DE2735000B2 - Diagnostic procedure for an electric starter motor - Google Patents

Description

The invention relates to a diagnostic method for an electric starter motor of an internal combustion engine with simultaneous measurement of battery voltage, starter current and speed.

In the computer-controlled diagnosis of motor vehicles that has become common in recent years the function of the starter motor should also be checked.

A test stand for motor vehicle starters is known, with the help of which the motor vehicle Removed starter motor with a third-party battery with simultaneous measurement of the battery voltage, des The starter current and the speed of the starter can be checked. Such a test procedure does not take into account the natural conditions under which the starter motor operated in the motor vehicle will.

A rational test procedure must assume that the starter is installed, i.e. during of his company to be checked on the spot. Such a test is then not only dependent on the condition of the Starter motor dependent, but also on the state of charge of the vehicle battery and the cranking the torque required by the racing engine. This; in turn depends on the compression of the motor, the condition of the bearings and the viscosity of the lubricating oil.

The object on which the invention is based is to develop a diagnostic method for an electric starter motor of an internal combustion engine with simultaneous measurement of battery clamping, starter current κ. and speed, at which the above-mentioned environmental influences are taken into account. According to the invention, the solution is seen in the fact that the three values are measured during a starting process of the internal combustion engine and the third value is calculated from two de is compared.
In this method, the internal combustion engine

is with its starter motor and battery as one The analog computer for a function linking the three variables is considered The value output by the machine is combined with a setpoint that is calculated according to the known function was compared. All possible states of the battery and the internal combustion engine are thus taken into account

A power / speed function is expediently selected as a link between the three variables

A circuit arrangement for carrying out the method is characterized in that a first, Input of a computing unit provided for the rotational speed via a tachometer with an electrical one Scanners connected by marks attached to the flywheel of the internal combustion engine, a second input for the starter current via an ammeter with a measuring resistor in the starter circuit and a third input for the battery voltage via a voltmeter with the terminals connected to a starter battery.

Tachometers, voltages and ammeters are advantageously designed as digital measuring devices and as A digital small computer is provided for the arithmetic unit. The arithmetic unit contains a comparator and a Printer and / or display output.

The invention is explained with the aid of three figures.

Fig. 1 represents the basic circuit diagram of an electrical Starter motor.

In Fig. 2 are various power functions with deviating from one another in a diagram Parameters shown.

F i g. 3 shows, as a block diagram, a circuit arrangement for carrying out the method.

From Fig. 1 it can be seen that the starter motor of an internal combustion engine is connected as a series motor is, d. H. the excitation winding and the armature are connected in series to the battery voltage. For one such motor type applies to the speed

/ 1 =

and for the torque

M = K ₁ -Ii,

where η stands for the speed, U for the battery voltage , 1 _Λ for the current through the field and armature winding, RiA for the internal resistance and Ki for a constant, in

the properties of the field or excitation winding enter. the end

M = K ₂ -Il results for the armature current

I, =

If the relationship for the torque is inserted into the above formula for the speed, the result is for the speed '

10

η =

K ₁

and from it finally

15th

20th

25th

After further transformations, a relationship between Power, voltage and speed are set up, which is as follows:

ρ ₌

U ¹

35

Where P is the performance resulting from the product of Terminal voltage of the starter motor and the armature current results.

In Fig. 2, three curves are shown in a diagram in which the speed η is plotted on the abscissa axis and the power P is plotted on the ordinate axis Curve corresponds to operation with a different constant As noted above, the constant reflects the conditions of the field or excitation circuit. From these three diagrams it can be seen that, due to minor changes, the behavior of the starter no longer achieves the typical curve during normal operation

It is expedient to equip the arithmetic unit so that instead of a single one stored in it Comparison function two limit functions can be saved. All values that are in that of these functions A limited tolerance band fall indicate a satisfactory result for the starter motor. All outside lying values are signs of a malfunction. Should the diagnosis for motor vehicles with different battery voltages are used, it can also be useful to use a set of curves of current / speed characteristics for storing the different battery voltages represent different parameters.

In Fig. 3, an internal combustion engine K is indicated by a crankshaft with pistons. A flywheel 5 is seated at one end of the crankshaft. Marks are attached to the flywheel and are scanned by an inductive transmitter OT. Coupled with the flywheel of the starter motor M, which is fed via a measuring resistance R at a battery B, the voltage on the battery B is applied via a voltage meter UM to a corresponding input of an arithmetic unit C Two are taps of the measuring resistor R connected to respective inputs of an amplifier V tied together. The output of the amplifier V feeds a signal representing the current through the measuring resistor R to an ammeter IM , the output of which is connected to a corresponding input of the arithmetic unit C. The output of the inductive transmitter OT is connected to a corresponding input of the arithmetic unit C via a tachometer nM. A fourth input of the arithmetic unit C is connected to a programming unit SP , in which the values for limit functions are stored, between which the value calculated in the arithmetic unit C must lie if the starter is in order. From two indicator lights £. 1, L 2 each light up to indicate whether the starter is OK or not.

1 sheet of drawings

Claims (4)

Patent claims: 1. Diagnostic method for an electric starter motor of an internal combustion engine under simultaneous measurement of battery voltage, starter current and speed, characterized in that the three values are measured during a starting process of the internal combustion engine and from two of the measured values in an arithmetic unit corresponding to one the three variables linking relationship the third value is calculated and in a comparator with the measured one third value is compared. 2. Diagnostic method according to claim 1, characterized in that as a link between the three Sizes a power / speed function is selected 3. Circuit arrangement for carrying out the method according to claim 1, characterized in that a first, provided for the speed input of a computing unit (C) via a tachometer (nM) with an electrical scanner (OT) from on the flywheel (S) of the internal combustion engine (K) , a second input for the starter current via an ammeter (IM) with a measuring resistor (R) in the starter circuit and a third input for the battery voltage via a voltmeter (UM) with the terminals of a starter battery (^. 4. Circuit arrangement according to claim 3, characterized in that the speed, voltage and ammeter (nM, UM, IM) are digital measuring devices and a digital small computer is used as the arithmetic unit (C) , and that the arithmetic unit (C) has a comparator and one Includes printer and / or display output.