GB2345738A

GB2345738A - I.c. engine cylinder lubricating system and connecting member

Info

Publication number: GB2345738A
Application number: GB0000941A
Authority: GB
Inventors: Erik Rosenlund Hansen; Otto Winkel; Ole Christensen; Ole Rosler Sorensen; Per Aaes Christoffersen
Original assignee: MAN B&W Diesel GmbH; MAN B&W Diesel AS
Current assignee: MAN B&W Diesel GmbH; MAN B&W Diesel AS
Priority date: 1999-01-18
Filing date: 2000-01-14
Publication date: 2000-07-19
Anticipated expiration: 2020-01-14
Also published as: JP2000213322A; FI113488B; DK199900056A; GB0000941D0; KR20000076469A; FI20000083A0; DE10001518B4; GB2345738B; KR100405373B1; CN1261644A; DK173533B1; FI20000083A; DE10001518A1; CN1125237C; JP3411874B2

Abstract

The cylinder 1 of the engine, eg a low-speed, two-stroke, crosshead engine, is lubricated by means of a at least one lubrication unit 10 supplying oil to lubrication point(s) 11 on the cylinder. An electronic control unit 17 controls the lubrication units 10 on the basis of the varying cylinder pressures at the current operating mode of the engine. Each lubrication unit 10 is associated with a pressure sensor 14 arranged at diametrically opposed lubrication points. The pressure data may be saved and analyzed. A correcting member, fig. 10, comprises a housing 33 with a channel 32 between a connection 31 for the lubricating pipe 12 and a discharge opening 34. The channel 32 has a non-return valve 35. A pressure sensor 36, eg a strain gauge, is located in connection with the channel 32.

Description

A METHOD OF LUBRICATING A CYLINDER IN AN INTERNAL COMBUSTION ENGINE, AND A CYLINDER LUBRICATING SYSTEM AND A CONNECTING MEMBER The present invention relates to a method of lubricating a cylinder of an internal combustion engine, in which at least one lubrication unit for supply of lubricating oil to at least one lubrication point on the cylinder is controlled electronically by means of an associated control unit.

Such method is known from the applicant's Danish patent application No. 1119/96, in which the lubrication unit has an actuator piston driving several dosing pistons in a common movement for lubrication of a number of lubrication points on the cylinder every time the lubrication unit is actuated by the electronic control unit. The hydraulically driven lubrication unit is fastacting and supplies the lubricating oil to the lubrication points at an advantageously high lubricating oil pressure.

For a number of years it has been desired to deliver the lubricating oil in the cylinder just when the piston passes the lubrication point, vide, for example Danish patent No. 81275 from 1954, Swiss patent No. 406 735 from 1966, German patent publication No. 28 27 626 from 1979 and European patent No. 0 678 152 from 1997.

In practice it has proved extremely difficult to realize this desire because many factors influence the actual time of delivery of the lubricating oil. A few examples can be given. The delay between actuation of the lubrication unit and delivery of the oil at the lubrication point depends on, i. a., the viscosity of the oil. The actual delay is an absolute time interval, while the delay for obtaining correct lubrication varies with the rpm of the engine. In the known, electronically actuated lubrication units, the actuation is made on the basis of the angular position of the crankshaft. During operation, the crankshaft twists more or less depending on the current load of the engine and on the distance of the cylinder in question from the signalling device that detects the rotational movement of the shaft, which introduces varying inaccuracies in the time of lubrication.

The object of the present invention is to improve delivery of the lubricating oil to the at least one lubrication point in the cylinder.

In view of this object, the method according to the invention is characterized in that actuation of the lubrication unit during one or more engine cycles is controlled by the electronic control unit on the basis of measurement of the varying cylinder pressures in the cylinder while the engine is running.

Measuring of the actual cylinder pressures in the cylinder provides a true view of the current piston movements, which is the basis for being able to deliver the lubricating oil during the very short period when the piston passes the lubrication point or lubrication points. The measurements provide the electronic control unit with information on the time when the piston passes the lubrication point, and on the time interval between each passage. Based on these data and any stored information on the desired dosing volume and on the delay from the actuation signal is sent until the lubricating oil is actually supplied to the lubrication point, the control unit calculates when the next actuation signal is to be given. As the varying cylinder pressures are measured while the engine is running at the mode of operation relevant in terms of lubrication, the current data are continuously updated and thus continuously adapted to the time of actuation according to the current piston movements in the cylinder.

It is possible to measure the cylinder pressure by means of techniques well-known in the art, such as strain gauges mounted on the cover studs of the cylinder cover, but such measurement of the general pressure level in the cylinder provides only a relatively rough indication of the current position and movement of the piston.

Preferably, the pressure variations generated by the passage of piston rings on a piston in the cylinder past a pressure measuring point are measured at the pressure measuring point in the cylinder, and these pressure measurements are used in connection with control of the actuation time of the lubrication unit.

Pronounced, characteristic pressure changes occur when the piston rings pass the pressure measuring point, and the pressure changes are local to the area immediately around the piston rings. This provides a very accurate measurement of the current position of the piston and thus an accurate starting point for the determination by the control unit of the actuation of the lubrication unit.

In an especially advantageous embodiment according to the invention, the varying cylinder pressures and lubricating oil pressures are measured at the lubrication point. This provides a number of advantages. The measurement provides information on the cylinder pressure at the lubrication point, thus obviating the need for the control unit to compensate in time for the piston movement between the measuring and lubrication points, which time correction varies with the rpm of the engine. Furthermore, the same measuring point provides information on the precise time of delivery of the lubricating oil at the lubrication point because this delivery results in a clear increase in the pressure measured. Such measurement of the actual delivery time of the lubricating oil prevents the known problems of predicting variations in the delay between actuation of the lubrication unit and arrival of the lubricating oil to the lubrication point.

Another advantage is that between the pressure sensor and the gases in the cylinder there is a protective amount of lubricating oil that has a cooling effect and ensures reasonably uniform operating conditions for the pressure sensor. Furthermore, the supply of lubricating oil has a cleaning effect in the area around the pressure sensor and ensures removal of residual products from the combustion if they are deposited at the pressure sensor.

Actuation of the lubrication unit can suitably depend on the current operating condition or operating mode of the cylinder. Monitoring of the operating condition may be based on a well-known system, such as an anti-scuffing system and/or measurement of selected operating temperatures of the cylinder, but preferably, during an operating period, the lubrication unit is actuated a smaller number of times than the number of engine cycles in the operating period, and the control unit is supplied with pressure measuring data for analysis of the operating condition of the piston rings based on pressure measurements during the engine cycles in which the lubrication unit is inactive. When the lubrication takes place at correct timing in relation to the piston movement, a pressure sensor arranged in the lubrication point cannot measure pressure data that can be used for determination of the operating condition of the rings during engine cycles with lubrication, because as a consequence of the lubrication the pressure increase"drowns"the small pressure changes that indicate incipient operating problems. Omission to lubricate the cylinder during every engine cycle renders it possible for the pressure measurements from the engine cycles without lubricating oil supply to be applicable for analysis of the operating condition of the piston rings. The longer intervals between each actuation of the lubrication unit furthermore provide the advantage that the volume of lubricating oil per actuation becomes larger, which promotes good lubrication because the larger amount of lubricating oil is distributed more efficiently along the circumference of the cylinder.

The operating condition monitoring allows reference data on the varying cylinder pressures that indicate the normal operating condition of the cylinder to be stored in the control unit while the engine is running. When a new engine has been run in, the reference data on each cylinder can be recorded and stored so that they can subsequently be used as a basis of comparison of whether the currently measured operating data indicate a normal operating condition or an abnormal condition that requires a change in operating parameters, such as increased dosage of lubricating oil. As the reference data are established for each cylinder on the basis of its actual operating situation, even small deviations from normal operation can be ascertained. The operating condition monitoring can therefore give warning of an abnormal operating situation at a far earlier time than prior-art anti-scuffing systems based on detection of abnormal temperature increases in the cylinder wall.

Preferably, the reference data on the normal operating condition of the cylinder are updated by the control unit to compensate for long-term changes in the varying cylinder pressures resulting from normal cylinder wear. Such updating, which can be effected periodically, improves the possibility of the control unit of detecting small deviations from the normal operating condition.

The operating condition monitoring automatically gives notice whether the pressure drops across the individual piston rings are normal, which indicates normal operation. Moreover, if desired, it is possible to obtain a very advantageous monitoring of whether the piston rings rotate about the longitudinal axis of the piston, as reference data on the transient changes in the varying cylinder pressures caused by the periodical passage of a ring gap in a piston ring past the pressure measuring point can be included in the reference data of the control unit on the normal operating conditions of the cylinder. On the basis of this, the operating condition monitoring can record at what frequency each piston ring is rotating, and if the frequency for a piston ring drops at continuous engine operation, the control unit can signal that the piston ring is showing signs of getting stuck in the associated annual groove.

Preferably, the control unit controls the lubrication unit for temporary dosing of more lubricating oil if the measurements of the varying cylinder pressures indicate an abnormal operating condition for the cylinder, including the piston, piston rings or cylinder liner. Often, the temporary extra lubricating oil dosing will be sufficient to re-establish the normal operating condition. At indication of deviations from the normal operating condition, the control unit can notify the operating staff or a central control unit that the operating conditions are changing. This may give very early warning to the effect that the cylinder should be checked and possibly repaired, and on this basis any spare parts can be ordered, and the check-up planned.

For the engine cylinders, this may allow the usual periodical routine checks to be replaced by checks based on the actual operating situation of the cylinder. The check may be either of a preventive nature when the control unit indicates a possible future operating disturbance that may be prevented from developing by early intervention, or may be necessary due to actual fault-reporting of a cylinder.

Conventionally, dosing of the lubricating oil is set by predetermined minimum doses of lubricating oil being determined on the basis of operating experience from many engines at normal continuous operation at maximum continuous rating (100 per cent engine load).

These standard doses are sufficiently large to compensate for the variations in lubrication due to manufacturing tolerances in the lubricating system and the cylinder members.

The present invention provides a suitable possibility of obtaining substantial savings on the consumption of lubricating oil in that the control unit automatically detects the requisite minimum dosage of lubricating oil to the cylinder by reducing the dosage until the varying cylinder pressures measured indicate that the operating condition of the cylinder begins deviating from the normal operating conditions. Thus, the minimum dosage for the cylinder in question is the dosage used a suitable period before the deviation from the normal operating condition occurred.

It is possible to use a lubrication unit which is capacity-adjusted by varying the dosing volume per actuation and then actuating the dosing unit at a specific frequency in relation to the engine cycles.

Alternatively, a lubrication unit can be used that doses the same volume per actuation, and the dosing of lubricating oil by the lubrication unit is then varied by varying the number of engine cycles passing between each actuation of the lubrication unit. This form of actuation of the lubrication unit provides the advantage that the dosing volume of the individual actuation may be a volume sufficiently large to ensure good distribution of the lubricating oil in the cylinder.

In an optional further development thereof, the control unit has information on a number of standard groups of engine cycles in which a single actuation of the lubrication unit is effected for each group, and the amount of lubricating oil dosed by the lubrication unit is varied by changing the composition of consecutive standard groups of engine cycles. There may, for example, be standard groups of 3,4,5 and 6, etc., engine cycles, each with a single actuation of the lubrication unit, and over an operating period of, for example, 500 engine cycles it is possible to obtain continuous variation of the dosing volume by selecting a suitable combination of consecutive standard groups.

If, for example, only the standard group with one actuation per four engine cycles is used at an operating mode, the dosing may be reduced slightly by selecting a standard group with five engine cycles after every fourth standard group of four engine cycles. In terms of control engineering, this is extremely simple to manage in the control unit.

In a design which makes few demands on mechanical equipment and is thus advantageous to implement on an engine in terms of cost, especially in case of a retrofit of an already existing engine not already provided with equipment for detecting the rotational movement of the crankshaft, the method is characterized in that the control unit actuates the lubrication unit at a random time during an engine cycle immediately upon start of the engine, and that the control unit adjusts the actuation timing of the lubrication unit during an engine cycle on the basis of measurements of the varying cylinder pressures in the cylinder, so that the lubricating oil runs out at the lubrication point while the ring pack of the piston is opposite to the lubrication point during the upward stroke of the piston. After a very short operating period the control unit knows, on the basis of the measurements of the varying cylinder pressures, when the piston passes the lubrication point, and then actuation of the lubrication unit can be adjusted in a simple manner so that delivery of the lubricating oil occurs when the piston passes the lubrication point.

The present invention also relates to a cylinder lubricating system for an internal combustion engine, having at least one lubrication unit for supply of lubricating oil to at least one lubrication point on the cylinder and having a control unit for electronic control of the lubrication unit. The cylinder lubricating system is characterized in that it comprises at least one pressure sensor for measuring varying cylinder pressures in the cylinder, and that the control unit receives pressure measuring data on the pressure variations in the cylinder at the pressure sensor via a data input. This system allows collection of data for the purpose of analyzing the operating condition of the cylinder and adjusting the actuation of the lubrication unit, which can be used to obtain the above advantages.

The pressure sensor can advantageously be arranged in the side of the cylinder and measure the pressure at a running surface area which the piston rings pass during each engine cycle, the local pressure variations around the piston rings providing information on the operating condition for each individual ring.

In a suitable embodiment, the control unit comprises an intelligent, self-learning program for processing pressure measuring data, such as a neural network and/or a program with generic algorithms or fuzzy logic. On the basis of measured data from the cylinder during operation and of predetermined information on typical error conditions, such program can detect small deviations from normal operation and give early warning of an incipient error condition.

Furthermore, the invention relates to a connecting member for mounting at a lubrication point on a cylinder in an internal combustion engine and comprising a housing for insertion into a bore in the cylinder wall and a channel formed in the housing and extending from a connection for a lubricating pipe to a discharge opening at the lubrication point and containing a nonreturn valve which opens towards the discharge opening.

The connecting member is characterized in that a pressure sensor communicates with the channel section extending from the non-return valve to the discharge opening. When the connecting member is mounted on a cylinder, the pressure sensor is thus in permanent communication with the area located inside the cylinder at the lubrication point. The pressure sensor may be incorporated in the housing of the connecting member.

The invention will now be described in more detail below with reference to the highly schematic drawing, in which Fig. 1 shows a partially sectional view of a cylinder formed in accordance with the invention, Fig. 2 is another embodiment of a lubricating system according to the invention, Figs. 3-6 are diagrams of measured pressure sequences in a cylinder during a compression stroke, Fig. 7 is a diagram of a measured pressure sequence in the same cylinder during an expansion stroke, Figs. 8 and 9 schematically show data processing sequences, and Fig. 10 is a side view of a connecting member according to the invention.

A cylinder 1 indicated in Fig. 1 of an internal combustion engine comprises a cylinder liner 2, a cylinder cover 3 with an exhaust valve 4 and a piston 5 mounted on top of a piston rod 6. On its outer surface, the piston has a number of annular grooves with piston rings 7. The number of piston rings may vary with the engine type, but typically there are at least three and at the most six piston rings. To provide correct sealing, the rings must be able to move in the associated annular grooves, and the ring movements normally include both a displacement up and down in the annular groove and a rotation about the longitudinal axis 8 of the piston.

The cylindrical inner surface of the cylinder liner 2 constitutes a running surface 9 for the piston rings.

The lower end of the running surface is located at the lower edge of the bottom-most piston ring at the bottom dead centre of the piston, and the upper end of the running surface is located at the upper edge of the top piston ring in the top dead centre of the piston. The piston rings and the cylinder liner only function correctly if a suitable supply of lubricating oil is provided continuously to the running surface. In a crosshead engine, an intermediate bottom separates the sump in the bedplate from the cylinders so that separate cylinder lubrication is required, which is carried out by a lubrication unit 10, for example of the type described in the applicant's German patent publication DE-A 19743955, in which an electronically actuated and hydraulically driven actuator drives a number of dosing pistons in a common delivery stroke, or, for example, a mechanically driven pump in combination with electronic release of each dosing volume of lubricating oil as described in EP-B 0 678 152.

The lubrication unit 10 can supply lubricating oil to several lubrication points 11 on the same cylinder or on several cylinders. In the latter case, the lubrication unit is actuated at timings adapted to one and the other cylinder, respectively. Large engines will typically have at least one lubrication unit per cylinder, and the lubrication points connected to the lubrication unit will typically be located at the same longitudinal position (level) in the cylinder liner, but spaced along its circumference. If lubrication is desired at several levels and/or lubrication with more than one type of lubricating oil, typically more lubrication units per cylinder will be used.

The internal combustion engine may be a low-speed, two-stroke crosshead engine with a maximum rpm in the range of 60-275 rpm, an output per cylinder in the range of 300-6000 kW, a cylinder bore in the range of 25-100 cm and a stroke in the range of 90-300 cm. The invention may also advantageously be used for four-stroke engines with pressure lubrication of the cylinders.

The lubrication unit 10 is connected with the lubrication points 11 via conduits or lubricating pipes 12, and near the lubrication point there is a non-return valve 13, which only permits flow to the lubrication point and prevents the relatively high cylinder pressure during the working stroke from spreading to the lubrication unit. When the lubricating oil is delivered to the lubrication point on the cylinder side of the non-return valve, the lubricating oil pressure exceeds the current pressure in the cylinder at the lubrication point. The lubrication point may, for example, be located so that this cylinder pressure will be in the range of from 5 to 30 bar, which permits the use of a pressure sensor that measures over a relatively small pressure interval and has a genuine zero, i. e., a pressure sensor without signal amplification.

Between at least one of the lubrication points and the associated non-return valve, a pressure sensor 14 (pressure pick-up) is connected which, due to its connection on the delivery side of the non-return valve, measures the cylinder pressure immediately at the lubrication point. A signal wire 15 from the pressure sensor 14 transmits pressure measuring date to. a data input 16 in a control unit 17 which determines, on the basis of the measuring data and any stored data, when the lubrication unit is to be actuated, and accordingly gives a control signal via a signal wire 18 to the lubrication unit 10, which is supplied with lubricating oil through a conduit 19. Fig. 1 indicates that the control unit 17 controls two lubrication units 10 that may both lubricate the same cylinder. The timing of the actuation of the lubrication unit in relation to the piston movement only requires use of a single pressure sensor 14, but preferably at least one pressure sensor is used for each lubrication unit 10 because this allows control of the correct functioning of each of the lubrication units.

For the sake of simplicity, the following description of other embodiments utilises the same reference numerals as are used above for details of the same type.

Fig. 2 shows a cylinder in an engine having an embodiment with two lubrication units 10 per cylinder, the lubrication points 11 along the circumference of the cylinder being connected alternately to one and the other lubrication unit. Should one of the lubrication units fail, the other lubrication unit can be actuated to dose at least double of its normal lubricating oil volume and thus keep the cylinder in normal operation until the failure condition is remedied.

Each of the lubrication units 10 is associated with a pressure sensor 14 arranged at lubrication points that are mutually spaced in the circumferential direction and suitably diametrically opposite to each other. When the measuring data from the pressure sensors are used for condition analysis of the piston rings, cf. below, the two pressure sensors render it possible to ascertain in a simple manner whether a deviant pressure sequence measured at one pressure sensor is due to passage of a ring gap, which is ascertained by measuring a normal pressure sequence at the other pressure sensor, or whether it is due to a fault condition of the piston ring, which results in deviant pressure sequences at both sensors. The two sensors also improve operational reliability because correct operation of the lubrication units 10 can be maintained even though one pressure sensor fails. The operational reliability of the lubricating system can further be increased by making it possible for the lubrication units, as a back-up, to be controllable by another control unit, such as the control unit 10 associated with another cylinder of the engine. There may be one control unit 10 for each cylinder, or the control unit 10 may be common to a group of cylinders or to the entire engine.

The diagrams shown in Figs. 3-6 show pressure sequences measured as a function of time during the compression stroke of the piston in a turbocharged twostroke diesel engine. The pressure sensor is located at the lubrication point, and its zero is adjusted according to the charging air pressure. The piston has four piston rings. Fig. 3 shows a pressure sequence a measured during an engine cycle without supply of lubricating oil at the measuring point. The graph has a clear peak at b, which shows the time tl when the top piston ring passes the measuring point. Shortly afterwards, the graph has peaks c, d, e, which characteristically show the passage of the three other piston rings in the form of a small pressure increase followed by a noticeable pressure drop. After passage of the upward piston the cylinder pressure at the measuring point is seen to be largely unaffected by the substantially higher pressures present in the combustion chamber above the piston. If the measuring point is not located at the running surface in the cylinder, but measures, for example, the pressure load on the cylinder cover, global data on the piston position will be obtained, but not local data on pressure variations at the individual piston rings.

Figs. 4-6 show examples of measured pressure sequences f, g, and h, when the lubrication is too early, correct and too late, respectively. In all three cases, delivery of the lubricating oil to the lubrication point generates a marked pressure increase at a time t2, and the passage of the first piston ring a marked pressure drop at the time tl. It is desirable that lubricating oil is delivered during the period between tl and the time e for passage of the bottom-most piston ring. Such correct timing is shown in Fig. 5.

The pressure variations measured can be used for accurate adaptive control of the timing of the dosing of the lubricating oil in relation to piston passage, the control unit correcting actuation of the lubrication unit until the times tl and t2 substantially coincide.

Preferably, lubricating oil is delivered while at least the three uppermost piston rings pass the lubrication point, and the crossectional area of the outlet opening at the lubrication point preferably is adapted to the lubricating oil volume delivered per actuation of the lubrication unit so that this is obtained at maximum continuous rating. When the engine is running at low load, the piston moves more slowly past the lubrication point, and as the flow period of the lubricating oil is often kept unchanged, the control unit may actuate the lubrication unit with a periodical delay, for example at every second or third actuation, so that delivery at the lubrication point does not start until the first piston ring has passed. This ensures lubrication both at the top and the bottom of the ring pack of the piston.

When the lubricating oil is not delivered during passage of the piston past the measuring point on the running surface, it is possible, as shown in Fig. 3, to obtain detailed data on the condition of the piston rings, as the pressure drops at passage of each piston ring can verify the correct functioning of the rings.

Because the rings rotate in the annular grooves and the rings may have an inclined ring gap in which gas flows past the ring, periodical transient measuring data are generated for each ring resulting in pressure measurements according to which the pressure drop across the ring is substantially smaller than normal. As the piston ring rotates slowly, passage is effected during a number of engine cycles and with a recognizable course.

Fig. 7 shows a pressure sequence measured during the expansion stroke of the piston. The vertical line marked by i shows that the piston rings pass down past the pressure sensor, which is uncovered to the pressure in the combustion chamber, and after some introductory pressure fluctuations, the pressure drops in an even course down to the charging air pressure. In the control unit, this information on the pressure sequence at the current operating mode can be used to adjust the opening time of the exhaust valve.

In the electronic control unit 17, the pressure measuring data collected can be saved and analyzed, and an example of this in-a schematic form is shown in Fig.

8, where the information 20 transmitted via the signal wire 15 is stored in a step 21, possibly after filtering off undesired information. In a step 22 a suitable selection of the data is analyzed for determination of the time tl, and in a step 23 a corresponding determination of the time t2 is made, whereupon, in a step 24, the control unit determines by comparing the times tl and t2 whether a correction of timing or otherwise of the actu

The analysis in step 28 may be performed by means of an intelligent, self-learning program, such as a neural network and/or a program with generic algorithms or fuzzy logic. Programs of this type are known in the art for operating condition monitoring and analysis.

When an engine is delivered, the program may be trained and adjusted by means of standard operating and error modes for the cylinders of the engine type in question, and after running-in of the cylinders the program can, by analysis of the live information from pressure measuring data from the running engine, carry out final adjustment of the program and determine the reference data on the associated cylinder. When this has been done and the control unit runs in normal operation, a step 29 can determine information for the purpose of control of the engine and signals for actuation of the lubrication unit.

A connecting member 30 shown in Fig. 10 has a connection 31 for the lubricating pipe 12 which communicates with a discharge opening 34 via a channel 32 in the housing 33 of the connecting member. The channel 32 has a non-return valve 35, which opens towards the discharge opening. A pressure sensor 36 is located in connection with the channel 32 between the non-return valve and the discharge opening. The pressure sensor is a standard component and may, for example, comprise a strain gauge. It is, of course, possible to arrange the pressure sensor as an independent unit, but its incorporation with the connecting member provides good protection against harmful influences and easy installation, as a connecting member is normally required to pass a lubricating channel in through the cylinder wall, which may be a wall in a cylinder liner or walls in both a cylinder liner and a cooling jacket.

The internal combustion engine may also be a four-stroke engine and may have trunk pistons.

It will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Claims

PATENT CLAIMS

1. A method of lubricating a cylinder of an internal combustion engine, in which at least one lubrication unit for supply of lubricating oil to at least one lubrication point on the cylinder is controlled electronically by means of an associated control unit, c h a r a c t e r i z e d in that actuation of the lubrication unit during one or more engine cycles is controlled by the electronic control unit on the basis of measurement of the varying cylinder pressures in the cylinder while the engine is running

2. A method according to claim 1, c h a r a c- t e r i z e d in that the pressure fluctuations generated by the passage of piston rings on a piston in the cylinder past a pressure measuring point are measured at the pressure measuring point in the cylinder, and that these pressure measurements are used in connection with control of the actuation time of the lubrication unit.

3. A method according to claim 2, c h a r a c- t e r i z e d in that the varying cylinder pressures and lubricating oil pressures are measured at the lubrication point.

4. A method according to any one of claims 1-3, c h a r a c t e r i z e d in that during an operating period, the lubrication unit is actuated a smaller number of times than the number of engine cycles in the operating period, and that the control unit is supplied with pressure measuring data for analysis of the operating condition of the piston rings based on pressure measurements during the engine cycles in which the lubrication unit is inactive.

5. A method according to claim 4, c h a r a c- t e r i z e d in that reference data on the varying cylinder pressures that indicate the normal operating condition of the cylinder are stored in the control unit while the engine is running.

6. A method according to claim 5, c h a r a c t e r i z e d in that the reference data on the normal operating condition of the cylinder are updated by the control unit to compensate for long-term changes in the varying cylinder pressures resulting from normal cylinder wear.

7. A method according to any one of claims 4-6, c h a r a c t e r i z e d in that reference data on the transient changes in the varying cylinder pressures caused by the periodical passage of a ring gap c piston ring past the pressure measuring point can be included in the reference data of the control unit or the normal operating condition of the cylinder.

8. A method according to any one of claims 5-7, c h a r a c t e r i z e d in that the control unit controls the lubrication unit for temporary dosing oi more lubricating oil if the measurements of the varyinc cylinder pressures indicate an abnormal operatinc condition for the cylinder.

9. A method according to any one of claims 4-8, c h a r a c t e r i z e d in that the control unit automatically detects the requisite minimum dosage cd lubricating oil to the cylinder by reducing the dosage until the varying cylinder pressures measured indicate that the operating condition of the cylinder begins deviating from the normal operating condition.

10. A method according to any one of claims 4-9, c h a r a c t e r i z e d in that the dosing oi lubricating oil of the lubrication unit is varied b varying the number of engine cycles passing between eac} actuation of the lubrication unit.

11. A method according to claim 10, c h a r a ct e r i z e d in that the control unit has informatioi on a number of standard groups of engine cycles in which a single actuation of the lubrication unit is effected for each group, and that the volume of lubricating oil dosed by the lubrication unit is varied by changing the composition of consecutive standard groups of engine cycles.

12. A method according to any one of claims 1-11, c h a r a c t e r i z e d in that the control unit actuates the lubrication unit at a random time during an engine cycle immediately upon start of the engine, and that the control unit adjusts the time of actuation of the lubrication unit during an engine cycle on the basis of measurements of the varying cylinder pressures in the cylinder so that the lubricating oil runs out at the lubrication point while the ring pack of the piston is opposite to the lubrication point during the upward stroke of the piston.

13. A method according to any one of claims 1-12, c h a r a c t e r i z e d in that on the basis of the measurements of the varying cylinder pressures in the cylinder while the engine is running, the electronic control unit gives signals used for controlling at least one further operating parameter, such as the timing of the opening of the exhaust valve.

14. A cylinder lubricating system for an internal combustion engine, having at least one lubrication unit for supply of lubricating oil to at least one lubrication point on the cylinder and having a control unit for electronic control of the lubrication unit, c h a r- a c t e r i z e d in that it comprises at least one pressure sensor for measuring varying cylinder pressures in the cylinder and that the control unit receives pressure measuring data on the pressure variations in the cylinder at the pressure sensor via a data input.

15. A cylinder lubricating system according to claim 14, c h a r a c t e r i z e d in that the pressure sensor is arranged in the side of the cylinder and measures the pressure at a running surface area which the piston rings pass during each engine cycle.

16. A cylinder lubricating system according to claim 15, c h a r a c t e r i z e d in that the lubricating oil discharge of the lubrication unit is connected to the lubrication point via a lubricating oil conduit containing a non-return valve which cuts off the lubricating oil conduit from the cylinder pressure when the latter exceeds the lubricating oil pressure, and that the pressure sensor is arranged in connection with the lubricating oil conduit on the cylinder side of the non-return valve.

17. A cylinder lubricating system according to any one of claims 14-16, c h a r a c t e r i z e d in that the control unit comprises an intelligent, self-learning program for processing pressure measuring data, such as a neural network and/or a program with generic algorithms or fuzzy logic.

18. A connecting member for mounting at a lubrication point on a cylinder in an internal combustion engine and comprising a housing for insertion into a bore in the cylinder wall and a channel formed in the housing and extending from a connection for a lubricating pipe to a discharge opening at the lubrication point and containing a non-return valve which opens towards the discharge opening, c h a r a c t e r i z e d in that a pressure sensor communicates with the channel section extending from the non-return valve to the discharge opening.

19. A connecting member according to claim 18, c h a r a c t e r i z e d in that the pressure sensor is incorporated into the housing of the connecting member.

20. A connecting member substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

21. A cylinder lubrication system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

22. A method of lubricating a cylinder of an internal combustion engine substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.