Internal combustion engine liner

Abstract

An inside surface of an internal combustion engine liner is treated to have a surface roughness Ra smaller than 0.06 m, and then receives a DLC coating. A method of producing the internal combustion engine liner includes: forming the liner from a metal material, polishing an inside surface of the liner to obtain a polished inside surface of roughness Ra smaller than 0.06 m, and applying the DLC coating to the polished inside surface.

Claims

1. A liner for an internal combustion engine wherein an inside surface of said liner has no honing grooves, is treated by material removal ensuring a surface roughness Ra smaller than 0.06 m, and then receives a DLC coating, all performed outside of the internal combustion engine.

2. The internal combustion engine liner of claim 1, wherein thickness of the coating is smaller than 10 m.

3. The internal combustion engine liner of claim 1, wherein thickness of the coating is smaller than 7 m.

4. The internal combustion engines liner of claim 1, wherein thickness of the coating is smaller than or equal to 4 m.

5. A method of producing a liner for an internal combustion engine, with no honing operation, comprising: forming the liner from a metal material, polishing an inside surface of the liner by material removal to obtain a polished inside surface of roughness Ra smaller than 0.06 m, and applying a DLC coating to the polished inside surface, wherein the polishing by material removal and the applying of the DLC coating are performed with the liner outside of the internal combustion engine.

6. The method of producing the internal combustion engine liner of claim 5, wherein the DLC coating is applied to the polished inside surface by a vacuum deposition technique comprising an ion etching step and a step corresponding to actual deposition of the coating.

7. The method of producing the internal combustion engine liner of claim 5, wherein value of the roughness Ra of the polished inside surface, before applying said coating, is smaller than 0.04 m.

8. The internal combustion engine liner of claim 1, wherein value of the surface roughness Ra of the inside surface of the jacket, before receiving said coating, is smaller than 0.04 m.

9. The method of producing the internal combustion engine liner of claim 5, wherein the applied coating has a thickness smaller than 10 m.

10. The method of producing the internal combustion engine liner of claim 5, wherein the applied coating has a thickness smaller than 7 m.

11. The method of producing the internal combustion engine liner of claim 5, wherein the applied coating has a thickness smaller than or equal to 4 m.

12. A method of producing a liner for an internal combustion engine, with no honing operation, consisting of: forming the liner from a metal material, polishing an inside surface of the liner by material removal to obtain a polished inside surface of roughness Ra smaller than 0.06 m, and applying a DLC coating to the polished inside surface wherein the polishing by material removal and the applying of the DLC coating are performed with the liner outside of the internal combustion engine.

13. The method of producing the internal combustion engine liner of claim 12, wherein the DLC coating is applied to the polished inside surface by a vacuum deposition technique comprising an ion etching step and a step corresponding to actual deposition of the coating.

14. The method of producing the internal combustion engine liner of claim 13, wherein the vacuum deposition technique further comprises, after the etching step, forming a sub-layer which bonds to the material of the liner and to the material of the coating, followed by the actual deposition of the coating.

15. The method of producing the internal combustion engine liner of claim 14, wherein the sub-layer comprises a tungsten carbide deposition.

16. The method of producing the internal combustion engine liner of claim 15, wherein, during forming of the sub-layer, acetylene is introduced at an increasing flow rate so that structure of the sub-layer varies from tungsten carbide to an amorphous carbon matrix comprising tungsten.

17. The method of producing the internal combustion engine liner of claim 14, wherein the sub-layer comprises a chromium carbide deposition.

18. The method of producing the internal combustion engine liner of claim 17, wherein, during forming of the sub-layer, acetylene is introduced at an increasing flow rate so that structure of the sub-layer varies from chromium carbide to an amorphous carbon matrix comprising chromium.

Description

DETAILED DESCRIPTION

(1) The invention is discussed hereafter in further detail by means of the different examples and embodiments, considering the application of a DLC coating inside of a liner entirely polished according to the features of the invention and inside of a liner having undergone a honing operation, according to the state of the art.

(2) In a first embodiment, two steel engine liners, having a 72-mm diameter and a 150-mm length have been coated with DLC. The internal surface of one of the liners is has been, according to the invention, previously polished by a tribofinishing polishing type technique, so that the Ra is smaller than 0.02 m. The second engine liner has been submitted to a honing operation, such as performed according to the state of the art. The Ra of this second liner is 0.25 m, and it has a negative RSk. The negative RSk value indicates the presence of the honing grooves.

(3) After cleaning, the liners have been placed in a vacuum enclosure. During the pumping, the vacuum chamber and the liners are conventionally degassed by radiative heating at 200 C. When the vacuum has reached a pressure on the order of 1 10.sup.5 mbar, argon has been introduced into the vacuum chamber to obtain a 1-Pa pressure and the liners have been taken to a high negative value of 500 V to perform an ion etching, enabling to remove the natural oxide covering the steel to promote the bonding of the coating. After the etching, a deposition of tungsten carbide type has been performed inside of each of the liners by using a cylindrical magnetron cathode having a 30-mm diameter, placed inside of the liner. The target used for this deposition is made of tungsten carbide. The power density applied to the cathode is on the order of 5 W/cm.sup.2. During the tungsten carbide deposition, acetylene has been introduced at an increasing flow rate so that the structure of the deposit varies from tungsten carbide to an amorphous carbon matrix comprising tungsten. Finally, the DLC-type carbon layer is deposited by taking the part to a 450-V voltage in an acetylene atmosphere at a 0.9-Pa pressure.

(4) These operations result in a DLC-type deposition inside of each liner, which characterizes by a bonding by Rockwell indentation, noted HF1 to HF3. The thickness of the deposit, determined by calotest, indicates that the sub-layer has a 0.7-m thickness and the DLC has a 2.5-m thickness.

(5) In a second approved embodiment, two steel engine liners having a 72-mm diameter and a 150-mm length, have been coated with DLC. The internal surface of the first liner has been, according to the invention, previously polished by a buffing-type technique, where disks of fabric impregnated with abrasive paste are rotated inside of the liner, so that the Ra is smaller than 0.04 m. The second engine liner has been submitted to a honing operation, such as performed according to the state of the art, and its Ra is 0.25 m.

(6) After cleaning, the liner have been placed in a vacuum enclosure. During the pumping, the vacuum chamber and the liner are conventionally degassed by radiative heating at 200 C. When the vacuum has reached a pressure on the order of 110.sup.5 mbar, argon has been introduced into the vacuum chamber to obtain a 1-Pa pressure and the jackets have been taken to a high negative value of 500 V to perform an ion etching, enabling to remove the natural oxide covering the steel to promote the bonding of the coating. After the etching, a chromium carbide type deposition has been performed inside of each liner by using a cylindrical magnetron cathode having a 30-mm diameter, placed inside of the liner. In this example, the cylindrical magnetron cathode is covered with a chromium carbide target, to which a 5-W/cm.sup.2 power density is applied. During the chromium carbide deposition, acetylene has been introduced at an increasing flow rate so that the structure of the deposit varies from chromium carbide to an amorphous carbon matrix comprising chromium. Finally, the DLC-type carbon layer is deposited by taking the part to a 450-V voltage in an acetylene atmosphere at a 0.9-Pa pressure.

(7) These operations result in a DLC-type deposition inside of each liner, which characterizes by a bonding by Rockwell indentation, noted HF1 to HF3. The thickness of the deposit, determined by calotest, indicates that the sub-layer has a 0.8-m thickness and the DLC has a 2.7-m thickness.

(8) In a third approved embodiment, two stainless steel engine liners having a 86-mm diameter and a 150-mm length, have been coated with DLC. The internal surface of the first liner has been previously polished by an electrolytic polishing technique, so that the Ra is smaller than 0.03 m. The second engine liner has been submitted to a honing operation, such as performed according to the state of the art, providing a Ra of 0.25 m.

(9) The rest of the method is identical to the second embodiment.

(10) These operations result in a DLC-type deposition inside of each liner, which characterizes by a bonding by Rockwell indentation, noted HF1 to HF3. The thickness of the deposit, determined by calotest, indicates that the sub-layer has a 0.8-m thickness and the DLC has a 2.7-m thickness.

(11) In a fourth approved embodiment of the invention, two steel engine liners, having a 92-mm internal diameter and a 88-mm length, have been coated with DLC. The internal surface of the first liner has been submitted to a fabric polishing providing a roughness smaller than 0.03 p.m. The length of the liner compared to its inner diameter enables to use a more conventional deposition technique, that is, the plasma sources are placed outside of the liner. The second engine liner has been submitted to a honing operation, such as performed according to the state of the art, and its Ra is 0.25 m.

(12) After these liners have been cleaned, they are positioned on a mechanical assembly enabling the liners to rotate on themselves and inside the machine, according to a planetary motion, enabling the treatment to penetrate from the 2 ends of the liner. After degassing of the vacuum machine by heating at 200 C., the liners are etched in an argon atmosphere at a 0.3-Pa pressure. The etching is performed by taking the jackets to a 150-V voltage with respect to the machine walls. The argon plasma is formed from an ECR microwave system, at a 350-W power. The etching is followed by the deposition of a thin chromium layer having a thickness ranging from 0.1 to 0.2 m, formed from planar magnetron cathodes equipped with a chromium target to having a 5 W/cm.sup.2 power density applied thereto. A tungsten carbide layer is then formed by sputtering of a planar magnetron cathode to obtain a 1.5-m thickness. To achieve this, the second cathode is equipped with a tungsten carbide target having a 5 W/cm.sup.2 power density applied thereto. Then, acetylene is introduced an increasing flow rate to obtain a layer capable of bonding with DLC. Finally, the DLC is deposited in an acetylene atmosphere by polarizing the liner to 500 V under a 1-Pa pressure, to obtain a 2.2-m thickness.

(13) These operations result in a DLC-type deposition inside of the liner, which characterizes by a bonding by Rockwell indentation, noted HF1 to HF2. The thickness of the deposit, determined by calotest, indicates that the sub-layer has a 1.7-m thickness (0.2+1.5) and the DLC has a 2.2-m thickness.

(14) In a fifth embodiment, two steel engine liners, intended for automobile competition, having a 92-mm diameter and a 80-mm length, have been coated with DLC. The internal surface of one of the liners has been previously polished by a tribofinishing polishing type technique, so that the Ra is smaller than 0.06 m. The second engine liner has been submitted to a honing operation, such as performed according to the state of the art, and its Ra is 0.25 m.

(15) After cleaning, the liners have been placed in a vacuum enclosure. During the pumping, the vacuum chamber and the liners are conventionally degassed by radiative heating at 200 C. When the vacuum has reached a pressure on the order of 110.sup.5 mbar, argon has been introduced into the vacuum chamber to obtain a 0.3-Pa pressure, and the liners have been taken to a high negative value of 150 V in a plasma generated by microwave sources positioned on the machine walls to perform an ion etching, enabling to remove the natural oxide covering the steel to promote the bonding of the coating. All along the treatment, the liners displace in the machine according to a planetary motion in order to be exposed to the different plasma sources. After the etching, a deposition of tungsten carbide type has been performed inside of the liner by using a planar magnetron cathode on the walls of the deposition equipment. The planar target is formed of tungsten carbide and a 5-W/cm.sup.2 power density is applied thereto to perform the deposition. During the tungsten carbide deposition, acetylene has been introduced at an increasing flow rate so that the structure of the deposit varies from tungsten carbide to an amorphous carbon matrix comprising tungsten. Finally, the DLC-type carbon layer is deposited by taking the part to a 380-V voltage in an acetylene atmosphere at a 0.4-Pa pressure. The plasma is generated by the microwave sources positioned on the machine walls.

(16) These operations result in a DLC-type deposition inside of each liner, which characterizes by a bonding by Rockwell indentation, noted HF1 to HF2. The thickness of the deposit, determined by calotest, indicates that the sub-layer has a 1.7-m thickness and the DLC has a 2.5-m thickness.

(17) After the different treatments, a strip of a 10-mm width has been cut according to the length of the liner to tribologically characterize the coatings.

(18) For these tests, an A.C. linear tribometer has been used. A steel ball coated with a CrN deposit or with a DLC coating has been used to perform the friction test on the different liner portions. The balls have been conventionally coated with CrN by PVD (magnetron cathode sputtering) except that the thickness of the deposit was 15 m to be representative of a layer deposited on a ring. Similarly, the coating of the steel balls with DLC comprises a PVD sub-layer of pure Cr having a 1-m thickness, followed by a PVD layer containing tungsten carbide, which is progressively carbon enriched as it is drawn away from the steel surface, having a 3-m thickness. Finally, the DLC layer has been formed by PECVD, its thickness is 6 m, which provides a total coating thickness of 10 m. A planar polished reference element having an initial Ra of 0.02 m has been coated with DLC simultaneously to the balls. After the deposition, the roughness on this planar reference element has become 0.08 m. This roughness increase is induced by the coating thickness.

(19) A 5-N load is applied to the ball, which results in an initial average contact pressure of 540 MPa. The ball has an alternating sliding motion against the liner portions, at an average 35-mm/s speed. The speed varies according to a sinusoidal law obtained by a cam. The travel length is 10 mm. For these tests, a drop of engine oil, of type SAE 5W30, is introduced into the contact. The tests are carried out at a 110 C. temperature. After 15,000 cycles, the friction coefficient is raised, as well as the wearing on the ball and the wearing on the liner portion. The wearing on the ball is quantified by measurement of the diameter of the friction mark, while the wearing on the liner portion is quantified by profilometry across the friction mark. The selected parameters altogether enable to operate at a limiting load, corresponding to the load encountered close to the high neutral point and to the low neutral point. This load is responsible for a great part of the friction loss and of the wear of the parts in contact.

(20) TABLE-US-00001 Liner Deposition Test Ra example Ball Track N Liner (m) N Ball COF wear wear 1 honing 0.11 CrN 0.15 105 m N.M. 2 honing 0.11 DLC 0.10 100 m 3 m 3 Polished + 0.02 1 CrN 0.11 110 m N.M. DLC 4 Honing + 0.12 1 CrN 0.12 240 m N.M. DLC 5 Polished + 0.04 2 CrN 0.11 120 m N.M. DLC 6 Polished + 0.04 2 DLC 0.06 110 m N.M. DLC 7 Honing + 0.12 2 DLC 0.09 180 m N.M. DLC 8 Polished + 0.03 3 CrN 0.10 110 m N.M. DLC 9 Honing + 0.11 3 CrN 0.11 230 m N.M. DLC 10 Polished + 0.03 4 CrN 0.10 125 m N.M. DLC 11 Honing + 0.12 4 CrN 0.11 220 m N.M. DLC 12 Polished + 0.02 5 CrN 0.10 105 m N.M. DLC 13 Honing + 0.12 5 CrN 0.12 215 m N.M. DLC

(21) In test n 1, the behavior at the limiting load of the contact of a ring coated with chromium nitride in front of a liner formed according to a conventional method is reproduced. It can be observed that the friction coefficient is the highest of all tests. The CrN-coated ball does not wear, the friction diameter corresponds to the initial contact area. An examination of the ball also shows a coloring induced by the forming of an anti-wear film on the ball, induced by the oil additives.

(22) In test n 2, the behavior of a ring coated with DLC is reproduced. The DLC coating enables to decrease the friction coefficient. No wear can be measured on the ball. However, wear can be observed on the liner. This wear is probably induced by the hardness of the deposit on the ball, combined with its roughness.

(23) The test results can then be gathered in 4 large categories: DLC-coated polished liner / DLC-coated ball (test 6)
In this configuration, the friction coefficient is particularly low (0.06) and the wear of the coated ball is negligible. This example is consistent with the use in an engine. DLC-coated polished liner/CrN-coated ball (tests 3, 5, 8, 10, and 12)

(24) In this configuration, the friction coefficient approximately ranges between 0.10 and 0.11, and is thus lower than that obtain with no DLC coating. The wear of chromium nitrides is negligible. It can also be observed that the anti-wear oil additives have reacted on the chromium nitride and form an anti-wear film. This series of tests is consistent with the invention. DLC-coated liner with a honing-type surface state / DLC-coated ball (test 7)

(25) In this configuration, the surface state of the liner is kept as defined in liners used with no DLC coating. Although the antagonists are DLC as in test 6, the friction coefficient is notably higher (0.09). It can also be observed that the DLC deposit on the ball has significantly worn-off (180 m). This configuration is not consistent with the invention. The roughness of the liner associated with the presence of a DLC coating has resulted in a significant wear of the liner antagonist representing the ring. DLC-coated liner with a honing-type surface state/CrN-coated ball (tests 4, 9, 11, and 13)

(26) In this configuration, the surface state of the liner is kept as defined in liners used with no DLC coating. The friction coefficients approximately range between 0.11 and 0.12. This value is slightly greater than for tests 3, 5, 8, 10, and 12. However, a relatively high wear, ranging between 215 and 240 m, can be observed on the CrN-coated balls. This configuration is not consistent with the invention. The roughness of the liner associated with the presence of a DLC coating has resulted in an excessive wear of the liner antagonist.

(27) Finally, these tests clearly show that the sub-layers of the DLC or the method for forming the coating do not significantly influence the wear and friction result.

(28) The advantages can be easily gathered from the description, and it should in particular be underlined and reminded that the replacing of the honing operation inside of the liner with a polishing operation and a DLC coating enables to minimize the ring wear and to decrease friction losses, and thus to decrease CO.sub.2 emissions in the case of a combustion engine, especially in the automobile field.