of the patent for an industrial invention having the title:

CONTROL OF A METERING SOLENOID VALVE IN A PUMP UNIT FOR SUPPLYING FUEL TO AN INTERNAL COMBUSTION ENGINE

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The present invention relates to a system and a method for controlling a metering solenoid valve in a pump unit for supplying fuel to an internal combustion engine.

In particular, the present solution relates to a pump unit of the type comprising a high-pressure pump, for example a piston pump, adapted to supply fuel, for example diesel oil, to an internal combustion engine; a low- pressure pre-supply pump, for example a gear pump, adapted to supply the fuel from a containing tank to the high- pressure pump; and a hydraulic circuit for interconnecting the containing tank, the pre-supply pump, the high-pressure pump, and the internal combustion engine.

The hydraulic circuit comprises a metering solenoid valve (generally known as an EMU, from the English "Fuel Metering Unit", or ZME, from the German "Zumesseinheit") , adapted to control the instantaneous flow rate of fuel supplied to the high-pressure pump, on the basis of the values of a plurality of operating parameters of the internal combustion engine.

The metering solenoid valve comprises a valve body, mounted in the hydraulic circuit, and a plug engaged slidably in the valve body so as to be movable between an open and a closed position.

Known pump units of the type described above have a number of drawbacks, mainly due to the fact that the pressure waves generated as a result of the outflow of fuel from the cylinders of the high-pressure pump may interfere with the control of the plug of the aforesaid metering solenoid valve, thus compromising the supply of the correct flow of fuel to said high-pressure pump and consequently to the internal combustion engine.

The object of the present invention is to provide an improved solution for controlling the metering solenoid valve of the pump unit, which can overcome the drawbacks described above and which can be implemented in a simple and economical way.

According to the present invention, a control system and method are provided, as claimed in the attached claims.

The present invention will now be described with reference to the attached drawings, which show a non limiting example of embodiment of the invention, in which:

- Figure 1 is a hydraulic diagram of a pump unit for supplying fuel to an internal combustion engine; - Figure 2 is a schematic sectional view, with parts removed for clarity, of a portion of the pump unit of

Figure 1, including a corresponding metering solenoid valve ;

- Figure 3 shows an excitation signal of an

electromagnetic actuator of the metering solenoid valve of the pump unit;

- Figure 4 shows a possible trend of the mean value and oscillation amplitude of the aforesaid excitation signal ;

- Figure 5 shows the mean value of the excitation signal of Figure 4 and an associated trend of the fuel flow in the pump unit;

- Figure 6 shows a possible trend of pressure peaks of the fuel supplied, as a function of the mean value of the aforesaid excitation signal;

- Figure 7 shows the trend of the excitation signal generated in accordance with a control scheme according to an aspect of the present solution;

- Figure 8 shows the trend of the oscillation

amplitude and of the mean value of the excitation signal of Figure 7;

- Figure 9 is an outline block diagram of an

electronic control unit of the metering solenoid valve according to an aspect of the present solution; - Figure 10 shows a first embodiment of a drive module of the electronic control unit of Figure 9;

- Figure 11 shows a second embodiment of the drive module of the electronic control unit of Figure 9; and

- Figure 12 is an outline block diagram of a variant of the electronic control unit of the metering solenoid valve according to a further aspect of the present

solution .

Figure 1 shows a pump unit, indicated as a whole by 1, for supplying fuel, for example diesel oil, from a tank 2 to an internal combustion engine 3, for example a diesel engine .

The engine 3 comprises a fuel distribution manifold 4, commonly known as a "common rail", and a plurality of injectors 5 connected to the manifold 4 and adapted to spray the fuel into corresponding combustion chambers (not shown here) .

The pump unit 1 comprises a high-pressure pump 6, particularly a piston pump, for supplying the fuel to the engine 3, and a low-pressure or pre-supply pump 7,

particularly a gear pump, of the electrically actuated type for example, for supplying the fuel from the tank 2 to the high-pressure pump 6.

The high-pressure pump 6 comprises a pump body 8 and, in the illustrated example, two cylinders 9, formed in the pump body 8 and having respective longitudinal axes 10 substantially parallel to one another.

The cylinders 9 are slidingly engaged by respective pistons 11, movable by the force of an actuation device 12, in a reciprocating rectilinear motion comprising a stroke for the intake of the fuel into the corresponding chambers 9 and a stroke for delivering the fuel to the engine 3.

The actuation device 12 comprises a transmission camshaft 13, housed in a first containing chamber 14 formed in the pump body 8, and capable of moving the pistons 11 in their delivery stroke.

The actuation device 12 further comprises, for each piston 11, a respective spring (not illustrated), which is housed in a second containing chamber (not illustrated) formed in the pump body 8, and which is capable of moving the piston 11 in its intake stroke. In particular, the shaft 13 is configured so that it simultaneously moves one piston 11 in its intake stroke and the other piston 11 in its delivery stroke.

The pump unit 1 further comprises a hydraulic circuit 15 which in turn comprises a first branch 16 for

interconnecting the tank 2 and the low-pressure pump 7, a second branch 17 for interconnecting the low-pressure pump 7 and the high-pressure pump 6, and a third branch 18 for interconnecting the high-pressure pump 6 and the manifold 4.

The second branch 17 is provided with a filter device 19 for filtering the fuel supplied to the cylinders 9, and also has a metering solenoid valve 20 (usually called an 'EME' or 'ZME' ) , mounted downstream of the filter device 19 in a direction 21 of advance of the fuel along said second branch 17.

The metering solenoid valve 20 is actuated to control the instantaneous flow rate of fuel supplied to the high- pressure pump 6, on the basis of the values of a plurality of operating parameters of the engine 3; in a possible implementation, to which reference will be made here, the metering solenoid valve 20 is of the normally open

("normally on") type.

An electronic control unit 100 (provided with a processing unit using a microcontroller, microprocessor or similar digital processing element, coupled to a non volatile memory, and with a suitable drive stage or

"driver") is coupled for operation to the metering solenoid valve 20 for the purpose of controlling the actuation of the valve on the basis of the aforesaid operating

parameters of the engine 3.

It should be noted that this electronic control unit 100 may be coupled for operation to a unit (not illustrated here) for managing and monitoring the engine 3, or may be integrated into the aforesaid unit for managing and monitoring the engine 3.

The second branch 17 and the third branch 18 are connected to each cylinder 9 via an intake valve 22 and a delivery valve 23 respectively.

The aforesaid hydraulic circuit 15 also comprises further circuit branches, having known functions not directly relevant to the present discussion, and therefore not described in detail herein.

As illustrated in greater detail in Figure 2, the second branch 17 of the hydraulic circuit 15 comprises a supply manifold (or tunnel) 29, and, for each cylinder 9 (not illustrated here) , a respective intake conduit 30 for connecting the supply manifold 29 to said cylinder 9.

The metering solenoid valve 20 comprises a valve body 31 of generally tubular shape, mounted in the supply manifold 29 coaxially with a longitudinal axis 32 of said supply manifold 29, and has an inlet channel 33 of annular shape, which extends about the longitudinal axis 32 and communicates with the second branch 17 for supplying the fuel through the valve body 31.

The valve body 31 is engaged slidingly by a cup-shaped plug 34, limited axially by an end wall 35 substantially perpendicular to the longitudinal axis 32, and is also limited by a substantially cylindrical lateral wall 36 provided with a plurality of connecting holes 37 distributed about the same longitudinal axis 32.

The plug 34 is movable between an open position, in which the connecting holes 37 are aligned radially with the inlet channel 33, and a closed position, in which said connecting holes 37 are axially offset from the inlet channel 33.

The plug 34 is moved into its open position, and normally retained there, by a spring 38 interposed between the plug 34 and a stop ring 39 fixed to a free end of the valve body 31 (it should be noted, therefore, that the metering solenoid valve 20 is of the "normally open" type) .

The plug 34 is moved from its open position to its closed position against the action of the spring 38 by an electromagnetic actuator 40 comprising a cup-shaped body 41 fastened to the valve body 31 coaxially with the

longitudinal axis 32.

The electromagnetic actuator 40 further comprises an actuating armature 42, made of ferromagnetic material and mounted slidably in the cup-shaped body 41. The actuating armature 42 has a plunger 43, which is engaged slidably in a pair of guides 44 and is positioned in contact with the end wall 35.

The electromagnetic actuator 40 further comprises an electrical circuit 45, consisting of a coil which extends around the actuating armature 42 and along the longitudinal axis 32 and is supplied with electricity to move the actuating armature 42 against the action of the spring 38.

In particular, the aforesaid control unit 100 is coupled for operation to the electrical circuit 45 and is configured so as to supply suitable drive signals S _d to said electrical circuit 45 to excite the coil and control the actuating armature 42 and consequently the opening and closing of the metering solenoid valve 20, in order to regulate the amount of fuel supplied to the engine 3.

As indicated above, pressure fluctuations in the supply manifold 29, which occur because of the outflow of fuel from the cylinders 9 of the high-pressure pump 6, create an instability of the fuel flow to said high- pressure pump 6 and consequently to the engine 3.

In particular, the variations of pressure

(particularly the pressure peaks in the supply manifold 29) affect the equilibrium axial oscillation of the aforesaid plunger 43 of the electromagnetic actuator 40; the result is that the flow rate supplied by the low-pressure pump 7 is not correctly regulated, and similarly the flow of the high-pressure pump 6 is not regulated.

The aforesaid pressure peaks depend, among other factors, on the filling efficiency of the high-pressure pump 6 and on the speed (or number of revolutions) of said high-pressure pump 6 (a higher speed corresponds to greater instability in the flow delivery) .

In particular, the axial equilibrium of the plunger 43 is due to the equilibrium between the magnetic forces (indicated by the solid arrow in the aforesaid Figure 2), originating from the actuation of the electromagnetic actuator 40, and the hydraulic forces (indicated by the arrow in broken lines in said Figure 2), associated with the pressure waves in the supply manifold 29.

If the hydraulic forces (due to the aforesaid pressure peaks, for example) overcome the magnetic force, the axial equilibrium of the plunger 43 cannot be correctly

controlled, and neither can the flow rate, resulting in the appearance of instability in the flow rate of the high- pressure pump 6.

The present applicant has found that the existing control solutions are insufficiently robust in respect of disturbances created by the aforesaid oscillations of the hydraulic pressure.

In particular, existing control solutions provide for the regulation of the mean value of the excitation current in the coil of the electromagnetic actuator 40 by

controlling the duty cycle of a fixed-frequency PWM (pulse width modulation) drive voltage signal supplied to said electromagnetic actuator 40. Figure 3 shows a portion of the excitation current signal for the electromagnetic actuator 40, indicated by Iz _ME r in a given time interval. Figure 3 indicates the mean value of the excitation signal I _ZME ^ as well as the peak-to- peak amplitude of the oscillation about the mean value, called the 'ripple amplitude' .

In particular, as indicated above, the mean value of the excitation current determines the flow rate of the supply flow through the metering solenoid valve 20, while the ripple amplitude determines the oscillation amplitude of the plunger 43 of said metering solenoid valve 20, and therefore the capacity of the magnetic force generated by the excitation signal I _Z ME to oppose the hydraulic

disturbance forces, in other words the oscillations or peaks of pressure.

With this control technique, the ripple amplitude increases with an increase in the mean value of the

excitation current, as shown in Figure 4, which illustrates a ramplike trend of the excitation signal I _ZME ^

demonstrating the increase of the corresponding ripple amplitude as the mean value increases.

It should be noted, in particular, that, since the metering solenoid valve 20 is of the normally open type, a zero excitation current corresponds to a maximum flow, while a maximum excitation current (valve closed) corresponds to a minimum flow. High magnetic forces (high excitation current) are therefore reached in conditions of partial or reduced loading of the pump (that is to say, when the pressure peaks in the supply manifold 29 are lower) .

As demonstrated in Figure 5, which shows, the trend of the supply flow of the pump, indicated by F, for a ramplike trend of the excitation signal I _Z ME (only the mean value of which is shown) , the combination of high pressure peaks and reduced current amplitude may lead to instability of the pump flow.

In particular, the aforesaid Figure 5 demonstrates (within the circled portion of the graph) an area of instability in the control of the metering solenoid valve 20, in which the magnetic force generated is not sufficient to control the pressure oscillations, resulting in an instability in the flow rate.

Therefore, one aspect of the present solution provides that, in view of the aforesaid finding, the control

strategy of the metering solenoid valve 20 is to be

suitably modified to exert a control action on the value of the ripple amplitude, as well as on the mean value of the excitation signal I _ZME ^ in order to obtain sufficient control capacity (in opposition to the pressure peaks) over the whole of a desired operating range of the metering solenoid valve 20. In other words, the ripple amplitude is directly controlled by the electronic control unit 100, instead of having a value resulting from the control of the mean value of the excitation signal I _Z ME (as is the case in known solutions) .

In a possible embodiment, the reference value (or set point) of the ripple amplitude for the control may have a constant value, suitably selected to obtain the aforesaid sufficient capacity to oppose the pressure peaks.

In a preferred embodiment, the value of the ripple amplitude is variable and is controlled in a desired manner, particularly on the basis of a trend of the

pressure peaks, in order to determine an optimized value of the ripple amplitude on the basis of the corresponding value of the hydraulic disturbance forces.

In this context, Figure 6 shows a possible trend of the pressure peaks in the supply manifold 29, as a function of the mean value of the excitation signal I _ZME ^ for a given velocity of the high-pressure pump 6. In particular, this trend includes a sharp rise and a corresponding peak in a specific operating range of the metering solenoid valve 20, which in this case, for example, is between 40% and 60% of the whole operating range (considered between the zero value and the maximum value of the excitation current) .

Figure 7 shows the corresponding trend of the excitation signal I _ZME ^ according to the present control solution; in particular, Figure 7 demonstrates the upper and lower envelopes of said excitation signal I _ZME ^ together with the trend of its mean value.

Figure 8 shows the trend of the ripple amplitude

(considered as the difference between the aforesaid upper and lower envelopes) of the excitation signal I _ZME -

In particular, the ripple amplitude follows the corresponding trend of the pressure peaks, at least in a portion of the operating range of the metering solenoid valve 20, and shows a corresponding peak, which in the example is in the portion between 40% and 60% of the whole operating range. Outside this portion of the operating range (particularly for higher mean values of the

excitation signal I _ZME ) t the trend of the ripple amplitude rises linearly with the mean value.

Because of this trend, the ripple amplitude is

therefore sufficient to oppose the pressure oscillations (by ensuring that the magnetic force is equal to or greater than the corresponding hydraulic forces) .

The control scheme of the metering solenoid valve 20, implemented by the corresponding control unit 100, will now be described with initial reference to Figure 9.

In particular, the aforesaid control unit 100

comprises a first map module 101, which stores a map of the position of the pressure peaks within the supply manifold 29, as a function of the mean current value of the

excitation signal I _Z ME and also of the speed (or number of revolutions) of the high-pressure pump 6. This map may be determined on the workbench, during the characterization of the engine 3, and is stored in the non-volatile memory of the control unit 100, which also stores a suitable software program for the implementation of the aforesaid control scheme .

The control unit 100 further comprises a second map module 102, which stores a corresponding map of the ripple amplitude of the excitation signal I _ZME ^ plotted on the map of the pressure peaks supplied by the first map module 101. This map may also be determined on the workbench, during the characterization of the engine 3, and is stored in the non-volatile memory of the control unit 100.

As discussed above with reference to Figures 6-8, the second map module 102 returns the value of the ripple amplitude of the excitation signal I _Z ME for each operating point of the metering solenoid valve 20, so that the disturbance represented by the pressure peaks present in the supply manifold 29 (with the trend supplied by the first map module 101) can be balanced in the desired manner. For example, the second map module 102 supplies at its output the ripple amplitude based on the trend shown in the aforesaid Figure 8.

The control unit 100 further comprises a drive stage (driver) 104 coupled to the metering solenoid valve 20, configured so as to drive the corresponding electrical circuit 45 (and the corresponding coil) to generate the excitation signal I _ZME ^ which in this case has both a variable duty cycle and a variable frequency.

In a first embodiment, described in greater detail below, the drive stage 104 comprises a drive module 105 which implements a control of the ripple amplitude of the excitation signal I _ZM E·

In a second possible embodiment, shown in the same Figure 9, said drive stage 104 comprises a third map module 106 and a corresponding driver module 108 which implements a control of the duty cycle of the excitation signal I _ZME , which in this case has a frequency determined by the aforesaid third map module 106.

This third map module 106 stores a map of the value of the frequency of the excitation signal I _ZMEJ as a function of the ripple amplitude value supplied by the second map module 102. This map may be determined on the workbench, during the characterization of the engine 3, and is stored in the non-volatile memory of the control unit 100. When the mean value of the excitation signal I _ZM E has been fixed, the frequency of the excitation signal I _ZM E determines the ripple amplitude of said excitation signal I _Z ME (which increases as the frequency decreases) .

In greater detail, and as shown in Figure 10, the drive module 105 of the drive stage 104, in the first embodiment, comprises a comparator unit with hysteresis 110, which receives at its input a reference mean value (or set point) for the excitation signal I _Z ME (as a function of the desired value of the flow rate of fuel supplied to the high-pressure pump 6) , and also, as a further reference or control set point, the desired ripple amplitude value supplied by the second map module 102.

The comparator unit with hysteresis 110 also receives at its input, as feedback for the control action, the effective excitation signal I _ZM E, that is to say the current flowing through the electrical circuit 45 of the metering solenoid valve 20, measured by a suitable sensor coupled to said metering solenoid valve 20.

The comparator unit with hysteresis 110 generates at its output a square-wave pulsed signal Si _{mp (} of the on/off type) , which has a first value, for example a high value, when the effective excitation signal I _ZM E lies within the amplitude window defined by the aforesaid reference mean value and by the reference ripple amplitude (in particular, the ripple semi-amplitude is added to/subtracted from the mean value) and a second value, for example a low value, when the effective excitation signal I _Z ME lies outside said amplitude window.

The drive module 105 further comprises a power unit 112, supplied by a supply voltage V _ai , provided for example by the battery of the motor vehicle, and configured so as to generate a drive signal V _{P M} , in particular a pulse width modulation voltage signal, on the basis of the aforesaid pulse signal Si _mp generated by the comparator stage with hysteresis 110; this power unit 112 may comprise a DC/DC voltage converter, of the boost type for example (which is a known type not described here in detail) .

The drive signal V _{P M} is then supplied to the

electrical circuit 45 of the metering solenoid valve (ZME) 20, resulting in the generation of the excitation signal IZME and the corresponding magnetic force.

As illustrated in Figure 10, the drive module 105 may also comprise a measurement unit 114, which receives at its input the aforesaid effective excitation signal I _Z ME and calculates its mean current value. This mean value is sent to the input of the aforesaid first map module 101 of the control unit 100 and/or used for further control actions (in a way which is not illustrated here), as a feedback signal .

As shown in Figure 11, in the second embodiment the drive module 108 of the drive stage 104 comprises a control unit 120, of the PI (proportional integral) or PID

(proportional integral derivative) type for example, which receives at its input the reference mean value for the excitation signal I _Z ME (indicative of the desired value of the flow rate of fuel supplied to the high-pressure pump 6) , and also, as feedback, the mean current value of the effective excitation signal I _Z ME measured by a measurement unit, again indicated by 114, which receives at its input the aforesaid effective excitation signal I _ZM E and

calculates its mean current value.

Said control unit 120 also receives at its input the desired value of the frequency of the excitation signal I _ZM E supplied by the third map module 106 (on the basis of the desired value of the ripple amplitude) , and generates at its output the pulse signal Si _{mp (} of the on/off type) , for the power unit, which is again indicated here by 112; this power unit 112 is supplied, in this case also, by the supply voltage V _ai , and also receives at its input the frequency value supplied by the third map module 106.

In particular, the pulse signal Si _mp therefore has a frequency equal to the aforesaid frequency value supplied by the third map module 106 and a duty cycle determined by the feedback control action performed by the control unit

120.

In this case also, the power unit 112 is configured so as to generate, from the aforesaid pulse signal Si _mp , the drive signal V _{P M} which is supplied to the electrical circuit 45 of the metering solenoid valve 20.

The advantages of the present solution are evident from the preceding description.

In any case, it should be emphasized again that the control strategy described makes it possible to compensate suitably for the hydraulic forces due to the pressure peaks in the supply manifold 29 with the magnetic force generated by the metering solenoid valve 20, so as to reduce the flow disturbances for the high-pressure pump 6 (and for the engine 3) .

In particular, at full load, the frequency of the excitation signal I _Z ME may advantageously be lower (meaning that the current ripple amplitude is higher and the

magnetic force peaks are higher) , so as to reduce the fluctuation of the flow rate of the pump. Conversely, in conditions of low pump load, it is possible to use a high frequency of said excitation signal I _ZME ^ which is better than the low frequency because, in this case, the hydraulic forces are lower and a lower magnetic force is therefore sufficient to compensate for them.

In other words, the control strategy makes it possible to obtain the optimal control solution for any operating point, by contrast with the conventional control solutions (with a fixed frequency and a variable duty cycle) , thereby obtaining a more stable and controlled fuel supply.

Finally, it will be evident that what is described and illustrated can be modified and varied without departure from the protective scope of the present invention, as defined in the attached claims.

In particular, as illustrated in Figure 12, a further variant of the control scheme implemented by the control unit 100 may be provided.

In this case, the first map module 101, which stores the map of the position of the pressure peaks within the supply manifold 29, is not provided.

The control unit 100 comprises a pressure sensor 130, configured so as to detect the fluid pressure within the supply manifold 29 and to generate a pressure signal S _P ; and a processing module 131, coupled to the pressure sensor 130 and configured to detect the position and trend of the pressure peaks on the basis of the analysis of the

aforesaid pressure signal S _P (an example of the trend of which, showing the corresponding peaks, is illustrated in said Figure 12 ) .

In this case, the processing module 131 supplies to the second map module 102 the information recorded about the "map" (that is to say, the position in time) of the pressure peaks, for the determination, in a manner entirely similar to that discussed above, of the corresponding value of the ripple amplitude of the excitation signal

Iz _ME , such that the disturbance represented by the said pressure peaks can be balanced in the desired manner.

In this embodiment also, the control unit 100

comprises the drive stage 104 (not illustrated here) , configured so as to generate and supply the drive signal VP _W M to the electrical circuit 45 (and to the corresponding coil) of the metering solenoid valve 20, for the generation of the excitation signal I _ZME ; in particular, this drive stage 104, in this case also, may be made according to the first or the second embodiment (discussed above with reference to Figure 9 and Figure 10, respectively) .

It will also be apparent that the aforesaid first map module 101, where present, might receive at its input further parameters indicative of the operating point of the engine 3, in addition to the pump speed, including, for example, the amount of injection, the pressure in the common manifold ("common rail") , or other relevant

quantities .