WO2009000879A1

WO2009000879A1 - Internal combustion engine with reduced fuel content in the lubricating oil

Info

Publication number: WO2009000879A1
Application number: PCT/EP2008/058140
Authority: WO
Inventors: Josef Lenz
Original assignee: Josef Lenz
Priority date: 2007-06-26
Filing date: 2008-06-26
Publication date: 2008-12-31
Also published as: DE102007029360A1

Abstract

An internal combustion engine (1) having an oil circuit, in which lubricating oil circulates, for lubricating interfaces of parts of the internal combustion engine (1) that move relative to one another. A separator (12) is disposed in the lubricating oil circuit in order to separate the fuel, which has been introduced into the lubricating oil during continuous operation, at least partially from the lubricating oil.

Description

Internal combustion engine with reduced fuel content in the lubricating oil

Description

Background of the invention

The present invention relates to an internal combustion engine having a lubricating oil circuit, in which lubricating oil circulates, and to a method of operating an internal combustion engine.

Background art

For the background art numerous types of internal combustion engine are known, for example reciprocating piston engines that convert the change in volume of a gas in a cylinder to a rotational movement by means of reciprocating pistons. A feature common to all internal combustion engines is that they comprise numerous components that are movable relative to one another, for example pistons and cylinders. In order to lubricate the interfaces of such parts that are movable relative to one another, the engines are equipped with a lubricating oil circuit that conveys lubricating oil under pressure to the points to be lubricated so that it forms a lubricating film there. At the same time, in the crankcase of the engine the lubricating oil passing out of the bearing points and piston rings is collected, usually in an oil sump, before being conveyed once more to the points to be lubricated.

For this purpose, the engine is generally equipped with an oil pressure pump, which sucks the lubricating oil out of the oil sump and delivers it at a pressure of several bars through a system of lubricating oil lines to the points of the engine that are to be lubricated.

It is known that in internal combustion engines to a certain extent fuel may be introduced into the lubricating oil, especially through the cylinder- and piston walls. An increased introduction of fuel is to be observed particularly in the event of imprecise combustion, substantial engine wear and other problems. This may be disadvantageous if the introduced fuel has a detrimental effect on the lubricating properties of the lubricating oil. The rate and repercussions of the introduction of fuel depend to a great extent upon the engine type, the mechanical conditions and the nature of the introduced fuel.

It is further known that, particularly in internal combustion engines that run on vegetable oil, unforeseen damage often occurs as a result of failure of the lubricating oil circuit.

From the prior art internal combustion engines are moreover known, in which the lubricating oil circuit is equipped in the primary flow or in a secondary flow with a particulate filter or a mechanical rotary separator as a lubricating oil filter in order to separate particles, in particular metal swarf or other metal impurities from the engine oil.

From the sport of motor racing a so-called dry sump technique is known, whereby suitable measures prevent the accumulation of too large a quantity of engine oil in the engine, in particular in the oil sump of the engine. This is conventionally achieved by means of an oil scavenge pump that conveys the oil into an oil reservoir, from which the lubricating oil circuit is supplied. The dry sump technique is used here to guarantee a reliable circulation of the engine oil under the extreme conditions of motor racing.

Likewise known from the sport of motor racing is a so- called oil plane, which separates the crank space of the engine from the oil sump in order to prevent engine oil from the oil sump from moving back for example as a result of splashing up into the crank space and being swirled and/or churned up there by crankshaft or connecting rods, in particular with simultaneous foaming. The oil plane for example takes the form of a slotted metal sheet disposed between crankcase and oil sump. Through the slots the oil is able to drain away from the crank space into the oil sump. On the other hand, oil splashing up from the oil sump is substantially retained by the metal sheet.

Finally, marine diesel engines are known, which are equipped with a so-called clarifier, which with the aid of a centrifugal technique filters small particles, in particular metal swarf, out of the engine oil.

The underlying problem of the invention

The underlying problem of the invention is to provide an improved internal combustion engine having a lubricating oil circuit, in which lubricating oil circulates. A further underlying problem of the invention is to provide an improved method of operating an internal combustion engine having a lubricating oil circuit, in which lubricating oil circulates. Solution according to the invention

For solving the problem the present invention teaches an internal combustion engine having the features of claim 1 and a method of operating an internal combustion engine having the features of claim 12.

An interruption of the lubricating film may cause considerable damage to an engine. The invention is based i.a. on the discovery that an undesirable interruption of the lubricating film may originate at least partially from an introduction of fuel into the lubricating oil. The experiments of the inventor have demonstrated i.a. that particularly vegetable oil as a fuel reacts with the lubricating oil in a way that may promote flocculation and/or crystallization, i.a. also the formation of crystalline calcium compounds, in the lubricating oil and may therefore impair the lubricity of the lubricating oil, i.a. as a result of a thickening of the engine oil. It is suspected that this is related i.a. to a pH difference between the generally rather acidic vegetable oil and the usually rather alkaline lubricating oil. Analysis of thickened oil samples indicates that the integration of vegetable oil into the lubricating oil is based predominantly on covalent, i.e. atomic bonds and not on electrovalence .

The inventor has moreover observed that known lubricating oil filters are not capable of separating the residues, which have been introduced from the vegetable oil combustion, from the engine oil in order to prevent an integration and thickening of the engine oil. The fact that according to the invention the fuel in the oil circuit may to a large extent be separated once more from the lubricating oil advantageously makes it possible to reduce the fuel content in the lubricating oil. The invention may therefore prevent or at least reduce an introduction of fuel into the lubricating oil and hence counteract the drawbacks thereof. It is an achievable advantage of the invention that the vegetable oil may be separated from the engine oil before a hydrolysis of the engine oil brought about by the introduction of vegetable oil sets in. In particular, by virtue of the invention a substantially acid-free operation of the lubricating oil circuit in the internal combustion engine may be ensured.

From provisional results of the inventor it is anticipated that the invention will make it possible to lengthen oil change intervals in vegetable oil engines. It is moreover possible to counteract a sudden and unexpected failure of the lubricating film, thereby increasing the operating reliability of the engine.

Preferred embodiments of the invention

Advantageous constructions and developments that may be used individually and in combination with one another are the subject matter of the dependent claims.

The separator of the internal combustion engine according to the invention preferably comprises at least one centrifugal separator that utilizes the different specific gravity of the lubricating oil and the fuel to separate from the lubricating oil at least a fraction of the fuel that has been introduced into the lubricating oil. The centrifugal separator operates preferably by centrifuging the lubricating oil/fuel mixture. The separator may also comprise a plurality of centrifugal separators connected in parallel or in a plurality of successive stages.

The separator may also, in addition to or instead of the centrifugal separator (s) , comprise a purifier that utilizes the different viscosity of the lubricating oil and the fuel to separate from the lubricating oil at least a fraction of the fuel that has been introduced into the lubricating oil. The purifier preferably comprises one or more rolls for effecting the viscosity separation. The separator may also comprise a plurality of purifiers connected in parallel or in a plurality of successive stages.

In a particularly preferably manner the separator has one, two or three stages. The separator may take the form of a mechatronic device.

The vegetable oil separated into the separator is preferably stored in a vegetable oil collecting container. In a conceivable construction of the invention, it is recycled as fuel to the engine. The separator may be driven directly by the internal combustion engine, or one or more independent drives, preferably electric motors, are provided.

In a preferred construction of the invention, a lubricating oil filter is provided as a particle filter or particulate filter for filtering particles, for example metal swarf or other metal impurities, out of the engine oil. The lubricating oil filter may for example take the form of a paper filter, an open meshed steel fabric or a rotary separator (then described as a clarifier) , particularly preferably a free jet centrifuge. Particularly preferred are clarifiers that operate in accordance with the functional method known for marine diesel engines. The lubricating oil filter is preferably designed so as to be able to filter out particles having diameters of down to 20 μm, particularly preferably to 10 μm, particularly preferably to 1 μm, particularly preferably down to diameters of 500 nm. Also conceivable is the use of lubricating oil filters that are even capable of filtering out particles of even smaller diameters. The lubricating oil filter is preferably disposed downstream of an oil pressure pump in the oil circuit. In a preferred construction of the invention, a centrifugal separator of the separator also performs the function of the lubricating oil filter described here.

In a preferred construction of the invention, the lubricating oil circuit comprises at least one oil pressure pump for generating the necessary oil pressure for lubricating the internal combustion engine. The preferred lubricating oil circuit further comprises an oil feed portion for feeding lubricating oil from the engine to the oil pressure pump. The separator is preferably disposed in the oil feed portion of the lubricating oil circuit. Preferably, the oil feed portion removes the lubricating oil from the crankcase, particularly preferably from an oil sump of the crankcase. As a result of the separation of the oil removal through the oil feed portion and the pressure generation by the oil pressure pump it is advantageously possible to achieve the effect whereby the lubricating oil is fed without pressure or at low pressure to the separator and the fuel is separated before the lubricating oil arrives at the oil pressure pump. It is therefore possible to prevent this fuel in the oil pressure pump or in the oil circuit disposed downstream of the oil pressure pump from being further mixed with the engine oil or from being further suspended therein and therefore being more difficult or no longer possible to separate at all by means of the separator.

The lubricating oil circuit operates preferably in a dry sump mode, i.e. suitable measures prevent the accumulation of too large a quantity of engine oil in the engine, in particular in the oil sump of the engine. By virtue of the dry sump mode, preferably in combination with an oil plane, for example in the form of a slotted metal sheet between crank space and oil sump, it is advantageously possible to counteract a mixing of the oil with the introduced fuel in the engine, in particular in the the oil sump, for example as a result of immersion of the crankshaft or as a result of sloshing to and fro in the case of an engine installed in a vehicle. Such a mixing, promoted by the oil being churned to a greater or lesser extent in the crank space of a normal engine, might lead to the fuel being more difficult or no longer possible to separate at all from the engine oil in the separator.

In a preferred construction of the invention, the oil feed portion comprises at least one oil scavenge pump that extracts lubricating oil passing out of the engine. In a particularly preferred manner, an oil scavenge line is further provided for feeding the oil from the oil sump to the oil scavenge pump. Preferably, the oil scavenge pump delivers the lubricating oil to the separator. However, constructions of the invention are also conceivable, in which the lubricating oil without the assistance of an oil scavenge pump passes to the separator, for example in that it drains off substantially freely as a result of gravitational force from the oil sump to the separator, or is delivered to the separator by means of a partial vacuum generated upstream by the separator.

In a preferred oil circuit, the oil scavenge pump builds up a pressure that is lower than the oil pressure built up by the oil pressure pump. The effect achievable thereby is that the oil is conveyed from the oil scavenge pump at low pressure to the separator. Preferably the pressure built up by the oil scavenge pump, particularly preferably the pressure in the entire oil feed portion upstream of the separator, is lower than 4 bar, particularly preferably lower than 2 bar, particularly preferably lower than 1 bar, particularly preferably lower than 500 mbar, particularly preferably lower than 200 mbar, particularly preferably lower than 100 mbar.

A preferred oil feed portion comprises a lubricating oil reservoir, from which the lubricating oil is fed to the oil pressure pump. With this construction of the invention it is advantageously achievable that the oil no longer has to be stored or has to be stored at least to a lesser extent in or at the crankcase, in particular in the oil sump of the crankcase. Thus, in the crankcase and/or the oil sump it is possible to counteract a further mixing or suspension of the fuel in the lubricating oil, for example as a result of the crankshaft dipping into the lubricating oil supply in the oil sump or as a result of the lubricating oil sloshing to and fro. The lubricating oil reservoir is preferably disposed between separator and oil pressure pump, so that it receives lubricating oil already purified by the separator. A preferred lubricating oil reservoir is equipped with at least one sensor for monitoring the oil quality. Additionally or alternatively, a sensor for monitoring the oil level is preferably provided. The sensors are preferably connected to an electronic evaluation unit. They may also be functionally connected, preferably by the electronic evaluation unit, to an electronic controller of the internal combustion engine in order to control the engine and/or the separator, for example drive motors of the separator, in dependence upon the acquired measured values. In the oil feed portion a pump may be provided between separator and lubricating oil reservoir for feeding the lubricating oil leaving the separator to the lubricating oil reservoir.

As a means of preventing a mixing or suspension of fuel in the lubricating oil in the oil sump, the oil sump is preferably provided with a grid-like or lamellar splash guard. The splash guard guides dripping lubricating oil from the crankcase into the oil sump but makes it difficult for the lubricating oil to pass in the reverse direction from the oil sump into the crankcase.

The preferred internal combustion engine may be run on vegetable oil. Suitable vegetable oils may be for example rapeseed oil, palm oil, sunflower oil or soya bean oil. However, the invention is not restricted to vegetable oil engines but may be used advantageously also in internal combustion engines that run on other fuels. A preferred internal combustion engine is equipped with a fuel injection device. A preferred fuel injection device comprises one or more mechanical injection pumps, pump nozzle systems or a common-rail injection system.

The preferred internal combustion engine is a reciprocating piston engine. However, the invention may be used advantageously also in other types of internal combustion engine, for example in rotary piston engines such as for the example the Wankel engine.

The preferred internal combustion engine is operable in a stationary manner, for example as the drive of a stationary construction machine or as a unit of an engine-based cogeneration system. The internal combustion engine according to the invention may however also be used in a motor vehicle, wherein the motor vehicle may be for example a land-, water- or aircraft.

The preferred internal combustion engine is a diesel engine but the invention is usable advantageously also in other types of engine, for example in spark ignition engines or pilot injection engines

Brief description of the drawing

Further particulars of an embodiment of the invention are described in detail below with reference to a diagrammatic drawing.

The drawing shows : Fig. 1: a diagrammatic cross-sectional representation of an internal combustion engine according to the invention .

Detailed description of an embodiment

The internal combustion engine 1 represented in Fig. 1 comprises four cylinders 3, which are equipped with cylinder heads 2 and in which pistons 4 move up and down. The represented engine 1 is a four-cylinder engine only by way of example; it is also perfectly conceivable for the invention to be used in engines having any desired number of cylinders, starting with a single-cylinder engine. The cylinders are functionally connected in such a way to a crankshaft 6 disposed in a crankcase 5 that they set the crankshaft 6 in rotation. Lubricating oil leaving the crankcase 5 is collected in an oil sump 7. Particularly in the region between piston wall 8 and cylinder wall 9 fuel may pass into the lubricating oil.

In the internal combustion engine 1 the purifying and return of the lubricating oil to the lubricating oil circuit is effected in three stages. In the first stage, the oil contaminated with fuel passes through two oil scavenge lines 10 to two oil scavenge pumps 11 operating in parallel and is conveyed from these at a low pressure of ca. 100 mbar to the separator 12.

There, in the second stage, some of the fuel is separated from the lubricating oil by a centrifugal effect and supplied to a fuel reservoir 13. The purified lubricating oil is passed on from the separator 12 to a lubricating oil reservoir 14. A sensor 15 at the lubricating oil reservoir 14 monitors the quality of the lubricating oil and the oil level of the lubricating oil reservoir 14.

In the third stage, the purified lubricating oil is pumped out of the lubricating oil reservoir 14 by an oil pressure pump 16 at approximately 2 to 6 or more bar back into the oil circuit. Both the oil scavenge pumps 11 and the oil pressure pump 16 and the separator 12 are driven via a drive connection 17 directly by the internal combustion engine 1.

By virtue of the invention the fuel content in the engine oil may be substantially to completely reduced. Thus, oil change intervals may be markedly lengthened and unforeseen engine damage may be counteracted.

The drive of the pumps and separators may be realized also by means of electric motors.

The features disclosed in the above description, the claims and the drawings may be significant both individually and in any desired combination for the realization of the invention in the various developments thereof.

Claims

1. Internal combustion engine (1) having an oil circuit, in which lubricating oil circulates, for lubricating interfaces of parts of the internal combustion engine

(I) that move relative to one another, characterized in that a separator (12) is disposed in the lubricating oil circuit in order to separate fuel, which has been introduced into the lubricating oil, at least partially from the lubricating oil.

2. Internal combustion engine (1) according to claim 1, characterized in that the separator (12) comprises at least one centrifugal separator .

3. Internal combustion engine (1) according to claim 1 or 2, characterized in that the lubricating oil circuit comprises an oil pressure pump (16) for generating the necessary oil pressure for lubricating the internal combustion engine (1) as well as an oil feed portion for feeding lubricating oil from the engine to the oil pressure pump (16), and the separator is disposed in the oil feed portion of the lubricating oil circuit.

4. Internal combustion engine (1) according to claim 3, characterized in that the oil feed portion comprises an oil scavenge pump

(II) for delivering the lubricating oil to the separator (12) .

5. Internal combustion engine (1) according to claim 4, characterized in that the oil scavenge pump (11) during operation builds up an oil pressure that is lower than the oil pressure built up by the oil pressure pump (16) .

6. Internal combustion engine (1) according to one of claims 3 to 5, characterized in that the oil feed portion comprises a lubricating oil reservoir (14), from which the lubricating oil may be fed to the oil pressure pump (16) .

7. Internal combustion engine (1) according to one of the preceding claims, characterized in that it may be run almost trouble-free on vegetable oil.

8. Internal combustion engine (1) according to one of the preceding claims, characterized in that it is equipped with a fuel injection device or fuel carburation device.

9. Internal combustion engine (1) according to one of the preceding claims, characterized in that it operates on the reciprocating piston or rotary piston principle.

10. Internal combustion engine (1) according to one of the preceding claims, characterized in that it is operable in a stationary manner.

11. Internal combustion engine (1) according to one of claims 1 to 9, characterized in that it drives a motor vehicle.

12. Internal combustion engine (1) according to one of claims 1 to 9, characterized in that it drives a water craft.

13. Method of operating an internal combustion engine (1) having a mechanical or mechatronic lubricating oil circuit, in which lubricating oil circulates, for lubricating interfaces of parts that are movable relative to one another, characterized in that fuel that has been introduced into the lubricating oil is at least partially separated from the lubricating oil in the lubricating oil circuit.

14. Method of operating an internal combustion engine (1) according to claim 13, characterized in that the lubricating oil circuit operates in accordance with the dry sump technique.

15. Method of operating an internal combustion engine (1) according to claim 13 or 14, characterized in that lubricating oil leaving the internal combustion engine (1) is extracted by means of an oil scavenge pump (11)