Well supported with MAHLE bearings

Bearings support rotating shafts such as crankshafts, camshafts, rocker arm shafts or balancer shafts in the engine block or in the connecting rods. The mechanical stress in internal combustion engines is extremely high. Our bearings have to meet a number of quality characteristics. They have to be fatigue-resistant, adaptable, tolerate high loads and be resistant to wear and corrosion.

In cooperation with engine manufacturers, we develop and test the bearings for every single engine type. Ongoing basic research and further development of materials and production technologies ensure economically and technically optimized products of highest quality. Our product range comprises bearings and thrust washers in diameters ranging from 27 to 140 mm as well as bushings with diameters from 6 to 105 mm.

Material development is extremely important so that our bearings can meet the high demands. Thanks to years of experience and developments, MAHLE has a large number of bearing alloys available, such as aluminum and bronze alloys. Depending on the application, our bearings consist of a high-strength steel backing that is coated with different bearing materials. With regard to their applications, the bearing materials are chosen so that their properties complement one another.

During the production process, we use different coating methods that depend on the relative bearing load.

Solid bearings
Solid bearings are made completely from special bearing metals that consist of specialized alloys.

Two-material bearings
Two-material bearings are used for low to medium loads in gasoline and naturally aspirated diesel engines. They consist of a steel backing, an intermediate layer and a layer of bearing metal. Aluminum alloys are the primary material used as bearing metal.

Three-material bearings
Three-material bearings are mainly used in engines that are subject to higher loads. They consist of a steel backing, a bearing layer, a barrier layer and the sliding layer. Sputter bearings are special three-material bearings with significantly increased hardness and wear resistance due to a special production method (sputtering). Therefore, sputter bearings are suited for supercharged engines with charge cooling and are also increasingly used in diesel passenger car engines.

Sputtering
Sputtering is a coating method based on the principle of cathode sputtering, in which atoms are ejected from a metal cathode due to the impacting ions from a gas discharge process. The resulting atomized metal condenses on the bearing surface of the bearing as a uniform layer.

A sputter bearing from MAHLE can be recognised by the label 'SPUTTER' stamped at the back (see picture)—and the "m" that is well-known in workshops.

Sputter bearings are indispensable for high performance diesel and petrol engines. But what is sputtering actually? How is it done? And why? MAHLE aftermarket news is answering here the most important questions on this topic.

Sputtering—what is it?
In a vacuum container with just some traces of noble gas, a positively charged anode and a negatively charged cathode that is covered with a metal layer are located, together with the threematerial bearing that is to be sputtered. A voltage is applied between cathode and anode. Electrons are accelerated towards the anode and ionize the noble gas atoms. The noble gas atoms that are now positively charged are then accelerated towards the cathode and knock out atoms from the metal layer covering the cathode. This will also release secondary electrons that will in turn ionize more noble gas atoms. This results in a mixture of free electrons, positive ions and neutral particles of the noble gas—a so-called steady state plasma. The neutral atoms that were knocked out of the metal layer of the cathode, condense then as thin, extremely resistant metal coating on the bearing surface.

1. Supply of argon (plasma gas)
2. Ion flow
3. Atomic material flow (dispersion)

What is the purpose of friction bearings?
Rotating shafts such as crankshafts, camshafts, rocker arm shafts and balancer shafts operate in engine blocks and connecting rods. Bearings provide support to these parts. The mechanical load on the bearings is respectively high—at ignition pressures up to 200 bar for instance. But this is not all. Internal combustion engines are refined continuously, specific engine performance is increased and size is reduced—and thereby also the size of the bearing surfaces. At the same time, the oil change intervals are extended successively. All this increases the mechanical loads on the bearings.

What are the particular loads on bearings?
The specific surface loads, especially for connecting rod bearings and main bearings, have significantly increased in recent years. For engines with diesel direct injection, surface pressures up to 120 N/mm2 have to be managed in the bearings. Conventional two- or three-material bearings with galvanically applied bearing layers reach their limits here. For modern engines, bearing materials with significantly increased fatigue strength and reduced wear rate are therefore required, especially in the mixed friction range. At the same time, good corrosion resistance has to be assured, also at higher temperatures.

Solid bearings
Solid bearings are made completely from bearing metal that consists of special alloys.

Two-material bearing
Two-material bearings are used for low to medium loads in petrol and naturally aspirated diesel engines in passenger vehicles. They consist of a steel backing, an intermediate layer and a layer of bearing metal. Mainly aluminum alloys are used as bearing metal.

Three-material bearings
Three-material composite bearings are mainly used in engines under heavier loads. They consist of a steel backing, a bearing layer, a barrier layer and the sliding layer. Sputter bearings are special three-material bearings with significantly increased hardness and wear-resistance due to a special production method (sputtering).

Why is a sputter bearing the right solution?

A sputter bearing is composed of a three-material composite bearing which has a bearing layer that is not applied galvanically but by means of cathode sputtering. This coating method works only in a high vacuum. Smallest particles are knocked from the sputter cathode and propelled onto the bearing surface by means of high voltage. The coating is fine-grained, finely dispersed and adheres extremely well to the substrate material. Due to the small grain size, the produced layers are extremely hard with high yield strength and outstanding wear properties.

Where are sputter bearings used?
For highly loaded bearings, the bearing couples consist always of a sputter bearing and a conventional three-material bearing. The sputter bearing is used at the higher load end and the softer three-material bearing is used opposite. For connecting rod bearings, the sputter bearing is therefore fitted in direction rod and the three-material bearing in direction bearing cap. For main bearings this is exactly the other way round. The sputter bearing is here used in the bearing cap and the three-material bearing in direction engine block.

How can you recognize a sputter bearing?
Considering how complex and complicated the coating process is and how impressive the performance, it is difficult to see the difference in the sputtered bearings. They look completely ordinary. To make it possible to recognize the sputtered half-bearings, the sputter bearings are marked with the identification 'SPUTTER'. This ensures correct fitting, especially as the correct assembly position of the sputtered bearing shells is crucial for reliable working and the service life of the bearings.

Why are sputter bearings and three-material bearings always combined in pairs?

One of the reasons is the high production cost for the sputter coating. At the location with low load, they are not necessary and are therefore not fitted. The second reason is the extreme hardness of the sputter layer, which does not tolerate engine oil contaminations. However, the softer three-material bearing can embed dirt particles in its galvanized bearing layer and renders them therefore harmless.

Why sputter bearings from the expert?
As the world's largest piston manufacturer and development partner of the automotive and engine industry, MAHLE is highly competent in research, testing and production of engine components.

Sputter bearings are also used in the following engines:

Audi/VW series TDI: 1.9 / 2.0 / 2.5 / 4.0 / 5.0 l
Audi petrol engines: 6.0 l (W12) / 1.8 l (225 hp)
MAN: D2865
Mercedes-Benz commercial vehicles: BR 400, BR 500, BR 900
Mercedes-Benz passenger vehicles: CDI-engines BR 600
PSA series HDI: 1.4 / 1.6 / 2.0 / 2.2 / 2.7 l

THE PERFORMANCE OF BEARINGS—IS A QUESTION OF MATERIALS, ALLOYS AND SLIDE LAYERS

In addition to their actual function of supporting moving parts, bearings in engines have another important task: the accommodation and embedding of abrasion particles. These abrasive particles are generated during normal engine operation and are so small that they cannot be separated by the oil filter, and—if not embedded—can lead to increased wear. These key functions of bearings in achieving concentric running and low-wear operation of the engine require special design considerations.

Bearings in engines are subject to several different friction states. For this reason, they are designed to withstand the wear intensive mixed friction that exists during cold start as well as the high pressures of the combustion. Due to these different demands, bearings are generally made from several materials:On the one hand a material has to be chosen that is highly wear resistant, on the other hand it must still provide sufficient embeddability.

IT IS THE MATERIAL THAT MATTERS
MAHLE bearings consist of a high-strength steel backing that is coated with different bearing metals depending on the particular application. The bearing materials are selected so that the different positive properties of the materials complement each other and the combination is optimal for the particular application. Material development takes therefore a key role in meeting today's and future demands on bearings. Thanks to years of development activities and experience, MAHLE disposes over a large number of high-quality bearing alloys such as aluminium and bronze alloys.

MULTI-LAYER DESIGN
Strength, good close fit, good running quality—these are demands that are contradictory in terms of material technology. The solution: multi-layer bearings, designed according to the principle of work-sharing. This is because the basic performance of bearings, above all their dynamic load capacity, is not only influenced by the material, but also by the structure and thickness of the layers as well as design measures such as the bearing surface configuration. The base of a MAHLE bearing is a high-strength steel backing that is coated with different bearing metals depending on the particular application. Here is an overview of bearing designs.

Solid bearings are made completely from one kind of metal, mostly a hard bronze alloy. These bearings are often used in large engines, however, they are also used in passenger cars as piston pin bushings, thrust washers or camshaft bearings.

Two-material bearings consist of a steel backing, an intermediate layer and a layer of bearing metal. Aluminium alloys are used mainly for the bearing metal. Two-material bearings are used in petrol and naturally aspirated diesel engines under low to medium loads in passenger cars—depending on the alloy, as piston pin bushings, valve rocker bushings, thrust washers, camshaft bearings, main bearings or connecting rod bearings.

Three-material bearings consist of a steel backing, a bearing layer, a barrier layer and the slide layer. The bearing layer is mainly made from a type of lead bronze and is generally applied through an electro-plating process. Three-material bearings are predominantly used in engines subject to higher loads—as large piston pin bushings, connecting-rod bearings, main bearings and crankshaft bearings.



Sputter bearings belong to the bearing types of the highest quality. In terms of their structure, they are also three-material bearings and are made from the same materials. However, an extremely resistant aluminium layer is deposited onto the bearing material—by means of a special production method, the sputter process (see box “Sputter process”). Due to this coating, these bearings feature significantly greater hardness and wear resistance. The bearings are especially suitable for high-performance engines such as turbocharged engines in passenger cars and commercial vehicles and are then used especially in the connecting rod and crankshaft area.

In the sputter process, the bearings that consist of the steel backing, the bearing layer and the barrier layer, are placed in the sputter machine under a vacuum. The material of the slide layer is deposited on the bearing shells by means of cathode sputtering. This produces the extremely hard and wear resistant slide layer of the half-bearings.

SPUTTER BEARINGS: PERFECT WORK-SHARING
The sputtered slide layer is extremely hard and wear resistant, however, embeddability for the above mentioned abrasion particles is therefore low. In order to provide embeddability, only one half-bearing of a sputter bearing is sputtered. The other half of the bearing is a three-material bearing with conventional coating that can accommodate the abrasive particles perfectly.

IMPORTANT: TO KNOW WHICH IS UP OR DOWN
The sputtered half-bearing is always fitted to the side subject to the higher load. For example, the sputtered half-bearing has to be fitted to the upper half circle of the big end of connecting rods, as this is where the combustion pressure has its effect (see picture 1 below). At the crankshaft, however, the combustion pressure affects the half-bearing that is directed downwards. The sputtered half-bearing can be recognised by the labelling “Sputter” on the outside of the bearing. For safety reasons, the sputtered bearings are often packaged and sealed separately.

CAUTION, OIL HOLE!
An additional error source during fitting of bearings is the fitting position. For most half-bearing pairs, only one half-bearing has a hole. If the bearing site is lubricated via a lubrication hole (as for instance with crankshafts), it has to be assured that the hole in the half-bearing is positioned exactly over the hole of the corresponding seat. If the half-bearings are fitted the wrong way round, the bearing site is not at all or only insufficiently supplied with lubrication oil. The result: severe seizing, which can cause the bearing to weld to the journal due to the enormous heat that is generated. (Picture 2 below shows such welding of the bearing to the crankshaft.)

Picture 1

In the connecting rod, the sputtered half-bearing is fitted to the upper half circle, where the combustion pressure results in the higher load.

Picture 2

The result of a fitting error: As the half-bearings have been fitted the wrong way round, the lubrication bore was blocked—and this led to seizing with extreme heat generation, causing the bearing to weld to the crankshaft.