GB2505918A

GB2505918A - Method of Controlling an Electromagnetic Valve of a Fuel Injection System

Info

Publication number: GB2505918A
Application number: GB201216443A
Authority: GB
Inventors: Stefano Nieddu; Gennaro Merlino
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-09-14
Filing date: 2012-09-14
Publication date: 2014-03-19
Also published as: GB201216443D0

Abstract

The invention provides a method of controlling an electromagnetic valve of a fuel injection system for an internal combustion engine, comprising closed loop controlled current regulation, wherein the herein said current regulation comprising the following steps: using a current setpoint (I*, fig.4) to calculate 22 a voltage feed forward contribution (VFF), calculating 21 a current error (I*-I, fig.4) between said current setpoint value (I*) and a current measured value and using said current error (I*-I) to calculate 23 a voltage proportional contribution (VKP) and 24 a voltage integral contribution (VKP) using said voltage integral contribution (VK1) to calculate 25 an adjustment coefficient (Î±adj), determining 26 an electromagnetic valve voltage (Vmv*) from the following equation: Vmv* = Î±adj x (VFF+VKP+VKI). The invention provides improved pressure regulation by improving the current regulation, particularly where an inaccuracy is caused by a reverse voltage drop of a recovery diode associated with a solenoid coil acting as an actuator of an electromagnetic fuel metering valve.

Description

METHOD OF CONTROLLING AN ELECTROMAGNETIC VALVE

TECHNICAL FIELD

The present disclosure relates to a method of controlling an electromagnetic valve, particularly a metering valve of a fuel injection system (namely, Common Rail System) for Diesel engines, said metering valve being actuated by an Electronic Control Unit of an automotive system to regulates the pressure in the injection system.

BACKGROUND

It is known that modem Diesel engines are provided with.a fuel injection system for directly injecting the fuel into the cylinders of the engine. Nowadays, the so called Common Rail System (CRS) is the most used one. The CRS generally comprises a fuel pump, hydraulically connected to 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.

As also known, the injection pressure is one of the most important parameter determining the quality of the fuel injection into the engine (for example, the fuel spray penetration in the cylinder head) and must be regulated as function of the engine working conditions, for example, according to a map engine load vs. engine speed.

A possible way to regulate the injection pressure is to laminate the fuel flowrate incoming in the fuel pump, by means of an electromagnetic valve. In particular said valve is known as fuel metering valve and is mounted in the inlet area of the fuel pump.

S The metering valve comprises a solenoid coil, acting as an actuator, which is the main part of an electrical circuit, which further comprises a recovery diode. The metering valve is driven by the current and regulates the fuel quantity by means of a PWM signal.

As known, such PWM control signal needs a constant current (close loop regulated) during its on states for providing a sufficient control signal, i.e. current signal.

Such current flows in the electromagnetic circuit, realized in the metering valve, and the magnetic force, thus generated, determines the hydraulic passage in the valve and, consequently, the fuel flowrate entering the high pressure pump.

A problem of actual metering valve control strategy is that it does not provide a fast and accurate current regulation and therefore the fuel pressure regulation performance are decreased. In particular, the inaccuracies of the current regulation are due to the reverse voltage drop of the recovery diode and further non idealities of the circuit of the metering valve. In fact, during transient condition, the current regulation technique is not capable to compensate in a fast way the effect of reversing diode drop voltage affecting the Pulse Width Modulation (PWM) actuation, thus creating remarkable errors on fuel quantity delivery and on rail pressure regulation. Moreover, the current regulation, using a linear closed-loop control, is limited by the metering valve coil resistance variation with temperature, the loop-gain having to be calibrated for the cold operation.

Therefore a need exists for improving the metering valve control strategy which could reach a fast current regulation and a full compensation of the resistance behavior of the metering valve coil. Furthermore such new strategy should be able to compensate diode voltage drop perturbation. Finally, the new control method should allow a fuel injection system calibration easier and more robust respect to production spread.

An object of an embodiment of the invention is to provide a better current regulation for the PWM signal, which is solved by a new metering valve control strategy. In particular, such new control strategy performs the above target, by means of a combined feed forward and closed loop control, thus realizing a better pressure regulation and all possible linked advantages, including cost savings and flexible use of the metering valve in fuel injection system, whose components are realized by different suppliers.

Another object is to provide an apparatus which allows to perform the above method.

These objects are achieved by a method, by an apparatus, by an engine, by a computer program and computer program product, and by an electromagnetic signal 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 method of controlling an electromagnetic valve of a fuel injection system for an internal combustion engine, comprising closed loop controlled current regulation, wherein the herein said current regulation comprising the following steps: -using a current setpoint to calculate a voltage feed forward contribution, -calculating a current error between said current setpoint value and a current measured value and using said current error to calculate a voltage proportional contribution and a voltage integral contribution -using said voltage integral contribution to calculate an adjustment coefficient, -determining an electromagnetic valve voltage.

Consequently, an apparatus is disclosed for controlling an electromagnetic valve, the apparatus comprises -means using a current setpoint to calculate a voltage feed forward contribution, -means for calculating a current error between said current setpoint value and a current measured value and using said current error to calculate a voltage proportional contribution and a voltage integral contribution -means using said voltage integral contribution to calculate an adjustment coefficient, -means for determining an electromagnetic valve voltage.

An advantage of this embodiment is that it provides a better current regulation, closed loop controlled, by means of a new control strategy of the metering valve. The new strategy is based on the metering valve current feed forward and closed loop controls and also on an adjustment coefficient control, which takes into account the actual electromagnetic valve resistance vs. a nominal resistance. A further advantage is that this improvement does not require any hardware amendments.

According to an aspect of the invention, said electromagnetic valve voltage divided over a battery voltage determines an electromagnetic valve duty cycle, by applying it a current circulates in the electromagnetic valve and can also be measured.

An advantage of this embodiment is that it allows to pilot the electromagnetic valve and S at the same time get the current value for the closed loop control.

According to another embodiment, said voltage feed forward contribution is the product of the current setpoint value with the nominal coil resistance of the electromagnetic valve.

An advantage of this embodiment is that the feed forward contribution provkies a good estimation of the valve voltage.

According to a further embodiment, said voltage proportional contribution is the product of said current error with a calibrated proportional factor.

An advantage of this embodiment is that, said voltage proportional contribution is based on the current error.

According to a still further embodiment, said voltage integral contribution is the product of the integral of said current error with a first calibrated integral factor.

An advantage of this embodiment is that this voltage integrative contribution could take into account different and not known effects acting on the electromagnetic valve.

According to a still further embodiment, wherein said adjustment coefficient is the product of the integral of said voltage integrative contribution and a second calibrated integral factor.

An advantage of this embodiment is that said adjustment coefficient, being based on this voltage integrative contribution and not on a current error is more effective in the self-learning of the valve coil resistance.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.

The computer program product can be embodied as a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program alt the steps of the method described above are carried out.

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

A still further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

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 a flow chart of a known control strategy of a meteuing valve.

Figure 4 is a graph depicting the current and pressure behavior by using the known control strategy Figure 5 is a flow-chart of the method according to the invention.

Figure 6 is a graph depicting the current and pressure behavior by using the method according to the invention.

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 EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGS 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, including, 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 out the steps of such methods and control the ICE 110.

Turning back to the fuel injection system, to explain the new control strategy, some background information have to be provided. As already mentioned, the injection pressure is one of the most important parameter determining the quality of the fuel injection into the engine (for example, the fuel spray penetration in the cylinder head) and must be regulated as function of the engine working conditions, for example, according to a map engine load vs. engine speed.

The metering valve comprises a solenoid coil, acting as an actuator, which is the main part of an electrical circuit, which further comprises a recovery diode. The metering valve is driven by the current and regulates the fuel quantity by means of a PWM signal.

Such current flows in the electromagnetic circuit, realized in the metering valve, and the magnetic force, thus generated, determines the hydraulic passage in the valve and, consequently, the fuel flowrate entering the high pressure pump. In fig, 3 the flowchart of a known control strategy is described. The current I of the electromagnetic valve is measured 13 and controlled in a feed forward way. The error (ll*), where 1* is the setpoint value 10 and such error is zero in steady state conditions when I is equal to 1*, is used to determine an adjustment coefficient aadj which is 14 the integral of the current error multiplied per K (calibrated integral factor) and is used to take into account the resistance variation of the electromagnetic valve. In steady state conditions, ctauj is the ratio between R, the actual valve resistance and R*, valve nominal resistance. Then, the metering valve voltage Vw is calculated 11 as the product of the current setpoint value, the nominal resistance R* of the valve and the adjustment coefficient aadj, so the voltage is calculated by means of a feed forward technique. Finally, the duty cycle D, which will pilot the valve is determined 12 by dividing the valve voltage VMV by the measured battery voltage Vbat and the so determined pulse with modulation (PWM) command is applied to the valve and the actual current I is measured 13 and used for the current closed loop control.

A problem of actual metering valve control strategy is that it does not provide a fast and accurate current regulation and therefore the fuel pressure regulation performance are decreased. In particular, the inaccuracies of the current regulation are due to the reverse voltage drop of the recovery diode and further non idealities of the circuit of the metering valve. The main reasons are the followings: -the reversing diode used in the PWM generator introduces an additional equivalent resistance in series with the valve resistance and varying with the duty cycle D. The adjustment coefficient Uadj includes this term also; -the closed loop for the calculation of the adjustment coefficient a3d] has a limited bandwidth, this is because the regulation closed loop is not linear, -the variation of the current setpoint 1* produce a variation of duty cycle D and then a variation of the equivalent resistance due to the reversing diode voltage drop.

Therefore a transient error on current regulation appears since the new value for the adjustment coefficient aadj is slowly regulated.

This limitations determine: -higher errors on fuel quantity delivery and on rail pressure regulation, -A limited fuel pressure loop bandwidth.

Moreover, the current regulation using a linear closed-loop is limited by the MV coil resistance variation with temperature, the loop-gain must be calibrate for the cold operation (minimum bandwidth at normal operation), thus determining: -higher transient errors on fuel delivery -fuel pressure loop bandwidth limited.

Consequence of the mentioned limitations are the following: the fuel pressure regulation is slow and this creates, on one side, high pressure overshoot and therefore combustion noise and risk of over-pressure valve opening; on the other side, slow recovery of pressure undershoot during cut-off with smoking and particulate matter increment.

Moreover, the fuel pressure loop calibration results hard, determining high sensitivity to the metering valve production spread and the fact that the pressure slow-rate during high engine loads must be limited. Summarizing, during transient operations, a change in the fuel request means a different electromagnetic valve operating point and the present feed forward current regulation slowly recover the error. This in turn means a metering valve fuel delivery error and consequently a rail pressure transient error magnified. What has been described can be observed in Fig. 4, where in the upper diagram the comparison between the current setpoint value and the current actual value is shown, while in the lower diagram the same comparison between the rail pressure setpoint pa* and the actual rail pressure Prau is also represented.

Therefore, aim of the present invention is to provide a better current regulation for the PWM signal, which is solved by a new metering valve control strategy. In particular, such new control strategy performs the above target, by means of a combined feed forward and closed loop control. The new control strategies should have the following capabilities: fast current regulation and full compensation of the valve coil resistance variation effects including the reversing diode voltage drop variation effect; metering valve current loop bandwidth constant and maximized at any temperature; easier and more robust respect to production spread. fuel injection system calibration.

With reference to Fig. 5, the new method of controlling the metering valve also comprises the steps of calculating 21 the current error 1*_I between the current setpoint value (1*) and the current measured 28 value I. Differently from the old technique, this new one is a combination of feed forward technique and a closed loop control regulated by means of a proportional and integrative regulator. In fact the electromagnetic voltage V, is the contribution of four terms. A first term is the voltage feed forward contribution V1, which is calculated 22 by using the current setpoint value 1* and multiplying it with the nominal coil resistance R* of the electromagnetic valve. This feed forward contribution provides a good estimation of the valve voltage.

The second term of the valve voltage is the voltage proportional contribution Vp, which is the product 23 of said current error l*l with a calibrated proportional factor Kp. 14.

Therefore, this proportional contribution directly takes into account the current error. The third term is a voltage integral contribution VKI, wherein said voltage integral contribution VK, is the product 24 of the integral of the current error l*l with a first calibrated integral factor Ki. The voltage integral contribution allows to take into account different and not known effects acting on the electromagnetic valve. Finally the fourth term to determine the metering valve voltage is an adjustment coefficient 0a, which is always the ratio RMV/R in steady state conditions as for the known strategy, and is calculated 25 as the integral of said voltage integral contribution VKI, multiplied per K, a second calibrated integral factor. The adjustment coefficient, being based on this voltage integral contribution and not on a current error as in the previous strategy, is more effective in the self-learning of the valve coil resistance.

Finally, the electromagnetic valve voltage VMV* is determined 26 from the following equation: VW = 0adj X (VFF+VKP+VKI).

where all the terms have been already defined.

Then the electromagnetic valve voltage Vd is divided over the measured battery voltage Vb2( to determine 27 the electromagnetic valve duty cycle 0, by applying it, as in the known control strategy, the current I circulates in the electromagnetic valve and can also be measured 28. This new strategy allows a fast control of the electromagnetic valve, based on two closed loop controls, the first one on the metering valve current and the second one on an adjustment coefficient, which takes into account the actual electromagnetic valve resistance vs. a nominal resistance.

The new method allows remarkable improvements of the metering valve performances, due to the fact that the control strategy actuates a very fast current regulation thanks to closed-loop and the additional feed-forward, making negligible the metering valve fuel delivery error. As consequence, the rail pressure control performances are really optimized. These advantages can be observed in Fig. 6, where in the upper diagram the comparison between the current setpoint value and the current actual value is shown, while in the lower diagram the same comparison between the rail pressure setpoint prail* and the actual rail pressure Praii is also represented.

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 block

11 block 12 block 13 block 14 block block 21 block 22 block 23 block 24 block block 26 block 27 block 28 block data carrier automotive system 110 internal combustion engine engine block cylinder cylinder head camshaft 140 piston crankshaft combustion chamber cam phaser fuel injector 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 aftertreatment 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 360 coolant temperature and level sensors 365 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 450 ECU I current measured value 1* current setpoint value VFF voltage feed forward contribution VKP voltage proportional contribution VKI voltage integral contribution aadj adjustment coefficient V electromagnetic valve voltage Vbat measured battery voltage D electromagnetic valve duty cycle RMV actual coil resistance of the electromagnetic valve R* nominal coil resistance of the electromagnetic valve Praji rail pressure Prail* rail pressure setpaint K calibrated integral factor

Claims

CLAIMS1. Method of controlling an electromagnetic valve of a fuel injection system for an internal combustion engine (110), comprising closed loop controlled current regulation, wherein the herein said current regulation comprising the following steps: -using a current setpoint (1*) to calculate (22) a voltage feed forward contribution (VFF)I -calculating (21) a current error (1*_I) between said current setpoint value (1*) and a current measured value and using said current error (1*_I) to calculate (23) a voltage proportional contribution (VKP) and (24) a voltage integral contribution (VKI) -using said voltage integral contribution (VKI) to calculate (25) an adjustment coefficient (a3dj), -determining (26) an electromagnetic valve voltage N*) from the following equation: V7 = QadjX (VFF+VKP+VKI).
2. Method according to claim 1, wherein said electromagnetic valve voltage (V*) divided over a battery voltage (Vbat) determines (27) an electromagnetic valve duty cycle (D), by applying it a current (I) in the electromagnetic valve and can also be measured (28).
3. Method according to claim 1 or 2, wherein said voltage feed forward contribution (VFF) is the product of the current setpoint value (1*) with the nominal coil resistance (R*) of the electromagnetic valve.
4. Method according to one of the previous claim, wherein said voltage proportional contribution (VKp) is the product of said current error (l*l) with a calibrated proportional factor (Kp).
5. Method according to one of the previous claim, wherein said voltage integral contribution (VKI) is the product of the integral of said current error (1*_I) with a first calibrated integral factor (Ki).
6. Method according to claim 1, wherein said adjustment coefficient aadj is the product of the integral of said voltage integrative contribution 0/K) and a second calibrated integral factor (K).
7. Internal combustion engine (110) comprising a fuel injection system equipped with an electromagnetic valve for actuating the injection pressure, said electromagnetic valve being controlled according to one of the claims 1-6.
8. Automotive system (100) comprising an electronic control unit (450) configured for controlling an electromagnetic valve according to one of the claims 1 -6.
9. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-6.
10. Computer program product on which the computer program according to claim 9 is stored.
11. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a computer program according to claim 9 stored in a memory system (460).
12. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 9.