SE2150171A1 - Fuel line for handheld power tool - Google Patents

Abstract

A fuel line for a handheld power tool is provided. The fuel line comprises a first free end arranged to be connected to a fuel filter to be positioned within a fuel tank of the handheld power tool, a second end arranged to be in fluid connection to a fuel supply device arranged to introduce fuel into an internal combustion engine in the power tool. The fuel line further comprises a particle trap section which comprises a tubular magnet positioned within the fuel line. Since the magnet is positioned within the fuel line between the fuel filter and the fuel delivery device, it will stop any magnetic material that passes through the fuel filter to reach the fuel supply device and adhere to the magnetic valves.

Description

FUEL LINE FOR HANDHELD POWER TOOL Field of the invention The present disclosure relates to a fuel line in a hand-held power toolcomprising particle trap for capturing magnetic particles. The presentdisclosure further relates to a handheld power tool comprising such a fuel line.

Backqround of the invention A two-stroke engine is a type of internal combustion engine which completesa power cycle with two strokes of the piston during only one crankshaftrevolution. The uppermost position of a piston in a cylinder is usually referredto as the top dead centre and the lowermost position of the piston in thecylinder is usually referred to as the bottom dead centre. Compared to four-stroke engines, two-stroke engines have a smaller number of moving parts,and consequently can be made more compact and significantly lighter.Therefore, two-stroke petrol engines are used in applications wheremechanical simplicity, light weight, and high power-to-weight ratio are mainconcerns. Typical applications are handheld tools such as chainsaws.

Most small sized two-stroke engines are crankcase-scavenged enginesmeaning that these engines use the area below the piston as a chargingpump to build up pressure in the crankcase during the power stroke of thepiston. Traditionally, two-stroke engines have been provided with fuel supplydevices in the form of carburettors with mechanically controlled valves,arranged at the inlet of the engine to supply an air/fuel mixture to thecrankcase. To adjust the air/fuel mixture provided to the engine by thecarburettor, the valves are manually adjusted. However, development has led to fuel systems comprising electronically controlled fuel supply devices such as carburettors or injectors for injecting fuel into an injection space of theengine. Typically, in electronically controlled carburettors and injectors thefuel flow is partly or fully controlled by electromagnetic valves. This providesseveral advantages over fully mechanically controlled valves, among them ahigher controllability of the amount of injected fuel to provide a more preciseair fuel ratio in the engine, providing higher power and/or less emissions fromthe engine.

Magnetic particles in the fuel may get stuck to the electromechanicallyactuated valve(s) and cause malfunction of the valve. Magnetic particles inthe fuel may be metal shavings from fuel tanks, fuel pump handles etc.

To prevent dirt contaminations in the fuel to reach the fuel system, handheldpower tools are provided with a fuel filter (also known as suction head) that isfitted to the end of the fuel line and positioned in the fuel tank. The fuel filtermay move in the tank, so that gravity pulls it to the bottom of the tankregardless which direction the tool (and thereby the tank) is oriented. Therebythe engine may get fuel regardless of the orientation of the tool.

However, magnetic particles may pass through such fuel filters and adhere toan electromagnetic valve, and potentially impair the function of the valve. lt has been suggested in US20130133620 to add a magnet to the fuel filter ina fuel tank of a chainsaw. This solution has drawbacks. The filter is aconsumable and needs to be replaced at intervals. A magnet, however, cankeep its function during the lifetime of the tool. To be able to reuse a magnetin a filter, it must be possible to open filter and move the magnet from a usedfilter to a new filter. This makes the filter complex, expensive and prone tofailure. Further, tests have shown that enough metallic particles may passthrough such filters to impair the function of the fuel supply device.

Summary of the invention lt would be advantageous to achieve a fuel line overcoming, or at leastalleviating, the above-mentioned drawbacks. ln particular, it would bedesirable to enable a robust and cost-efficient fuel supply system that mayprevent magnetic particles from reaching the fuel supply device of a handheld power tool such as a chainsaw.

To better address one or more of these concerns, a fuel line and a handheldpower tool having the features defined in the independent claims are provided. Preferable embodiments are defined in the dependent claims.

Hence, according to an aspect, a fuel line for a handheld power tool isprovided. The fuel line comprises a first free end arranged to be connected toa fuel filter to be positioned within a fuel tank of the handheld power tool, asecond end arranged to be in fluid connection to a fuel supply devicearranged to introduce fuel into an internal combustion engine in the powertool. The fuel line further comprises a particle trap section which comprises a tubular magnet positioned within the fuel line.

Since the magnet is positioned within the fuel line between the fuel filter andthe fuel delivery device, it will stop any magnetic material that passes throughthe fuel filter to reach the fuel supply device and adhere to the magneticvalves. And as the magnet is positioned within the fuel line, standarddisposable fuel filters can be used and be replaced without moving orchanging the magnet. Since the magnet is placed in the fuel line, the systemmay be removed for cleaning if needed. lt may also be also be retrofitted toexisting products. Thereby, a cost effective, robust filtering of magneticcontaminations in the fuel is achieved.

The fuel delivery device may be an electronically controlled or adjustable carburettor or a fuel injector.

Optionally, the particle trap section is positioned between the first end of thefuel line and the part the fuel line arranged to be attached to the wall of thefuel tank. Thereby, the particle trap section will be positioned in the fuel tankwhen the fuel line is used in a power tool and magnetic particles in the fuel inthe fuel tank may accumulate on outside of the particle trap section. Thereby,a large portion of the magnetic particles in the fuel is kept from entering thefuel filter 21. This improves the efficiency of filtering of magnetic particles.

Optionally, the fuel line is being made of an elastic material, preferably a polymer, such as nitrile rubber.

Optionally, the tubular magnet is friction fitted in the fuel line. Thereby, areliable fastening of the magnet in the fuel line which allows for efficientmanufacturing of the fuel line, is achieved. ln addition, or as an alternative, the magnet may be glued, or form fitted in the fuel line.

Optionally, the inner radius of the tubular magnetic trap is at least 90% of theinner radius of the fuel line outside the particle trap section. Thereby filtering is achieved without impairing the fuel flow through the fuel line.

Optionally, the length of the tubular magnet in its axial direction is between 2and 4 times the inner diameter (DM) of the tubular magnet (4). Therebyeffective filtering and stable fitting of the tubular magnet in the file may beachieved.

Optionally the tubular magnet is a neodymium magnet. Thereby a good weight to efficient ratio of the magnet is achieved.

According to an aspect, a handheld power tool is provided. The power toolcomprises a fuel tank, an internal combustion engine, a fuel delivery devicearranged to introduce liquid fuel into the internal combustion engine and a fuelfilter positioned in the fuel tank (9). The fuel filter and the fuel supply device are in fluid connection via a fuel line described above.

Optionally, the engine is a one cylinder, crankcase scavenged two-strokeengine. Thereby a handheld power tool with good power to weight ratio is made possible.

The handheld power tool may be a chainsaw. lt may also be a power cutter, blower, a trimmer, a brushcutter, or similar. lt is noted that embodiments of the invention relate to all possible combinations of features recited in the claims.

Brief description of the drawinqs Various aspects of the invention, including its particular features andadvantages, will be readily understood from the example embodimentsdiscussed in the following detailed description and the accompanyingdrawings, in which: Figure 1 shows a handheld power tool according to embodiments.Figure 2 shows a known fuel line, a fuel filter and a fuel delivery device.

Figure 3a shows a fuel line comprising a particle trap section according to embodiments.

Figure 3b shows a cross section of the fuel line and the particle trap section in Figure 3a.

All the figures are schematic, not necessarily to scale, and generally onlyshow parts which are necessary in order to elucidate the embodiments,wherein other parts may be omitted. Like reference numerals refer to likeelements throughout the description.

Detailed description of embodiments Fig. 1 shows, as an exemplary embodiment of a handheld power tool, anengine-driven chainsaw 1. The invention is particularly advantageous forportable, handheld power tools that are moved and swivelled duringoperation, such as chainsaws, hedge trimmers, power cutters, brushcutters,blowers and the like. The chainsaw 1 has a housing 8 on which a rear handle3 is arranged. Within the housing 8 there is arranged an internal combustionengine 2, which propels a saw chain 17 around a guide bar 16. A fuel tank 8is integrated into the housing 8. A fuel line 9 opens into the fuel tank. A firstend 12 of the fuel line 9 is connected to a fuel supply device. A fuel filter isfixed to the second end 11 of the fuel line 9, this end is free and projectinginto the fuel tank 8. The fuel line 9 may preferably be formed in one piecebetween the fuel supply device 22 and the filter 21 and be passed through thewall of the fuel tank 8. However, it is also possible to form the fuel line 9 froma plurality of segments, which may be connected, for example, in the area ofthe wall of the fuel tank.

The fuel supply device may be, for example, a carburettor 22. Metering of fuelcan be achieved by the prevailing negative pressure in the intake port, or, in addition, via a valve, in particular an electromagnetic valve. However, it is also possible to supply the fuel directly via a fuel injector, for example into a crankcase or a transfer channel of internal combustion engine.

As Figs. 2 and 3 show, the fuel line 9', 9 is curved and includes severalthickenings 15a, 15b, 15a', 15b', which may serve for stabilizing and forpositioning the fuel line in the power tool 1.The first thickening 15a', 15 mayfixate the fuel line in the via hole in wall of the fuel tank 8 where the fuel lineenters the tank as well as sealing between the fuel line and the tank wall. Thefuel line 9', 9 is made of a flexible material, such as a polymer like plastic orrubber, preferably nitrile rubber. The fuel filter 21 comprises a porous housingwhich is substantially cylindrical. lnside the filter 21, a cylindrical weight maybe positioned, to help keep the fuel filter at the bottom of the fuel tank 6.

Fig. 2 shows a known fuel line 9' without a particle trap section. Fig. 3a showsa fuel line 9 with a particle 10 positioned a short distance from the second end11 of the fuel line which is arranged to be attached to a fuel filter 21 in the fueltank 6 of the handheld tool 1. The fuel line 9' in Fig. 2 and the fuel line 9 in Fig. 3 may be interchangeable in a fuel system.

As can be seen in Figs. 3a and 3b, and the diameter of the fuel line 9 isincreased at the particle trap section 10. This widening of the fuel line isachieved by the tubular magnet 4 being pressed into the elastic fuel line 9,thereby increasing the diameter at the position of the particle trap section 10.Preferably, the fuel line is made in one piece, at least from the second end 11to the first thickening 15a. By providing the fuel line without anyjoints at theparticle trap section, the risk of fuel leakage is decreased, and cost-effectivemanufacturing may be achieved.

By positioning the tubular magnet 4 just above the fuel filter 21 inside the fuelhose 9, the fuel is passed through the magnet 4 and a magnetic particles thatmay pass through the fuel filter 21 will stick to the inner wall 5 of the tubularmagnet 4. Thereby, the magnetic particles are prevented from getting furtherup through the fuel system to the fuel supply device. Thereby, the risk ofmagnetic particles sticking to, and impairing the function of, electromagneticvalves in a carburettor or injector is overcome, or at least alleviated.

Since the tubular magnet 4 is placed a short distance from the fuel filter 21 inthe fuel line, the tubular magnet will be positioned in the fuel tank of the powertool and magnetic particles in the fuel tank will, at least to some extent,accumulate on the outside of the fuel line 9 at the particle trap section 10.Thereby, a portion of the magnetic particles in the fuel is kept away from thefuel filter 21 where the fuel enters the fuel line 9, decreasing the number ofparticles entering the fuel filter. This improves the efficiency of the magneticparticle filtering, and lessens the need for cleaning or replacing the fuelsystem, and if needed, magnetic particles can be removed from the outside ofthe fuel line, e.g. when refilling the fuel tank, without disassembling the fuelsystem.

The tubular magnet 4 is preferably fitted to the fuel line by pressing themagnet into position in the elastic fuel line 9. The elastic forces of the fuel linecreate a friction fitting that holds the magnet in place, but it is also possibleimprove the bond between magnet and fuel line using an adhesive. Otherfastening means, such as form fitting, may be utilised.

By placing the tubular magnet 4 in the fuel line 9, it may be possible to addthe particle trap as an extra step at the production of an existing fuel line 9,without the need for changes of existing tools. Thereby the same productionline may be used both for fuel lines without and with magnetic particle trapsections 10. Further, with the particle trap section 10 placed in the fuel line,the mounting of the fuel line and the fuel filter into the fuel tank on toolassembly line is not affected, and tools with and without particle trap sections may me assembled at the same line.

The tubular magnet is designed in such a way that its inner diameter ispreferably equal or larger, or at least 90% of the than the inner diameter ofthe fuel hose to prevent the fuel supply from being restricted. However, thediameter of the tubular magnet is restricted as the diameter of the fuel line atthe particle trap section 10 should be smaller than the diameter of the via holein the fuel tank (less the diameter of the fuel line at the first thickening 15a) , to allow the fuel line to be mounted in the fuel tank.

The length of the magnet may be adapted to its ability to collect magneticparticles. Several magnets in a row can be used. By using neodymiummagnet, satisfactory filtering can be achieved with a magnet as short asapproximately 2-4 times the inner diameter of the inner diameter Divi of the magnet.

The person skilled in the art realizes that the present invention by no meansis limited to the embodiments described above. On the contrary, manymodifications and variations are possible within the scope of the appended claims.

Additionally, variations to the disclosed embodiments can be understood andeffected by the skilled person in practicing the claimed invention, from a studyof the drawings, the disclosure, and the appended claims. ln the claims, theword "comprising" does not exclude other elements or steps, and theindefinite article "a" or "an" does not exclude a plurality.

Claims (1)

1. A fuel line (9) for a handheld power (1) tool, wherein the fuel line (9)comprises: - a first free end (11) arranged to be connected to a fuel filter (21) to bepositioned within a fuel tank (9) of the handheld power tool - a second end (12) arranged to be in fluid connection to a fuel supplydevice (22) arranged to introduce fuel into an internal combustionengine (2) in the power tool (1), characterized in that the fuel line comprises - a particle trap section (10), wherein the particle trap section comprises a tubular magnet (4) positioned within the fuel line. The fuel line (9) of claim 1 wherein the particle trap section (10) ispositioned between the first end (12) of the fuel line (9) and the part thefuel line (15a) arranged to be attached to the wall of the fuel tank (9). The fuel line (9) of any of the previous claims, wherein the fuel line isbeing made of an elastic material, preferably a polymer, such as nitrile rubber. The fuel line (9) of any of the previous claims wherein the tubularmagnet (4) is friction fitted in the fuel line. The fuel line (9) of any of the previous claims wherein the inner radius(Divi) of the tubular magnetic trap is at least 90% of the inner radius(DL) of the fuel line outside the particle trap section. The fuel line (9) of any of the previous claims wherein the length (Livi)of the tubular magnet (4) in its axial direction is between 1 and 4 times the inner diameter (DM) of the tubular magnet (4). The fuel line (9) of any of the previous claims wherein the tubular magnet (4) is a neodymium magnet. 8 A handheld power tool (1) comprising a fuel tank (6), an internal combustion engine (2), a fuel supply device (22) arranged to introduceliquid fuel into the internal combustion engine (2), a fuel filter (21)positioned in the fuel tank (6) wherein the fuel filter (21) and the fuel 5 delivery device (22) are in fluid connection via a fuel line (9) accordingto anyone of claims 1 - 9. 9 The handheld power tool according to claim 8 wherein the particle trapsection is positioned within the fuel tank (6). 10 The handheld power tool according to claim 8 or 9, wherein the engine10 is a one cylinder, crankcase scavenged two-stroke engine.