EP2546499A1

EP2546499A1 - Electrical drive arrangement for a fuel injection system

Info

Publication number: EP2546499A1
Application number: EP11174004A
Authority: EP
Inventors: Joseph Engel
Original assignee: Delphi Technologies Holding SARL
Current assignee: BorgWarner Luxembourg Automotive Systems SA
Priority date: 2011-07-14
Filing date: 2011-07-14
Publication date: 2013-01-16
Anticipated expiration: 2031-07-14
Also published as: EP2546499B1

Abstract

An electrical drive arrangement for at least one fuel injector (54) of a fuel injection system comprises: a buffer capacitor (60) adapted to store energy; a charging stage (64) for charging said buffer capacitor (60) to a target charge voltage (V_charge); and an injector driver stage (52) operatively connected to a fuel injector (54). A voltage regulation device (62) is operatively connected between the buffer capacitor (60) and the injector driver stage (52) and configured to supply an operating voltage to the driver stage. A controller (82) is configured to determine said target charge voltage (V_charge) for the buffer capacitor (60) depending on pre-set conditions, while the charging stage (64) is adapted to receive from the controller an input representative of the target charge voltage.

Description

FIELD OF THE INVENTION

The present invention generally relates to automotive fuel injection and, more particularly, to an electrical drive arrangement for use in such a fuel injection system.

BACKGROUND OF THE INVENTION

Modern automotive vehicle engines are generally equipped with fuel injectors for injecting fuel (e.g. gasoline or diesel fuel) into the individual cylinders of the engine. The fuel injectors are coupled to a source of high-pressure fuel that is delivered to the injectors by way of a fuel delivery system. The fuel injectors typically employ a valve needle that is actuated to disengage and re-engage an associated valve seat so as to control the amount of high-pressure fuel that is metered from the fuel delivery system and injected into a corresponding engine cylinder. It is known to use solenoid-operated injectors in which an electrically driven solenoid is operably connected to the valve needle. Energizing the solenoid causes the valve needle to disengage from its seat, thus permitting fuel delivery, and de-energizing the solenoid causes the valve needle to re-engage its seat, thus preventing fuel delivery.
The injectors of the engine are controlled by an electrical drive arrangement that typically includes an injector driver stage that is supplied with power from a vehicle power supply, typically the vehicle battery, and provides power and control inputs to one or more fuel injectors.
The injector driver stage is a circuit arrangement that is configured to select a specific one of the injectors for operation and to apply an operating voltage thereto. The functionality of the injector driver stage is controlled by an Engine Control Unit (ECU) of the vehicle within which it is installed. A known problem is that such electrical drive arrangements do not operate under ideal conditions and are typically supplied with electrical power that is subject to spurious electrical oscillations, also referred to as 'noise'. A significant proportion of power supply noise can be compensated for by the injector drive stage under the control of the ECU since some sources of noise are predictable. However, some sources of noise are not predictable and such noise affects detrimentally the level of control that the ECU has over the operational timing of the injectors.
Voltage instability or voltage droop are particularly problematic with solenoid-actuated injectors because in such electromagnetic devices, the current flowing through the coil builds-up following an exponential curve when a constant driving voltage is applied. The slope at the beginning of this curve is a function of the applied voltage.
Another conventional design of electrical drive arrangement for fuel injectors employs a boost voltage supply 2 to drive the solenoid in the fuel injectors 4. This arrangement, illustrated in Fig.1, avoids a direct connection of the battery 6 to the injector drive stage 8. The boost voltage supply 2 typically comprises a DC-to-DC converter, which stores energy in a buffer capacitor 10 at a fixed voltage. The buffer capacitor 10 is then discharged into the solenoid of injector 4 to perform the scheduled injections. Because the buffer capacitor 10 is always fully charged to a fixed voltage prior to discharge, the pull-in current waveform is very repeatable. Also, the use of such capacitor permits, by way of the boost converter 2, to be loaded at a higher voltage than the battery voltage, and thus to pull open the injector with a higher voltage, thereby reducing its response time.
A shortcoming of such injector drive arrangement is however the temperature dependence of the capacitors, namely of widely used electrolytic type capacitors. Indeed, at cold temperatures a non-negligible voltage drop may exist in the capacitor, which will affect the available voltage for charging the injector coils and thus delay the actuation of the injectors.

OBJECT OF THE INVENTION

The object of the present invention is to provide an improved electrical drive arrangement for a fuel injector.
This object is achieved by an electrical drive arrangement as claimed in claim 1.

SUMMARY OF THE INVENTION

According to the present invention, an electrical drive arrangement for a fuel injector of a fuel injection system comprises:

a buffer capacitor adapted to store electric energy;
a charging stage for charging said buffer capacitor to a target charge voltage; and
an injector driver stage operatively connected to a fuel injector, the driver stage being operatively connected to the buffer capacitor.

According to an important aspect of the invention, a voltage regulation device is operatively connected between the buffer capacitor and the injector driver stage and configured to supply an operating voltage to the driver stage from the buffer capacitor.
A controller is configured to determine the target charge voltage for the buffer capacitor depending on pre-set conditions; the charging stage being in turn adapted to receive from the controller an input representative of the so-determined target charge voltage.
In the inventive present injector drive arrangement, a voltage regulation device is thus inserted between the buffer capacitor and the injector driver. The charging voltage of the buffer capacitor may be adapted (increased) under certain predetermined conditions, while the set point of the voltage regulation device is unaffected. This design allows providing an operating margin in the buffer capacitor, while the output voltage regulation device is not meant to be modified.
As it will be appreciated by those skilled in the art, increasing the charge voltage of the buffer capacitor allows compensating for low temperatures (i.e. high resistance) of the capacitor electrolyte, in order to alleviate (or avoid) droop in the voltage supplied by the voltage regulator device to the injector driver stage and thus maintain an acceptable response time of the injectors.
Accordingly, the controller may be configured to receive as input a temperature information representative of the operating temperature of the buffer capacitor and to adapt the target charge voltage depending on this temperature information. In practice, a calibrated map of target charge voltage vs. temperature may be used, as an increased target charge voltage would be required when the capacitor operating temperature is less than normal temperature (say 20-25°C).
Another possible measure against droop is closed loop monitoring of the output voltage delivered by the voltage regulation device. The controller may thus be configured to receive as input a voltage information representative of the voltage at the output of the voltage regulation device, and to adapt (typically increase) the target charge voltage when the voltage information indicates that the voltage at the output of said voltage regulation device falls outside a prescribed operating voltage range.
A further droop counter-measure may be to purposively adapt the target charge voltage ahead of an upcoming injection scheme, where it is known that it will increase the load on the drive arrangement, e.g. due to overlapping injection actuations.
It may be noted that the charging stage may comprise a boost converter or a step-down converter, or both. On most car systems, it will be desirable to charge the buffer capacitor to a target charge voltage higher than the conventional 12 V of the battery, and the boost converter is thus appropriate. In one embodiment, the boost converter comprises an input terminal connected to the power source (e.g. battery) and an inductance connected to the input terminal and serially connected with a MOSFET connected such that the coil is connected to input terminal and return.
However, with higher voltage batteries one could use a step down converter where the operating voltage of the injector driver stage is less than the battery nominal voltage.
Regarding the voltage regulation device, it may be designed in any appropriate way to deliver a constant output voltage. It may for example include a field effect transistor connected between the buffer capacitor and the injector driver stage in a source follower configuration. A filter device may be operatively connected between the gate terminal of the field effect transistor and the input of terminal of the voltage regulation device, thereby supplying a filtered voltage from the buffer capacitor as an input to the gate terminal.
According to another aspect of the present invention, a corresponding method of operating a fuel injection system with an electrical drive arrangement is proposed in claim 11. The buffer capacitor is charged to a target charge voltage that is determined depending on pre-set conditions, and the so-determined target charge voltage is applied as input parameter to said charging stage. Hence, the target charge voltage is dependent on operating circumstances, and used as charging set-point in the buffer capacitor.
Preferred embodiments of this method are recited in the appended dependent claims 12-14.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1:: is a diagram of a conventional and simple electrical drive arrangement for a fuel injector;
FIG. 2:: shows two graphs illustrating the effect of a cold capacitor electrolyte on the injector drive: a) injector current vs. time graph and b) capacitor voltage vs. time;
FIG. 3:: is a principle diagram of the present electrical drive arrangement for fuel injector;
FIG. 4:: shows two graphs illustrating the benefit of the electrical drive arrangement on the injector drive: a) voltage vs. time graph and b) injector current vs. time graph;
FIG. 5:: is a principle electrical circuit according to an embodiment of the present electrical drive arrangement.
FIG. 6:: is an alternative principle electrical circuit of the power supply side upstream of the voltage regulation device, comprising both step down and boost converters.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

As already explained, Fig.1 shows a conventional electrical drive arrangement for fuel injectors comprising a boost converter and buffer capacitor.
The main interest of such arrangement is that the injector actuation can be performed by supplying the injector solenoid from the buffer capacitor 10 and not directly from the battery 6. Thanks to the boost converter 2, the voltage in the buffer capacitor 10 can be set much higher than in the battery 6, which allows pulling open the injector 4 with a much higher voltage. Since this capacitor 10 is typically only partially discharged during injector actuation (opening), the voltage remains as constant as possible.
However, the electrolyte temperature may significantly affect the performance of the arrangement.
Without willingness to be bound by theory, it is recalled that in a solenoid actuator, the motion starts once sufficient magnetic energy has been accumulated and stored in the coil, the former being proportional to the square of the coil current.
For a coil, the applicable equation is U = L·dI/dt, where U is the voltage applied across the coil, L represents the coil inductance and di/dt is the current delta in a given time period. Solving this equation leads to a simplified integral expressing that the applied voltage will be integrated to form a product in Volts x seconds [V.s].
This implies that to reach this product value, the applied voltage is a key parameter to accurate reaction. A change in supply voltage will thus lead to errors in the injector response.
Turning now to Fig.2, there is shown the effect of the temperature on a buffer capacitor of the electrolytic type (widely used for cost reasons). At low temperatures, the resistance of the electrolyte increases significantly and leads to a perceptible voltage drop.
The voltage drop across the electrolyte reduces the voltage available for driving the solenoid and affects the response time of the solenoid and thus of the injector. This can be observed in Fig. 2a), where line 20 indicates the current level in the solenoid vs. time, when the electrolyte is at normal (ambient) temperature. Conversely, line 22 indicates the increase of the current in the solenoid over the same time period, when the capacitor electrolyte is cold (below 0°C). As can be seen, a given current level (e.g. 14 A) is reached later when the electrolyte is cold.
Fig.2 b) shows the voltage level in the buffer capacitor over the same time period. Line 24 indicates the relatively constant voltage when the electrolyte is at ambient temperature. Line 26 by contrast shows the significant voltage drop in the case of a cold electrolyte.
Fig.3 shows a principle diagram of one embodiment of the present electrical drive arrangement 50 for a fuel injector system in which an injector driver stage 52 provides power and control inputs to one or more fuel injectors 54 (only two are shown). The injector driver stage 52 is a circuit arrangement that is configured to select a specific one of the injectors 54 for operation and to electrically drive the latter (by application of an operating voltage) in order to deliver a predetermined quantity of fuel. The functionality of the injector driver stage 52 is controlled by an Engine Control Unit 56 (ECU) of the internal combustion engine on which it is installed. The configuration of the injector driver stage 52 is known in the art and is not the focus of the invention, and so will not be described in further detail herein.
It will be appreciated that the injector driver stage 52 is electrically supplied from a buffer capacitor 60 via a voltage regulation device 62. To perform an injection event, i.e. to open an injector 54 and deliver fuel, the buffer capacitor 60 is discharged into the injector 54 solenoid under the control of the driver stage 52. Reference sign 64 indicates a charging stage of the buffer capacitor 60, preferably a DC-to-DC boost converter. Such boost converter 64 permits charging the buffer capacitor 60 at a voltage higher than the power source 65 (e.g. a battery) to which it is connected, this being favorable for response time of the injector solenoid as explained above. Accordingly, the charging stage 64 is connected to an input terminal 66 of the buffer capacitor 60 via a first voltage supply line 68 and an output terminal 70 of the buffer capacitor 60 is connected to an input 72 of the voltage regulator device 62 via a second voltage supply line 74. The voltage regulator device 62 has an output terminal 76 connected to an input terminal 78 of the injector driver stage 52 via a third voltage supply line 80.
In this arrangement the buffer capacitor 60 with the boost converter 64 thus form the power supply of the injector driver stage 52.
The voltage regulator device 62, inserted between the buffer capacitor 60 and the injector driver stage 52 is, by definition, designed to maintain a constant voltage level at its output. This constant voltage is typically set in accordance with the operating voltage of the injector driver stage 52 as required for the driving the injectors. Accordingly, the voltage Vreg at terminal 76 is normally substantially equal to the operating voltage required for the driver stage 52. The regulator device 62 is also advantageously designed to stabilize the voltage supplied to the injector driver stage 52 against the voltage instabilities from the power supply side.
It shall be appreciated that the use of the voltage regulation device 62 furthermore allows operating the power supply formed by the buffer capacitor 60 with a higher voltage than the regulator output voltage Vreg at terminal 76. In other words, the buffer capacitor 60 can be charged to a target voltage that is higher than the regulator output voltage Vreg. This hence allows storing more energy than required in the buffer capacitor 60, in order to be able to discharge enough energy there from, as may be required under certain operating conditions.
Based on this capability, the present electrical drive arrangement 50 includes a controller 82 configured to determine a target charge voltage level for the buffer capacitor 60 depending on pre-set conditions. As it will be understood, this controller may be part of the ECU 56.
As explained above, one parameter that may significantly affect the charging of the injector solenoid, and thus the injector response time, is the operating temperature of the buffer capacitor 60. And this is particularly critical for electrolytic capacitors, where at low temperatures (say below room temperature ― less than 20-25°C) of the electrolyte, the internal losses in the buffer capacitor start to sensibly increase.
Therefore, the controller 82 is advantageously configured to receive a temperature information reflecting the temperature of the buffer capacitor and adapt the target charge voltage V_charge of the capacitor 60 depending on the operating temperature of the buffer capacitor 60. The temperature may be measured by a sensor and the corresponding temperature signal, indicated T in Fig.3, is applied as input to the controller 82. Based on this temperature signal T, the controller 82 in turn determines the appropriate target charge level of the buffer capacitor 60 and then a signal representative of the target charge voltage V_charge is applied to the boost converter 64. In practice, the controller 82 may use a map of the target charge voltages in function of the buffer capacitor temperature. Above 20 or 25°C, no compensation is needed and a single target value V_charge may be used. The map is thus calibrated to compensate for the losses in the buffer capacitor 60 due to temperature.
As it will appear to those skilled in the art, a higher target charge voltage will be used in practice at lower electrolyte temperatures. This implies a larger amount of heat dissipation in the voltage regulator. However, as the electrolyte temperature will increase, the controller 82 will decrease the target charge voltage.
This is how the present arrangement allows operating under "normal" operating condition with a "normal", constant target charge level, while being able of adapting the target charge level to higher voltages in order to increase the energy stored in the buffer capacitor 60 and thereby cope with situations of increased load.
Alternatively or additionally, the present arrangement may include a closed loop control of the regulator output voltage Vreg. Accordingly, a line 86 may connect output terminal 76 to an input in the controller 82. The controller may then be configured to increase the target charge voltage in case Vreg is too low (i.e. Vreg is less than a predetermined threshold). This closed-loop measure can be implemented alone or together with the buffer capacitor temperature control.
As a further possible compensation for increased load, the controller 82 may be configured to adapt the charging voltage on the basis of an upcoming injection scheme. This information is available in the ECU, e.g. from the fuel injection scheduler 84, which computes the injection parameters. If the controller 82 determines (is informed) that upcoming injection events are to be performed, where there may be concomitant or overlapping injection events, it can be programmed so as to increase in advance the target charge voltage to be able to cope with the increased load. Again, this control scheme may be conducted alone or in combination with the other schemes.
The benefits of the present electrical drive arrangement can be observed in Fig.4. In Fig.4a), lines 90 and 92 show, respectively, the hot (room temperature) and cold voltage traces of the buffer capacitor output in a conventional drive arrangement as in Fig.2. The result of the dramatic decrease of buffer cap voltage indicated by line 92 leads to a wrong current through the injector as indicated by line 94 in Fig.4b), compromising the injection timing.
Turning back to Fig.4a), line 96 represents the voltage regulation output voltage Vreg in the present drive arrangement as obtained with a cold electrolyte in the buffer capacitor 60. It is to be appreciated that the cold injector current trace as obtained with the present drive arrangement coincides with the hot current trace obtained with the conventional drive arrangement of Fig.1, as indicated by line 98.
Fig.5 now illustrates a principle electrical diagram corresponding to an embodiment of the present drive arrangement according to Fig.3. Same elements are indicated by same reference signs.
As can be seen, the boost converter 64 may comprise an inductance 100 connected to an input terminal 102 and serially connected with a MOSFET 104 connected such that the coil 100 is connected to input terminal 102 and return. Hence the coil will be charged with magnetic energy during the ON-state of the transistor, until the transistor 104 is commanded off. During off state of the transistor 104, the stored energy and the associated current in the coil 100 is transferred across the diode 106 into the capacitor 60, closing the loop across the return wire and the engine supply system. This operation will be repeated until the charge state of the capacitor 60 matches the target charge voltage.
It may be noted that the boost converters are known in the art and any appropriate circuit able to charge the capacitor 60 at a voltage higher than supply 65 may be considered instead of the above described converter design.
For the buffer capacitor 60, only one capacitor is illustrated, but it may comprise an assembly of capacitors.
The voltage regulation device 62 may be designed as described e.g. in WO 2008/152039 . It comprises an N-channel metal oxide semiconductor field-effect transistor 110 (hereinafter 'MOSFET'), which includes a drain terminal 112, a source terminal 114 and a gate terminal 116. The drain terminal 112 of the MOSFET 110 is connected to the input terminal 72 of the voltage regulation device 62 and the source terminal 114 of the MOSFET 110 is connected to the output terminal 76 of the voltage regulation device 62.
The gate terminal 116 of the MOSFET 110 is connected to the input terminal 72 of the voltage regulation device 62 through a low pass filter 118 comprising a resistor element 120 and a capacitor element 122 that are connected to each other at a node 124. The gate terminal 116 of the MOSFET 110 is connected to the node 124 and is, therefore, connected to the input terminal 72 through the resistor element 120 and is connected to a ground connection 126 through the capacitor element 122. The low pass filter 118 generates a filtered output voltage V_F at the node 124, which forms an input voltage signal to the gate terminal 116 of the MOSFET 110.
The values of the resistor element 120 and the capacitor element 122 are advantageously configured to the electrical dynamics of the injector such that the low pass filter 118 operates to block those frequencies present on the voltage supply line 74 that the ECU 56 cannot compensate and pass those frequencies which the ECU 56 can compensate.
Particularly advantageous values of the resistor element 120 and capacitor element 122 are preferably selected so as to provide the low pass filter 118 with a time constant of approximately 1 millisecond (ms), which corresponds to a filter cut-off frequency of approximately 160 Hertz (Hz). Furthermore, the value of the capacitor element 122 is selected to be significantly greater than the parasitic capacitance of the MOSFET 110, preferably, between ten and one hundred times greater than the parasitic capacitance.
As is shown in Figure 5, the MOSFET 110 is arranged in a 'source follower', or 'common drain', configuration such that voltage between the gate terminal 116 and the source terminal 114, which is derived from the low pass filter 118, determines the conductivity of the MOSFET 110 from the drain terminal 112 to the source terminal 114.
Since the gate terminal 116 is shielded from the high frequency noise present on the power supply line 74 by the low pass filter 118, the conductivity of the MOSFET 110 from the drain terminal 112 to the source terminal 114 is substantially constant. As a result, the voltage present at the source terminal 114 of the MOSFET 110, and therefore the voltage present at the output terminal 76 of the voltage regulation device 62 , are substantially free from noise.
As it will be understood, while a particular electrical circuitry has been described herein for the various components of the present electrical drive arrangement, those skilled in the art may devise other electrical circuits for achieving similar functions. In particular, alternative designs for the voltage regulation device 62 may be found in WO 2008/152039 .
As already stated above, the charging stage of the buffer capacitor 60 can be designed as step up converter, (see Figs. 3 and 5), or as step down converter to charge the buffer capacitor at lower voltages than the power source 65, or even with both types of converters.
This latter option is illustrated in Fig.6, where a step down converter and a step up converter are arranged in sequence before the buffer capacitor 60. For simplicity, only the buffer capacitor and its charging stage are shown in Fig.6; it is however clear that downstream terminal 70 may be connected to terminal 72 of the voltage regulation device as in Fig. 5. As can be seen, the step down converter 130 has an input terminal 132 connected to the power supply 65 and an output terminal 134 connected to the input of the boost converter 64. A MOSFET 136 is commutated such that the coil 100 is connected to input terminal 132 and the output diode 106. Hence the coils will be charged with magnetic energy during the ON-state of the transistor, until the transistor 136 is commanded off. During off state of the transistor 136, the stored energy and the associated current in the coil 100 is transferred across the diode 140 into the capacitor 60, closing the loop across the return wire. This operation will be repeated until the charge state of the capacitor matches the target.

Claims

An electrical drive arrangement for at least one fuel injector (54) of a fuel injection system comprising:
a buffer capacitor (60) adapted to store energy;

a charging stage (64; 130) for charging said buffer capacitor (60) to a target charge voltage (V_charge);

an injector driver stage (52) operatively connected to a fuel injector (54),

said driver stage being operatively connected to said buffer capacitor (60);

characterized by

a voltage regulation device (62) operatively connected between said buffer capacitor (60) and said injector driver stage (52) and configured to supply an operating voltage to said injector driver stage; and

a controller (82) configured to determine said target charge voltage (V_charge) for said buffer capacitor (60) depending on pre-set conditions;

wherein said charging stage (64; 130) is adapted to receive from said controller (82) an input representative of said target charge voltage (V_charge).
The arrangement according to claim 1, wherein said controller (82) receives as input a temperature information representative of the operating temperature of said buffer capacitor (60) and is configured to adapt said target charge voltage (V_charge) depending on said temperature information.
The arrangement according to claim 1 or 2, wherein said buffer capacitor (60) is of the electrolytic type.
The arrangement according to claim 1, 2 or 3, wherein said controller (82) receives as input a voltage information representative of the voltage (V_reg) at the output of said voltage regulation device (62), and adapts said target charge voltage (V_charge) when said voltage information indicates that the voltage at the output of said voltage regulation device falls outside a prescribed operating voltage range.
The arrangement according to any one of the preceding claims, wherein said controller (82) is configured to adapt said target charge voltage (V_charge) depending on an upcoming injection scheme at said fuel injector.
The arrangement according to any one of the preceding claims, wherein said buffer capacitor (60) comprises one or more capacitors.
The arrangement according to any one of the preceding claims, wherein said charging stage (64) comprises a boost converter and/or a step-down converter.
The arrangement according to claim 7, wherein said boost converter (64) comprises an input terminal (102) connected to a power source (65) and an inductance (100) connected to said input terminal (102) and serially connected with a MOSFET (104) connected such that the coil (100) is connected to input terminal (102) and return.
The arrangement according to any one of the preceding claims, wherein the voltage regulation device (62) includes a field effect transistor connected between said buffer capacitor (60) and the injector driver stage (52) in a source follower configuration.
The arrangement according to claim 9, wherein a filter device is operatively connected between the gate terminal of the field effect transistor and the input of terminal of the voltage regulation device, thereby supplying a filtered voltage from the buffer capacitor as an input to the gate terminal.
A method of operating a fuel injection system with an electrical drive arrangement comprising: a buffer capacitor (60) adapted to store energy; a charging stage (64; 130) for charging said buffer capacitor (60); an injector driver stage (52) operatively connected to a fuel injector (54), said driver stage being operatively connected to said buffer capacitor (60); a voltage regulation device (62) operatively connected between the buffer capacitor (60) and the injector driver stage (52) and configured to supply an operating voltage to the driver stage;
wherein said buffer capacitor is charged to a target charge voltage that is determined depending on pre-set conditions, and the so-determined target charge voltage is applied as input parameter to said charging stage.
The method according to claim 11, wherein said target charge voltage is determined depending on said operating temperature of said buffer capacitor (60).
The method according to claim 11 or 12, wherein said target charge voltage is adapted when the voltage at the output of said voltage regulation device falls outside a prescribed operating voltage range
The method according to claim 11, 12 or 13, wherein said target charge voltage is adapted depending on a fuel injection scheme.