Fuel injector

Abstract

A fuel injector (200) comprises: - a fuel valve (VAL2) comprising a valve element (PIN2) and a sealing surface (SRF1), - a return spring (SPR1) configured to close the fuel valve (VAL2) by pressing the valve element (PIN2) against the sealing surface (SRF1), - a hydraulic actuator (ACU1) arranged to deflect the return spring (SPR1), - a damper cylinder (CYL2), - a damper piston (M2) arranged to move with respect to the damper cylinder (CYL2), wherein the damper piston (M2) is coupled to move with the valve element (PIN2), wherein the damper piston (M2) defines a damper space (SPC2) and a control aperture (THR2) with the damper cylinder (CYL2), wherein the control aperture (THR2) is arranged to control a flow rate (Q2) of a hydraulic fluid (LIQ1) displaced from the damper space (SPC2), wherein a position (z) of the damper piston (M2) determines at least one variable dimension (dTHR2) of the control aperture (THR2).

Description

[0001] FUEL INJECTOR

[0002] FIELD

[0003] The present invention relates to injecting a fuel into a cylinder of an internal combustion engine.

[0004] BACKGROUND

[0005] Fuel may be injected into a cylinder of an internal combustion engine by using a fuel injector. The fuel injector may comprise an internal fuel valve, which is opened by using a hydraulic actuator. Opening of the internal fuel valve may allow a flow of pressurized fuel to atomizing orifices of the fuel injector. The fuel may be injected to the cylinder as atomized droplets.

[0006] The fuel valve of the fuel injector may be closed by moving a valve element to a closed position. The moving valve element may hit a sealing surface when the fuel valve is closed.

[0007] SUMMARY

[0008] An object is to provide a fuel injector. An object is to provide a method for injecting fuel. An object is to provide an engine, which comprises the fuel injector. An object is to provide a method for operating the engine.

[0009] According to an aspect, there is provided a fuel injector (200) for injecting a liquid fuel (FUEL1) into a cylinder (ECYL1) of an internal combustion engine (ENG1), comprising:

[0010] - a fuel valve (VAL2) comprising a valve element (PIN2) and a sealing surface (SRF1),

[0011] - a return spring (SPR1 ) configured to close the fuel valve (VAL2) by pressing the valve element (PIN2) against the sealing surface (SRF1 ),

[0012] - a hydraulic actuator (ACU1) arranged to deflect the return spring (SPR1),- a damper cylinder (CYL2),

[0013] - a damper piston (M2) arranged to move with respect to the damper cylinder (CYL2),

[0014] wherein the damper piston (M2) is coupled to move with the valve element (PIN2),

[0015] wherein the damper piston (M2) defines a damper space (SPC2) and a control aperture (THR2) with the damper cylinder (CYL2),

[0016] wherein the control aperture (THR2) is arranged to control a flow rate (Q2) of a hydraulic fluid (L IQ 1 ) displaced from the damper space (SPC2),

[0017] wherein a position (z) of the damper piston (M2) determines at least one variable dimension (dTHR2) of the control aperture (THR2).

[0018] According to an aspect, there is provided a fuel injector according to claim 1.

[0019] Further embodiments are defined in the other claims.

[0020] The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0021] The fuel injector comprises a fuel valve to control a flow rate of a liquid fuel. The liquid fuel is injected into a cylinder of an internal combustion engine via one or more atomizing orifices. Pressurized liquid fuel is delivered to the atomizing orifices via the fuel valve. The fuel valve may be opened and closed according to a control signal obtained from an engine control unit of the engine. The fuel valve may be opened to allow the flow of the fuel to the atomizing orifices. The fuel valve may be closed to stop the flow of the fuel.

[0022] The fuel valve comprises a valve element and a first stationary sealing surface. The valve element comprises a second sealing surface. The fuel valve may be opened by lifting the valve element away from the stationary sealing surface. The fuel valve may be closed by pressing the valve element firmly against the stationary sealing surface. The valve element may also be called e.g. as a needle or as a pin.The length of the movement of the valve element from an open position to a closed position may be e.g. in the range of 0.5 mm to 5 mm. The fuel injector may comprise a return spring to press the valve element against the stationary sealing surface. The spring force generated by the return spring may be e.g. in the range of 1000 N to 10000 N. The return spring may accelerate the valve element to a significant velocity, and the valve element may hit the stationary sealing surface at a significant impact velocity. The present fuel injector comprises a hydraulic damper for controlling the impact velocity.

[0023] The damper may operate as a brake, to reduce the velocity in a controlled manner. The damper may be arranged to control the velocity of the valve element e.g. so that the velocity of the valve element at a distance of 0.1 mm from the closed position of the valve element is smaller than a limit value. The limit value may be e.g. 1 m / s, 0.5m / s, 0.2 m / s, or even 0.1 m / s.

[0024] The hydraulic damper comprises a damper piston which is arranged to move with respect to a damper cylinder. The damper piston is coupled to move together with the valve element. In particular, the damper piston may be mechanically coupled to the valve element.

[0025] The damper piston defines a damper space and a control aperture together with the damper cylinder. The control aperture controls and restricts the flow rate of the hydraulic fluid displaced from the damper space. The control aperture may restrict the flow as a function of the vertical position of the damper piston. The control aperture may be e.g. an annular gap between the damper piston and the damper cylinder. The position of the damper piston may determine at least one variable dimension of the control aperture together with the damper cylinder. For example, the control aperture may restrict the flow rate less when the damper piston is above a reference position, and the control aperture may restrict the flow rate more when the damper piston is below the reference position. For example, the damper piston may substantially block the control aperture when the damper piston is near the bottom position.

[0026] Restricting the flow rate of the hydraulic fluid may cause a rapid increase of the internal pressure below the damper piston when the descending damper pistonapproaches a selected reference position. The internal pressure acting on the damper piston may cause a high hydraulic braking force for limiting the impact velocity of the valve element.

[0027] The fuel injector comprises a hydraulic actuator, and a return spring. The return spring is arranged to generate a high spring force for keeping the fuel valve firmly closed when needed. The hydraulic actuator is configured to open the fuel valve by deflecting the return spring away from the closed position. The hydraulic actuator may e.g. compress the return spring so that pressurized liquid fuel acting on the valve element may move the valve element from the closed position to the open position.

[0028] The damper may be located e.g. above the hydraulic actuator, or below the hydraulic actuator. The braking effect of the damper may be abrupt, or gradual. The hydraulic actuator may comprise an actuator piston, which is arranged to move in an actuator cylinder. The damper piston may be separate from the actuator piston, or the damper piston may be integrated with the actuator piston. In an embodiment, the actuator piston may be arranged to operate as the damper piston. In an embodiment, the damper piston may be arranged to operate as the actuator piston.

[0029] The valve element may move upwards when the fuel valve is opened, and the valve element may move downwards when the fuel valve is closed. The hydraulic damper may be arranged to exhibit asymmetric direction-dependent operation so that the magnitude of the braking force depends on the direction of movement of the valve element. The asymmetric operation may be implemented e.g. so that the damper generates a high hydraulic braking force when the valve element is moving downwards near the closed position, and so that the damper does not significantly contribute to the velocity of the valve element when the valve element is moving upwards away from the bottom position. The damper may comprise e.g. a one-way valve to facilitate the asymmetric operation.

[0030] BRIEF DESCRIPTION OF THE DRAWINGSIn the following examples, several variations will be described in more detail with reference to the appended drawings, in which

[0031] Fig. 1a shows, by way of example, in a cross-sectional side view, a fuel injector, which comprises a hydraulic damper, wherein the valve element is near the top position,

[0032] Fig. 1b shows, by way of example, in a cross-sectional side view, the fuel injector of Fig. 1a, wherein the valve element is near the bottom position,

[0033] Fig. 2 shows, by way of example, in a cross-sectional side view, a vertical position of the damper piston with respect to the damper cylinder,

[0034] Fig. 3a shows, by way of example, in a cross-sectional side view, an actuator and a damper when the damper piston is near the top position, wherein the damper piston is moving downwards,

[0035] Fig. 3b shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the bottom position, wherein the damper piston is moving downwards,

[0036] Fig. 3c shows, by way of example, in a cross-sectional side view, a braking force generated by the damper piston when the damper piston moves downwards near the bottom position,

[0037] Fig. 4a shows, by way of example, in a three-dimensional view, a combination of the actuator piston and the damper piston,

[0038] Fig. 4b shows, by way of example, in a three-dimensional view, a combination of the actuator cylinder and the damper cylinder,

[0039] Fig. 4c shows, by way of example, in a three-dimensional view, an actuator space and a damper space defined by the pistons of Fig. 4a and by the cylinders of Fig. 4b,Fig. 5 shows, by way of example, the flow resistance of the control aperture as a function of time, and as a function of the vertical position of the damper piston,

[0040] Fig. 6 shows, by way of example, a fuel injecting apparatus, which comprises a fuel injector with a damper,

[0041] Fig. 7 shows, by way of example, evolution of flow resistance, valve element position, valve element velocity, valve element acceleration, fluid volume, and fluid flow rate in a fuel injector, which comprises a damper,

[0042] Fig. 8a shows, by way of example, in a cross-sectional side view, a first vertical position of the damper piston with respect to the damper cylinder,

[0043] Fig. 8b shows, by way of example, in a cross-sectional side view, a second vertical position of the damper piston with respect to the damper cylinder,

[0044] Fig. 8c shows, by way of example, in a cross-sectional side view, a third vertical position of the damper piston with respect to the damper cylinder,

[0045] Fig. 8d shows, by way of example, dimensions of the control aperture as functions of vertical position of the damper piston,

[0046] Fig. 8e shows, by way of example, the flow resistance of the control aperture as a function of the vertical position of the damper piston,

[0047] Fig. 9a shows, by way of example, in a cross-sectional side view, a first vertical position of the damper piston with respect to the damper cylinder,Fig. 9b shows, by way of example, in a cross-sectional side view, a second vertical position of the damper piston with respect to the damper cylinder,

[0048] Fig. 9c shows, by way of example, in a cross-sectional side view, a third vertical position of the damper piston with respect to the damper cylinder,

[0049] Fig. 9d shows, by way of example, dimensions of the control aperture as functions of vertical position of the damper piston,

[0050] Fig. 10a shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the bottom position, wherein the damper piston is moving upwards,

[0051] Fig. 10b shows, by way of example, in a cross-sectional side view, the diameter of the actuator piston and the diameter of the damper piston,

[0052] Fig. 10c shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the top position, wherein the damper piston is moving upwards,

[0053] Fig. 10d shows, by way of example, in a cross-sectional side view, the actuator and the damper, wherein the damper piston is an extension of the actuator piston,

[0054] Fig. 11a shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the bottom position, wherein the damper piston is moving upwards, wherein the damper space receives hydraulic fluid via a one-way valve,

[0055] Fig. 11b shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the top position, wherein the damper piston is moving upwards,Fig. 11c shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the top position, wherein the damper piston is moving downwards,

[0056] Fig. 11d shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the bottom position, wherein the damper piston is moving downwards,

[0057] Fig. 12a shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the bottom position, wherein the damper piston is moving upwards, wherein the damper space receives hydraulic fluid via a one-way valve,

[0058] Fig. 12b shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the top position, wherein the damper piston is moving upwards,

[0059] Fig. 12c shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the top position, wherein the damper piston is moving downwards,

[0060] Fig. 12d shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the bottom position, wherein the damper piston is moving downwards,

[0061] Fig. 13a shows, by way of example, in a cross-sectional side view, the actuator and the damper, wherein hydraulic fluid is displaced from the damper space via a flow resisting element,

[0062] Fig. 13b shows, by way of example, in a cross-sectional side view, the actuator and the damper, wherein hydraulic fluid is displaced from the damper space via a flow resisting element,

[0063] Fig. 14a shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the top position, wherein the damper piston is moving downwards,Fig. 14b shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the bottom position, wherein the damper piston is moving downwards,

[0064] Fig. 14c shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the bottom position, wherein the damper piston is moving upwards,

[0065] Fig. 14d shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the top position, wherein the damper piston is moving upwards,

[0066] Fig. 14e shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the top position, wherein the damper piston is moving downwards,

[0067] Fig. 14f shows, by way of example, in a cross-sectional side view, the actuator and the damper when the damper piston is near the bottom position, wherein the damper piston is moving downwards,

[0068] Fig. 15a shows, by way of example, in a three-dimensional view, a combination of two pistons,

[0069] Fig. 15b shows, by way of example, in a three-dimensional view, a cylinder,

[0070] Fig. 15c shows, by way of example, in a three-dimensional view, the pistons of Fig. 15a moving in the cylinder of Fig. 15b,

[0071] Fig. 16 shows, by way of example, in a cross-sectional side view, a fuel injector where the damper is located between the return spring and the actuator,

[0072] Fig. 17a shows, by way of example, in a cross-sectional side view, the actuator and the damper of Fig. 16,Fig. 17b shows, by way of example, in a cross-sectional side view, an actuator and a damper, wherein the damper comprises a one-way valve,

[0073] Fig. 17c shows, by way of example, in a cross-sectional side view, a fuel injection apparatus,

[0074] Fig. 18a shows, by way of example, in a cross-sectional side view, a fuel injector when the piston is near the top position, wherein the actuator comprises two ports at different heights,

[0075] Fig. 18b shows, by way of example, in a cross-sectional side view, the fuel injector of Fig. 18a when the piston is near the bottom position,

[0076] Fig. 18c shows, by way of example, in a cross-sectional side view, the actuator which comprises two ports at different heights,

[0077] Fig. 18d shows, by way of example, a fuel injecting apparatus, wherein the actuator comprises two ports at different heights,

[0078] Fig. 19a shows, by way of example, in a cross-sectional side view, a fuel injector which comprises several fuel valves for controlling the flow rate of a first fuel,

[0079] Fig. 19b shows, by way of example, in a three-dimensional view, valve elements which are opened and closed with a common actuator,

[0080] Fig. 20 shows, by way of example, in a cross-sectional side view, an internal combustion engine.

[0081] DETAILED DESCRIPTION

[0082] Referring to Figs. 1a and 1b, the fuel injector 200 comprises a fuel valve VAL2, a hydraulic actuator ACII1 , a return spring SPR1 , and a hydraulic damper DAM1. The damper DAM1 may be arranged to control the velocity v(t) of the valve element PIN2 in a position-dependent manner.Fig. 1a shows a situation where the fuel valve FAL2 is open. Fig. 1b shows a situation where the fuel valve VAL2 is closed.

[0083] The fuel valve VAL2 comprises a valve element PIN2 and a stationary sealing surface SRF1. The return spring SPR1 may be configured to close the fuel valve VAL2 by pressing the valve element PIN2 against the sealing surface SRF1. The hydraulic actuator ACLI1 may be arranged to deflect the return spring SPR1 away from the closed position.

[0084] The fuel injector 200 comprises the hydraulic damper DAM1 to control the velocity v(t) of the valve element PIN2. The damper DAM1 comprises a damper piston M2 and a damper cylinder CYL2. The damper piston M2 is arranged to move with respect to the damper cylinder CYL2. The damper piston M2 is coupled to move together with the valve element PIN2. The damper piston M2 defines a damper space SPC2 and a control aperture THR2 with the damper cylinder CYL2. The control aperture THR2 is arranged to control a flow rate Q2 of hydraulic fluid LIQ1 displaced from the damper space SPC2. The vertical position (z) of the damper piston M2 may determine at least one variable dimension dTHR2 of the control aperture THR2. The damper piston M2 may define at least one variable dimension dTHR2 of the control aperture THR2 together with the damper cylinder CYL2. The dimension dTHR2 may vary as a function dTHR2(z) of the vertical position (z) of the damper piston M2.

[0085] The variable control aperture THR2 may also be called e.g. as a throttle, throttling valve, constriction, or passage.

[0086] The fuel valve VAL2 may be opened by using the hydraulic actuator ACLI1 to deflect the return spring SPR1 away from the closed position. The valve element PIN2 may be coupled to follow the movements the return spring SPR1. The valve element PIN2 may be moved from a bottom position to a top position by guiding pressurized hydraulic fluid LIQ1 into the hydraulic actuator ACLI1. The position of the valve element PIN2 may be changed by a pressurized hydraulic fluid LIQ1 so that by guiding the fluid LIQ1 to the actuator ACLI1 the valve element PIN2 may be urged away from its closed position.The fuel valve VAL2 may be closed by releasing hydraulic fluid LIQ1 from the hydraulic actuator ACLI1 so that the return spring SPR1 may press the valve element PIN2 from the top position back to the bottom position. By releasing the hydraulic fluid LIQ1 from the actuator ACLI1 the valve element PIN2 may be allowed to move back to the closed position.

[0087] The damper piston M2 may be coupled to the valve element PIN2 so that the damper piston M2 is arranged to move in the same direction and at the same velocity v(t) as the valve element PIN2. The valve element PIN2 may be coupled to the damper piston M2 to move in the same direction and at the same velocity v(t) as the damper piston M2. The damper piston M2 may be e.g. mechanically coupled to the valve element PIN2 to move together with the valve element PIN2. The valve element PIN2, the actuator piston M1 , the damper piston M2, and the lower end of the return spring SPR1 may be mechanically coupled to each other and may move at the same velocity in the same direction, e.g. downwards.

[0088] The symbol v(t) may refer to the velocity of the valve element PIN2. The velocity of the pistons M1 , M2, the velocity of the shafts SHF1 , SHF2, and the velocity of the bottom of the return spring SPR1 may be equal to the velocity v(t) of the valve element PIN2.

[0089] The damper piston M2 may displace hydraulic fluid LIQ1 away from the damper space SPC2 when the return spring SPR1 pushes the damper piston M2 downwards. The control aperture THR2 may restrict the flow rate Q2 of the displaced hydraulic fluid LIQ1 so that the pressure of the damper space SPC2 rises when the damper piston M2 approaches the bottom position. The pressure of the damper space SPC2 may rise abruptly e.g. when the annular gap between the lower edge of the moving piston M2 and the upper edge of the damper cylinder becomes almost closed. The rising pressure of the hydraulic fluid LIQ1 of the damper space SPC2 may act on the damper piston M2 so that the damper piston M2 generates a high hydraulic braking force. The hydraulic braking force of the damper piston M2 may limit the velocity of the closing valve element PIN2 by resisting the closing force of the return spring SPR1.

[0090] The control aperture THR2 may restrict the flow rate Q2 less when the lower edge of the damper piston M2 is above a reference position, and the control apertureTHR2 may restrict the flow rate Q2 more when the lower edge of the damper piston M2 is below the first reference position.

[0091] The position of the valve element PIN2 may be changed by using the hydraulic actuator ACLI1. The actuator ACLI1 may be arranged to move the valve element PIN2 of the valve VAL2 with respect to a stationary sealing surface SRF1. The valve element PIN2 may also be called e.g. as a pin, or as a needle. The fuel valve VAL2 may be e.g. a needle valve.

[0092] The valve VAL2 may be in a closed state when a sealing surface SRF2 of the movable valve element PIN2 is in contact with the stationary sealing surface SRF1 . The valve VAL2 may be in an open state when the distance between the sealing surfaces SRF1, SRF2 is substantially greater than zero. The second sealing surface SRF2 may be a part of the valve element PIN2 and may move together with the valve element PIN2.

[0093] The fuel injector 200 may comprise a fuel channel CH2 for guiding a liquid fuel FUEL1 from a fuel inlet port IN2 to the fuel valve VAL2. The fuel injector 200 may comprise one or more atomizing orifices OR1 for converting a flow of pressurized liquid fuel FUEL1 into a plurality of droplets DR1. The fuel injector 200 may comprise a nozzle NOZ1, which comprises one or more atomizing orifices OR1.

[0094] The valve VAL2 may prevent the fuel flow to the orifices OR1 in the closed state. The valve VAL2 may have a gap GAP1 between the sealing surfaces SRF1, SRF2 in the open state. The valve VAL2 may allow a flow of the fuel FUEL1 from the fuel inlet port IN2 via the channel CH2 and via the gap GAP1 to the orifices OR1 in the open state of the valve VAL2. The fuel injector 200 may be arranged to form one or more jets JET1 of atomized fuel droplets DR1 in a combustion space CSPC1 of a cylinder ECYL1 of an internal combustion engine ENG1 (Fig.

[0095] 20). The jet JET1 may also be called e.g. as a spray JETI . The atomized fuel droplets DR1 may be combusted in the combustion space CSPC1.

[0096] The valve VAL2 may be periodically opened and closed during operation of the engine ENG1. Opening and closing of the valve VAL2 may be synchronized with the rotation of a crankshaft (CRANK1) of the engine ENG1. Forming of the fuel jets JET1 may be synchronized with the rotation of a crankshaft (CRANK1) of theengine ENG1. The frequency of closing the valve VAL2 may be e.g. equal to the rotation speed of the crankshaft (in case of a two-stroke engine), or equal to a half of the rotation speed of the crankshaft (in case of a four-stroke engine).

[0097] The engine ENG1 may comprise a camshaft for operating one or more valves (EVAL1) of cylinders (ECYL1) of the engine ENG1. Rotation of the camshaft may be synchronized with the rotation of the crankshaft. Rotation speed of the camshaft of a four-stroke engine is (typically) half of the rotation speed of the crankshaft. Opening and closing of the valve VAL2 may be synchronized with the rotation of the camshaft. Opening and closing of the valve VAL2 may be synchronized with the rotation of the crankshaft e.g. by synchronizing opening and closing of the valve VAL2 with the rotation of the camshaft.

[0098] The sealing surface SRF2 of the closing valve element PIN2 may hit the stationary sealing surface SRF1. The valve element PIN2 may hit the stationary sealing surface SRF1 e.g. over a million times during the lifetime of the fuel injector 200.

[0099] The moving valve element PIN2 may have a velocity v(t) with respect to the stationary sealing surface SRF1. Repetitive hitting may cause erosion of the surfaces SRF1, SRF2.

[0100] The damper DAM1 may be arranged to limit the impact velocity v(t) of the valve element PIN2, so as to reduce or avoid erosion of the surfaces SRF1 , SRF2.

[0101] The actuator ACLI1 may comprise a cylinder CYL1 and a piston M1, which is movable in the cylinder CYL1. The piston M1 may be moved hydraulically by pressurized hydraulic fluid LIQ1, which is guided into the cylinder CYL1 and / or out of the cylinder CYL1. The actuator ACLI1 may comprise an inlet port PORT1 for guiding the hydraulic fluid LIQ1 into the cylinder CYL1 and / or out of the cylinder CYL1. The return spring SPR1 may be coupled to move with the piston M1. The valve element PIN2 may be coupled to move with the piston M1.

[0102] The fuel injector 200 may be arranged to operate such that the valve VAL2 is caused to be opened by a hydraulic force generated by the actuator ACU1. Pressurized hydraulic fluid LIQ1 may be fed into the internal space SPC1 ofcylinder CYL1 the actuator ACLI1 in order to generate an actuating force, which compresses the spring SPR1. The hydraulic force generated by the actuator ACU1 may compress (or extend) the return spring SPR1 so as to allow lifting the valve element PIN2 away from the sealing surface SRF1. The valve element PIN2 may be lifted e.g. by a force generated by fuel pressure acting on a piston surface M3 of the valve element PIN2, by the actuator ACLI1 and / or by an additional lifting spring (not shown).

[0103] The pressurized fuel FUEL1 may act on the valve element PIN2 so as to keep the valve element PIN2 mechanically coupled to the shaft SHF2, which transmits the force of the return spring SPR1 to the valve element PIN2. The pressurized fuel FUEL1 may act on the valve element PIN2 so as to lift the valve element PIN2 upwards.

[0104] The fuel injector 200 comprises the return spring SPR1 , which may be arranged to move the valve VAL2 into the closed position when hydraulic fluid LIQ1 is allowed to flow away from the internal space SPC1 of the actuator ACLI1. The position of the valve element PIN2 may be changed from the open position to the closed position by releasing hydraulic fluid LIQ1 away from the actuator ACLI1. Releasing the hydraulic fluid allows the piston M1 of the actuator ACLI1 to move downwards so that the return spring SPR1 may push the valve element PIN2 firmly against the sealing surface SRF1. The fuel injector 200 may be arranged to operate such that the valve VAL2 is closed by a spring force generated by the return spring SPR1, in a situation where hydraulic fluid LIQ1 is ejected from the actuator ACU1. The spring force may bring the sealing surface SRF2 into contact with the sealing surface SRF1. The spring force generated by the return spring SPR1 may press the sealing surface SRF2 of the valve element PIN2 against the stationary sealing surface SRF2. The spring force may keep the sealing surface SRF2 in contact with the sealing surface SRF1. The fuel injector 200 may be arranged to operate such that the valve VAL2 is kept in the closed state by the spring force generated by the return spring SPR1.

[0105] The position of the valve element PIN2 may be changed from the closed position to the open position by guiding pressurized hydraulic fluid LIQ1 into the hydraulic actuator ACU1. The pressurized hydraulic fluid LIQ1 may lift the piston M1 of the actuator ACLI1 upwards so that the actuator ACLI1 may deflect the return springSPR1 from a bottom position of the return spring to a top position of the return spring. The valve element PIN2 may be coupled to move together with the piston M1 and with the return spring SPR1. The valve element PIN2 may be lifted upwards e.g. by the pressure of the fuel FUEL1, which acts on the valve element PIN2. The pressure of the fuel FUEL1 may act e.g. on a piston portion M3 of the valve element PIN2. The valve element PIN2 may follow the movement of the piston M1 so that the valve element PIN2 moves from the closed position to the open position.

[0106] The fuel injector 200 may comprise a shaft SHF1 to transfer a deflecting hydraulic force from the piston M1 to the spring SPR1. The fuel injector 200 may comprise a shaft SHF2 to transfer a closing spring force from the spring SPR1 to the valve element PIN2.

[0107] The injector unit 200 may comprise a first shaft SHF1 to transmit a hydraulic force FMI from the actuator piston M1 to the return spring SPR1, so as to deflect the return spring SPR1 away from the bottom position where the fuel valve VAL2 is closed. The injector unit 200 may comprise a second shaft SHF2 to transmit a closing force from the return spring SPR1 to the valve element PIN2, together with the first shaft SHF1. The damper piston M2 may be coupled to the valve element PIN2 to move together with the valve element PIN2. The damper piston M2 may be mechanically coupled to the valve element PIN2 e.g. via the shaft SHF2.

[0108] The damper DAM1 may be located e.g. between the hydraulic actuator ACLI1 and the valve element PIN2. The damper piston M2 may be located e.g. between the hydraulic actuator ACLI1 and the fuel valve VAL2. The damper DAM1 may also be integrated into the actuator ACLI1.

[0109] The control aperture THR2 may be e.g. a gap between the damper piston M2 and the damper cylinder CYL2. The control aperture THR2 may be e.g. a curved gap. The control aperture THR2 may be e.g. an annular gap between the damper piston M2 and the damper cylinder CYL2. The control aperture THR2 may be e.g. a portion of an annular gap.The control aperture THR2 may be e.g. at least partly open when lower edge of the damper piston M2 is above the upper edge of the damper cylinder CYL2. The control aperture THR2 may be e.g. nearly closed when lower edge of the damper piston M2 is below the upper edge of the damper cylinder CYL2.

[0110] The hydraulic fluid LIQ1 may sometimes carry e.g. contaminant particles, which may clog small openings. The control aperture THR2 may be repetitively opened and closed with a mechanical movement of the damper piston M2 so that the control aperture THR2 may have a self-cleaning property. The control aperture THR2 may be resistant clogging.

[0111] The damper DAM1 may also be designed such that the wear of the damper piston M2 is negligible. For example, the damper DAM1 may be designed such that there is always a small gap between the damper piston M2 and the damper cylinder CYL2 even when the damper piston M2 is near the bottom position. The damper DAM1 may be arranged to operate such that the outer perimeter of the damper piston M2 is not in contact with the damper cylinder CYL2.

[0112] In an embodiment, the control aperture THR2 may may arranged to restrict all flow which is displaced from the damper space SPC2.

[0113] The fuel injector 200 may have a longitudinal axis AX1. The valve element PIN2 and the piston M1 may be arranged to move in the direction of the longitudinal axis AX1.

[0114] The actuator piston M1 and the damper piston M2 may have e.g. circular shape, when viewed in the direction of the longitudinal axis AX1 of the fuel injector 200.

[0115] SX, SY, SZ denote orthogonal directions. The direction SZ may be parallel with the longitudinal axis AX1 of the fuel injector 200. The direction +SZ may refer to the longitudinal direction of the fuel injector 200 upwards. The direction -SZ may refer to the longitudinal direction of the fuel injector 200 downwards. The direction -SZ may also deviate from the direction of gravity. The longitudinal axis AX1 does not need to be parallel with the direction of gravity. The longitudinal axis AX1 may have any orientation with respect to the direction of gravity. The term "upwards" means herein "in a first direction away from the stationary sealing surface SRF1".The term "downwards" means herein in a second direction towards the stationary sealing surface SRF1".

[0116] The fuel injector 200 may comprise one or more stationary body parts 210, 220, 140. The fuel injector 200 may comprise one or more intermediate elements 150 to transmit actuating force(s). For example, an intermediate element 150 may transmit a deflecting force from the actuator ACLI1 to the return spring SPR1 and / or the intermediate element 150 may transmit a closing force from the return spring SPR1.

[0117] A maximum distance between the sealing surfaces SRF1 , SRF2 in the fully open state of the valve VAL2 may be e.g. in the range of 0.5 mm to 5 mm. A closing force generated by the spring SPR1 may be e.g. in the range of 1000 N to 10000 N. The combined mass of the moving parts (e.g. SPR1, 150, M1, M2, SHF1, SHF2, PLA2, ROD2, PIN2) may be e.g. in the range of 0.1 kg to 1 kg (Figs 19a, 19b).

[0118] The control aperture THR2 may restrict the flow of the hydraulic fluid LIQ1 displaced from the damper space SPC2. The fuel injector 200 may optionally comprise an additional flow restricting element RES2 (Fig. 13a, 13b, 17b) to restrict at least a part of the flow of the hydraulic fluid LIQ1 displaced from the damper space SPC2. A flow restricting element RES2 may be located e.g. between the damper space SPC2 and the actuator space SPC1. A flow restricting element RES2 may be used e.g. in parallel with a one-way valve (VAL4).

[0119] The damper DAM1 may control the velocity v(t) of the valve element PIN2 by converting movement of the damper piston M2 into heat. The moving piston M2 may displace hydraulic fluid LIQ1 away from the damper space SPC2 through a constriction and / or through one or more flow-restricting elements (RES2). The control aperture THR2 may be arranged to operate as the constriction, or the damper DAM1 may comprise one or more flow restricting elements (RES2) to convert energy of the displaced hydraulic fluid LIQ1 into heat. The damper piston M2 may force displaced hydraulic fluid LIQ1 through one or more flow restricting elements (RES2). The damper DAM1 may convert potential energy of the return spring SPR1 into heat by restricting the flow Q2 of the hydraulic fluid LIQ 1 , which is displaced from the damper space SPC2.The actuator ACLI1 may be operated by pressurized hydraulic fluid LIQ1, which acts may act on the lower side of the actuator piston M1. In addition, also the upper side of the actuator piston M1 may displace ordraw low-pressure hydraulic fluid LIQ1 when the pistons M1, M2 are moving. The resulting periodic motion of the low-pressure hydraulic fluid LIQ1 may be called e.g. as breathing. The fuel injector 200 may optionally comprise one or more pathways for enabling the breathing, i.e. the internal flows of the low-pressure hydraulic fluid LIQ1 outside the spaces SPC1 , SPC2.

[0120] The fuel injector 200 may have further arrangements to provide sealing and / or lubrication of moving internal parts such as, for example, the valve element PIN2 or shaft SHF2. Due to the schematical illustration, these details are not shown in Fig.1a or in the other drawings unless related to the description of the relevant functionalities.

[0121] Referring to Fig. 2, the actuator piston M1 may define an actuator space SPC1 with the actuator cylinder CYL1. The damper piston M2 may define a damper space SPC2 and a control aperture THR2 together with the damper cylinder CYL2. The damper piston M2 may displace hydraulic fluid LIQ1 away from the damper space SPC2 when the damper piston M2 is moving downwards. The control aperture THR2 may restrict the flow rate Q2 of the hydraulic fluid LIQ1, which is displaced from the damper space SPC2.

[0122] The control aperture THR2 may be defined e.g. by the lower edge (E2) of the moving damper piston M2 and by the upper edge U2 of the stationary damper cylinder CYL2.

[0123] The moving damper piston M2 may have a tracking point E2. The damper piston M2 may have a tracking point E2, which represents the vertical position of the damper piston M2. The tracking point E2 may be e.g. a point of the lower edge of the damper piston M2. The symbol E2 may denote also to the lower edge of the damper piston M2. The tracking point E2 moves together with the piston M2, i.e. the tracking point E2 is fixed to the moving piston M2.The damper cylinder CYL2 may define a reference position ZREF. The tracking point E2 may move with respect to the reference position ZREF of the damper cylinder CYL2. The reference position ZREF may be e.g. the vertical position of an upper edge U2 of the damper cylinder CYL2. The reference position ZREF may be stationary and fixed with respect to the stationary sealing surface SRF1.

[0124] The symbol ZMAX may denote the uppermost vertical position of the damper piston M2, i.e. the top position. In particular, the symbol ZMAX may denote the uppermost vertical position of the tracking point E2 of the damper piston M2. The symbol ZMIN may denote the lowermost vertical position of the damper piston M2, i.e. the bottom position. In particular, the symbol ZMIN may denote the lowermost vertical position of the tracking point E2 of the damper piston M2. The reference position ZREF is between the lowermost position ZMIN and the uppermost position ZMAX. The lowermost position ZMIN is below the reference position ZREF. The uppermost position ZMAX is above the reference position ZREF.

[0125] Referring to Fig. 3a, the fuel valve VAL2 may be closed by allowing the hydraulic fluid LIQ1 to flow away from the actuator space SPC1 e.g. via the port PORT1. The actuator piston M1 and the damper piston M2 may move downwards. The actuator ACU1 comprises an actuator piston M1 and an actuator cylinder CYL1. The piston M1 may move downwards at a velocity v(t) in the cylinder CYL1. The piston M1 defines an actuator space SPC1 with the cylinder CYL1. The actuator ACU1 comprises a port PORT1 for guiding pressurized hydraulic fluid LIQ1 into the actuator space SPC1. The port PORT1 may also be arranged to discharge hydraulic fluid LIQ1 away from the actuator space SPC1. The descending piston M1 may reduce the volume of the actuator space SPC1. The descending piston M1 may displace hydraulic fluid LIQ1 away from the actuator space SPC1 e.g. via the port PORT1.

[0126] The damper DAM1 may comprise a damper piston M2 and a damper cylinder CYL2. The damper piston M2 may be e.g. near the top position ZMAX. The piston M2 may move downwards at the velocity v(t) with respect to the damper cylinder CYL2. The damper piston M2 defines a damper space SPC2 with the cylinder CYL2.The damper piston M2 defines a control aperture THR2 with the damper cylinder CYL2. The control aperture THR2 may control a flow rate Q2 of the hydraulic fluid LIQ1, which is displaced from the damper space SPC2. The vertical position (z) of the damper piston M2 may determine at least one variable dimension dTHR2 of the control aperture THR2 together with the damper cylinder CYL2. The damper piston M2 may have one or more positions where the control aperture THR2 restricts the flow rate Q2 of the hydraulic fluid LIQ1 , which is displaced away from the damper space SPC2.

[0127] The control aperture THR2 may restrict the flow rate Q2 less when a tracking point E2 of the damper piston M2 is above a first reference position ZREF, and the control aperture THR2 may restrict the flow rate Q2 more when the tracking point E2 of the damper piston M2 is below the first reference position ZREF.

[0128] The flow resistance R of the control aperture THR2 may be rapidly increased when the damper piston M2 approaches the damper cylinder CYL2. The flow resistance R of the control aperture THR2 may be rapidly increased when a lower edge of the damper piston M2 approaches an upper edge of the damper cylinder CYL2.

[0129] The control aperture THR2 may be e.g. an annular gap, which is defined by the damper piston M2 and the damper cylinder CYL2. The control aperture THR2 may be e.g. an annular gap, which is defined by the lower circular edge of the damper piston M2 and by the upper circular edge of the damper cylinder CYL2.

[0130] The control aperture THR2 may be at least partly open when the lower edge of the damper piston M2 is above the upper edge of the damper cylinder CYL2.

[0131] The control aperture THR2 may operate as a fluid communication pathway between the damper space SPC2 and the actuator space SPC1. The control aperture THR2 may allow displaced hydraulic fluid LIQ 1 to flow from the damper space SPC2 to the actuator space SPC1.

[0132] The piston M2 may move inside the cylinder CYL2 when the piston M2 is near the bottom position ZMIN. In an embodiment, the piston M2 may be outside the cylinder CYL2 when the piston M2 is near the top position ZMAX.Referring to Fig. 3b, the control aperture THR2 and the damper space SPC2 may be closed or nearly closed when the damper piston M2 has moved downwards so that the lower edge of the damper piston M2 is below the upper edge of the damper cylinder CYL2.

[0133] The damper DAM1 may control the velocity of the valve element PIN2. In particular, the hydraulic fluid LIQ1 displaced from the damper space SPC2 may be forced to pass via the restricting control aperture THR2 and / or via an additional flow restricting element RES2 when the damper piston M2 is moving downwards near the bottom position. The pressure of the damper space SPC2 may be high when the damper piston M2 is moving downwards near the bottom position.

[0134] Referring to Fig. 3c, the internal pressure pspc2 of the hydraulic fluid LIQ1 enclosed in the damper space SPC2 may rapidly increase when the damper piston M2 continues to move downwards in the damper cylinder CYL2. The internal pressure pspc2 may momentarily be e.g. higher than 10 MPa, higher than 20 MPa, higher than 50 MPa, or even higher than 100 MPa (=1000 bar). The internal pressure pspc2 acting on the bottom side of the damper piston M2 may generate a high hydraulic braking force FM2, which may effectively counteract the spring force of the return spring SPR1 , and which may effectively slow down the velocity v(t) of the moving components PIN2, M1 , M2, SHF1 , SHF2, SPR1. The hydraulic braking force FM2 may momentarily be e.g. higher than 1000 N, higher than 2000 N, higher than 5000 N, or even higher than 10000 N.

[0135] Fig. 4a shows a combination of an actuator piston M1 and a damper piston M1. Fig. 4b shows a combination of an actuator cylinder CYL1 and a damper cylinder CYL2. Fig. 4c shows a damper space SPC2 and a control aperture THR2 defined by the damper piston M2 of Fig. 4a and by the damper cylinder CYL2 of Fig. 4b.

[0136] Fig. 5 shows, by way of example, the flow resistance R of the control aperture THR2 as a function of time t and as a function of vertical position z of the damper piston M2 in a situation where the damper piston M2 is moving downwards. The control aperture THR2 may restrict the flow rate Q2 of the hydraulic fluid LIQ1 according to a function R(z) of vertical position z of the damper piston M2.The combination of the damper piston M2 and the damper cylinder CYL2 may be arranged to change the flow resistance R of the control aperture THR2 from a lower value RLOW to a higher value RHIGH. The flow resistance of the control aperture THR2 may be varied as a function R(z) of the vertical position z of the damper piston M2. For example, a radial width and / or height of the control aperture THR2 may be decreased in the vicinity of the reference position ZREF, when the damper piston M2 moves downwards.

[0137] The flow resistance R of the control aperture THR2 may be changed from a lower value RLOW to a higher value RHIGH e.g. when the lower edge E2 of the damper piston M2 passes the reference position ZREF at a time td, and wherein the damper piston M2 is moving downwards.

[0138] The damper piston M2 may be at an uppermost position ZMAX at the time tc. The damper piston M2 may be at the intermediate reference position ZREF at the time td. The damper piston M2 may be at the lowermost position ZMIN at the time te.

[0139] A tracking point E2 of the moving damper piston M2 may pass a reference position ZREF of the damper cylinder CYL2 at the time td. The tracking point E2 may be e.g. at a lower edge of the damper piston M2. The reference position ZREF may be e.g. at an upper edge of the damper cylinder CYL2. For example, an annular gap between the damper piston M2 and the damper cylinder CYL2 may be closed when the lower edge of the damper piston M2 approaches the upper edge of the damper cylinder CYL2.

[0140] The flow resistance R of a hydraulic component may refer e.g. to a ratio of a pressure difference (pressure loss) over the hydraulic element to a flow rate via the hydraulic element, in a situation where the pressure difference is caused by the flow rate.

[0141] The control aperture THR2 may be e.g. an annular gap, which is defined by the lower circular edge of the damper piston M2 and by the upper circular edge of the damper cylinder CYL2. The control aperture THR2 may be at least partly open when the lower edge of the damper piston M2 is above the upper edge of the damper cylinder CYL2. The flow resistance R of the control aperture THR2 may be rapidly increased when the damper piston M2 approaches the damper cylinderCYL2. The flow resistance R of the control aperture THR2 may be rapidly increased when the damper piston M2 is moving downwards and a lower edge of the damper piston M2 approaches an upper edge of the damper cylinder CYL2.

[0142] In an embodiment, the control aperture THR2 may be at least partly open when the tracking point E2 of the damper piston M2 is above a reference position ZREF. The control aperture THR2 may be closed or almost closed when the tracking point E2 of the damper piston M2 is below the reference position ZREF.

[0143] Referring to Fig. 6, an injector apparatus 1000 may comprise the fuel injector 200 to inject the fuel FUEL1 into a cylinder of an engine, and a control valve VAL1 to control a flow of hydraulic fluid LIQ1 into the hydraulic actuator ACLI1 and / or out of the hydraulic actuator ACLI1. The fuel valve VAL2 may be opened and / or closed with the hydraulic actuator ACLI1. The fuel injector 200 comprises the internal hydraulic damper DAM1 for controlling the velocity of the valve element PIN2 when the valve element PIN2 is moving downwards. The fuel injector 200 comprises one or more atomizing orifices to convert the liquid fuel FUEL1 into fuel droplets DR1 when the fuel valve VAL2 is open and allows a flow of the pressurized liquid fuel FUEL1 to the atomizing orifices.

[0144] The control valve VAL1 may be e.g. a three-way valve, which may connect a port N2 either with a port N1 or with a port N3. The position of the control valve VAL1 may be changed based on a control signal SVALI received from the engine control unit ECU1.

[0145] Pressurized hydraulic fluid L IQ 1 may be guided via the ports N1 , N2, PORT 1 into the actuator ACLI1. Ejected hydraulic fluid LIQ1 may be discharged from the actuator ACU1 via the portsPORTI , N2, N3 and via a line LIN3 to an outlet OLIT3.

[0146] The symbol POS1 denotes the position of the control valve VAL1 where pressurized hydraulic fluid LIQ1 is fed into the actuator ACLI1 for opening the fuel valve VAL2. The symbol POS2 denotes the position of the control valve VAL1 where hydraulic fluid LIQ1 is ejected from the actuator ACLI1 for closing the fuel valve VAL2.The injector apparatus 1000 may comprise a hydraulic pump PUMP1, and accumulator ACC10, and a fluid line LIN10 to provide pressurized hydraulic fluid LIQ1 for the control valve VAL1. The discharged hydraulic fluid LIQ1 may be recirculated from the outlet OLIT3 back to the pump PUMP1.

[0147] The injector apparatus 1000 may comprise a fuel pump PUMP2, and accumulator ACC20, and fuel line LIN20 to provide pressurized liquid fuel FUEL1 for the injector unit 200. The fuel line LIN20 may feed the pressurized fuel FUEL1 to the injector 200 via an inlet port IN2.

[0148] Referring to Fig. 7, the flow rate Q2 of the hydraulic fluid LIQ1 ejected from the damper space SPC2 may be restricted in a position-dependent manner, so as to reduce the velocity at which the moving valve element PIN2 hits the stationary sealing surface SRF1.

[0149] For example, the damper piston M2 of the hydraulic damper DAM1 may substantially block the control aperture THR2 when the lower edge of the damper piston M2 is below a reference position. Consequently, the flow resistance R(z) of the control aperture THR2 may be changed from a low value RLOW to a higher value RHIGH at a time td, before the valve element PIN2 contacts the sealing surface SRF1 at a time te.

[0150] The increased flow resistance may restrict the flow rate Q2 of the hydraulic fluid LIQ1 after the time td so that the velocity of the valve element PIN2 may be reduced before the valve element PIN2 contacts the stationary sealing surface SRF1 at the time te. Consequently, deceleration of the valve element at the time temay be reduced. Consequently, a risk of erosion of the sealing surfaces SRF1, SRF2 may be reduced or eliminated.

[0151] The uppermost curve of Fig. 7 shows, by way of example, a flow resistance R of the control aperture THR2 as a function of time t and as a function angular position (p of the crankshaft CRANK1 of the engine ENG1. The flow resistance may have a lower value RLOW at a time tcand a higher value RHIGH at a time td.

[0152] The second curve from the top of Fig. 7 shows a distance h between the sealing surfaces SRF1 , SRF2 as a function of time t. The distance h may also specify thevertical position of the valve element PIN2. The distance h between the sealing surfaces SRF1, SRF2 is zero (h=0) when fuel valve is closed, i.e. when the sealing surface SRF1, SRF2 are in contact with each other. The fuel valve is opening between the times taand tb. The fuel valve VAL2 may be open during the time period from tb to tc. The distance h may have a maximum value IIMAX during the time period from tb to tc. The valve element PIN2 may be at the uppermost position during the time period from tb to tc. The fuel valve is closing between the times tcand te. The fuel valve VAL2 may be in the closed state at the times taand te. The distance h may be zero at the times taand te.

[0153] The third curve from the top of Fig. 7 shows the velocity of the valve element PIN2 as a function of time t. The moving valve element PIN2 has a velocity v(t) with respect to the stationary sealing surface SRF1. The velocity v(t) may be substantially parallel with a longitudinal axis AX1 of the fuel injector 200. The valve element PIN2 may have a maximum velocity upwards VMAX.UP when the valve element PIN2 is moving away from the stationary sealing surface SRF1. The valve element PIN2 may have a maximum velocity downwards VMAX.DOWN when the valve element PIN2 is moving towards the stationary sealing surface SRF1 . The velocity v(t) may be considered to have a positive sign (+) when the valve element PIN2 is moving towards the stationary sealing surface SRF1 . The valve element PIN2 may have a reduced velocity VMOD,2e.g. after the time td. The velocity v(t) may be reduced by restricting the flow of the hydraulic fluid. The reduced velocity VMOD,2 may be e.g. smaller than 1 m / s, advantageously smaller than 0.5 m / s. The valve element PIN2 may have the reduced velocity VMOD,2e.g. at the position h=0.1 mm.

[0154] The velocity v(t) of the valve element PIN2 may be zero when the fuel valve VAL2 is fully closed and fully open. The velocity of the valve element PIN2 may reach a value VMAX.UP when the valve element moves upwards between the times taand tb. The velocity of the valve element PIN2 may be arranged to reach a value VMAX.DOWN when the valve element moves downwards between the times tcand td. The velocity of the valve element PIN2 may be reduced at the time td, before the valve element PIN2 contacts the stationary sealing surface SRF1. The velocity of the valve element PIN2 may have a reduced value VMOD,2 immediately before the valve element PIN2 contacts the stationary sealing surface SRF1.The closing of the fuel valve VAL2 may start at the time tc, and the closing of the fuel valve VAL2 may stop at the time te. The fuel feeding apparatus 1000 may be arranged to operate such that the time interval from tcto tehas an optimum value. The fuel feeding apparatus 1000 may be arranged to operate such that the time interval from tcto tehas a predetermined value. A reduced velocity VMOD,2 of the valve element PIN2 after the time td may be at least partly compensated by increasing the velocity VMAX.DOWN of the valve element PIN2 before the time td, so as to keep the duration of the time interval from tcto teat the desired value.

[0155] The fourth curve from the top of Fig. 7 shows the acceleration and deceleration of the valve element PIN2. The acceleration of the valve element PIN2 may have peaks when the velocity is changed at the times ta, tb, tc, td, te. The valve element PIN2 may have reduced deceleration 3MOD at the time te, thanks to the modified velocity VMOD,2.The velocity of the valve element PIN2 may be accelerated and decelerated during operation. The acceleration of the valve element PIN2 may be e.g. in the range of -3MOD to +3MAX. The symbol -3MOD may denote maximum deceleration of the valve element PIN2 in a situation where flow of the hydraulic fluid ejected from the actuator ACLI1 restricted. The symbol -3MAX may denote maximum deceleration of the valve element PIN2 in a comparative situation where flow of the hydraulic fluid ejected from the actuator ACLI1 is not restricted.

[0156] The second curve from the bottom of Fig. 7 shows the volume of hydraulic fluid LIQ1 stored in the actuator ACLI1. A minimum volume VACU.MIN may be stored in the actuator ACLI1 when the fuel valve VAL2 is in the closed state. A maximum volume VACU.MAX may be stored in the actuator ACLI1 when the fuel valve VAL2 is in the open state. VACU.MAX may denote the maximum volume of hydraulic fluid LIQ1 contained in the hydraulic actuator ACLI1. VACU.MIN may denote the minimum volume of hydraulic fluid LIQ1 contained in the hydraulic actuator ACLI1. The volume of hydraulic fluid LIQ1 ejected during a single stroke of the actuator ACLI1 may be equal to the difference VACU.MAX - VACU.MIN.

[0157] The distance h between the sealing surfaces SRF1 , SRF2 may be decreased by discharging hydraulic fluid LIQ1 from the actuator ACLI1. The distance h between the sealing surfaces SRF1, SRF2 may be increased by guiding pressurized hydraulic fluid L IQ 1 into the actuator ACLI1.The lowermost curve of Fig. 7 shows the flow rate Q of the hydraulic fluid LIQ1 , which is guided into the actuator ACLI1 and out of the actuator ACLI1. QMAX.OUT may denote a maximum flow rate Q of the hydraulic fluid LIQ1 ejected from the actuator ACU1 when the valve element PIN2 is closing, i.e. moving towards the stationary sealing surface SRF1. QMAX.IN may denote a maximum flow rate Q of the hydraulic fluid into the actuator ACLI1 when the actuator ACLI1 is opening the fuel valve VAL2. The flow rate may be considered to be positive (+) when the hydraulic fluid LIQ1 ejected from the actuator ACLI1. The flow rate into the actuator may reach a value QMAX.IN between the times taand tb. The flow rate out of the actuator may reach a value QMAX.OUT between the times tcand td. The control aperture THR2 may be arranged to restrict the flow rate of the hydraulic fluid LIQ1 displaced from the damper space SPC2 such that the flow rate of the fluid LIQ1 ejected from the actuator ACU1 has a first higher value QMAX.OUT before the time td, and a second lower value QMOD,2 after the time td. The flow rate Q may be restricted after the time td. QMOD,2 may denote a reduced flow rate Q. The reduced flow rate QMOD,2 may be obtained by restricting the flow rate of the hydraulic fluid LIQ1 ejected from the actuator ACII1. In particular, the flow rate Q out of the actuator ACU 1 may be restricted by restricting the internal flow Q2 from the damper space SPC2.

[0158] The damper DAM1 may be arranged to limit the velocity of the valve element PIN2. The damper DAM1 comprises the control aperture THR2. The control aperture THR2 may be arranged to restrict the flow rate Q2 of hydraulic fluid LIQ1 displaced from the damper space SPC2 such that a closing speed v(t) of the valve element PIN2 at a distance of 0.1 mm from the closed position (h=0) of said valve element PIN2 is smaller than 1 m / s, advantageously smaller than 0.5 m / s.

[0159] The control aperture THR2 may be arranged to restrict the flow rate of the displaced hydraulic fluid LIQ1 so that the velocity v(t) of the valve element PIN2 is e.g. smaller than 1 m / s when the valve element PIN2 is closing and the distance h between the sealing surfaces SRF1 , SRF2 is equal to 0.1 mm.

[0160] The limit value of the closing velocity of the valve element may also be e.g. 0.5 m / s in order to further reduce the risk of damaging the sealing surfaces SRF1, SRF2. The control aperture THR2 may be arranged to restrict the flow rate of the displaced hydraulic fluid LIQ1 so that the velocity v(t) of the valve element PIN2is e.g. smaller than 0.5 m / s when the valve element PIN2 is closing and the distance h between the sealing surfaces SRF1, SRF2 is equal to 0.1 mm.

[0161] The valve element PIN2 may be lifted by a maximum distance IIMAX from the lowermost closed position (h=0) during normal operation of the engine. The control aperture THR2 may be arranged to restrict the flow rate of the displaced hydraulic fluid LIQ1 so that the velocity v(t) of the valve element PIN2 is e.g. smaller than 1 m / s when the valve element is closing at the distance h, which is 5% of the maximum distance IIMAX.

[0162] The control aperture THR2 may be arranged to restrict the flow rate of the displaced hydraulic fluid LIQ1 so that the closing speed v(t) of the valve element PIN2 at the distance of h = 0.1 mm from the closed position (h=0) is smaller than a maximum closing speed VMAX.DOWN of the valve element PIN2.

[0163] The control aperture THR2 may be arranged to restrict the flow rate of the displaced hydraulic fluid LIQ1 so that the closing speed v(t) of the valve element PIN2 at the distance of h=0.1 mm from the closed position (h=0) is smaller than a maximum opening speed VMAX.UP of the valve element PIN2.

[0164] Fig. 8a shows the damper piston M2 at the lowermost position ZMIN. The damper piston M2 and the damper cylinder CYL2 define the control aperture THR2, which may be e.g. an annular gap between the damper piston M2 and the damper cylinder CYL2. The gap may have a radial width bTHR2. The gap may force the hydraulic fluid LIQ1 to pass through the gap in the vertical direction along the length 3THR2 of the gap.

[0165] Fig. 8b shows the damper piston M2 at a position zi. The hydraulic fluid LIQ1 may pass through the gap also in the horizontal direction when the lower edge E2 of the damper piston M2 is above the upper edge U2 of the damper cylinder CYL2. The dimension dTHR2 may denote the difference between the vertical position of the lower edge E2 of the damper piston M2 and the upper edge U2 of the damper cylinder CYL2. The dimension dTHR2 may be called e.g. as the height of the gap. The dimension dTHR2 may be defined to zero when the lower edge E2 of the damper piston M2 is below the upper edge U2 of the damper cylinder CYL2.Fig. 8c shows the damper piston M2 at the uppermost position ZMAX. The large height dTHR2 of the gap may allow the hydraulic fluid L IQ 1 to pass through the gap also in the horizontal direction.

[0166] Fig. 8d shows, by way of example, the dimensions 3THR2, bTHR2, dTHR2 as functions 3THR2(Z), bTHR2(z), djHR2(z) of the vertical position z of the damper piston M2. The length 3THR2 of the narrow gap may be reduced from a maximum value 3MAX to zero when the piston M2 moves from the lowermost position upwards to the reference position ZREF. The radial dimension bTHR2 of the narrow gap may be substantially independent of the vertical position z. The radial dimension bTHR2 of may remain at a constant value bMiN. The height dTHR2 of the gap may be increased from zero to a maximum value diw\x when the damper piston M2 moves upwards from the reference position ZREF to the uppermost position ZMAX.

[0167] A variable dimension (dTHR2) of the control aperture THR2 may have a first smaller value (dTHR2,i) when a tracking point (E2) of the damper piston M2 is at a first vertical position (zi), wherein the variable dimension (dTHR2) of the control aperture (THR2) may have a second greater value (dTHR2,i) when the tracking point (E2) of the damper piston M2 is at a second vertical position (Z2).

[0168] Fig. 8e shows, by way of example, the flow resistance R(z) of the control aperture THR2, which corresponds to Figs. 8a to 8d. The flow resistance R(z) may have a high value RMAX e.g. when the tracking point E2 of the damper piston M2 is below the reference position ZREF. The flow resistance R(z) may have a low value RMIN e.g. when the tracking point E2 of the damper piston M2 is above the reference position ZREF.

[0169] Referring to Figs. 9a to 9d, the damper piston M2 and / or the damper cylinder CYL2 may comprise an inclined surface INC2. The inclined surface INC2 is a surface, which is not parallel with the axis AX1, and which is not perpendicular to the axis AX1. The inclined surface INC2 may at least partly define the control aperture THR2. The inclined surface INC2 may provide additional freedom to tailor the flow resistance R(z) of the control aperture THR2 as a function of the position z of the damper piston M2. The inclined surface INC2 may provide additional freedom to tailor the flow restricting properties of the control apertureTHR2 e.g. when the tracking point E2 of the damper piston M2 is below the reference position ZREF.

[0170] Fig. 9a shows the damper piston M2 at the lowermost position ZMIN. Fig. 9b shows the damper piston M2 at the reference position ZREF. Fig. 9c shows the damper piston M2 at the uppermost position ZMAX. Fig. 9d shows, by way of example, the corresponding dimensions 3THR2, bTHR2 as functions 3THR2(Z), bTHR2(z) of the vertical position z of the damper piston M2. The length 3THR2 of the gap may be reduced from a maximum value 3MAX to zero when the piston M2 moves from the lowermost position ZMIN to the uppermost position ZMAX. The radial width bTHR2 of the gap may remain constant at a minimum value bMiN when the piston M2 moves from the lowermost position ZMIN to the reference position ZREF. The radial width bTHR2 of the gap may increase from the minimum value bMiN to a maximum value bMAx when the piston M2 moves from the reference position ZREF to the uppermost position ZMAX.

[0171] The radial dimension bTHR2 of the gap (THR2) between an inclined surface INC2 of the damper piston M2 and the damper cylinder CYL2 may depend on the vertical position (z) of the damper piston M2 and / or the radial dimension bTHR2 of the gap (THR2) between the damper piston M2 and an inclined surface INC2 of the damper cylinder CYL2 may depend on the vertical position (z) of the damper piston M2

[0172] Figs. 10a to 10c illustrate operation of the actuator ACLI1 and the damper DAM1 when the pistons M1, M2 are moving upwards away from the stationary sealing surface SRF1 (i.e. in the direction +SZ).

[0173] Referring to Fig. 10a, the fuel valve VAL2 may be opened by feeding pressurized hydraulic fluid LIQ1 into the actuator space SPC1 via the port PORT1. The pressurized hydraulic fluid LIQ1 may act on the actuator piston M1 to generate the hydraulic force FMI. The hydraulic force FMI of the actuator piston M1 may deflect the return spring SPR1 upwards away from the position where the fuel valve VAL2 is closed. The internal pressure pspci of the actuator space SPC1 may act on the actuator piston M1 generating the hydraulic force FMI, which deflects the return spring SPR1 upwards from the closed position where the fuel valve VAL2 is closed, i.e. where the valve element PIN2 is in contact with thestationary sealing surface SRF1. The hydraulic force FMI of the piston M1 may move the pistons M1 , M2 and the shafts SHF1 , SHF2 upwards.

[0174] The hydraulic force FMI may also lift the damper piston M2 and the shafts SHF1 , SHF2 upwards, overcoming any forces generated by the damper piston M2. The valve element PIN2 may also move upwards away from the closed position. The valve element PIN2 may be move upwards e.g. by a hydraulic force generated by the pressurized fuel FUEL1.

[0175] The internal pressure pspci of the actuator space SPC1 may also act on the damper piston M2 generating a hydraulic counterforce FM2.

[0176] Referring to Fig. 10b, the diameter DMI of the actuator piston M1 may be greater than the diameter DM2 of the damper piston M2, in order to ensure that the hydraulic force FMI of the actuator piston M1 may be greater than the hydraulic counterforce FM2 of the damper piston M2.

[0177] Pressurized hydraulic fluid acting on the actuator piston may act also on the damper piston by generating a hydraulic counterforce, which is opposite to the hydraulic force of the actuator piston. The hydraulic counterforce may act against the hydraulic force of the actuator piston. The hydraulic counterforce may reduce the total force generated by the combination of the actuator piston and the damper piston. The actuator piston may be dimensioned to overcome the damper piston when the pistons are lifted away from the bottom position. The diameter of the actuator piston may be e.g. greater than the diameter of the damper piston, in order to ensure that the hydraulic force of the actuator piston is greater than the maximum hydraulic counterforce of the damper piston. The diameter of the actuator piston may be e.g. greater than 1.2 times the diameter of the damper piston

[0178] The damper piston M2 may generate a temporary partial vacuum in the damper space when the damper piston is moved upwards from its bottom position. The vacuum may slightly increase the pressure difference across the damper piston. Thus, the vacuum may slightly increase the hydraulic counterforce of the damper piston. The damper piston M2 may generate a partial vacuum in the closeddamper space SPC2 when the damper piston M2 moves upwards. The partial vacuum may cause force component, which may be called e.g. as a suction force.

[0179] The partial vacuum generated in the damper space SPC2 may also cause e.g. cavitation and / or formation of gas bubbles.

[0180] Referring to Fig. 10c, the control aperture THR2 may become open e.g. when the lower edge E2 of the damper piston M2 rises above the reference position ZREF. The open control aperture THR2 may operate as a fluid communication pathway between the actuator space SPC1 and the damper space SPC2. The control aperture THR2 may allow pressurized hydraulic fluid LIQ1 to flow from the actuator space SPC1 to the damper space SPC2. The pressurized hydraulic fluid LIQ1 may rapidly fill any void space, which might have been formed below the damper piston M2. Rapid filling of the partial vacuum may cause pressure waves which propagate in the spaces SPC1, SPC2. Filling of the partial vacuum may equalize any pressure difference across the damper piston M2 and may eliminate the corresponding counterforce generated the damper piston.

[0181] The pressurized hydraulic fluid LIQ1 in the actuator space SPC1 may push the actuator piston M1 upwards until the piston M1 reaches a top position of the piston M1. The damper piston M2, the shafts SHF1 , SHF2, and the lower end of the return spring SPR1 may be arranged to move together with the actuator piston M1. The valve element PIN2 may be arranged to follow the movement of the shaft SHF2. The valve element PIN2 may be coupled to the pistons M1 , M2 e.g. via the shaft SHF2.

[0182] Referring to Fig. 10d, the damper piston M2 may also be an adjoining extension of the actuator piston M1.

[0183] Referring to Figs. 11a to 11 d, the fuel injector may optionally comprise e.g. a oneway valve VAL4 to introduce hydraulic fluid LIQ1 into the damper space SPC2, so as to at least partly compensate the vacuum. The one-way valve VAL4 may be called also as a check valve. The one-way valve VAL4 may allow a flow of the hydraulic fluid LIQ1 into the damper space SPC2 via the one-way valve VAL4. The one-way valve VAL4 may prevent a flow of the hydraulic fluid L IQ 1 from the damper space SPC2 via the one-way valve VAL4. The one-way valve VAL4 mayforce the displaced hydraulic fluid LIQ1 to flow via the control aperture THR2 and / or via a flow restricting element, away from the damper space SPC2.

[0184] The one-way valve VAL4 may provide a fluidic connection e.g. from the actuator space SPC1 to the damper space SPC2. Consequently, the high pressure of the hydraulic fluid LIQ1 guided to the actuator space SPC1 may also increase the flow rate of the hydraulic fluid LIQ1 via the one-way valve VAL4 to the damper space SPC2.

[0185] The one-way valve VAL4 may be arranged to guide pressurized hydraulic fluid LIQ1 from the actuator space SPC1 to the damper space SPC2. The one-way valve VAL4 may be arranged prevent a flow of the hydraulic fluid LIQ1 from the damper space SPC2 to the actuator space SPC1. Fig. 11a shows a situation where the damper piston M2 is moving upwards near the bottom position. Pressurized hydraulic fluid LIQ1 may flow into the damper space SPC2 via the one-way valve VAL4. The damper space SPC2 may be pressurized with the hydraulic fluid LIQ1 so as to prevent formation of a vacuum. Pressurized hydraulic fluid LIQ1 of the damper space SPC2 may also act on the damper piston M2 so that the damper piston M2 may also generate a hydraulic force, which lifts the damper piston M2 upwards. Fig. 11b shows a situation where the damper piston M2 is moving upwards near the top position. The hydraulic fluid LIQ1 may have practically unrestricted flow from the actuator space SPC1 into the damper space SPC2 also via the control aperture THR2. Fig. 11c shows a situation where the damper piston M2 is moving downwards near the top position. The hydraulic fluid LIQ1 may have practically unrestricted flow from the damper space SPC2 into actuator space SPC1 via the control aperture THR2. Fig. 11d shows a situation where the damper piston M2 is moving downwards near the bottom position. The one-way valve VAL4 may prevent the flow of the hydraulic fluid LIQ1 from the damper space SPC2 to the actuator space SPC1 via the one-way valve VAL4. The hydraulic fluid LIQ1 is forced to flow from the damper space SPC2 to the actuator space SPC1 via the control aperture THR2 and / or via an optional flowrestricting element (RES2).

[0186] The one-way valve VAL4 may be attached e.g. to the moving damper piston M2.Figs. 11 a to 11 d show an embodiment where the one-way valve VAL4 may move together with the moving damper piston M2. Referring to Figs. 12a to 12d, the one-way valve VAL4 may also be stationary. The one-way valve VAL4 may be attached e.g. to the (stationary) damper cylinder CYL2 and / or to the actuator cylinder CYL1. The one-way valve VAL4 may be implemented e.g. in the damper cylinder CYL2 and / or in the actuator cylinder CYL1. Attaching the one-way valve VAL4 to a stationary structure (e.g. CYL1, CYL2) may e.g. increase operating reliability of the one-way valve VAL4. Attaching the one-way valve VAL4 to a stationary structure may limit harmful effects which may be caused if the one-way valve VAL4 breaks during use.

[0187] Referring to Fig. 13a and 13b, a one-way valve VAL4 may also be arranged to feed hydraulic fluid LIQ1 from a reservoir (ACC2) to the damper space SPC2. The one-way valve VAL4 may prevent a flow of the hydraulic fluid L IQ 1 from the damper space SPC2 to the reservoir (ACC2) via the one-way valve VAL4. The one-way valve VAL4 may force the displaced hydraulic fluid LIQ1 to flow via the control aperture THR2 and / or via a flow restricting element RES2, away from the damper space SPC2.

[0188] The damper DAM1 may optionally comprise a flow restricting element RES2 to restrict the flow rate of the hydraulic fluid LIQ1 displaced from the damper space SPC2. The flow restricting element RES2 may comprise e.g. one or more constrictions and / or a porous sintered element.

[0189] The damper DAM1 may comprise a one-way valve VAL4 to prevent a flow of the hydraulic fluid LIQ1 via the one-way valve VAL4 when the damper piston M2 is moving downwards. The control aperture THR2 may restrict or prevent the flow via the control aperture THR2 when the damper piston M2 is below the reference position (e.g. when the tracking point E2 of the damper piston is below the reference position ZREF). Consequently, at least a part of the hydraulic fluid LIQ1 displaced from the damper space SPC2 may be forced to pass via the flow restricting element RES2 when the damper piston M2 is below the reference position and is moving downwards.Referring to Figs. 14a and 14b, the shape of the damper piston M2 and / or the damper cylinder CYL2 may be selected to provide the flow resistance as a desired function R(z) of the position z of the damper piston M2.

[0190] The damper piston M2 may also be arranged to generate the hydraulic force, which deflects the return spring SPR1. The damper DAM1 may be arranged to operate such that the pressurized hydraulic fluid LIQ1 may flow from the port PORT1 to the damper space SPC2 via the control aperture THR2 so that the pressurized hydraulic fluid LIQ1 of the damper space SPC2 may lift the damper piston M2 from the lowermost position ZMIN to the uppermost position ZMAX.

[0191] The diameter DMI of the actuator piston M1 may be selected to allow a lower leakage rate of the hydraulic fluid LIQ1 via a gap between the actuator piston M1 and the actuator cylinder CYL1 when the tracking point E2 of the damper piston M2 is below the reference position ZREF, wherein the pressure difference across the actuator piston M1 is set to a first value. The above-mentioned lower leakage rate includes also zero leakage rate and negligible leakage rate. The diameter DM2 of the damper piston M2 may be selected to allow a higher leakage rate (Q2) of the hydraulic fluid LIQ1 via a gap between the damper piston M1 and the damper cylinder CYL1 when the tracking point E2 of the damper piston M2 is below the reference position ZREF, wherein the pressure difference across the actuator piston M2 is set to said first value.

[0192] The diameter DMI of the actuator piston M1 may also be substantially equal to the diameter DM2 of the damper piston M2.

[0193] The difference (DMI-DM2) between the diameter DMI of the actuator piston M1 and the diameter DM2 of the damper piston M2 may be e.g. substantially equal to two times the smallest radial width (bTHR2) of the control aperture THR2.

[0194] The difference (DMI-DM2) between the diameter DMI of the actuator piston M1 and the diameter DM2 of the damper piston M2 may be e.g. smaller than 5% of the diameter DMI, smaller than 1% of the diameter DMI, smaller than 0.5% of the diameter DMI, or even smaller than 0.1% of the diameter DMI.The diameter DMI of the actuator piston M1 be substantially equal to the diameter DM2 of the damper piston M2, wherein the inner diameter of the actuator cylinder CYL1 may be equal to the inner diameter of the damper cylinder CYL2.

[0195] Referring to Figs. 14c to 14f, the fuel injector 200 may comprise a one-way valve VAL4 to guide pressurized hydraulic fluid LIQ1 into the damper space SPC2 via the one-way valve VAL4, and to prevent a flow of the hydraulic fluid LIQ1 away from the damper space SPC2 via the one-way valve VAL4.

[0196] The one-way valve VAL4 may increase the opening velocity of the valve element PIN2 when the damper piston M2 is moving upwards near the bottom position. The one-way valve VAL4 may decrease the pressure difference (pspci-pspc2) between the pressure pspci of the actuator space SPC1 and the pressure pspc2 of the damper space SPC2 when the damper piston M2 is moving upwards near the bottom position.

[0197] Fig. 14c shows a situation where the damper piston M2 is moving upwards near the bottom position. Pressurized hydraulic fluid LIQ1 may flow into the damper space SPC2 via the one-way valve VAL4 so as to reduce or eliminate the pressure difference (pspci-pspc2). Consequently, the hydraulic force generated by the lower surface of the damper piston M2 may at least partly cancel the hydraulic force generated by the upper surface of the damper piston M2. Consequently, the hydraulic force FMI generated by the actuator piston M1 can deflect the return spring SPR1 and open the fuel valve VAL2 also in the situation where the diameter DMI of the actuator piston M2 is substantially equal to the diameter DM2 of the damper piston M2.

[0198] Fig. 14d shows a situation where the damper piston M2 is moving upwards near the top position. The hydraulic fluid LIQ1 may have practically unrestricted flow from the actuator space SPC1 into the damper space SPC2 also via the control aperture THR2.

[0199] Fig. 14e shows a situation where the damper piston M2 is moving downwards near the top position. The hydraulic fluid LIQ1 may have practically unrestricted flow from the damper space SPC2 into actuator space SPC1 via the control aperture THR2.Fig. 14f shows a situation where the damper piston M2 is moving downwards near the bottom position. The one-way valve VAL4 may prevent the flow of the hydraulic fluid LIQ1 from the damper space SPC2 to the actuator space SPC1 via the one-way valve VAL4. Consequently, the hydraulic fluid LIQ1 is forced to flow from the damper space SPC2 to the actuator space SPC1 via the flowrestricting control aperture THR2 and / or via an optional flow-restricting element (RES2).

[0200] Referring to Figs. 15a to 15c, the damper cylinder CYL2 may further comprise e.g. one or more slots or recesses SLOT1 to define the control aperture THR2.

[0201] The slot or the recess SLOT1 of the damper cylinder CYL2 may define e.g. a curved control aperture THR2. The control aperture THR2 may be a gap between the damper piston M2 and the damper cylinder CYL2. The control aperture THR2 may be e.g. a curved gap. The control aperture THR2 may be e.g. a portion of an annular gap.

[0202] Fig. 15a shows a combination of the actuator piston M1 and the damper piston M2. Fig. 15b shows a combination of the actuator cylinder CYL1 and the damper cylinder CYL2, wherein the damper cylinder CYL2 comprises slots SLOT1. Fig.

[0203] 15c shows a damper space and a control aperture defined by the damper piston M2 of Fig. 15a and by the damper cylinder CYL2 of Fig. 15b.

[0204] Referring to Fig. 16, the damper DAM1 may also be located e.g. between the actuator ACU1 and the return spring SPR1.

[0205] Referring to Fig. 17a, the damper piston M2 may be attached e.g. to an intermediate element 150, which may be in contact with the lower end of the return spring SPR1.

[0206] Referring to Fig. 17b, the damper DAM1 may comprise a one-way valve VAL4 to introduce hydraulic fluid LIQ1 from a reservoir (e.g. CHM1) into the damper space SPC2 via the one-way valve VAL4. The one-way valve VAL4 may prevent a flow of the hydraulic fluid LIQ1 from the damper space SPC2 via the one-way valve VAL4. The one-way valve VAL4 may force the displaced hydraulic fluid LIQ1 toflow via the control aperture THR2 and / or via a flow restricting element RES2, away from the damper space SPC2.

[0207] Referring to Fig. 17c, the fuel injector 200 may comprise one or more reservoirs ACC1, ACC2, ACC3, CHM1 for receiving and / or for providing hydraulic fluid LIQ1. One or more reservoirs may e.g. receive leaked hydraulic fluid LIQ1 from the actuator ACLI1 and / or from the damper DAM1. One or more reservoirs may e.g. allow the reciprocating movement of the pistons M1, M2 and the shafts SHF1, SHF2.

[0208] The fuel injector 200 may comprise one or more reservoirs ACC1 , ACC2, ACC3, CHM1 for receiving, storing, and / or providing hydraulic fluid LIQ1. The return spring SPR1 may be located in a spring chamber CHM1. In an embodiment, the spring chamber CHM1 may also operate as a reservoir for the hydraulic fluid L IQ 1. The fuel injector 200 may comprise one or more pathways for allowing a flow of (low-pressure) hydraulic fluid LIQ1 to be displaced into a reservoir ACC1 , ACC2, ACC3, CHM1 and / or for allowing flow of hydraulic fluid LIQ1 to be returned back from the reservoir ACC1 , ACC2, ACC3, CHM1.

[0209] The fuel injector 200 may comprise a spring chamber CHM1 to accommodate the return spring SPR1. The damper piston M2 may be arranged to displace hydraulic fluid LIQ1 from the damper space SPC2 to the spring chamber CHM1 via the control aperture THR2 when the damper piston M2 is moving downwards (-SZ).

[0210] The apparatus 1000 may comprise a control valve VAL1 for guiding pressurized hydraulic fluid LIQ1 into the actuator ACLI1 and / or for releasing hydraulic fluid LIQ1 from the actuator ACLI1.

[0211] Referring to Figs. 18a to 18d, the actuator ACLI1 of the fuel injector 200 may comprise two ports PORT1, PORT2 at different heights. The control aperture THR2 may be arranged to operate as the second port PORT2. The fuel injector 200 may comprise an inlet opening PORT1 and a control aperture THR2, which are at different heights. Pressurized hydraulic fluid LIQ1 may be introduced into the actuator ACLI1 via the inlet opening PORT1, and separately also via the control aperture THR2.The actuator piston M1 be arranged to operate as the damper piston M2. The actuator space SPC1 may be arranged to operate as the damper space SPC2. The actuator cylinder CYL1 may be arranged to operate as the damper cylinder CYL2.

[0212] The inlet opening PORT1 may be at a first vertical position, and the control aperture THR2 may be at a second different vertical position, such that the inlet opening PORT1 remains open when the control aperture THR2 is restricted by the damper piston M1, and such that the inlet opening PORT1 remains open when the control aperture THR2 is closed by the damper piston M1. In particular, the inlet port PORT1 may be located below the control aperture THR2

[0213] Displaced hydraulic fluid L IQ 1 may flow via the control aperture THR2 and via the port PORT1 when the bottom edge (E2) of the piston M1 is above the reference position ZREF. The flow resistance R(z) of the control aperture THR2 may increase when the bottom edge of the piston M1 descends below the reference position ZREF. The piston M1 may close the control aperture THR2 when the bottom edge of the piston M1 is below the reference level ZREF. The inlet port PORT1 may remain open also when the piston M1 is at the bottom position ZMIN.

[0214] Referring to Fig. 18d, the fuel valve VAL2 of the fuel injector 200 may be opened by guiding pressurized hydraulic fluid LIQ1 into the space SPC1 e.g. via a oneway valve VAL4 and via the port PORT1. The control valve VAL1 may be set to a first (opening) position POS1 so as to guide pressurized hydraulic fluid LIQ1 to the port PORT1 and to the control aperture THR2. The control aperture THR2 may be initially closed when the valve element PIN2 is at the bottom position. The control aperture THR2 may be opened when the bottom edge (E2) of the piston M1 rises above the reference position ZREF. Thus, pressurized hydraulic fluid LIQ1 may be guided into the space SPC1 via the port PORT1 and also via the control aperture THR2 when the bottom edge (E2) of the piston M1 is above the reference position ZREF.

[0215] The fuel valve VAL2 may be closed by allowing the hydraulic fluid LIQ1 to flow away from the space SPC1 via the control aperture THR2 and via the port PORT1. The control valve VAL1 may be set to a second (closing) position POS2so as to allow the hydraulic fluid LIQ1 to flow away from the space SPC1 via the control aperture THR2 and via the port PORT1.

[0216] The one-way valve VAL4 may now prevent the flow from the port PORT 1 via the one-way valve VAL4, so as to force the flow from the port PORT1 to the control valve VAL1 to pass via a flow restricting element RES1. The piston M1 may close the control aperture THR2 when the bottom edge (E2) of the piston M1 descends below the reference position ZREF. Thus, all flow of hydraulic fluid LIQ1 displaced from the space SPC1 is forced to flow via the flow restricting element RES1. The flow restricting element RES1 may increase pressure of the space SPC1 so that the piston M1 (M2) may reduce the velocity of the moving parts by generating a braking force FM2.

[0217] Referring to Figs. 19a and 19b, the fuel injector 200 may also comprise more than one fuel valve VAL2.

[0218] The fuel injector 200 may comprise one or more fuel valves VAL2. The fuel injector 200 may comprise more than one fuel valve VAL2. The fuel injector 200 may comprise one or more valve elements PIN2. The fuel injector 200 may comprise more than one valve element PIN2. The fuel injector 200 may comprise one or more return springs SPR1. The fuel injector 200 may comprise one or more actuators ACLI1. The fuel injector 200 may comprise one or more dampers DAM1.

[0219] The fuel injector 200 may comprise several valve elements PIN2a, PIN2b, PIN2c for controlling the flow of the fuel FUEL1 into the cylinder ECYL1 of the engine ENG1 (Fig. 20). The fuel injector 200 may extend through the cylinder head EHEAD to the combustion space CSPC1 of the cylinder ECYL1 of the engine ENG1.

[0220] Each fuel valve VAL1 may allow and prevent a flow of pressurized liquid fuel L IQ 1 to at least one atomizing orifice OR1. The atomizing orifices OR1 may form droplets DR1 by atomizing the pressurized liquid fuel LIQ1. Each atomizing orifices OR1 may form a spray JET1 , which comprises atomized droplets DR1 of the liquid fuel FUEL1.The fuel injector 200 may comprise e.g. three fuel valves VAL2, wherein each fuel valve VAL2 may comprise a valve element PIN2. The fuel injector 200 may comprise e.g. three valve elements PIN2a, PIN2b, PIN2c arranged in a triangular formation. The valve elements PIN2a, PIN2b, PIN2c may be pressed by the spring force of a single common return spring SPR1. The return spring SPR1 may be deflected away from the bottom position by a common actuator ACLI1. The spring force generated by the return spring SPR1 may be distributed to the three valve elements PIN2a, PIN2b, PIN2c e.g. by a distributor plate PLA2. The velocity of the valve elements PIN2a, PIN2b, PIN2c may be controlled with a common damper DAM1. The fuel injector 200 may optionally comprise one or more auxiliary elements ROD2 to transfer the spring force from the distributor plate PLA2 to the valve elements PIN2a, PIN2b, PIN2c. The auxiliary elements ROD2 may also be called e.g. as pushrods.

[0221] Several valve elements PIN2a, PIN2b, PIN2c may be moved with a common actuator ACLI1. Closing forces may be distributed from the common actuator ACU1 to several pins PIN2a, PIN2b, PIN2c e.g. via a distributor plate PLA2 and via pushrods ROD2.

[0222] The fuel injector 200 may optionally comprise an auxiliary unit 550. The auxiliary unit 550 may be arranged to inject e.g. a second fuel FUEL2 into the combustion space CSPC1. The auxiliary unit 550 may form one or more auxiliary sprays JET2, which comprises atomized droplets of the second fuel FUEL2.

[0223] The fuel injector 200 may comprise one or more auxiliary units 550 for performing one or more additional functions, e.g. for injecting a second fuel FUEL2 into the cylinder of the engine ENG1. The fuel injector 200 may comprise one or more first orifices OR1 for injecting a first liquid fuel FUEL1 into the cylinder, and the fuel injector 200 may comprise an auxiliary unit 550, which has one or more further orifices for injecting a second different fuel FUEL2 into the cylinder. The fuel injector 200 may comprise e.g. a central injecting unit 550 for injecting a pilot fuel FUEL2. The additional units 550 may form e.g. a spray JET2 of the second fuel FUEL2.

[0224] The auxiliary unit 550 of the fuel injector 200 may be arranged to perform e.g. one or more functions selected from the following list: measurement of cylinderpressure, optical measurement of combustion, injection of a liquid reactant, injection of a liquid catalyst, spark ignition, plasma ignition, electrical heating.

[0225] As an example, the return spring SPR1 may have a mass of several hundred grams, the intermediate element 150, the piston M1 of the actuator, the piston M2 of the damper DAM1, the distributor plate PLA2, push rods ROD2 and pins PIN2a, PIN2b, PIN2c may each have a mass in the order of ten or more grams. A first end of the return spring SPR1 is stationary and a second end of the return spring SPR1 is moving. An effective moving mass of the return spring SPR1 may be e.g. 1 / 3 of the total mass of the return spring SPR1. A total effective mass of all moving parts the injector unit 200 may cause a kinetic energy of some tenths of a Joule, for example 0.15 J, when the mass moves at a velocity of 1 m / s. The kinetic energy of the moving parts may be transmitted to the sealing surfaces SRF1 , SRF2 when the fuel valve VAL2 closes.

[0226] The complex and multi-part power transmission solution of the 3-needle nozzle from the return spring SPR1 to all three valve elements PIN2a, PIN2b PIN2c may be partly responsible for a phenomenon where the long mechanism with its many interconnections may promote vibration and / or may distribute forces somewhat unevenly to the different valve elements PIN2a, PIN2b PIN2c. Vibration and / or uneven distribution of forces may be at least partly responsible for wear of the parts of the fuel injector 200.

[0227] In an embodiment, each valve element PIN2a, PIN2b, PIN2c may have a different damper DAM1 , actuator ACLI1 , and return spring SPR1.

[0228] Referring to Fig. 20, the fuel injector 200 according any of the examples mentioned above may be installed in a reciprocating internal combustion engine ENG1. An engine ENG1 may comprise the fuel injector 200. An engine ENG1 may comprise a fuel injecting apparatus 1000, wherein the fuel injecting apparatus 1000 may comprise the fuel injector 200. The engine ENG1 and the fuel injector 200 may form a combination.

[0229] The fuel injector 200 may be arranged to inject liquid atomized fuel FUEL1 into the combustion space CSPC1 of a cylinder ECYL1 of a reciprocating internalcombustion engine ENG1. The fuel FUEL1 may be injected e.g. directly into the cylinder.

[0230] The fuel FUEL1 may be e.g. diesel oil.

[0231] The fuel FUEL1 may comprise or consist of e.g. alcohol, methanol, ethanol, liquid ammonia, liquid propane, liquid butane. The fuel FUEL1 may be e.g. a low-viscosity fuel. The low-viscosity fuel may be e.g. alcohol, methanol, ethanol, liquified ammonia, liquified propane, and / or liquified butane. The low-viscosity fuel FUEL1 may comprise a mixture of two or more of fuels. The dynamic viscosity of the low-viscosity fuel FUEL1 may be e.g. less than 0.001 Pa s at the temperature of 80°C and at the pressure of 100 MPa. (0.001 Pa = 1 mPa). The use of the low-viscosity fuel may cause an increased risk of erosion of the sealing surface SRF1. The use of the low-viscosity fuel may cause an additional need to control the velocity of the valve element PIN2.

[0232] The dynamic viscosity of methanol is 0.0004 Pa s at the temperature of 80°C and at the pressure of 100 MPa. The dynamic viscosity of ethanol is 0.0007 Pa s at the temperature of 80°C and at the pressure of 100 MPa. The dynamic viscosity of ammonia is 0.0001 Pa s at the temperature of 80°C and at the pressure of 100 MPa. The dynamic viscosity of propane is 0.0002 Pa s at the temperature of 80°C and at the pressure of 100 MPa. The dynamic viscosity of butane is 0.0002 Pa s at the temperature of 80°C and at the pressure of 100 MPa.

[0233] The hydraulic fluid LIQ1 may be e.g. hydraulic oil. The hydraulic fluid may also be called e.g. as control fluid. In an embodiment, also the pressurized fuel LIQ1 may be used as the hydraulic fluid LIQ1. The hydraulic fluid LIQ1 may be substantially incompressible, so as to ensure stable and safe operation.

[0234] The engine ENG1 may comprise an engine control unit ECII1. The engine ENG1 may comprise a position sensor ESEN1 , which may provide a position signal SCRI indicative of angular position of the crankshaft CRANK1 of the engine ENG1. The engine control unit ECLI1 may control operation of the engine ENG1 based on the position signal SCRI. The engine control unit ECII1 may form a control signal SVALI for changing the state of the control valve VAL1 based on the position signal ScR1.The control signal SVALI received from the engine control unit ECLI1 may be e.g. an electrical signal, an optical signal, a hydraulic signal, or a mechanical signal. A mechanical signal may be transmitted e.g. by moving a mechanical element (e.g. a pushrod or a cable). A hydraulic signal may be transmitted e.g. by changing pressure of a hydraulic fluid contained in a conduit, or by moving an amount of the hydraulic fluid via the conduit.

[0235] The engine ENG1 may be a reciprocating internal combustion engine. The engine ENG1 may be a piston engine.

[0236] The engine ENG1 may comprise a cylinder ECYL1, a piston EPIS1, a cylinder head EHEAD1, and one or more gas valves EVAL1. The piston EPIS1 may be arranged to move in the cylinder ECYL1. Combustion of the fuel FUEL1 in the combustion space CSPC1 of the cylinder ECYL1 may increase the gas pressure in the combustion space CSPC1 so that the piston EPIS1 may be pushed downwards to rotate the crankshaft CRANK1 via a connecting rod CONROD1.

[0237] The engine ENG1 may have a common rail fuel injection system, which in turn may comprise the fuel feeding apparatus 1000. The fuel feeding apparatus 1000 may comprise one or more fuel injectors 200.

[0238] The fuel injector 200 may comprise the injector valve element PIN2. The injector valve element PIN2 may be arranged to prevent or allow fuel injection flow from the fuel feeding apparatus 1000 based on the position of the injector valve element PIN2. The position of the valve element PIN2 may be changed by the pressurized control fluid LIQ1 so that the valve element PIN2 may be moved away from its closed position by applying the pressurized control fluid LIQ1 into the actuator ACII1. The valve element PIN2 may be caused to move towards its closed position by releasing the pressurized control fluid LIQ1 from the actuator ACU1,

[0239] Hydraulic fluid LIQ1 ejected from the actuator ACII1 may be guided to an outlet OUT3 via the control valve VAL1 and via a hydraulic line LIN3. The outlet OLIT3 may feed the hydraulic fluid LIQ1 into a reservoir (not shown). The hydraulic fluid LIQ1 may be recirculated from the reservoir back to the hydraulic pump PUMP1.The control aperture THR2 may cause a pressure loss by converting energy of the pressurized hydraulic fluid LIQ1 into heat. A flow restricting element RES2 may cause a pressure loss by converting energy of the pressurized hydraulic fluid LIQ1 into heat.

[0240] The fuel injector 200 may comprise one or more orifices OR1 for atomizing the fuel FUEL1 which has been admitted through a gap GAP1 between a sealing surface SRF2 of the moving valve element PIN2 and a stationary sealing surface SRF1 of a body of the fuel injector 200.

[0241] The (main) hydraulic actuator ACLI1 of the fuel injector 200 may be fluidly separated from the sealing surfaces SRF1, SRF2 of the fuel injector 200. The fuel feeding apparatus 1000 may be arranged to operate such that the pressurized fuel FUEL1 does not contaminate the hydraulic fluid LIQ1 ejected from the actuator ACLI1 to a significant degree.

[0242] In an embodiment, the pressure of the pressurized fuel FUEL1 may cause a lifting force on the valve element PIN2. The valve element PIN2 may also be arranged to operate as an auxiliary actuator, which is moved by the pressure of the pressurized fuel FUEL1. The valve element PIN2 may optionally comprise a piston surface (M3) to increase the lifting force. The lifting force caused by the valve element PIN2 may open the fuel valve VAL2 and / or the lifting force may eliminate a clearance (i.e. a gap) between the valve element PIN2 and the actuator ACLI1. The return spring SPR1 of the fuel injector 200 may be compressed mainly by the (main) hydraulic actuator ACLI1, but also the lifting force caused by the valve element PIN2 may partly contribute to deflecting the return spring SPR1 of the fuel injector 200.

[0243] The fuel feeding apparatus 1000 may comprise the hydraulic pump PUMP1 for pressurizing the hydraulic fluid L IQ 1 , and the accumulator ACC10 for storing the pressurized hydraulic fluid LIQ1 before the hydraulic fluid LIQ1 is admitted to the hydraulic actuator ACLI1 via the control valve VAL1. The pressurized hydraulic fluid LIQ1 may be delivered to the actuator ACLI1 e.g. via a fluid line LIN10. The pressure of the hydraulic fluid LIQ1 provided via the fluid line LIN10 may be e.g. in the range of 10 MPa to 100 MPa.The fuel feeding apparatus 1000 may comprise the fuel pump PUMP2 for pressurizing the fuel FUEL1, and the accumulator ACC20 for storing the pressurized fuel FUEL1. The pressurized fuel FUEL1 may be delivered to the fuel injector 200 e.g. via a fuel line LIN20.

[0244] The admission of the pressurized fuel FUEL1 into the combustion space CSPC1 of a cylinder ECYL1 of the engine ENG1 is accomplished by means of the fuel valve VAL2 of the fuel injector 200. The fuel feeding apparatus 1000 may be e.g. a part of a common rail fuel injection system.

[0245] The accumulator ACC20 may be e.g. a part of a common rail fuel injection system of the engine ENG1. The accumulator ACC20 may operate as a part of the fuel line of the engine ENG1. The accumulator ACC20 may be located at any position between the fuel pump PUMP2 and the fuel valve VAL2. The accumulator ACC20 may be arranged e.g. within the injector 200.

[0246] The fuel feeding apparatus 1000, in particular the fuel injector 200 may optionally comprise one or more flow fuses to limit flow of fuel into the cylinder SCYL1 in case of a possible failure of the fuel valve VAL2.

[0247] The fuel feeding apparatus 1000 may further comprise sealings to limit leaking of the fluid and the fuel. For example, the fuel injector 200 may have sealings to limit a flow of the hydraulic fluid LIQ1 via a gap between the actuator ACII1 and a body part (210) of the fuel injector 200. One or more components of the fuel feeding apparatus 1000 may be sealed by using a sealing oil. The fuel feeding apparatus 1000 may further comprise recirculation conduits to collect and recirculate leaked fluid, fuel and / or sealing oil. The fuel feeding apparatus 1000 may further comprise arrangements to provide lubrication to various moving parts of the system including one or more moving parts within the injector 200.

[0248] The pressure and the quantity of the fuel FUEL1 supplied via the fuel valve VAL2 may have an effect on the amount and composition of combustion gases generated by the combustion process, which takes place in the cylinder ECYL1. Thus, the operation of the fuel valve VAL2 may have an effect on the efficiency and emissions of the engine ENG1. The efficiency and / or the emissions may beoptimized e.g. by shaping the temporal profile of the fuel feeding rate. The fuel feeding apparatus may allow increased freedom to shape the temporal profile of the fuel feeding rate.

[0249] The fuel valve VAL2 of the fuel injector 200 may comprise the valve element PIN2, the first stationary sealing surface SRF1, and the second moving sealing surface SRF2. The material of the first sealing surface SRF1 may be e.g. metal or ceramic. The material of the second sealing surface SRF2 may be e.g. a metal or a ceramic. Controlling the velocity of the valve element PIN2 with the damper DAM1 may allow reducing the velocity of the valve element PIN2 to a safe level. The fuel feeding apparatus may reduce a risk of damaging a metallic sealing surface. The damper may e.g. reduce a risk of damaging a ceramic sealing surface. The damper may e.g. enable safe use of a fuel injector, which has one or more ceramic sealing surfaces.

[0250] The control aperture THR2 may be arranged to restrict the flow rate Q2 of the hydraulic fluid LIQ1 displaced from the damper space SPC2 e.g. such that the velocity of the valve element PIN2 at the distance h=0.1 mm from the closed position (h=0) of the fuel valve VAL2 is e.g. smaller than 1 m / s, smaller than 0.5m / s, smaller than 0.2 m / s, or even smaller than 0.1 m / s. The distance h=0.1 mm refers to the distance between the sealing surfaces SRF1 , SRF2 of the fuel valve VAL2, wherein said distance h is measured in the direction of the movement of the valve element PIN2.

[0251] The control aperture THR2 may be arranged to restrict the flow rate Q of the hydraulic fluid LIQ1 displaced from the damper space SPC2 e.g. such that the velocity of the valve element PIN2 at the distance h=0.1 mm from the closed position (h=0) of the fuel valve VAL2 is e.g. smaller than 70% of the maximum closing velocity of the valve element PIN2, smaller than 50% of the maximum closing velocity of the valve element PIN2, smaller than 20% of the maximum closing velocity of the valve element PIN2, or even smaller than 10% of the maximum closing velocity of the valve element PIN2.The control aperture THR2 may be arranged to restrict the flow rate Q2 of the hydraulic fluid LIQ1 displaced from the damper space SPC2 e.g. such that the kinetic energy of the internal closing mechanism at the distance of h=0.1 mm from the closed position is e.g. smaller than 50% of the maximum kinetic energy of the internal closing mechanism, smaller than 20% of the maximum kinetic energy of the internal closing mechanism, smaller than 10% of the maximum kinetic energy of the internal closing mechanism, smaller than 5% of the maximum kinetic energy of the internal closing mechanism, smaller than 2% of the maximum kinetic energy of the internal closing mechanism, or even smaller than 1% of the maximum kinetic energy of the internal closing mechanism. The maximum kinetic energy of the internal closing mechanism of the injector unit 200 may be e.g. in the range of 0.05 J to 1 J.

[0252] The control valve VAL1 may be positioned outside the fuel injector 200.

[0253] The control valve VAL1 may be e.g. a 3-way 2-position valve as shown in the drawings. The 3-way 2-position valve may have three ports N1 , N2, N3, wherein the port N2 may have a fluid connection either with the port N1 or with the port N3, depending on the state (POS1 or POS2) of the control valve VAL1. The control valve VAL1 itself may be actuated e.g. with an electromagnetic actuator or with a piezoelectric actuator. The control valve VAL1 may comprise an electromagnetic actuator or a piezoelectric actuator.

[0254] The flow of the hydraulic fluid LIQ1 may also be controlled with two control valves. The control valve VAL1 may be e.g. a 2-way 2-position valve, which is arranged to allow and prevent the flow of the hydraulic fluid LIQ1 out of the actuator ACLI1. Another control valve may be arranged to allow and prevent the flow of the hydraulic fluid L IQ 1 into the actuator ACLI1.

[0255] The present method of controlling the velocity of the valve element PIN2 with the hydraulic damper DAM1 may be combined with other means and arrangements inside the fuel injector 200. Such internal approaches may relate e.g. to one or more of the following:

[0256] - selecting a material of the valve element PIN2,

[0257] - selecting a material of a sealing surfaces SRF1 , SRF2 of the fuel valve VAL2, - improving shock resistance of the fuel valve VAL2,- using an elastic arrangement to reduce impact forces,

[0258] The movable valve element PIN2 may comprise the sealing surface SRF2. The fuel valve VAL2 prevents the flow of the fuel FUEL1 to the one or more orifices OR1 when the movable sealing surface SRF2 of the valve element PIN2 is pressed against the stationary sealing surface SRF1. The fuel valve VAL2 allows the flow of the fuel FUEL1 to the one or more orifices OR1 when the movable sealing surface SRF2 of the valve element PIN2 has been lifted apart from the stationary sealing surface SRF1. The valve element PIN2 may have e.g. a blunt end. The valve element PIN2 does not need to have a sharp end, even if said valve element would be called as a "needle". The sealing surface SRF2 of the valve element may have e.g. the shape of a side face of a truncated cone.

[0259] The engine ENG1 may comprise one or more cylinders ECYL1. The engine ENG1 may comprise e.g. six or more cylinders ECYL1. The engine ENG1 may be a two-stroke engine or a four-stroke engine. The maximum nominal rotation speed of the engine ENG1 may be e.g. in the range of 50 RPM to 1500 RPM. RPM means rotations per minute. The nominal power of the engine ENG1 may be e.g. higher than 1 MW. The nominal power of a single cylinder of the (multicylinder) engine ENG1 may be e.g. higher than 100 kW.

[0260] The engine ENG1 may be arranged to rotate e.g. an electric generator, a propeller, or a pump. For example, a power plant may comprise the engine ENG1 and the fuel feeding apparatus 1000. The engine ENG1 may be arranged to rotate e.g. an electric power generator. For example, a ship or a boat may comprise the engine ENG1 and the fuel feeding apparatus 1000. The engine ENG1 may be arranged to rotate e.g. an electric power generator of the ship or boat. The engine ENG1 may be arranged to rotate a propeller of the ship or boat. The engine ENG1 may be arranged to operate e.g. as a part of the propulsion system of the ship or boat. For example, a pump of a mine, a pump of an industrial facility, or a pump of a municipal infrastructure (e.g. water treatment plant, water level regulating system) may be powered with the engine ENG1.

[0261] For the person skilled in the art, it will be clear that modifications and variations of the devices and methods according to the present invention are perceivable.The figures are schematic. The particular embodiments described above with reference to the accompanying drawings are illustrative only and not meant to limit the scope of the invention, which is defined by the appended claims.

Claims

CLAIMS1. A fuel injector (200) for injecting a liquid fuel (FUEL1) into a cylinder (ECYL1) of an internal combustion engine (ENG1), comprising:- a fuel valve (VAL2) comprising a valve element (PIN2) and a sealing surface (SRF1),- a return spring (SPR1 ) configured to close the fuel valve (VAL2) by pressing the valve element (PIN2) against the sealing surface (SRF1 ),- a hydraulic actuator (ACLI1) arranged to deflect the return spring (SPR1), - a damper cylinder (CYL2),- a damper piston (M2) arranged to move with respect to the damper cylinder (CYL2),wherein the damper piston (M2) is coupled to move with the valve element (PIN2),wherein the damper piston (M2) defines a damper space (SPC2) and a control aperture (THR2) with the damper cylinder (CYL2),wherein the control aperture (THR2) is arranged to control a flow rate (Q2) of a hydraulic fluid (L IQ 1 ) displaced from the damper space (SPC2),wherein a position (z) of the damper piston (M2) determines at least one variable dimension (dTHR2) of the control aperture (THR2).

2. The fuel injector (200) of claim 1, wherein the control aperture (THR2) restricts the flow rate (Q2) less when a tracking point (E2) of the damper piston (M2) is above a first reference position (ZREF), andwherein the control aperture (THR2) restricts the flow rate (Q2) more when the tracking point (E2) of the damper piston (M2) is below the first reference position (ZREF).

3. The fuel injector (200) of claim 1 or 2, wherein the control aperture (THR2) is a gap between the damper piston (M2) and the damper cylinder (CYL2).

4. The fuel injector (200) according to any of the claims 1 to 3, wherein the control aperture (THR2) is a larger gap when a tracking point (E2) of the damper piston (M2) is above a first reference position (ZREF), wherein the control aperture (THR2) is a narrower gap when the tracking point (E2) of the damper piston (M2) is below the first reference position (ZREF).

5. The fuel injector (200) according to any of the claims 1 to 4, wherein at least one of the damper piston (M1) and the damper cylinder (CYL1) comprises an inclined surface (INC2), which defines a dimension (t>THR2) of the control aperture (THR2) when a lower edge (E2) of the damper piston (M2) is below an upper edge (U2) of the damper cylinder (CYL2).

6. The fuel injector (200) according to any of the claims 1 to 5, wherein the damper piston (M2) is mechanically coupled to the valve element (PIN2) to move together with the valve element (PIN2).

7. The fuel injector (200) according to any of the claims 1 to 6, wherein the damper piston (M2) is arranged to displace hydraulic fluid (LIQ 1 ) from the damper space (SPC2) to the hydraulic actuator (ACLI1) via the control aperture (THR2) when the damper piston (M2) is moving downwards (-SZ).

8. The fuel injector (200) according to any of the claims 1 to 6, wherein the damper piston (M2) is arranged to displace hydraulic fluid (LIQ 1 ) from the damper space (SPC2) to a reservoir (CHM1) via the control aperture (THR2) when the damper piston (M2) is moving downwards (-SZ).

9. The fuel injector (200) according to any of the claims 1 to 8, wherein the hydraulic actuator (ACLI1 ) comprises an actuator piston (M1 ), wherein a diameter (DMI) of the actuator piston (M1 ) is greater than a diameter (DM2) of the damper piston (M2).

10. The fuel injector (200) according to any of the claims 1 to 9, comprising a oneway valve (VAL4) to prevent the flow of hydraulic fluid (LIQ1) away from the damper space (SPC2) when the damper piston (M2) is moving downwards (-SZ), wherein the one-way valve (VAL4) is arranged to introduce hydraulic fluid (LIQ1) into the damper space (SPC2) when the damper piston (M2) is moving upwards (+SZ).

11. The fuel injector (200) according to any of the claims 1 to 10, wherein the control aperture (THR2) is arranged to restrict the flow rate (Q) of hydraulic fluid (LIQ1 ) displaced from the damper space (SPC2) such that a closing speed (v(t))of the valve element (PIN2) at a distance of 0.1 mm from the closed position of said valve element (PIN2) is smaller than 1 m / s, advantageously smaller than 0.5 m / s.12 The fuel injector (200) of claim 1, wherein the hydraulic actuator (ACLI1) comprises an actuator cylinder (CYL1) and an actuator piston (M1) movable in the actuator cylinder (CYL1), wherein the actuator piston (M1) operates also as the damper piston (M2), wherein the damper cylinder (CYL2) comprises an inlet port (PORT1) for introducing pressurized hydraulic fluid (LIQ1) into the damper space (SPC2) when the actuator piston (M1) is moving upwards (+SZ), wherein the inlet port (PORT1) is located below the control aperture (THR2).

13. A method for injecting a liquid fuel (FUEL1) into a cylinder (ECYL1) of an internal combustion engine (ENG1) by using the fuel injector (200) according to any of the claims 1 to 12.

14. An internal combustion engine (ENG1) comprising the fuel injector (200) according to any of the claims 1 to 12.

15. A method of operating the internal combustion engine (ENG1) of claim 14, wherein a liquid fuel (FUEL1) is injected via the fuel valve (VAL2), the fuel (FUEL1) comprising or consisting of a fuel selected from a group consisting of methanol, ethanol, liquified ammonia, liquified propane, and liquified butane.

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