DE102019218502A1 - Method and test circuit for testing the insulation between a circuit and a vehicle body - Google Patents

Abstract

The invention relates to a method and a test circuit (10) for testing the insulation between a circuit (12) and a vehicle body (16). The test circuit (10) has a first input (20) which is in contact with the first pole (14), a second input (22) which is in contact with the second pole (18) and a third input (24) which is in contact with the vehicle body (16). A first measuring path (26) with at least one first measuring resistor (R3) and a first voltage tap point (28) for a first voltage (U1) runs between the first input (20) and the second input (22), a second measuring path (32) with a second voltage tap point (34) for a second voltage (U2) runs between the second input (22) and the third input (24). A first changeover switch (40) can establish a connection between the first voltage tap point (28) and the third input (24) in the closed state. When the first changeover switch (40) is open and closed, a value is recorded for the first and / or the second voltage (U1, U2), and from the recorded values of the first voltage (U1) and / or the second voltage (U2) electrical resistance of the first and second insulation resistance (R1, R2) is determined. After the first changeover switch (40) has been opened and closed, the time profile of the first voltage (U1) and / or the second voltage (U2) is recorded and the values of the first and / or the second voltage (U1, U2) are recorded in Determined as a function of the time courses of the first and / or the second voltage (U2).

Description

The invention relates to a method and a test circuit for testing the insulation between a circuit and a vehicle body, in particular between a high-voltage circuit and a vehicle body.

In vehicles, especially in electric vehicles, circuits with high voltages are used more and more frequently. For safety reasons, these high-voltage circuits in the vehicle must be electrically insulated, i.e. shielded in such a way that people cannot come into contact with the high-voltage circuit or that parts of the vehicle that people come into contact with are isolated from the high-voltage circuit. This shielding must be guaranteed over the entire service life of the vehicle for all loads that occur during vehicle operation, for example vibrations, environmental influences or accidents.

This shielding must be constantly checked in order to quickly identify errors in the shielding and to be able to take appropriate safety measures. For example, after a defective shielding has been detected, the battery can be disconnected from the consumer and / or a charging unit or an optical or acoustic warning signal can be output. The quality of the shielding is also referred to as the insulation resistance between the high-voltage circuit and the vehicle body, with the insulation resistance having to be as high as possible.

A passive measurement approach can be used, for example, to test the shielding or the insulation resistance.

In the case of a passive measurement approach, a high-resistance test circuit, that is to say a test circuit with a very high electrical resistance, is connected between the high-voltage side and the vehicle body side. The electrical resistance of this test circuit is so high that the currents applied to the vehicle body via the test circuit are harmless in terms of safety. The insulation resistances can be calculated from the ratios of the electrical resistances of the test circuit and the insulation resistances by means of voltage measurements at certain measuring points of the test circuit.

The test circuit can usually be switched between at least two different resistance states, with the insulation resistances between the vehicle body and the two poles of the circuit or the battery being able to be determined from the different voltage distributions in the two states. After switching between the resistance states, however, there are initially charging processes, since in addition to the insulation resistances between the high-voltage side and the vehicle body side, there are also electrical capacitances, the size of which is unknown. The charging processes of these capacities must be awaited before a reliable resistance measurement can take place. The transient processes or the charging processes, however, require time, which means that the measurement of the insulation resistance, i.e. the testing of the shielding, requires a defined time.

The object of the invention is to provide a method and a test circuit for testing the insulation between a circuit and a vehicle body, in particular between a high-voltage circuit and a vehicle body, which enable the insulation resistance to be determined more quickly and thus a faster test of the shielding between the high-voltage circuit and the vehicle body. Furthermore, the test circuit should be able to carry out a self-diagnosis.

To solve the problem, a method for testing the insulation between a circuit and a vehicle body is provided, in particular for testing a first insulation resistance between a first pole of a power source and the vehicle body and a second insulation resistance between a second pole of the vehicle body and the vehicle body, with a Test circuit which has a first input that is contacted with the first pole, a second input that is contacted with the second pole and a third input that is contacted with the vehicle body. The test circuit has a first measuring path between the first input and the second input, with a first measuring resistor and a first voltage tap point for a first voltage and a second measuring path between the second input and the third input, with a second voltage tap point for a second voltage . Furthermore, the test circuit has a changeover switch which, in the closed state, establishes a connection between the first voltage tap point and the third input. With the first changeover switch open and the first changeover switch closed, a value for the first voltage and a value for the second voltage are recorded, and from the respective in the values of the first voltage and the second voltages recorded according to the switching states, the first and the second insulation resistance are determined. After opening and closing the first changeover switch, the time profile of the first voltage and the time profile of the second voltage are recorded and the values of the first and second voltage are determined as a function of the time profiles of the first and second voltage.

So far, after opening and closing the first switch, a defined period of time has been waited for, in which the charging processes within the system are ended, taking into account all possible negative circumstances. However, this period is several seconds. That is, in order to be able to carry out a measurement both with the first changeover switch open and with the first switch closed, it was previously necessary to wait several seconds before a reliable measurement could take place.

According to the invention, the settling time is no longer viewed as an absolute time period, but rather is determined individually. For this purpose, after opening and closing the first changeover switch, the temporal progressions of the first voltage and the second voltage are considered and conclusions are drawn about the transient behavior of the system or the duration of the charging processes is estimated or calculated. As a result, the point in time at which a charging process is ended can be determined or estimated very precisely, so that the first voltage and the second voltage can be measured without a time delay. As soon as the first voltage and the second voltage are determined in one state, the changeover switches can be opened or closed to establish the second state and the duration of the charging process can also be estimated for this state and, after the charging process has ended, the first voltage and the second can be determined Voltage to be carried out.

Since a measurement of the first voltage and the second voltage can be carried out immediately after the end of the charging process, the values for the first voltage and the second voltage can be determined much faster, so that the calculation of the insulation resistance can be carried out much faster.

In particular, if the insulation resistance should be low, for example due to a defect, this method enables the insulation resistance to be determined much more quickly and thus a defect to be detected more quickly, so that the necessary measures to establish a safe state can be initiated much more quickly.

If the insulation resistance is high, as is usual with functioning insulation, this charging process can take longer. As an alternative, a maximum time can be set here at which the system is assumed to have settled.

In addition, a second changeover switch can be provided which, in the closed state, switches a second measuring resistor parallel to the second voltage tap point between the second input and the third input, with values of the first voltage and the second voltage with the second changeover switch open or closed when the first changeover switch is open or closed are compared and if there is a discrepancy between the values, an error message is output, with the time profile of the first voltage and the time profile of the second voltage being recorded after the second switch is opened and closed, and the values of the first and second voltage are recorded as a function of the time courses of the first and the second voltage can be determined.

The second switch can produce two different states with different paths for the current within the test circuit. The first and the second voltage tap point are selected in such a way that the same voltage or the same voltage curve must be applied to the voltage tap point in both states produced by the second changeover switch. If these differ from one another, an error within the test circuit must be assumed and an error message is output. With the method described above, a self-diagnosis of the test circuit is thus possible in order to check the correct function of the test circuit.

For example, the temporal progression, in particular the temporal change, of the first voltage and the temporal progression, in particular the temporal change, of the second voltage are each compared with a limit value and the values for the first and second voltage are recorded when the limit value is undershot. As the charging process increases, the first voltage and the second voltage approach a limit value, ie the change in the first voltage and the second voltage over time decreases, so that the first voltage and the second voltage approach a limit value. Fall below the If changes over time in the first voltage and the second voltage exceed a defined limit value, it can be assumed that the charging process has ended and the end is imminent. In particular, the course of the temporal change in the first voltage and the second voltage can be viewed and a point in time can be calculated from this in advance at which the temporal change in the first voltage and the second voltage will likely fall below the limit value.

In order to carry out the method for testing the insulation resistance as quickly as possible, the first and / or the second changeover switch are opened or closed immediately after the values for the first and second voltages have been recorded with the first changeover switch closed or open.

A warning message can also be output if the time profile of the first voltage and / or the time profile of the second voltage lie outside a limit range.

The limit range can be a maximum charging time, for example. If there are no constant values for the first voltage and / or the second voltage after this maximum time has elapsed, an error signal can be output, since it can be assumed that in this case there is a defect in the test circuit or the insulation resistance.

Alternatively, the limit value can be a maximum or a minimum slope of the change over time in the first voltage or the second voltage. For example, a limit range can be defined which represents the change over time in the first voltage and the second voltage when the insulation resistance is functioning and / or when the test circuit is functioning. If the change over time in the first voltage and / or the second voltage lies outside this limit range, it must be assumed that there is a defect in the test circuit or in the insulation resistance. In this way, a corresponding defect can be detected before a charging process has ended, so that the defect can be detected very quickly.

In addition, temporal fluctuations in the power consumption in the circuit can be recorded and calculated from the temporal course of the first voltage and the temporal course of the second voltage. Changes in voltage over time can also be caused by fluctuations in power consumption. These are preferably also recorded in order to be able to calculate them out of the temporal changes in the first voltage and the second voltage, so that a reliable observation of the transient processes is possible.

The values of the first voltage and the second voltage can also be estimated from the time profiles of the first voltage and the second voltage. By considering the temporal change in the first voltage and the second voltage, an end value for the first voltage and the second voltage can already be calculated or estimated, for example if the temporal change in the first voltage and / or the second voltage decreases so that the first Voltage and / or the second voltage approaches a limit value. It is therefore not necessary to wait for the complete charging process, which enables the insulation resistance to be checked even more quickly.

The measuring circuit can additionally have a memory in which the time profiles of the first voltage and the second voltage, the stored time profiles of the first voltage and the second voltage being used to determine the values for the first voltage and the second voltage. Older stored time profiles of the first voltage and / or the second voltage can be used to estimate the current time profiles of the first voltage and / or the second voltage. For example, if a similar or the same time curve of the first voltage and / or the second voltage is already stored in the memory, it can be assumed that a similar or the same value is achieved for the first voltage and / or the second voltage.

To solve the problem, a test circuit for testing the insulation between a circuit and a vehicle body is also provided, in particular for testing a first insulation resistance between a first pole of a power source and the vehicle body and a second insulation resistance between a second pole of the vehicle body and the vehicle body. The test circuit has a first input that is contacted with the first pole, a second input that is contacted with the second pole and a third input that is contacted with the vehicle body. Furthermore, the test circuit has a first measuring path between the first input and the second input, with a first measuring resistor and a first voltage tap point for a first voltage, as well as a second measuring path between the second input and the third input, with a second voltage tap point for a second voltage. The test circuit also has a changeover switch which, in the closed state, establishes a connection between the first voltage tap point and the third input. The test circuit has a controller for carrying out a method described above.

The test circuit can have a second changeover switch which, in the closed state, switches a second measuring resistor in parallel with the second voltage tap point between the second input and the third input, the test circuit values the first voltage and the second voltage with an open and closed second changeover switch when the first changeover switch is open or closed Can compare changeover switches and an error message is output if the values differ.

• 1 eine Testschaltung zur Prüfung der Isolation zwischen einem Stromkreis und einer Fahrzeugkarosserie in einem ersten Schaltzustand;
• 2 ein Ersatzschaubild der Testschaltung aus 1;
• 3 die Testschaltung aus 1 in einem zweiten Schaltzustand;
• 4 ein Ersatzschaubild der Testschaltung aus 2;
• 5 die Testschaltung aus 1 in einem dritten Schaltzustand;
• 6 die Testschaltung aus 1 in einem vierten Schaltzustand;
• 7 Einen Schaltungsaufbau mit einer Testschaltung aus den 1 bis 6;
• 8 zeitliche Verläufe der Spannungen innerhalb des Schaltungsaufbaus aus 9;
• 9 Einen zweiten Schaltungsaufbau mit einer Testschaltung aus den 1 bis 6;
• 10 zeitliche Verläufe der Spannungen innerhalb des Schaltungsaufbaus aus 9; und
• 11 Einen dritten Schaltungsaufbau mit einer Testschaltung aus den 1 bis 6.

Further advantages and features can be found in the following description in conjunction with the accompanying drawings. In these show:

• 1 a test circuit for testing the insulation between a circuit and a vehicle body in a first switching state;
• 2 an equivalent diagram of the test circuit 1 ;
• 3rd the test circuit off 1 in a second switching state;
• 4th an equivalent diagram of the test circuit 2 ;
• 5 the test circuit off 1 in a third switching state;
• 6th the test circuit off 1 in a fourth switching state;
• 7th A circuit structure with a test circuit from the 1 to 6th ;
• 8th Time curves of the voltages within the circuit structure 9 ;
• 9 A second circuit structure with a test circuit from the 1 to 6th ;
• 10 Time curves of the voltages within the circuit structure 9 ; and
• 11 A third circuit structure with a test circuit from the 1 to 6th .

In 1 is a test circuit 10 for testing the insulation between a circuit in a vehicle and a vehicle body.

In modern vehicles, in particular in electric vehicles, circuits with relatively high voltages, for example 400 V, are used. For safety reasons, there must be no electrical connection between these circuits and vehicle parts with which people can come into contact. An insulation must therefore be present between the circuit and the other parts of the vehicle, that is to say the vehicle body, which provides a reliable separation between the circuit and the other parts of the vehicle. This insulation must ensure a reliable separation of the circuit from the other vehicle parts in the event of loads occurring in the vehicle, for example environmental influences, vibrations or even in the event of extraordinary events such as accidents.

Furthermore, this insulation must be constantly monitored during operation of the vehicle in order to be able to initiate necessary measures immediately in the event of a fault in the insulation, for example a complete separation of the circuit from the power source.

The test circuit 10 for this purpose determines the insulation resistance between the high-voltage circuit and the vehicle body, in particular a first insulation resistance R1 between a first pole 14th of the circuit 12th and the vehicle body 16 and a second insulation resistor R2 between a second pole 18th of the circuit 12th and the vehicle body 16 . With intact insulation between the circuit 12th and the vehicle body 16 need the insulation resistances R1 , R2 be very high, so that no or only a very low current flow between the poles 14th , 18th of the circuit 12th and the vehicle body 16 is present. If the electrical resistance falls below one of the insulation resistances R1 , R2 a defined value, protective measures can be triggered, for example an error message or a disconnection of the battery from the circuit.

The test circuit 10 has a first entrance 20th , the one with the first pole 14th is contacted, a second input 22nd , the one with the second pole 22nd is contacted as well as a third input 24 that with the vehicle body 16 is contacted.

The test circuit 10 has a first measurement path 26th on that is from the first entrance 20th about a first resistance R3 and a first voltage tap point 28 to the second entrance 22nd extends. At the first voltage tap point 28 is a voltage divider 30th provided, which consists of two partial resistors R4.1 , R4.2 is formed, which together have a resistance R4 form. The first voltage tap point 28 is with a first exit 29 connected.

A second measurement path 32 is between the second entrance 22nd and the third entrance 24 formed, this measuring path 32 a second voltage tap point 34 having. There is also a voltage divider 36 provided by two partial resistors R5.1 , R5.2 is formed, which together have a resistance R5 form. The second voltage tap point 34 is with a second exit 35 connected.

Between the first resistance R3 and the first voltage tap point 28 a first line branches off 38 from the first measurement path 26th starting with the third entrance 24 connected is. The administration 38 can through a toggle switch 40 closed or interrupted.

There is also a second line 42 with a second resistor R6 and a second switch 44 provided parallel to the second voltage tap point 34 is arranged or from the first line 38 between the first switch 40 and the third entrance 24 branches off and after the first voltage tap point 28 in the first measuring path 26th flows out.

The first switch 40 and the second switch 44 are each with a contact point 41 , 45 connected through which the switch 40 , 44 can be controlled.

About the exits 29 , 30th as well as the contact points 41 , 45 is the test circuit 10 with a control circuit 46 connected ( 7th ). The control circuit 46 instructs a controller 48 on that with the contact points 41 , 45 is contacted and through which the switch 40 , 44 can be controlled. Furthermore, the control circuit 46 an evaluation circuit 50 on that with the controller 48 as well as the outputs 29 , 35 connected to and from the controller 48 and the exits 29 , 35 received signals the electrical resistances of the insulation resistors R1 , R2 can calculate. The calculated electrical resistances of the insulation resistances R1 , R2 are connected to a communication interface 52 issued. Furthermore, the control circuit 46 a second communication interface 54 to receive various signals or control commands.

The electrical resistances of the resistors R3 , R6 as well as the electrical resistances of the resistors R4.2 , R4.2 , R5.1 . R5.2 the voltage divider 30th , 36 are known. The resistances R3 , R6 are chosen so large that the resistances R3 , R6 between the circuit 12th and the vehicle body 16 flowing currents are very low and therefore safe from a safety point of view. Furthermore, the one between the first pole 14th and the second pole 18th applied battery voltage U _Bat known.

The electrical resistances of the insulation resistances R1 , R2 are unknown and should be determined using the circuit described above.

In a first state, which in 1 is the second toggle switch 44 opened and the first toggle switch 40 closed.

The resulting switching status is shown schematically in 2 shown.

Between the first pole 14th and the vehicle body 16 is the first resistance R3 parallel to the first insulation resistance R1 arranged.

Between the second pole 22nd and the vehicle body 16 are the two voltage tap points 28 , 34 with the associated voltage divider 30th , 36 or their resistances R4 or. R5 each parallel to the second insulation resistor R2 arranged.

In a second state, which is in 3rd is the second toggle switch 44 closed and the first toggle switch 40 open.

The resulting switching status is shown schematically in 4th shown. Between the first pole 14th and the vehicle body 16 is just the insulation resistance R1 arranged, because over the open first changeover switch 40 no power between the first input 20th and the third entrance 24 about the first resistance R3 can flow. Between the second pole 22nd and the vehicle body 16 are the second insulation resistance R2 the second voltage tap point 34 with the resistors R5.1 , R5.2 as well as the second resistor R6 arranged in parallel.

A third state can be achieved by closing both changeover switches 40 , 44 be produced (see 5 ). The first resistor is in this third state R3 parallel to the first insulation resistance R1 between the first pole 14th and the vehicle body 16 arranged. Between the second pole 18th and the vehicle body are the two stress application points 28 , 34 with the voltage dividers 30th , 36 or their resistances R4 and R5 as well as the second resistor R6 parallel to the second insulation resistance R2 switched.

In a fourth state ( 6th ) are both toggles 40 , 44 opened so that between in the first pole 14th and the vehicle body 16 only the first insulation resistance R1 is connected and between the second pole 18th and the vehicle body only the resistors R5.1 , R5.2 of the second voltage divider 36 parallel to the second insulation resistance R2 are switched.

By measuring the first voltage U ₁ at the first voltage tap point 30th and / or the second voltage U ₂ at the second voltage tap point 34 in two selected of the above-described states can be with the known electrical resistances of the resistors R3 , R4.1 , R4.2 , R5.1 , R5.2 , R6 and the known battery voltage U _bat, a system of equations can be set up in these two states, by solving the electrical resistances of the insulation resistances R1 , R2 can be determined.

The procedure for determining the electrical resistances of the insulation resistances R1 , R2 is described below using the first and second states, for example.

In the first state, the battery _{voltage U bat.1 is applied} and the first voltage U _{1.1 is applied} at the first voltage tap point 30th measured.

bzw. $$\frac{U_{\mathrm{1,1}}}{U_{Bat\mathrm{,1}}}=1+\frac{\frac{1}{R_2}+\frac{1}{R_4}+\frac{1}{R_5}}{\frac{1}{R_1}+\frac{1}{R_3}}$$

oder $$\left[\frac{U_{\mathrm{1,1}}}{U_{Bat\mathrm{,1}}}-1\right]\ast \left[\frac{1}{R_3}+\frac{1}{R_1}\right]=\frac{1}{R_2}+\frac{1}{R_4}+\frac{1}{R_5}$$

In the first state: $$\frac{U_{\mathrm{B.}at\mathrm{,1}}}{U_{1.1}}=\frac{\frac{1}{\frac{1}{{\mathrm{R.}}_2}+\frac{1}{{\mathrm{R.}}_{\mathrm{4th}}}+\frac{1}{{\mathrm{R.}}_5}}}{\frac{1}{\frac{1}{{\mathrm{R.}}_2}+\frac{1}{{\mathrm{R.}}_{\mathrm{4th}}}+\frac{1}{{\mathrm{R.}}_5}}+\frac{1}{\frac{1}{{\mathrm{R.}}_1}+\frac{1}{{\mathrm{R.}}_{\mathrm{3rd}}}}}$$

or. $$\frac{U_{1.1}}{U_{\mathrm{B.}at\mathrm{,1}}}=1+\frac{\frac{1}{{\mathrm{R.}}_2}+\frac{1}{{\mathrm{R.}}_{\mathrm{4th}}}+\frac{1}{{\mathrm{R.}}_5}}{\frac{1}{{\mathrm{R.}}_1}+\frac{1}{{\mathrm{R.}}_{\mathrm{3rd}}}}$$

or $$\left[\frac{U_{1.1}}{U_{\mathrm{B.}at\mathrm{,1}}}-1\right]\ast \left[\frac{1}{{\mathrm{R.}}_{\mathrm{3rd}}}+\frac{1}{{\mathrm{R.}}_1}\right]=\frac{1}{{\mathrm{R.}}_2}+\frac{1}{{\mathrm{R.}}_{\mathrm{4th}}}+\frac{1}{{\mathrm{R.}}_5}$$

Then by closing the first toggle switch 40 and opening the second switch 44 changed to the second state and in this the first voltage U _1.2 at the first voltage tap point 30th measured at the battery _{voltage U Bat.2.}

In the second state: $$\frac{1}{{\mathrm{R.}}_1}=\left[\frac{1}{{\mathrm{R.}}_2}+\frac{1}{{\mathrm{R.}}_5}+\frac{1}{{\mathrm{R.}}_{\mathrm{6th}}}\right]\ast \frac{U_{\mathrm{B.}at\mathrm{,\; 2}}}{U_{1.2}-U_{\mathrm{B.}at\mathrm{,\; 2}}}$$

Inserted into the transformed equation of the first state, the following applies: $$\left[\frac{U_{1.1}}{U_{\mathrm{B.}at\mathrm{,1}}}-1\right]\ast \left[\frac{1}{{\mathrm{R.}}_{\mathrm{3rd}}}+\left[\frac{1}{{\mathrm{R.}}_2}+\frac{1}{{\mathrm{R.}}_5}+\frac{1}{{\mathrm{R.}}_{\mathrm{6th}}}\right]\ast \frac{U_{\mathrm{B.}at\mathrm{,\; 2}}}{U_{1.2}-U_{\mathrm{B.}at\mathrm{,\; 2}}}\right]=\frac{1}{{\mathrm{R.}}_2}+\frac{1}{{\mathrm{R.}}_{\mathrm{4th}}}+\frac{1}{{\mathrm{R.}}_5}$$

so dass $$\left[\frac{U_{\mathrm{1,1}}-U_{Bat\mathrm{,1}}}{U_{Bat\mathrm{,1}}}\right]\ast \left[\frac{1}{R_3}+\left[\frac{1}{R_2}+\frac{1}{R_5}+\frac{1}{R_6}\right]\ast \frac{U_{Bat\mathrm{,2}}}{U_{\mathrm{1,2}}-U_{Bat\mathrm{,2}}}\right]=\frac{1}{R_2}+\frac{1}{R_4}+\frac{1}{R_5}$$

Furthermore applies $$\frac{U_{1.1}}{U_{\mathrm{B.}at\mathrm{,1}}}-1=\frac{U_{1.1}-U_{\mathrm{B.}at\mathrm{,1}}}{U_{\mathrm{B.}at\mathrm{,1}}}$$

so that $$\left[\frac{U_{1.1}-U_{\mathrm{B.}at\mathrm{,1}}}{U_{\mathrm{B.}at\mathrm{,1}}}\right]\ast \left[\frac{1}{{\mathrm{R.}}_{\mathrm{3rd}}}+\left[\frac{1}{{\mathrm{R.}}_2}+\frac{1}{{\mathrm{R.}}_5}+\frac{1}{{\mathrm{R.}}_{\mathrm{6th}}}\right]\ast \frac{U_{\mathrm{B.}at\mathrm{,\; 2}}}{U_{1.2}-U_{\mathrm{B.}at\mathrm{,\; 2}}}\right]=\frac{1}{{\mathrm{R.}}_2}+\frac{1}{{\mathrm{R.}}_{\mathrm{4th}}}+\frac{1}{{\mathrm{R.}}_5}$$

so dass gilt $$R_2=\frac{1-\left[\frac{U_{\mathrm{1,1}}-U_{Bat\mathrm{,1}}}{U_{Bat\mathrm{,1}}}\ast \frac{U_{Bat\mathrm{,2}}}{U_{\mathrm{1,2}}-U_{Bat\mathrm{,2}}}\right]}{\left[\frac{U_{\mathrm{1,1}}-U_{Bat\mathrm{,1}}}{U_{Bat\mathrm{,1}}}\ast \left[\frac{U_{Bat\mathrm{,2}}}{U_{\mathrm{1,2}}-U_{Bat\mathrm{,2}}}\ast \left[\frac{1}{R_5}+\frac{1}{R_6}\right]+\frac{1}{R_3}\right]\right]-\frac{1}{R_4}+\frac{1}{R_5}}$$

This equation can be used according to R2 to be resolved $$\begin{array}{l}\frac{1}{{\mathrm{R.}}_2}\left[\left[\frac{U_{1.1}-U_{\mathrm{B.}at\mathrm{,1}}}{U_{\mathrm{B.}at\mathrm{,1}}}\ast \frac{U_{\mathrm{B.}at\mathrm{,\; 2}}}{U_{1.2}-U_{\mathrm{B.}at\mathrm{,\; 2}}}\right]-1\right]\hfill \\ =\frac{1}{{\mathrm{R.}}_{\mathrm{4th}}}+\frac{1}{{\mathrm{R.}}_5}+\frac{1}{{\mathrm{R.}}_{\mathrm{3rd}}}\ast \left[\frac{U_{1.1}-U_{\mathrm{B.}at\mathrm{,1}}}{U_{\mathrm{B.}at\mathrm{,1}}}\right]-\left[\frac{U_{1.1}-U_{\mathrm{B.}at\mathrm{,1}}}{U_{\mathrm{B.}at\mathrm{,1}}}\ast \frac{U_{\mathrm{B.}at\mathrm{,\; 2}}}{U_{1.2}-U_{\mathrm{B.}at\mathrm{,\; 2}}}\right]\hfill \end{array}$$

so that applies $${\mathrm{R.}}_2=\frac{1-\left[\frac{U_{1.1}-U_{\mathrm{B.}at\mathrm{,1}}}{U_{\mathrm{B.}at\mathrm{,1}}}\ast \frac{U_{\mathrm{B.}at\mathrm{,\; 2}}}{U_{1.2}-U_{\mathrm{B.}at\mathrm{,\; 2}}}\right]}{\left[\frac{U_{1.1}-U_{\mathrm{B.}at\mathrm{,1}}}{U_{\mathrm{B.}at\mathrm{,1}}}\ast \left[\frac{U_{\mathrm{B.}at\mathrm{,\; 2}}}{U_{1.2}-U_{\mathrm{B.}at\mathrm{,\; 2}}}\ast \left[\frac{1}{{\mathrm{R.}}_5}+\frac{1}{{\mathrm{R.}}_{\mathrm{6th}}}\right]+\frac{1}{{\mathrm{R.}}_{\mathrm{3rd}}}\right]\right]-\frac{1}{{\mathrm{R.}}_{\mathrm{4th}}}+\frac{1}{{\mathrm{R.}}_5}}$$

The equation thus only contains known values or values determined in the two states, so that R2 can be calculated. Is R2 known, the equation for the second state can after R1 dissolved and R1 be calculated.

Instead of the above-described system of equations for the first and the second state, two other states can be used for setting up the system of equations if the insulation resistances are determined by solving the system of equations R1 , R2 is possible.

Furthermore, through a suitable choice of the states for the two measurements of the voltages U ₁ and U ₂ a self-diagnosis of the test circuit 12th be performed.

For self-diagnosis of the test circuit, two of the four states described above are used, in which at the first voltage tap point 28 and / or at the second voltage tap point 34 the same tension U1 or. U2 must create.

The resistance between the poles 14th , 18th and the vehicle body 16 but cannot be described as ohmic resistances alone. Rather, they are between the poles 14th , 18th and the vehicle body capacities 47 , 49 of unknown size, which are charged after the first and second states have been established. The loading processes of these capacities must be awaited before a reliable voltage measurement at the first and / or voltage tap point 28 , 34 and thus a reliable determination of the insulation resistance R1 , R2 can be done.

Usually, a fixed time is assumed for the charging processes after the first or the second state has been established, within which the charging processes are ended in any case, even under the most unfavorable conditions. After this time has elapsed, the voltages are measured at the first and / or voltage tap point 28 , 34 carried out in the first or in the second state.

In regular vehicle operation, especially when the vehicle is started, the insulation resistance measurements are much faster R1 , R2 required.

About the time to detect the first voltage U1 and / or the second voltage U2 Shortening in the various states is made after opening and closing the first toggle switch 40 and / or the second switch 44 each time the course of the first voltage U1 and the time course of the second voltage U2 detected. The values of the first voltage U1 and the second voltage U2 depending on the time course of the first voltage U1 and the second voltage U2 determined.

In principle, there is no fixed period of time before the measurements of the first voltage U1 and the second voltage U2 respectively. Instead, the time of the measurements becomes the first voltage U1 and the second voltage U2 determined individually, depending on the time course of the first voltage U1 and the second voltage U2 .

For example, the time course of the first voltage is considered U1 and the second voltage U2 determines whether charging has ended.

For example, the course over time, in particular the change over time a1, a2, of the first voltage U1 and the second voltage U2 detected ( 8th ) and in advance in a filter unit 56 filtered or voltage voltages compensated.

As the charging process progresses, the change a1, a2 over time in the first voltage increases U1 and the second voltage U2 from. The time change a1, a2 of the first voltage U1 and the second voltage U2 is after the acquisition and filtering in a comparison unit 58 each with one in a memory 60 stored limit value compared.

When the change a1, a2 of the first voltage falls below a limit value U1 and the second voltage U2 that is in a store 60 is stored, it can be assumed that the loading processes have ended or are almost finished. Then the values of the first voltage U1 and the second voltage U2 to calculate the electrical resistance of the insulation resistance R1 , R2 and / or used to perform a self-diagnosis.

The point in time at which the transient processes are ended is therefore determined in order to be able to measure the first voltage immediately after the transient processes have ended U1 and the second voltage U2 perform. You can then open or close a toggle switch 40 , 44 a further state is established and in this, after the end of the settling time has been determined again with the method described above, the measurement of the first voltage U1 and the second voltage U2 be performed. With the two values of the first voltage U1 and the second voltage U2 can then determine the electrical resistance of the insulation resistance R1 , R2 and / or self-diagnosis. The time to determine the electrical resistances of the insulation resistances R1 , R2 and / or to carry out a self-diagnosis can thus be significantly shortened.

Optionally, the previously used maximum time for the transient processes can still be stored in the controller or in the memory 60 be saved. If, after the maximum time has elapsed, the time change a1, a2 in the first voltage U1 and the second voltage U2 is above a defined limit value, so the charging processes are not completed, for example because the electrical resistances of the insulation resistances R1 , R2 have changed during the measurement or there is a defect in the test circuit, a warning message can be output.

Optionally or additionally can be stored in the memory 60 Limit values, in particular limit ranges for the time courses, in particular the changes over time, of the first voltage U1 and the second voltage U2 be stored, which has a regular temporal course of the voltages U1 , U2 with intact insulation resistances R1 , R2 describe ( 10 ). The limit values and / or limit ranges are compared with a second comparison unit 62 (please refer 9 ) with the time courses of the first voltage U1 and / or the second voltage U2 compared. The time change of the first voltage lies U1 and / or the second voltage U2 At a defined point in time or a certain period of time outside the limit values or limit ranges stored in the memory, it is assumed that the electrical resistances of the insulation resistances are outside a defined range and an error message is output.

This procedure enables the detection of irregularities in the insulation resistance R1 , R2 before the charging of the system after establishing a state by opening or closing at least one of the changeover switches 40 , 44 is finished, allowing a faster insulation resistance test R1 , R2 is possible.

In addition, another memory 64 be provided in which the determined curves of the first voltage U1 and the second voltage U2 get saved. These historical values can be used to keep track of those in memory 60 to correct stored limit values or limit ranges or to correct the current curves of the voltages U1 , U2 to be able to assess better.

If fixed limit values or limit ranges are used, they must record all conditions that occur during vehicle operation as well as time-related changes. The limit values or the limit ranges must therefore be at a sufficiently large distance from the normal time profile of the voltages U1 , U2 to avoid false error messages.

Irregularities in the timing of the tensions U1 , U2 are therefore only recorded if they exceed a certain value. By compensating with historical values, the limit values or the limit ranges can be closer to the regular curves of the voltages U1 , U2 must be adjusted, since the charging curve does not change or changes only very slowly if the insulation resistances are intact.

The time courses of the first tension U1 and the second voltage U2 3.4 . can also be used to calculate the final values of the voltages U1 , U2 to calculate or interpolate. For example, it can be the time courses of the first voltage U1 and the second voltage U2 be E-functions, so that a limit value for the first voltage and / or the second voltage can be calculated.

This method of voltage calculation can take place very quickly, so that, for example, when a vehicle is started, a first determination of the electrical resistances of the insulation resistances is very quick R1 , R2 is present. The accuracy of this calculation is sufficient in any case to estimate whether the insulation resistance R1 , R2 are intact. A more precise determination can be made as soon as the correct functioning of the insulation resistances R1 , R2 was determined to be carried out during operation using one of the methods described above.

Claims (10)

Method for testing the insulation between a circuit (12) and a vehicle body (16), in particular for testing a first insulation resistance (R1) between a first pole (20) of a power source and the vehicle body (16) and a second insulation resistance (R2) between a second pole (18) and the vehicle body (16), with a test circuit (10) having a first input (20) which is contacted with the first pole (14), a second input (22) which is connected to the second Pole (18) is contacted and has a third input (24) which is in contact with the vehicle body (16), the test circuit (10) having a first measurement path (26) between the first input (20) and the second input ( 22), with at least a first measuring resistor (R3) and a first voltage tap point (28) for a first voltage (U1), and wherein the test circuit (10) has a second measuring path (32) between the second input (22) and the third Input ng (24), with a second voltage tap point (34) for a second voltage (U2), and wherein the test circuit (10) has a first changeover switch (40) which, in the closed state, establishes a connection between the first voltage tap point (28) and the third input (24), with a value for the first voltage (U1) and / or a value for the second voltage (U2) being recorded in each case with the first changeover switch (40) open and the first changeover switch (40) closed, and off the values of the first voltage (U1) and / or the second voltage (U2) recorded in the respective switching states, the electrical resistance of the first insulation resistor (R1) and the second insulation resistor (R2) are determined, characterized in that after opening and the Closing the first changeover switch (40) in each case the time profile of the first voltage (U1) and / or the time profile of the second voltage (U2) is recorded and the values of the first voltage (U1) and / or the second voltage (U2) depending on the time profiles of the first voltage (U1) and / or and the second voltage (U2 ) be determined. Procedure according to Claim 1 , characterized in that a second changeover switch (44) is provided which, when closed, switches a second measuring resistor (R6) parallel to the second voltage tap point (34) between the second input (22) and the third input (24), with values of the first voltage (U1) and / or the second voltage (U2) are compared with the first changeover switch (40) and second changeover switch (44) open or closed, and an error message is output if the values differ, after opening and closing the first changeover switch and / or the second changeover switch (44) the time profile of the first voltage (U1) and / or the time profile of the second voltage (U2) can be detected and the values of the first and second voltage (U1, U2) as a function can be determined from the time curves of the first and the second voltage (U1, U2). Method according to one of the Claims 1 and 2 , characterized in that the course over time, in particular the change over time (a1), the first voltage (U1) and the course over time, in particular the change over time (a2), the second voltage (U2) are each compared with a limit value and at If the limit value falls below the values for the first and / or the second voltage (U1, U2) are recorded. Method according to one of the Claims 1 and 2 , characterized in that immediately after the values for the first voltage / U1) and / or the second voltage (U2) have been recorded, with the first and / or second changeover switch (40, 44) closed or open, the first and / or the second changeover switch (40 , 44) is opened or closed. Method according to one of the Claims 2 and 3rd , characterized in that a warning message is output when the time profile of the first voltage (U1) and / or the time profile of the second voltage (U2) are outside a limit range. Method according to one of the preceding claims, characterized in that temporal fluctuations in the power consumption in the circuit (12) are recorded and calculated from the temporal course of the first voltage (U1) and the temporal course of the second voltage (U2). Method according to one of the preceding claims, characterized in that the values of the first voltage (U1) and the second voltage (U2) are estimated from the time curves of the first voltage (U1) and the second voltage (U2). Method according to one of the preceding claims, characterized in that the measuring circuit (10) has a memory (66) in which the time profiles of the first voltage (U1) and the second voltage (U2), the stored time profiles of the first voltage ( U1) and the second voltage (U2) can be used to determine the values for the first voltage (U1) and the second voltage (U2). Test circuit (10) for testing the insulation between a circuit (12) and a vehicle body (16), in particular for testing a first insulation resistance (R1) between a first pole (14) of a power source and the vehicle body (16) and a second insulation resistance ( R2) between a second pole (18) and the vehicle body (16), with a first input (20) which is in contact with the first pole (14), a second input (22) which is in contact with the second pole (18) is contacted and a third input (24) which is contacted with the vehicle body (16), wherein the test circuit has a first measuring path between the first input and the second input, with a first measuring resistor and a first voltage tap point for a first voltage, wherein the test circuit (10) has a first measuring path (26) between the first input (20) and the second input (22), with at least a first measuring resistor (R3) and a first Voltage tap point (28) for a first voltage (U1), and wherein the test circuit (10) has a second measuring path (32) between the second input (22) and the third input (24), with a second voltage tap point (34) for a second voltage (U2), and wherein the test circuit (10) has a first changeover switch (40) which, in the closed state, establishes a connection between the first voltage tap point (28) and the third input (24), characterized in that the test circuit has a Control (46) for performing a method according to one of the preceding claims. Test circuit after Claim 9 , characterized in that a second changeover switch (44) is provided which, when closed, switches a second measuring resistor (R6) parallel to the second voltage tap point (34) between the second input (22) and the third input (24), and that the Test circuit (10) compares values of the first voltage (U1) and / or the second voltage (U2) with the first changeover switch (40) and second changeover switch (44) open or closed and outputs an error message if the values deviate, whereby after opening and when the first changeover switch and / or the second changeover switch (44) are closed, the time profile of the first voltage (U1) and / or the time profile of the second voltage (U2) are recorded and the values of the first and second voltage (U1, U2) can be determined as a function of the time curves of the first and second voltage (U1, U2).

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