FR2756595A1 - OPENING SLOWDOWN AND LEAKAGE REDUCTION DEVICE FOR CONSTANT PRESSURE INJECTION SYSTEMS USED ON DIESEL ENGINES - Google Patents

Abstract

The device is characterised in that it comprises a control valve (25), returned by a valve spring (28), used as actuator operating on the injecting needle (6) when the injecting nozzle (1) is closed, and closing the internal volume of the injecting nozzle holder (3) which communicates with the bottom of the injecting nozzle (1). This valve ensures, with the decompression orifice (27), the retarding of the opening of the injecting nozzle (1) at the beginning of the injection controlled by the operation of the electrovalve (4). The device is particularly designed for completing and improving the quasi-constant pressure injection devices for diesel engines.

Description

 The present invention relates to a device for slowing down opening and reducing leakage, which can be integrated into the injector holders, for constant pressure injection systems more particularly used on diesel engines.

 By opening slowdown is meant here the slowing down of the speed of opening of the injector needle, the only way to limit the instantaneous flow of fuel at the start of injection.

 By reduction of leaks is meant here the strictest possible limitation of the flow coming from the high pressure and returned directly to the low pressure by the valves or the guides of the components of the system. Which flow, in addition to the flow injected, implies an additional discharge often very important.

 Traditional constant pressure injection systems, also known by their Anglo-Saxon Common-Rail name, are mainly based on an injector holder assembly permanently supplied with fuel by an almost constant pressure supply channel, an injector kept closed by a spring and the push of a piston, and of a solenoid valve whose function is to suppress this push during the time when the injection is desired.

 The performance of traditional constant pressure injection systems, as briefly described above, is essentially conditioned by the fuel supply pressure and the dimensional characteristics of the injector. The speed of opening and closing of the injector allows very little modulation on the fuel introduction law.

These devices, whose performance is recognized, generally have some functional drawbacks:
- The often too rapid opening which penalizes them in the environmental field: emissions of pollutants (nitrogen oxides, hydrocarbons, particles ...) and noise emitted by the engine.

 - The energy cost of pressurizing the fuel which is unnecessarily returned to low pressure by leaking guides.

The need to optimize combustion systems to obtain both pollution control, noise reduction and good performance from the diesel engine requires a particular effort on the injection process which is characterized by:
- The introduction of low-flow fuel at the start of the injection process in order to avoid excessive accumulation of fuel in the engine combustion chamber during the time necessary for the self-ignition of this fuel. The expected result is mainly the reduction of combustion noise and vibration stresses on engine components.

 - The clearest possible closure of the injector at the end of injection to prevent a significant amount of fuel from being introduced late under poor conditions compared to the need for rapid mixing with air, more and more free of oxygen, contained in the combustion chamber.

The expected result is mainly the reduction of soot emissions and greater flexibility on the compromise to be established between fuel consumption and pollutant emissions, including nitrogen oxides.

 This last characteristic is precisely that which motivates the use of constant pressure injection systems which ensure a clean closure at full injection pressure.

The practical arrangements adopted, leading to the device according to the invention, are mainly chosen for:
- Dampen the opening of the injector, by performing a step, in order to limit the fuel flow at the start of the injection phase.

 - Control as well as possible the quantity of short circuit fuel existing during the operation of the solenoid valve by closing the supply by a valve.

 - Limit as much as possible the amount of fuel returned to the low pressure unnecessarily, in particular the leaks at the level of the guides during the long period between injections. To this end, communication with the return is limited exclusively to that of the main orifice of the solenoid valve, closed between injections.

 The device according to the invention, installed in the injector holders of constant pressure injection systems for diesel engines, ensures the opening slowdown and the reduction of leaks according to the objectives set out above.

 It includes, for this purpose, a control valve, the guide diameter of which is greater than or equal to that of the guide of the injector needle and the diameter of support on its seat close to the latter, and which, brought back in its rest position by a valve spring, interrupts the communication, ensured by a supply port, between the supply channel, and the solenoid valve, on the one hand, and, on the other hand, closes the volume of injector holder communicating with the bottom of the injector and not communicating with the discharge volume and the return circuit, to ensure pressurization.

 A characteristic associated with the previous one consists in the fact that a decompression orifice places the closed volume of the injector holder in communication with the thrust volume of the control valve so that, when the solenoid valve is open, the decompression of the volume of injector holder is progressive in order to gradually release the closing hydraulic thrust applied to the needle and that when the solenoid valve is closed, the pressures in the thrust volume and the injector holder volume can balance. This decompression orifice can be, for example, made directly in the body of the control valve.

 Another characteristic consists in the fact that a main spring ensures, by pressing on a needle plunger, a closing force on the injector needle complementary to the hydraulic thrust, of the pressure in the volume of the injector holder. This type of spring is very commonly used in almost all injection devices.

 Another characteristic consists in the fact that a push rod, the length of which leaves a clearance greater than the maximum stroke of the injector needle, allows the control valve to act as a jack and ensures rapid closing of the injector when the solenoid valve is closed. This push rod can be independent, or be part of either the control valve or the needle plunger.

 Another characteristic consists in the fact that the valve spring can be interposed between the push rod and the control valve so that, when the latter two are not in contact, a minimum push on the push rod is ensured.

 Another characteristic consists in the fact that an intermediate stop can neutralize the thrust of the valve spring on the push rod as long as the lift of the injector needle does not reach a threshold defined by this stop.

 Another characteristic, alternative to the previous one, consists in the fact that an intermediate stop can neutralize the thrust of the main spring on the needle plunger as long as the lift of the injector needle does not reach a threshold defined by this stop.

 A final characteristic consists in the fact that a hydraulic return sheath replaces or comes to supplement the thrust of the main spring on the needle plunger, more particularly in combination with the intermediate stop.

 The step, imposed by the intermediate stop on the needle in its opening path, corresponds to the time required to decompress the injector volume so that the change in hydraulic thrust on the needle corresponds to the change in thrust required when crossing this intermediate stop.

The duration of this stage is therefore sensitive to various characteristics:
- The ratio between the volume to be decompressed and the section of the decompression orifice compared to the speed of sound in the fuel.

 - The ratio between the force required to cross the intermediate stop and that applied by the injection pressure on the injector needle.

 The adjustment of the operation of the device will mainly be carried out by the authorized stroke before the action of the intermediate stop as well as the adjustment of the load in place of the spring subjected to this stop.

 Each of the engine injector holders will receive the same device.

The invention will be better understood with the aid of the following description, with reference to the appended schematic drawing representing, by way of examples, embodiments of this device for slowing down opening and reducing leakage:
- Figure 1 shows an example, seen in section, of an injector holder assembly according to one of the traditional solutions of injection device supplied by a constant high pressure for which the needle is maneuvered by a piston subjected to a pressure controlled by the combination of a supply port and a two-way solenoid valve, normally closed.

 - Figure 2 shows the diagram of the device corresponding to Figure 1.

 - Figure 3 shows the diagram of a variant of the device corresponding to Figure 1, for which the supply port is removed and the two-way solenoid valve is replaced by a three-way solenoid valve whose common conduit is in connection with the thrust volume of the control piston.

 - Figure 4 shows a diagram of an injector holder assembly according to the patent for which the push rod is integral with the control valve. Piloting is ensured, as for the device of FIG. 1 by the association of a supply orifice and of a so-called two-way solenoid valve, normally closed, but a three-way solenoid valve could have been used.

 - Figure 5 shows a diagram of an injector holder assembly according to the patent, variant of Figure 4, for which the push rod is supported and comes into abutment with an intermediate stop before receiving the thrust from the valve spring.

 - Figure 6 shows a diagram of an injector holder assembly according to the patent, variant of Figure 4, for which the push rod is separated from the control valve by the valve spring and the action of the main spring is subjected to crossing of the intermediate stop.

 - Figure 7 shows a diagram of an injector holder assembly according to the patent, variant of Figure 6, for which the main spring is replaced by a hydraulic return sleeve.

 FIG. 8 represents a schematic view, in section, of an injector holder assembly according to the patent, the diagram of which is described in FIG. 4.

 FIG. 9 represents a diagrammatic view, in section, of an injector holder assembly according to the patent, the diagram of which is described in FIG. 5.

 FIG. 10 represents a diagrammatic view, in section, of an injector holder assembly according to the patent, the diagram of which is described in FIG. 6.

 - Figure 11 shows a more partial schematic view, in section, of another example of construction of an injector holder assembly according to the patent, the diagram of which, common to that of Figure 10, is described by Figure 6 .

 FIG. 12 represents a diagrammatic view, in section, of an injector holder assembly according to the patent, the diagram of which is described in FIG. 7.

 FIG. 13 represents an operating diagram corresponding to a traditional constant pressure injection system, described in FIGS. 1 and 2.

 FIG. 14 represents an operating diagram corresponding to an injection device according to the patent, with intermediate stop on the shouldered push rod, described in FIGS. 5 and 9.

 FIG. 15 represents an operating diagram corresponding to an injection device according to the patent, with intermediate stop between the injector needle and a hydraulic return sheath, described in FIGS. 7 and 12.

 - Figure 16 shows an operating diagram corresponding to the same injection device as for Figure 15, described in Figures 7 and 12, but used for the precise metering of a pre-injection, by a double operation of the solenoid valve.

 - Figure 17 shows an operating diagram corresponding to an injection device according to the patent, with intermediate stop installed between the injector needle and the main spring, described in Figures 6 and 10, for which are described the operations from the quantity of fuel required for engine no-load operation (0%), up to that for full-load operation (100%).

In general, with reference to these figures, it is considered that the injector holder assembly, without counting the assembly elements, mainly consists of:
- An injector 1, itself comprising an injector body 5, in which is housed and guided an injector needle 6, ensuring by pressing on a needle seat 7, the control of the supply of the holes d injector 8, the role of which is to distribute the fuel in the combustion chamber of the engine.

 - A spacer 2, possibly merged with the injector holder 3, which acts as the main stop 9 and is generally crossed by a needle plunger 10.

 - An injector holder 3, itself comprising an injector holder body 11, which comprises a supply channel 12, a return of leaks 13, an internal volume of injector holder 14, a thrust volume 15 connected to the supply channel 12 through a supply port 16 and, in the case of the traditional constant pressure injection system, contains a main spring 17, often called a calibration spring, and a device for adjusting its load in place 18 and a control piston 19 which separates the internal volume of the injector holder 14 from the thrust volume 15.

 - A solenoid valve 4, itself comprising a solenoid valve body 20, a solenoid with a frame and a return spring, not shown, and a valve head 21, putting the thrust volume 15 into communication with the discharge volume 22 , itself in communication with the low pressure return circuit. This solenoid valve being able, depending on the configuration of the device, to be a two-way solenoid valve 23, or a three-way solenoid valve 24.

The device according to the invention does not include the control piston 19 or the return of leaks 13, but includes essential elements, which are installed in the injector holder 3:
- A control valve 25 whose contact with its seat at its upper part makes it possible to isolate the thrust volume 15. This contact is identified 26 in the diagrams of FIGS. 4 to 7.

 - A decompression orifice 27, preferably incorporated into the control valve 25 connecting the internal volume of injector holder 14 to the thrust volume 15 in order to decompress the internal volume of injector holder 14 when the solenoid valve 4 is open and authorize the opening of the injector 1.

 - A valve spring 28 whose main purpose is, at rest, to bring the control valve 25 into contact with its seat.

 - A push rod 29 making it possible to use the control valve 25 as a jack, ensuring effective closure of the injector 1.

 These components have the effect of reducing the quantity of fuel returned to the low pressure circuit to the quantity just necessary to control the operation of the injector.

The device according to the invention comprises optional additional elements, which, depending on the options, are installed in the injector holder 3, or the spacer 2:
- An intermediate stop 30, shown in FIGS. 5 6, 7, 9, 10, 11 and 12, making it possible to combine the evolution of the return thrusts applied to the injector needle 6 to carry out a step in its path during opening of the injector 1.

 - A hydraulic return sleeve 31, present in FIGS. 7, and 12, replacing or complementing the main spring 17, with the aim of changing the mode of evolution of the timing of the intermediate opening stage as a function injection pressure.

 These optional additional components, used separately or jointly, more particularly the intermediate stop, have the effect of modulating the operation of the injector when it is opened.

The curves appearing on the operating diagrams of the various devices, traditional or according to the invention (FIGS. 13 to 17) represent:
- The displacement 32 of the valve head 21.

 - The displacement 33 of the injector needle 6.

 - The displacement 34 of the control valve 25.

 - The flow 35 of fuel actually injected.

 - The general supply pressure 36 of the device.

 - The pressure 37 in the thrust volume 15.

 - The pressure 38 in the volume of the injector holder 14.

 The abscissa of these diagrams represents time and, for the part represented, is limited to less than 12% of the period of a complete cycle. The injector opening time does not exceed, in these examples, 5% of the period of a cycle.

The operation of a traditional constant pressure injection system, used as a reference, described in FIGS. 1 and 2 and illustrated by the diagram in FIG. 13, can be described as follows:
- At rest the injector is kept closed by the effect of the main spring (or calibration) 17 combined with the hydraulic thrust applied by the pressure 37 in the thrust volume 15 to the control piston 19. This thrust is always greater than that applied by the supply pressure 36 and the pressure of the combustion chamber of the engine under the injector needle 6.

 - When the solenoid valve opens, the pressure 37 in the thrust volume 15 decreases rapidly and decreases the thrust on the control piston 19. The movement 33 of the injector needle 6, coincident with that of the piston control element 19 is relatively rapid and subject to the sole control of the flow rates passing through the supply orifice 16 and the orifice of the solenoid valve opened by the valve head 21. Under the effect of the supply pressure 36, the flow 35, introduced into the combustion chamber of the engine, increases rapidly.

 - As soon as the injector is fully open, the flow 35, introduced into the combustion chamber of the engine, remains almost constant.

 - When the solenoid valve closes, the pressure 37 in the thrust volume 15 increases rapidly thanks to the communication through the supply orifice 16 and pushes on the control piston 19. The movement 33 of the needle d the injector 6, combined with that of the control piston 19, is relatively quick and ensures the clean closure of the injector 1.

 The device then returned to its rest position without the pressure in the injector holder volume 14 having changed significantly, taking into account the permanent communication established by the leak return 13.

The operation of the injection device according to the patent, described in FIGS. 4 to 12 and illustrated by the diagrams in FIGS. 14 to 17, can be described as follows:
- At rest, the injector is kept closed by the effect of the main spring 17 or of the valve spring 28 combined with the hydraulic thrust applied by the pressure 38 in the volume of the injector holder 14 to the upper face of the needle d injector 6. This thrust is always greater than that applied by the supply pressure 36 and the pressure of the combustion chamber of the engine under the injector needle 6.

 - When the solenoid valve opens, the pressure 37 in the thrust volume 15 decreases rapidly, releasing a flow rate through the decompression orifice 27. The pressure 38 in the injector holder volume 14 gradually decreases.

 - When the thrust on the needle is balanced, the movement 33 of the injector needle 6 ensures a gradual opening of the injector 1. Under the effect of the supply pressure 36, the flow 35, introduced into the engine combustion chamber gradually increases.

 - In the case where the intermediate stop 30 exists, the movement 33 of the injector needle 6 marks a pause and it is the same for the flow 35, introduced into the combustion chamber of the engine.

 - When the decrease in pressure 38 in the volume of injector holder 14 allows the intermediate stop 30 to be crossed, the movement 33 of the injector needle 6 is relatively rapid and, under the effect of the pressure 36 d supply, the flow 35, introduced into the combustion chamber of the engine, increases rapidly.

 - As soon as the injector is fully open, the flow 35, introduced into the combustion chamber of the engine, remains almost constant.

 - When the solenoid valve closes, the pressure 37 in the thrust volume 15 increases rapidly thanks to the communication by the decompression orifice 27 and the control valve 25, pushed by the supply pressure 36 applied to the part between the guide of the valve and the seat of the valve 26, takes off from its seat. The pressure 37 in the thrust volume 15 then increases very quickly thanks to the communication through the supply orifice 16. The control valve 25, whose movement is shown at 34, comes into contact with the thrust rod 29 and plays the role of a jack, pushing the injector needle 6, the displacement 33 of which is relatively rapid and ensures the clean closure of the injector 1.

 When the injector 1 is closed, the pressure 37 in the thrust volume 15 ensures, through the decompression orifice 27, the progressive pressurization of the volume of the injector holder 14.

 - When the pressure 38 of the injector holder volume 14 is close to the pressure 37 in the thrust volume 15, the control valve 25 closes again under the effect of the valve spring 28.

 The device then returns to its rest position and the pressure 38 in the injector holder volume 14, like the pressure 37 in the thrust volume 15, gradually approaches the supply pressure 36, under the effect of the leaks from the injector needle 6 and control valve 25 guides.

The particular operation with pre-injection of the injection device according to the patent, described in FIGS. 7 and 12 and illustrated by the diagram in FIG. 16, can be described as follows:
- If during the pause due to the intermediate stop 30, the solenoid valve is closed, the pressure 37 in the thrust volume 15 increases rapidly thanks to the communication by the decompression orifice 27 and the control valve 25, pushed by the supply pressure 36 applied to the part between the guide of the valve and the seat of the valve 26, takes off from its seat.

The displacement 34 of the control valve 25 ensures a sufficient increase in the pressure 38 in the volume of the injector holder 14 to ensure the closure of the injector 1, the displacement of the needle of which is shown at 33, and the flow 35 of injection is interrupted.

 - When the solenoid valve is reopened, the pressure 37 in the thrust volume 15 decreases rapidly, the control valve 25 returns to its rest position and the movement 33 of the injector needle, like the flow 35 of injection, resume substantially with the advancement of the injection acquired before the interruption.

 - The continuation of the injection, except for the consequences of the pressure waves caused by the interruption, continues as in the case of the injection without interruption.

The device according to the invention allows:
- Control of the flow rate at the start of injection, by the section of the decompression orifice 27, by the injector needle path authorized by the intermediate stop 30 and by the thrust applied to this stop by the main spring 17 , the hydraulic return sheath 31 or possibly the valve spring 28.

 - Neutralization of leakage from the guides of the elements constituting the injection device, by closing the volumes between injections.

 The device according to the invention is particularly intended to supplement and improve the injection devices supplied at almost constant pressure for diesel engines.

Claims (7)

 - And a decompression orifice (27) which puts the closed volume of the injector holder (14) into communication with the thrust volume (15) of the control valve (25) so that, when the solenoid valve (4) is open , the decompression of the injector holder volume (14) is progressive and that when the solenoid valve (4) is closed, the pressures in the thrust volume (15) and the injector holder volume (14) can balance . This decompression orifice (27) can, for example, be produced directly in the body of the control valve (25).  - A control valve (25), the guide diameter of which is greater than or equal to that of the guide of the injector needle (6) and the diameter of support on its seat close to the latter, and which, brought back in its rest position by a valve spring (28), interrupts the communication, ensured by a supply orifice (16), between the supply channel (12), and the solenoid valve (4), of a on the one hand, and, on the other hand, closes the volume of the injector holder (14) communicating with the bottom of the injector (1) and not communicating with the discharge volume (22) or the return circuit, in order to pressurizing,  1- Device to slow down opening and reduce leakage for constant pressure injection systems for diesel engines, characterized in that it comprises:  2- Device according to claim 1, characterized in that a main spring (17) ensures, by pressing on a needle plunger (10), a closing force on the injector needle (6) complementary to that pressure in the injector holder volume (14).  3- Device according to claim 2, characterized in that a push rod (29), the length of which leaves a clearance greater than the maximum stroke of the injector needle (6), allows the control valve (25 ) to serve as a cylinder and ensures rapid closure of the injector when the solenoid valve (4) is closed. This push rod (29) can be independent, or be part of either the control valve (25) or the needle plunger (10).  4- Device according to claim 3, characterized in that the valve spring (28) is interposed between the push rod (29) and the control valve (25).  5- Device according to claim 4, characterized in that the thrust of the valve spring (28) loads the push rod (29) only for a lifting of the injector needle (6) sufficient for the rod thrust (29) is in contact with an intermediate stop (30) to mark a slight step when crossing this stop.  6- Device according to claim 4, characterized in that the thrust of the main spring (17) loads the needle plunger (10) only for raising the injector needle (6) sufficient for the pusher to 'needle (10) or the needle itself is in contact with an intermediate stop (30) to mark a clear step when crossing this stop.  7- Device according to claim 6, characterized in that the thrust of the main spring (17) is replaced or supplemented by that of a hydraulic return sheath (31) whose thrust varies with the difference between the pressure of the supply (12), observed downstream of the supply orifice (16), and that of the volume of the injector holder (14).