GB2471528A

GB2471528A - Two-Stroke Engine with Oil Injection to the Piston/Cylinder Interface

Info

Publication number: GB2471528A
Application number: GB0912414A
Authority: GB
Inventors: Dan Merritt
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-07-03
Filing date: 2009-07-17
Publication date: 2011-01-05
Also published as: GB0913900D0; GB0911564D0; GB0912414D0

Abstract

A reciprocating piston two-stroke engine is lubricated by the intermittent injection of oil to the engine cylinder bore 2 via a lubrication hole 12. The engine has a lubrication groove 14 (20 fig 3) cut around the cylinder bore or around the piston's skirt 19, and pressurised oil is injected under the control of a control module and an associated valve 25 in communication with the lubrication hole. The engine includes a connecting rod and a gudgeon pin 7 which may be hollow, and the lubrication hole may align with the axis of the gudgeon pin at some point during the engine cycle. The cylinder may include a circumferential channel or gutter 15 to collect excess oil, and the excess oil may be delivered to an extraction duct 17. The oil is injected for a predetermined duration during engine operation, and in use, the invention reduces oil contamination of air pumped through the crankcase, therefore reducing exhaust emissions.

Description

INTERNAL COMBUSTION ENGINE

This invention relates to reciprocating internal combustion engines operating on the two stroke cycle. In particular it relates to a lubricating system for such engines. It describes a device capable of lubricating the cylinder bore to ease the motion of the piston within it as well as to meet the lubrication needs of the gudgeon pin at the small end of the connecting rod.

Some two stroke spark ignited engines, which use the crankcase as an air pump, achieved their lubrication needs by mixing oil in the gasoline which entered the crankcase with the air intake.

Such engines are out of favour nowadays because they caused excessive emission of unburnt hydrocarbons in the exhaust. One application for the device described in this invention is to meet the lubrication needs of the piston and gudgeon pin in a two stroke engine which uses the crankcase as its air pump whilst minimising the entrapment of oil into the air in the crankcase so reducing the emission of hydrocarbons from the engine's exhaust.

A new type of engine is described, by way of an example, in international patent publication W02005/052335. Its two stroke embodiment is illustrated in Figure-i it has an external combustion chamber 6 and uses a fuel injector 11 to deliver fuel directly into the combustion chamber and not into the crankcase 35. Such an engine cannot mix lubricating oil with fuel entering the crankcase and the need to provide lubrication without causing excessive exhaust emissions of unburnt hydrocarbons has led to the need to invent the device described here as an alternative to spraying oil mist into the air intake. One advantage of constructing this new type of engine as a two stroke is to increase its brake thermal efficiency due to the reduction of mechanical friction when operating as a two stroke.

Accordingly this invention provides an internal combustion reciprocating engine operating on the two stroke cycle comprising; a piston reciprocating in a cylinder comprising a piston crown and a piston skirt; a connecting rod attached to the piston; a gudgeon pin attached to the piston and to the connecting rod; a lubricating groove around the circumference of either the piston skirt or around the circumference of the cylinder bore oil valve means capable of starting and stopping lubricating oil supply; lubricating hole means communicating with the oil valve means and cylinder bore; a pressurised lubricating oil supply means; control means for activating the oil valve means; characterised in that the oil valve means is activated to open intermittently for predetermined durations, between selected intervals of engine cycles, to deliver a quantity of oil to the said lubricating hole; Preferably the oil valve means 25 is electrically actuated by the control means to deliver a small quantity of oil at intervals of predetermined number of engine revolutions, for example every one thousand revolutions.

The oil valve means can be similar to a solenoid type fuel injector in construction or an electrically actuated on/off valve capable of rapid actuation and will be connected to a pressurised lubricating oil supply.

Preferably the lubricating hole 12 will have a sufficiently small diameter to produce a jet of oil when it is being delivered.

Preferably, for the purpose of lubricating the gudgeon pin, at least one lubricating hole 12 supplied by the oil valve means 25 will be aligned with the axis of the gudgeon pin 7 when facing it.

Preferably the gudgeon pin will be hollow and partially blocked at its ends. Alternatively the end furthest from the lubricating oil when facing it can be fully blocked to retain oil within the pin. The pin will have a radial hole connected with the bearing surrounding it.

In a multi cylinder engine lubricating holes 12 may be connected together into an oil gallery and oil valve means 25 can deliver oil to a number of cylinders communicating with such a gallery provided the pistons in those cylinders reach a suitable position at the same crankshaft position.

For the purpose of lubricating the cylinder bore, If the lubricating groove 14 is cut into the piston skirt, the oil valve means will be energised to deliver oil during the short duration synchronised with the time when the piston reaches the position for the lubricating hole 12 to be opposite the said grove 14. Preferably such a groove cut into the piston skirt 19 should be positioned so as to avoid it sliding over the transfer port, or exhaust port if used, when the piston reaches the inner dead centre position.

If the lubricating groove 20 is cut into the cylinder bore 2 the oil valve means can be energised for a short duration at any piston position. Preferably such a groove 20 cut into the bore 2 should be positioned so as to avoid the piston rings sliding over it.

Preferably irrespective of the location of the lubricating groove, the lower part of the cylinder may be provided with a circumferential channel functioning as a gutter 15 to collect any oil descending from the cylinder bore and allowing it to be extracted through a piped passage 17 to an oil return gallery, so as to be removed from the crankcase and delivered by suction, towards a recirculation oil pump.

Some pistons are designed with a skirt which does not extend over the full circumference at the lower end of the piston, furthest from the crown, in order to reduce weight. In such cases the lubricating groove may need to be placed around the cylinder bore.

The advantages of cutting the lubricating groove into the cylinder bore are: a) The duration of oil delivery can be prolonged, in terms of time, which is advantageous for high speed engines.

b) The timing of oil delivery need not synchronised exactly with a piston position.

c) Direct oil delivery to the gudgeon pin bearing may not be necessary if the pin's aperture in the piston side is designed to pass over the lubricating groove where it may collect some oil.

Therefore the location of the lubricating hole need not align with the gudgeon pin axis and can be placed to advantage at the thrust face of the cylinder, for example.

The advantages of cutting the lubricating groove into the piston skirt are: a) Easier groove machining operation.

b) This location is suitable for slower larger engines where more time is available for oil delivery to be synchronised with piston location over a small crank angle arc.

c) Possibly a more effective oil si-nearing process over the cylinder bore since the piston itself transports the oil over the cylinder bore during its movement.

The operation of this lubricating system is described by way of an example of one possible embodiment of this invention with the aid of Figure-2. In this diagram the lubricating groove 17 is cut into the piston skirt 20, the inlet port is 3, the exhaust port is 4, the transfer port is 8 and the transfer duct is shown as 31.

For the purpose of lubricating the small end bearings of the gudgeon pin, the oil valve means is actuated once when lubricating hole 12 is opposite the gudgeon pin's bore. It will not be actuated again in this position until, for example, one thousand engine revolutions are counted, such duration to be determined experimentally.

For the purpose of lubricating the cylinder bore the actuation when the oil valve means takes place when hole 12 is opposite groove 14. This can take place during another engine revolution if desirable at higher engine speeds.

Such actuation is best operated when the piston reaches dead centre position as this gives more time for oil delivery. To achieve this position of the groove and lubricating hole is chosen to coincide at this piston position. The oil valve means is actuated electromagnetically and supplied with pressurised lubricating oil. The timing of opening and closure is determined by the control means and the duration of opening is influenced by the engine speed, the temperature of the oil and the quantity of oil desired to be delivered..

The small quantity of oil delivered to by the oil valve will find its way into the bearings and cylinder bore and the quantity delivered should be minimised to avoid excessive oil dropping into the sump.

Any small quantity such as the occasional drop of oil will not contaminate the air being pumped through the crankcase sufficiently to cause excessive exhaust emissions of hydrocarbons particularly if the sump is kept dry by extracting any oil from the lowest collecting point.

Any excess oil dripping into the crankcase below the piston can be collected by the circumferential channel or gutter 15 from where it is removed by suction through ducting 17 and extracted from the crankcase, for recirculation by an oil pump. In this way the engine will be operating with effectively a dry sump.

Oil delivered into the lubricating groove 14 in the piston crown will move around the grove until it surrounds the piston. If this is not achieved with a single lubricating hole 12 additional such holes may be positioned on the same peripheral circle around the cylinder bore to allow good circumferential distribution but, for smaller engines, a single lubricating hole 12 may be sufficient.

This oil delivered to the lubricating groove will be smeared over the cylinder bore surface when the piston reciprocates within it and the piston rings will ensure that it is not allowed to seep above the piston crown.

If a lubricating groove does not extend over the full circumference of a piston a second groove may be added to the piston to extend over the missing portion.

The operation of a two stroke engine where the lubricating groove is positioned in the cylinder bore is described by way of a second example of another possible embodiment of this invention with the aid of Figure-3. In this diagram the lubricating groove is shown as 20, the inlet port 3 is located below the piston's skirt at its outer dead centre position, the transfer port 8 is shown exposed and the exhaust port is replaced by an exhaust valve in the cylinder head, not shown.

The oil valve means 25 can be actuated for a short predetermined time or crank angle duration at any suitable piston position. If the lubricating hole is positioned on the axis of the gudgeon pin, as shown in Figure-3, and the oil valve is opened when the two are aligned, oil jet emerging form the lubricating hole will be delivered into the gudgeon pin. When the oil valve is opened at another piston position the oil jet will impinge on the piston skirt and some of it will be deflected back into the lubricating groove. Alternatively If the lubricating hole is positioned away from the axis of the gudgeon pin the pin may still receive lubricating oil when the groove is positioned to advantage so that the gudgeon pin's aperture in the piston's body 21 slides over the lubricating groove 20.

The provision of a multiplicity of lubricating holes and also of grooves which do not extend over the complete circumference of the bore can be designed into this embodiment of the invention as well.

Claims

CLAIMS1. An internal combustion engine operating on the two-stroke cycle comprising; a piston reciprocating in a cylinder comprising a piston crown and a piston skirt; a connecting rod attached to the piston; a gudgeon pin attached to the piston and to the connecting rod; a lubricating groove around the circumference of either the piston skirt or around the circumference of the cylinder bore oil valve means capable of starting and stopping lubricating oil supply; lubricating hole means communicating with the oil valve means and cylinder bore; a pressurised lubricating oil supply means; control means for activating the oil valve means; characterised in that the oil valve means is activated intermittently, for a predetermined duration, between selected intervals of engine cycles, to deliver a quantity of lubricating oil to the said lubricating hole;
2. An engine according to claim 1 wherein the lubricating hole delivers directly into the lubricating groove cut around the circumference of the cylinder bore;
3. An engine according to claim 1 or claim 2 wherein the oil valve means is a fast response electrically operated valve fed with pressurised lubricating oil supply;
4. An engine according to claim 1 or claim 2 wherein a plurality of lubricating holes are situated on the same circle around the circumference and communicate with oil valve means;
5. An engine according to claim 1 or claim 2 where one lubricating hole is positioned to align with the axis of the gudgeon pin when the two are at the same position;
6. An engine according to claim 4 where a plurality of oil valve means communicate with a plurality of lubricating holes;
7. An engine according to claim 1 where the lower end of the cylinder is fitted with a circumferential channel or gutter to collect excess oil and deliver it to an extraction duct;
8. An engine according to all preceding claims where oil is extracted from the sump to render it substantially dry;
9. An engine according to claim 1 or claim 2 wherein the gudgeon pin is hollow and has a closed or partially closed end at the end furthest from the lubricating hole position;
10. An engine according to claim 1 or claim 2 wherein a number of lubricating grooves are provided some not extending around the full circumference of the piston.