EP1793118A1

EP1793118A1 - Injector for large diesel engines operating with heavy fuel oil, controlled by an electronically controlled valve

Info

Publication number: EP1793118A1
Application number: EP05425866A
Authority: EP
Inventors: Marco Coppo
Original assignee: OMT Officine Meccaniche Torino SpA
Current assignee: OMT Officine Meccaniche Torino SpA
Priority date: 2005-12-02
Filing date: 2005-12-02
Publication date: 2007-06-06
Anticipated expiration: 2025-12-02
Also published as: EP1793118B1; ATE393876T1; DK1793118T3; DE602005006430D1; DE602005006430T2

Abstract

An injector for diesel engines, in particular for engines supplied with heavy fuel oil, comprising:
- a needle valve (25), which includes: a delivery chamber (9), connected to a fuel-supply line (8); an injection chamber (12) communicating with injection holes (13); and an injection needle (10), which can move between an open position and a closed position, in which, in the open position, the delivery chamber (9) and the injection chamber (12) communicate with one another and, in the closed position, the injection chamber (12) is isolated from the delivery chamber (9); and
- a control actuator (51) having a control rod (15) that co-operates with the injection needle (25) to push it towards the closed position,
The injector comprises an electronically controlled control-valve unit (21) including a two-way valve (23) and a three-way valve (24), in which the two-way valve (23) has a first chamber (35), connected to the control chamber (14) of the control actuator (51), and a second chamber (27), connected to the fuel- supply line (8).

Description

The present invention relates to a valve capable of operating with heavy fuel oil for driving injectors of common-rail systems for diesel marine engines, stationary engines, and propulsive land engines.
High-pressure injection systems of a common-rail type comprise a pump, usually with a fixed engine displacement, designed to pressurize the fuel fluid in a purposely provided high-pressure accumulator (common-rail), which supplies the injectors. The latter are equipped with at least one injection hole and with an injection needle, which can move in the injector body between a closed position and an open position. The position of said needle is determined by the intensity of two forces, which are generated by the action of fluid under pressure on appropriate surfaces of influence and act in opposite directions. The fuel pressurized in the chamber upstream of the section of sealing of the injection needle acts in the direction of raising of the needle from its seat and hence in the direction of opening. An electronically controlled control valve modulates the pressure in a control chamber, which acts on a surface in order to generate a force, which, in conditions of rest, is greater than the first force and acts in the direction of closing the needle. The activation of the valve causes a reduction of the level of pressure in the control chamber up to the point where the force generated by the fuel fluid and acting so as to bring about opening prevails over the first, causing the needle to rise and hence fuel injection.
Traditionally, in systems operating with heavy fuel oil, the control valve processes hydraulic oil, which must be pressurized by an additional control unit, so as to be able to achieve the forces required for movement of the injection needle. Said solution affords the advantage of operating with a fluid having characteristics that are ideal for said application, with the disadvantage of having to equip a circuit for pressurization, treatment, supply, and draining-off of the hydraulic oil, in addition to the equipment that is already present for the heavy fuel oil.
The working principle of traditional control valves envisages that the control chamber is connected to the high-pressure line via an appropriate calibrated orifice and that, by means of an open/close element controlled by an electromechanical actuator, a second calibrated orifice is opened, connecting the control chamber to the exhaust. In this way, the pressure in said chamber is stabilized on a value that is intermediate between that of supply and that of exhaust, enabling opening of the injection needle and hence injection. When the exhaust orifice is re-closed, the fuel at high pressure entering through the supply orifice causes the pressure to rise in the control volume until a force is generated that is sufficient to close the injector.
Said solution presents the advantage of simplicity of construction, but entails the disadvantage of having to send to the exhaust a given flow rate of hydraulic oil under pressure for the entire period in which the control valve is switched to enable injection. This involves a considerable expenditure in terms of energy in so far as the energy spent for pressurizing the hydraulic oil is dissipated in the form of heat on account of its continuous lamination in the calibrated orifices.
The object of the present invention is to provide a control valve for injectors of a common-rail type that process heavy oil which will overcome the problems of the prior art. In particular, the object of the invention is to provide a control valve that will be able to operate with the same fuel oil. A further object of the invention is to provide a valve for controlling the injector capable of limiting to a minimum the volume of fuel that flows back during operation.
According to the present invention, said objects are achieved by a control valve having the characteristics forming the subject of the annexed claims.
The present invention will now be described in detail with reference to the attached drawings, provided purely by way of non-limiting example, in which:

Figure 1 is a schematic view illustrating operation of the valve and of the injector controlled thereby, according to the invention; and
Figure 2 is a hydraulic diagram of an injector according to the present invention.

Figures 1 and 2 are schematic illustrations of a non-limiting example of a system for the injection of fuel for large diesel engines, in particular marine engines, supplied with heavy fuel oil. Typically, large diesel marine engines are supplied with fuel referred to as heavy fuel oil (HFO) having a viscosity at 50°C higher than 50 cs. Normally, before being sent to the injectors the heavy fuel oil is heated to a temperature in the region of 150°C in such a way that the viscosity of the fuel is in the region of approximately 16 cs and not higher than a maximum limit of approximately 25 cs.
The injection system illustrated in the figures comprises a feed pump 1 driven mechanically by means of a drive shaft 2. The feed pump 1 has a delivery pipe 4 that sends the fuel under pressure to a high-pressure accumulator (common rail) 3. The accumulator 3 of fuel under pressure is provided with a plurality of outlet lines 5, each of which is connected to a respective injector 6 by means of high-pressure pipes 7.
Each injector 6 has a body in which a fuel-supply line 8 is formed, which communicates with the supply pipe 7.
The injector 6 comprises a needle valve 25 built in a way in itself known. The needle valve 25 comprises a delivery chamber 9 connected to the line 8 for supply of fuel under pressure. The needle valve 25 comprises an injection needle 10, which co-operates with a sealing seat 11. The needle valve 25 moreover comprises an injection chamber 12, from which there branch off injection holes 13. The injection needle 10 has a surface 18 exposed to the pressure of the fuel contained in the delivery chamber 9, and a surface 20 exposed to the pressure of the fuel contained in the injection chamber 12. The injector needle 10 is movable in the direction of its own longitudinal axis between an open position and a closed position. In the open position the delivery chamber 9 and the injection chamber 12 communicate with one another. In the closed position the conical tip of the injection needle 10 is pushed into contact with the sealing seat 11, and the injection chamber 12 is isolated from the delivery chamber 9.
The injector 6 comprises, in a known way, a control actuator 51 having a control rod 15, which can move in the same direction as the injection needle 10. The control rod 15 has at its top end an enlarged head that is movable in a control chamber 14. The pressure of the fuel in the control chamber 14 acts on a top surface 19 of the control rod 15 and produces a force that tends to push the control rod 15 downwards. The bottom end of the control rod 15 is in contact with an adjustment spacer 16, which is in turn in contact with the top end of the injection needle 10. A compression spring 17 exerts upon the adjustment spacer 16 a force directed downwards, which tends to push the injection needle 10 towards its closed position.
According to the present invention, the injector 6 comprises an electronically controlled control-valve unit 21 that uses as control fluid the same fuel supplied to the needle valve 25.
The control-valve unit 21 comprises a two-way valve 23 and a three-way valve 24. The two valves 23, 24 have respective open/ close elements 30, 32 aligned and coaxial to one another and movable in one and the same rectilinear direction coinciding with the mutually aligned longitudinal axes of the two open/ close elements 30, 32. The two open/ close elements 30, 32 are in contact with one another along a front contact surface 31.
The two-way valve 23 has two cylindrical guiding surfaces 49, 50 that guide movement of the open/close element 32 in the longitudinal direction. The two-way valve 23 comprises a first chamber 27 and a second chamber 35, situated between which is a sealing seat 34 that co-operates with a surface having the shape of a truncated cone 52 of the open/close element 32. The first chamber 27 communicates with the supply line 8 via a pipe 26. The second chamber 35 communicates with the control chamber 14 of the control actuator 51 via a line 36. In the open position, the two chambers 27, 35 communicate with one another. When, instead, the open/close element 32 is in the closed position, the two chambers 27, 35 are isolated from one another. A compression spring 33 tends to push the open/close element 32 towards its closed position.
The three-way valve 34 comprises a first chamber 37, a second chamber 39, and a third chamber 43. A first sealing seat 38 is defined between the first chamber 37 and the second chamber 39. A second sealing seat 42 is defined between the second chamber 39 and the third chamber 43. The open/close element 30 of the three-way valve 24 has two surfaces having the shape of a truncated cone 53, 54 that co-operate alternatively with the first sealing seat 38 or with the second sealing seat 42.
The first chamber 37 of the three-way valve 24 communicates with the control chamber 14 of the control actuator 51 via the same line 36 that sets in communication the first chamber 35 of the two-way valve 23 with the same control chamber 14. The second chamber 39 of the three-way valve 24 communicates with an expansion chamber 41 via a line 40. The volume of the expansion chamber can be fixed or adjustable. The third chamber 43 of the three-way valve 24 is in communication with an exhaust line 44, which leads to a tank 22 at atmospheric pressure. The open/close element 30 of the three-way valve 24 has two cylindrical guiding surfaces 47, 48 that guide movement in a longitudinal direction of the open/close element 30.
The open/close element 30 is fixed to an anchor 29 constituting the mobile core of an electromagnetic actuator. The anchor 29 faces a permanent magnet 28 fixed to the body of the injector 6. The permanent magnet 28 tends to attract the anchor 29 and generates on the open/close element 30 a force tending to push it downwards. The permanent magnet 28 could be replaced by a compression spring set to push the open/close element 30 downwards. The anchor 29 moreover co-operates with an electromagnet 46 controlled by a control unit for controlling injection 45.
Operation of the injection system referred to above is described in what follows.
The pump 1 is driven in rotation, via the shaft 2, at a velocity correlated by a constant factor to the velocity of rotation of the engine. It continuously supplies the high-pressure fuel accumulator (common-rail) 3 via the pipe 4.
The pressurized fluid is sent to the delivery chamber 9 via the internal line 8. According to whether the injection needle 10 is forced onto the sealing seat 11 or separated therefrom, it prevents or allows the passage of fuel towards the injection chamber 12 and through the injection holes 13. For this reason the hydraulic diagram of Figure 2 illustrates this component as a two-way valve 25.
The pressure of the fuel present in the chamber 9 acts on the part 18 of the section of the injection needle 10, generating a force directed upwards and thus tending to displace the needle 10 into the open position and enable injection. A further contribution to said force of opening is provided by the pressure existing inside the injection chamber 12 and acting on the surface 20.
The pressure of the fuel present in the control chamber 14 acts upon the top surface 19 of the control rod 15, generating a thrust downwards, which is transferred to the adjustment spacer 16 and therefrom to the injection needle 10, pressing it onto the seat 11.
In resting conditions, the pressure in the control chamber 14 is equal to the pressure in the chamber 9; consequently, by appropriately sizing the section 19 with respect to the sections 18 and 20, it is possible to generate a net force in the direction of closing.
Unlike what occurs in injectors for traditional injection systems, the spring 17 has low pre-loading and contributes only marginally to the determination of the force of closing, serving principally for positioning the needle on the seat in the case where the fuel is at a low pressure.
To open the injector and to enable injection of the fuel into the cylinder of the engine, it is necessary to reduce the pressure in the control chamber 14 in order to unbalance the forces acting on the needle 10, so obtaining a resultant directed upwards. To stop injection it is necessary to bring the pressure in the control chamber 14 back to the level of the supply pressure.
The injector control valve 21 has the task of modulating the pressure in the control chamber 14. According to the present invention, said function is performed by means of the two-way valve 23 and the three-way valve 24.
The pipe 26 continuously supplies the first chamber 27 with fuel at high pressure. In resting conditions, the permanent magnet 28 attracts the anchor 29, fixed to the open/close element 30, pushing it downwards. Through the front contact 31, said action is transferred to the open/close element 32 and, since the spring 33 has a pre-loading that is considerably smaller than the force generated by the magnet 28, the open/ close elements 30 and 32 displace downwards into the position represented in Figure 1.
In said conditions, the open/close element 32 is separated from the sealing seat 34, enabling the fluid present in the first chamber 27 to reach the second chamber 35, and therefrom, through the line 36, to reach the control chamber 14 and the chamber 37. In this way, by means of the two-way valve 23, the working positions of which correspond to the ones delineated by the position of the open/close element 32, the supply pressure reaches the control volume 14, so guaranteeing closing of the needle valve 25.
In the same conditions, the open/close element 30 of the three-way valve 24 is in contact with the sealing seat 38, preventing the fuel at high pressure from passing from the chamber 37 to the chamber 39.
The latter chamber 39 is connected via the line 40 to the expansion chamber 41, the dimensions of which are correlated by a constant factor to those of the control chamber 14.
In the resting position, the open/close element 30 is not in contact with the section of sealing 42, enabling connection of the chambers 39 and 41 to the chamber 43, which is permanently connected to the line 44 for return of the fuel to the tank 22. Consequently, the fluid in the chambers 39, 41 and 43 is, in resting conditions, at a pressure close to the atmospheric pressure.
When the control unit for controlling injection 45 activates the electromagnet 46, this generates a force of attraction on the anchor 29 that is sufficient to overcome the force applied to it by the permanent magnets 28, causing lifting of the open/close element 30.
Consequently, when the downward thrust applied via the contact 31 is absent, the spring 33 pushes the open/close element 32 upwards.
The stroke allowed to the open/close element 32 is smaller than the one available for the open/close element 30. Consequently, in the first step of rising the open/ close elements 30 and 32 are in contact, so that the spring 33 contributes to raising both of the open/close elements in the step in which the force generated by the electromagnet 46 is smaller, since the latter is inversely proportional to the distance between the electromagnet 46 and the anchor 29.
In the second step of rising, the open/close element 32 is brought to bear upon the seat 34, isolating connection between the chambers 27 and 35 and thus preventing the fuel at the supply pressure from possibly reaching the control chamber 14.
The open/close element 30 proceeds its stroke until it comes to bear upon the sealing seat 42, isolating the chamber 39 and the expansion chamber 41 from connection with the line 44 for return of the fuel to the tank 22 via the chamber 43.
The different maximum stroke of the two open/close elements allows a perfect sealing to be ensured on both of the seats 34 and 42.
Switching of the connections inside the three-way valve 24, obtained by the displacement upwards of the open/close element 30, sets the chamber 37 in communication with the chamber 39, in effect enabling the fuel fluid present in the control chamber 14 to expand in the expansion chamber 41. Said expansion leads to a reduction in the pressure of the fluid present in the control chamber 14.
By appropriately sizing the volumes of the chambers 14 and 41 it is possible to stabilize the pressure of the fluid contained therein at a value equal to a fraction of the supply value, sufficient to cause rising of the needle 10 and hence fuel injection.
When the control unit 45 draws current from the electromagnet 46, the resultant of forces that kept the two valves 23 and 24 in the resting position is reestablished, thus switching them again.
This causes re-connection of the control volume 14 with the supply pipe 7 and setting of the expansion chamber 41 into the discharge condition.
Consequently, excluding the negligible leakages on the guides 47, 48, 49 and 50, the volume of fluid at high pressure that is discharged by the valve 21 to perform its function consists just in the amount of fuel that must be drawn from the expansion volume 41 to bring it back to a pressure equal to the one of the line of return to the tank.
This differs considerably from the working principle of traditional control valves, which entail having to get an amount of fuel of the same order of magnitude as the one injected to flow back into the tank for the entire duration of injection.
The benefits deriving from the working principle characteristic of the present invention can be quantified in terms of a saving of 1% of fuel to obtain the same power from the engine.
Furthermore, the capacity of the valve according to the present invention for functioning with fuel oil allows a reduction in the costs of equipping the auxiliary systems of the engine since it eliminates the need for a purposely provided system of treatment and pressurization of hydraulic oil.

Claims

An injector for diesel engines, in particular for engines supplied with heavy fuel oil, comprising:
- a needle valve (25), which includes: a delivery chamber (9), connected to a fuel-supply line (8); an injection chamber (12) communicating with injection holes (13); and an injection needle (10), which can move between an open position and a closed position, in which in the open position the delivery chamber (9) and the injection chamber (12) communicate with one another and in the closed position the injection chamber (12) is isolated from the delivery chamber (9); and

- a control actuator (51) having a control rod (15) that co-operates with the injection needle (25) to push it towards the closed position,
said injector being characterized in that it comprises an electronically controlled control-valve unit (21) including a two-way valve (23) and a three-way valve (24), in which the two-way valve (23) has a first chamber (35), connected to the control chamber (14) of the control actuator (51), and a second chamber (27), connected to the fuel-supply line (8), and in which the three-way valve (24) has a first chamber (37), connected to the control chamber (14) of the control actuator (51), a second chamber (39), connected to an expansion chamber (41), and a third chamber (43), connected to a discharge line (44).
The injector according to Claim 1, characterized in that the two-way valve (23) and the three-way valve (24) have respective open/close elements (32, 30), which can move in one and the same direction and co-operate with one another in a relationship of contact along respective contact surfaces (31).
The injector according to Claim 2, characterized in that the open/close element (32) of the two-way valve (23) has a stroke with a maximum amplitude smaller than the maximum amplitude of the stroke of the open/close element (30) of the three-way valve (24).
The injector according to Claim 1, characterized in that the expansion chamber (41) has a volume correlated to the volume of the control chamber (14) of the control actuator (51).
The injector according to Claim 3, characterized in that the three-way valve (24) is associated to an electromagnetic actuator (29, 46), controlled by an electronic control unit (45).
The injector according to Claim 1, characterized in that the expansion chamber has an adjustable volume.