porous and rigid structure. Due to this structure, this powder can adsorb plentiful lubricants and fall to the micro cavities on the surface of the piston ring and then roll freely. But Cerium dioxide powder made from Cerium metal powder through precipitation in water has not above said porous structure, which is main reason why the present inventors select Ce-containing rare-earth metal powder (preferably, Ce metal powder) rather than Cerium dioxide as reaction additive.
[0014] The present inventors have prepared the section of the piston ring surface-treated as described in this invention and observed the section by magnifying it 500 times under a microscope. It could be observed that there was an about 0.01mm thick layer of adhesive material on the surface of the piston ring. And it could be observed by magnifying the section 2000 times under an electronic microscope that the adhesive material was rolling in a spherical state. It can be decided that the rolling particles in a spherical state are Ce-containing rare-earth oxide (especially, Cerium dioxide) according to chemical component and chemical reactive property of above said additive. The free rolling of Ce-containing rare-earth oxide particles in the micro cavities on the surface of the piston ring makes the friction essential on the reciprocating of the piston ring in the cylinder change from the conventional sliding-friction model to rolling-friction model as described in the present invention. Thus the friction between the metal surfaces is largely decreased. As above described reasons, the friction between the piston ring and the piston ring groove is decreased in the same measure.
[0015] Of course, if similar etch for forming the micro cavity is used on piston, the friction between the piston, especially, the piston skirt and the cylinder can be decreased and the friction between the piston ring and the piston ring groove can be further decreased. The material of the piston is alloy aluminum rather than alloy cast-iron so that etch for forming the micro cavity on the piston is different from that on the piston ring according to the present invention, which is beyond the limits of this invention. The present inventors will apply for another application.
[0016] If the operating temperature is less than 220°C, the rate of the etch for forming the micro cavity may be too low that isn't advantageous for productivity. But if the operating temperature is more than 250°C, the rate may be too high, which can make the micro cavity too large and even affect the slip property of the metallic surface. And the operating temperature that is more than 250°C will lead to partial carbonization of machine oil so as to affect the uniformity of the etch for forming the micro cavity. Thus the operating temperature is limited to 220-250°C, preferably 230-240°C.
[0017] What's more, if the maintaining time of said operating temperature is less than 10 hours, the micro cavity can not be formed adequately. But if the maintaining time of said operating temperature is more than 24 hours, the micro cavity may be overly formed. Thus the maintaining time of said operating temperature is limited to 10-24 hours, preferably 13-16 hours.
[0018] Compared with the conventional surface treatment techniques, the present invention has the following advantageous effects:
I. The effect of present invention on the overall design of the cylinder
1. The clearance space of the piston ring is evidently reduced, which is about 0.10-025 per cent of the diameter of cylinder that is below a half of that in the conventional design. The clearance space is vanished when the piston ring is heated and then elongated owing to the running of the cylinder. The cylinder scratch can not appear even though the clearance space was vanished because friction model between the piston ring and the cylinder wall is changed from the conventional sliding-friction model to rolling-friction model as described in the present invention, which results in the improvement of tightness and work efficiency;
2. The cost of the cylinder reduces by using the cylinder without reticular pattern or the cylinder with shallower reticular pattern;
II. The advantageous effect of present invention on internal-combustion engine
1. The compressive force of cylinder is increased, the ignition lag of diesel engine is decreased and the dynamical and economical performance is improved;
2. The consumption of lubricant and the particulate exhaust of internal-combustion engine are reduced;
3. The operational life of the cylinder is prolonged by 1-2 times;
4. The cold-start ability is improved;
5. Idle speed performance is enhanced;
6. The running noise is decreased;
7. The oil-film on the surface of the cylinder is not broken and the cylinder scratch is evidently decreased;
8. Aging of the lubricant is delayed and the oil drain period is prolonged by one times;
III. The advantageous effect of present invention on the piston -air compressor
1. The suction vacuum degree and the suction flow are increased and the seal of the cylinder is improved;
2. The oil content in the compressed gas is decreased;
3. The operational life of the cylinder and the piston is prolonged by 1-2 times;
MODE OF CARRYING OUT THE INVENTION
[0019] This present invention is more specifically explained with reference to following embodiments and working examples. However, these examples are not to be construed to limit the scope of the present invention.
EXAMPLE 1: 30 piston rings of gasoline engine are put in a metal container.
All of said piston rings are immersed with 4830g 32# machine oil and are electric-heated gradually to 235°C under the condition that the machine oil is not spilt. Add the following components to form a mixture by using a scoop within several times for about 15 minutes:
| sodium carbonate | 15g | (0.30wt%) |
| sodium nitrite | 15g | (0.30wt%) |
| sodium chloride | 10g | (0.20wt%) |
| potassium nitrate | 40g | (0.80wt%) |
| acidic manganese phosphate | 35g | (0.70wt%) |
| Ce metal powder | 30g | (0.60wt%) |
| and machine oil | (97.1 wt%) |
The % contents of above said components are based on the total weight of the whole solid additives and machine oil.
Then the container is maintained about 235°C for 14 hours, then is cooled naturally to 40°C and the piston rings are taken out.
Example 2: The conditions of the process are similar to the Example 1, except that the Ce metal powder was replaced by the Ce-containing rare-earth metal powder, in which the content of Ce is about 50wt%.
Example 3: The conditions of the process are similar to the Example 1, except that the piston ring of gasoline engine was replaced by the piston ring of diesel engine.
Example 4: The conditions of the process are similar to the Example 1, except that the piston ring of gasoline engine was replaced by the piston ring of air compressor.
Example 5: The conditions of the process are similar to the Example 2, except that the piston ring of gasoline engine was replaced by the piston ring of diesel engine.
Example 6: The conditions of the process are similar to the Example 2, except that the piston ring of gasoline engine was replaced by the piston ring of air compressor.
WORKING EXAMPLE 1: The effect of piston ring of gasoline engine treated alone according to present invention
[0020] A piston ring of gasoline engine surface-treated as described above in Example 1 is used to improve the gasoline engine in a transit bus that belongs to CA6102 gasoline engine made from CHANGCHUN FIRST AUTOMOBILE ENGINE FACTORY of China. The original design of said engine is as follows:
The design of clearance space of the piston ring is as follows: the first air ring is between 0.5mm and 0.7mm; the second air ring is between 0.4mm and 0.6mm; the third air ring is between 0.4mm and 0.6mm and the fourth oil ring is between 0.3mm and 0.5mm. And the clearance is between 0.02mm and 0.06mm. The improved engine has the following design: the clearance space of the first ring is 0.12mm and that of the second and the third air rings are 0.10mm and that of the fourth ring is 0.06mm. The tests show that the suction vacuum degree is obviously increased and the dynamic and economic performances are obviously improved.
WORKING EXAMPLE 2: The effect of the piston ring of diesel engine treated alone according to present invention
[0021] A piston ring of diesel engine surface-treated as described above in Example 3 is used to improve the diesel engine in a transit bus that belongs to D6114 diesel engine made from Shanghai Diesel Engine Factory of China. The original design of said engine is as follows:
[0022] The design of clearance space of piston ring ring is as follows: the first air ring is between 0.4mm and 0.6mm; the second air ring is between 0.4mm and 0.6mm; the third oil ring is between 0.3mm and 0.5mm and the clearance is between 0.17mm and 0.23mm. The improved engine has the following design: the clearance space of the first air ring is 0.15mm and that of the second ring is 0.19mm and that of the third rings is 0.07mm. The transit bus maintains excellent dynamic performance after driving for 25 thousand kilometer. The consumption of fuel is decreased by 8.0% when compared with that before the engine is improved. And the consumption of lubricant is obviously decreased. The oil drain period is prolonged by one times. The free acceleration smoke is less than 2 and that is 5 according to national standard. The compressive force of the cylinder is increased by about 20%. Inspect result on the opened engine is excellent. The cylinder liner has nearly no wear. The wear quantity of the piston ring is very small and can be used again.
WORKING EXAMPLE 3: The effect of both piston and piston ring of gasoline engine treated synchronously
[0023] A piston ring of gasoline engine surface-treated as described above in Example 1 and a piston treated by similar etch for forming the micro cavity are used to improve the gasoline engine in transit bus that belongs to CA6102 gasoline engine made from CHANGCHUN FIRST AUTOMOBILE ENGINE FACTORY of China. The result is better than the result of working example 1. For example, The improved engine has the following design: the clearance space of the first ring is decreased to 0.10mm and that of the fourth ring is decreased to 0.05mm. Thus it can be seen that the two clearance spaces are much smaller than those of original one (corresponding to 10-20 per cent of that of original one) and smaller obviously than the least clearance between the piston ring in the present invention and conventional piston. The cylinder liner is embedded to the original cylinder and then ground, which makes the clearance is between -0.02mm(that is, the size of piston skirt is larger than the diameter of cylinder) and 0(non-slot). The result of the driving tests on the transit bus is better than that of working example 1.
WORKING EXAMPLE 4: The effect of both piston and piston ring of diesel treated synchronously
[0024] A piston ring of diesel engine surface-treated as described above in Example 1 and a piston treated by similar etch for forming the micro cavity are used to improve the diesel engine in a transit bus that belongs to D6114 diesel engine made from Shanghai Diesel Engine Factory of China. The result is better than the result of working example 2. For example, The improved engine has the following design: the clearance space of the second ring is decreased to 0.18mm and will be decreased to 0.07mm if the shallower reticular pattern cylinder liner having small diameter is used. Thus it can be seen that the two clearance spaces are smaller than those of original one and smaller obviously than the least clearance between the piston ring in the present invention and conventional piston. The result of the driving tests on the transit bus is better than that of working example 2.
WORKING EXAMPLE 5: The effect comparison of using Ce-containing rare-earth metal powder and using Ce metal powder
[0025] A piston ring of gasoline engine surface-treated as described above in Example 2 is used. The result of the test is the same as that of working example 1.
WORKING EXAMPLE 6: The effect comparison of using Ce-containing rare-earth metal powder and using Ce metal powder
[0026] A piston ring of diesel engine surface-treated as described above in Example 5 is used. The result of the test is the same as that of working example 2.
[0027] The result of the tests according to both working example 5and 6 show that there are comparable effects for forming the micro cavity using Ce-containing rare-earth metal powder or using Ce metal powder, but yet using Ce metal powder is better.
INDUSTRIAL APPLICATION
[0028] The above examples show that present invention can be used to improve various piston rings of the cylinder including engines such as gasoline engine and diesel engine as well air compressors etc. The process can obviously improve the work efficiency of piston ring and cylinder and prolong the operational life of the whole cylinder. It can not only save fuel but also reduce exhaust pollution from vehicles and air compressors, which results in good prospect in industry.
putting the piston ring in a container, adding machine oil to the container and immersing whole piston ring in the oil, heating gradually to 220-250°C under the condition that the machine oil is not spilt, adding the following components to form a mixture:
| alkali-metal carbonate | 0.15-0.50wt% |
| alkali-metal nitrite | 0.15-0.50wt% |
| alkali-metal chloride | 0.10-0.30wt% |
| alkali-metal nitrate | 0.50-1.2wt% |
| acidic manganese phosphate | 0.40-1.1wt% |
| Ce-containing rare-earth metal powder | 0.30-0.90wt% |
| machine oil | rest, |