WO2009015666A1

WO2009015666A1 - Lubricating apparatus and hydraulic piston for engine cylinder lubrication

Info

Publication number: WO2009015666A1
Application number: PCT/DK2008/000281
Authority: WO
Inventors: Peer Bak
Original assignee: Hans Jensen Lubricators A/S
Priority date: 2007-07-30
Filing date: 2008-07-29
Publication date: 2009-02-05
Also published as: JP2010534788A; KR20100051087A; CN101842560A; DK176924B1; DK200701104A; CN101842560B

Abstract

There is described a hydraulic lubricating apparatus and a hydraulic piston for a dosing system for cylinder lubrication oil, e.g. in marine engines. The lubricating apparatus includes at least on hydraulic piston (106) which may be pressurised by hydraulic oil, a number of dosing pistons (21) and a distributor plate (7) which at one side of it is in contact with the dosing pistons (21) and which at its other side is in contact with the at least one hydraulic piston (106) for displacing the distributor plate for actuating the dosing pistons. The hydraulic piston (106) is provided with an inner boring (B) extending in the direction of displacement of the hydraulic piston, the boring being provided with an insert (C5E) including an insert cylinder (C) in which is provided a hollow insert piston (E) in contact with a supply opening (H) for hydraulic oil. Hereby is achieved that the hydraulic piston (106) can be moved faster such that improved pressure and flow conditions and thus substantially enhanced pressure and flow in the atomising nozzles may be attained, and consequently improved performance of the lubricating system.

Description

Lubricating apparatus and hydraulic piston for engine cylinder lubrication

Field of the Invention

The present invention concerns a hydraulic lubricating apparatus for a dosing system for cylinder lubricating oil, for example in marine engines, the hydraulic lubricating apparatus being hydraulically powered for feeding lubricating oil and including at least one hydraulic piston, wherein the apparatus may be pressurised by hydraulic oil, the apparatus further including a number of dosing pistons and a distributor plate which at one side is in contact with the dosing pistons and which at its other side is in contact with the at least one hydraulic piston for displacing the distributor plate for actuating the dosing pistons.

Furthermore, the invention concerns a hydraulic piston for such a lubricating apparatus.

Background of the Invention hi traditional cylinder lubricating apparatuses, mainly for large two-stroke diesel engines, two or more central lubricating apparatuses are used, each providing lubrication at points in a single or a plurality of cylinders, i.e. by feeding portions of oil under pressure through respective connecting lines to the various points to be lubricated at relevant time intervals. See for example EP 0 678 152. These relevant intervals may typically be when the piston rings are provided opposite to the relevant point of lubrication during the compression stroke when the piston is moving upwards.

Lubricating apparatuses are traditionally designed as pumping units which are mounted in close association with respective cylinders and which are connected with a feeding reservoir for lubricating oil and with lubricating points in the form of oil injection nozzles at different points on the cylinder wall. Each pump unit includes a plurality of reciprocating pumps that feed various lubricating points with oil and which are driven by a common rotating control shaft with cams provided thereon. By the rotation of the shaft, the cams with pressing heads act on respective axially displacing pistons which are spring biased in direction towards the control shaft, so

# that the pistons at the rotation of the shaft will perform reciprocating movements for activating the pistons of the reciprocating pumps.

For many years, lubricating apparatuses have operated under the condition that the discharge pressure from the piston pumps was not to be very great, as it is a fixed Standard that the oil is to be injected into the cylinder during the upwards return stroke of the engine piston, i.e. during the compressing action, however before the subsequent power stroke by the ignited combustion. Hereby, it has been necessary to operate with injection or pump pressures of the magnitude 10 bar.

In recent years it has been proposed to increase the efficiency of the lubrication by injecting the oil through pressurised atomising nozzles for achieving oil mist lubrication during the upwards movement of the piston. However, hereby the oil is applied a far higher pressure for ensuring fine atomisation through atomising nozzles, e.g. a pressure up to 100 bar or more.

Furthermore, in recent years there has been a tendency that electronically based diesel engines are produced to a wider extent, and on these engines the mechanical drives traditionally used for driving mechanical lubricating apparatuses have been removed.

Lubricating points will thus, as mentioned in the present application, include oil injecting nozzles and/or pressurised atomising nozzles.

hi both systems, the control shaft is driven through a direct or indirect mechanical coupling with the crankshaft of the engine, whereby it is possible to provide power for the activation of pumps and at the same time to achieve synchronisation between the crankshaft of the engine and the control shaft of the lubricating apparatus.

A pump unit may e.g. include a box-shaped apparatus housing, from where connecting pipes extend to the lubricating points on the associated engine cylinder, e.g. in a number of 6-24. The pistons are traditionally operated by means of activation cams/rocker arms on a through-going control shaft which is rotated synchronously with the crankshaft of the engine. The pistons are spring biased towards the activation cams. There is provided a set screw defining the extreme position of an associated activation cam. The set screws may be operated for determining individual operative strokes of the pistons and thereby the associated yield of the individual piston pumps.

As the cylinder lubricating oil is typically to be dosed with one portion per engine revolution, the only possibility of adjusting the dosage is to change the stroke of the pumps. A system for this purpose is e.g. described in DK patent application 4998/85. This system is operated by a cam disk mechanism for adjusting the pump stroke in dependence on the engine load. Changing this dependence may only be effected by replacing the cam disks with other cam disks with a different transfer function.

It has also been proposed to adjust the pump stroke by means of a controllable motor, e.g. a step motor. This has been used for point lubrication, but it is difficult to establish in connection with conventional lubricating apparatuses. Such a system is e.g. disclosed in International patent application WO 02/35068 Al.

Furthermore, from DE 28 27 626 there is known a lubricating system based on lubricating oil supplied in measured quantities for predetermined time intervals through openings in the cylinder wall. Here, there is not indicated any possibility of a stepless controlling of the dosing to be performed at the individual lubricating points.

Furthermore, from GB 834533 A, DK 173512 Bl or CH 673506 A5 systems of the type mentioned in the introduction are known, where a hydraulic cylinder via a distributor plate or similar structure acts on a plurality of dosing pistons. In these designs, there will be one hydraulic cylinder for the activation. This will cause disruption of operation for all dosing pistons if the hydraulic cylinder fails.

In connection with traditional cylinder wall lubrication, it has hitherto been the practice to use simple spring-biased non-return valves that can resist the internal pressure in the cylinder, but which yield to a slightly higher external injection pressure. However, in connection with pressurised atomised injection, it is desirable and necessary that the valve system opens only at a much higher oil pressure in order that the oil injection can assume the character of a pressurised atomising injection right from the beginning.

In DK patent application PA 2005 01629 it has previously been proposed with a hydraulically powered lubricating apparatus and a method for dosing cylinder lubricating oil of the type mentioned in the introduction. By the principle described in the mentioned patent application it is possible to establish the cylinder lubrication in a way so that there may be achieved a flexible electronic control and a central stepless control of the dosing to the lubricating points. Furthermore, there may also be attained precise and simple control of the timing. In this system is also described the use of a distributor plate.

By the hydraulic systems it is desired to utilise the ratio between the cross-sectional area of the at least one hydraulic piston and the dosing pistons. Thus is indicated in DK 173512 Bl that the hydraulic piston has a cross-sectional area which is 4 times and preferably 6 to 15 times greater than the cross-sectional areas of the dosing pistons for establishing the required pressure conditions in the lubricating oil. Large ratios of area are unfavourable as this requires excessive space.

In connection with testing these prior art lubricating apparatuses, problems have been observed with the lubricating apparatus being unable to deliver the lubricating oil rapidly enough for use in atomising nozzles, e.g. of the type described in EP 1 129 275. This has inter alia been observed in connection with lubricating apparatuses of the type indicated in DK 173512 Bl, in spite of the indicated art in fact seeks a solution that achieves a rapidly operating cylinder lubricating system which can provide rapid and precise dosing right at the point of lubrication at the inner side of the liner. Experiments have been performed with increasing the pressure in the hydraulic system, but they showed not did not have any appreciable effect. The reason was, among others, that solenoid valves in the system did not have sufficient capacity. Solenoid valves are not easily replaced, and the problem cannot just be solved by replacing the solenoid valves. It has been desired to solve the problem in order to use efficient pressurised atomising nozzles in existing and in newly developed cylinder lubricating systems.

Object of the Invention It is the object of the present invention to relieve the above drawbacks and to indicate a hydraulically powered lubricating apparatus with which it is possible to provide a very reliable and cheap system, wherein it is possible to feed the lubricating oil rapidly enough at high operating pressure such that the risk of malfunction is eliminated or reduced.

Description of the Invention

According to the present invention, this is achieved by a hydraulic lubricating apparatus of the type mentioned in the introduction, which is peculiar in that the hydraulic piston has an inner boring extending in the direction of displacement of the hydraulic piston, that the boring is provided with an insert including an insert cylinder in which is provided a hollow insert piston, which is in contact with a supply opening for the hydraulic oil.

The hydraulic piston according to the invention is similarly peculiar in that it has an inner boring extending in the direction of displacement of the hydraulic piston, that the boring is provided with an insert including an insert cylinder in which is provided a hollow insert piston, which is in contact with a supply opening for the hydraulic oil.

The present invention may be used in connection with an apparatus as disclosed in the above mentioned patent publications, where hydraulic lubricating apparatuses with a distributor plate are used.

However, the present invention may also be used in connection with other kinds of lubricating apparatuses and other methods where hydraulic lubrication using hydraulic pistons is applied for acting on injection units that include dosing pistons for the cylinder lubricating oil, and wherein one or more hydraulic pistons act on a distributor plate which is used for actuating the dosing pistons. Thus it has appeared that the insert provides a changed diameter on the hydraulic piston, thereby ensuring that the hydraulic piston can be moved faster, substantially improving the pressure and flow conditions such that a substantially improved pressure and flow in the atomising nozzles can be achieved and thereby improved performance of the lubricating system. Moreover, the modified hydraulic piston ensures that the flow capacity does not put too great demands on solenoid valves in the system in order to attain optimal pressure and flow for the atomising nozzles. This is achieved in a technically simple way which may be adapted for use in existing systems just by modifying the used hydraulic piston or pistons.

Thus there will be need for a smaller amount of hydraulic oil for actuating the dosing pistons, and hereby is attained sufficient and rapid feeding of the lubricating oil to the atomising nozzles.

According to a further embodiment, the lubricating apparatus and the hydraulic piston according to the invention is peculiar in that the insert piston is screwed into a boring through which the hydraulic oil is supplied. Hereby is ensured tight connection by delivery of hydraulic oil to the reduced cross-sectional area provided within the bottom of the insert piston.

According to a further embodiment, the lubricating apparatus and the hydraulic piston according to the invention are peculiar in that the ratio between the cross-sectional area of the at least one hydraulic piston and the cross-sectional area of the dosing pistons is less than 7 and preferably less than 5.

As a concrete example can be mentioned changing a hydraulic piston of the type shown in Figs. 2 and 3, as follows:

- standard hydraulic piston: Hydraulic piston: 031 mm Dosing piston: 5 x 03.5

Ratio = 31^Λ2 / (5 x 3.5^Λ2) = 15.7

- modified hydraulic piston: Hydraulic piston insert: ølό mm Dosing piston: 5 x ø3.5 Ratio = 16^Λ2 / (5 x 3.5^Λ2) = 4.2

By this change is achieved a cycle for pressure build-up and pressure relief of the lubricating oil for the atomising nozzles which is 50% faster with the hydraulic piston according to the invention.

According to a further embodiment, the lubricating apparatus and the hydraulic piston according to the invention are peculiar in that between the outer side of the insert piston and the boring of the hydraulic piston there is provided a drain for the hydraulic oil. Leak oil may be conducted out through the hydraulic piston such that no accumulation of hydraulic oil occurs inside the chamber in which the hydraulic piston is disposed. If that was the case, it would mean that the hydraulic oil was to act on the entire cross-sectional area inside the chamber. A reduced need of oil flow would thereby not exist, a fact which is the basis of achieving the technical advantage of the present invention.

According to a further embodiment, the lubricating apparatus and the hydraulic piston according to the invention are peculiar in that the boring of the hydraulic piston, the insert cylinder and the insert piston have circular cross-section and are disposed concentrically about a central axis. This is a particularly simple embodiment which is easy to make.

According to a further embodiment, the lubricating apparatus according to the invention is peculiar by the dosing system including:

- a supply line and a return line connected with the lubricating apparatus via one or more valves for supplying hydraulic oil;

- a central hydraulic oil feed pump which via the supply line is connected with hydraulic cylinders each having a hydraulic piston and which may be subjected to pressure by hydraulic oil;

- a number of injection units corresponding to a multiple of the cylinder number in the engine, and which are connected with each their dosing cylinder with a dosing piston;

- a supply line for cylinder lubricating oil. Hereby, the required supply of hydraulic oil and lubricating oil is ensured. It is noted that oil from the same supply source can be used, as the same type of oil may be used for lubrication and for actuation of the hydraulic piston.

Description of the Drawing

The invention will then be explained in more detail with reference to the accompanying drawing, where:

Fig. 1 shows a schematic overview of a system with a plurality of lubricating apparatuses according to the invention; Fig. 2 shows a schematic drawing of a second embodiment of a system with a lubricating apparatus according to the invention; Fig. 3 shows a longitudinal section through an embodiment of a cylinder lubricating unit which may form part of a lubricating apparatus according to the invention; and Fig. 4 shows a further embodiment of a lubricating apparatus according to the invention for use in the system shown in Fig. 1.

Detailed Description of the Invention

Fig. 1 shows a system made in accordance with the specifications indicated in PCT/DK2007/000364.

Fig. 1 shows schematically four cylinders 250 and on each cylinder appears eight injection nozzles 251. The lubricating apparatuses 252 are connected with a central computer 253, with local control units 254 typically for each single lubricating apparatus 252. The lubricating apparatuses 252 are adapted as explained in detail in the following.

The central computer 253 is coupled in parallel with a further control unit 255 constituting a backup for the central computer. In addition, there is established a monitoring unit 256 monitoring the pump (can be a hydraulic pump or a hydraulic station), a monitoring unit 257 monitoring the load and a monitoring unit 258 monitoring the position of the crankshaft. In the upper part of Fig. 1 there is shown a hydraulic station 259 comprising a motor 260 driving a pump 261 in a tank 262 for hydraulic oil. The hydraulic station 259 furthermore includes a cooler 263 and a filter 264. System oil is pumped via supply line 265 on to the lubricating apparatus via a valve 220. The hydraulic station is furthermore connected with a return line 266 which is also connected with the lubricating apparatus via a valve.

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

In Figs. 2 and 3 is seen a system of the type which in principle is known from the description of DK patent 173 512.

Fig. 2 shows a cylinder lubricating system where two cylinders 2 are shown. Each of the cylinders 2 are provided with four lubricating points 6 provided with injection units 6'. Each of the lubricating units 6' are connected via connecting lines 29 with a central lubricating unit 30 which is connected with a control valve 31. Via the line 32, the control valve 31 is connected with an electronic control unit 9. Furthermore, there is illustrated a pressure control unit 33 which also via lines 34, 35 is connected with the control unit 9, and which via lubricating oil supply lines 36, 37 are connected with the cylinder lubricating units 30.

The cylinder lubricating units 30 are shown more clearly in Fig. 3.

The cross-section in Fig. 3 shows that a central cylinder lubricating unit 30 is provided with a supply gate 38 for lubricating oil. Moreover, it has a return gate 39 for the drive oil which in the shown embodiment is identical with the lubricating oil. The control valve 31 is connected with a valve 40 regulating oil supply and discharge. The cylinder lubricating unit 30 comprises a hydraulic piston 41 provided with flanges 42. Each of the flanges 42 engage dosing pistons 43 feeding lubricating oil via gates 44 and via the connecting lines 29 to the lubricating points 6, as shown on Fig. 2. In Fig. 3 is thus shown a hydraulic piston 41 with flanges 42 acting as a distributor plate, as it acts on several dosing pistons 43.

The unit 30 has an adjustable stop element 45 determining the travel of the hydraulic piston 41. The stop element 45 determines the stroke of the hydraulic piston 41 and thereby also the dosing pistons 43 that act as dosing pumps.

A compression spring 46 pre-loads the hydraulic piston 41 in direction of the starting position. The adjustable stop element 45 is screwed into a thread 47 in the end part 48 of the unit. Screwing in the adjustable stop element 45 will thus limit the stroke of the hydraulic piston 41 and thereby the portion of lubricating oil discharged from the dosing pistons 43. The adjustable stop element 45 thus functions as adjusting device for the stroke of the reciprocating pump. The adjustable stop element 45 is connected with an electronically controlled regulating means 49. Via wires 50, the regulating means 49 is connected with the central electronic control unit 9. Electronic control of the stroke of the reciprocating pump will thus be possible so that in a flexible way it is possible to achieve a central and stepless control of the dosing to be performed at the individual lubricating points 6.

The hydraulic piston 41 is cylindric and placed in a chamber A which in a traditional lubricating apparatus would act as cylinder in which the piston is displaced. The hydraulic piston 41 has a central boring B in which an insert cylinder C is mounted. This insert cylinder C is hollow and has an inner boring D, wherein an insert piston E is accommodated, and ending in a closed bottom F. The insert piston E is mounted in an opening H via a screw thread G for feeding the hydraulic oil into the chamber A. The insert piston E has an inner boring through which the hydraulic oil flows for acting on the bottom F in the insert cylinder. Hereby, the hydraulic piston is displaced and thereby also the flange 42 such that the dosing pistons are actuated. The hydraulic piston 41 has a drain opening J such that leak oil may seep between spaces between the outer side of the insert cylinder C and the boring B and out via drain openings J. Hereby, accumulation of oil in the chamber A behind the hydraulic piston 41 is avoided. The lubricating apparatus shown in Fig. 4 is made up of a bottom part 110 where solenoid valves 115 and 116 for activating the apparatus are mounted. At the side of the bottom part 110, screw joints are provided for system oil pressure supply 142 and system oil pressure return to tank 143.

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

In the initial position, it is the primary solenoid valve 116 which is active. The driving oil is hereby conducted from the associated supply screw joint 142 to the primary solenoid valve 116 and via a switch valve 117 into the apparatus through a distribution channel to the group of associated hydraulic pistons.

In case that the primary solenoid valve 116 fails it is possible automatically to connect the secondary solenoid valve 115. This valve is connected by activating the secondary solenoid valve 115.

The associated distribution channel is hereby pressurised. This pressure entails that the switch valve 117 is displaced to the right, whereby the connection between the primary solenoid valve 116 and the associated distribution channel is interrupted. The pressure is hereby removed from the hydraulic pistons connected to this solenoid valve 116.

By activating the secondary solenoid valve 115, the associated distribution channel and the associated hydraulic pistons are pressurised. This causes that the distribution plate 7 is then driven by the oil conducted into the apparatus via the secondary solenoid valve 115.

The switch valve 117 may be equipped with a spring 119. In case of lack of supply pressure through the secondary solenoid valve, the spring will thus automatically put the switch valve 117 back to the above initial position. The switch valve may be equipped with a restrictor such that this returning of the switch valve can be delayed. In this way is avoided/restricted that the switch valve 117 goes back and forth between the activations. On Fig. 4, the restriction is determined by a slot formed between a drain-pin 118 and the switch valve 117.

When each of the solenoid valves is connected to a separate group of hydraulic pistons, independence between the solenoid valves is ensured. When shifting between the primary solenoid valve 116 and the secondary solenoid valve 115, the switch valve 117 will ensure that the pressure is removed from the primary group of hydraulic pistons and thereby enable operation of the secondary solenoid valve 115, even in cases where the primary solenoid valve is blocked.

Pos. 121 shows a blanking screw.

Pos. 122 shows a combined blanking screw/end stop that partly act as end stop for the pawl 120 of the switch valve 117 and partly has a sealing function also via a (not shown) packing.

Above the hydraulic pistons 106 there is a distributor plate 7. The plate is shown here as a two-part design with an upper distributor plate member 125 and a lower distributor plate member 123. The dosing pistons 21 are mounted in/on the upper distributor plate member 125. In apparatuses where various oils are used for drive and lubrication, there is a piston packing 124 between the upper and lower distributor plate member, hi principle, one may also suffice with using one kind of oil for drive oil as well as for lubricating oil.

Each hydraulic piston 106 is cylindric and placed in a chamber A which in a traditional lubricating apparatus would act as cylinder in which the piston is displaced. The hydraulic piston 106 has a central boring B in which an insert cylinder C is mounted. This insert cylinder C is hollow and has an inner boring D, wherein an insert piston E is accommodated, and ending in a closed bottom F. The insert piston E is mounted in an opening H via a screw thread G for feeding the hydraulic oil into the chamber A. The insert piston E has an inner boring through which the hydraulic oil flows for acting on the bottom F in the insert cylinder. Hereby, the hydraulic piston is displaced and thereby also the distributor plate 7 such that the dosing pistons 21 are actuated. The hydraulic piston 106 has a drain opening J such that leak oil may seep between spaces between the outer side of the inset cylinder C and the boring B out via drain openings J. Hereby, accumulation of oil in the chamber A behind the hydraulic piston 106 is avoided.

Around the dosing pistons 21 there is a common return spring 109 which returns the pistons 21 after disconnecting the supply pressure on the hydraulic pistons 106. Around the return spring 109 there is a small lubricating oil reservoir 147 which is externally delimited by a base block 111. The lubricating oil is supplied through a separate screw joint with packings 138 and 139. The apparatus may optionally be equipped with a venting screw with packing.

Above the base block 111 the cylinder block 112 is located where the dosing pistons 21 are disposed for their reciprocating movement. Above the dosing pistons 21 there is a pump chamber 148. In this chamber there is an outlet with a non-return valve ball 13 which is biased by a spring 14. Furthermore, there is provided a screw joint 128 connected directly with the non-return valves/SIP valves in the cylinder wall.

For adjusting the stroke, in this embodiment there is shown an arrangement with a motor 132 coupled to a worm drive 131 which via a worm wheel 130 adjusts the stroke by changing the position on set pin/set screw 66.

1 In this embodiment, it is possible to adjust the stroke by changing the position of the stroke stop. This is different from the previous embodiments where a fixed point of origin was used and where the stroke was adjusted subsequently.

In order to control the actual stroke length, a sensor/pickup unit 114 is mounted in continuation of set pin/set screw 66 for detecting the stroke, e.g. in the form of an encoder or a potentiometer.

Pos. 113 shows a housing for the set pin/set screw arrangement. Pos. 124 shows a piston packing sealing between the two spaces 149 and 147 with leak oil bypassing the hydraulic pistons 6 at the drive oil side at the bottom and the lubricating oil at the top, respectively.

Pos. 127 shows an O-ring sealing between the base block 111 and the cylinder block 112.

Pos. 133 shows a fastening screw for fastening a bearing case for the worm wheel 130.

Pos. 134 shows an O-ring sealing between the bottom plate 110 and the base block 111.

Claims

1. A hydraulic lubricating apparatus for a dosing system for cylinder lubricating oil, for example in marine engines, the hydraulic lubricating apparatus being hydraulically powered for feeding lubricating oil and including at least one hydraulic piston, wherein the apparatus may be subjected to pressure by hydraulic oil, further including a number of dosing pistons and a distributor plate which at one side is in contact with the dosing pistons and which at its other side is in contact with the at least one hydraulic piston for displacing the distributor plate in order to actuate the dosing pistons, characterised in that the hydraulic piston has an inner boring extending in the direction of displacement of the hydraulic piston, that the boring is provided with an insert including an insert cylinder in which is provided a hollow insert piston, which is in contact with a supply opening for the hydraulic oil.

2. Hydraulic lubricating apparatus according to claim 1, characterised in that the insert piston is screwed into a boring through which the hydraulic oil is delivered.

3. Hydraulic lubricating apparatus according to claim 1 or 2, characterised in that the ratio between the cross-sectional area of the at least one hydraulic piston and the cross- sectional area of the dosing pistons is less than 7 and preferably less than 5.

4. Hydraulic lubricating apparatus according to any preceding claim, characterised in that a drain for the hydraulic oil is provided between the outer side of the insert piston and the boring of the hydraulic piston.

5. Hydraulic lubricating apparatus according to any preceding claim, characterised in that the boring of the hydraulic piston, the insert cylinder and the insert piston have a circular cross-section and are disposed concentrically about a central axis.

6. Hydraulic lubricating apparatus according to any preceding claim, characterised in that the dosing system includes a supply line and a return line connected with the lubricating apparatus via each one or more valves for supplying hydraulic oil, a central hydraulic oil feed pump connected with hydraulic cylinders via the supply line, the hydraulic cylinders each having a hydraulic piston and able to be subjected to pressure by hydraulic oil, a number of injection units corresponding to a multiple of the cylinder number in the engine and which are connected with each their dosing cylinder with a dosing piston and a supply line for cylinder lubricating oil.

7. A hydraulic piston for use in a hydraulic lubricating apparatus for a dosing system for cylinder lubricating oil, for example in marine engines, the hydraulic lubricating apparatus being hydraulically powered for feeding lubricating oil and including at least one hydraulic piston, wherein the apparatus may be pressurised by hydraulic oil, further including a number of dosing piston and a distributor plate which at one side is in contact with the dosing pistons and which at its other side is in contact with the at least one hydraulic piston for displacing the distributor plate for actuating the dosing pistons, characterised in that it has an inner boring extending in the direction of displacement of the hydraulic piston, that the boring is provided with an insert including an insert cylinder in which is provided a hollow insert piston, which is in contact with a supply opening for the hydraulic oil.

8. Hydraulic piston according to claim 7, characterised in that the insert piston is screwed into a boring through which the hydraulic oil is delivered.

9. Hydraulic piston according to claim 7 or 8, characterised in that the ratio between the cross-sectional area of the at least one hydraulic piston and the cross-sectional area of the dosing pistons is less than 7 and preferably less than 5.

10. Hydraulic piston according to any of claims 7 -9, characterised in that a drain for the hydraulic oil is provided between the outer side of the insert piston and the boring of the hydraulic piston.

11. Hydraulic piston according to any of claims 7 -10, characterised in that the boring of the hydraulic piston, the insert cylinder and the insert piston have a circular cross-section and are disposed concentrically about a central axis.