WO2016041658A1

WO2016041658A1 - Calibration of current sensors by means of reference current

Info

Publication number: WO2016041658A1
Application number: PCT/EP2015/066379
Authority: WO
Inventors: Wolfgang Jöckel; Wolfgang Fritz
Original assignee: Continental Teves Ag & Co. Ohg
Priority date: 2014-09-17
Filing date: 2015-07-17
Publication date: 2016-03-24

Abstract

The invention relates to a method for calibrating a current sensor (20) in a vehicle (2), said sensor being designed to measure an electric current (6) through a measuring resistor (28) on the basis of a voltage drop (32) across the measuring resistor (28) and a rule (46) depending on the measuring resistor (28) for comparing the voltage drop (32) and the electric current (6). Said method comprises the following steps: - impressing a known electric calibration current (58) onto the measuring resistor (28), - measuring a calibration voltage drop (32) produced by the calibration current (58) across the measuring resistor (28), and - calibrating the rule (44) depending on the measuring resistor (28) on the basis of a comparison of the calibration current (58) and the calibration voltage drop (32).

Description

Calibration of current sensors by means of reference current

The invention relates to a method for measuring a current with a current sensor.

Electric currents in and out of a vehicle battery are measured, for example, in DE 10 2009 044 992 A1 and in DE 10 2004 062 655 A1 with a current sensor via a measuring resistor, also called a shunt.

It is an object of the present invention to improve the known method for current measurement.

The object is solved by the features of the independent claims. Preferred further developments are subject of the dependent claims from ^¬.

According to one aspect of the invention, a method of calibrating a current sensor in a vehicle, which is turned ^¬ aligned, an electric current based on a voltage drop across the sensing resistor and a dependent measuring resistor provision for a comparison ^¬ position of the voltage drop and the electrical through a measuring resistor To capture current, comprising:

Impressing a known electrical calibration current into the measuring resistor,

Detecting a calibration voltage drop caused by the calibration current at the measuring resistor, and

Calibrate the regulation dependent on the measuring resistor based on a comparison of the calibration current and the calibration voltage drop.

The specified method is based on the consideration that used in vehicles, especially in motor vehicles Reach prediction current sensors could detect the state of charge of a battery in the vehicle. For this purpose, the current sensor has a high requirement for its accuracy over a long period of more than 15 years. However, an age-related long-term drift of the current sensor can not be avoided. This is seen in conventional current sensors at over 1.5% to the aforementioned 15 years. However, the long-term drift should be much smaller than 1%. This is where the specified method with the suggestion not to suppress the long-term drift, because technically this would probably only be possible with an economically unreasonable effort, but a processing instruction for a measurement signal in the current sensor, from which the electrical current to be measured is determined to calibrate. In herkömm ^¬ present current sensors is detected as a measuring signal a voltage drop across a measuring shunt through which the electric current flows to be measured. In a per se known manner, a Ge ^¬ genüberstellung of the voltage drop and the current to be measured to the electric resistance of the measurement leads Hunts. If, in the basic principle, the electrical resistance of the measuring shunt is known, the electric current can therefore be determined if the measuring shunt is known. However, the resistance value of the electric resistance is subject to the aforementioned long-term drift. Therefore, a stored resistance value for the measurement shunt can be calibrated, ie readjusted, by applying a known calibration current to the measurement shunt and detecting the resulting calibration voltage drop, whereby the effect of the long-term drift is masked out.

In a further development, the specified method comprises the step impressing the calibration current into the measuring resistor a power source. A current source outputs a constant current independent of the applied electrical load. This is particularly favorable in the present case, because the shunt and thus the electrical load are not known. The constant current source thus ensures that a guaranteed calibration current flows through the measuring shunt.

In a particular embodiment, the specified method comprises the steps:

Charging an energy store, and

Applying an energy storage voltage of the charged energy storage to the power source for impressing the calibration current in the measuring resistor. The energy storage can temporarily provide correspondingly high power levels to operate the constant current source. In this way, less stringent requirements need to be made of the electrical power supply of the current sensor itself.

In a particularly preferred embodiment, the energy store is a capacitor. The capacitor serves in addition to the aforementioned energy storage at the same time for smoothing the retrieved from the actual power supply electrical power and thus reduces the power loss that would occur without smoothing in a sudden retrieval of the aforementioned high performance.

Conveniently, an electrolytic capacitor should be used as a capacitor, because they have particularly small capacities in particularly high capacity of the specified method exporting current sensor does not increase excessively in size. In another development of the procedure given a height of the Kalibrierstromes is detected at a series-connected to resistor Messwi ^¬ reference resistor. This development is based on the consideration that high technical requirements must be made of the aforementioned power source to guarantee the constant current. In order to minimize these requirements, it is proposed to measure the calibration current output from the current source a second time, independently of the measuring shunt. In this way even smaller fluctuations in the calibration current can be accepted.

Furthermore, the reference resistor has the advantage that the height of the calibration current can be detected in a simple manner with an analog-to-digital converter and thus further processed digitally. In this way, the entire process can be performed digitally with a computing device, such as a microcontroller.

In a particular embodiment of the specified method, a resistance value of the reference resistor is greater than a resistance value of the measuring resistor. For this purpose, the re ference ^¬ resistance should be seen in the direction of Kalibrierstromes arranged upstream of the measuring resistor. This development is based on the consideration that the reference resistor dominates the voltage drop in the additional detection of Kalibrierstromes in this arrangement so that the calibrated and unknown resistance value of the measurement resistor can be ver ^¬ careless. For this purpose, the resistance of the reference resistor should be at least ten times greater than the resistance value of the measuring resistor.

In a further development of the specified method, the calibration of the regulation dependent on the measuring resistor is completed by closing a resistor connected in series with the measuring resistor Switch started. In this way, the current sensor using the specified method can perform the calibration at times when no current actually to be detected is passed through the measurement shunt, whereby the current actually to be detected would be corrupted by the calibration current.

Furthermore, the switch has the advantage that, even in normal operation, the calibration current can be conducted as a test through the measuring resistor and the reaction of the measuring resistor can be checked thereon. In this way it can be verified at regular intervals, whether the measured resistance is still in effect ^¬ We circle the Kalibrierstromes. Because the calibration current is then superimposed on the current to be measured, it can be concluded at the same time that the Messwi ^¬ resistor also is within the purview of the current to be measured and in the overall circuit no galvanic interruptions are present.

According to a further aspect of the invention, a control device is set up to carry out a method according to one of the preceding claims.

In a development of the specified control device, the specified device has a memory and a processor. In this case, the specified method is stored in the form of a Compu ^¬ terprogramms in the memory and the processor is provided for performing the method when the computer program from the memory is loaded into the processor.

According to a further aspect of the invention, a computer program comprises program code means for performing all the steps of one of the specified methods when the computer program is executed on a computer or one of the specified devices. According to a further aspect of the invention a computer program product comprises a program code which is stored on a data carrier and the compu ^¬ terlesbaren, when executed on a data processing device, carries out one of the methods specified.

According to another aspect of the invention, a current sensor for measuring an electric current comprises an electrical measuring resistor, via which the electrical current to be measured is feasible, one of the specified control devices.

According to another aspect of the invention, a vehicle includes one of the specified controllers and / or the specified current sensor.

The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings, in which:

Fig. 1 is a schematic diagram of a vehicle with an electric drive;

FIG. 2 is a schematic diagram of a vehicle electrical system with a current sensor in the vehicle of FIG. 1; FIG. and

Fig. 3 shows a schematic diagram of a vehicle electrical system with an alternative current sensor in the vehicle of Fig. 1 show.

In the figures, the same technical elements are provided with the same reference characters and described only once. Reference is made to Fig. 1, which shows a schematic diagram of a vehicle 2 with a vehicle battery 4, from which an electric current 6 is discharged. With the electric power 6 2 different electrical loads are supplied with electrical energy 8 in the vehicle.

An example of this electrical load is an electric motor 10, of the front wheels 12 of the vehicle 2 drives ^¬ 8 with the electric power through a drive shaft 14 at. The rear wheels 16 of the vehicle 2 are therefore free ^¬ running wheels. Such, for driving the vehicle 2 ver ^¬ applied electric motors 10 are typically designed as an alternating-current motors, while the electric current 6 is a direct current from the vehicle battery. 4 In this case, the electric current 6 must first be converted via a converter 18 into an alternating current. In vehicles, such as the vehicle 2, a current sensor 20 is generally installed, which measures the electric current 6 emitted by the vehicle battery 4. Based on the measured electric current 6, various functions can then be realized. These include, for example protection functions, as known from DE 20 2010 015 132 Ul, with which the vehicle battery 4 can be protected, for example against a Tie ^¬ fenentladung.

If the current 6 measured with the current sensor 2 corresponds only to the electrical current which is supplied to the converter 18, this current can also be used to regulate the drive power of the vehicle 2. The drive power is usually specified by the driver of the vehicle 2 with a driver request 22. An engine controller 24 then compares one of the driver's desired electrical current resulting with the measured electric current 6 and controls the converter 18 with control signals 26 such that the measured electric current 6 is adjusted to the desired current resulting from the driver's request. Such regulations are well known and should therefore not be further explored.

The current sensor 20 comprises a preferably as a measuring resistor 28, also called shunt formed sensor and an evaluation device 30. The measuring resistor 28 is traversed in the present embodiment, the electric current 6, which Messwi ^¬ resistor results in a voltage drop 32 on the 28th This voltage drop 32 is ^detected as measuring voltage by the evaluation device 30 via an input-side electrical potential 34 on the measuring resistor 28 and an output-side electrical potential 36 on the measuring resistor 28 as viewed in the direction of the electric current 6. From these two electrical potentials 34, 36, the evaluation unit 30 calculates the voltage drop 32 and the resistance value of the measuring resistor 28 to elekt ^¬ generic stream 6 flowing through the measuring resistor 28th

Based on Fig. 2 will be discussed in more detail below on the determination of the electric current 6.

After the two electrical potentials 34, 36 would be detected with corresponding voltage measuring devices 38, for example, a reference potential 40 shown in FIG. 3 opposite, from these via a subtraction element 42, the measuring voltage 32 can be determined.

The electrical current 6 and the measuring voltage 32 can be compared according to a predetermined rule 44. This predetermined rule 44 basically corresponds to the ohmic law, so that in the predetermined rule, for example, the resistance of the measuring resistor 28 is received. In addition, rule 44 also takes into account other effects, such as temperature effects, etc. The predetermined rule 44 may be stored in a memory 46, a calculating device 48, this retrieve based on the measured voltage 32 over the predetermined Before ^¬ magazine 44 can calculate the electric current. 6 The measuring resistor 28 differs as an electrical conductor usually from the other electrical conductors that carry the electric current 6 from the vehicle battery 4 to the converter 18. For example, his aforementioned resistance value should change less than 1% over a comparatively long period of more than 15 years. These demands on the accuracy of the resistance value of the measuring resistor 28 can not be achieved with economically reasonable measures in the rule. Typically, gauge resistor 28, which is typically made of manganese, a copper-manganese alloy having a composition of 82-84% copper, 12-15% manganese, and optionally 2-4% nickel, drifts in the vehicle range above 1.5%. ,

This leads to the fact that the calculation of the electric current 6 based on the predetermined rule 44 and the measuring ^¬ voltage 32 inevitably leads to false results.

In the context of the present embodiment, it is proposed to avoid the consequences of the long-term drift and thus the erroneous determination of the electric current 6 by calibrating the current sensor. This will be explained below with reference to FIG. 2. While it was assumed in Fig. 1 that the electric current 6 is delivered only from the vehicle battery 4, an example is shown in FIG. 2, in the context of which the vehicle ^¬ battery 4 can also be fed with the electric current 6. For this purpose, a current path controller 52 is present in the electrical system 50 of the vehicle 2, the electrical current 6 from the vehicle battery 4 to the consumer, so for example, the electric motors 10 or the electric current 6 from a charging unit 56 to the vehicle battery 4 via a switch 54 can.

The current sensor 20 may be clamped in the context of FIG. 2 at the directly negative pole of the vehicle battery 4. This has the advantage that for detecting the measuring voltage 32, only a single one of the two potentials 34, 36 must be detected, which in turn directly corresponds to the measuring voltage 32.

To calibrate the current sensor 20, a calibration current 58 from a current source 60 can be applied to the measuring resistor 28. For this purpose, for example, the evaluation device 30 via a trigger signal 62 close an on / off switch 52, which may be arranged in series between the power source 60 and the measuring resistor 28. The current source 60 can be supplied with electrical energy via a capacitor 64, for example in the form of an electrolytic capacitor, wherein the capacitor 64 can be charged via a precharge resistor 66 with a supply voltage 68.

If the calibration of the current sensor 20 is started, the evaluation device 30 with the trigger signal 62 closes the on / off switch 52 and thus directs the calibration current 46 through the measuring resistor 28. The insertion point of the

Calibration current 46 should start from the reference potential ^¬ tial 40, ie mass, behind the measuring resistor 28 and before Vehicle battery 4 may be arranged. Optionally, the values from ^¬ means may set the changeover switch 42 in a neutral position 30, so that the battery 4, and other consumers are separated 10 from one circuit with the calibration current 46th

Now, the evaluation device 30 detects the measurement voltage 32. Since both the calibration current 46 and the measurement voltage 32 are known, the evaluation means 30 can now determine the provision vorbe ^¬ voted 44 and store this in the memory 46 for further use. Thus, the current sensor 20 is calibrated.

In the current sensor 20 of FIG. 3, however, the current source 60 must output the calibration current 58 with a very high accuracy in order to be able to reliably calibrate the predetermined regulation 44 in the memory 46. This is associated with a correspondingly high technical complexity.

To reduce this technical complexity and thus the requirements of the power source 60 is in the context of FIG. 4 proposed to detect adjacent to the measurement voltage 32, an additional reference voltage 70, which drops across the measuring resistor 28 and a in series between the sense resistor 28 and the current source 60 switched ver ^¬ reference resistor 72nd A resistance value of the reference resistor 72 should be chosen at least ten times greater than a resistance of the Messwi ^¬ DERS tandes 28. In this way, the influence of the unknown for the calibration measurement resistor can be neglected 28 to Refe ^¬ ence voltage 70th

However, the reference resistor 72 should be highly accurate and durable selected, which is guaranteed as a rule, when the reference resistor 72 is arranged outside the circuit of the MES send ^¬ stream 6 and so only the relatively low selectable calibration current 58 is flowed through. In this way, the reference resistor 72, for example, only slightly thermally loaded. The longevity can, for example, also be influenced by the time duration of the calibration current 58 applied via the trigger signal 62, if it is selected to be less than 10 s, for example.

The evaluation device 30 can close the calibration current 58 from the reference voltage 70 and the resistance value of the reference resistor 72 and then complete calibration as described in connection with FIG. 3.

Claims

claims

1. A method of calibrating a current sensor (20) in a vehicle (2) which is arranged an electrical current (6) through a measuring resistor (28) based on a clamping ^¬ voltage drop (32) at the measuring resistor (28) and one from ^¬ measuring resistance (28) dependent regulation (46) for a counterelectrode ^¬ rendition of the voltage drop (32) and the electric current (6) to be detected, comprising:

- Imprinting a known electrical

Kalibrierstromes (58) in the measuring resistor (28),

Detecting a calibration voltage drop (32) caused by the calibration current (58) at the measuring resistor (28), and

- Calibration of the measuring resistor (28) dependent regulation (44) based on a comparison of the calibration current (58) and the calibration voltage drop (32).

2. The method of claim 1, comprising:

- Impressing the calibration current (58) in the Messwider ^¬ stand (28) from a power source (60).

3. The method of claim 2, comprising:

Charging an energy store (64), and

- Applying an energy storage voltage of the charged energy storage device (64) to the power source (60) for impressing the calibration current (58) in the measuring resistor (28).

4. The method of claim 3, wherein the energy store (64) is a capacitor, in particular an electrolytic capacitor.

5. The method according to any one of the preceding claims, wherein a height of the calibration stream (58) on a in series to Messwi derstand (28) interconnected reference resistor (72) is detected.

6. The method of claim 5, wherein a resistance value of the reference resistor (72) is greater than a resistance value of the measuring resistor (28).

7. The method of claim 6, wherein the resistance of the reference resistor (72) is at least ten times greater than the resistance of the measuring resistor (28).

8. The method according to any one of the preceding claims, wherein the calibration of the measuring resistor (28) dependent rule (44) by closing a series connected to the measuring resistor (28) switch (52) is started.

A device (30) adapted to perform a method according to any one of the preceding claims.

A current sensor (20) for measuring an electric current (6), comprising:

an electrical measuring resistor (28), via which the electrical current (6) to be measured can be guided,

a device (30) according to claim 9 for determining the electrical current (6) based on the voltage drop across the electrical measuring resistor (32) and the predetermined regulation (44) and for calibrating the regulation (44).