GB2119024A

GB2119024A - Ignition cut out for internal combustion engine

Info

Publication number: GB2119024A
Application number: GB08208787A
Authority: GB
Inventors: James Steel
Original assignee: Ogden Electronics Ltd
Current assignee: Ogden Electronics Ltd
Priority date: 1982-03-25
Filing date: 1982-03-25
Publication date: 1983-11-09

Abstract

Apparatus for controlling operation of an ignition system of an internal combustion engine used for powering a chain saw comprises a chamber (21) for connecting a source of liquid fuel from a fuel tank (12) to a carburettor of the engine (11) and a float (26) contained within the chamber (21), the float having means (27) for operating a switch (28, 30, 31) contained in the system so that, as the fuel drains from the chamber (21) the float (26) is lowered in the chamber (21) with a result that the switch (28, 30, 31) operates to disconnect supply of power in the ignition system. <IMAGE>

Description

SPECIFICATION Ignition cut out for internal combustion engine This invention relates to an ignition cut out for an internal combustion engine and, more particularly, an internal combustion engine of a chain saw.

It is known to provide a chain saw with an internal combustion engine for providing motive powerto the saw. It is also known to provide such a chain sawwith an abrasive wheel attachmentforcutting building blocks.

Although a chain saw having an abrasive wheel attachment may operate satisfactorily below a predetermined speed of rotation ofthe abrasive wheel, for example below 10,000 r.p.m., ifthe speed of rotation exceeds the predetermined value, there is a tendency forthe wheel to disintigrate.

While an operator of a chain saw provided with an abrasive wheel attachment may be careful to ensure thatthe speed of rotation ofthewheel does not exceed a predetermined maximum, it has been found that, due to the characteristics of two stroke internal combustion engines generally used to power chain saws, such engines will increase in speed when fuel starvation isaboutto occur.

In consequence, if a chain saw having an abrasive wheel attachment is being used such thatthe speed of rotation ofthewheel is substantially the predeterminedspeed and supply of liquid fuel to an internal combustion engine ofthe saw is cut of or used up, the speed ofthe engine will increase at an instant prior to fuel starvation with a resultthatthe abrasive wheel will be rotated at a speed above the predetermined speed and, in consequence, maydisintigrate.

According to the present invention, there is provided apparatusforcontrolling operaton of an ignition system of an internal combustion engine comprising a chamberfor connecting a source of liquid fuel to a carburettor of the engine and a float within the chamberforfloating on fuel also contained within the chamber, the float having means for operating a switch contained in the system so that, as the fuel drains from the chamber, the float is lowered in the chamber with a result that the switch operates to disconnect supply of power in the ignition system.

In this manner, the ignition system is cut out priorto the carburettor ofthe engine being starved of fuel and the speed of operaton of the engine will not increase as would occur if the carburettorwereto be starved of fuel. Furthermore, since the carburettor will not be starved of fuel,the engine, afterthe supply tank has been filled, can be restarted without having to draw the fuel into the carburettor.

Following is a description, byway of example only and with reference to the accompanying drawings, of one method of carrying the invention into effect.

In the drawings: Figure lisa perspective view of a chain saw having an abrasive wheel mounted thereon and, Figure 2 is a diagrammatic cross section of apparatus for controlling operation of ignition system of an internal combustion engine of the chain saw in accordance with the present invention.

Referring to the drawings, a chain saw 10 comprises an internal combustion engine 11 having a liquid fuel tank 12, a pair of spaced handles 13,14 and an elongate arm 15 extending forwardly from the engine 11. An end portion of the arm 15 remote from the engine 11 is provided with a shaft 16 which is rotated on a central longitudinal axis thereof from a drive mechanism comprising a chain 17 driven bythe engine 11.

The saw 10 is provided with an attachment in the form of a wheel 18 having a circumferential abrasive surface 19. The wheel 18 is provided with means 20 for securing the wheel 18 to the shaft 16 in co-axial relationship therewith.

The fuel tank 12 has attached to the underside thereof a chamber 21 having an inlet 22 and an outlet 23. The chamber 21 is provided with a bore 24 and an upper surface ofthe chamber 21 adjacent the bore is provided with a recess 25. The chamber 21 has located therein afloat 26 having a pin 27 upstanding therefrom, the pin extending through the bore 24 and having secured thereto an upper surface thereof a metallic plate 28.

The chamber 21 is located adjacent a base member 29 of electric non-conductive material,the base member 29 having a pair of spaced metallic terminals 30,31 arranged such that, when the float 26 is in a raised position inthe chamber21,the plate-28 connects the terminals 30,31 oneto another. The terminal 30 has secured thereto one end of a lead 32 of an ignition system of the engine 11 1 the lead 32 being connected to a power source of the system, and the terminal 31 has connected thereto one end of a lead 33 of the system, the lead 33 being connected to a spark plug of the engine 11.

The inlet 22 ofthe chamber 21 has connected thereto one end of a conduit34for supplying fuel by gravity from the tank 12 to the chamber 21. The outlet 23 of the chamber 21 is connected to a conduit (not shown) for supplying fuel to a carburettor (not shown).

When the fuel tank 12 contains liquid fuel, the fuel passes through the conduit 34, the chamber 21 and the conduit connecting the chamber 21 to the carburettor and thereby fills the chamber 21 causing the float 26 to be raised in the chamber 21 to the position shown in Figure 2 wherein the plate 28 is urged againstthe terminals 30,31. In consequence electric connection is made in the ignition system from the power source to the spark plug. However, if fusel in the tank 12 depletes to an extent such thatthefuel drains from the chamber 2l,thefloat 26 is lowered in the chamber 21 as the level of liquid fuel in the chamber decends. In consequence, the pin 27 is lowered in the bore 24 and the plate 28 attached to the pin 27 is withdrawn from contact with the terminals 30,31 and suppply of power to the spark plug in the ignition system is cut off. The engine 11 thereby is rendered inoperative although the carburettor has not been starved offuel.

In this manner, the ignition system of the engine is cut out before fuel starvation occurs thereby reducing any tendency of the speed of the engine to increase priorto supply of fuel thereto being cut off. Furth ermoreitisunnecessarytodrawfuel intothe carburettorwhen the engine isto be restarted, after fuel has been re-supplied to the chamber 21, because the carburettor has not been starved offuel.

Claims

1. Appratusforcontrolling operation of an ignition system of an internal combuston engine comprising a chamberfor connecting a source of liquid fuel to a carburettorofthe engine and a float contained within thechamberforfloating on fuel also contained within the chamber, the float having means for operating a switch contained in the system so that, as the fuel drains from the chamber, the float is lowered in the chamberwith a resultthat the switch operates to disconnect supply of power in the ignition system.

2. Apparatus as claimed in Claim 1 wherein the chamber is contained in a conduitforsupplying fuel to the carburettor bygravityfeed.

3. Apparatus for controlling operation of an ignition system of an internal combustion engine substantially as hereinbefore described and as illustrated in the accompanying drawings.