GB2468354A - Combustion engine lubricant circuit - Google Patents

Abstract

A lubricant circuit for a combustion engine comprises a pump 3 and plural paths 7, 9, 12, 22, 23 from the output port of the pump 3 to an input port thereof via at least one lubricating point 8, 10, 13, 16, 19. At least one of the paths comprises a metering valve 6 to control the flow rate of the lubricant at its associated lubricating point. The metering valve 6 can have a simple design of a solenoid 24 surrounding a lubricant passage 25 if the lubricant is a magneto-rheologic fluid. The metering valve 6 can be provided upstream of lubricating points such as cylinder jackets, a crankshaft 14, camshaft 11 and tappets 8. The metering valve can be controlled electronically according to engine operating conditions such as speed; temperature; time since engine start; and time and mileage since lubricant change.

Description

Lubricant circuit for a combustion engine

Description

The present invention relates to a lubricant circuit for a combustion engine, for providing lubricant to various points of the engine such as bearings, cylinders, etc. Conventionally, a lubricant circuit comprises a pump and a plurality of paths extending from an output port of the pump to an input port thereof via at least one lubricating point. The various paths of the lubricant circuit have their flow rates designed into them, i.e. the flow rate of a path depends on the flow resistance of its lubrication point or points and on the shape, in particular on length and cross sections, of lubricant ducts. When designing such a lubricant circuit, care must be taken to ensure that each lubricant point is sufficiently supplied with lubricant at all times and under all operating conditions. Since the flow resistance of lubricating points and/or the necessary lubricant flow rate at a point may vary according to operating conditions of the engine, the flow rate of the pump must be sufficient to provide sufficient lubricant even under the most adverse conditions. Therefore the pump tends to be oversized for normal operating conditions, and there are lubricating points which will receive lubricant beyond their needs.

Since the cost of a pump is generally proportional to its power, an oversized pump will unnecessarily increase the production cost of an engine in which it is used. Further, a pump which is more powerful than necessary consumes energy without need.

Since the pump is conventionally driven by the combustion engine it lubricates, the fuel efficiency of the combustion engine is decreased.

The object of the invention is therefore to provide a lubricant circuit for a combustion engine which can ensure sufficient lubrication using a low power pump.

The object is achieved by a lubricant circuit for a combustion engine comprising a lubricant pump and a plurality of paths from an output port of the pump to an input port thereof via at least one lubricating point, in which at least one of the paths comprises a metering valve for controlling the flow rate of the lubricant at its associated lubricating point. Depending on the lubricant flow rate at the associated lubricating point, the metering valve can be controlled to admit just this flow rate. The smaller this flow rate is, the larger is the proportion of the total pump flow rate which will be available for the other paths. Since no lubricant flows unnecessarily through the at least one valve-controlled path, the flow rate of the pump can be adjusted precisely to the requirements of the engine.

Such a metering valve is most conveniently located at an upstream side of the lubricating point.

There may be different types of lubricating points associated to a given valve-controlled path. For example, one path comprising a metering valve may have cylinder jackets for lubricating points, whereas another has a crank shaft, and still another may have a camshaft or tappets for lubricating points.

According to a preferred embodiment the lubricant is a magneto-rheologic oil. Valves for controlling the flow rate of such an oil can be of a particularly simple design, comprising simply a solenoid extending around a lubricant passage. Since such a metering valve has no moving parts, it is practically maintenance-free.

Preferably, an electronic metering valve controller for controlling the flow rates of the metering valves according to operating conditions of the engine is associated to the lubricant circuit.

The operating conditions on which operation of the valve controller is based may comprise one ore more of engine speed, engine temperature, the time elapsed since engine start, the time elapsed since the last lubricant change or the mileage since the last lubricant change.

Further features and advantages of the invention will become apparent from the subsequent description of embodiments thereof referring to the appended drawings.

Fig. 1 is a diagram of a combustion engine with a lubricant circuit according to the present invention; Fig. 2 is a diagram of a combustion engine according to a second embodiment of the invention; and Fig. 3 is a schematic cross section of a metering valve.

Fig. 1 is a schematic cross section of a four-piston combustion engine. At the bottom of an engine casing 1, there is an oil pan 2. Oil having ferromagnetic particles dispersed in it is drawn from the oil pan 2 by a pump, e.g. a gear pump 3. The pump 3 delivers pressurized oil to an oil filter 4. At an output side of oil filter 4 there is a manifold 5 for distributing oil to various paths. In each of these paths, a metering valve 6 is provided between the manifold 5 and one or more lubricating points associated to that path.

An uppermost path 7 in Fig. 1 provides oil in parallel to hydraulic tappets 8 associated to intake and exhaust valves of the engine. A second path 9 lubricates bearings 10 of a camshaft 11 acting on the tappets 8.In a third path 12, bearings 13 of crankshaft 14 are lubricated in parallel. A plurality of bores 15 is formed in crankshaft 14, where each of which extends from one of the crankshaft bearings 13 to bearing 16 at the big end of piston rods 17. Another bore 18 extends through each piston rod 17 from big end to small end bearings 19 inside pistons 20. Path 12 can thus be said to have four parallel branches, in each of which three bearings 13, 16, 19 are lubricated in series.

An electronic controller 21 is connected to each of the metering valves 6 for controlling its flow resistance and, thereby, the flow rate in each path 7, 9, 12. The controller 21 receives input data from various sensors and timers, not shown.

One such sensor is e.g. a temperature sensor for measuring the engine temperature, and the controller 21 is adapted to reduce the flow resistance of all metering valves 6 to a minimum if the temperature sensor detects the engine to be cold, and the oil can be expected to have a high degree of viscosity.

Instead of the temperature sensor, a timer can be used which is reset at each start of the engine, assuming that the engine will be cold upon start-up and that a certain time is necessary for reducing the viscosity of the oil.

A second timex can be provided which is reset upon each oil change, so as to enable the controller 21 to control flow resistances of the metering valves 6 taking account of long-term variations of oil viscosity associated with aging.

Further, a rotation speed sensor can be provided for detecting e.g. the speed of crankshaft 14.

If the engine is running for a long time at a low rotation speed, it may be assumed that splashing of crankshaft 14 in oil pan 2 is insufficient to ensure sufficient lubrication of the cylinder inner surfaces. In that case, valve 6 of path 12 can be opened to a maximum, whereas the flow rates of the other paths 7, 9 is reduced, in order to ensure a. sufficient flow of oil to the small end bearings 19 of the piston rods 17 so that oil which escapes from the bearings 19 can spread to the cylinder walls. If desired, oil spraying nozzles can be provided along the bores 18 in order to spray oil directly onto the cylinder walls.

Similarly, oil flow through path 12 can be favoured at the expense of paths 7 and 9 if the engine has been running for a long time at an extremely high speed, in order to ensure cooling of the pistons 20 by the flow of oil.

A slightly modified embodiment of the invention S is shown in Fig. 2. In this figure path 12 is replaced by two parallel paths 22, 23 one of which comprises the crank shaft bearings 13, whereas the other path 23 extends within crankshaft 14 and has branches for lubricating big end bearings 16 of the piston rods 17 and, by internal bores 18 of the piston rods 17, the little end bearings 19 thereof. By placing crankshaft bearings 13 and piston rod bearings 16, 19 in different paths, the fraction of the total oil flow rate which is delivered to the piston rod bearings and which is available for piston cooling can be made still larger than in the embodiment of Fig. 1.

Since the oil has magnetic particles in it, the metering valves 6 can have a particularly simple design which is totally devoid of moving parts. As shown in Fig. 3, a metering valve 6 can be formed simply by a solenoid 24 extending around a piece of oil tubing 25. If an electric current is applied to solenoid 24, a magnetic field forms inside tubing 25, attracting the magnetic particles suspended in the oil. These particles therefore tend to resist the oil flow, forming inside the tubing 25 what might be referred to as a "leaky plug". In general, the metering valve 6 may not be able to block the oil flow completely, but this is not desirable, either. If the oil flow could be blocked completely, parts of the engine might be left unlubricated in case of a failure of controller 21 or a metering valve 6. With the valve 6 of Fig. 3, the only possible failure is a failure of the current in solenoid 24, which would leave the metering valve 6 completely open.

List of reference signs 1. engine 2. oil pan 3. pump 4. oil filter 5. manifold 6. meteing valve 7. path 8. tappet 9. path 10. bearing 11. crankshaft 12. path 13. bearing 14. crankshaft 15. bore 16. bearing 17. piston rod 18. bore 19. bearing 20. piston 21. controller 22. path 23. path 24. solenoid 25. tubing