Technical field [001 ] The present invention relates to fuel injection valve unit for an internal combustion piston engine and a method of operating the fuel injection valve unit.

Background art

[002] Internal combustion piston engine where fuel is injected directly to its combustion chambers and where ignition is based on so called compression ignition, the flow rate ramp during the injection effects on the pressure and temperature in the combustion engine, and therefore the a so called rate shaping during the fuel injection is of importance and interest.

[003] EP 0723076 (A2) discloses a fuel injection nozzle assembly which oper- ates in a conventional, pressure controlled manner. In other words the fuel pressure is used for opening the injection needle. There is disclosed a rate shaping control device including an injection spill circuit for spilling a portion of the fuel to be injected to produce a predetermined time varying change in the flow rate of fuel injected into a combustion chamber. The spill circuit includes a spill passage integrally formed in the nozzle valve element.

[004] A more advantageous fuel injection system is a so called common rail fuel injection system. In such a system the generation and controlling of the injection pressure is separated from controlling the timing of the injection and it is more versatile in its controlling possibilities. [005] WO 2012072881 (A1 ) discloses a fuel injection unit for a large internal combustion engine having a common rail fuel system. A way of operating the fuel injection unit has also been disclosed. The fuel injection unit is constructed of a high pressure fuel accumulator specific for the fuel injection unit, a flow fuse, a first fuel injection valve with a control valve, and a second fuel injection valve with a control valve. These are arranged in a single fuel injection unit.

[006] Another document, US 5860597 (A), discloses a nozzle assembly for servo-controlled fuel injectors which includes a needle valve control device in- eluding a rate shaping control device for producing a predetermined time varying change in the flow rate of fuel injected into the combustion chamber during an injection event. The rate shaping control device includes an injection control valve positioned along a drain circuit connected to a control volume positioned at one end of the needle valve element. The injection control valve includes a con- trol valve element positioned in the control volume adjacent the needle valve element for cooperating with the needle valve element to control the drain flow of fuel through the drain circuit during the injection event. The needle valve element may include a valve surface wherein positioning of the control valve member relative to the valve surface controls drain flow through the drain circuit. In other words movement of the needle valve element is controlled precisely by the injection control valve to achieve desired injection rate shaping. The injection control valve functions as a rate shaping control device by utilizing an actuator assembly which is designed to precisely and variably control the movement of control valve member. [007] Both of these two above mentioned documents are relating to the flow rate control of fuel injection. The methods to control the flow are however different. On the first mentioned publication the flow rate is controlled by spilling a portion of the fuel which is intended to be injected to a combustion chamber through the injector. The second publication discloses the flow rate shaping by modulating outlet flow from the control volume by using different geometries of the control valve.

[008] EP1260701 (A1 ) discloses a fuel injection device where fuel fed from a pressure storage chamber to a valve housing with a nozzle is led to a needle valve back pressure chamber through a groove provided on the peripheral sur- face of a needle valve. A fuel pressure in the back pressure chamber is controlled by opening and closing a pressure regulating port provided in the valve housing by a pilot valve so as to move the needle valve, whereby the nozzle is opened and closed. [009] Document EP 1066466 A1 discloses that fine grooves arranged to run very close to one another are configured in at least one part of the guiding surface of an injection needle. The grooves ensure hydraulic pressure compensation on the periphery of the guiding surface, thus reducing wear, and prevent leakage in a longitudinal guiding direction.

[0010] Document EP0789142 A1 discloses a storage type fuel injection device which comprises a needle valve for closing an injection nozzle, a balance chamber formed in casing so as to impart a fuel pressure to a head portion of the needle valve, a supply path including a slit for supplying fuel from a fuel supply port to the balance chamber, a discharge path which is an orifice for discharging fuel from the balance chamber, and a solenoid valve for opening and closing the discharge path. There is a lift control mechanism provided with allows the opening of the solenoid valve into two different positions thus effecting on the opening of the injection nozzle. [001 1 ] An object of the present invention is to provide an injection valve structure which provides improved fuel injection reliability and stability.

Disclosure of the Invention

[0012] The objects of the invention can be met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

[0013] Fuel injection valve unit for an internal combustion piston engine, comprising a fuel inlet connectable to a common rail system of the internal combustion piston engine for feeding pressurized fuel into the valve unit, at least one fuel injection opening arranged at an end of the fuel injection unit for controllably injecting fuel, a fuel space with which the fuel inlet is in flow communication, a control space with which the fuel inlet is flow communication, a control valve arranged in connection with the control space, which control valve is arranged to open or close a flow connection from the control space to a fuel discharge chan- nel. The fuel injection valve unit is further provided with a fuel injection valve needle comprising a first end and a second end, in which the first end of fuel injection valve needle is arranged to open or close a flow communication between the fuel space and the at least one fuel injection opening, and in which the second end of the fuel injection valve needle is arranged to extend into the control space. The fuel injection valve needle is partially circumscribed by a cylindrical support section arranged between the fuel space and the control space and through which the valve needle is arranged to extend in supported manner into the control space wherein a contact area between the cylindrical support section and the valve needle is provided with a grooving which grooving extends at least over the contact area. [0014] The grooving is arranged at least partially at an angle in respect to the center axis of the valve needle and thus the flow path via the grooving is longer than the direct length of the contact area between the cylindrical support section and the valve needle in the direction of the center axis of the valve needle.

[0015] According to an embodiment of the invention the control space is in flow communication with the fuel inlet via a fuel supply channel which the fuel supply channel is provided with a straight section having a circular cross section and which section has a length to diameter ratio greater than 10.

[0016] According to an embodiment of the invention the fuel injection unit comprises two independently operable fuel injection valve needles, each provided with a dedicated fuel space, control space, control valve, and the cylindrical support section, wherein the contract area of the each cylindrical support section is provided with individually selected grooving.

[0017] Advantageously the fuel injection unit comprises at least two independently operable fuel injection valve needles and the contract area of the each cylindrical support section is provided with differently dimensioned grooving.

[0018] According to an embodiment of the invention that the control space is in flow communication with the fuel inlet solely via the grooving.

[0019] A method of operating the fuel injection valve unit according to the invention comprises steps of supplying pressurized fuel to the fuel inlet and leading the pressurized fuel to the control space, wherein the pressure in the control space creates a force urging the injection valve needle towards the first end of the valve needle, supplying pressurized fuel to the fuel inlet of the injector and leading the pressurized fuel to the fuel space, wherein the pressure in the fuel space creates a force urging the injection valve needle towards the second end of the valve needle, opening the control valve and the flow connection from the control space to the fuel discharge channel and discharging fuel from the control space changing the pressure balance between the control space and the fuel space thus opening the valve needle, during the control valve is open leading fuel from the fuel space to the control space via the grooving in the contact area between the support section and the valve needle to partially compensate the amount of fuel discharged to the fuel discharge channel.

[0020] According to an embodiment of the invention the flow path of the fuel in the grooving is longer than a direct length of the support section axial direction of the valve needle.

[0021 ] According to an embodiment of the invention during the control valve is open fuel from the fuel space to the control space is led solely via the grooving.

[0022] According to an embodiment of the invention during the control valve is open fuel from the fuel space to the control space is led via the grooving and a fuel supply channel. In this case advantageously fuel led from the fuel space to the control space via the grooving is 5 - 35 % of the amount of fuel discharged to the fuel discharge channel.

[0023] 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 depending 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 [0024] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates a valve unit according to an embodiment of the invention,

Figure 2 illustrates a fuel injection valve needle according to an embodiment of the invention,

Figure 3 illustrates a valve unit according to another embodiment of the invention, and

Figure 4 illustrates a fuel injection valve needle according to another embodiment of the invention.

Detailed Description of Drawings

[0025] Figure 1 depicts schematically a valve unit 1 for injecting fuel into a combustion chamber of an internal combustion piston engine and being connected to a common rail system 40. The fuel injection valve unit comprises here two independently operating fuel injection valve needles 2, 22 in a common body, each provided with a necessary devices for operating the valve needle, even if not shown here. In the following mainly the first fuel injection valve needle 2 is referred to for describe the structure and the operation of the both needles 2,22. That is, because they are of similar structure regarding to operation and are comprised of corresponding elements although they may be dimensioned for use with different manner.

[0026] A fuel is supplied to the valve unit via a fuel inlet 9 which is connectable to a common rail system 40 of the combustion piston engine. The fuel injection valve unit is provided with means arranged to the flow path, and for controlling the fuel flow, between the common rail system 40 and the fuel inlet 9 of the valve needles 2, 22. Seen upstream in the fuel flow direction from the inlet 9 firstly there is a flow fuse 24 which closes the flow connection in case the pressure difference over the flow fuse 24 increases over a predetermined value. Thus the flow fuse cuts the fuel flow e.g. in case the valve needles do not close as intended between the injections. Upstream the flow fuse 24 there is a pressure accumulator 16 arranged into the valve unit 1. The accumulator 16 is arranged to supply the high pressure fuel to the fuel inlet 9 and to the fuel space 6. The accumulator 16 is a common to the both fuel injection needle 2, 22.

[0027] The valve needle 2, 22 comprises a first end 3 and a second end 4. The first end comprises the needle tip and sealing surfaces of the needle and the second end comprises a piston part used for controlling the position of the valve needle 2, 22. The valve unit 1 is provided with a space 6 for each one of the valve needles, which is called here as a fuel space 6 since the fuel inlet 9 is arranged to open into the fuel space 6 and the fuel space 6 is provided with fuel injection opening 8 i.e. one or more orifices at it first end. Even the in the figure 1 each valve needle is provided with a dedicated fuel space 6, it is conceivable that a valve unit can be provided with a common fuel space for multiple needles. The first end of fuel injection valve needle is arranged to open or close a flow communication between the fuel space 6 and the fuel injection opening 8 by its longitudinal i.e. axial movement. The valve unit 1 in provided with a spring 18 which is arranged to urge the valve needle 2 towards its closing position i.e. towards moving the first end against the opening 8. [0028] The valve unit 1 is provided with a cylindrical support section 12 which is arranged to support the valve needle 2, 22 and guide the valve needle to be movable along its central axis A. The cylindrical support section 12 has a cylindrical space inside into which the second end of fuel injection valve needle is arranged to extend. The space defined and bordered by the second end of the injection valve needle 5, the side wall of the cylindrical support section and the bottom (or top in the figure) of the cylindrical support section forms a control space 7. The control space 7 is provided with a discharge channel 10 via which the control space 7 is connectable with a low pressure part of the fuel system such as a fuel return 26 line to a fuel tank 28. The control space 7 is also provided here with a fuel supply channel 34 which connects continuously the control space 7 to the fuel inlet channel 9 at a position downstream the fuel fuse 24. The fuel supply channel serves for introduction of pressurized fuel into the control space. Advantageously the fuel supply channel is provided with a constriction part by means of which the flow rate into the control space is kept at desired level.

[0029] There is a control valve 5 arranged in connection with the control space 7, in the discharge channel 10. The function of the control valve is to open or close a flow connection from the control space 7 to a fuel discharge channel 10 thus selectively lowering the pressure in the control space 7. The control valve is controlled by a solenoid 19.

[0030] The fuel injection valve needle is at least partially circumscribed by the cylindrical support section 12. The valve needle is arranged to extend into the control space through said supporting section 12. The valve needle 2 has a cylindrical outer surface which is arranged against the inner surface of the cylindrical support section 12. A contact area 14 between the cylindrical support section 12 and the valve needle 2 is provided with a grooving 13. The grooving is arranged in the embodiment of the figure 1 into the outer surface of the valve nee- die 2. It is also conceivable that the grooving is arranged into the inner surface of the cylindrical support section 12 - or both. The grooving arranged at least partially at an angle with the center axis A of the valve needle 2. Said grooving 13 extends at least over the contact area 14. The flow path via the grooving is longer than the direct length D of the contact area between the cylindrical support sec- tion and the valve needle in the direction of the center axis of the valve needle.

[0031 ] The cylindrical support section 12 is provided with a first control edge 30 and a second control edge 32 arranged at an axial distance D from each other and the contact area 14 of the cylindrical support section 12 is formed between the control edges 30, 32. The control edge at the side of the control space 7 is formed such that the cylindrical support section 12 has a first diameter where the contact area 14 is formed and a second diameter, greater than the first diameter, in the control space 7. This way there is a distinct edge formed into the wall of the cylindrical support section 12 and the axial length of the contact area and support section 12 is independent on the position of the valve needle 2 and it has a constant length D. The control edges 30,32, are formed by a change in the diameter of the cylindrical support section 12. This way also the length of a flow path of fuel flowing from the fuel space 6 through the grooving is independent on the actual position of the valve needle 2, 22. [0032] The fuel injection unit operates so that in its non-active state i.e. when no injection take place, the control valve 5 is closed. The fuel space 6 is always filled with pressurized fuel ready to be injected via the opening 8. Also the control space is now filled with pressurized fuel and as a result of the balance of forces created by the fuel pressure in the control space 7 and in the fuel space 6, and the force of the spring 18 to the valve needle 2, the valve needle 2 stays at the its closing position pressing the tip at its first end against a sealing surface at the opening 8.

[0033] The opening movement of the valve needle 2 is activated by opening the control valve 5. This opens the flow connection from the control space 7 to the low pressure part of the fuel system i.e. the return line 26 to the tank 28. Now, the removal of the fuel from the control space 7 causes the pressure in the control space to decrease and as a result of the decreased pressure the balance of forces subjected to the valve needle 2 changes such that the valve needle starts to move away from the opening 8. While the control valve 5 is open and the pressure in the control space 7 has decreased a predetermined flow rate of fuel is entering into the control space via the grooving 13 in the contract area 14 between the support section 12 and the valve needle 2. The fuel supply channel 34 provides also a continuous flow connection between the control space 7 and the pressurized fuel in the fuel inlet channel 9. This flow of fuel into the control space 7 only partially compensates amount of fuel discharged from the control space 7 and effects on the opening rate or speed of the valve needle 2.

[0034] In the embodiment of the figures 1 and 3 where, in addition to the grooving 13 in the contact are between the cylindrical support section 12 and the valve needle 2, there is a fuel supply channel 34 providing a continuous flow connection between the control space 7 and the pressurized fuel in the fuel inlet channel 9 the grooving is dimensioned so that while the control valve is open the fuel flow through the grooving 13 is 5 - 35 % of the total flow through the discharge channel 10. [0035] When the control valve 5 is closed again the control space 7 fills with pressurized fuel and the force balance acting on the valve needle 2 changes such that the needle is moved back to close the opening 8.When the pressurized fuel is introduced into the control space 7, the pressure in the control space creates a force urging the injection valve needle 2 towards the first end of the valve needle 2, 22.

[0036] Figure 1 discloses particularly an embodiment of the invention where the fuel supply channel 34 between the inlet channel 9 and the control space 7 is short and is provided with a throttle. The grooving 13 in turn is dimensioned so that it operates in a viscosity sensitive manner such that when in use the fuel flow in the grooving, during the control valve 5 is open as described above, is fully developed and the Reynolds number is below its critical value. Advantageously the length/cross sectional area of the grooving is more than 10. In addition, ad- vantageously the Reynolds number is preferred to be relatively low so that the flow is to occur as laminar flow.

[0037] In the figure 2 there is shown one fuel injector valve needle 2 where in addition to the grooving 13 in the contact are between the cylindrical support section 12 and the valve needle 2 there is a fuel supply channel 34 which oper- ates in a viscosity sensitive manner. Thus according to the invention the opening rate of the injector needle 2 is effected by the viscosity of the fuel used. The fuel supply channel 34 in the figure 2 has a straight section 34' having a circular cross section and its length/diameter ratio greater than 10.

[0038] The shape of the groove can be of any possible groove geometries, for instance rectangular, v-, bell or round shapes. The groove pitch can be different and variable. Also using multiple grooves is conceivable.

[0039] In the figure 3 there is shown an embodiment which is otherwise similar and which operates similar to that in the figure 1 except that the grooving 13 in connection with the second injection needle 22 is arranged to the inner wall of the cylindrical support section 12.

[0040] In the figures 1 and 3 the fuel injection unit 1 comprises two independently operable fuel injection valve needles 2,22. The needles are dimensioned differently for injecting different amounts of fuel. Also the grooving 13 in the contact area 14 is dimensioned based on the individual requirement of the respective injection needle 2, 22. Advantageously the contact area 14 of each cylindrical support section 12 is provided with different grooving 13 and this way the opening rate of the first valve needle 2 is different from the opening rate of the second valve needle 22 even when using the same fuel at substantially same pressure and temperature level. Different grooving 13 affects to net flow in the control space 7. Therefore the needle opening rate is different for differently grooved needles and/ or contact area 14.

[0041 ] In the figure 4 there is shown one fuel injector valve needle 2 where the grooving 13 in the contact are between the cylindrical support section 12 and the valve needle 2 is a sole connection from the fuel inlet 9 to the control space 7. Thus, in this embodiment the grooving serves as a supply channel which con- nects continuously the control space 7 to the fuel inlet channel 9 at a position downstream the fuel fuse 24. In other words the grooving 13 alone serves for introduction of pressurized fuel into the control space. Thus according to this embodiment of the invention the opening rate of the injector needle 2 is effected by the viscosity of the fuel used when flowing through the grooving 13. [0042] Also in this embodiment the shape of the groove can be of any possible groove geometries, for instance rectangular, v-, bell or round shapes. The groove pitch can be different and variable. Also using of multiple grooves is conceivable.

[0043] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred em- bodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in connection with any embodiment above may be used in connection with another embodi- ment when such combination is technically feasible.