GB2504315A - I.c. engine common rail system with each fuel injector connected to the rail by two fuel delivery channels to reduce transient pressure wave propagation - Google Patents

Abstract

A fuel injector (160, fig.1) of an internal combustion engine comprises a fuel inlet (169, fig.3) connected to a fuel rail (170, fig.1) of a common-rail system. The fuel inlet is connected to a delivery chamber 165 of each injector nozzle by a first delivery channel 163 and a second delivery channel 166 which provide different wave characteristics for a transient hydraulic signal. The second delivery channel 166 may include a throttle 167 to provide phase shifting. The second delivery channel 166 may have the same diameter as the first second delivery channel 163. The lengths of the second and first delivery channels 166, 163 may be in the range 1:2 to 1:1. The injector may comprise a damping chamber 168 which is a sort of second rail (minirail) to provide additional wave damping. The fuel injector may have a solenoid or piezoelectric actuator.

Description

FUEL INJECTOR FOR AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a fuel injector for an internal combustion engine, the fuel injector being characterized by a particular design which results in a wave balanced injector fora transient hydraulic signal, in particular transient pressure waves.

BACKGROUND

It is known that modem engines are provided with a fuel injection system for directly injecting the fuel into the cylinders of the engine. The fuel injection system generally comprises a fuel common rail and a plurality of electrically controlled fuel injectors, which are individually located in a respective cylinder of the engine and which are hydraulically connected to the fuel rail through dedicated injection pipes.

Each fuel injector generally comprises an injector device, a nozzle and a movable needle which repeatedly opens and closes this nozzle; the fuel, coming from the rail and passing through the injection pipe and, inside the injector device, a delivery channel, reaches the nozzle and can thus be injected into the cylinder giving rise to single or multi-injection patterns at each engine cycle.

The needle is moved with the aid of a dedicated actuator, typically a solenoid actuator or a piezoelectrjc actuator, which is controlled by an electronic control unit (ECU). The ECU operates each fuel injection by generating an electric opening command, causing the actuator to open the fuel injector nozzle for a predetermined amount of time, and a subsequent electric closing command, causing the actuator to close the fuel injector nozzle.

The time between the electric opening command and the electric closing command is generally referred as energizing time of the fuel injector, and it is determined by the ECU as a function of a desired quantity of fuel to be injected.

As known, one of the main problem of an injection system and in particular of a fuel injector is related to transient hydraulic signal behavior during injections and in particular to pressure waves fluctuations. In fad, simplifying the phenomenon when an injection starts, the pressure inside the nozzle delivery chamber, just on top of the injection holes, suddenly falls down generating a pressure wave (p-Ap) going backward the delivery channel inside the injector and the injection pipe up to the rail. Once reached the rail, a pressure wave (pi-LXp) is reflected forward through the injection pipe, the injection channel up to the nozzle delivery chamber. Same effect arises when the injection ends: a pressure wave (p-'-Ap) moves from the nozzle to the rail and then is reflected (p-Ap). In conclusion, the single injection takes place under different pressure conditions and, in case of multiple injections, subsequent injections run under different pressure conditions in the same injector and between injector to injector.

This has brought to the fact that current injector design requires software compensation strategies to damp the pressure waves effect with big calibration effort.

Therefore a need exists for a new injection design which could neutralize as much as possible the effect of transient hydraulic signal (particularly, pressure waves propagation), thus allowing possible removal or simplification of the software compensation algorithms, increasing injection repeatability and improving the potential for closer injections in a multi-injection pattern.

An object of an embodiment of the invention is to provide a fuel injector with a new hydraulic layout, namely with an additional delivery channel providing additional and different wave characteristics. By the balance of such waves, the nozzle delivery chamber of the injector will get more stable characteristics, in particular a well stabilized presure.

These objects are achieved by a fuel injector, by an internal combustion engine and by an automotive system provided with an electronic control unit able to control the fuel injections, having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a fuel injector of an internal combustion engine comprising a fuel inlet connectable to a fuel rail of a common-rail system, an injector device with a first delivery channel connecting the fuel inlet to a delivery chamber of an injector nozzle, wherein the fuel injector further comprising a second delivery channel connecting the delivery chamber and the fuel inlet, wherein the first delivery channel and the second delivery channel providing different wave characteristics for a transient hydraulic signal.

An advantage of this embodiment is that, the fuel injector is provided with two delivery channels having different wave characteristics. A transient shock wave caused by the opening and/cr closing of the injector nozzle is propagated in a different way, while running through the different delivery channels. By tuning the channels characteristics, the waves running through the two channels get different phases and amplitudes after the wave forming. The principle of destructive interference when superposing the two waves causes the wave balancing which should be achieved. As a result, this wave (for example, pressure waves) balance, will provide a stabilized signal, i.e. pressure, in the nozzle delivery chamber. This, in turn, will provide more accurate injections, allowing closer multiple injections and possibly removing or simplifying the software compensation strategies.

According to another embodiment, said second delivery channel comprises a throttle, providing a phase shifting of said wave characteristics of the two delivery channels.

The presence of a throttle in the second delivery channel also contributes to differentiate the wave characteristics (e.g. a wave phase shifting) inside the two delivery channels.

According to an aspect of the invention, said throttle is a press fit bushing inserted in the second delivery channel.

This solution has the advantage to be easily manufactured. In fact according to this solution the throttle only needs to be mounted with a certain interference inside the second delivery channel and the solution does not require difficult machining of the channel itself.

According to another embodiment, the diameter of said throttle ranges between 1/4 and 1/3 of said second delivery channel diameter.

An advantage of this embodiment is that such throttle range ensures a remarkable wave delay, without creating a high hydraulic loss: smaller diameter would increase throttling too much, while higher diameter would not create a remarkable waves counter phase.

According to a further embodiment, the length of said second delivery channel ranges between 1/2 and 1:1 of said first delivery channel length.

An advantage of this embodiment is that the range of the second delivery channel length allows to reach a good compromise between wave delay and packaging constraints in the injector design.

According to a still further embodiment, said second delivery channel diameter is equal to the diameter of the first delivery channel.

An advantage of this embodiment is that by using the same diameter in the two delivery channels is possible to have the same waves amplitude.

Another embodiment of the invention foresees a fuel injector which further comprises a damping chamber.

An advantage of this embodiment is that the damping chamber, also called "minirail", would provide a pressure damping effect just on top of the delivery channels, thus improving the damping function of the rail in a common rail system.

According to another embodiment, the fuel injector further comprises a solenoid actuator.

An advantage of this embodiment is the fact that the new injector design is applicable to any solenoid injector, which is, as known, the standard in the majority of common rail systems.

According to an alternative embodiment, the fuel injector further comprises a piezoelectric actuator.

An advantage of this embodiment is the fact that the new injector design is also applicable to any piezoelectric injector, which represents the "premium" application in common rail systems.

A further aspect of the disclosure provides an internal combustion engine of an automotive system equipped with one or more fuel injectors according to one of the previous embodiments.

A still further aspect of the disclosure provides an automotive system comprising an electronic control unit configured for controlling one or more fuel injectors of an internal combustion engine according to one of the previous embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an automotive system.

Figure 2 is a section of an internal combustion engine belonging to the automotive system of figure 1.

Figure 3 is an external view of a fuel injector Figure 4 is a schematic hydraulic lay-out of the fuel injector according to an embodiment of the invention.

Figure 5 show a comparison of pressure waves behavior in injectors according to the invention with different sizing of the hydraulic lay-out, obtained by a simulation model.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures land 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.

A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.

A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190. The fuel injection system with the above disclosed components is known as Common Rail Diesel Injection System (CR System). It is a relative new injection system for passenger cars. The main advantage of this injection system, compared to others, is that due to the high pressure in the system and the electromagnetically controlled injectors it is possible to inject the correct amounts of fuel at exactly the right moment. This implies lower fuel consumption and less emissions. Further advantage of the Common Rail system is the presence of the rail itself: as known, former injection systems suffered transient hydraulic signal propagation through the injection pipes from the nozzle up to pump and vice versa. The rail can be easily imagined as a quiet tank where (due to its volume) all transient hydraulic signals and in particular the pressure are damped. It is to be understood that the rail does not completely solve this issue, but just limits the waves propagation to the channel and the pipe between the injector nozzle and the rail. This residual issue represents, as stated in the introduction, the technical problem the present invention aims to solve.

Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200.

An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may -reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200 The EGS system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110 and equipped with a data carrier 40. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including1 but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices.

The program may embody the methods disclosed herein, allowing the CPU to carryout outthe steps of such methods and controlthe ICE 110.

S

Turning back to the fuel injection, in Fig. 3 the fuel injector 160 comprises an actuator controlled by the ECU 450 (solenoid actuator 161 or piezoelectric actuator), an injector fuel inlet 169 an injection device 162, comprising means for feeding and discharge the injector and a nozzle 164, provided with a needle which, with its controlled movement, covers and uncovers the injection holes. The ECU 450 operates each fuel injection by generating an electric opening command, causing the actuator to open the fuel injector nozzle 164 (up movement of the needle) for a predetermined amount of time, and a subsequent electric closing command, causing the actuator to close the fuel injector nozzle (down movement of the needle).

Particularly, as schematized in Fig. 4, the injection device comprises a first delivery channel 163, providing the fuel, coming from the rail and the injection pipe, from the injector inlet to the injector nozzle 164. Said injector nozzle also comprises a delivery chamber 165 on top of the injection holes.

According to a preferred embodiment, said injector device 162 further comprises a damping chamber 168, also called "minirail'. Aim of such chamber is to provide a wave damping effect just on top of the delivery channel, being a sort of second rail and therefore improving the damping function of the rail in a common rail system, as described above.

As mentioned in the introduction, the hydraulic layout of a fuel injector, particularly the presence of a delivery channel 163 in the form of a long pipe, causes the propagation of transient hydraulic signals, typically pressure waves, established at the opening and the closing of the injector nozzle during injections. These waves travel back and forward the delivery channel, resulting in different conditions (above all pressure) in the nozzle delivery chamber 165. This phenomenon leads to the conclusion, that single and multiple injections run under different pressure conditions in the same injector and between injector to injector. A way to solve this issue is to implement software compensation strategies, which cannot be standardized and require a big calibration effort.

Aim of the invention is to provide a fuel injector with a new hydraulic layout, which allows to damp as much as possible transient hydraulic signals and, in particular, pressure waves, in the nozzle delivery chamber, thus allowing possible removal or simplification of the software compensation algorithms, increasing injection repeatability and improving the potential for closer injections in a multi-injection pattern. The purpose of the invention is reached by adding a second delivery channel 166 having different wave characteristics with respect of the first delivery channel ones. In fact, whenever a transient shock wave caused by the opening and/or closing of the injector nozzle happens, this is propagated in a different way, while running through the different delivery channels. By tuning the channels characteristics the waves running through the two channels get different phases and amplitudes after the wave forming. When superposing the two waves, their interference causes the wave balancing which should be achieved. As a result, this wave (for example, pressure waves) balance, will provide a stabilized signal, i.e. pressure, in the nozzle delivery chamber. This, in turn, will provide more accurate injections, allowing closer multiple injections and possibly removing or simplifying the software compensation strategies.

As mentioned, the new layout foresees a second delivery channel 166 with different characteristics with respect the first one. In particular, tuning the second delivery channel 166 it is possible to obtain "counter phased" transient waves which will damp the main channel one resulting in a stabilized behavior (for example, the pressure) in the nozzle delivery chamber 165. More particularly, the length of the two channels has an influence on the phase of the transient waves: the higher is the difference between the two channels length, the higher is the hase shifting between the two transient hydraulic signals, generates into the delivery channels. The diameters of the two channels have an effect to the amplitude of the waves: higher diameters imply smaller wave amplitudes.

According to a preferred embodiment, the second delivery channel can also comprise a throttle 167. As known, a throttle is a lumped hydraulic resistance. Inserted inside the second delivery channel, the throttle provides a hydraulic decoupling effect between the upper channel portion and the lower channel portion, thus realizing a phase shifting to the transient pulse. Advantageously, the throttle 167 can be a press fit bushing with a calibrated intemal diameter inserted in the second delivery channel 166. According to this solution, the throttle only needs to be mounted with a certain interference inside the channel and the solution does not require difficult machining of the channel (eg channel having two diameters) and therefore is quite easy to be manufactured in large series production.

The new hydraulic layout of the injector has been modeled in order to get comprehensive ranges for the design parameters of the second delivery channel. The main results, related to a typical injector configuration, are showed in table 1 and in Fig. 5. Dimensions of the first dehvery channel, in all tests, are: length 20 mm and diameter 2 mm.

____________________________ TABLE 1 _____ _____ _______ Test i 2 3 4 5 2nd delivery channel length [mm] 20 20 5 NO 2.5 2nd delivery channel diameter [mm] 2 1 2 NO 2 Throttle diameter [mm] 0.5 0.2 NO NO 0.1

S

The table shows five different test cases. In particular test n. 4 can be considered the baseline: the injector has no second delivery channel, i.e. the known hydraulic lay-out. In the other four cases, the length and the diameter of the second channel and the throttle diameter have been varied. In Fig. 5, with 6 is indicated the injection actuation command, while reference 1-5 represent the behavior of the pressure oscillations in the nozzle delivery chamber. Of course, reference 1-5 corresponds to test cases 1-5. The results clearly show that the test case 1 is the best compromise and has a fast pressure stabilization. Similarly, also test 3 (in Fig. 5 represented with a dotted line and very close to test 1) gives very good results. From the above table, it is to observe that this configuration does not have a throttle 167 in the second delivery channel 166, thus confirming that the very essential feature of thus hydraulic layout is the presence of a second channel.

From these preliminary results and according to the chosen typical configuration of the injector, some optimal ranges of the design parameters have been defined. The diameter of the throttle 167 should accomplish a trade-off between wave delay and hydraulic loss: a good compromise would be a range between 1/4 and 1/3 of the second delivery channel diameter, thus ensuring a remarkable wave delay, without creating a high hydraulic loss: smaller diameter would increase throttling too much, while higher diameter would not create a right waves counter phase.

As far as the second delivery channel 166 is concerned, its length ideally would range between 1/2 and 2 the first delivery channel 163 length. In fact each boundary of such range should ideally provide a phase shifting of 180°, which would represent the best solution to reach the balance between the two different waves. On the other side, to avoid packaging issues in the injector design the length of the second channel cannot overcome the length of the first channel. Therefore a compromise range has been defined between 1/2 and 1:1 (of the first delivery channel length). The diameter of the channel 166 would be preferably equal to the diameter of the first delivery channel 163.

In this way, it will be possible to get in the two delivery channels the same waves amplitude.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

1-5 injection pressure curves 6 Injection actuation curve data carrier 100 automotive system internal combustion engine engine black cylinder cylinder head 135 camshaft piston crankshaft combustion chamber cam phaser 160 fuel injector 161 solenoid actuator 162 injector device 163 first delivery channel 164 injector nozzle 165 nozzle delivery chamber 166 second delivery channel 167 throttle of the second delivery channel.

168 injector damping chamber 169 injector fuel inlet 170 fuel rail fuel pump fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 after-treatment devices 290 VGT actuator 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 4SOECU