HK1176387B - A method for lubricating cylinders in large diesel engines - Google Patents

Description

Method for lubricating cylinders in large diesel engines

Technical Field

The invention relates to a method for lubricating cylinders in a large diesel engine, such as a marine engine, wherein the injection of lubricating oil is performed via a plurality of injection units corresponding to multiples of the number of cylinders in the engine, wherein the lubricating oil is supplied as an injected combination of at least two portions of lubricating oil, wherein the at least two portions of lubricating oil are delivered at least two different piston positions, wherein the at least two different piston positions are selected from the piston positions used for injection before, during and after the piston passes beside the injection unit, and wherein at least a portion of the lubricating oil is supplied by direct injection onto an annular area of the cylinder wall, wherein the lubricating oil is supplied by a combination of: injecting a first portion of the lubricating oil directly onto the annular region of the cylinder wall above the piston before the piston passes; and injecting the second portion and/or the third portion of the lubricating oil when the second portion of the lubricating oil is injected directly onto the piston during passage of the piston and when the third portion of the lubricating oil is injected directly onto the annular region of the cylinder wall below the piston after passage of the piston.

Background

The background technology of the application is as follows: three different methods are commonly described today for cylinder lubrication.

The first method involves conventional cylinder lubrication.

For this purpose, systems with mechanical lubricating apparatuses are used, which are directly driven via the drive chain (chain drive) of the engine. Thereby achieving synchronous operation of the lubricating apparatus and the engine. Such systems typically include a mechanical lubrication device having a piston pump and associated check valves. At the outlet of the lubricating apparatus, a check valve is provided, which is coupled to an injection unit (injector/check valve) by a lubricating oil pipe. In this type of system, the lubricating oil is supplied to the cylinder immediately before the uppermost piston ring of the piston passes through the injection unit. Lubricating oil is typically supplied to the cylinder by each engine stroke.

In these conventional cylinder lubricating apparatuses, two or more central lubricating apparatuses are used, mainly for large two-stroke diesel engines, each providing lubrication at various points in a single or multiple cylinders, i.e. by means of feeding portions of oil under pressure to the various points to be lubricated through respective connecting lines at related time intervals. These relevant time intervals may typically be: the piston rings are disposed opposite the associated lubrication points during the compression stroke when the piston is moving upward.

The second method for cylinder lubrication occurs on newer engines and is described as high speed cylinder lubrication.

A hydraulically powered lubricating apparatus is used for this purpose, wherein the mechanical drive train is replaced by a hydraulic system which is clocked via timing sensors which are mounted directly on the flywheel of the marine engine. For such cylinder lubrication, a piston pump is also typically used. In such systems, the lubricating oil is fed into the cylinder as the piston passes, so that substantially all of the lubricating oil is supplied directly onto the piston, typically between the uppermost and lowermost piston rings. When feeding lubricating oil between these piston rings, it is desirable that they retain the lubricating oil better, and that the piston subsequently distributes the lubricating oil along the travel path of the piston. There are also systems such as those disclosed in WO 2008/009291, in which a hydraulic power plant is used, in which both the injection quantity and the timing for the delivery of the injection quantity can be adjusted.

Since the stroke of the piston pump is constant, the lubricating oil is intermittently supplied so that the amount is adjusted based on the actuation frequency of the piston pump. Lubricating oil is supplied by these systems via an injection unit comprising a conventional check valve, injector or atomizing valve. Examples of such techniques are known from, for example, DK 173512 or DE 10149125.

With this high speed lubrication variant. Thus a system is provided in which the piston pump principle is not used. But the amount of lubricating oil injected is controlled by controlling the opening and closing times. An example of such a technique is known from e.g. EP 1426571.

The injection may occur by means of the passage of a piston in an upward or downward direction. If the injection takes place during the downward movement, the lubricating oil is distributed from the point to be lubricated on the cylinder running surface and down in the cylinder liner. However, it is preferred that the injection takes place during the upward passage of the piston relative to the hot end of the cylinder, where the need for lubrication is greatest.

The traditional way of distributing oil over the cylinder surface is by means of creating two inclined grooves or troughs at each point on the cylinder surface to be lubricated, where both grooves or troughs start from the lubrication point and are directed away from the top of the cylinder. When the piston ring passes such a groove, a pressure drop occurs in the groove on the piston ring, which forces the oil away from the lubrication point. However, these and other approaches have been inadequate because, in practice, significant variations in wear occurring along the circumference of the cylinder are observed.

The development towards greater utilization of the engine has led to increased mechanical and thermal loads on the cylinder liner and piston rings, which has traditionally been achieved by an increase in the metering of lubricating oil. However, it has appeared that if the metering is increased above a certain limit, which is not clearly defined, when lubricating oil is injected into the cylinder with said conventional lubrication, the speed of the lubricating oil is so high that it does not remain on the cylinder running surface, but it forms a jet into the cylinder cavity and thus disappears. If metering is performed as desired when the piston ring is positioned opposite the lubrication unit, it is not as critical, but if metering occurs outside this period, there is no benefit to a portion of the oil metered.

Both of the above methods may also be considered to relate to systems in which lubrication is established by piston distribution of lubricating oil.

A third method for cylinder lubrication uses systems that feed the lubricating oil directly into the cylinder, directly onto the cylinder wall and before the piston passes.

In these systems, injectors are used which supply the lubricating oil in atomized form or in the shape of one or more small jets. To supply the lubricant to the injector, a conventional mechanically driven lubrication device or hydraulic device is used.

The advantage of this method is that the lubricating oil is already distributed to a large extent on the cylinder wall before the piston passes. According to this method, the lubricating oil is distributed at the top of the cylinder before the piston arrives, and it is desirable for the piston to carry the lubricating oil down into the cylinder during the expansion stroke. Examples of such techniques are known from, for example, WO 0028194, EP 1350929 or DK 176129.

EP 1350929 describes a method in which a lubricating oil jet (in which atomization of the lubricating oil is largely avoided) can be delivered to the cylinder running surface by injection before, during and/or after the passage of the piston. This means that the total amount of lubricating oil is injected onto the cylinder active face in at least two portions, as indicated in the introduction.

Since the cylinder wall is supplied with oil before the piston passes, timing is not as important for this third method as for the first-mentioned two systems, in which oil is supplied accurately during the very short time intervals when the piston rings are positioned opposite the lubricating unit.

Tests have shown that the cylinder lubrication according to WO 0028194 (so-called SIP lubrication) provides a maximum oil film thickness where the wear is greatest in the cylinder, which corresponds to the piston in the top position and in the area of the uppermost piston ring. In contrast, it has emerged that conventional lubrication or high speed lubrication provides a thicker oil film on the rest of the running surface.

The pressure present by means of SIP lubrication is required in the lubrication oil line between the pump and the nozzle in order to ensure that the aimed atomization is significantly higher than that produced by the pressure present by means of conventional lubrication methods, which operate by means of a pressure of a few bar. The SIP valve operates at a preset pressure of 35-40 bar.

Furthermore, the supply of lubricating oil has the purpose of neutralizing the action of the acids on the cylinder walls. The acid effects are produced by combustion of sulfur-containing fuels, and they are best counteracted by feeding lubricating oil directly at the top of the cylinder. Measurements show that SIP lubrication provides minimal wear. It appears in practice that corrosive wear is the most critical factor for the service life of a cylinder.

The drawbacks of conventional lubrication or high speed lubrication (both of which are systems that primarily use pistons to distribute the lubricating oil) are: some excess lubrication is required in order to ensure sufficient lubrication for the top of the cylinder. In particular, lubrication on the piston requires an increase in the amount of lubricating oil in relation to the sulfur content of the fuel in order to achieve satisfactory cylinder conditions.

Accordingly, for lubrication by means of a system in which the lubricating oil is fed directly onto the cylinder wall, disadvantages may be: an insufficient amount of oil is provided at the bottom of the cylinder when an amount of lubricating oil sufficient to avoid corrosive wear is applied. This is due to the fact that: the piston ring also produces a scraping action in addition to the above-mentioned distribution function. Measurements show that SIP lubrication results in less downward scraping of the lubricating oil than lubrication by means of the lubricating oil dispensed by the piston.

Another difference in lubrication by means of a system in which the lubricating oil is fed directly to the cylinder wall and by means of a piston-distributed lubrication system is the consequence of providing different amounts of lubricating oil downwards in the cylinder. The discharge oil (scavenge drain oil) of a system lubricated by means of pistons, in which only the pistons dispense the lubricating oil, is thus measurably less lubricated by SIP (according to WO 0028194) than by pistons. This means that one of the parameters used for estimating the cylinder state (i.e. a measure of the Fe content in the exhaust oil) cannot be used directly by comparing the cylinder state, since the same Fe content would result in a concentration that varies according to the lubrication method.

The scavenging air apertures in a longitudinally scavenged two-stroke diesel engine are arranged in such a way that during scavenging the rotational movement of the gas mixture starts simultaneously with the gas moving upwards in the cylinder, leaving it through the exhaust valve at the top of the cylinder. The gas in the cylinder thus follows a spiral path or vortex (whirl) on its way from the scavenging air aperture to the exhaust valve. Due to centrifugal forces, sufficiently small oil particles located in such a vortex will be forced to hit the cylinder wall, eventually depositing on the wall. This effect is exploited by introducing portions of oil into the cylinder as a mist of suitably sized oil particles atomized by the nozzle. By adjusting the size of the nozzle, the injection speed and the oil pressure in front of the nozzle, the average size of the oil droplets in the oil mist can be controlled. If the oil particles or droplets are too small, it will "float" too long in the gas stream and eventually be removed by the scavenging air without hitting the cylinder walls. If it is too large, it travels too far in its initial path due to its inertia and does not reach the cylinder wall, as it is caught up by the piston and is positioned at the top of the piston.

The orientation of the nozzles with respect to the flow in the cylinder may be arranged such that the interaction between the individual droplets in the cylinder and the gas flow ensures that the droplets hit the cylinder wall over an area largely corresponding to the circumferential distance between the two lubricating points. In this way, the lubricating oil is more or less evenly distributed over the cylinder surface before the piston rings pass. In addition to this, the nozzle may be adjusted so that the oil hits the cylinder wall higher than the nozzle. Thus, before being introduced into the cylinder, the lubricating oil will not only be better distributed over the cylinder surface, but will also be distributed over the cylinder surface closer to the top of the cylinder, where it is most needed for lubrication. Both of these facts will lead to improved oil utilization and to an improvement in the relation between the cylinder service life and the oil consumption as considered.

The supply of oil to the cylinder surface is effected in the measuring section, which is almost the case with the two above-mentioned conventional systems. The supply device may be a conventional lubrication system, but other supply devices with corresponding properties are also conceivable.

In order to ensure that the pressure in the cylinder does not return into the oil line, a check valve is arranged in the usual manner at the end of the lubrication line, immediately before the cylinder liner of the inner cylinder face. The check valve allows passage of oil from the oil line to the cylinder liner, but does not allow passage of gas in the opposite direction. These check valves usually have a moderate opening pressure (a few bar).

The characteristics of the three above-mentioned methods for lubricating the cylinder are:

lubrication timing-when in the engine cycle lubricating oil is supplied?

Supply quantity-how to adjust the relevant injection quantity?

Pump characteristics-how and how fast lubricating oil is supplied?

It is concerned with finding ways to minimise the consumption of lubricating oil by providing improvements in cylinder lubrication for large diesel engines, such as marine engines.

Disclosure of Invention

It is therefore an object of the present invention to propose a method of the type specified in the introduction, in which an efficient distribution of the lubricating oil is achieved not only on the periphery of the cylinder but also along the travel path of the piston in the cylinder, in order thereby to reduce the lubricating oil consumption and/or to reduce the wear in the entire cylinder.

According to the invention, this is achieved by a method of the type specified in the introduction, which is peculiar in that detection of an indirect or direct parameter for the actual cylinder load is carried out and that a distribution is made between the first and second and/or third portion of lubricating oil, whereby the second and/or third portion is increased proportionally for a reduced cylinder load.

It is noted that with high pressure is meant the pressure present in the pre-set SIP valve, for example the above mentioned pressure of 35-40 bar. However, higher pressures may also be used.

Alternatively, the lubricating oil may be supplied at a low pressure, so that a small jet of lubricating oil is established.

Depending on the operating parameters, there are several possible options for performing this control of the oil injection.

A system may be used which measures wear via sensors in the cylinder wall (e.g. indirectly in the form of temperature measurements) and on the basis of this changes the distribution between the lubricating oil supplied in the first or second portion (or possibly also as a third portion for delivery after passage of the piston). The first portion may be supplied as SIP lubrication and the second portion may be supplied according to a conventional timing system. This means that in addition to establishing an adjustment of the amount of lubricating oil, one can also use the parameters for the relative distribution of lubricating oil according to one or another principle, for example as a result of detecting increased wear.

Alternatively, a system may be used in which the adjustment takes place in dependence on the distribution in the first, second and third parts (and thus in dependence on the lubricating oil distribution), which first, second and third parts use direct or indirect measurements of the cylinder state as a parameter via one or more sensors. Such as rotation, cylinder liner temperature, load, amount of fuel injected, quality of lubricating oil, viscosity of lubricating oil, TBN content of lubricating oil, analysis result on discharged waste oil (residual TBN, Fe content, etc.). A system may be applied which uses, for example, sulfur measurement in fuel oil. The increased sulfur content requires more lubricating oil to neutralize the sulfur. The method according to the invention can thus be adapted such that an improved neutralization relationship can be achieved at a position below the lubricating oil injector of the injection unit, further down in the cylinder, by switching between the two lubrication principles. Reference is made here to the principle shown in fig. 11. In this way, the neutralization state above and below the injection unit becomes more uniform.

Alternatively, the area ratio above and below the injection unit may be used to calculate the minimum amount fed on the piston. Here, it is important to note that the load, which includes piston speed, temperature, compression and combustion pressure, is typically highest at the top of the cylinder. This means that only the area relation cannot be used as a parameter. The distribution (i.e. the basis of the latter) is then found in particular as a function of the area state in the cylinder.

Alternatively, one may determine the minimum amount of lubrication oil to be supplied to the piston based on the entire area of the cylinder liner or based only on the area under the injection unit. The distribution (i.e. the basis of the latter) is then found in particular as a function of the state of the area in the cylinder (possibly in combination with some of the other parameters).

Alternatively, one can use an analysis of the discharged used oil as a functional control parameter. The analysis of the discharged oil may be performed on-line or manually. A closed loop adjustment may be provided in which the control automatically attempts to reduce the wear particles in the first position. The wear particles may be represented, for example, by the number of Fe particles. If this does not improve the measurement over a given period of time, one could instead increase the amount of lubrication oil or increase the amount and dispense key (key).

Alternatively, one could use an analysis of the on-line measurement of residual TBN directly to adjust the dispense, or as a combination of increased lubricant volume and dispense variation.

As mentioned before, one will typically use a distribution for feeding onto or above the piston, but as an alternative distribution to this distribution one can also combine the above embodiments with a system in which some of the amount of lubricating oil is fed below the piston. The amount of oil "dropped" into the cylinder can thereby be increased.

The lubricating oil of at least two portions is preferably supplied according to the principle in which the lubricating oil is supplied only once per engine cycle. This means that a first part of the lubricating oil is supplied in one engine cycle, while a second part of the lubricating oil is supplied in another engine cycle, and so on. Alternatively, all portions of the lubricating oil may be supplied in the same engine cycle.

When a combination of several parts of lubricating oil is used, an adjustment of the control will take place, resulting in algorithms which are based on the injection of three partial quantities of lubricating oil at different lubricating moments.

By means of the invention, a combination of prior art methods for cylinder lubrication is thus applied, whereby the advantages of each principle can be achieved and at the same time the disadvantages are avoided.

The direct feed over the annular region can take place in atomized form or in the form of small oil jets.

The supply of lubricating oil takes place via lubricating oil injectors which form part of the injection unit and are arranged in the cylinder wall.

Basically, a combination of a first part injected with lubricating oil and a second part injected with lubricating oil is used: injecting a first portion of the lubricating oil into the cylinder, directly onto the cylinder wall and before the passage of the piston, so that the first portion of the lubricating oil is already substantially distributed on the cylinder wall before the passage of the piston, thereby achieving a better cylinder condition above the injection unit; the second part of the lubricating oil is injected by conventional lubrication of the lubricating oil distributed by means of the piston, so that an increased average oil film thickness is obtained below the injection unit.

Whereby the cylinder condition becomes better in the area at the top of the cylinder and in the area below the injection unit.

The advantage of this combination is that wear is minimized while lubrication oil consumption is minimized, since it can be operated with the smallest possible feed rate. In summary, a better method of operation is achieved, wherein the best aspects are taken from all systems and combined into a new system.

The distribution in the amount of lubricating oil for the first and second and/or third portion of lubricating oil, respectively the timing of the injection onto the piston above/below the piston, will preferably be parameter controlled. The actual operating conditions in the cylinders can thus be determined for distribution and timing.

It can be said that a multiplicity of timed cylinder lubrications in combination with functionally determined cylinder lubrications is achieved. It can be applied in different situations, for example by means of sulfur-dependent distribution of the various parts of the lubricating oil, as described below.

By using the method according to the invention, further principle embodiments of the application of the method according to the invention can be realized:

a) an electronic control device is provided, the time of oil injection being used as a parameter for adjusting the distribution of lubricating oil in the longitudinal direction of the cylinder, and the control device automatically distributing different portions of lubricating oil to at least two different piston positions. These positions may be arranged at the same height in the cylinder or at different heights in the cylinder, i.e. by operating by means of the same injection unit or different injection units in order to inject different portions of the lubricating oil.

b) The system mentioned in a) is peculiar in that a fixed percentage of lubricating oil:

-on passing the cylinder piston through the lubricant injector during the passage of the piston upwards or downwards.

-feeding directly on the cylinder wall below the piston after the piston has passed the oil injector during the upward movement of the piston.

During the downward movement of the cylinder piston, the cylinder piston is fed directly onto the cylinder wall before passing through the lubricant injector.

In these cases, the rest of the lubricating oil (first portion) will be supplied directly to the cylinder wall above the piston during the upward movement of the piston.

c) The system mentioned in a) is peculiar in that a fixed amount of lubricating oil:

-on passing the cylinder piston through the lubricant injector during the passage of the piston upwards or downwards.

-feeding directly on the cylinder wall below the piston after the piston has passed the oil injector during the upward movement of the piston.

-feeding directly on the cylinder wall during the downward movement of the cylinder piston, before the cylinder piston passes the lubricant injector.

In these cases, the rest (first part) of the lubricating oil will be supplied directly to the cylinder wall above the cylinder piston during the upward movement of the piston.

This means that the amount of lubricating oil will become proportional to e.g. the actual load, rotation, etc. by the use of load regulation or another form of regulation distribution by MEP regulation.

d) The system mentioned in a), b) or c), wherein off-line or on-line wear measurements are made on the cylinder wall, and is peculiar in that these wear measurements are used to correct the distribution in the first, second and third sections (and thereby the distribution of the lubricating oil).

e) The system mentioned in any of the above a) -d), wherein off-line or on-line oil film thickness measurements are made on the cylinder wall, and is peculiar in that these oil film thickness measurements are used to correct the distribution in the first, second and third sections (and thereby the distribution of the lubricating oil).

f) The system mentioned in a), which is peculiar in that the distribution between at least two parts of the lubricating oil is made directly or indirectly dependent on the actual sulphur content in the fuel supplied to the cylinder.

The above principle embodiments a) -f) can be combined with the following method steps comprising:

I) regulated distribution of lubricating oil

Load regulated oil distribution may be applied. Here, a distribution algorithm may be applied which starts with feeding a fixed amount of the total amount of lubricating oil on or under the piston. These algorithms may be based on different distribution percentages between the first and second portions of lubricating oil required at 100% load. In the same way, the distribution of the lubricating oil between the first and third portions can be varied. In addition, a lubricant distribution can be established in which the lubricant distribution in the first, second, and third portions is applied.

These algorithms may be based on a non-decreasing state of the total amount of lubrication oil (in addition to decreasing based on rotational changes), which is why the distribution is defined as a fixed ratio between the first and second portions of the amount of lubrication oil.

A distribution algorithm is applied by means of the reduction of the total amount of lubricating oil, which distribution algorithm provides a varying relation between the first and the second part of the amount of lubricating oil. In a first example, a given ratio of e.g. 1/10 at 100% load may be used, where 10% of the total amount of oil is supplied to the piston and 90% to the cylinder wall above the piston. The distribution between the first portion and the second portion is varied so as to ensure that a certain quantity (corresponding to 1/10 of the stroke of the piston of the metering pump at 100%) is fed onto the piston. This means that by using a lubrication oil adjustment algorithm in which the stroke of the pump piston for the lubrication oil is changed, it has to be compensated for. The adjustment of the stroke of the pump piston can thus correspond to 25% of the stroke at 25% load. Examples of these are shown in figure 9.

Alternatively, MEP regulated lubricant distribution may be applied. Here, a distribution algorithm starting from feeding a fixed amount of the total amount of lubricating oil on or under the piston may also be applied. These algorithms may be based on different distribution percentages between the first and second portions of lubricating oil required at 100% load.

By reducing the total amount of lubricating oil, a distribution algorithm is applied that provides a varying relationship between the first and second portions of lubricating oil mass by means of MEP regulation. The adjustment may take place correspondingly, such as by load adjustment by means of varying the stroke on the pump piston for the lubricating oil. However, operation is typically performed with smaller variations in the dispense percentage. In a first example, a given ratio of 1/10 at 100% load may be used, where 10% of the total amount of oil is supplied to the piston and 90% to the cylinder wall above the piston. The dispense percentage at 60% RPM may thus result in a dispense percentage of 15%. Examples of these are shown in fig. 10.

II) a corresponding embodiment of the fixed or regulated distribution of the lubricating oil by means of intermittent lubrication. The above embodiment I assumes in advance that lubricating oil is supplied in each engine stroke. However, a corresponding solution in a lubrication system with intermittent lubrication may be used. I.e. where the lubricating oil is not supplied in every engine stroke.

III) depending on the distribution of sulfur. Depending on the sulphur content of the fuel supplied in the cylinder, one can vary the first part of the lubricating oil supplied directly onto the cylinder wall above the piston during its upward movement. For higher sulphur contents one can thus increase the first part of the lubricating oil supplied directly to the cylinder wall above the piston during its upward movement. Thereby, the amount of lubricating oil at the top of the cylinder will be increased in order to neutralize relatively larger amounts of acids that are formed due to the higher sulphur content in the feed fuel.

The parameter levels will be determined empirically. However, shown in FIG. 11 is an example of how the allocation may proceed.

Note that in some cases a fixed percentage portion may be achieved by a variable parameter-dependent portion. For example, 10% fixed lubrication below the piston may be accomplished by an additional load proportion portion that varies somewhat in proportion to the load and is also injected below the piston.

According to a further embodiment, the method according to the invention is peculiar in that the injection of the first part of the lubricating oil is carried out immediately before and in connection with the upward passage of the piston through the annular region. As the lubricating oil delivered from each injection unit is directed to the area of the cylinder wall near each injection unit in the annular area in which the injection unit is mounted, the injected lubricating oil will form a largely adherent annular lubricating oil film on the cylinder running surface in time before the actual piston passes. The advantages are described in more detail in WO 0028194 and in EP 1350929.

According to a further embodiment, the method according to the invention is peculiar in that the injection of the second part of the lubricating oil is carried out in connection with the upward passage of the piston and in the area between the uppermost and the lowermost piston rings of the piston. The piston is thus lubricated during its upward movement. The optimal procedure is to start the supply of lubricating oil when the upper piston ring is in front of the injection unit and to end when the last piston ring is passing (most pistons have four piston rings).

However, in some cases a compromise may be required with the distribution between the piston rings, because the injection time is volume dependent, and because the piston speed also varies.

Alternatively, with conventional mechanical power lubrication devices having a check valve, one may start the injection of lubricating oil typically earlier than the first piston ring passes, thereby ensuring that the lubricating oil is in place while the piston is passing.

Alternatively, the injection of lubricating oil may be performed during the downward movement of the piston if it appears that there is a greater need for lubricating oil on the lower part of the cylinder wall below the piston than expected.

According to a further embodiment, the method according to the invention is peculiar in that each of the injection portions for injecting lubricating oil is used with the same injection unit.

The same injection unit as applied in prior art systems may be used. In principle, it is ensured that the injection unit can be supplied with lubricating oil before, during and possibly also after the passage of the piston. No change of the nozzles/valves in the injection unit will be required, but only a control embedded in the control unit, resulting in algorithms that establish different lubrication times and injection amounts/characteristics depending on the operating parameters (e.g. cylinder load).

According to a further embodiment, the method according to the invention is peculiar in that the injection of the first part of the lubricating oil takes place at high pressure by means of injection units, which are used to form a complete or partial atomization of the lubricating oil, and takes place immediately before the piston passes upwards through the annular region. The advantage of SIP lubrication is thereby achieved, wherein the lubricating oil is atomized and the atomized lubricating oil will in time form a substantially adhering annular lubricating oil film on the cylinder running surfaces before the actual piston passes. The advantages are described in more detail in WO 0028194.

According to a further embodiment, the method according to the invention is peculiar in that the injection of the second and/or third part of the lubricating oil takes place at high pressure by means of injection units, which are used to form a complete or partial atomization of the lubricating oil. Thereby, oil is provided in a groove in the cylinder wall for subsequent entrainment by the piston rings, or alternatively, an atomized spray of oil is formed which is injected onto and dispensed by the piston.

According to a further embodiment, the method according to the invention is peculiar in that the second and/or third portion of the lubricating oil constitutes at least 10% of the total amount of lubricating oil.

There is a need to define a certain minimum amount of lubrication oil to be supplied to the piston. This minimum amount will be determined by experiments, but it will be assumed that a minimum of 10% of the lubricating oil is always supplied directly to the piston, i.e. as the second part of the lubricating oil.

The allocation may thus be based on the actual load and/or another direct/indirect parameter indicative of the cylinder load and/or state, as already mentioned above. This allocation may mean: the lubricating oil delivered directly to the piston will always constitute a minimum percentage of the total supply of lubricating oil. In addition, this allocation may mean: the lubricant delivered above the piston will always constitute a minimum percentage of the total supply of lubricant.

The allocation may be made in proportion to the actual load. As an example, for a 90% load, a 90% supply of lubricating oil above the piston may thus be achieved, for a 60% load, a 60% supply of lubricating oil above the piston may be achieved, and for a 40% load, a 40% supply of lubricating oil above the piston may be achieved, etc.

According to a further embodiment, the method according to the invention is peculiar in that the position and movement of the piston are detected directly or indirectly, and that timing of the delivery of the lubricating oil, adjustment of the amount of lubricating oil and determination of the injection characteristic are carried out.

For example, reference means can be applied which are connected to the spindle and indicate the position of the spindle, and thus also of the piston, directly or indirectly. They can interact with sensor means which detect the position of the reference means and with a control unit which is connected to the sensor means and which receives signals from the sensor means and which comprises means for detecting the angular position and angular velocity of the reference means and thereby of the spindle, and which is connected to the piston pump and controls the actuation of the piston pump in order to meter the lubricating oil.

According to a further embodiment, the method according to the invention is peculiar in that it comprises computerized control, monitoring and/or detection of the operation of the method. Such computer control may be used as a control unit for adjusting parameters for the lubricating oil injection according to a customized algorithm.

The method according to the invention can be easily implemented in the system described in EP 2044300 or alternatively in the system described in WO 2008/141650. These documents are hereby incorporated by reference.

In the latter system, it is possible that the devices may have different strokes. These strokes are controlled by solenoid valves which supply hydraulic oil pressure to the distributor plate. In principle, the injection on the piston may be provided by one solenoid valve and the injection above the piston may be provided by another solenoid valve.

Alternatively, it would be possible, based on the control, that the same solenoid valve provides timing at two different times and thus for injection on the piston and for injection above the piston.

Drawings

The invention will now be explained more closely with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic cross-sectional view through a cylinder, wherein a first portion of lubricating oil is injected into the cylinder;

FIG. 2 shows a cross-sectional view corresponding to that of FIG. 1, but with a second portion of the lubricating oil injected into the cylinder;

FIG. 3 shows a cross-sectional view corresponding to that of FIG. 1, but with a third portion of the lubricating oil injected into the cylinder;

figure 4 shows the injection timing according to two different principles for the injection of the first and second portions of lubricating oil;

fig. 5a +5b show two possible principles for injected, regulated or fixed distribution of the first and second portions of lubricating oil;

fig. 6 shows an example of variation in the thickness of an oil film in the longitudinal direction of a cylinder;

fig. 7 shows an example of reduction of waste oil emission by injecting lubricating oil as a first part of the lubricating oil (SIP principle);

fig. 8 shows an example of a wear process by injecting lubricating oil as a first part of the lubricating oil (SIP principle) or injecting lubricating oil as a second part of the lubricating oil (conventional);

FIG. 9 illustrates a distribution algorithm utilizing a fixed amount of lubrication oil supplied as a second or third portion of lubrication oil (on or under the piston) as compared to the load adjusted amount of lubrication oil;

figure 10 shows an alternative distribution algorithm with a fixed amount of lubricating oil supplied as a second or third part of the lubricating oil (on or under the piston) compared to the amount of so-called MEP-regulated lubricating oil;

FIG. 11 shows an example of a distribution algorithm that utilizes different sulfur content in the fuel supplied to the engine;

FIG. 12 shows a schematic overview of a system with a plurality of lubricating apparatuses for use with the method according to the invention; and

fig. 13 shows a cross-sectional view through embodiments of the lubricating apparatuses for use with the method according to the invention.

Detailed Description

Fig. 1 to 3 show a sectional view through a cylinder 51, which cylinder 51 has a piston 52 and a plurality of injection units 53, which injection units 53 are arranged in an annular region 54 of a cylinder wall 55 and are connected to a lubricating device, not shown.

In fig. 1, the piston 52 is seen in the lower position. The injection of oil 58 takes place from each injection unit directly on the annular region 54 of the cylinder wall 55. Injection occurs at a location above the piston 52 immediately prior to the piston passing through the annular region 54 during its upward movement.

In fig. 2, the piston 52 is shown in an intermediate position, wherein the injection unit 53 is located at a position between the upper piston ring 56 and the lower piston ring 57. During the upward movement of the piston through the annular region 54, oil 58 from each injection unit is injected directly onto the piston 52 between the upper piston ring 56 and the lower piston ring 57.

In fig. 3, the piston 52 is present in the upper position. The injection of oil 59 takes place from each injection unit directly on the annular region 54 of the cylinder wall 55. Injection occurs at a location below the piston 52 immediately prior to the piston passing through the annular region 54 during its upward movement.

In fig. 4, two different lubrication times are shown according to SIP lubrication or conventional lubrication.

In both cases, the lubricating oil is delivered to the cylinder during the upward movement of the piston. This means from Bottom Dead Center (BDC) to Top Dead Center (TDC).

Where the "window" for SIP timing is located before the piston passes through the oil injector. The "window" for conventional lubrication is narrower and is simply expressed as being located after the top of the piston has passed through the oil injector.

Fig. 5a shows the load dependent lubrication distribution, wherein the distribution between SIP and conventional lubrication is changed such that for low loads the lubricating oil is fed further down the cylinder wall to a greater extent.

Fig. 5b shows a constant lubrication distribution. This means that the allocation between SIP and conventional lubrication is not made dependent on operating parameters. Instead, a fixed dispense key is provided in the control. While it can be considered whether more oil is needed farther down the cylinder wall. In this case, this will be taken into account based on a measurement of wear or by a visual inspection of the cylinder wall.

In fig. 6 is shown an example of how the thickness of the oil film varies in the longitudinal direction of the cylinder, depending on whether SIP or conventional lubrication is used. I.e. depending on whether lubrication by means of injection of the first part of the lubricating oil or by injection of the second part of the lubricating oil is employed.

In the figure, the hole 60 of the injection unit 3 is shown without machining for the SIP valve. When the piston in operation is at the top position (i.e. closer to the cylinder top 61), this point is called top dead center. At the bottom of the cylinder, a corresponding bottom dead center position 63 is defined and in this position the scavenging air port 62 is exposed.

In this figure, the upper and lower oil film thicknesses are shown at different loads and depending on whether it is SIP or conventional lubrication. Oil film thickness measurements were performed at different loads. The width of the "band" indicates that the oil film changes to some extent under different loads. The figure shows in principle the oil film at both the highest load and the lowest load.

A SIP valve (also referred to as a lube oil injector) is shown in the figure. When looking at the area between the cylinder top and the lube oil injector, it is seen that the oil film in this area is thicker for SIP lubrication than for conventional lubrication.

This is to be compared with the fact that: the feed (amount of oil supplied per unit power) is 25% lower in the example shown. The trend is clear.

Looking at the area under the lube oil injector, it is further seen that a significantly thicker oil film is formed for conventional lubrication.

In fig. 7, a set of examples of waste oil emissions reduced by injecting lubricating oil as a first part of the lubricating oil (SIP principle) is shown. These values are numbered and come from the same trial as the numbers originally used in fig. 6. The figure shows six different cylinders, wherein the first three columns show cylinders operating with conventional timing and wherein the last three columns operate with SIP timing. The figure shows a clear difference in the discharged oil (difference in the amount between the first three cylinders and the last three cylinders), which in turn shows that the lubricating oil supplied as the first part (SIP principle) produces less discharged oil.

In fig. 8, it is shown how the cylinder wears differently in the longitudinal direction when SIP lubrication is used. In this figure, a combination with the average oil film thickness is made in order to indicate the relationship between the oil film thickness and the wear. In the figure, the dashed line represents conventional lubrication, while the solid line represents SIP lubrication. The two upper curves a and B represent the wear rate every 1000 hours, while the two lower curves C and D represent the average of the values shown in fig. 6. At the same time, the figure shows that SIP lubrication generally reduces the wear level.

Fig. 9 shows a dispensing algorithm that starts with a fixed amount of lubricating oil being supplied on or under the piston. The different lines numbered 1 to 10 show which percentage of distribution is required at 100% load.

It is shown from the figure that a fixed fraction of 20% of the total stroke (at 100% engine load) is supplied as the second or third fraction, for example by means of the line marked "2" in the figure. Meanwhile, the graph predicts the application of load adjustment of the amount of lubricating oil. This means that the total stroke is reduced when operating at engine loads below 100%. For example, for a 50% engine load, only 50% of the full load amount of lubricating oil is used. The load-regulated quantity of lubricating oil then means that for a defined fixed quantity delivered as second or third portion, the lubricating oil distribution will take this into account. In the example, there is a fixed portion of 20% of the total stroke for 100% engine load, which means that the lubricating oil distribution is changed so that up to 50% of the lubricating oil is delivered as the second or third portion.

If operating without any reduction in the amount of lubricating oil (other than a reduction in rotation), a fixed amount of oil fed on or under the piston may be defined as a fixed fraction represented by a constant percentage value.

Fig. 10 shows a different allocation algorithm. Here, the basis is taken to keep a fixed portion of the lubricating oil fed on or under the piston and to make a correction after proportionally reducing the amount of lubricating oil by a so-called MEP adjustment.

It is shown that MEP adjustment according to the curve shown in fig. 10 implies a small change in percentage distribution.

FIG. 11 shows an example of a distribution algorithm that utilizes different sulfur content in the fuel supplied to the engine; depending on the sulphur content in the supplied fuel, one can vary the first part of the lubricating oil, i.e. the part of the lubricating oil that is supplied directly to the cylinder wall above the piston during the upward movement of the piston. A variation may be made to increase the first part of the lubricating oil supplied directly to the cylinder wall above the piston during upward movement of the piston by a higher sulphur content. In this way, the amount of lubricating oil at the top of the cylinder is increased, thereby achieving improved neutralization of a relatively greater amount of acid formed due to the higher sulfur content in the feed fuel. In the figure, two different lubricating oil feed amounts are shown, but a variation of the lubricating oil distribution can be achieved both in dependence of the lubricating oil feed amount and independently of the lubricating oil feed amount.

Fig. 12 and 13 depict a design known per se from the above mentioned EP 2044300.

Fig. 12 schematically shows four cylinders 250 with eight injection nozzles 251 on each cylinder. The lubricating apparatuses 252 are connected to a central computer 253, which central computer 253 has a local control unit 254, which local control unit 254 is typically used for each individual lubricating apparatus 252. The central computer 253 is coupled in parallel with a further control unit 255, which control unit 255 constitutes a backup for the central computer. In addition, a monitoring unit 256 that monitors the pump, a monitoring unit 257 that monitors the load, and a monitoring unit 258 that monitors the position of the crankshaft are established.

In the upper part of fig. 12, a hydraulic station 259 is shown, which hydraulic station 259 comprises a motor 260, which motor 260 drives a pump 261 in a tank 262 for hydraulic oil. The hydraulic station 259 furthermore comprises a cooler 263 and a filter 264. System oil is pumped via supply line 265 to the lubricating apparatus via valve 220. Furthermore, the hydraulic station is connected to a return line 266, which return line 266 is also connected to the lubricating apparatus via a valve.

Lubricating oil is carried from a lubricating oil supply tank (not shown) to lubricating apparatus 252 via line 267. The lubricating oil is carried from the lubricating apparatus via line 110 to the injection nozzle 251.

Via the local control unit one can adjust the amount of lubrication oil (in the form of frequency and stroke) and the injection timing. The adjustment of the injection time and amount can be made automatically by varying the operating state based on various lube oil adjustment algorithms (e.g. load dependent lube oil reduction) and a distribution key for the injection time (thereby changing the ratio between the first, second and third parts). These changes can be made based on engine load and conditions and directly or indirectly on parameters necessary for the cylinder conditions, such as rotation, cylinder liner temperature, engine load, amount of fuel injected, amount of lubricating oil, viscosity of lubricating oil, TBN content of lubricating oil, analysis results for discharging waste oil (residual TBN, Fe-content, etc.).

Fig. 13 shows an embodiment of the lubricating apparatuses for use with the method according to the invention.

The lubricating apparatus comprises a bottom part 110 where solenoid valves 115 and 116 are mounted for actuating the apparatus. At the side of the bottom part 110, there are nipples for system oil pressure supply 142 and system oil pressure return to the oil tank 143.

The driving oil may be provided by means of two solenoid valves, one of which is a primary solenoid valve 116 and the other of which is a secondary solenoid valve 115.

In the initial position, the primary solenoid valve 116 is active. The oil thus driven is led from the relative feed screw socket 142 to the primary solenoid valve 116 and via the on-off valve 117 into the apparatus, through the distribution channel 145 to the relative group of hydraulic pistons.

In the event of a failure of the primary solenoid valve 116, the secondary solenoid valve 115 may be automatically connected. The valve is connected by actuating the secondary solenoid valve 115.

Thereby pressurizing the associated dispensing passage 146. This pressure causes the on-off valve 117 to move to the right, thereby interrupting the connection between the primary solenoid valve 116 and the associated dispensing passage 145. Thereby removing pressure from the hydraulic pistons that are connected to the solenoid valve 116.

By actuating the secondary solenoid valve 115, the associated distribution channel 146 and the associated hydraulic piston are pressurized. This causes the distributor plate 7 to be subsequently driven by the oil, which is led into the apparatus via the secondary solenoid valve 115.

The on-off valve 117 may be equipped with a spring 119. In the absence of supply pressure through the secondary solenoid valve, the spring will thus automatically place the on-off valve 117 back to the above initial position.

The switching valve may be equipped with a restrictor so that this return of the switching valve can be delayed. In this way, the on-off valve 117 is prevented/limited from reciprocating back and forth between actuations. In fig. 12, the throttling is determined by a groove formed between the discharge pin 118 and the on-off valve 117.

When each of the solenoid valves is connected to a separate set of hydraulic pistons, independence between the solenoid valves is ensured. When switching between the primary solenoid valve 116 and the secondary solenoid valve 115, the on-off valve 117 will ensure that pressure is removed from the primary hydraulic piston set and thereby enable the secondary solenoid valve 115 to operate, even in situations where the primary solenoid valve is deactivated.

Position 121 shows an occlusion screw (blanking screw).

Position 122 shows a combined blocking screw/end stop which partly functions as an end stop for the pawl 120 of the on-off valve 117 and partly has a sealing function also via (not shown) seals (packing).

Above the hydraulic pistons 6 a distributor plate 7 is provided. The plate is here shown as a two-part design with an upper distribution plate part 125 and a lower distribution plate part 123. The metering piston 21 is mounted in/on the upper distributor plate part 125. In equipment where various oils are used for drive and lubrication, a piston seal 124 is provided between the upper and lower distributor plate members. In principle, one can also suffice to use one oil for the drive oil and for the lubricating oil.

Around the metering piston 21 there is a normal return spring 9, which normal return spring 9 returns the piston 21 after the supply pressure on the hydraulic piston 6 is released. Around the return spring 9, a small lubricating oil reservoir 147 is provided, which lubricating oil reservoir 147 is delimited externally by the base body 111. The lubrication oil is supplied through a separate threaded socket having seals 138 and 139. The device may optionally be equipped with a venting screw (venting screw) having seals 15 and 16.

Above the base body 111, a cylinder block 112 is arranged, where the metering pistons 21 are arranged for their reciprocating movement. Above the metering piston 21 a pump chamber 148 is provided. An outlet is provided in the chamber, the outlet having a check valve ball 13, the check valve ball 13 being biased by a spring 14. Furthermore, a threaded socket 128 is provided, which threaded socket 128 is directly connected to the check valve/SIP valve in the cylinder wall.

To adjust the stroke, in this embodiment, a device is shown having a motor 132, the motor 132 being coupled to a worm drive 131, the worm drive 131 adjusting the stroke by changing the position on the dowel pin/set screw 66 via the worm gear 130.

In this embodiment, the stroke may be adjusted by changing the position of the stroke stop. This is different from the previous embodiment where a fixed origin point is used and the stroke is subsequently adjusted.

To control the actual stroke length, a sensor/pick-up unit 114, for example in the form of an encoder or potentiometer, is mounted in the continuation of the positioning pin/screw 66 in order to detect the stroke.

Position 113 shows the housing for the dowel/set screw arrangement.

Position 124 shows the piston seal between the two voids 149 and 147, keeping the leakage oil out of the way (bypass) of the hydraulic piston 6 at the drive oil side at the bottom and the lubrication oil at the top, respectively.

Position 127 shows the O-ring seal between the base body 111 and the cylinder block 112.

Position 133 shows a fastening screw which is used to fasten the bearing housing for the worm wheel 130.

Location 134 shows an O-ring seal between the bottom plate 110 and the base body 111.

Claims (32)

1. Method for lubricating cylinders in a large diesel engine, wherein the injection of lubricating oil is performed via a plurality of injection units, which injection units correspond to multiples of the number of cylinders in the engine, wherein the lubricating oil is supplied in an injected combination of at least two parts of lubricating oil, wherein the at least two parts of lubricating oil are delivered at least two different piston positions, wherein the at least two different piston positions are selected among the piston positions used for injection before, during and after the piston passes beside the injection unit, wherein the lubricating oil is supplied by a combination of: injecting a first portion of the lubricating oil directly onto the annular region of the cylinder wall above the piston before the piston passes; and injecting the second and third portions of lubricating oil when the second portion of lubricating oil is injected directly onto the piston during passage of the piston and when the third portion of lubricating oil is injected directly onto the annular region of the cylinder wall below the piston after passage of the piston, characterized in that detection of an indirect or direct parameter for the actual cylinder load is performed and a distribution between the first and second portions of lubricating oil is performed such that the second portion is increased proportionally to the reduced cylinder load.

2. The method of claim 1, wherein the injecting of the first portion of the lubricating oil occurs immediately prior to and in association with the upward passage of the piston through the annular region.

3. Method according to claim 1 or 2, characterized in that the injection of the second part of the lubricating oil is performed in connection with the upward passage of the piston and on the area between the uppermost and the lowermost piston ring of the piston.

4. Method according to claim 1 or 2, characterized in that the same injection unit is used for injecting each of the respective injection portions of lubricating oil.

5. Method according to claim 1 or 2, characterized in that the injection of the first part of the lubricating oil takes place at high pressure by means of injection units for forming a complete or partial atomization of the lubricating oil immediately before the piston passes upwards through the annular area.

6. Method according to claim 1 or 2, characterized in that the injection of the second and/or third part of the lubricating oil takes place at high pressure by means of injection units for forming a complete or partial atomization of the lubricating oil.

7. A method according to claim 1 or 2, characterized in that the second and/or third part of the lubricating oil constitutes at least 10% of the total amount of lubricating oil.

8. Method according to claim 1 or 2, characterized in that the position and movement of the piston are detected directly or indirectly and the timing of the delivery of the lubricating oil, the adjustment of the amount of lubricating oil and the determination of the injection characteristic are carried out.

9. A method according to claim 1 or 2, characterized in that the method comprises computerized control, monitoring and/or detection in the operation of the method.

10. Method according to claim 1, characterized in that an electronic control device is provided, the time of lubricating oil injection being used as a parameter for adjusting the distribution of lubricating oil in the longitudinal direction of the cylinder, and that the electronic control device automatically distributes different portions of lubricating oil over the at least two different piston positions.

11. The method of claim 10, wherein a fixed percentage of the lubricating oil:

-feeding on the cylinder piston during its passage upwards or downwards, when the latter passes by the injection unit; or

-feeding directly on the cylinder wall below the piston after the piston has passed the injection unit during the upward movement of the piston; or

-feeding directly on the cylinder wall during the downward movement of the cylinder piston, before the cylinder piston passes through the injection unit.

12. The method of claim 10, wherein a fixed amount of lubricating oil:

-feeding on the cylinder piston during its passage upwards or downwards, when the latter passes by the injection unit; or

-feeding directly on the cylinder wall below the piston after the piston has passed the injection unit during the upward movement of the piston; or

-feeding directly on the cylinder wall during the downward movement of the cylinder piston, before the cylinder piston passes through the injection unit.

13. Method according to claim 10, characterized in that off-line or on-line wear measurements are made on the cylinder wall and these wear measurements are used for correcting the distribution.

14. Method according to claim 10, characterized in that off-line or on-line oil film thickness measurements are made on the cylinder wall and these are used for correcting the distribution.

15. A method according to claim 10, characterised in that the distribution between the lubricating oil of the at least two portions is made directly or indirectly dependent on the actual sulphur content in the fuel supplied to the cylinder.

16. The method of claim 1, wherein the large diesel engine is a marine engine.

17. Method for lubricating cylinders in a large diesel engine, wherein the injection of lubricating oil is performed via a plurality of injection units, which injection units correspond to multiples of the number of cylinders in the engine, wherein the lubricating oil is supplied in an injected combination of at least two parts of lubricating oil, wherein the at least two parts of lubricating oil are delivered at least two different piston positions, wherein the at least two different piston positions are selected among the piston positions used for injection before, during and after the piston passes beside the injection unit, wherein the lubricating oil is supplied by a combination of: injecting a first portion of the lubricating oil directly onto the annular region of the cylinder wall above the piston before the piston passes; and injecting the second and third portions of lubricating oil when the second portion of lubricating oil is injected directly onto the piston during passage of the piston and when the third portion of lubricating oil is injected directly onto the annular region of the cylinder wall below the piston after passage of the piston, characterized in that detection of an indirect or direct parameter for the actual cylinder load is performed and a distribution between the first and third portions of lubricating oil is performed such that the third portion is increased proportionally to the reduced cylinder load.

18. The method of claim 17, wherein the injecting of the first portion of the lubricating oil occurs immediately prior to and in association with the upward passage of the piston through the annular region.

19. Method according to claim 17 or 18, characterized in that the injection of the second part of the lubricating oil is performed in connection with the upward passage of the piston and on the area between the uppermost and the lowermost piston ring of the piston.

20. Method according to claim 17 or 18, characterized in that the same injection unit is used for injecting each of the respective injection portions of lubricating oil.

21. Method according to claim 17 or 18, characterized in that the injection of the first part of the lubricating oil takes place at high pressure by means of injection units for forming a complete or partial atomization of the lubricating oil immediately before the piston passes upwards through the annular area.

22. Method according to claim 17 or 18, characterized in that the injection of the second and/or third part of the lubricating oil takes place at high pressure by means of injection units for forming a complete or partial atomization of the lubricating oil.

23. A method according to claim 17 or 18, characterized in that the second and/or third part of the lubricating oil constitutes at least 10% of the total amount of lubricating oil.

24. Method according to claim 17 or 18, characterized in that the position and movement of the piston are detected directly or indirectly and the timing of the delivery of the lubricating oil, the adjustment of the amount of lubricating oil and the determination of the injection characteristic are carried out.

25. A method according to claim 17 or 18, characterized in that the method comprises computerized control, monitoring and/or detection in the operation of the method.

26. Method according to claim 17, characterized in that an electronic control device is provided, the time of lubricating oil injection being used as a parameter for adjusting the distribution of lubricating oil in the longitudinal direction of the cylinder, and that the electronic control device automatically distributes different parts of lubricating oil over the at least two different piston positions.

27. The method of claim 26, wherein a fixed percentage of the lubricating oil:

-feeding on the cylinder piston during its passage upwards or downwards, when the latter passes by the injection unit; or

-feeding directly on the cylinder wall below the piston after the piston has passed the injection unit during the upward movement of the piston; or

-feeding directly on the cylinder wall during the downward movement of the cylinder piston, before the cylinder piston passes through the injection unit.

28. The method of claim 26, wherein a fixed amount of lubricating oil:

-feeding on the cylinder piston during its passage upwards or downwards, when the latter passes by the injection unit; or

-feeding directly on the cylinder wall below the piston after the piston has passed the injection unit during the upward movement of the piston; or

-feeding directly on the cylinder wall during the downward movement of the cylinder piston, before the cylinder piston passes through the injection unit.

29. Method according to claim 26, characterized in that off-line or on-line wear measurements are made on the cylinder wall and these wear measurements are used for correcting the distribution.

30. Method according to claim 26, characterized in that off-line or on-line oil film thickness measurements are made on the cylinder wall and these are used for correcting the distribution.

31. A method according to claim 25, characterised in that the distribution between the lubricating oil of said at least two portions is made directly or indirectly depending on the actual sulphur content in the fuel supplied to the cylinder.

32. The method of claim 17, wherein the large diesel engine is a marine engine.