TECHNICAL FIELD The present invention relates to a lubricating system for a combustion engine, which system comprises an ion exchanger, a combustion engine comprising a lubricating system, a vehicle comprising the combustion engine, and a method for removal of hydrogen ions from motor oil intended for the lubricating system.

BACKGROUND Today, the standards are high with respect to combustion engine emitting as small amounts as possible of environmentally hazardous emissions, while it is desirable to increase the intervals between vehicle service occasions. It is also desirable to carry out vehicle service on as many components as possible during one and the same service occasion. In order for an engine to meet this requirement, the requirements relating to the oil used to lubricate and cool the engine are stringent. A well-functioning combustion engine consumes less fuel and emits a smaller amount of substances that damage the environment. In order for a combustion engine to emit a smaller amount of pollutants, e.g. the pressure and the temperature at which the combustion occurs may be increased. In this case, the components in the engine and the motor oil are subject to even more stringent requirements. Engines in heavy goods vehicle are subjected to substantial stress, since they must provide a very great power for the vehicle and its cargo to be transported in a desirable manner.

Motor oil is used as lubricant in combustion engines. By way of contact with acid combustion gases the motor oil which is acidified and degraded by this, and it may become corrosive, which impacts both the motor oil's tribological (lubricating) characteristics and the lubricating system's surface negatively.

In order to improve the characteristics of the motor oil, different additives are added to the motor oil. Among others, acidity regulating (buffering) additives are added, but viscosity regulating, antioxidant, and anti-wear additives are also added to handle high pressures and temperatures. These additives are consumed over time, and when the amount of additive in the motor oil has dropped to a certain level, the motor oil must be replaced. The consequence of additives being consumed is among others that the motor oil's tribological characteristics deteriorate and, in the worst case, the motor oil causing a corrosive wear of the components with which it comes into contact. Additives are important for the motor oil to function in a desirable manner, but they also lead to increased levels of ash in the exhaust stream.

Excessively high levels of ash in the exhausts result in a higher load on the exhaust purifying components, e.g. the particulate filter. It is therefore of interest to keep the amount of additives in the oil as low as possible. Today, there is a technology, COT (Clean Oil Technology), which continuously purifies the oil during operation. The system is fitted as a bypass-channel, and the oil passes through a fine mesh particulate filter where very small solid pollutants are removed, and also through a vaporisation device, which separates liquid pollutants having a lower vapour pressure than that of the motor oil. This technology does not, however, impact the increased acidity of the motor oil.

WO2013028122 describes a device to reduce acidity in a motor oil. The device comprises a container that comprises a cation exchanger in the form of small particles. The cation exchanger in the document consists of particles of solid material, e.g. with a carbon/silicon- based basic structure, that may catch positive ions. The cation exchanger is monovalent and may thus bind free hydrogen ions from the motor oil. A certain amount of motor oil may flow through the container and the container is placed in the normal flow of the motor oil, but construction changes in the oil system may be needed to make space for the container. The container has the additional disadvantage, apart from being bulky, that it may increase the back pressure in the oil system. Furthermore, the container of this prior art type must be equipped with, for example, a fine mesh net to avoid contamination with ion exchanger particles of the oil in the system. Accordingly, the ion exchanger's efficiency may become lower than the theoretical efficiency. Accordingly, there is a need to efficiently reduce the acidity of a motor oil (oil). At the same time, there is a need to reduce the acidity of the motor oil with a system that requires as few construction changes as possible. Furthermore, there is a need to avoid power losses, which may be caused by the back pressure in the normal flow of the oil, since this may lead to increased fuel consumption.

One objective of the invention is thus to rectify the problems existing in prior art technology. Specifically, the objective of the invention is to provide an ion exchanger in a lubricating system, without any substantial construction changes, while achieving an efficient ion exchange in the lubricating system without negatively impacting the engine's efficiency. An additional objective is to achieve a lubricating system with an ion exchanger that may be regenerated in a simple way.

These objectives are achieved with a lubricating system that is defined in claim 1, and a method for removal of hydrogen ions from the motor oil intended for the lubricating system that is defined in claim 13.

According to the invention, the objectives mentioned above are achieved with a lubricating system for a combustion engine, which lubricating system comprises several components comprising an oil sump, an oil pump arranged to feed the motor oil from the oil sump further along into the lubricating system, a cooling device for cooling of the motor oil, an oil filter device for filtering the motor oil, and a main oil conduit intended to transport the motor oil in the lubricating system to the system's and the combustion engine's moveable parts. Each one of the components comprises a contact surface, intended to be in contact with the motor oil. According to the invention, at least one of the components comprises a surface modified contact surface comprising an ion exchanger which is immobilised on the contact surface. The term ion exchanger, as used in this application, means materials which are molecules, and which may have one or several charges in their structure, positive or negative. The ion exchanger has at least one position with an ionic bond in its molecule structure. The ion exchanger may, for example, be an organic salt, a base, a biomolecule, but is not limited to these molecules. The ion exchanger in the lubricating system is preferably a cation exchanger with at least one functional group that may catch positive hydrogen ions in the motor oil, and that emits positive ions of another type to the motor oil. Preferably the cation exchanger is monovalent. Thus, a maximum exchange of hydrogen ions may occur in the oil, so that the acidity of the oil may be reduced. The cation exchanger is preferably a weak cation exchanger, so that a more efficient exchange of hydrogen ions may be achieved in the oil, while other additives in the motor oil are minimally impacted.

The contact surface of the components may consist of metal, so that a component that is simple to surface modify, and that tolerates high temperatures and pressure, may be obtained.

The contact surface may also consist of a polymer material, such as plastic. Plastic is flexible, and may be easily adapted to confined spaces and formed to the desired shape. Plastics are also easily surface modified.

According to one embodiment, the cooling device may comprise the surface modified contact surface. The cooling device comprises a number of channels and the oil may circulate around the channels, so that a large contact surface for the oil may be obtained in a small volume. Thus, an efficient ion exchange may be obtained.

According to another embodiment, the oil sump may comprise the surface modified contact surface. The surface modified contact surface may be provided in a simple manner on the oil sump's contact surface. Additionally, all oil in the system will come into contact with the oil sump, and therefore all the oil may come into contact with the ion exchanger, and accordingly a maximum amount of cation exchange may occur.

According to an additional embodiment, in which the main oil conduit is connected via channels to bearings in a crank shaft, the bearings are arranged in such a way that they comprise the surface modified contact surface. The bearings may be made of different materials, and therefore the surface modified contact surface may be obtained in a flexible manner.

Preferably the lubricating system also comprises a regeneration arrangement, connected to the component that comprises the surface modified contact surface. The regeneration arrangement may comprise a by-pass valve to lead the oil past the component, or alternatively a valve arrangement both downstream and upstream of the component, in order to prevent the oil's flow through the component. A pump device may be connected to the component via a coupling device to feed saline solution through the component, which saline solution regenerates the ion exchanger. The pump device may be external, and may be arranged so that it is connected to the system only when needed. Since the ion exchanger is on the contact surface, no dismantling of the component is required and accordingly the ion exchanger may be regenerated easily, for example, when the vehicle is serviced, such as when the oil is replaced. In one embodiment the modified contact surface is comprised in the cooling device, and the regeneration arrangement is connected to the cooling device. In this manner, the regeneration arrangement may be connected to the system in a simple manner.

The invention also relates to a combustion engine comprising the lubricating system as described above. The invention also relates to a vehicle comprising the combustion engine.

The invention also relates to a method for removal of hydrogen ions from an oil intended for a lubricating system. The method comprises the steps i. to provide a motor oil intended for the lubricating system;

ii. to provide a lubricating system that comprises several components, comprising an oil sump, an oil pump arranged to feed the motor oil from the oil sump further along into the lubricating system, a cooling device for cooling of the motor oil, an oil filter device for filtering the motor oil, and a main oil conduit intended to transport the motor oil in the lubricating system to the system's and the combustion engine's moveable parts, wherein each one of the components comprises a contact surface intended to be in contact with the motor oil;

iii. to provide a surface modified contact surface in at least one of the components, comprising a monovalent cation exchanger which is immobilised on the contact surface;

iv. to lead the motor oil through at least one of the components comprising the surface modified contact surface, so that positive hydrogen ions in the motor oil are replaced with positive ions of another type, and the acidity of the motor oil thus is reduced.

With the present invention it is possible to achieve an efficient ion exchange in a motor oil of a combustion engine, e.g. in a vehicle such as a truck or a bus. The surface modified contact surface allows for an efficient integration with the oil in the system, and accordingly an efficient ion exchange is obtained, while the need for construction changes in the lubricating system may be substantially reduced or even eliminated. With the help of the present invention, the impact on the oil flow is minimal, and accordingly power losses may be minimised and the risk of an increased fuel consumption reduced. The ion exchange extends the life of the motor oil by way of removing the acidifying substances, so that longer service intervals are possible.

Additional advantages and objectives of the invention are described below in the details description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description, as an example, of preferred embodiments of the invention with reference to the enclosed drawings, in which:

Fig. 1 shows a schematic side view of a vehicle, comprising a lubricating system for a combustion engine according to the present invention,

Fig. 2 shows a coupling diagram for a lubricating system according to the present invention,

Fig. 3 shows a schematic side view of a combustion engine, comprising a lubricating system according to one embodiment of the present invention,

Fig. 4 shows a side view of an oil sump

Fig. 5 shows a perspective view of a cooling device for oil,

Fig. 6 shows a schematic drawing of the steps to immobilise an ion exchanger on a surface. DETAILED DESCRIPTION OF THE INVENTION

The invention is described below with reference to the lubricating system and the method, which were described generally above. The lubricating system according to the invention is intended for a combustion engine that may be comprised in a vehicle. Fig. 1 shows a schematic side view of an example vehicle 1, which vehicle comprises a lubricating system 4 for a combustion engine 2, with an oil sump 20 in direct contact with the combustion engine 2. The combustion engine 2 is connected to a gearbox 6, which is further connected to the driving wheels 8 of the vehicle 1 via a transmission. The vehicle also comprises a chassis 10. Lubricating system

A lubricating system is used in combustion engines to lubricate moveable parts in the system and in the combustion engine with the help of motor oil, also referred to as "oil" in this application, and which comprises suitable additives for this objective. The lubricating system comprises several components: at least an oil sump intended for storage of motor oil, an oil pump arranged to feed the motor oil from the oil sump further along into the lubricating system, a cooling device for cooling of the motor oil, an oil filter device for filtering the motor oil, and a main oil conduit intended to transport the motor oil in the lubricating system to the system's and the combustion engine's moveable parts.

The oil sump may be arranged in direct connection with the combustion engine's motor block. When the oil sump is arranged in direct connection with the combustion engine's motor block, the motor oil may then be fed from and recycled to the oil sump from the engine's moveable parts in a simple way.

The motor oil is fed further along from the oil sump with the help of an oil pump, which may for example be a peristaltic pump. The peristaltic pump generates a pump flow fluctuating over time, so that the pump's emitted pressure varies, but is sufficient for lubrication of the moveable parts in the system and in the combustion engine.

A cooling device for the motor oil may be arranged downstream of the oil pump and a cold start valve, which is used at cold starts to lead the oil back to the oil sump before the operating temperature is achieved. The cooling device comprises conduits facilitating cooling with the help of air, or by connecting the cooling device to a cooling system, for example to the engine's cooling system, so that the oil is cooled down when it circulates in the cooling device.

At normal operation the oil is fed from the cooling device to an oil filter device, arranged downstream of the cooling device. The oil filter device purifies the oil from particles, e.g. soot, with the help of a filter element. Preferably the filter element is arranged with a by-pass valve, whose objective is to control the amount of oil passing through the filter. In this way, a smaller amount of oil may be fed through the filter element, for example if the filter becomes too clogged before the replacement/cleaning, without resulting in too high a back pressure in the lubricating system.

Downstream of the oil filter device, an oil pressure converter may be arranged to control the pressure in the oil. The cooled oil may then be led further to e.g. piston cooling. The oil may be led from the oil filter directly, via the main oil conduit, to the engine's other moveable parts or to other components of the lubricating system, such as valve trains, compressors, high pressure pumps, etc.

Fig. 2 shows a coupling diagram for an example lubricating system 4 for a combustion engine 2, according to the present invention. The oil system 4 comprises an oil sump 20, an oil pump 22, a cooling device 24, and an oil filter device 26. The oil sump comprises motor oil 21. The oil pump 22 is connected to the lubricating system's main conduit 40, which transports oil through the lubricating system 4 to the combustion engine's 2 moveable parts. The oil pump 22 pumps oil from the oil sump 20, through the cooling device 24 arranged downstream and the oil filter device 26, and further to the moveable parts 28, for example a crank shaft (not displayed) and other users, such as valve trains, compressors, high pressure pumps. The oil pump 22 may be a peristaltic pump and may, for example, be operated by engine transmission or by an electric motor. The oil filter device 26 comprises a filter element 32, through which the oil from the oil sump 20 is filtered. A by-pass valve 36 is arranged in connection with the oil filter device 26, to lead the oil past the oil filter device 26 when needed, e.g. if the amount of oil passing through the filter device 26 must be controlled. The by-pass valve 36 may for example be an electrically controlled valve 36, and it is arranged in a by-pass conduit 38 to control the oil flow. The example system 4 in Fig. 2 also shows that a cold start valve 42 may be arranged downstream of the oil pump 22, in order to lead the oil back to the oil sump 20 via a branch conduit 52, before the operating temperature has been reached.

Downstream of the cooling device 24, an over pressure valve 44 may be arranged via a branch conduit 53, in order to recirculate a part of the oil to the oil sump 20 via a recirculation conduit 54 if the pressure in the system 4 increases. Alternatively, the oil may, via a branch conduit 55, be led to an oil cleaning centrifuge 46, which cleans the oil of particles, and subsequently the oil is returned to the oil sump 20 via a recirculation conduit 56.

At normal operation the oil is fed from the cooling device 24 to the oil filter device 26, which is arranged downstream of the cooling device 24. The oil filter device 26 cleans the oil of particles, e.g. soot. Preferably the oil filter device 26 is arranged with a by-pass valve 36, as described above.

Downstream of the oil filter device 26, an oil pressure converter 48 may be arranged to control the pressure in the oil. Via a branch conduit 58 the cooled and filtered oil may then be led further along to a piston cooling device 60, which cools down and lubricates the pistons. The piston cooling device 60 is activated when the oil pressure becomes sufficiently high at normal operation and when the valve 68 upstream of the piston cooling device 60 is opened. This means that in normal operation the oil always goes to the piston cooling device 60, and the valve 68 is open. If the oil pressure becomes too high, a restrictor 83 is activated, which lets oil through and returns the oil to the oil sump 20. The oil may be returned from the piston cooling device 60, back to the oil sump 20, via a recirculation conduit 59.

Via the main oil conduit 40 the oil may also be led directly from the oil filter device 26 to the engine's 2 other moveable parts 28, such as the crank shaft, the valve train, compressor, high pressure pump, etc. The oil from these components 28 may be returned back to the oil sump via recirculation conduits 62 and 64.

The lubricating system in Fig. 2 also comprises a crank house cleaner 70, whose objective is to clean the crank house gas, which is an oily gas. A part of the oil from the main conduit 40 may be led to the cleaner via a branch conduit 51. The cleaner may function so that it, for example, separates heavier particles and small oil drops from the gas by centrifugation. The gas is led out of the cleaner and the oil is returned back to the oil sump 20 through a conduit 72.

The lubricating system in Fig. 2 also comprises a number of restrictors 81, 82 and 83. For example, the objective of the restrictor 81, which is placed downstream of the oil pump 22, is to provide resistance in the oil flow to improve the function of the oil pump 22. The objective of the restrictors 81, 82, and 83 is to prevent too great an over pressure in the system. At a pressure increase to an excessive level in the lubricating system, the restrictors 81, 82, and 83 function as open valves, letting the oil through and returning the oil to the oil sump 20.

Fig. 3 shows a schematic drawing of a combustion engine 2 that comprises a lubricating system according to the present invention, for example the system in Fig. 2. The combustion engine 2 comprises an engine block 80. The main oil conduit 40 is arranged, e.g. drilled, through the entire length of the engine block 80, and is connected via channels to the engine's moveable parts, such as bearings in the crank shaft (not displayed). The oil pump 22 is connected to the lubricating system's main conduit 40, which transports oil through the lubricating system 4 to the combustion engine's 2 moveable parts. The oil pump 22 pumps oil from the oil sump 20 through the cooling device 24 and the oil filter device 26, arranged downstream of the oil pump 22. The cooling device 24 may be, for example, air cooled, or it may be connected to the engine's cooler 71.

Preferably, the lubricating system's component, whose contact surface is surface modified by immobilisation of an ion exchanger on the contact surface, is selected from the lubricating system's components, consisting of an oil sump, a cooling device, an oil filter device, a main oil conduit, and bearings in a crank shaft connected to the main conduit; and one or several of the components may comprise the surface modified contact surface.

In the example embodiment displayed in Fig. 2 and Fig. 3, the oil sump 20 comprises the surface modified contact surface 200, which comprises the ion exchanger immobilised on the surface, according to the invention.

Fig. 4 shows an oil sump 20 in more detail in a cross section in the oil sump's longitudinal direction. The oil sump 20 comprises the surface modified contact surface 200, which comprises the ion exchanger immobilised on the surface, according to the invention. The contact surface is the surface in contact with the oil. If the contact surface is arranged in the oil sump, the contact surface covers at least the area below the oil level, and preferably the area below the maximum oil level.

Fig. 5 shows a perspective view of a cooling device 24, comprising several channels 240.

Cooling devices are often made of aluminium, and aluminium is a metal that may be surface modified easily. In this embodiment, the top surface 260 and the channels 240 comprise the surface modified contact surface 200, comprising the ion exchanger immobilised on the surface, according to the invention.

Ion exchangers As described previously, an ion exchanger or ion exchanging materials relate to molecules with an ability to bind positive or negative ions (cation and anion exchangers, respectively). A cation exchanger may catch positive ions of one type, while it emits positive ions or another type. Similarly, an anion exchanger catches negative ions of one type, while it emits negative ions of another type. The ions caught/emitted by an ion exchanger are called counter ions. In the present invention, one objective of the ion exchanger, or the ion exchanging material, is to reduce the acidity in the oil. Therefore, the ion exchanger must interact with hydrogen ions in the oil, but it is important that the ion exchanger interacts minimally with additives in the oil, to avoid deactivating favourable additives in the oil. This, in turn, could lead to a deterioration of the oil's functional and tribological characteristics. In order to minimise the risk of additives being adsorbed on the ion exchanger, it is therefore preferred that the ion exchanger is a monovalent cation exchanger, whose objective is to catch hydrogen ions to as great an extent as possible. The monovalent cation exchanger may replace hydrogen ions in the motor oil with other, non-acidifying types of ion. Below are two examples of how a cation exchanger might look.

R is the molecule which the ion exchanger is bound to, and may be any matrix which functions as an ion exchanger. An example of a matrix might be polystyrene. The counter ion in these two cases is Na+.

The monovalent cation exchanger's counter ions are mainly monovalent. The cation exchanger's counter ions may be e.g. alkali metals. The cation exchanger's counter ions may e.g. be selected from among Na+ and K+, which are often used today in cation exchangers. Examples of functional groups in an ion exchanger are, for example, COO-, S03-, As03-, C6H40-, HP02-, S-, Se03-, but other functional groups are also possible.

There are two forms of ion exchangers, charged and uncharged. Charged cation exchangers are e.g. [COO]-, [S03]-, and in uncharged cation exchangers the counter ion is bound via ionic bonds to the ion exchanger, e.g. [COO]Na, [S03]Na.

The motor oil is acidified via contact with acid combustion gases, i.e. the level of free hydrogen ions in the motor oil increases. A cation exchanger has the ability to bind these hydrogen ions, which leads to a reduction of the motor oil's acidity and an increased base number.

The ion exchanger in the present invention may be a strong or a weak cation exchanger. The pKa-value is an equilibrium constant, which for aqueous solutions describes the pH at which there is an equilibrium between the ion exchanger's protonated, i.e. uncharged, form and its deprotonated, i.e. charged, form. Examples of cation exchangers' deprotonated form are COO-, S03-, and HP02-, and examples of corresponding protonated forms are COOH, S03H, and H2P02. This means that weak cation exchangers lose their charge at a low pH, while strong cation exchangers maintain their charge. Strong cation exchangers have a pKa below 0, while weak cation exchangers have a pKa of between 0 and 7.

In the present invention, the cation exchanger is preferably a weak cation exchanger, which may provide a higher exchange of hydrogen ions in a motor oil than a strong ion exchanger. Weak and strong ion exchangers and their respective exchange of hydrogen ions in a motor oil have been studied, among others, in the thesis "Ceco, Mima; Master's Thesis, 28 June 2013: Evaluation and optimisation of cation exchange materials for life-span optimisation of engine oil".

It is also important that the ion exchanger is able to cope with high temperatures and pressures. One example of a weak ion exchanger is acetic acid:

Acetic acid has a pKa of approximately 4.7-4.8. It is also possible to use other weak ion exchangers in the present invention.

Surface modification As described above, the lubricating system for a combustion engine comprises several components, whose objective may be, for example, to store, transport or treat the oil in the lubricating system, and each one of these components comprises a structural contact surface intended to be in contact with the motor oil. Instead of arranging a separate container comprising an ion exchanger in the form of particles in the lubricating system, according to the invention the contact surface of at least one of the lubricating system's components is surface modified by binding an ion exchanger to the surface.

The term contact surface means a surface, which is a part of the component's normal construction, and the contact surface is intended to be in contact with the oil in the lubricating system. For example, the contact surface may be the entire, or parts of, the oil sump's inner surface, which is in contact with the oil when the oil is stored in the oil sump. The term surface modification means that the characteristics of the contact surface are altered through a chemical reaction or treatment, e.g. by way of binding molecules on the surface. According to the present invention the binding of the ion exchanger is carried out by way of immobilising, i.e. binding, a cation exchanger to the contact surface. As mentioned above, if the acidity of the oil must be reduced, a monovalent cation exchanger, with at least one function group that may catch hydrogen ions in the oil and emit positive ions of another type to the oil, is used.

Immobilisation may be carried out with the help of conventional methods, which are well known e.g. within biotechnology. Through immobilisation, different molecules may be bound into or connected to a fixed carrier or surface. Molecules may be ion exchangers, e.g.

monovalent cation exchangers. The fixed carrier may be made of e.g. metal or a polymer material, such as plastic.

According to the present invention, the immobilisation may be carried out in many different ways, and the coupling technology as such is not crucial to the invention. The objective of the immobilisation is for the ion exchanger, i.e. the molecule with the functional groups, to be bound to the contact surface of a component. The molecules may for example be bound to the contact surface by covalent bonding. The bonding may either be direct, or indirect via one or several linking molecules, i.e. intermediate molecules between the ion exchanger and the contact surface. Mainly, the method for the immobilisation of the ion exchanger on the contact surface comprises the steps of first activating groups in the contact surface, i.e. the substrate, in order to facilitate adsorption of the ion exchanger to the surface. The activation may be carried out with the help of different methods, for example with the help of PVD (Physical Vapour Deposition)-coating technology on metal surfaces, or with the help of flaming on polymer surfaces. Subsequently, the activated metal surface may react with e.g. the ion exchanger and/or with the linking molecules. The ion exchanger and/or the linking molecules may be applied at the same time, or one at a time, by way of applying the linking molecules first. At the next step, the activated groups are deactivated on the surface, in order to prevent immobilisation of other molecules than the ion exchanger on the contact surface. At the last step, the contact surface is dried and washed, and the contact surface is then ready for use. Examples of different coupling methods, showing how molecules may be immobilised on different polymer surfaces or metal surfaces, are described in more detail in the book "Buddy D. Ratner et al.; Biomedical engineering; Elsevier, p. 330-334", which is also published on the Internet via Google Books. Fig. 6 schematically shows the principle for immobilisation of an ion exchanger on a metal or polymer surface. Step A) shows that the contact surface 200' in a component 400 is activated through, for example, ionising radiation, such as oxygen plasma 90', which is provided by a device 90 intended for this purpose. Step B) shows that the contact surface 200' has been activated and contains groups 201, which may react with an ion exchanger 300 directly or via linking molecules (not displayed). Step C) shows that the activated groups 201 have reacted with the ion exchanger 300, which has thus been immobilised or bound to the contact surface, and has accordingly formed a surface modified contact surface 200, comprising an ion exchanger 300 immobilised on a surface.

More examples of how molecules may be immobilised on polymer surfaces are described in "Leute, A. et al.; Static SIMS Investigation of Immobilised Molecules on Polymer Surfaces; Advanced Materials, 1994, 6, No. 10, p. 775-780" and "Tabata, Y. et al.; Immobilisation of collagen onto polymer surfaces having hydroxyl groups; Biomaterials 1986, Vol 7 May 1986; p. 234-238".

Further examples of coupling methods, showing in more detail how organic molecules may be immobilised on different metal surfaces, are described e.g. in "Touahir, L, et al.; Molecular monolayers on silicon substrates for biosensors; www.elsevier.com/locate/bioelechem" and "Schickle, K. et al. Towards osseointegration of bioinert ceramics: Can agents be immobilised on alumina substrates using self-assembled monolayer technique?; www.sciencedirect.com; Journal of the European Ceramic Society 22 (2013) 2705-2713", and "Nanci et al.; Chemical modification of titanium surfaces for covalent attachment of biological molecules; 1998 John Wiley&Sons, Inc. J Biomed Mater Res., 40, 324-335, 1998".

Regeneration of ion exchangers Ion exchangers may be regenerated, and may accordingly be used over and over again following regeneration. Regeneration entails that the ion exchanger's ability to replace desired ions is recreated.

Ion exchangers may, according to the present invention, be regenerated by arranging a regeneration arrangement (not displayed in the drawings), connected with a component that comprises the surface modified contact surface. The arrangement may comprise a by-pass valve to lead the oil past the component. The advantage herein is that the regeneration may be carried out without otherwise switching off the lubricating system. Another alternative is to arrange a valve arrangement both downstream and upstream of the component, to prevent the flow of the oil through the component. In this way, a simple construction may be obtained and the regeneration may be carried out, for example when the vehicle is serviced. In both cases, a pump device is arranged, which may be connected to the component via a coupling device, to feed a saline solution through the component. The saline solution may then regenerate the ion exchanger with the help of its flow through the component, until the active groups in the ion exchanger are activated again. The component is then emptied of saline solution and filled with new oil. The valves are switched again, so that the oil in the lubricating system may flow through the component. For example, the saline solution may be an alkaline solution with a high salt content. A typical pH value for such a solution is 8-10. Since the saline solution in the regeneration arrangement is arranged to flow through the component with the surface modified contact surface, the regeneration becomes efficient.

The invention has been described above as applied in a lubricating system for a combustion engine in a vehicle. The present invention is not limited, however, to the above described embodiments, but may be used in other applications where similar problems and conditions prevail. The invention may for example be used in engines intended for marine or industrial operation where, analogously, there may be a risk of the oil becoming acidic, and where there is no room for, or possibility of, construction alterations. The invention is accordingly only limited as set out in the enclosed claims.