GB2471530A

GB2471530A - A reciprocating two stroke engine

Info

Publication number: GB2471530A
Application number: GB0915574A
Authority: GB
Inventors: Dan Merritt
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-07-03
Filing date: 2009-09-07
Publication date: 2011-01-05
Also published as: GB0915574D0

Abstract

A reciprocating two stroke engine is presented which uses a method of lubrication for the cylinder bore 2 by the delivery and extraction of oil to and from intercommunicating grooves 14, 114, 214 in the piston's skirt, through small delivery and extraction holes 25, 125 in the cylinder bore trapping oil between an upper oil scraping ring 41 and a lower oil scraping ring 42 positioned around the piston 1. This method avoids contamination of air pumped through the crankcase with lubricating oil which in turn reduces 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 but does not mix the air with lubricating oil mist. Minimising the entrapment of oil into the air in the crankcase reduces the emission of hydrocarbons from the engine's exhaust.

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; gas transfer ports around the circumference of the cylinder exchanging gases between the cylinder and the space outside it; an upper oil scraping piston ring situated around the piston above the gudgeon pin; a lower oil scraping piston ring situated around the piston below the gudgeon pin; oil dispensing means capable of controlling pressurised lubricating oil supply; lubrication oil supply hole means communicating with the oil dispensing means and cylinder bore; lubrication oil return hole means, situated away from the lubricating oil supply hole means also communicating with the cylinder bore and an external oil collecting receptacle; intercommunicating oil conveying grooves cut into the piston skirt also communicating with both the lubrication oil hole supply means and lubrication oil hole return means such grooves do not communicate directly with any of the gas transfer ports, or with the crankcase, at any time in the engine cycle; a crankcase used for inducing air and delivering it into the engine's cylinder; characterised in that both the lubrication oil supply hole means and lubrication oil return hole means in the cylinder bore remain situated in between the upper oil scraping piston ring and the lower oil scraping piston ring during the complete engine cycle and in that the oil dispensing means delivers oil to the grooves in the piston skirt which can be extracted through the lubrication oil return hole means and that the circumferential lubrication groove distributes some of this oil around the periphery of the piston and smears it along the cylinder bore during the movement of the piston in order to lubricate the movement of the piston in the cylinder bore.

Preferably a circumferential lubrication groove 14 is located a short distance above the lower oil scraping ring. This groove and the ring below it must always remain in the cylinder bore and also remain situated below the gas transfer ports 8 when the piston reaches its inner dead centre position.

Preferably a supply axial lubrication groove 114, which is parallel with the axis of the cylinder, is located facing the lubrication oil supply hole means 12 and also communicates with the circumferential lubrication groove 14, Preferably a second return axial lubrication groove 214 is located substantially diametrically opposite axial groove 114 facing the lubrication oil return hole means 125 and also communicates with the circumferential lubrication groove 14, both oil supply and oil return holes 12 and 125 should be positioned on the cylinder circumference as far as possible from the gas transfer ports 8 in order to prevent the axial grooves 114 and 214 from communicating directly with the gas transfer ports during the motion of the piston.

One of the functions of the circumferential lubrication groove 14 is to allow a temporary storage capacity for lubricating oil following the accumulation of oil scraped by the lower oil scraping piston ring during the compression stroke. The same purpose may be served by the groove containing the oil scraping ring when the ring design allows for unoccupied volume within the ring's groove.

Preferably oil flow from the lubrication oil supply hole means 12 at entry to the cylinder to the lubrication oil return hole means 125 is induced by suction applied at the lubrication oil return hole means 125 so that the oil pressure downstream of the lubrication oil supply hole means 12 remains slightly below the pressure in the crankcase during the compression stroke of the piston. This will ensure that there is no pressure gradient to induced oil to flow from the supply axial lubrication groove 114 to adjacent air inlet gas transfer port 8 during the compression stroke of the piston, when the axial lubrication groove 114 rises, as this can contaminate the air entering the cylinder with lubrication oil.

Oil can be delivered by the oil dispensing means 25 either continuously or intermittently as only a small quantity of oil may be sufficient to meet the piston lubrication needs.

Preferably the lubrication oil supply hole 12 will have a sufficiently small diameter to control the quantity of oil delivered, to maintain a slight vacuum pressure in this oil downstream of hole 12 and to produce a jet of oil which enters into the supply axial lubrication groove 114 when t is being delivered.

Preferably lubrication oil supply hole 12 should be positioned in the cylinder on the thrust face of the cylinder where the piston presses against the cylinder bore during the expansion stroke.

Preferably the lubrication oil supply hole means and the lubrication oil return hole means are situated on the cylinder face at some distance underneath the gas transfer ports apertures mid way on cylinder face between the two adjacent gas transfer ports situated above the holes in order to allow the two vertical grooves which communicate with the two holes to avoid communicating directly with any gas transfer port. The piston's upper oil scraping ring remains above both the lubrication oil supply hole means and the lubrication oil return hole means even when the piston is at its outer dead centre position. The terms referring to up or down situations regard the cylinder head as being at the uppermost position for the sake of this description.

Preferably the gudgeon pin 13 will be hollow to allow oil to enter its inside space. The pin will have a radial hole connected with the bearing surrounding it.

As additional means to capture any lubrication oil escaping from the cylinder bore, 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.

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-i and Figure-2. Figure-2 is similar to Figure-i but shows some detail not shown in Figure-i. These diagrams show the piston 1 and cylinder 2 with the piston at its outer dead centre position uncovering the gas transfer ports 8 which are inlet ports in this example where the exhaust is discharged through a cam driven valve situated in the cylinder head which is not shown, hence there is no exhaust gas transfer port in the cylinder liner. The transfer duct 31 conveys air from the crankcase, not shown, to the cylinder via gas transfer ports 8.

The upper oil scraping ring is 41 and the lower oil scraping ring 42 has a lower circumferential lubrication groove 14 situated above it. The circumferential lubrication groove 14 is cut into the piston skirt 19. The lubrication oil supply hole 12 delivers a jet of oil to the thrust face of piston 1 directly into the supply axial lubrication grove 114 shown in Figure-2.

Preferably though not essentially oil is being sucked into the lubrication oil return hole means 125 either by an external vacuum or suction pump or by a Venturi device which provides suction whilst passing oil delivered by a pressure pump. This should minimise or even eliminate oil leakage from the vertical groves into the gas transfer ports. If however the oil is pumped by above atmospheric pressure delivered at the lubrication oil supply hole means and such pressure exceeds the air pressure in the engine's crankcase during the compression stroke of the piston, some oil leakage may take place from the vertical grooves and into the inlet gas transfer ports resulting in some exhaust pollution but the extent of such pollution may be small if the pressure difference across the leakage paths is also kept small.

Oil flows through the supply axial lubrication groove 114 into the circumferential lubrication groove 14 and flows out through return axial lubrication groove 214 into the lubrication oil return hole 125 from where it returns to the oil tank to be recirculated by an oil pump. The circumferential lubrication groove 14 will be full of oil which will be smeared around the cylinder bore during the compression stroke with the lower piston ring 42 scraping it along the bore until the piston reaches its inner dead centre position. Any oil adhering to the piston skirt will be dragged into the upper portion of the cylinder and lubricate it and will then be scraped in the opposite direction by the upper piston ring 41 during the expansion stroke. Some of this oil remains trapped between the upper and lower oil scraping piston rings as it is conveyed up and down the cylinder bore by the movement of the piston. Some of this oil will find its way into the gudgeon pin's aperture in the piston to lubricate the connecting rod's little end which is advantageously a rolling element needle bearing, requiring little lubrication.

Any excess oil escaping the lower oil scraping ring 42 through its gap which drips into the crankcase below piston ring 42 can be collected by the circumferential channel or gutter 15 from where it is removed through ducting 17 and extracted from the crankcase, for recirculation. In this way the engine will operate with effectively a dry sum.

Claims

CLAIMS1. 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; gas transfer ports around the circumference of the cylinder exchanging gases between the cylinder and the space outside it; an upper oil scraping piston ring situated around the piston above the gudgeon pin; a lower oil scraping piston ring situated around the piston below the gudgeon pin oil dispensing means capable of controlling pressurised lubricating oil supply; lubrication oil supply hole means communicating with the oil dispensing means and cylinder bore; lubrication oil return hole means, situated away from the lubrication oil supply hole means also communicating with the cylinder bore and an external oil collecting receptacle; intercommunicating oil conveying grooves cut into the piston skirt also communicating with both the lubrication oil hole supply means and the lubrication oil hole return means such grooves do not communicate directly with any of the gas transfer ports or with the crankcase at any time during the engine cycle; a crankcase used for inducing air and delivering it into the engine's cylinder, characterised in that both the lubrication oil supply hole means and the lubrication oil return hole means in the cylinder bore remain situated in between the upper oil scraping piston ring and the lower oil scraping piston ring during the complete engine cycle and in that the oil dispensing means delivers oil to the grooves in the piston skirt which can be extracted through the lubrication oil return hole means and that a circumferential lubrication groove distributes some of this oil around the periphery of the piston and smears it along the cylinder bore during the movement of the piston in order to lubricate the movement of the piston in the cylinder bore.
2 An engine according to claim 1. where the circumferential lubrication groove is located around the skirt of the piston above the lower oil scraping piston ring and below the gudgeon pin; 3 An engine according to claim-i where the circumferential lubrication groove is the groove that contains the lower oil scraping piston ring; 4 An engine according to claim-i where a supply axial lubrication groove, parallel to the cylinder axis, is provided along the piston skirt located in a position facing the lubrication oil supply hole means and extending into the said circumferential lubrication groove to provide communication for oil flow between the lubrication oil supply hole means and the said circumferential lubrication groove; An engine according to claim-i where a return axial lubrication groove, parallel to the cylinder axis is provided along the piston skirt located in a position facing the lubrication oil return hole means and extending into the circumferential lubrication groove to provide communication for oil flow between the said circumferential lubrication groove and the lubrication oil return hole means; 6 An engine according to claim-i where oil flow from the lubrication oil supply hole means to the lubrication oil return hole means is induced by suction applied to the lubrication oil return hole means 7 An engine according to claim-i 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 claim-i where the oil dispensing means delivers oil intermittently; 9 An engine according to claim-i operating with a crankcase sump which does not contain any substantial amount of lubricating oil.