TECHNICAL FIELD

The present disclosure relates to a fuel supply arrangement for a crankcase scavenged two stroke engine. The present disclosure further relates to a crankcase scavenged two stroke engine and a hand-held power tool comprising such an engine.

BACKGROUND

A two-stroke engine is a type of internal combustion engine which completes a power cycle with two strokes of the piston during only one crankshaft revolution. The uppermost position of a piston in a cylinder is usually referred to as the top dead centre and the lowermost position of the piston in the cylinder is usually referred to as the bottom dead centre. Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts, and consequently can be made more compact and significantly lighter. Therefore, two-stroke petrol engines are used in applications where mechanical simplicity, light weight, and high power-to-weight ratio are main concerns. Typical applications are hand-held power tools, such as chainsaws.

Most small sized two-stroke engines are crankcase-scavenged engines meaning that these engines use the area below the piston as a charging pump to build up pressure in the crankcase during the power stroke of the piston. Such engines usually comprise an inlet connected to the crankcase and a transfer duct connecting the crankcase and the combustion chamber. In the power stroke of a two-stroke engine, the increased pressure and temperature in the cylinder obtained by the combustion of fuel is partially converted into mechanical work supplied to a crankshaft of the engine. At the same time, the pressure in the crankcase increases as a result of the movement of the piston towards the bottom dead centre. An exhaust port arranged in the cylinder wall is opened to allow exhaust gases to flow out from the cylinder when the piston reaches a first position relative the cylinder in its movement towards the bottom dead centre. The piston continues the movement towards the bottom dead centre and when it reaches a second position, below the first position, an inlet port arranged in the cylinder wall is opened. The inlet port is fluidly connected to the crankcase via the transfer duct. The air/fuel mixture in the crankcase is forced to flow into the cylinder via the inlet port by the overpressure in the crankcase.

Traditionally, two-stroke engines have been provided with a carburettor arranged at the inlet of the engine to supply an air/fuel mixture to the crankcase. However, development has led to fuel injection systems comprising an injector for injecting fuel into an injection space of the engine. The injection space may be form part of one or more of the crankcase, the inlet, the combustion chamber, and the transfer duct. Fuel injection systems provides several advantages over carburettors, among them a simpler and more robust design, a higher controllability of the amount of injected fuel and the possibility to inject fuel closer to the combustion chamber to obtain a better response of the engine. However, fuel injection systems of crankcase scavenged two stroke engines are also associated with some problems, drawbacks, and design difficulties.

A combustion engine generates a lot of heat and vibration during use and components of a fuel injection system, especially the fuel injector thereof, are needed to be arranged in close proximity to hot components of the engine. Therefore, a problem associated with fuel injection systems is the formation of fuel vapor in the system. Fuel vapor may cause an engine to run poorly and may make an engine difficult to start. The problem is especially prevalent for engines of hand-held power tools because hand-held power tools are usually operated at high output levels during use and are usually started and stopped frequently. Fuel vapor may form after operation of the engine which may make the engine difficult to start, and/or run poorly when started, and may form during operation which may make the engine to run poorly.

As indicated above, a fuel injection system comprising a fuel injector provides a better possibility to regulate the amount of supplied fuel than a carburettor system. The amount of supplied fuel affects the air/fuel ratio which is commonly referred to as the lambda value. In turn, the air/fuel ratio affects many aspects of an engine, including the fuel efficiency, the combustion temperature, the emission levels, and the startability, i.e. the ability of the engine to start. However, also with a fuel injection system comprising a fuel injector, it can be difficult to obtain a correct and accurate amount of injected fuel in all operational conditions without using complex and costly components and systems. Moreover, in general, on today’s consumer market, it is an advantage if products, such as two-stroke engines and associated products, components, and systems, have conditions and/or characteristics suitable for being manufactured and assembled in a cost-efficient manner.

The document US 2013340722 A1 relates to an internal combustion engine having a fuel system that has a fuel valve with a housing, wherein in the housing a fuel chamber is formed. A fuel pump pumps fuel from a fuel tank into the fuel chamber. A conveying pump provides forced conveyance of fuel into the fuel system. A feed line is connected to the fuel chamber of the fuel valve. The conveying pump is arranged in the feed line and supplies fuel to the fuel chamber. A relief line is connected to the fuel chamber of the fuel valve and a first valve is arranged in the relief line. The fuel system described in the document US 2013340722 A1 comprises a fuel pressure regulator arranged downstream of the fuel pump and upstream of a fuel injector of the fuel system, i.e. arranged at a position between the fuel pump and the fuel injector.

SUMMARY

It is an object of the present invention to overcome, or at least alleviate, at least some of the above-mentioned problems and drawbacks.

According to a first aspect of the invention, the object is achieved by a fuel supply arrangement for a crankcase scavenged two stroke engine. The fuel supply arrangement comprises a fuel tank, a fuel injector comprising a fuel inlet and a fuel return outlet, and a fuel pump configured to pump fuel from the fuel tank to the fuel inlet of the fuel injector. The fuel supply arrangement further comprises a return conduit connecting the fuel return outlet to the fuel tank. The fuel supply arrangement comprises a fuel pressure regulator configured to regulate an operating fuel pressure of the fuel injector. The fuel pressure regulator is arranged in the return conduit.

Since the fuel supply arrangement comprises the fuel pressure regulator arranged in the return conduit, the operating fuel pressure of the fuel injector is regulated to a precise level in a simple, robust, and cost-efficient manner. Thereby, conditions are provided for regulating the amount of injected fuel in a more accurate manner reducing the need for using costly and complex systems and arrangements. The operating fuel pressure of the fuel injector, as referred to herein, is the pressure of fuel at the fuel injector upon injection of fuel by the fuel injector into an injection space during regular operation of an engine comprising the fuel supply arrangement. The term regular operation of the engine is further defined below.

Moreover, since the fuel pressure regulator is arranged in the return conduit, a cooling flow of fuel is provided over the fuel injector during operation of the fuel supply arrangement and an engine comprising the fuel supply arrangement which significantly reduces the risk of formation of fuel vapor in the fuel supply arrangement. That is, as compared to systems comprising a fuel pressure regulator upstream of the fuel injector, it can be ensured that a cooling flow of fuel is provided over the fuel injector during at least a wide operational range operation of the fuel supply arrangement and an engine comprising the fuel supply arrangement. Formation of fuel vapor is particularly likely to occur in and around a fuel injector because the fuel injector is needed to be arranged in close proximity of high temperature components of the engine. Thus, by the cooling flow of fuel over the fuel injector obtained in the fuel supply arrangement according to the present disclosure, such formation of fuel vapor can be avoided in a simple and cost-effective manner.

Accordingly, a fuel supply arrangement is provided having conditions for providing a more reliable operation of a two stroke engine comprising the fuel supply arrangement. Moreover, a fuel supply arrangement is provided having conditions for providing a more fuel efficient and environmentally friendly two stroke engine.

Accordingly, a fuel supply arrangement is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above- mentioned object is achieved.

Optionally, the fuel pressure regulator is configured to open at a first predetermined pressure so as to regulate the operating fuel pressure of the fuel injector. Thereby, the operating fuel pressure of the fuel injector is regulated to a precise level in a simple, robust, and costefficient manner. Thereby, conditions are provided for regulating the amount of injected fuel in an accurate manner reducing the need for using costly and complex systems and arrangements.

Optionally, the fuel injector comprises a valve body movably arranged between an open position and a closed position so as to control fuel injection of the fuel injector, and wherein the fuel inlet is fluidly connected to the fuel return outlet via a flow path at least partially enclosing the valve body. Thereby, a cooling is ensured of vital components of the fuel injector which reduces the risk of formation of fuel vapor.

Optionally, the fuel inlet is fluidly connected to the fuel return outlet via the flow path regardless of whether the valve body is in the open or closed position. Thereby, a substantially continuous cooling flow of fuel can be provided over the fuel injector during operation of the fuel supply arrangement so as to lower the risk of fuel vapor.

Optionally, the arrangement comprises a fuel supply conduit fluidly connecting the fuel pump and the fuel inlet of the fuel injector, and wherein the arrangement comprises a purge bulb connected to the fuel supply conduit. Thereby, a fuel supply arrangement is provided allowing a user to prime the arrangement before starting an engine comprising the arrangement. Optionally, the fuel pressure regulator comprises a valve body, a flexible membrane and a valve cavity fluidly connected to the fuel return outlet, wherein the flexible membrane forms a delimiting surface of the valve cavity and is biased towards the valve cavity, and wherein the flexible membrane is operably connected to the valve body and is configured to displace the valve body between an open and a closed position based on the pressure in the valve cavity. Thereby, a fuel supply arrangement is provided having conditions for regulating the operating fuel pressure of the fuel injector to an even more precise level in a simple, robust, and costefficient manner. As a further result thereof, conditions are provided for regulating the amount of injected fuel in a more accurate manner.

Optionally, the fuel pressure regulator comprises a valve seat, and wherein the valve body is configured to abut against the valve seat when in the closed position to close a fluid connection between the fuel return outlet and the fuel tank, and wherein the valve body is configured to be lifted from the valve seat when in the open position to open a fluid connection between the fuel return outlet and the fuel tank. Thereby, a fuel supply arrangement is provided having conditions for regulating the operating fuel pressure of the fuel injector to a precise level in a simple, robust, and cost-efficient manner.

Optionally, the fuel pump is a membrane pump configured to pump fuel from the fuel tank to the fuel inlet of the fuel injector using pressure variations generated by the engine. Thereby, a simple, robust, and cost-efficient fuel pump is provided.

Optionally, the arrangement comprises a fuel pressure damper arranged downstream of the fuel pump and upstream of the fuel pressure regulator. Thereby, a more constant operating fuel pressure is provided which provides conditions for regulating the amount of injected fuel in an even more accurate manner without using costly and complex systems and arrangements. Furthermore, since the arrangement comprises a fuel pressure damper arranged downstream of the fuel pump and upstream of the fuel pressure regulator according to these embodiments, the fuel pressure regulator may open and close less frequently which further provides conditions for obtaining a more constant operating fuel pressure of the fuel injector.

Optionally, the fuel injector comprises one or more fuel openings through which the fuel injector is configured to inject fuel into an injection space of the engine, and wherein the fuel pressure damper is arranged upstream of the one or more fuel openings. Thereby, conditions are provided for obtaining a more constant operating fuel pressure. Optionally, the fuel pressure damper is arranged on, or immediately adjacent to, the fuel injector. Thereby, conditions are provided for obtaining a more constant operating fuel pressure. In addition, a fuel supply arrangement is provided having conditions for being manufactured and assembled in a cost-efficient manner.

Optionally, the fuel pressure damper comprises a fuel chamber and a flexible membrane forming a delimiting surface of the fuel chamber, and wherein the flexible membrane is biased in a direction towards the fuel chamber. Thereby, conditions are provided for obtaining a more constant operating fuel pressure of the fuel injector.

Optionally, the flexible membrane is arranged to move in order to increase the volume of the fuel chamber when the fuel chamber is subjected to a pressure above a threshold pressure, and wherein the threshold pressure is lower than the first predetermined pressure. Thereby, since the threshold pressure is lower than the first predetermined pressure, a more constant operating fuel pressure is ensured at fuel pressures at and below the first predetermined pressure.

Optionally, the arrangement comprises a pressure relief valve in fluid communication with an inner volume of the fuel tank. Thereby, excessive over pressure in the fuel tank is avoided in an efficient manner.

Optionally, the pressure relief valve is configured to open at a second predetermined pressure being lower than the first predetermined pressure. Thereby, a pressure regulating capability of the fuel pressure regulator is ensured also in cases of over pressures in the fuel tank, for example caused by a rise in temperature of the fuel tank and any matter therein. That is, since the second predetermined pressure, at which the pressure relief valve is configured to open, is lower than the first predetermined pressure, excessive pressures on the fuel tank will not disturb or limit the pressure regulating capability of the fuel pressure regulator.

According to a second aspect of the invention, the object is achieved by a crankcase scavenged two stroke engine comprising a fuel supply arrangement according to some embodiments of the present disclosure.

Since the engine comprises a fuel supply arrangement according to some embodiments of the present disclosure, an engine is provided in which the operating fuel pressure of the fuel injector is regulated to a precise level in a simple, robust, and cost-efficient manner. Thereby, an engine is provided having conditions for regulating the amount of injected fuel in a more accurate manner thereby reducing the need for using costly and complex systems and arrangements.

Moreover, an engine is provided in which the risk of formation of fuel vapor is reduced in the fuel supply arrangement thereof.

Accordingly, an engine is provided having conditions for a more reliable operation. Moreover, an engine is provided having conditions for operating in a more fuel efficient and environmentally friendly manner.

Accordingly, an engine is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

Optionally, the engine comprises a crankcase, an inlet connected to the crankcase, a combustion chamber, and a transfer duct connecting the crankcase and the combustion chamber, and wherein the fuel injector of the fuel supply arrangement is configured to inject fuel into an injection space at least forming part of one of the crankcase, the inlet, the combustion chamber, and the transfer duct.

Optionally, the fuel supply arrangement comprises a pressure relief valve in fluid communication with an inner volume of the fuel tank, and wherein the fuel supply arrangement comprises a venting duct fluidly connecting an outlet of the pressure relief valve to one or more of the crankcase, the inlet, and the transfer duct. Thereby, a more environmentally friendly engine is provided because any gaseous fuel vented from the fuel tank can be burnt in the combustion chamber of the engine instead of being vented to the surroundings. Moreover, a more user-friendly engine can be provided because a user thereof can be exposed to less gaseous fuel.

Optionally, the engine comprises a control arrangement configured to control an opening state of the pressure relief valve. Thereby, the transfer of hydrocarbons from the fuel tank to the engine can be controlled in a manner reducing the impact on the operation and functioning of the engine. In addition, according to some embodiments herein, the control of the pressure relief valve can be performed in a manner allowing higher operating fuel pressures of the fuel injector, as is further explained herein. Optionally, the venting duct comprises a fuel vapor trapping device. Thereby, a steadier release of hydrocarbons to the engine can be provided. Thereby, the hydrocarbons transferred to the engine can have a lower impact on the operation and functioning of the engine.

Optionally, the fuel supply arrangement comprises a first pressure sensor configured to sense the fuel pressure at a location between the fuel pump and the fuel pressure regulator and a second pressure sensor configured to sense the fluid pressure at the injection space, and wherein the fuel supply arrangement comprises a control arrangement configured to control the amount of fuel injected by the fuel injector based the pressures sensed by the first and second pressure sensors. Thereby, a further improved control of the amount of injected fuel is provided. In addition, the amount of injected fuel can be controlled in an efficient manner also in cases in which the operating fuel pressures of the fuel injector rises above the first predetermined pressure, as is further explained herein. Accordingly, conditions are provided for a more reliable operation of the engine and operation in a more fuel efficient and environmentally friendly manner.

Optionally, the engine is a small sized hand-held engine. Thereby, a small sized hand-held engine is provided in which the operating fuel pressure of the fuel injector is regulated to a precise level in a simple, robust, and cost-efficient manner. Accordingly, a small sized handheld engine is provided having conditions for regulating the amount of injected fuel in a more accurate manner thereby reducing the need for using costly and complex systems and arrangements.

Moreover, a small sized hand-held engine is provided in which the risk of formation of fuel vapor is reduced in the fuel supply arrangement thereof. Accordingly, a two stroke small sized hand-held engine is provided having conditions for a more reliable operation.

Moreover, a two stroke small sized hand-held engine is provided having conditions for operating in a more fuel efficient and environmentally friendly manner.

According to a third aspect of the invention, the object is achieved by a hand-held power tool comprising a tool and an engine according to some embodiments of the present disclosure, wherein the engine is configured to power the tool.

Since the power tool comprises an engine according to some embodiments, a power tool is provided in which the operating fuel pressure of the fuel injector of the engine is regulated to a precise level in a simple, robust, and cost-efficient manner. Accordingly, a power tool is provided having conditions for regulating the amount of injected fuel into the engine thereof in a more accurate manner thereby reducing the need for using costly and complex systems and arrangements.

Moreover, a power tool is provided in which the risk of formation of fuel vapor is reduced in the fuel supply arrangement thereof. Accordingly, a power tool is provided having conditions for a more reliable operation. Moreover, a power tool is provided having conditions for operating in a more fuel efficient and environmentally friendly manner.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the invention, including its particular features and advantages, will be readily understood from the example embodiments discussed in the following detailed description and the accompanying drawings, in which:

Fig. 1 illustrates a hand-held power tool, according to some embodiments,

Fig. 2 illustrates a cross section of a crankcase scavenged two stroke engine of the power tool illustrated in Fig. 1 ,

Fig. 3 illustrates a fuel supply arrangement according to some embodiments for the engine illustrated in Fig. 1 and Fig. 2,

Fig. 4 illustrates a fuel supply arrangement according to some further embodiments for the engine illustrated in Fig. 1 and Fig. 2,

Fig. 5 illustrates a fuel supply arrangement according to some further embodiments for the engine illustrated in Fig. 1 and Fig. 2,

Fig. 6 illustrates a cross section of a fuel injector according to some embodiments of the present disclosure, and

Fig. 7 illustrates a second cross section of the fuel injector illustrated in Fig. 6.

DETAILED DESCRIPTION

Aspects of the present invention will now be described more fully. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

Fig. 1 illustrates a hand-held power tool 20, according to some embodiments. The hand-held power tool 20 comprises a tool 61 and a crankcase scavenged two stroke engine 1 configured to power the tool 61. For reasons of brevity and clarity, the crankcase-scavenged two-stroke engine 1 is in some places herein referred to as “the two stroke engine 1” or simply “the engine 1”. According to the illustrated embodiments, the hand-held power tool 20 is a chainsaw comprising a tool 61 in the form of a cutting chain. According to further embodiments, the hand-held power tool 20 may be another type of hand-held power tool 20, such as a power cutter, a hedge trimmer, a leaf/debris blower, a multi-tool, or the like. The wording ’’hand-held” implies that the power tool 20 is portable and is configured to be supported by one or two hands of a user during operation of the power tool 20. The handheld power tool 20 is in some places herein referred to as the “power tool 20” for reasons of brevity and clarity. As is further explained herein, the power tool 20 comprises a fuel supply arrangement 10. The fuel supply arrangement 10 is configured to store and supply fuel to the engine 1 of the power tool 20. In Fig. 1 , a fuel tank 5 of the fuel supply arrangement 10 is indicated. The engine 1 may be configured to run on gasoline, also referred to as petrol, alcohol, similar volatile fuels, or combinations thereof. The fuel supply arrangement 10 may thus be configured to store and supply such a fuel to the engine 1 of the power tool 20.

Fig. 2 illustrates a cross section of the crankcase scavenged two stroke engine 1 of the power tool 20 illustrated in Fig. 1. The engine 1 is a small sized crankcase-scavenged two- stroke engine 1. The engine 1 comprises a cylinder 62 and a piston 63 arranged to reciprocate in the cylinder 62. The cylinder 62 and a piston top of the piston 63 forms a combustion chamber 45. The engine 1 further comprises a crankcase 41 and a crankshaft 64 arranged to rotate in the crankcase 41. Moreover, the engine 1 comprises a connecting rod 65 connecting the piston 63 to the crankshaft 64 such that the piston 63 reciprocates in the cylinder 62 between a bottom dead centre BDC and a top dead centre TDC upon rotation of the crankshaft 64. In Fig. 2, the piston 63 is illustrated in the bottom dead centre.

The engine 1 comprises an inlet 43 connected to the crankcase 41. The inlet 43 may also be referred to as an air inlet. The engine further comprises a throttle 44 configured to regulate the amount of air flowing through the inlet 43. The cylinder 62 of the engine 1 is provided with an exhaust port 66 and an inlet port 47’. The exhaust port 66 is connected to an exhaust system and the inlet port 47’ is connected to the crankcase 41 via a transfer duct 47 of the engine 1. The transfer duct 47 may also be referred to as a transfer channel, a scavenging channel, or a scavenging duct.

When the piston 63 moves from the top dead centre towards the bottom dead centre illustrated in Fig. 2, the exhaust port 66 is opened to allow exhaust gases to flow out from the cylinder 62 when the piston 63 reaches a first position relative the cylinder 62 in its movement towards the bottom dead centre. The piston 63 continues the movement towards the bottom dead centre and when it reaches a second position, below the first position, the inlet port 47’ is opened. Moreover, during the movement of the piston 63 towards the bottom dead centre the pressure in the crankcase 41 increases. The area below the piston 63 is thus used as a charging pump to build up pressure in the crankcase 41 during the power stroke of the piston 63. Due to the increased pressure in the crankcase 41 , air or an air/fuel mixture is forced into the cylinder 62 via the transfer duct 47 when the inlet port 47’ is opened.

When the piston 63 moves from the bottom dead centre towards the top dead centre, the inlet port 47’ and the exhaust port are closed to allow compression of air or an air/fuel mixture in the cylinder 62. The engine further comprises a spark plug 68 configured to ignite fuel in the cylinder 62 so as to initiate combustion in the cylinder 62. Moreover, when the piston 63 is in the region of the top dead centre, an air inlet port 69 is opened. The air inlet port 69 is connected to the inlet 43 and to the crankcase 41 to allow air or an air/fuel mixture to flow into the crankcase 41 when the piston 63 is in the region of the top dead centre. According to further embodiments of the present disclosure, the inlet 43 may be directly connected to the crankcase 41 such that air can flow into the crankcase 41 regardless of the position of the piston 63. According to such embodiments, as well as in further embodiments herein, the engine 1 may comprise one or more reed valves between the inlet 43 and the crankcase 41 preventing flow of air or an air/fuel mixture from the crankcase 41 to the inlet 43.

As is further explained herein the engine 1 comprises a fuel supply arrangement 10. The fuel supply arrangement 10 comprises a fuel injector 7 configured to inject fuel into an injection space 29 of the engine 1. According to the illustrated embodiments, the injection space 29 forms part of the crankcase 41. In other words, the fuel injector 7 according to the illustrated embodiments is configured to inject fuel into the crankcase 41 of the engine 1. According to further embodiments, the injection space 29 may form part of one or more of the inlet 43, the combustion chamber 45, and the transfer duct 47. Thus, according to further embodiments, the fuel injector 7 of the fuel supply arrangement 10 may be configured to inject fuel into one or more of the inlet 43, the combustion chamber 45, and the transfer duct 47. The fuel injector 7 may be of a low-pressure type, e.g. a fuel injector 7 having a fuel injection pressure less than 300 kPa, or less than 180 kPa.

Fig. 3 illustrates a fuel supply arrangement 10 according to some embodiments for the engine 1 illustrated in Fig. 1 and Fig. 2. The engine 1 illustrated in Fig. 1 and Fig. 2 may thus comprise a fuel supply arrangement 10 according to the embodiments illustrated in Fig. 3. The fuel supply arrangement 10 is in some places herein referred to as “the arrangement 1” for reasons of brevity and clarity. The fuel supply arrangement 10 comprises a fuel tank 5 configured to accommodate fuel. Moreover, the fuel supply arrangement 10 comprises a fuel injector 7 configured to inject fuel into an injection space 29 as described with reference to Fig. 2. The fuel injector 7 comprises a fuel inlet 9 and a fuel return outlet 11. The fuel supply arrangement 10 comprises a fuel pump 13 configured to pump fuel from the fuel tank 5 to the fuel inlet 9 of the fuel injector 7. The fuel pump 13 may be a membrane pump configured to pump fuel from the fuel tank 5 to the fuel inlet 9 of the fuel injector 7 using pressure variations generated by the engine 1. In more detail, such a membrane pump may comprise a membrane in fluid communication with the crankcase 41 of the engine 1 , wherein the fuel pump 13 is configured to pump fuel from the fuel tank 5 to the fuel inlet 9 of the fuel injector 7 using pressure variations in the crankcase 41 generated during operation of the engine 1. The arrangement 10 comprises a fuel supply conduit 23 fluidly connecting the fuel pump 13 and the fuel inlet 9 of the fuel injector 7. The fuel pump 13 is thus configured to pump fuel to the fuel inlet 9 of the fuel injector 7 via the fuel supply conduit 23.

According to the illustrated embodiments, the fuel supply arrangement 10 further comprises a purge bulb 25 connected to the fuel supply conduit 23. The purge bulb 25 comprises a flexible body and a set of one-way valves allowing a user to prime, i.e. pump fuel to, the fuel injector 7 before starting an engine comprising the fuel supply arrangement 10.

The fuel supply arrangement 10 further comprises a return conduit 15 connecting the fuel return outlet 11 of the fuel injector 7 to the fuel tank 5. Moreover, according to embodiments of the present disclosure, the fuel supply arrangement 10 comprises a fuel pressure regulator 17 arranged in the return conduit 15. The fuel pressure regulator 17 is configured to regulate an operating fuel pressure of the fuel injector 7. As is further explained herein, the fuel pressure regulator 17 may be configured to regulate an operating fuel pressure of the fuel injector 7 by opening at a first predetermined pressure. Due to these features, a predetermined operating fuel pressure of the fuel injector 7 can be obtained in a simple, robust, and cost-efficient manner. Moreover, a cooling flow of fuel can be provided over the fuel injector 7 which reduces the risk of formation of fuel vapor in the fuel supply arrangement 10, as is further explained herein.

In more detail, according to embodiments herein, the fuel pressure regulator 17 is configured to open, i.e. assume an open position, when the fuel pressure in the return conduit 15 upstream of the fuel pressure regulator 17 reaches the first predetermined pressure. When the fuel pressure regulator 17 is open, i.e. when the fuel pressure regulator 17 is in the open position, the fuel pressure regulator 17 opens a fluid connection between the fuel return outlet 11 and the fuel tank 5. Moreover, according to embodiments herein, the fuel pressure regulator 17 is configured to close, i.e. assume a closed position, when the fuel pressure in the return conduit 15 upstream of the fuel pressure regulator 17 declines below the first predetermined pressure. When the fuel pressure regulator 17 is closed, i.e. when the fuel pressure regulator 17 is in the closed position, the fuel pressure regulator 17 closes the fluid connection between the fuel return outlet 11 and the fuel tank 5.

According to the illustrated embodiments, the fuel pressure regulator 17 comprises a valve body 32, a flexible membrane 36 and a valve cavity 34 fluidly connected to the fuel return outlet 11 of the fuel injector 7. The flexible membrane 36 forms a delimiting surface 36’ of the valve cavity 34. Moreover, the flexible membrane 36 is biased towards the valve cavity 34. Furthermore, the flexible membrane 36 is operably connected to the valve body 32 and is configured to displace the valve body 32 between an open and a closed position based on the pressure in the valve cavity 34. The fuel pressure regulator 17 further comprises a valve seat 38. The valve body 32 is configured to abut against the valve seat 38 when in the closed position to close the fluid connection between the fuel return outlet 11 and the fuel tank 5. The valve body 32 is configured to be lifted from the valve seat 38 when in the open position to open the fluid connection between the fuel return outlet 11 and the fuel tank 5. In this manner, a fuel supply arrangement is provided having conditions for regulating the operating fuel pressure of the fuel injector 7 to a precise level in a simple, robust, and cost-efficient manner.

Since the fuel pressure regulator 17 comprises a valve body 32 and a valve seat 38, the fuel pressure regulator according to the illustrated embodiments, may also be referred to as a pressure regulating valve, a fuel pressure regulating valve, or the like.

Moreover, according to embodiments herein, the fuel injector 7 comprises a valve body 19 movably arranged between an open position and a closed position so as to control fuel injection of the fuel injector 7. The fuel injector 7 comprises one or more fuel openings 27 through which the fuel injector 7 is configured to inject fuel into the injection space 29 of the engine 1. The valve body 19 is configured to cooperate with the one or more fuel openings 27 such that fuel can flow through the one or more fuel openings 27 when the valve body 19 is in the open position and such that fuel is blocked from flowing through the one or more fuel openings 27 when the valve body 19 is in the closed position. Moreover, the fuel injector 7 comprises an actuator 24 configured to move the valve body 19 between the open and closed positions. The actuator 24 may comprise a solenoid, a piezo electric element, or the like.

According to the illustrated embodiments, the fuel supply arrangement 10 comprises a sensor 52 configured to sense a current fluid pressure at the injection space 29, i.e. at the crankcase 41 according to the illustrated embodiments. Moreover, the fuel supply arrangement 10 comprises a control arrangement 21 operably connected to the sensor 32 and to the actuator 24. The control arrangement 21 is configured to control fuel injection of the fuel injector 7, i.e. control the actuator 24 of the fuel injector 7, based on the pressure sensed by the sensor 52. In this manner, an accurate control of the injected amount of fuel into the injection space 29 can be performed. This because due to the fuel pressure regulator 17, the operating fuel pressure of the fuel injector 7 is at a known first predetermined pressure during operation of the fuel supply arrangement 10. By sensing the pressure at the injection space 29, the pressure difference between the fuel pressure in the fuel injector 7 and the injection space 29 is obtained. Thus, by controlling the actuator 24 of the fuel injector 7 based on the pressure sensed by the sensor 52, the fuel injector 7 can be controlled to inject an accurate amount of fuel into the injection space 29.

According to the illustrated embodiments, the fuel inlet 9 is fluidly connected to the fuel return outlet 11 via a flow path 22 at least partially enclosing the valve body 19, as is further explained herein. Moreover, the fuel inlet 9 is fluidly connected to the fuel return outlet 11 via the flow path 22 regardless of whether the valve body 19 is in the open or closed position. Thereby, a substantially continuous flow of fuel can be obtained cooling the fuel injector 7 which reduces the risk of formation of fuel vapor in the fuel supply arrangement 10.

According to the illustrated embodiments, the fuel supply arrangement 10 comprises a fuel pressure damper 31. The fuel pressure damper 31 is configured to damp, i.e. even out, pressure variations in the fuel supply arrangement 10. The pressure variations in the fuel supply arrangement 10 may be caused by the operation of the fuel pump 13 of the fuel supply arrangement 10. The fuel pressure damper 31 may be arranged downstream of the fuel pump 13 and upstream of the fuel pressure regulator 17. According to the illustrated embodiments, the fuel pressure damper 31 is arranged upstream of the one or more fuel openings 27 of the fuel injector. According to the illustrated embodiments, the fuel pressure damper 31 is arranged at a distance from the fuel injector 7. However, the fuel pressure damper 31 may be arranged on, or immediately adjacent to, the fuel injector 7, as is further explained herein. The fuel pressure damper 31 comprises a fuel chamber 33 and a flexible membrane 35 forming a delimiting surface 35’ of the fuel chamber 33. The flexible membrane 35 is biased in a direction towards the fuel chamber 33. Moreover, the flexible membrane 35 is arranged to move in order to increase the volume of the fuel chamber 33 when the fuel chamber 33 is subjected to a pressure above a threshold pressure. The threshold pressure is lower than the first predetermined pressure. In this manner, the fuel pressure damper 31 is able to even out variations in the fuel pressure at fuel pressures at and below the first predetermined pressure.

According to the illustrated embodiments, the arrangement 10 comprises a pressure relief valve 37 in fluid communication with an inner volume 5’ of the fuel tank 5. According to the embodiments illustrated in Fig. 3, the pressure relief valve 37 is a mechanical pressure relief valve configured to open at a second predetermined pressure. According to embodiments herein, the second predetermined pressure is lower than the first predetermined pressure. Purely as an example, the first predetermined pressure may be approximately 12 kPa and the second predetermined pressure may be approximately 2 kPa. According to further embodiments of the present disclosure, the pressure relief valve 37 may be an electronically controlled valve for example controlled by the control arrangement 21. According to still further embodiments of the present disclosure, the pressure relief valve 37 may be an electronically controlled valve, for example controlled by the control arrangement 21 , which electronically controlled valve also is configured to open when the pressure in the inner volume 5’ of the fuel tank 5 rises above a second predetermined pressure, such as the second predetermined pressure referred to above. In this manner, a failsafe fuel supply arrangement 10 is provided ensuring a steady operating fuel pressure of the fuel injector 7.

Fig. 4 illustrates a fuel supply arrangement 10 according to some further embodiments for the engine 1 illustrated in Fig. 1 and Fig. 2. The engine 1 illustrated in Fig. 1 and Fig. 2 may thus comprise a fuel supply arrangement 10 according to the embodiments illustrated in Fig. 4. The fuel supply arrangement 10 illustrated in Fig. 4 comprises the same features, functions, and advantages as the fuel supply arrangement 10 explained with reference to Fig. 3, with some differences explained below.

According to the embodiments illustrated in Fig. 4, the fuel supply arrangement 10 comprises a venting duct 39 fluidly connecting an outlet 37’ of the pressure relief valve 37 to the crankcase 41 of an engine comprising the fuel supply arrangement 10. As an alternative, or in addition, the venting duct 39 may fluidly connect the outlet 37’ of the pressure relief valve 37 to an inlet or a transfer duct of an engine comprising the fuel supply arrangement 10. Due to the venting duct 39, a more environmentally friendly fuel supply arrangement 10 is provided because any gaseous fuel vented from the fuel tank 5 can be burnt in a combustion chamber of the engine instead of being vented to the surroundings.

Moreover, according to the embodiments illustrated in Fig. 4, the venting duct 39 of the fuel supply arrangement 10 comprises a fuel vapor trapping device 49. The fuel vapor trapping device 49 may comprise a membrane restricting hydrocarbons, i.e. fuel, or a carbon canister which acts like a buffer to yield a slow steady release of hydrocarbons.

Likewise, in these embodiments, the pressure relief valve 37 may be an electronically controlled valve controlled by the control arrangement 21. In this manner, a controlled release of hydrocarbons to the engine can be provided. According to these embodiments, as well as in other embodiments explained herein, such as the embodiments explained with reference to Fig. 3, the control arrangement 21 may control the opening state of the pressure relief valve 37 based on data representative of a current pressure in the fuel tank 5, a current pressure in the crankcase 41 of the engine, a current rotational velocity of the engine, a current load of the engine, and/or a current estimated air/fuel ratio of the engine. As examples, the control arrangement 21 may control the pressure relief valve 37 to an open state in case of a high current pressure in the fuel tank 5, a low current pressure in the crankcase 41 of the engine, a low current rotational velocity of the engine, a low current load of the engine, and/or a low current estimated air/fuel ratio of the engine. In this manner, an efficient transfer of hydrocarbons from the fuel vapor trapping device 49 to the engine can be ensured in a manner having a low impact on the operation and functioning of the engine.

According to further embodiments, the fuel supply arrangement 10 may comprise a further electronically controlled valve downstream of the fuel vapor trapping device 49 as an alternative to, or in addition to, the pressure relief valve 37. The control arrangement 21 may be configured to control the opening state of such a further electronically controlled valve in a corresponding manner as the above described control of the pressure relief valve 37.

Fig. 5 illustrates a fuel supply arrangement 10 according to some further embodiments for the engine 1 illustrated in Fig. 1 and Fig. 2. The engine 1 illustrated in Fig. 1 and Fig. 2 may thus comprise a fuel supply arrangement 10 according to the embodiments illustrated in Fig. 5. The fuel supply arrangement 10 illustrated in Fig. 5 comprises the same features, functions, and advantages as the fuel supply arrangement 10 explained with reference to Fig. 4, with some differences explained below. In Fig. 5, the fuel supply arrangement 10 is illustrated as comprising an electronically controlled pressure relief valve 37 in fluid communication with the inner volume 5’ of the fuel tank 5. Moreover, the control arrangement 21 is configured to control an opening state of the pressure relief valve 37. The control arrangement 21 may control the opening state of the pressure relief valve 37 in a manner as described with reference to Fig. 4.

Moreover, according to the embodiments illustrated in Fig. 5, the fuel supply arrangement 10 comprises a first pressure sensor 51. The first pressure sensor 51 is configured to sense the fuel pressure at a location between the fuel pump 13 and the fuel pressure regulator 17. In more detail, according to the illustrated embodiments, the first pressure sensor 51 is configured to sense the fuel pressure at the fuel injector 7. Moreover, according to the embodiments illustrated in Fig. 5, the fuel supply arrangement 10 comprises a second pressure sensor 52. The second pressure sensor 52 is configured to sense the fluid pressure at the injection space 29, i.e. at the crankcase 41 according to the illustrated embodiments. According to these embodiments, the control arrangement 21 is configured to control the amount of fuel injected by the fuel injector 7 based the pressures sensed by the first and second pressure sensors 51 , 52. In more detail, according to these embodiments, the control arrangement 21 is configured to control the amount of fuel injected by the fuel injector 7 based the difference in pressure between the pressures sensed by the first and second pressure sensors 51 , 52. In this manner, an even more accurate control can be performed of the injected amount of fuel.

Moreover, according to these embodiments, an accurate control of the injected amount can be performed also in cases where the current pressure in the fuel tank 5 is higher than the first predetermined pressure. That is, in case the current pressure in the fuel tank 5 is higher than the first predetermined pressure, the pressure in the fuel tank 5 may cause the fuel pressure at the fuel injector 7 to rise above the first predetermined pressure. However, since the control arrangement 21 is configured to control the amount of fuel injected by the fuel injector 7 based the pressures sensed by the first and second pressure sensors 51, 52, an accurate control of the injected amount of fuel can be performed also in cases where the fuel pressure at the fuel injector 7 rises above the first predetermined pressure. Moreover, in these embodiments, the control arrangement 21 may be configured to control the pressure relief valve 37 to an open state when the pressure in the inner volume 5’ of the fuel tank 5 reaches a pressure level higher than the first predetermined pressure. In other words, according to these embodiments, the control arrangement 21 may be configured to keep the pressure relief valve 37 closed also when the pressure in the inner volume 5’ of the fuel tank 5 is higher than the first predetermined pressure. Below, simultaneous reference is made to Fig. 1 - Fig. 5, if not indicated otherwise. The fuel pressure regulator 17, according to the embodiments herein, is configured to regulate the operating fuel pressure of the fuel injector 7 during at least a major part of the engine's operating range, i.e. more than 50% of the operating range of the engine 1 comprising the fuel supply arrangement 10. The operating range of the engine 1 may encompass a rotational speed range and/or a power range of the engine 1 comprising the fuel supply arrangement 10. Therefore, according to embodiments herein, the fuel pressure regulator 17 may be referred to as a main fuel pressure regulator 17 for regulating the operating fuel pressure of the fuel injector 7.

The operating fuel pressure of the fuel injector 7, as referred to herein, is the pressure of fuel at the fuel injector 7 during injection of fuel by the fuel injector 7 into an injection space 29 during regular operation of an engine 1 comprising the fuel supply arrangement 10. The term regular operation of the engine 1 may encompass operational phases, conditions, and/or ranges of the engine 1 being separated from start-up and shut-down phases, conditions, and/or ranges of the engine 1.

According to embodiments herein, the fuel supply arrangement 10 may lack a fuel pressure regulator between the fuel pump 13 and the fuel injector 7. Instead, as is the case according to the illustrated embodiments, the operating fuel pressure of the fuel injector 7 is solely regulated via the return conduit 15, such as by the fuel pressure regulator 17 arranged in the return conduit 15 and optionally via a pressure in the return conduit 15 in cases where the pressure in the fuel tank 5 causes the fuel pressure at the fuel injector 7 to rise above the first predetermined pressure, as explained above.

According to the illustrated embodiments, the fuel pressure regulator 17 is a passive regulator in the sense that the fuel pressure regulator 17 is configured to regulate the operating fuel pressure of the fuel injector 7 by opening at a first predetermined pressure. However, according to further embodiments of the present disclosure, the fuel pressure regulator 17 may be an electronically controlled fuel pressure regulator for example controlled by the control arrangement 21. According to such embodiments, the fuel pressure regulator 17 may comprise one or more electronically controlled valves for example controlled by the control arrangement 21. As an example, the fuel pressure regulator 17 may be controlled to open at the first predetermined pressure. In this manner, more controlled and more precise operating fuel pressure levels can be obtained. According to these embodiments, the control arrangement 21 may utilize data from the first pressure sensor 51 for verifying a current operational fuel pressure of the fuel injector 7 and the control arrangement 21 may be configured to control the fuel pressure regulator 17 in response thereto. In this manner, an accurate control of the operational fuel pressure of the fuel injector 7 can be obtained.

Moreover, according to the embodiments illustrated in Fig. 3 - Fig. 5, the fuel pump 13 is a membrane pump configured to pump fuel from the fuel tank 5 to the fuel inlet 9 of the fuel injector 7 using pressure variations generated by the engine 1. However, according to further embodiments, the fuel pump 13 may be electronically controlled and/or electrically powered, such as by an electric motor, or the like. Also in these embodiments, the control arrangement 21 may be configured to control the operation of the fuel pump 13 for example based on data from the first pressure sensor 51. In this manner, an even more accurate control of the operational fuel pressure of the fuel injector 7 can be obtained at various operational conditions of the fuel supply arrangement 10 and of an engine 1 comprising the fuel supply arrangement 10.

In embodiments in which the fuel supply arrangement 10 comprises an electronically controlled and/or electrically powered fuel pump 13 and an electronically controlled fuel pressure regulator 13, the control arrangement 21 may be configured to perform a conjoint control of the operation of the fuel pump 13 and of the opening state of the fuel pressure regulator 13. The conjoint control may be set to obtain a sufficient cooling flow of fuel past the fuel injector 7 while avoiding surplus pumping work of the fuel injector 7 at various operational phases, conditions, and/or ranges of the fuel supply arrangement 10 and of an engine 1 comprising the fuel supply arrangement 10. In this manner, the risk of formation of vapor in the fuel supply arrangement 10 can be further avoided.

Fig. 6 illustrates a cross section of a fuel injector 7 according to some embodiments of the present disclosure. The fuel supply arrangement 10 explained with reference to Fig. 3 - Fig. 5 may comprise the fuel injector 7 according to the embodiments illustrated in Fig. 6. In Fig.

6, the valve body 19, the actuator 24, and a fuel opening 27 of the fuel injector 7 are visible. According to the embodiments illustrated in Fig. 6, the actuator 24 comprises a solenoid. Moreover, in Fig. 6, a portion of the fuel pressure damper 31 is visible. As can be seen in Fig.

7, according to these embodiments, the fuel pressure damper 31 is arranged on the fuel injector 7.

Fig. 7 illustrates a second cross section of the fuel injector 7 illustrated in Fig. 6. In Fig. 6, the fuel inlet 9 and the fuel return outlet 11 of the fuel injector 7 is visible. Moreover, at least portions of the flow path 22 fluidly connecting the fuel inlet 9 and the fuel return outlet 11 is visible. As clearly seen in Fig. 7, the design of the fuel injector 7 and the flow path 22 therethrough ensures a high degree of cooling of the fuel injector 7 when fuel is flowing from the fuel inlet 9 to the fuel return outlet 11.

Moreover, in Fig. 7, the fuel pressure damper 31 and the fuel chamber 33 thereof is visible. As can be seen when comparing Fig. 6 and Fig. 7, the fuel pressure damper 31 is arranged in close proximity to the fuel opening 27 of the fuel injector 7 and is arranged upstream of the fuel opening 27 of the fuel injector 7. Thereby, a more constant operating fuel pressure is provided which provides conditions for regulating the amount of injected fuel in an even more accurate manner. According to some embodiments, the fuel injector 7 illustrated in Fig. 6 and Fig. 7 may comprise a fuel inlet 9’ connected to the fuel chamber 33 of the fuel pressure damper 31 in a direction coinciding with the viewing direction of the cross section illustrated in Fig. 7. Such a fuel inlet 9’ is illustrated in dashed lines in Fig. 7. Likewise, the fuel injector 7 illustrated in Fig. 6 and Fig. 7 may comprise a fuel return outlet 1 T connected to the fuel injector 7 in a direction coinciding with the viewing direction of the cross section illustrated in Fig. 7. Such a fuel return outlet 1 T is illustrated in dashed lines in Fig. 7. According to such embodiments, each of the openings 9, 11 of the fuel injector 7 in Fig. 7 may be plugged.

The control arrangement 21 , as referred to herein, may comprise a calculation unit which may take the form of substantially any suitable type of processor circuit or microcomputer, e.g. a circuit for digital signal processing (digital signal processor, DSP), a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The herein utilised expression “calculation unit” may represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above.

The control arrangement 21 may further comprise a memory unit, wherein the calculation unit may be connected to the memory unit, which may provide the calculation unit with, for example, stored program code and/or stored data which the calculation unit may need to enable it to do calculations. The calculation unit may also be adapted to store partial or final results of calculations in the memory unit. The memory unit may comprise a physical device utilised to store data or programs, i.e. , sequences of instructions, on a temporary or permanent basis. According to some embodiments, the memory unit may comprise integrated circuits comprising silicon-based transistors. The memory unit may comprise e.g. a memory card, a flash memory, a USB memory, a hard disc, or another similar volatile or non-volatile storage unit for storing data such as e.g. ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), etc. in different embodiments.

The control arrangement 21 is connected to components of the power tool 20 for receiving and/or sending input and output signals. These input and output signals may comprise waveforms, pulses, or other attributes which the input signal receiving devices can detect as information and which can be converted to signals processable by the control arrangement 21. These signals may then be supplied to the calculation unit. One or more output signal sending devices may be arranged to convert calculation results from the calculation unit to output signals for conveying to other parts of the control system of the power tool 20 and/or the component or components for which the signals are intended. Each of the connections to the respective components of the power tool 20 for receiving and sending input and output signals may take the form of one or more from among a cable, an electronic communication bus, or a wireless connection.

In the embodiments illustrated, the power tool 20 comprises a control arrangement 21 but might alternatively be implemented wholly or partly in two or more control arrangements or two or more control units.

It is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended claims. A person skilled in the art will realize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the present invention, as defined by the appended claims.

As used herein, the term "comprising" or "comprises" is open-ended, and includes one or more stated features, elements, steps, components, or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions, or groups thereof.