PISTON RING COATING REDUCES GASOLINE ENGINE …

1 DE VELO PMENT friction PISTON ring COATING REDUCES . GASOLINE ENGINE friction . Federal-Mogul has developed a COATING system for PISTON rings under the name of Carboglide which decreases wear in highly charged GASOLINE engines and further REDUCES friction losses which occur between the ring pack and the cylinder running surface. The tailored composition of the specific layer structure of the carbon-based Carboglide COATING in combination with corresponding modified PISTON ring designs yields a potential to improve fuel efficiency by up to %. 40. A U T H OR S REQUIREMENTS bochemical reactions. In most tribologi- cal systems these properties result in a Manufacturers of internal combustion lower coefficient of friction under engines continually face the challenge boundary lubricated conditions when to reduce fuel consumption and emis- the COATING is compared to other COATING sions by improving ENGINE efficiency. In systems (such as metallic layers, hard particular this necessitates a substantial coatings and others).

2 DR. MARCUS KENNEDY reduction of mechanical frictional Using carbon-based coatings for pis- is Manager Physical Coatings at losses. The components of the power ton rings necessitated a significant fur- Federal-Mogul in Burscheid cylinder and crankshaft drive are at the ther development of this COATING tech- (Germany). center of these development efforts. The nology to meet the tougher require- PISTON ring pack has a significant poten- ments of surface fatigue resistance and tial for bringing down friction losses COATING fatigue. Based on the develop- due to its fairly high (24 %) share of ment of the GOE245 metal-doped, mechanical frictional losses, 1. At the hydrogenated carbon COATING the first same time measures such as direct series application for highly loaded pas- injection and turbocharging among others, senger car GASOLINE engines succeeded DR. STEFFEN HOPPE. which increase ENGINE performance, in 2006. GOE245 significantly reduced is Director Technology Rings and Liners at Federal-Mogul intensify the requirements for the func- the previously observed cylinder sur- in Burscheid (Germany).

3 Tional behaviour of PISTON rings. face scoring which led to scuff-mark When considering measures to opti- formation under the harsh tribological mise the tribological system of PISTON conditions in these AlSi cylinder sur- ring and cylinder surface, PISTON ring face engines. As the damage mecha- coatings play an increasingly important nism is most frequently seen under cold role as they can directly influence the start conditions, this carbon-based wear and friction behaviour and the COATING is typically chosen and used as JOHANNES ESSER resulting scuff resistance. By introduc- a running-in COATING applied onto a is Director Engineering Rings ing Carboglide Federal-Mogul is provid- wear resistant COATING (nitrided layer, and Liners at Federal-Mogul in ing a COATING for PISTON ring applications PVD layer) [2]. Burscheid (Germany). which meets the most stringent require- During the subsequent development ments for functional behaviour and work the level of COATING wear was sub- offers a considerable potential to reduce stantially reduced by introducing the frictional losses.

4 GOE247 COATING . This PISTON ring COATING consists of several layers which com- prise an amorphous hydrogenated car- CARBON-BASED PISTON ring . bon top layer which is applied onto a COATINGS. metal-doped and hydrogenated interme- Carbon-based coatings (DLC, Diamond- diate carbon layer. The PISTON ring coat- like Carbon) have a long track record in ing is applied with a layer thickness of applications for cutting tools and com- 3 to 5 microns and shows a wear resist- ponents that are tailored for the most ance in the ENGINE which is higher by a severe tribological requirements [1]. factor of 4 to 5 when compared to the Diamond-like carbon coatings have only performance of a metal-containing DLC. a low tendency for adhesive wear or tri- PISTON ring COATING . 1 Energy distribution diagram showing friction losses in GASOLINE engines with the proportionate share of the PISTON rings 0 5 I 2 012 Volume 73 41. DE VELO PMENT friction Schematic Scanning electron micrograph of the COATING representation of on a top ring on nitrided chromium steel the Carboglide layer structure on a PISTON ring COATING STRUCTURE AND carbide is embedded in the form of in demonstrate that the scuff resistance PROPERTIES nanocrystals found in a column-shaped is nearly twice that of a PVD coated pis- growth pattern.

5 The top layer is an ton ring running surface. The combination of direct injection and amorphous diamond-like carbon layer turbocharging with very smooth cylinder which is characterised by a specific ratio FUNCTIONAL BEHAVIOUR DURING. running surfaces, in GASOLINE engines, sig- of sp2 and sp3 bonded carbon. By adjust- ENGINE OPERATION. nificantly increases the demand for PISTON ing the layer thickness ratio of the top rings with excellent scuff resistance and layer to the intermediate layer to a value The beneficial functional behaviour of low cylinder running surface wear. between to while adjusting the the new COATING was extensively tested The necessity to reduce fuel consump- relation between top layer and total coat- under real ENGINE conditions. The first tion and thus CO2 emissions requires an ing thickness to between and the series applications in highly charged increasing contribution of the reduction level of residual COATING stress is modi- GASOLINE engines demonstrated the dura- of frictional losses.

6 Fied so that the total COATING thickness is bility under field conditions . The In order to meet these tough require- roughly 10 microns, . Furthermore the development of a new generation of ments which translate into very low high level of COATING hardness, measur- PISTON ring COATING that serves to signi- friction in combination with high wear ing between 1800 and 3100 , in ficantly reduced frictional losses has resistance and superior scuff resistance, combination with a COATING thickness, been successfully confirmed by COATING a new PISTON ring COATING had to be which is greater by a factor of 2 to 3 in applications in highly loaded GASOLINE developed. This was based on Federal- comparison to conventional DLC coat- engines. Frictional loss tests carried out Mogul's application experience with car- ings, leads to a significantly improved in a fired single cylinder ENGINE with bon-based PISTON ring coatings. The new wear resistance of the COATING .

7 Floating liner showed up to 20 % reduc- COATING , which is known under the Carbo- Owed to its layered structure, Carbo- tion in ring frictional losses using Carbo- glide name, employs a three-layered glide shows excellent friction properties. glide in the first and third grooves, . structure. The COATING architecture is A comparison with the coefficient of fric- The excellent thermal and chemical characterised by a very thin chromium tion of existing PISTON ring coatings for durability was confirmed via endurance adhesion layer in the transition zone to GASOLINE engines (nitrided, PVD coatings) testing in a highly charged GASOLINE the original PISTON ring surface. This is clearly shows the potential frictional ENGINE with cast iron cylinder running followed by an intermediate layer and a benefit [3], . In addition to that the tri- surfaces and inadequate lubrication lev- top layer, . The intermediate layer's bological behaviour was evaluated under els.

8 As can be seen, the nitrided steel structure consists of tungsten- and hydro- boundary lubrication conditions, using a top ring (first groove) shows strong genated carbon in which the tungsten so-called overload test. The results shown traces of seizure as well as material Coefficients of friction of typical GASOLINE PISTON ring coatings as measured with an oscillating, vibrating frictional wear tribometer (cast iron cylinder, stroke 30 mm, frequency 10 Hz, normal force 450 N, ester oil lubrication, temperature 190 C). 42. build-up in combination with cylinder scoring, while the Carboglide PISTON ring running surface shows a clear uniform wear pattern without any cylinder wall damage occurring. The positive effect becomes particularly evident in evaluat- ing cylinder wear. In cast iron cylinders Carboglide significantly REDUCES cylinder wear in the top dead center area. Non- ENGINE rig tests confirm a cylinder wear that is lower by a factor of up to 3 com- pared to PVD coated PISTON rings.

9 Relative scuff resistance of nitrided, PVD and Carboglide coated PISTON rings, (cast iron cylinder, stroke 4 mm, frequency 40 Hz, normal force continuously increasing to 700 N, lubrication Castrol Edge 5W30, temperature 120 C). SUMMARY AND OUTLOOK. The new COATING COATING combines extremely low friction values with high strength and durability of PISTON rings and cylinder running surfaces. By using this COATING , the ring pack's frictional losses can be reduced by up to 20 %. It significantly protects the cylinder run- ning surface against scoring, increased wear and scuffing during inadequate lubrication. Carboglide makes a substan- tial contribution to the development of high performance GASOLINE engines with even better fuel economy by up to % with consequently lowering CO2 Relative frictional losses of a PISTON ring package with Carboglide coated top and oil emissions. control ring in fired single-cylinder ENGINE in comparison to a conventional nitrided ring pack Future development work will focus on the combination with the design advan- tages of LKZ oil control rings addressing both frictional losses and low oil con- engines for delivery vans already resulted REFERENCES.

10 Sumption [5]. Due to the low friction and in a significant reduction of fuel consump- [1] VDi-richtlinie 2840 Kohlenstoffschichten, Grundlagen, Schichttypen, Eigenschaften the high wear resistance of Carboglide tion of around 1 % during the New Euro- [2] Hoppe, S.; M nchow, F.; Esser, J.: DLC . the combination with LKZ further pean Drive Cycle. This potential with oil Hochleistungsbeschichtung f r Kolbenringe, Poten- REDUCES the frictional losses of the ring control rings in diesel engines will be zial und Einsatzerfahrungen. VDi-Fachtagung pack. Initial customer tests in diesel examined during further research. Zylinderlaufbahnen, Kolben, Pleuel, Baden-Baden, June 2008. [3] Esser, J.; Hoppe, S.; Mittler, r.: Kolbenring- auslegung f r ottomotoren im Spannungsfeld von reibungsreduzierung und Funktionsverhalten. VDi- Fachtagung Zylinderlaufbahnen, Kolben, Pleuel, Baden-Baden, June 2010. [4] Esser, J.; M nchow, F.: labstreifringe mit konischem Steg.