A fuel injector for an internal combustion piston engine

Abstract

Invention relates to a fuel injector (10) for an internal combustion piston engine, comprising - a hydraulic amplifier (20) for pressurizing fuel to injection pressure arranged to an injector body assembly (102), - an injection valve assembly (30) arranged to the injector body assembly (102), and configured to administer fuel pressurized by the hydraulic amplifier (20) into a combustion chamber (104) of the engine, wherein the hydraulic amplifier (20) comprises: - a cylinder (202), and - an operating piston (204) arranged in the cylinder, which operating piston (204) partially borders a working space (208) in the cylinder, such that volume of the working space increases when the operating piston moves in first direction, - a control fluid conduit (206), arranged to the injector body assembly (102), which conduit opens into the working space (208), and - a pneumatic spring assembly (210) comprising a gas compression space (212), which is partially bordered by operating piston (204) in the cylinder (202) such that volume of the gas compression space (212) decreases when the operating piston moves in first direction, which pneumatic spring assembly (210) is ar- ranged to apply force to the operating piston (204) in a second direction opposite to the first direction for assisting returning of the operating piston (204) towards its initial position.

Description

A fuel injector for an internal combustion piston engineTechnical field

[0001] The present invention relates to fuel injector for an internal combustion piston engine according to the preamble of claim 1 .Background art

[0002] Large two-stroke internal combustion engines are commonly used as prime movers in large ocean-going vessel. A two-stroke engine can burn different kinds of fuels and hence reduce the running cost of the ship. The thermal and engine efficiency of two-stroke engine is considerably high. Two-stroke engines are also reliable in operation. As two-stroke engines are low-speed engines, there is no requirement of reduction gear or speed reduction arrangement for propulsion as required for higher rpm four-stroke engines. Conventionally large two-stroke engines have been operated mostly with heavy fuel oil.

[0003] There is an increasing interest in lowering carbon dioxide, nitric oxide and sulphur emissions from the operation of combustions engines and hence alternatives to the conventional fuel oil, as well as improved combustion control are desired. Particularly decarbonization is of particular interest. An effective solution for reducing emissions and lowering operating costs of large internal combustion engines both in ships and at power plants are so called dual or even tri-fuel engines, which can be operated using fuel which do not contain carbon or contain less carbon as the traditionally used fossil fuel. Often, such fuels are referred to as alternative fuels. Such alternative fuels have very much different characteristics to traditional fuels, such as heavy fuel oil, light fuel oil or other natural crude oil-based fuels. For example, such fuels have relatively poor lubrication properties, which need to be considered in clearances between moving parts of used fuel injection system. Moreover, being low flashpoint fuel, such fuel causes significant safety issues. Thus, there is a need to develop a fuel injector applicable for such fuels.

[0004] Typically, a hydraulic amplifier for increasing fuel pressure in connection with fuel injector, is operated with a double-acting hydraulic piston, where piston movement is controlled by supplying pressurized control fluid alternately to opposite sides of an operating piston. This requires substantially complicated hydraulic system.

[0005] An object of the invention is to provide a fuel injector for an internal combustion piston engine which is reliable in use and simple in structure.Disclosure of the Invention

[0006] Objects of the invention can be met substantially as disclosed in the independent claim and in the other claims describing more details of different embodiments of the invention.

[0007] According to the invention a fuel injector for an internal combustion piston engine, a fuel injector for an internal combustion piston engine comprises- a hydraulic amplifier for pressurizing fuel to injection pressure arranged to an injector body assembly,- an injection valve assembly arranged to the injector body assembly, and configured to administer fuel pressurized by the hydraulic amplifier into a combustion chamber of the engine, wherein the hydraulic amplifier comprises:- a cylinder, and- an operating piston arranged in the cylinder, which operating piston partially borders a working space in the cylinder, such that volume of the working space increases when the operating piston moves in first direction,- a control fluid conduit, arranged to the injector body assembly, which conduit opens into the working space, and- a pneumatic spring assembly comprising a gas compression space , which is partially bordered by operating piston in the cylinder such that volume of the gas compression space decreases when the operating piston moves in first direction, and which pneumatic spring assembly is arranged to apply force to the operating piston in a second direction opposite to the first direction for assisting returning of the operating piston towards its initial position.

[0008] The fuel injector according to the invention injection of fuel reliable in use and simple can be controlled reliable manner and its structure is robust for long term usage.

[0009] According to an aspect of the invention the fuel injector comprises control fluid flow control apparatus, which is configured to alternatively introduce pressurized control fluid into the working space of the cylinder, at one end of the operating piston, thus urging the operating piston to move in a first direction resulting in amplification action, and releasing pressure of the control fluid in the working space of the cylinder, thus allowing return of the operating piston to its initial position. This way the fuel injector can be operated with single acting hydraulics and provides simple construction and still providing proper controllability for fuel injection.

[0010] According to an aspect of the invention there is a gas conduit arranged to the injector body assembly which opens into the gas compression space. This way it is possible to connect the gas compression space with a source of pressurized gas for pressurizing the pneumatic spring assembly and provide reliable and fast return stroke for the operating piston.

[0011] According to an aspect of the invention the gas conduit comprises a gas flow restriction system which provides gas flow resistance in both directions, such that flow resistance in direction towards the gas compression space less than in direction from the gas compression space. This way the gas compression space can be pressurized to and maintained at desired pressure during or right after the returning movement of the operating piston back to its initial position.

[0012] According to an aspect of the invention the gas conduit comprises a oneway valve allowing gas flow only in direction towards the gas compression space. By means of a one-way valve it is possible to provide substantial gas flow towards the gas compression space and still maintain adequate counter pressure in the gas compression space for assisting return of the operating piston back to its initial position.

[0013] According to an aspect of the invention the gas conduit comprises a continuously open leakage channel parallel to the one-way valve. This feature prevents pressure in the gas compression space of the pneumatic spring to raise over a predetermined upper limit, even if the one-way valve prevents backflow of the gas.

[0014] According to an aspect of the invention the continuously open leakage channel is integrated into the one-way valve providing a continuously open constriction having a predetermined loss factor. This way the space requirement of the construction of the gas flow restriction system is minimized.

[0015] According to an aspect of the invention the leakage channel comprising a constriction having a predetermined loss factor. This provides controlled outflow from the gas compression space during the operating piston moves in the first direction.

[0016] According to an aspect of the invention the operating piston comprises a rod part and wherein a separate pneumatic spring piston is arranged to the rod part at a predetermined axial distance from a piston head of the operating piston such a collecting space for leakage control fluid is arranged between the operating piston and the pneumatic spring piston. This makes is possible to recover control fluid without entering into the gas compression space, at least in excess amount more than needed for lubrication of the pneumatic spring piston.

[0017] According to an aspect of the invention the operating piston comprises a rod part which is arranged to extend through the gas compression space via a sleeve part, and the gas compression space forms an annular space around the sleeve part, which extends axially at least partly on the sleeve part. This way the dimension of the pneumatic spring assembly in axial, or longitudinal direction can be minimized.

[0018] According to an aspect of the invention the sleeve part has a conical outer surface bordering the gas compression space and the pneumatic spring piston comprises an annular recess extending in axial direction, such that the pneumatic spring piston and the conical sleeve part can overlap during a stroke of theoperating piston. This way the dimension of the pneumatic spring assembly in axial, or longitudinal direction can be even more minimized.

[0019] According to an aspect of the invention the fuel injector is provided with a sensor arranged to the injector body assembly configured to monitor axial position of the operating piston. This way position of the operating piston can be determined more accurately, and thus the amount of fuel can be controlled in more precise manner.

[0020] According to an aspect of the invention the sensor configured to monitor axial position of the operating piston is a position sensor that detects position of the operating piston.

[0021] According to an aspect of the invention the sensor configured to monitor axial position of the operating piston may be a pressure sensor which is arranged to determine pressure in one or more of the working space, the gas compression space and a pump space of the hydraulic amplifier. In such a case, pressure behaviour in the space to which the pressure sensor is arranged, is transformed into position information of the operating piston by a computer control system.

[0022] According to an aspect of the invention the sensor configured to monitor axial position of the operating piston is a position sensor, such as a proximity sensor, and the operating piston comprises a tapering, preferably conical outer surface provided at measuring vicinity of the position sensor. This way the position sensor is based on measuring radial distance between the sensor and the outer surface of the operating piston and measurement is accurate due to substantially short measuring range needed.

[0023] According to an aspect of the invention the injection valve assembly comprises an injection needle which is biased against a mechanical spring and is configured to open by pressure of fuel. This way the start of and duration of injection is directly controlled by the hydraulic amplifier.

[0024] According to an aspect of the invention the operating piston has an axially extending cylindrical recess at its axial end, and the hydraulic amplifier comprises a control fluid inlet part which protrudes into the recess and comprises an axialchannel which extends axially to the end section of the control fluid inlet part, and that the operating piston comprises an radial extension in the recess at the end of the operating piston, such that the operating piston is provided with an auxiliary working space formed by the radial extension around the control fluid inlet part, when the operating piston is at its initial position, and a flow connection is arranged to extend between the axial channel in the control fluid inlet part and the auxiliary working space formed by the radial extension in the cylindrical recess, wherein cross sectional flow area is arranged to change in response to axial position of the operating piston.

[0025] This way an operation of soft-start and soft-stop of operating piston is accomplished in advantageous manner. Since the present invention comprises the pneumatic spring assembly such soft-start and soft-stop functionality does not require any complication control fluid control systems.

[0026] According to an aspect of the invention the fuel injector is provided with a sensor arranged to the injector body assembly configured to monitor axial position of the operating piston, and wherein the injection valve assembly comprises an injection needle which is biased against a mechanical spring and is configured to open by pressure of fuel, and the fuel injector is further provided an external computer control system which comprises predefined data information of relationship between axial position of the operating piston and injection duration, is configured to receive position information from the sensor, is configured to receive required duration of injection for coming injection and obtain required axial position of the operating piston from the data information, based on the required duration of injection, is configured to control feeding of pressurized control fluid into the working space, and is configured cease pressurizing the working space when the in-formation obtained from the sensor indicates that the operating piston has reached a desired axial position.

[0027] This way the fuel injector can be operated accurately making use of the position sensor.

[0028] According to an aspect of the invention the fuel injector does not include a sensor for monitoring axial position of the operating piston, but comprises an operating piston hydraulically operated by control fluid and a control fluid flow control apparatus, which is configured to activate hydraulic fluid to move the operating piston in first direction and deactivate hydraulic fluid for a predetermined duration of activation time between activation and deactivation, and an external computer control system, which comprises predefined data information of relationship between duration of the activation time and injection duration, is configured to receive required duration of injection for coming injection and obtain required activation time from the data information, based on the required duration of injection, is configured to control feeding of pressurized control fluid into the working space, and is configured cease pressurizing the working space when duration the activation time is lapsed.

[0029] This way the fuel injector can be operated accurately without use of a position sensor.

[0030] The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb “to comprise” is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims.Brief Description of Drawings

[0031] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in whichFigure 1 illustrates a fuel injector for an internal combustion piston engine according to an embodiment of the invention,Figure 2 illustrates a hydraulic amplifier according to an embodiment according to the invention, andFigure 3 illustrates a hydraulic amplifier according to another embodiment according to the invention.Detailed Description of Drawings

[0032] Figure 1 depicts very schematically a fuel injector 10 for an internal combustion piston engine. Thie fuel injector 10 comprises two main parts: a hydraulic amplifier 20 for pressurizing fuel to injection pressure and an injection valve assembly arranged to a common injector body assembly 102. The hydraulic amplifier 20 is configured to increase fuel pressure by a hydraulically driven operating piston 204 from lower, fuel feed pressure to injection pressure, which pressurized fuel is then administered into a combustion chamber 104 of the engine, when in use.

[0033] The hydraulic amplifier 20 comprises a cylinder 202, which is arranged into the injector body assembly 20, and an operating piston 204 arranged in the cylinder 202. The cylinder may include various sections at different longitudinal position with different diameter depending e.g. on practical dimensioning requirements. The injector body is an assembly of body parts removably assembled forming the injector body assembly. The operating piston 204 partially borders a working space 208 in the cylinder, such that volume of the working space increases when the operating piston moves in first direction. Movement of the operating piston 222 is accomplished by connecting the working space 208 with a source of pressurized control fluid 244, which, when the fuel injector 10 is installed for operation, is in controllable flow connection with a control fluid conduit 206 arranged to the injector body assembly 102, which conduit opens into the working space 208 and extends from the working space 208 outer surface of the injector body assembly. When the working space 208 is not pressurized it is in flow connection with a low-pressure part 228, such as a tank, of the control fluidsystem, such that control fluid may exit the working space 208 during returning movement of the operating piston 204. The operating piston is at its initial position prior to applying pressurized control fluid on top of the operating piston 204 This way the piston may be subjected to reciprocating movement which pressurises the fuel into desired injection pressure and determines amount of fuel injected. The controllable flow connection is realized with a control fluid flow control apparatus 226, which is configured to alternatively introducing pressurized control fluid into the working space 208 of the cylinder, thus urging the operating piston 204 to move in a first direction resulting in amplification action, and releasing pressure of the control fluid in the working space 208 of the cylinder, thus returning the operating piston to the initial position of the operating piston. The control fluid flow control apparatus 226 may be for example comprised of one or more directional valves.

[0034] The hydraulic amplifier comprises a pump space 230 which the operating piston 204 partially borders in the cylinder, such that volume of the pump space 230 decreases when the operating piston moves in first direction. The pump space 230 can be conceived as a first space in the fuel injector 10 the volume of which decreases when the operating piston moves in first direction. The pump space is, when assembled for use, in connection with a source of fuel 240 via a fuel inlet conduit 232 arranged to the body assembly 102. The fuel inlet conduit extends from the pump space 230 to outer surface of the injector body assembly. There is a one-way valve 234 arranged to the fuel inlet conduit for allowing fuel to enter the pump space 230 are prevent fuel flowing back towards the source of fuel 240, when volume of the pump space is decreased. There is a fuel outlet 236 provided to the pump space 230. The fuel outlet 236 is provided with a oneway valve 238 which allows fuel flowing out from the pump space 230 and prevents backflow of the fuel into the pump chamber 230. When the operating piston 204 is moved upwards in the figure, the pump space is filled with fuel via the fuel inlet conduit 232 and the operating piston is moved downwards in the figure, which is the first direction, the operating piston decreases the volume of the of the pump space and pressurises the fuel. Fuel pressured to injection pressure by the hydraulic amplifier 20 is guided to the injection valve assembly 30 arranged to one end of the injector body assembly. The pressurized fuel is administered into a combustion chamber 104 of the engine by the fuel injectionassembly 30. The fuel injection assembly 30 shown here very schematically because it can be realized in various manners in with the fuel injector body assembly in connection with the hydraulic amplifies 20. The fuel injection assembly 30 comprises an injection needle 302, the position of which rules the operational status - being open or closed - of the fuel injector 10. The injection needle 302 is maintained closed with assistance of a mechanical spring 308 which pushes the needle 302 against a seat 304. When the needle is raised up i.e. moved away from the seat 304 the fuel injection will take place. The fuel outlet 236 of the pump space 230 in the hydraulic amplifier 20 is fluidly connected to a sac 306 of the fuel injection valve assembly 30 and when the needle is moved away from the seat 304 pressurized fuel may flow past the seat 304 and out from the injection assembly though its injection orifices. In the embodiment shown in the figure the valve needle is lifted i.e. moved away from the seat 304 when axial force caused by fuel pressure in the sac 306 raises to a level which exceed the force subjected to the needle by the spring. This way operation of the injection assembly 30 is controlled by fuel pressure. In other words, the injection valve assembly comprises an injection needle 302 which is biased against a mechanical spring and is configured to open by pressure of fuel in the sac 306. In some practical applications the injection assembly may also be controlled making use of hydraulic pressure applied to the needle causing force in the same direction as the mechanical spring i.e., the injection valve assembly comprises an injection needle which is biased by a mechanical spring and hydraulic pressure, when in use, in which case injection needle is controlled to open electronically by releasing the hydraulic pressure with a solenoid valve.

[0035] The hydraulic amplifier comprises a pneumatic spring assembly 210 which has a gas compression space 212 for assisting returning of the operating piston 204 towards its initial position after pressurizing stroke of the hydraulic amplifiers operating piston 204. The gas compression space 212 is partially bordered by operating piston 204 in the cylinder 202. The volume of the gas compression space 212 decreases when the operating piston moves in first direction, that is downwards in the figure 1 , and therefore pressure in the gas compression space 212 increases. When stroke of the operation piston is stopped by the control fluid flow control apparatus 226, which is accomplished by ceasing pressurizing the working space 208 and connecting the working space 208 with the low-pressure part 228, the pressure in the gas compression space 212 will subject a returning force to the operating piston 222. The returning force is applied to the operating piston 222 in a second direction opposite to the first direction and it assists returning of the operating piston 204 to its initial position. There is a gas conduit 214 arranged to the injector body assembly which opens into the gas compression space 212 and extends from the gas compression space 212 a coupling arranged at an outer surface of the injector body assembly. The gas conduit is connected a source of compressed gas 242 when the fuel injector 10 is assembled for use in an engine. Most preferable gas for use in the pneumatic spring assembly is the air because of its non-toxic nature and good availability.

[0036] The gas conduit comprises a gas flow restriction system 213 which provides gas flow resistance in both directions, such that flow resistance in direction towards the gas compression space 212 considerably less than in direction from the gas compression space 212, at least twofold, preferably at least tenfold. This way the gas compression space is more easily and faster filled than the gas is purged from the gas compression space during compression, when the operating piston moves in the first direction. This may be realized such that the gas conduit 214 comprises a one-way valve 216. The one-way valve allows gas flow only in direction towards the gas compression space 212 and prevents back flow of the gas. However, there is a continuously open leakage channel arranged to the pneumatic spring assembly 210 which connects the gas compression space 212 continuously with the coupling - and with the source of compressed gas 242 when in use. The continuously open leakage channel 218 is parallel to the oneway valve 216, and therefore gas may escape from the gas compression space 212 when pressure in the compression gas space 212 is higher than gas pressure in the source of compressed gas 242, and flow back towards the source of compressed gas 242 - that is even if the one-way valve is closed. The leakage channel 218 is provided with a constriction 220, such as a small orifice, having a predetermined loss factor such it constricts the back flow of the gas and maintains desired pressure in the gas compression space. Thus, the gas compression space has a continuously open gas flow path with the coupling at an end of the leakage channel 218, and to the source of compressed gas, when being in connection with it.

[0037] The compression space 230 is a second space in the fuel injector 10 volume which decreases when the operating piston moves in first direction. Since both the compression space 230 and the pump space are spaces in the fuel injector volumes of which decreases when the operating piston moves in first direction, it is conceivable that their actual position in the hydraulic amplifier may vary, in different practical applications.

[0038] In the embodiment shown in the figure 1 the amount of fuel injected is directly proportional to movement of the working piston 204, and therefore the time which the working space 208 is pressurized determines the amount of injected fuel. For controlling injection duration, it may be accurate enough to provide correspondence between pressurizing time of the working space 208 and amount of injected fuel in less demanding practical applications. However, as a further improvement of the fuel injection 10, it is provided with a sensor 224 which is configured to monitor axial position of the operating piston 204. Axial position mean position in direction of movement of the operating piston 204. The sensor 224 is arranged to the injector body assembly such that it may be connected with desired wiring, and it is at measuring vicinity to the operating piston 204 as is depicted in the figure 1.

[0039] Preferably for controlling operation of the fuel injector may comprise an external computer control system 50, which is arranged in data transfer communication with the sensor 224 and the control fluid flow control apparatus 226. The computer control system 50 comprises predefined data information 52 of relationship between axial position of the operating piston and injection duration.

[0040] The computer control system 50, when applied in connection with the fuel injector according to figure 1 or 2, is configured to receive information from the sensor 224, and configured to receive or acquire required duration of injection for coming injection and obtain required axial position of the operating piston from the data information 52, based on the required duration of injection, and configured to control feeding of pressurized control fluid into the working space, and configured cease pressurizing the working space when the position information obtained from the sensor indicates the operating piston has reached a desired axial position.

[0041] The configuration of the computer control system comprises computer programs which, when executed in the computer control system in connection with an internal combustion engine, cause the injectors to operate as explained in the following.

[0042] Before injection the fuel injector is at position shown in the figure 1. The working space 208 is depressurized, and the pumping chamber 230 is substantially at a pressure of fuel in the source of fuel, which is lower than fuel injection pressure. The gas compression space 212 is filled with gas, preferably compressed air, from the source of compressed gas 242. The initial pressure is preferably about 600 - 700 kPa(g) pressure. When an instruction is received to inject fuel into the combustion, position of the directional valve 226 is changed to the one which Is not selected in the figure 1 , which connects the source of pressurized control fluid, such a hydraulic oil, to flow into the working space 208. The pressure in the working space will increase and the working piston 204 starts to move in the first direction towards the other end of the cylinder 202. When the piston moves pressure of the fuel will raise in the pump space 230 and in the sac 306 of the fuel injection valve assembly 30. When the operating piston move further, at some point of movement pressure in the sac 306 reaches a pressure which provides an axial force to the injection needle 302 which surpasses the force applied by the mechanical spring 308, and the needle 302 lifts from the seat 304 after which fuel flows out of the injection valve assembly 30. Position of the working piston 204 is preferably monitored by the sensor 224 while the operating piston moves in the first direction, and injection of fuel continues. For each injection there is a desired amount of fuel determined by a control system of the engine, to which the injector is installed, and amount of fuel injected is directly proportional to movement of the working piston 204. When data obtained from the sensor 224 indicates that the piston is at such position at which the desired amount of fuel has been injected, the position of the directional valve 226 is moved back to the one shown in the figure 1 . Thus, the working piston 204 keeps moving in the first direction until the working space 208 is again depressurized. That is accomplished by changing the position of the directional valve 226 back to the one shown in the figure 1.

[0043] Movement of the working piston in the first direction causes also pressure to rise in the gas compression space 212. Even if the one-way valve 216 is closed there is a small, continuous flow of gas out from the gas compression space 212, which prevents excessive pressure raise in the space 212. When the desired amount of fuel has been injected the working space 208 is depressurized. At this point pressurized gas in the gas compression space 212 moves the operating piston back to its initial position, for the next injection to commence. After that pressure in the gas compression space equalises with the pressure in the source of compressed gas 242 via the continuously open leakage channel 218.

[0044] The sensor which is referred to with the reference 224 in the figure 1 is a position sensor arranged at the end of the cylinder 202, which sensor may be for example a proximity sensor and it provides position information directly. In the figure 1 there is also shown an alternative, optional way of implementing the sensor configured to monitor axial position of the operating piston, which is a pressure sensor 224’, such as a piezo pressure sensor. Figure 1 discloses that such a pressure sensor 224’ can be arranged in connection with one or more of the spaces 208, 212, 230 in the injector 10 determine pressure behaviour therein. In the figure 1 there is a pressure sensor in connection with the working space208, the gas compression space 212 and the pump space 230 of the hydraulic amplifier 20, for illustration of different options. However, in practical application it is adequate to have a pressure sensor arranged in connection with only one of the spaces. Pressure behaviour i.e. pressure data, in the space to which the pressure sensor is arranged, is transformed into position information of the operating piston 222 by a computer control system50, by means of suitable computer assisted manipulation of the data.

[0045] Figure 2 discloses a hydraulic amplifier 20 according to an embodiment. Figure 2 discloses a hydraulically driven operating piston 204 according to a further development of the invention. The operating piston 204 comprises a rod part 222, to which a piston head 221 bordering the working space 208 assembled at the end of the rod part 22. Additionally, there is a separate pneumatic spring piston 223 arranged to the rod part 222 at a predetermined axial distance from the piston head 221 such that a collecting space 246 for leakage control fluid is arranged axially between the operating piston and the pneumatic spring piston.The collecting space is also bordered by inner wall of the cylinder 202. The pneumatic spring piston 223 is provided with a sealing ring 252 near its axial end opposite to the piston head 221. There is a drain conduit 250 arranged through the body assembly 102 to open into the lower part of the collecting space 246 at the initial position (in the figure 2 the topmost position) of the operating piston, for guiding any control fluid away from the collecting space 246. Separate means in this connection that the pneumatic spring 252 piston is removably attached to the rod part 222 independently from the piston head 221 . As it is shown in the figure 2 the cylinder 202 includes sections with different diameters.

[0046] The sensor 224 configured to monitor axial position of the operating piston 222 is a position sensor that detects position of the operating piston 222. The position sensor is arranged in connection with a side wall of the cylinder 202 in the injector body 102. More precisely, in the embodiment shown in the figure 2 the position sensor is configured to measure radial distance from outer surface of the pneumatic spring piston 223. The operating piston, and particularly in the embodiment shown in the figure 2, the pneumatic spring piston 223 in the rod part 222 is provided with a measurement section 248 on its outer surface at measuring vicinity of the position sensor 224. The measurement section comprises axially variable distance from the inner surface of the cylinder such that distance from the surface to the position sensor is different when the operating piston is at different axial positions. This way measurement of radial distance provides axial position of the operating piston 204. More precisely the operating piston comprises tapering, preferably conical measurement section, as is depicted by the angle 242 shown in the figure 2. Tapering form may be linear or non-linear, but with linear form calibration of the position information is easier. The pneumatic spring piston diameter is smaller at its end closer to the piston head 221 than at the other end, and thus when the operating piston 204 moves away from its initial position the position sensor 224 indicates gradually increasing distance. This provides very accurate axial position information of the operating piston 204.

[0047] As is depicted in the Figure 2 the rod part 222 of the operating piston 204 is arranged to extend through the gas compression space via a sleeve part 254, and the gas compression space forms an annular space around the sleeve part254, which compression space extends axially at least partly over the sleeve part. The compression piston 221 has a skirt section at its end opposite to the piston head 221 such that when the operating piston is moved in the first direction the sleeve part 254 and the compression piston overlap each other partially, which makes it possible to provide longer stroke or shorter hydraulic amplifier 20. The sleeve part 254 has conical outer surface bordering the gas compression space. The sleeve part has cylindrical inner surface 256 and the rod part has circular cross section, and the cylindrical inner surface 256 is provided with a sealing system 258, comprising for example one or more mechanical seals.

[0048] It is also disclosed in the figure 2 that the gas conduit 214 comprises a one-way 216 valve which allows gas flow only in direction towards the gas compression space 212, and the continuously open leakage channel 218 parallel to the one-way valve 216 channel is integrated into the one-way valve providing a continuously open constriction 220 having a predetermined loss factor. This is shown more precisely in the enlarged section of the drawing. This way the gas compression space 212 has a continuously open gas flow path through a valve element of the one-way valve, and less borings are needed to be made to the body assembly 102.

[0049] Figure 3 discloses an upper part, that is the part opposite to the injection valve assembly, of the hydraulic amplifier 20 according to an embodiment of the invention. The hydraulic amplifier 20 discloses an optional improvement to the invention, which can be utilized in connection with the embodiment shown in both figures 1 and 2, even if it is shown here in connection with the embodiment shown in the figure 2. As it has become clear in the description above, movement of the operating piston 222 is accomplished by connecting the working space 208 with a source of pressurized control fluid 244, which, when the fuel injector 10 is installed for operation, is in controllable flow connection with a control fluid conduit 206 arranged to the injector body assembly 102, which conduit opens into the working space 208. The hydraulic amplifier 20 comprises a modified piston head 221 , which has an axially extending cylindrical recess 260 at its axial end and a control fluid inlet part 262 which protrudes into the recess 260 and the control fluid conduit 206 is arranged to the control fluid inlet part 262. The control fluid inlet part is also generally cylindrical. An end section of the control fluid inlet part262 is shown in more detailed manner in the enlargement view above the hydraulic amplifier 20. Here the operating piston 222 is at its initial position. As it can be seen in the enlargement, the control fluid conduit 206 in the control fluid inlet part 262 comprises an axial channel 206’ which extends axially to the end section of the control fluid inlet part 262. At the end part of the control fluid inlet part the control fluid conduit has one or more radial channels 206.2 which extend radially through the end section of the control fluid inlet part 262. The radial channels 206.2 continue with an axially extending groove or a like 206.3 arranged to outer surface of the control fluid inlet part 262. The piston head 221 is provided with radial extension 260.1 in the cylindrical recess 260 which has increased diameter compared to the diameter of the cylindrical recess 260. The extension forms an outward step in the cross section of the recess 260. The extension is arranged at axial end of the piston head 221 , and it has axial distance L1 from the end face of the cylinder 202 in the injector body assembly 102. When the operating piston 222 is at its initial position, the extension 260.1 forms an annular space around the control fluid inlet part 262 which is in flow communication with the axially extending grooves 206.3 and the radial channels 206.2, as is depicted by the arrow A. The grooves extend axially to a position passing by a control edge 264 formed by the extension 260.1 .

[0050] When the operating piston is at its initial position, the grooves 206.3 comprise a first section 206.3’ which has a gradually decreasing flow area and a second section 206.3” which has constant flow area. The first section continues from the radial channels 206.2 and the second section is an end part of the axially extending grooves 206.3 in the direction depicted by the arrow A. This way cross sectional flow area is arranged to change in response to axial position of the operating piston. When the operating piston 222 moves in the first direction, downwards in the figure 3, axial distance L1 increases, and cross-sectional flow area increases, and flow restriction decreases due to the movement and shape of the grooves 206.3. Flow of control fluid into the 260.1 radial extension 260.1 has increasing velocity while the operating piston moves in the first direction. This provides a soft-start operation, i.e. gradual acceleration of the operating piston 222. When the operating piston moves in the second direction (upwards in the figure) this provides a soft-stop operation, i.e. graduate deceleration of the operating piston 222, because exit of control fluid from the radial extension 260.1become more and more restricted when the operating piston moves towards its initial position. The soft-start operation and soft-stop operation is particularly advantageously usable in connection with the present invention, the fuel injector comprising the pneumatic spring assembly, because there is no need for continuous control of control fluid flow.

[0051] The radial channel 206.2 and the axially extending groove or a like 206.3 constitutes a flow connection between the axial channel 206’ of the control fluid conduit 206 and the radial extension 260.1 in the cylindrical recess 260, when the operating piston is at its initial position. This way the operating piston is provided with an auxiliary working space 208’ formed by the radial extension 260.1 around the control fluid inlet part 262.

[0052] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is obvious to the skilled person that, along with the technical progress, the basic idea of the invention can be implemented in many ways. The invention and its embodiments are thus not limited to the examples and samples described above but they may vary within the contents of patent claims and their legal equivalents. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.

Claims

Claims1. A fuel injector (10) for an internal combustion piston engine, comprising- a hydraulic amplifier (20) for pressurizing fuel to injection pressure arranged to an injector body assembly (102),- an injection valve assembly (30) arranged to the injector body assembly (102), and configured to administer fuel pressurized by the hydraulic amplifier (20) into a combustion chamber (104) of the engine, wherein the hydraulic amplifier (20) comprises:- a cylinder (202), and- an operating piston (204) arranged in the cylinder, which operating piston (204) partially borders a working space (208) in the cylinder, such that volume of the working space increases when the operating piston moves in first direction,- a control fluid conduit (206), arranged to the injector body assembly (102), which conduit opens into the working space (208), characterized by a pneumatic spring assembly (210) comprising a gas compression space (212), which is partially bordered by operating piston (204) in the cylinder (202) such that volume of the gas compression space (212) decreases when the operating piston moves in first direction, which pneumatic spring assembly (210) is arranged to apply force to the operating piston (204) in a second direction opposite to the first direction for assisting returning of the operating piston (204) towards its initial position.

2. A fuel injector (10) according to claim 1 , characterized in that the fuel injector comprises control fluid flow control apparatus (226), which is configured to alternatively introduce pressurized control fluid into the working space (208) of the cylinder at one end of the operating piston (204), and releasing pressure of the control fluid in the working space (208).

3. A fuel injector according to claim 1 , characterized in that there is a gas conduit (214) arranged to the injector body assembly which opens into the gas compression space (212).

4. A fuel injector according to claim 3, characterized in that the gas conduit comprises a gas flow restriction system (213) which provides gas flow resistancein both directions, such that flow resistance in direction towards the gas compression space (212) less than in direction from the gas compression space (212).

5. A fuel injector according to claim 4, characterized in that the gas conduit comprises a one-way (216) valve allowing gas flow only in direction towards the gas compression space (212).

6. A fuel injector according to claim 5, characterized in that the gas conduit comprises a continuously open leakage channel (208) parallel to the one-way valve (216).

7. A fuel injector according to claim 6, characterized in that the continuously open leakage channel (218) is integrated into the one-way valve providing a continuously open constriction (220) having a predetermined loss factor.

8. A fuel injector according to claim 1 , characterized in that the operating piston comprises a rod part (222) and wherein a separate pneumatic spring piston (223) is arranged to the rod part at a predetermined axial distance from a piston head (221) of the operating piston (204) such a collecting space (246) for leakage control fluid is arranged between the operating piston and the pneumatic spring piston.

9. A fuel injector according to claim 1 , characterized in that the operating piston comprises a rod part (222) which is arranged to extend through the gas compression space via a sleeve part, and the gas compression space forms an annular space around the sleeve part, which extends axially at least partly on the sleeve part.

10. A fuel injector according to claim 9, characterized in that the sleeve part has a conical outer surface bordering the gas compression space, and pneumatic spring piston (223) comprises an annular recess extending in axial direction.

11. A fuel injector according to claim 1 , characterized in that the fuel injector is provided with a sensor (224, 224’) arranged to the injector body assembly configured to monitor axial position of the operating piston (204).

12. A fuel injector according to claim 11 , characterized in that the sensor (224) is a position sensor (224) and the operating piston (204) comprises a tapering, preferably conical outer surface provided at measuring vicinity of the position sensor (224).

13. A fuel injector according to anyone of the preceding claims, characterized in that operating piston (222) has an axially extending cylindrical recess (260) at its axial end, and the hydraulic amplifier (20) comprises a control fluid inlet part (262) which protrudes into the recess (260) and comprises an axial channel (206’) which extends axially to the end section of the control fluid inlet part (262), and that the operating piston comprises an radial extension (260.1) in the recess (260) at the end of the operating piston (222), such that the operating piston is provided with an auxiliary working space (208’) formed by the radial extension (260.1) around the control fluid inlet part (262), when the operating piston is at its initial position, and a flow connection is arranged to extend between the axial channel (206’) in the control fluid inlet part (262) and the auxiliary working space formed by the radial extension (260.1) in the cylindrical recess (260), wherein cross sectional flow area is arranged to change in response to axial position of the operating piston.

14. A fuel injector according to claim 11 , characterized in that the injection valve assembly (30) comprises an injection needle which is biased against a mechanical spring and is configured to open by pressure of fuel, and that the fuel injector (10) comprises an external computer control system (50), which comprises predefined data information of relationship between axial position of the operating piston and injection duration, is configured to receive position information from sensor, is configured to receive required duration of injection for coming injection and obtain required axial position of the operating piston from the data information, based on the required duration of injection, is configured to control feeding of pressurized control fluid into the working space, andis configured cease pressurizing the working space when the information obtained from the sensor indicates that the operating piston has reached a desired axial position.

15. A fuel injector according to claim 2, characterized in that the control fluid flow control apparatus (226) is configured to activate hydraulic fluid to move the operating piston (222) in first direction and deactivate hydraulic fluid for a predetermined duration of activation time between activation and deactivation, and an external computer control system (50), which comprises predefined data information of relationship between duration of the activation time and injection duration, is configured to receive required duration of injection for coming injection and obtain required activation time from the data information, based on the required duration of injection, is configured to control feeding of pressurized control fluid into the work- ing space, and is configured cease pressurizing the working space when duration the activation time is lapsed.

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