DE102007028344B4 - Current measuring module, current control circuit and current measuring method - Google Patents

Abstract

Current measuring module (40, 50) for measuring a current through a metering unit (70) for a common rail pump of an injection system in a motor vehicle, with
- two inputs (46; 47) connected to a first end and a second end, respectively, of a shunt resistor (21) connected in series with the metering unit (70) and across which a shunt voltage drops; and
a delta-sigma modulator (43) connected to the two inputs (46; 47) and converting the shunt voltage into a digital output whose average value corresponds to the shunt voltage;
a diode (41) which is connected on the anode side to a voltage source (Vdd),
a booster capacitor (42) having one side connected to the cathode of the diode (41) and the other side connected to one side of the shunt resistor (21),
- Wherein the node between the diode (41) and booster capacitor (42) is connected to a power supply input of the delta-sigma modulator (43).

Description

STATE OF THE ART

The present invention relates to a current measuring module and a method for measuring the current through a metering unit for a common rail pump of an injection system in a motor vehicle. The invention further relates to a current control circuit having such a current measurement module.

In modern injection systems, in particular in diesel injection systems, a common high-pressure fuel line, the so-called "common rail" (hereinafter also referred to as "rail"), is used to supply the cylinders with fuel with appropriate outlets to the individual cylinders. The pressure in the rail is kept constant via a control loop. In this case, the pressure is detected by a pressure sensor and regulated to a predetermined value. This predetermined value is calculated with the help of comparators and maps.

In such a map results from a calculated amount of fuel to be delivered a current setpoint with which the metering unit of a fuel delivery pump is driven. This metering unit has a solenoid valve which, in the opened state, allows fuel to flow from a fuel reservoir to the rail and, in the closed state, separates the connection between the fuel reservoir and the rail. Resistance and inductance of the solenoid valve are dependent on the temperature, so that a current control is provided, which regulates the current through the solenoid valve to a predetermined value.

1 FIG. 12 is a schematic representation of a typical current control circuit 10 for the current through the solenoid valve (shown here as impedance 71) of the metering unit of a common rail pump 70.

The current control circuit 10 in 1 has a shunt resistor 11 and a MOSFET transistor 12 on which in series with the solenoid valve 71 the metering unit are connected. The transistor 12 is with source and drain between the shunt resistor 11 and ground potential V_gnd connected. An analog operational amplifier 13 compares the potentials at both ends of the shunt resistor 11 with each other and outputs a comparison signal to an analog / digital converter 14 a microcontroller 15 out. Between the drain of the transistor 12 and the supply potential V_bat is also a freewheeling diode 16 intended.

The potential difference between the two ends of the shunt resistor 11 , and thus the size of the comparison signal, depends on the current through the shunt resistor 11 from. The microcontroller 15 compares the digitized comparison signal with a reference signal and thus determines whether the through the solenoid valve 71 flowing current corresponds to a predetermined value. If the microcontroller 15 Detects that through the solenoid valve 71 flowing current does not correspond to the predetermined value, then controls the microcontroller 15 the current to the specified value. For this purpose, an output PWM of the microcontroller 15 to the gate of the transistor 12 connected. The microcontroller 15 controls the gate by pulse width modulation (PWM), the microcontroller 15 the duty cycle of the PWM adapts to any deviations between the setpoint and the actual value of the current through the solenoid valve 71 auszuregeln.

The characteristic between solenoid valve current on the one hand and metered amount of fuel on the other hand is very steep. This means that even a very small change in the solenoid valve current leads to a large change in the metered amount of fuel. Consequently, the current detection must be very accurate. This in turn means that high demands are placed on the amplifier accuracy. Furthermore, in the case of a load dump, the supply voltage of, for example 24 V up to 60 V increase. For this reason, a high common-mode rejection of, for example, 80 dB is required. Finally, because of the high voltages occurring during the load dump, a high dielectric strength is also necessary. These requirements require that operational amplifiers be used with input-side, specially balanced, resistor networks; however, such opamps are relatively expensive.

The DE 102 00 650 A1 shows a device for detecting a load current through a load.

ADVANTAGES OF THE INVENTION

Accordingly provided is a current measuring module having the features of patent claim 1 and a method having the features of patent claim 11.

The idea underlying the invention is to convert the voltage drop via a shunt resistor, which is arranged in series with the metering unit, by means of a delta-sigma modulator into a digital signal. The mean value of this signal corresponds to the value of the voltage drop across the shunt resistor.

A major advantage of the proposed arrangement is that all the requirements that be placed on the measuring system, namely high accuracy, high common mode rejection and high DC voltage resistance, can be realized with significantly lower costs. In particular, the proposed arrangement does not require an expensive balanced operational amplifier with input-side resistor network.

The current measurement module may further comprise a level shifter which converts the potential of the digital signal into a value related to a reference potential (e.g., ground). Thus, the potential of the digital signal is converted to a uniform reference value and can be further processed by downstream components.

In addition, the current measuring module further comprises: a diode which is connected on the anode side to a voltage source, and a booster capacitor whose one side is connected to the cathode of the diode and the other side to one side of the shunt resistor, wherein the node between the diode and booster capacitor with a voltage supply input of the delta-sigma modulator is connected. Thus, a bootstrap circuit is realized, which ensures a voltage supply of the delta-sigma modulator, which satisfies the fluctuating level at the shunt resistor.

The current measurement module may further comprise a filter which converts the digital output signal into a low-pass filtered output signal. This filter can be designed as an analog low-pass filter, for example as an RC or LC network, or as a digital filter. A digital filter can be designed as an FIR filter. This has the advantage that the FIR filter can be programmed directly in the microcontroller of a control unit, which leads to cost savings.

There are also cost advantages of integrating the current measurement module with other functional modules in an ASIC or the like.

• - ein erfindungsgemäßes Strommessmodul,
• - ein Steuergerät, welchem das Ausgangssignal zugeführt wird, und
• - einen Schalter, welcher zwischen der von der Zumesseinheit abgewandten Seite des Shuntwiderstands und einem Versorgungspotential angeschlossen ist,
• - wobei das Steuergerät den Schalter in Abhängigkeit von dem Ausgangssignal ansteuert.

A current control circuit according to the invention for regulating a current through a metering unit for a common rail pump of an injection system in a motor vehicle, comprises the following:

• a current measuring module according to the invention,
• a controller to which the output signal is supplied, and
• a switch which is connected between the side of the shunt resistor facing away from the metering unit and a supply potential,
• - Wherein the controller drives the switch in response to the output signal.

It is advantageous if the switch is designed as a MOSFET transistor, which is driven by pulse width modulation of the control unit. In such an arrangement, the advantages of the proposed arrangement are particularly evident, since the level at the shunt resistor fluctuates due to the pulse width modulation between the two supply potentials. With the proposed arrangement can be accommodated by using a delta-sigma modulator, which can be realized inexpensively.

The controller may include an FIR filter which filters the output signal. Thus, the FIR filter can be inexpensively integrated, for example as a program module in the control unit.

list of figures

• 1 ein Blockschaltdiagramm, welches die Stromregelung in einer herkömmlichen Anordnung zeigt;
• 2 ein Blockschaltdiagramm, welches ein Strommessmodul und eine Stromregelungsschaltung nach einer ersten Ausführungsform der Erfindung darstellt; und
• 3 ein Blockschaltdiagramm, welches ein Strommessmodul und eine Stromregelungsschaltung nach einer zweiten Ausführungsform der Erfindung darstellt.

The invention will be explained in more detail with reference to the exemplary embodiments indicated in the schematic figures of the drawings. It shows:

• 1 a block diagram showing the current control in a conventional arrangement;
• 2 a block diagram illustrating a current measuring module and a current control circuit according to a first embodiment of the invention; and
• 3 a block diagram illustrating a current measuring module and a current control circuit according to a second embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

In all figures of the drawings, identical or functionally identical elements - unless otherwise stated - have been provided with the same reference numerals.

2 shows a block diagram, which is a current measuring module 40 and a current control circuit 20 represents a first embodiment of the invention.

The current control circuit 20 regulates the current flowing through the solenoid valve 71 (shown here as impedance) of the metering unit of a common rail pump 70 flows. Measures or records the current measurement module 40 the current through the solenoid valve 71 By reducing the voltage drop across a shunt resistor 21 converted into a digital output signal and this a control unit 60 supplies. The control unit 60 may preferably be designed as a microcontroller. If the value of the determined output signal deviates from a predetermined comparison value, then the control unit regulates 60 the current to the specified setpoint by controlling a switch 22 ,

This arrangement is described in more detail below: The solenoid valve 71 , the shunt resistor 21 and the switch 22 are in series between a first supply potential V_bat and a second supply potential V_grnd connected. In the illustrated embodiment, the switch 22 designed as a self-blocking n-MOSFET transistor whose source with the second supply potential V_gnd connected is. The solenoid valve 71 is with the first supply potential V_bat connected and the shunt resistor 21 is between the solenoid valve 71 and the drain of the transistor 22 arranged.

The two connections of the shunt resistor 22 are respectively with a first entrance 46 or a second input 47 of the current measurement module 40 connected. The first entrance 46 is
with the on the side of the solenoid valve 71 located connection of the shunt resistor 22 whereas the second entrance 47 with the on the side of the transistor 22 located connection of the shunt resistor 22 connected is. The current measurement module 40 has a diode 41 , a booster capacitor 42 , a delta-sigma modulator 43 , a level shifter 44 and a low-pass filter 45 on. The diode 41 is connected on the anode side to a third supply potential Vdd. The third supply potential can, to the second supply potential V_gnd referred, for example, 5 V, while the first supply potential V_bat , to the second supply potential V_gnd based, for example 24 V is. The cathode of the diode 41 is with one side of the booster capacitor 42 connected. The other side of the booster capacitor 42 is with the second entrance 47 connected. The node between the cathode of the diode 41 and the capacitor 42 is connected to a power supply input of the delta-sigma modulator 43 connected. The diode 41 and the booster capacitor 42 together form a bootstrap circuit, whose operation is explained below. Furthermore, the first entrance 46 and the second entrance 47 with corresponding first and second inputs of the delta-sigma modulator 43 connected. The node between the shunt resistor 21 and the transistor 22 (ie the second entrance 47 ) is via a freewheeling diode 23 with the first supply potential V_bat connected.

The delta-sigma modulator 43 converts the potential difference between the two inputs 46 and 47 into a digital signal. The delta-sigma modulator 43 may comprise a differential element, an integrator, a comparator and a 1-bit memory, which are connected in series. The output of the 1-bit memory is applied via a 1-bit digital / analog converter to the negative input of the differential element. Thus, the mean value of the output signal of the delta-sigma modulator 43 due to the negative feedback loop always equal to the input signal. The delta-sigma modulator 43 may be a first-order or higher-order delta-sigma modulator.

The delta-sigma modulator 43 Downstream is a level shifter 44 , which converts the potential of this digital signal into a reference potential V_gnd converted value. The level shifter 44 Consequently, it outputs a digital output signal which can assume two values (HI and LO, or 0 and 1), ie a binary signal. This output signal has an average of the voltage drop across the shunt resistor 21 and thus the current through the solenoid valve 71 equivalent. In particular, this average value is essentially the current through the solenoid valve 71 proportional.

The level shifter 44 output signal is from the low-pass filter 45 low-pass filtered and thus converted into an analog signal. The low pass filter 45 is an analog low-pass filter in the present embodiment 45 and may be implemented, for example, as an RC network or LC network.

The low pass filtered output becomes an analog to digital converter 61 of the control unit 60 supplied, which converts this analog signal into a digital signal. This digital signal thus corresponds to the mean value of the through the solenoid valve 71 flowing current (actual value) and can be further processed in the control unit 60 be used. In particular, the controller compares 60 the value of this digital signal with a setpoint of the through the solenoid valve 71 flowing electricity. In the event of a deviation between the actual value and the setpoint, the control unit controls 60 the current through the solenoid valve 71 to the setpoint. For this purpose, an output PWM of the controller 60 to the gate of the transistor 22 connected. The control unit 60 controls the gate of the transistor 22 by pulse width modulation (PWM), wherein the control unit 60 the duty cycle of the PWM adapts to any deviations between the setpoint and the actual value of the current through the solenoid valve 71 auszuregeln.

The current measurement module 40 , the control unit 60 and the series connection of shunt resistor 21 and transistor 22 together form a current control circuit 20 ,

In operation flows through the solenoid valve 71 a pulse width modulated current through the solenoid valve 71 and the shunt resistor 21 , Because the solenoid valve 71 is essentially an inductive load is a freewheeling diode 23 between the ground-side end of the shunt resistor 21 and the supply potential V_bat provided, which takes over the current flow when the transistor 22 locks.

Depending on whether the transistor 22 locks or conducts, the potential changes at the second input 47 between V_bat and V_gnd , For this reason, the bootstrap circuit is made of diode 41 and booster capacitor 42 intended. When the transistor 22 conducts (entrance 47 on V_gnd ) becomes the capacitor 42 over the diode 41 charged to Vdd. Locks the transistor 22 (Entrance 47 on V_bat ), then the capacitor potential is on V_bat + Vdd raised. This ensures that the supply potential which is the delta-sigma modulator 43 is supplied, always at Vdd above the shunt resistance potential at the second input 47 lies. Vdd can look like a voltage divider V_bat be provided or else be provided from a separate power source.

The output signal of the delta-sigma modulator 43 is thus a bitstream whose level is between V_gnd and V_bat commutes or "flies". This flying bitstream level is provided by the level shifter 44 pressed on a value that points to the supply potential V_gnd , that is, based on mass.

The use of the delta-sigma modulator 43 In the arrangement described above brings several advantages. The delta-sigma modulator 43 is the input signal of the voltage drop across the shunt resistor 21 fed. In other words, the delta-sigma modulator 43 "Only" sees the voltage drop across the shunt resistor 21 , Consequently, the arrangement described above has excellent common-mode rejection.

Furthermore, with the delta-sigma modulator 43 excellent measurement accuracy can be achieved. The measurement accuracy depends essentially on the sampling rate of the delta-sigma modulator 43 or from the delta-sigma modulator 43 supplied clock from. It is therefore advantageous if the sampling rate of the delta-sigma modulator 43 for example, at least 60 kHz.

Finally, a significant advantage of the arrangement described above is that it is relatively inexpensive to manufacture. Thus, the current measurement module can be made of comparatively low-cost standard components and does not require a costly analog operational amplifier or an expensive, elaborately balanced resistor network at the input of such an analog operational amplifier.

Another advantage of the arrangement described above is that the flying level at the output of the delta-sigma converter can be relatively easily converted with the level-shifter and brought to a ground-related value, since it is a digital signal. In contrast, this level conversion would be much more expensive when using an analog amplifier with booster capacitor.

The current measurement module 40 can be realized as an independent component, eg ASIC (application specific integrated circuit). It is also possible, the shunt resistor 21 to integrate into such an ASIC. The shunt resistor 21 but can, as in 2 shown, also be provided separately. Furthermore, the low-pass filter 45 , as in 2 shown in the current measurement module 40 be integrated, but it can also be provided as a separate component.

3 shows a block diagram, which is a current measuring module 50 and a current control circuit 30 represents a second embodiment of the invention.

In 3 are elements whose function is that of elements in 2 corresponds, have been provided with the same reference numerals and not explained in detail for reasons of scarcity.

According to the second embodiment, the current measuring module comprises 50 a diode 41 , a booster capacitor 42 , a delta-sigma modulator 43 and a level shifter 44 , These elements have substantially the same function as the corresponding elements of the first embodiment. In contrast to the first embodiment is in the current measurement module 50 but no low-pass filter 45 intended. In other words, this corresponds to the current measurement module 50 output signal to the (level-matched) digital output signal of the level shifter 44 in the first embodiment.

The output signal of the current measuring module 50 becomes a control device 80 (Which may be designed in particular as a microcontroller) and supplied by a digital filter 81 of the control unit 80 filtered. The digital filter 81 replaces the analog filtering with the low-pass filter 45 ,

The current measurement module 50 , the control unit 80 and the series connection of shunt resistor 21 and transistor 22 together form a current control circuit 30 ,

In addition to the advantages of the first embodiment, this arrangement has the advantage that a conversion of the output signal of the level shifter in analog and back into a digital signal with the associated tolerances and quantization errors omitted. So it is achieved a higher accuracy.

The digital filter 81 can be realized as a FIR filter in the control unit. This has the advantage that the FIR filter can be programmed as a software component in the control unit, resulting in further cost savings.

Although the above embodiment has been described above with reference to preferred embodiments, it is not limited thereto but modifiable in a variety of ways. In particular, various features of the embodiments described above can be combined with each other.

So that was the switch 22 designed in the embodiments described above as a MOSFET and by the solenoid valve 71 flowing current was pulse width modulated. However, the present invention is not limited thereto and is applicable to arrangements in which the switch 22 for example, designed as a bipolar transistor and the current through the solenoid valve 71 controlled in a different way.

Furthermore, the current measurement module 40 respectively. 50 shown as a separate module, for example as a stand-alone ASIC. However, it is also possible to use the current measurement module 40 respectively. 50 with other modules to a more complex ASIC or summarize the current measurement module 40 respectively. 50 as an add-on to a more complex ASIC. In this way, there are further cost advantages. Furthermore, it is also possible, the current measuring module 40 respectively. 50 in the control unit 60 respectively. 80 to integrate.

Claims (11)

Current measuring module (40, 50) for measuring a current through a metering unit (70) for a common rail pump of an injection system in a motor vehicle, with - two inputs (46; 47) connected to a first end and a second end, respectively, of a shunt resistor (21) connected in series with the metering unit (70) and across which a shunt voltage drops; and a delta-sigma modulator (43) connected to the two inputs (46; 47) and converting the shunt voltage into a digital output whose average value corresponds to the shunt voltage; a diode (41) which is connected on the anode side to a voltage source (Vdd), a booster capacitor (42) having one side connected to the cathode of the diode (41) and the other side connected to one side of the shunt resistor (21), - Wherein the node between the diode (41) and booster capacitor (42) is connected to a power supply input of the delta-sigma modulator (43). Current measuring module (40, 50) according to Claim 1 , further comprising: - a level shifter (44) which converts the potential of the digital signal into a value related to a reference potential (V_gnd). A current measuring module (40, 50) according to any one of the preceding claims, further comprising: - A filter (45, 81), which converts the digital output signal into a low-pass filtered output signal. Current measuring module (40, 50) according to Claim 3 , wherein the filter is designed as an analog low-pass filter (45). Current measuring module (40, 50) according to Claim 3 , wherein the filter is designed as a digital filter (81). Current measuring module (40, 50) according to Claim 5 , wherein the filter is designed as an FIR filter (81). Current measuring module (40, 50) according to one of the preceding claims, which is integrated with other functional modules in an ASIC. A current control circuit (20, 30) for controlling a current through a metering unit (70) for a common rail pump of an injection system in a motor vehicle, with a current measuring module (40, 50) according to one of the preceding claims, - A control unit (60, 80), to which the output signal is supplied, and a switch (22) which is connected between the side of the shunt resistor (21) facing away from the metering unit (70) and a supply potential (V_gnd), - Wherein the control unit (60, 80) controls the switch (22) in response to the output signal. Current control circuit (20, 30) after Claim 8 , wherein the switch (22) is designed as a MOSFET transistor, which is driven by pulse width modulation of the control unit (60, 80). Current control circuit (20, 30) after Claim 8 or 9 wherein the controller (60, 80) comprises an FIR filter (81) which filters the output signal. A method of measuring the current through a metering unit (70) for a common rail pump of an injection system in a motor vehicle, the method comprising the steps of: Providing a shunt resistor (21), connected in series with the metering unit and across which a shunt voltage drops, to a diode (41), which is connected on the anode side to a voltage source (Vdd), to a booster capacitor (42), one side thereof the cathode of the diode (41) and the other side thereof being connected to one side of the shunt resistor (21), the node between the diode (41) and the booster capacitor (42) being connected to a power supply input of the delta-sigma modulator (43); and - Converting the shunt voltage with a delta-sigma modulator (43) into a digital output signal whose mean value corresponds to the current to be measured.

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