EP2428673B1 - Method for determining the status of a starter motor - Google Patents

Description

The invention relates to a method and an arrangement for determining a condition of a starter motor.

State of the art

For starting or starting an internal combustion engine is usually a starter system with a DC motor, which includes a stator and a rotor used. The power supply of the rotor is ensured via a carbon brush-commutator arrangement, are pressed in the carbon brushes of a brush holder with a spring system on Kommutatorlamellen and grind during a movement of the armature on the commutator, with a current flowing between the carbon brushes and the commutator.

Over the life of a starter motor of the starter system there is an operational wear of the carbon brushes and commutator bars. The formation of a patina layer on the commutator bars and an oxide layer on the carbon brushes has a positive effect on the wear. However, both effects increase the contact resistance between the carbon brushes and the commutator and reduce the power output of the starter system.

In the following, both effects are not considered separately, but summarized under the term patina, which also includes the oxide layer. Even if the carbon brushes substances are added for lubrication and cleaning of the surfaces of commutator, it may be due to the application during operation to form an over-patination.

The German patent application not yet disclosed on the priority date DE 10 2009 045 265.6 describes a method for operating a DC machine, in particular a starter for an internal combustion engine, with an armature fed via brushes and a commutator from a DC voltage source. Here a patination of the commutator is determined by monitoring the machine-specific inrush current and corrected by changing the operating parameters of the DC machine. With the measures described there, an over-patination can be reduced or a Unterpatinierung be repealed. The US 2009/0309530 discloses a method for determining the functional state of a starter motor based on a regression model including the input quantities current and voltage. The WO 00/01943 discloses a method for turning off a starter based on measurements of current and voltage. Disclosure of the invention

Against this background, a method and an arrangement with the features of the independent claims are presented. Further embodiments of the invention will become apparent from the dependent claims and the description.

With the method u. a. a detection of a degree of patination and thus, for example, the detection of an over- or under-patination of a carbon brush-commutator system or a carbon brush-commutator arrangement of, for example, designed as a DC motor starter motor possible. The starter motor may be formed as part of a starter system for starting an internal combustion engine of a motor vehicle.

The method allows, for example, during vehicle operation, the detection of a change in resistance of the brush-commutator arrangement of the starter motor, which can be caused by conventional over-aging or under-patination outside of usual aging effects. By measuring a resistance at different, typically two, operating points of a detection cycle, the resistance of the brush-commutator arrangement can be determined indirectly. By determining resistances several times at the operating points and by subtracting the resistances determined in this way, at least one orientation value can be determined for the resistance of the brush-commutator arrangement to be detected. About the said difference formation, the resistance change, ie a change in the resistance of a first operating point to at least a second operating point, are determined.

Depending on a value of the determined resistance by checking the change in resistance between at least two different operating points, it is also possible to determine whether an over- or underpatinating is now present. In addition, several detection cycles can be provided over a longer period, over which a development of the resistance can be observed. Here is a series of detection cycles with otherwise unchanged operating parameters, for example. The temperature of the starter motor to make, where determined for each detection cycle for at least two operating points resistors and at least one change in resistance is determined.

In an embodiment of the invention, a detection of over- or under-patination between carbon brushes and commutator and thus fins of the commutator during vehicle operation by current and voltage measurements on the battery, which provides the starter motor with electrical energy, provided at defined operating points. The battery may be a battery of the electrical system of the motor vehicle. It is necessary to determine the resistance no knowledge of the battery condition.

If over-or under-patination is detected by the method, appropriate measures, i. H. by treatment, typically cleaning or additional coating, the commutator bars and / or carbon brushes, a reduction in the power loss of the starter motor or the starter wear are performed. The procedure also makes it possible to check the effectiveness of these measures.

In the method, the contact resistance between the carbon brushes and Kommutatorlamellen is usually determined indirectly. Nevertheless, by measuring current and voltage at selected operating points during at least one detection cycle by evaluating detection results, influences due to induced voltages, changing temperatures, and aging can be detected and minimized.

The arrangement according to the invention is designed to carry out all the steps of the presented method. In this case, individual steps of this method can also be carried out by individual components of the arrangement. Furthermore, functions of the arrangement or functions of individual components of the arrangement can be implemented as steps of the method. In addition, it is possible for steps of the method to be realized as functions of at least one component of the arrangement or of the entire arrangement.

In one embodiment of the invention, a determination of the resistance of the starter motor to defined operating points. This may mean, for example, that at least two operating points current and voltage measurements are made. Based on a measured current and a measured voltage, the resistance is determined for each operating point. The total determined resistances are compared and from this a statement about the degree of patination of the brush-commutator arrangement is made.

By measuring the current and the voltage of the battery at different operating points, the total resistance of a starter system can be determined. The resistance of the starter system is usually composed of several components. These include a line resistance, contact resistance, a relay resistance, a brush resistance, a resistance at the junction between carbon brushes and commutator bars, an ohmic armature resistance and a ground contact resistance.

By current and voltage measurements, which take place, for example, to a first operating point before a start and to a second operating point during the start, a resistance of the brush-commutator arrangement of resistances of other components of the starter system can be separated. For this purpose, it is assumed in an embodiment that the resistances of the other components change only slightly between the various operating points, whereas the resistance of the brush-commutator arrangement is operating point-dependent, which is due to different operating point-dependent rotational speeds for rotation of the rotor relative to the stator of the starter motor can be conditional.

In order to avoid inductive influences on the determination of the resistance during the start, may alternatively or additionally to an operating point without relative movement of the rotor to the stator, d. H. at standstill of the rotor (speed zero), and possibly at a high current of the starter motor, z. B. upon reaching a peak or peak value of the current to be measured.

In order to minimize temperature effects, the resistance determination for starter motor starts can be used for detection cycles in which the same temperature prevails, eg. B. in each case with a cold starter motor, performed.

Thus, a change in resistance by over-patinating in the brush-commutator arrangement can be estimated when corrosion and aging effects of the residual resistances resulting from the other components are known. The current and voltage measurement can be carried out via a battery sensor with a high sampling rate, which is less than or equal to 5 milliseconds, or via sensor lines within a motor control of the starter motor.

By taking into account an operating point in which a current maximum and a voltage minimum are present, the accuracy of the resistance determination can be increased. A state of the battery is not involved in the determination of the resistance and must not be considered. For this purpose, a high sampling rate less than or equal to 5 milliseconds of current and voltage measurement is provided in the event that a measurement of the current and the voltage is made to the said operating point, in which there is a maximum for the current and a minimum for the voltage. For this purpose, courses of the current and the voltage can be observed over a time interval and the said operating point can be determined.

Usually, the contact resistance of the brush-commutator arrangement is measured and estimated only in combination with other resistors of the starter system. To determine the resistance, corrosion and aging effects on resistances of further components of the starter system are considered in a further embodiment.

As a result, the detection of a change in the patination in several detection cycles by detecting the change in resistance provides high accuracy at a low cost, for example, by implementing the detection without sensor line for controlling the starter motor. However, other measures may be provided to supplement the described method.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

• Figur 1 zeigt in schematischer Darstellung ein Beispiel für eine Bürsten-Kommutator-Anordnung.
• Figur 2 zeigt Diagramme mit Betriebsparametern, die bei verschiedenen Ausführungsformen des erfindungsgemäßen Verfahrens verwendet werden.
• Figur 3 zeigt in schematischer Darstellung ein Beispiel für ein erstes Ersatzschaltbild eines ersten Bordnetzes eines Kraftfahrzeugs, das einen Startermotor aufweist.
• Figur 4 zeigt in schematischer Darstellung ein Beispiel für ein zweites Ersatzschaltbild einer Starteranlage mit einem Startermotor.
• Figur 5 zeigt in schematischer Darstellung Ersatzschaltbilder eines zweiten Bordnetzes und Details der Diagramme aus Figur 2 mit Betriebsparametern, die bei einer ersten Ausführungsform des erfindungsgemäßen Verfahrens verwendet werden.

Brief description of the drawings

• FIG. 1 shows a schematic representation of an example of a brush-commutator arrangement.
• FIG. 2 shows diagrams with operating parameters that are used in various embodiments of the method according to the invention.
• FIG. 3 shows a schematic representation of an example of a first equivalent circuit diagram of a first electrical system of a motor vehicle having a starter motor.
• FIG. 4 shows a schematic representation of an example of a second equivalent circuit diagram of a starter system with a starter motor.
• FIG. 5 shows a schematic representation equivalent circuit diagrams of a second electrical system and details of the diagrams FIG. 2 with operating parameters that are used in a first embodiment of the method according to the invention.

Embodiments of the invention

The invention is schematically illustrated by means of embodiments in the drawings and will be described in detail below with reference to the drawings.

The figures are described coherently and comprehensively, the same reference numerals denote the same components or operating parameters.

This in FIG. 1 schematically illustrated example of a brush-commutator arrangement 1 of a starter motor comprises a plurality of brushes, which are carbon brushes 3, of which in FIG. 1 only one is shown, as well as commutator 7 of a commutator. 5

The carbon brushes 3 of the starter motor are generally composed of graphite and copper, wherein lubricant and cleaning agents may be added. During operation of the starter motor in a motor vehicle, abrasion of the carbon brushes 3 and electrochemical processes lead to the formation of a patina layer 9 on the commutator blades 7 and / or an insulating layer on the surfaces of the carbon brushes 3. Both effects increase the contact resistance between the carbon brushes 3 and the commutator blades 7, but reduce the wear of the commutator 7 and carbon brushes 3. A certain patination is necessary for the low-wear operation. However, overpatinating is to be avoided since this can cause an increased power loss of the starter motor.

Possible chemical processes which result between the carbon brushes 3 and the commutator blades 7 during a relative movement of the carbon brushes 3 to the commutator blades 7 are a transport of Cu ²⁺ ions 11 from the carbon brushes 3 via an electric field, an oxidation 13 of copper by atmospheric moisture to Cu ₂ O at the surface of the carbon brush 3, a metallic channel formation by an oxide layer 15 (fritting) as a result of a breakdown and an electrochemical oxidation and reduction by atmospheric moisture (H ₂ O → H ⁺ + OH ^- ) followed by ion transport 17 in the electric field between the carbon brushes 3 and commutator 7.

These chemical processes change the contact resistance of the brush-commutator arrangement 1 and their temperature dependence in different ways. Due to the complexity of the processes, it is intended to analyze the relevant contributions in an application-specific manner. For this purpose, it should be checked whether the formation of the patination changed by varying the composition of the carbon brushes 3 or whether it can be reduced by suitable measures during operation of the starter motor. Thus, it is conceivable to influence the patination including the oxide layer on the surface of the carbon brushes 3. If overpatinating is detected in a method presented below, the rotor of the starter motor can be rotated at high speeds without load, whereby a cleaning effect is achieved for the brush-commutator assembly 1. In the following, with patination, both the material film, i. H. the patina layer 9 on the commutator blades 7, as well as the oxide layer on the surface of the carbon brushes 3.

In FIG. 2 three diagrams 21, 23, 25 are shown with operating parameters of a starter motor, resulting in its operation and are used in various embodiments of the method according to the invention. In this case, the time is plotted in all diagrams 21, 23, 25 along an abscissa 27. Along an ordinate 29 of the first diagram 21, a current intensity I _Bat (t) of a battery which supplies the starter motor with electrical energy is plotted in the unit Amperes. Furthermore, the first diagram 21 shows a curve 31 for the current flowing through the battery. Along an ordinate 33 of the second diagram 23 is a voltage U _Bat (t) applied to the battery applied. Furthermore, the second diagram 23 shows a first curve 35 and a second curve 37 for a curve of the voltage across the battery.

Along an ordinate 39 of the third diagram 25 is a speed n (t) for a run-up behavior of an internal combustion engine of a motor vehicle, which is started with the starter motor applied. In the third diagram 25, a curve 41 for the run-up behavior is also shown. Furthermore, for all three diagrams 21, 23, 25, a first time 43, in which an ignition takes place, a second time 45 before the start of the starter motor, in which the starter motor is energized, a third time 47, in which the starter motor starts and a maximum current flows through the starter motor, and a fourth time 49, in which a dropping of the starter motor takes place, indicated.

Various embodiments may be provided for carrying out the method according to the invention for detecting the patination of a brush-commutator arrangement of the starter motor. In a first embodiment, a measurement of a change in a resistance of the battery based on a measurement of the current and a measurement of the voltage to defined operating points 51, 53, here to a first operating point 51 and to a second operating point 53. At the first operating point 51 is reached the current value of the battery is a value 54 of 50 A (curve 31) and the voltage has a value 56 of 12 V (curve 35). Details of the first embodiment of the method according to the invention will become apparent from the diagrams and circuit diagrams FIG. 5 described.

In a second embodiment, a measurement of a voltage dip occurs .DELTA.U _SP 55. In a third embodiment of the method a change in voltage is made .DELTA.U ₄₅ 57 to terminal 45 of the starter motor in a so-called discharge of the starter motor. In a fourth embodiment, detection of power loss resulting from overpatinination occurs. This power loss is determined by measuring the run-up behavior (curve 41) of the internal combustion engine during a start-up process. The second, third and / or fourth embodiment may supplement the first embodiment of the method.

This in FIG. 3 schematically illustrated equivalent circuit diagram for a vehicle electrical system 71 of a motor vehicle shows a trained as a battery voltage source 73 U ₀ , a battery resistor 75 R _B and a second resistor 77 R _V for other consumers through which a current flows 79 I _V. By a third resistor 81 R ₃₀ , ie the supply line resistance to the terminal 30 of the starter motor, a current flows 83 I ₃₀ , through a fourth resistor 85 R ₅₀ , here a resistor of the starter relay with pull-in and holding winding, a current flows 87 I _50th In addition, the equivalent circuit as a fifth resistor 89 R _{31 shows} the resistance of the ground line. On a starter motor 91 is an induced voltage 93 U _I. Furthermore, a voltage 95 U ₃₀ and a discharge voltage 97 U _{45 of} the starter motor 91 are shown in the equivalent circuit diagram. The equivalent circuit diagram also shows the holding winding (HW) 99 and the pull-in winding (EW) 101.

In the equivalent circuit diagram of a starter system 103 off FIG. 4 are in addition to the starter motor 91 and the fifth resistor 89 R ₃₁ , the discharge voltage 97 U ₄₅ and the voltage 93 U _{I of} the starter motor, a line resistance 105, a brush resistor 107, a resistor 109 for a transition between the carbon brushes 3 and the commutator 7 and thus the resistance of the brush-commutator arrangement 1, an armature resistor 111 and an inductance 113 of the armature coil are shown schematically.

In FIG. 5 are again the two diagrams 21, 23 off FIG. 2 with the curves 31, 35 shown. Also shows FIG. 5 a schematic diagram of an equivalent circuit diagram of a second electrical system 121 and an embodiment of an inventive arrangement 123. From the electrical system 121 are, as already described with reference to FIGS. 3 and 4 indicated, the voltage source 73 U ₀ and their resistance 75 R _B , the resistor 77 R _V of other consumers, a starting resistor 125 R _{St of} a starter motor 126 and a line resistance 105 R _{L of} the starter motor 126 shown. In this case, the starter resistor 125 R _St comprises the brush resistor 107, the resistance 109 for the transition between the brushes and the commutator, the armature coil 111 and the inductance 113 L _{armature of} the armature coil, as already based on FIG. 4 is indicated.

As components of the embodiment of the arrangement 123 according to the invention are in FIG. 5 a current measuring device 127, a voltage measuring device 129 as measuring devices and an evaluation module 131 are shown. Here, the current measuring device 127 and the voltage measuring device 129 may be formed as components of a so-called battery sensor. An in FIG. 5 Furthermore illustrated first partial equivalent circuit diagram 133 of the electrical system 121 shows those components which are taken into account at the first operating point 51. A second partial equivalent circuit 135 shows those components which are taken into account at the second operating point 53.

The resistor 77 R _v of other consumers is determined before the start of the starter motor via a current and voltage measurement of the maximum load current of other consumers. This applies z. B. at the time of maximum glow current for diesel vehicles. It follows for the first operating point 51: $$R_v\left(T\right)=\frac{U_{\mathit{asked}}}{I_{\mathit{asked}}}$$

In the first embodiment of the method it follows that the battery state is not included in the calculation of the load resistance.

The total resistance R _tot comprises the resistor 77 R _{v of} the other consumers, the power resistor 105 R _L and the starter resistor 125 R _{St of} the starter motor 126. This total resistance R _{tot of} all consumers is on the current and voltage measurement at a time at which a maximum Current flows, calculated during the start of the starter motor and thus to the second operating point 53. $$R_{\mathit{ges}}\left(T\right)=\frac{U_{\mathit{asked}}}{I_{\mathit{asked}}}=\frac{R_v\left(R_{\mathit{management}}+R_{\mathit{St}}\right)}{R_v+\left(R_{\mathit{management}}+R_{\mathit{St}}\right)}\Rightarrow R_{\mathit{management}}+R_{\mathit{St}}$$

Here, the angular velocity of the rotor or armature of the starter motor 126 and the current change of I _{30 is} close to zero, so that induction effects can be neglected. The starter resistor R _St is composed of several components. These include contact resistances, a relay resistor, a brush resistor, a resistor at the junction between the carbon brushes and commutator bars, an ohmic armature resistance, and a resistance of the ground junction: $$R_{\mathit{St}}=R_{\mathit{contacts}}+R_{\mathit{to\; brush}}+R_{\mathit{crossing}}+R_{An\ker }+R_{\mathit{Mass\; transfer}}$$

At the time of the maximum flowing current I ₅₀ "I ₃₀ , the relay current is neglected. The listed resistors are temperature dependent. The specific resistance of metals generally changes as a function of temperature via: $${\mathrm{\rho }}_s\left(T\right)\approx {\mathrm{\rho }}_0\left(1+\mathrm{\alpha }T\right)$$

The temperature dependence of the contact resistance between the carbon brushes and the commutator lamella can be clearly differentiated from that of a metal by patination and the associated defect electron conduction and be like a semiconductor. To avoid temperature influences, a resistance measurement at a specified temperature must be provided, eg. B. each at a first start with a cold engine, wherein a detection cycle is made at each first start. In order to detect the influence of over- or under-patination, resistance measurements are compared and usual aging effects on contacts, brush resistance and ground transition are taken into account. The current and voltage measurements can z. B. be performed by a high-temporal resolution measurement of a battery sensor or via additional sensor lines within an engine control of the engine.

With the arrangement 123 shown, a current measurement and voltage measurement is carried out in at least one detection cycle at defined operating points 51, 53 at a voltage source 73, which supplies the starter motor 126, and resistances to the different operating points 51, 53 are calculated. The resistances thus determined are compared, wherein the resistance of the brush-commutator arrangement to be determined from the difference of the resistance of all consumers, d. H. the starter motor 126 with rotating armature and the other, other consumers, as determined at the second operating point 53, and the resistance of the other consumers, which is determined at the first operating point 51 with the armature of the starter motor 126 stationary.

The patination changes the contact resistance of the brush-commutator assembly and reduces the power of the starter motor. A degree of patination can thus be detected indirectly via an estimate of the resistance and additionally via the analysis of the power reduction.

In a second embodiment of the method according to the invention, a measurement of the voltage drop 55 ΔU _Sp during the start of the starter motor and / or by an analysis of the voltage curve can be made. For this purpose, reference is made to the second diagram 23 FIG. 2 directed. Both the change of the maximum voltage dip 55 ΔU _Sp and the variation of the voltage curve over the start give further information about the change of the patination. At the time of the maximum voltage dip 55 ΔU _{Sp, there} is only a slight movement of the rotor of the starter motor before, whereby the voltage dip 55 ΔU _{Sp is} purely on-board network dependent. The voltage curve (curves 35, 37 out FIG. 2 ) is dependent on both on-board and internal combustion engine. Different voltage curves can z. B. over the calculation of envelopes are compared. For this purpose, only a small number of measured variables must be taken into account. The measurement can be implemented, for example, by an additional sensor line within the engine control. In this case, a vehicle electrical system state for estimating the voltage dip 55 ΔU _Sp and a variation of friction, compression and drag torque of the internal combustion engine are taken into account for the analysis of the voltage profile.

It is also possible in this supplementary embodiment of the method to carry out an analysis of a profile of the voltage drop 55 .DELTA.U _Sp in a forward rotation of the rotor without starter intervention. A possible disadvantage of the influence of the internal combustion engine on the course of the voltage dip is avoided by a forward turning without starter intervention. This is suitable, inter alia, for starter motors, which have a separate drive for a pinion Einlern and a starter turning. For this purpose, a knowledge of the electrical system status for estimating a voltage dip and a power load of the motor control by Abschaltströme be taken into account via a sensor line. A circuit of a pinion and a main current are controlled independently compared to conventional starter motors.

$$\begin{array}{l}{U}_{45}=I_{30}\left(R_{\mathit{Leitung}}+R_{\mathit{Bürste}}+R_{\mathit{Übergang}}+R_{An\ker ,\mathrm{\Omega }}+R_{31}\right)+\dots \\ +I_{50}{R}_{31}+L_{An\ker }\frac{d{I}_{30}}{\mathit{dt}}+k\mathrm{\Phi \omega }\end{array}$$

In a third embodiment, the measurement of the voltage difference 57 .DELTA.U _{45 of} the discharge voltage takes place shortly before and shortly after the launch of the starter motor at the end of the starting process, whereby an estimate of the voltage drop between the carbon brushes and the commutator bars can be made. Where: $$U_{45}-U_{\mathit{management}}-U_{\mathit{brush}}-U_{\mathit{crossing}}-U_{An\ker .\mathrm{\Omega }}-U_{An\ker .L}-U_{\mathit{ind}}-{\mathrm{<figure-callout\; id="31"\; label="U"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">U</figure-callout>}}_{31}=0$$

$$\begin{array}{l}{\mathrm{<figure-callout\; id="45"\; label="U"\; filenames="imgf0002.png"\; state="\{\{state\}\}">U</figure-callout>}}_{45}=I_{30}\left(R_{\mathit{management}}+R_{\mathit{brush}}+R_{\mathit{crossing}}+R_{An\ker .\mathrm{\Omega }}+{\mathrm{<figure-callout\; id="31"\; label="R"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">R</figure-callout>}}_{31}\right)+...\\ +I_{50}{\mathrm{<figure-callout\; id="31"\; label="R"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">R</figure-callout>}}_{31}+L_{An\ker }\frac{d{I}_{30}}{\mathit{dt}}+k\mathrm{\Phi \omega }\end{array}$$

Here L _{An ker is} an inductance of the armature of the starter motor, Φ a magnetic flux through the armature and ω an angular velocity of the armature.

With regard to the operating parameters and components which are to be taken into account, reference is made to FIGS. 2 to 4 directed.

$$\begin{array}{l}U{\text{'}}_{45}=-I{\text{'}}_{30}\left(R_{\mathit{Leitung}}+R_{\mathit{Bürste}}+R_{\mathit{Übergang}}+\_R_{An\ker ,\mathrm{\Omega }}+R_{31}\right)+\dots \\ \dots -L_{An\ker }\frac{\mathit{dI}{\text{'}}_{30}}{\mathit{dt}}+k\mathrm{\Phi }\text{'}\mathrm{\omega }\text{'}\end{array}$$

After opening a contact, a voltage and thus a current I _{30 is} induced by the movement of the armature in the magnetic field of the permanent magnet on the pole housing of the starter motor. The current direction has reversed compared to I ₃₀ with contact closed: $$U{\text{'}}_{45}-U{\text{'}}_{\mathit{management}}-U{\text{'}}_{\mathit{brush}}-U{\text{'}}_{\mathit{crossing}}-U{\text{'}}_{An\ker .\mathrm{\Omega }}-U{\text{'}}_{An\ker .L}-U{\text{'}}_{\mathit{ind}}-U{\text{'}}_{31}=0$$

$$\begin{array}{l}U{\text{'}}_{45}=-I{\text{'}}_{30}\left(R_{\mathit{management}}+R_{\mathit{brush}}+R_{\mathit{crossing}}+\_R_{An\ker .\mathrm{\Omega }}+{\mathrm{<figure-callout\; id="31"\; label="R"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">R</figure-callout>}}_{31}\right)+...\\ ...-L_{An\ker }\frac{\mathit{dI}{\text{'}}_{30}}{\mathit{dt}}+k\mathrm{\Phi }\text{'}\mathrm{\omega }\text{'}\end{array}$$

From the measured voltage difference .DELTA.U ₄₅ results: $$\begin{array}{l}\mathrm{<figure-callout\; id="45"\; label="\Delta \; U"\; filenames="imgf0002.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}{U}_{}{}_{45}=\left(R_{\mathit{management}}+R_{\mathit{brush}}+R_{\mathit{crossing}}+R_{An\ker .\mathrm{\Omega }}+R_{31}\right)\left(I_{30+I{\text{'}}_{30}}\right)+...\\ ...-L_{An\ker }\left(\frac{d{I}_{30}}{\mathit{dt}}+\frac{\mathit{dI}{\text{'}}_{30}}{\mathit{dt}}\right)+k\left(\mathrm{\Phi \omega \; +\; \Phi }\text{'}\mathrm{\omega }\text{'}\right)+I_{50}{\mathrm{<figure-callout\; id="31"\; label="R"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">R</figure-callout>}}_{31}\end{array}$$

In this case: I _'30 «I ₃₀ , dI ₃₀ / dt ~ 0 at the end of the starting process, with Φ'« Φ and I ₅₀ «I _{30 the} above equation is simplified to: $$\begin{array}{l}\mathrm{<figure-callout\; id="45"\; label="\Delta \; U"\; filenames="imgf0002.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}{U}_{}{}_{45}=I_{30}\left(R_{\mathit{management}}+R_{\mathit{brush}}+R_{\mathit{crossing}}+R_{An\ker .\mathrm{\Omega }}+{\mathrm{<figure-callout\; id="31"\; label="R"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">R</figure-callout>}}_{31}\right)+k\mathrm{\Phi \omega }+...\\ ...+L_{An\ker }\frac{\mathit{dI}{\text{'}}_{30}}{\mathit{dt}}\end{array}$$

At constant Abstellbedingungen can be determined by changing the voltage difference .DELTA.U _45, a change in the resistance R _{transition of} the brush-commutator request. To estimate the magnetic flux constant storage conditions and the current I ₃₀ must be considered. The measurement depends on the electrical system status.

In carrying out a fourth embodiment of the method, a starter run-up over a rotational speed n (t) in engagement is analyzed (curve 41) FIG. 2 ). Within the engine control can thus a high resolution measurement of Start-up behavior to the speed n (t) during startup to provide information on derating by over-patination. Furthermore, the startup behavior of different starting processes at the same temperatures can be compared via an envelope. For this purpose, no additional measured variables except the information about the rotational speed n (t) are required. By a battery sensor and the influence of the vehicle electrical system state can be estimated. Inaccuracies can be taken into account by the influence of the internal combustion engine in the starter intervention, aging effects, friction change, compression change and a variation of the drag torque, which can change the run-up behavior.

Claims (6)

1. A method of determining a state of a starter motor (91, 126) which comprises a brush-commutator assembly (1), in which a current measurement and a voltage measurement are performed in each case in at least one detection cycle at defined operating points (51, 53) on a battery which supplies electrical energy to the starter motor (91, 126), and a resistance of the brush-commutator assembly (1) is determined therefrom, wherein the resistances are ascertained and compared with one another at different defined operating points (51, 53), and the resistance of the brush-commutator assembly (1) is detected by a difference in the resistances ascertained in the different defined operating points (51, 53), wherein the current measurement and the voltage measurement are performed at a first operating point (51) prior to the start-up of the starter motor (91, 126) when the armature of the starter motor (91, 126) is stationary, and are performed at a second operating point (53) during the start-up of the starter motor (91, 126), wherein the second operating point (53) is reached when the current reaches a peak.
2. The method as claimed in claim 1, which is performed for a starter motor (91, 126) which is designed for starting-up an internal combustion engine.
3. The method as claimed in any one of the preceding claims, in which a plurality of detection cycles are performed at time intervals, wherein during all of the detection cycles current and voltage measurements are carried out at the same defined operating points (51, 53).
4. The method as claimed in claim 3, in which the detection cycles are each performed at the same temperature of the starter motor (91, 126).
5. An assembly which has at least one measuring device and at least evaluating module (131) and is designed to determine a state of a starter motor (91, 126) which comprises a brush-commutator assembly (1), wherein the at least one measuring device performs a current measurement and a voltage measurement in each case in at least one detection cycle at defined operating points on a battery which supplies electrical energy to the starter motor (91, 126), and wherein the evaluating module (131) determines a resistance of the brush-commutator assembly (1) therefrom, wherein the resistances are to be ascertained and compared with one another at different defined operating points (51, 53), and the resistance of the brush-commutator assembly (1) is to be detected by a difference in the resistances ascertained in the different defined operating points (51, 53), wherein the current measurement and the voltage measurement are to be performed at a first operating point (51) prior to the start-up of the starter motor (91, 126) when the armature of the starter motor (91, 126) is stationary, and are to be performed at a second operating point (53) during the start-up of the starter motor (91, 126), wherein the second operating point (53) is reached when the current reaches a peak.
6. The assembly as claimed in claim 5, in which the at least one measuring device is designed as a battery sensor.

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