DE10227821B4 - Determining load torque and output current of a vehicle generator by measuring the excitation current - Google Patents

Abstract

Method for determining an output current (Igen) of a vehicle generator (9) whose output voltage is regulated by a generator controller (7), comprising the following steps: measuring a generator speed (n), measuring an excitation current (Ierr) by means (6) for measuring the excitation current, outputting the measured values to a processing device (10), and determining the generator output current (Igen) based on the measured values of the generator speed (n) and the measured values of the excitation current (Ierr).

Description

The invention relates to a method and a device for determining the output current of a vehicle generator according to the preamble of patent claims 1 and 7, respectively.

Lastmoment and output current of a vehicle generator are important parameters for establishing an energy balance in an electrical system or for performing an effective engine management in a motor vehicle.

The generator output current is usually from the generator speed n , the excitation current ierr and the air gap d calculated between the rotor and stator with the help of a specific generator for the specific map. This is the excitation current ierr from the duty cycle Tein / (Tein + Taus) of a switching transistor with which the exciter field is switched, the excitation field temperature T , which is determined indirectly, for example, via the temperature of the engine compartment, the excitation field resistance R and estimated parasitic loss resistances in the path of excitation Rpar. For the determination of the generator output current igen thus: $$\text{igen}=\text{f}\left(\text{n}.\text{T}.\text{R}.\text{Rpar}.\text{Ubat}.\text{d}\right)$$

In this case, the generator speed n and the generator output voltage Ubat are measured. In contrast, the excitation field temperature in particular form T , the exciter field resistance R due to its temperature dependence and the parasitic losses Rpar difficult to determine sizes that can greatly affect the result. Deviations in the actual temperature T of the exciter field, in the determination of exciter field resistance R and the voltage actually applied to the excitation field has an immediate effect on the calculation of the generator output current igen out.

From the US 5 712 786 A Devices or methods for determining an output current of a vehicle generator are known, in which the output current is determined as a function of the measured rotational speed and an estimate of the excitation current from the exciter current clock ratio and optionally other variables. A direct measurement of the excitation current is not performed.

From the DE 197 27 876 A1 Generator controls are known in which the control of the switching transistor of the generator controller by means of a pulse width modulation takes place. This ensures that the output voltage of the generator is within a tolerable range regardless of the speed.

Other generator regulations are for example from the DE 36 35 957 A1 , of the WO 96/10289 A1 , of the DE 196 08 992 A1 , as well as the EP 0 903 832 A1 known. The EP 1 193 825 A1 deals with a voltage regulator for a generator.

The following relationship applies to the calculation of the generator load torque Mgen: $$\text{Mgen}=\text{f}\left(\text{igen}.\text{Ubat}.\text{n}\right),$$

As can be seen, this is also the relatively inaccurate determinable generator output current igen with a.

The accuracy in calculating the generator output current igen or the generator load torque Mgen is too low for charge balance calculations or for an engine management, especially during engine idle. The determination of the sizes mentioned is also relatively expensive.

It is therefore the object of the present invention to increase the accuracy in the calculation of the generator output current or the load torque and at the same time to reduce the computational effort.

This object is achieved according to the invention by the features specified in claim 1 and 7 features. Further embodiments of the invention are the subject of dependent claims.

The essential idea of the invention is to measure the exciting current preferably directly in the generator controller and to output the measured value via a suitable interface to a control unit (processing unit) and to calculate therefrom the generator output current or the load torque. By directly measuring the excitation current, the inaccuracies in the estimation of the excitation current described above can be avoided and the calculation of the generator output current and the load torque can be substantially improved.

$$\text{Mgen}=\text{f}\left(\text{Igen},\text{Ubat},\text{n}\right)$$

This results in the calculation of the generator output current igen and the load torque Mgen in the control unit the following relationship: $$\text{igen}=\text{f}\left(\text{n}.\text{ierr}.\text{d}\right)$$

$$\text{Mgen}=\text{f}\left(\text{igen}.\text{Ubat}.\text{n}\right)$$

Generator output current and / or load torque are preferably determined from corresponding characteristics or tables, which may be stored for example in the control unit.

If, for example, a generator output current / speed characteristic field or a load torque / speed characteristic field is stored in the system, the generator output current or the generator load torque can be calculated taking into account the remaining quantities ( n , Ubat, d) are output directly. Alternatively, output current or load torque can also be calculated.

Due to the direct measurement of the exciter current (by means of a suitable current meter), essentially only identifiable quantities remain to determine the generator output current and the load torque. The only unknown major size is the air gap d of the generator. For the air gap d usually a mean value from production is used. This can vary depending on the actual air gap d be relatively inaccurate.

In order to achieve a further improvement in accuracy, the generator output current actually measured during a generator test (test bench measurement), which has been set at a given excitation current and predetermined rotational speed, can be used to compare the characteristic curves stored in the system and adapted to the actual air gap of the generator , For example, a correction factor can be determined with which the generator output current or the load torque stored in the system is corrected to determine the influence of the air gap d to eliminate. Optionally, based on the test bench measurement also on the actual air gap d be calculated back, which can then be used for the determination of generator output current or load torque.

The invention will now be described by way of example with reference to the accompanying drawings.

• 1 ein Beispiel eines Generatorausgangsstrom/Drehzahl-Kennlinienfeldes;
• 2 ein Flußdiagramm zur Darstellung des Verfahrens, mit dem der Generatorausgangsstrom ermittelt wird;
• 3 eine schematische Darstellung einer Vorrichtung zur Bestimmung des Ausgangsstroms eines Fahrzeuggenerators.

Show it:

• 1 an example of a generator output current / speed characteristic field;
• 2 a flowchart illustrating the method by which the generator output current is determined;
• 3 a schematic representation of a device for determining the output current of a vehicle generator.

1 shows a stored in the system generator output current / speed characteristic field in which the influence of excitation current ierr and air gap d on the generator output current igen is shown. As can be seen, the generator output current increases igen with increasing excitation current ierr (Ierr1> Ierr3).

At the lowest current characteristic ( Ierr3 ) is beyond the influence of the air gap d It can be seen that the generator output current igen slightly decreases with increasing air gap.

In the calculation of generator output current and generator load torque inaccuracy due to different sized air gaps d To eliminate, the genome measured in a test bench measurement real generator output current is pulled. From the test bench measurement results under defined conditions (excitation current ierr and speed n ) a generator output current, on the basis of which the characteristic curves can be corrected accordingly.

In addition to the current dividing lines, torque characteristic curves are preferably also stored in the system (not shown), from which the current load torque can be read out.

2 shows a flowchart illustrating a method with the generator output current igen is easily determined.

In the method for determining the output current igen be in a first step 1 first the generator speed n and in a second step 2 the excitation current ierr measured. In a third step then the generator output current igen determined on the basis of the measured values. This is done by means of curves or tables that are stored in a processing device (control unit).

When evaluating the characteristics, the actual size of the air gap d of the generator, which was previously determined in test bench measurements.

By directly measuring the excitation current ierr can the generator output current igen be determined very accurately.

3 shows a device for determining the output current igen a vehicle generator 9 , whose output voltage from a generator controller 7 is regulated. The device further comprises a device 8th for measuring the generator speed n and a facility 6 for measuring the excitation current ierr , The measured values become a processing device 10 fed to the generator output current igen determined on the basis of the measured values. The generator output current igen can be read out directly from tables or characteristic curves stored in the system.

LIST OF REFERENCE NUMBERS

1-3

steps

6

measuring device

7

regulator

8th

Rev counter

9

generator

10

processing unit

igen

Generator output current

ierr

excitation current

d

air gap

n

rotation speed

Claims (8)

Method for determining an output current (Igen) of a vehicle generator (9) whose output voltage is regulated by a generator controller (7), comprising the following steps: Measuring a generator speed (n), Measuring an exciter current (Ierr) by means of a device (6) for measuring the exciting current, - Output of the measured values to a processing device (10), and - determining the generator output current (Igen) based on the measured values of the generator speed (n) and the measured values of the excitation current (Ierr). Method according to Claim 1 , characterized in that the excitation current (Ierr) in the generator controller (7) is measured. Method according to Claim 1 or 2 , characterized in that the output current (Igen) and / or a load torque from characteristic curves or tables is determined, which are stored in the processing unit (10). Method according to one of the preceding claims, characterized in that, when determining the generator output current (Igen), a value comparison with a real measured generator output current (Igen) is carried out in order to take account of an actual air gap (d). Method according to Claim 1 , characterized in that a size of an actual air gap (d) is determined from test bench measurements and taken into account in the determination of the output current (Igen). Method according to one of the preceding Claims 2 to 3 , characterized in that a size of an actual air gap (d) is determined from test bench measurements and taken into account in the determination of the output current (Igen) and / or the load torque. Device for determining an output current (Igen) of a vehicle generator (9) whose output voltage is regulated by a generator controller (7), wherein - means for measuring a generator speed (n), and - A device (6) for measuring an excitation current (Ierr), are present and - wherein the measured values are forwarded to a processing device (10) which determines the generator output current (Igen) on the basis of the measured values of the generator speed (n) and the measured values of the excitation current (Ierr). Device after Claim 7 , characterized in that the means for measuring the excitation current (Ierr) in the generator controller (7) is arranged.

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