METHOD FOR MONITORING THE OPERATION OF A VEHICLE ELECTRICAL SYSTEM

Abstract

The invention relates to a method for monitoring the operation of a vehicle electrical system (50), in which the component temperature (62) of a component (56) in the vehicle electrical system channel (52, 54), the ambient temperature (66) of the component (56) and the current (70) flowing through the component (56) are ascertained in a vehicle electrical system channel (52, 54) of the vehicle electrical system (50), and then, if overloading of the component (56) is detected, a period of time (72) to overloading of the component (56) is calculated,
wherein a heat input (P.sub.in) into the component (56) and a heat loss (P.sub.out) of the component (56) are used to ascertain the period of time (72) to overloading of the component (56).

Claims

1-14. (canceled)

15. A method for monitoring an operation of a vehicle electrical system, the method comprising the following steps: ascertaining, in a vehicle electrical system channel of the vehicle electrical system, a component temperature of a component in the vehicle electrical system channel, an ambient temperature of the component, and a current flowing through the component; in response to detecting an overloading of the component, calculating a period of time to the overloading of the component; wherein a heat input into the component and a heat loss of the component are used to ascertain the period of time to the overloading of the component.

16. The method according to claim 15, wherein the heat loss (P.sub.out) is ascertained as a function of the component temperature (T(t)), an ambient temperature (T.sub.amb), and/or a thermal resistance (Rt) of the component, using the following formula: $P_{\mathrm{out}}=\frac{\left(T\left(t\right)-T_{\mathrm{amb}}\right)}{\mathrm{Rt}}.$

17. The method according to claim 15, wherein the heat input (P.sub.in) is ascertained as a function of the current, (i), an electrical resistance (R) of the component, and an initial temperature (Tstart) of the component, using the following formula: P.sub.in=i.sup.2*R.

18. The method according to claim 17, wherein the electrical resistance (R) of the component is temperature-dependent.

19. The method according to claim 15, wherein the period of time to the overloading of the component is ascertained using a thermal differential equation: $\frac{\mathrm{dT}\left(t\right)}{\mathrm{dt}}=\frac{\left(P_{\mathrm{in}}-P_{\mathrm{out}}\right)}{\mathrm{Ct}},$ wherein T(t) is a temporal progression of the component temperature, P.sub.in is the heat input, P.sub.out is the heat loss and Ct is a heat capacity of the component.

20. The method according to claim 15, wherein an overload operation is identified when the heat input exceeds the heat loss.

21. The method according to claim 15, wherein the method is carried out for an output channel of an electronic power distributor and/or a vehicle electrical system monitoring system and/or in which an electronic switch is used as the component to control a safety-relevant consumer.

22. The method according to claim 15, wherein an adapted emergency measure for the vehicle electrical system channel is taken as a function of the calculated period of time to the overloading in overload operation.

23. The method according to claim 15, in which an increase in current caused by the emergency measure is taken into account in the calculation of the period of time to overloading.

24. The method according to claim 15, wherein the vehicle electrical system channel is switched off as a function of the calculated period of time to overloading.

25. The method according to claim 15, wherein the period of time (t.sub.overload) to the overloading is calculated using the following equation: $t_{\mathrm{overload}}=\frac{\ln \left(\frac{R_{20}{T}_{\mathrm{end}}{i}^2-20R_{20}{i}^2+R_{20}{i}^2-{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{end}}+{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{amb}}}{R_{20}{T}_{\mathrm{start}}{i}^2-2R_{20}{i}^2+R_{20}{i}^2-{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{start}}+{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{amb}}}\right)}{{\mathrm{Ct}}_{\mathrm{inv}}\left(R_{20}{i}^2-{\mathrm{Rt}}_{\mathrm{inv}}\right)}.$ wherein R.sub.20 is an electrical resistance R of the component at 20 C., T.sub.start is an initial temperature of the component, : is temperature correction factor for the electrical resistance per degree Celsius, R.sub.tinv is an inverted thermal resistance, T.sub.amb is an ambient temperature of the component, C.sub.tinv is inverted thermal capacity of the component.

26. An arrangement for monitoring an operation of a vehicle electrical system, the arrangement configured to: ascertain, in a vehicle electrical system channel of the vehicle electrical system, a component temperature of a component in the vehicle electrical system channel, an ambient temperature of the component, and a current flowing through the component; in response to detecting an overloading of the component, calculate a period of time to the overloading of the component; wherein a heat input into the component and a heat loss of the component are used to ascertain the period of time to the overloading of the component.

27. The arrangement according to claim 26, wherein the arrangement comprises: a temperature sensor configured to acquire the component temperature of the component of a vehicle electrical system; a temperature sensor configured to acquire the ambient temperature of the component; and a current measuring device configured to measure the current flowing through the component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 shows a flow chart of a possible sequence of the presented method.

[0022] FIG. 2 shows a schematic illustration of a vehicle electrical system comprising an arrangement for carrying out the method.

EMBODIMENTS OF THE INVENTION

[0023] The invention is illustrated schematically in the drawings on the basis of embodiments and is described in detail in the following with reference to the drawings.

[0024] FIG. 1 shows a flow chart of a possible sequence of the here described method. Some of the variables used are shown in FIG. 2.

[0025] In a first step 10, the variables current 70 or i, component temperature 62 and ambient temperature 66 or T.sub.amb are measured.

[0026] In a subsequent step 12, there is a check to see whether an overload operation is taking place. In the embodiment example, there is a check to see whether a heat input P.sub.in is greater than a heat loss P.sub.out. Either the heat input P.sub.in and/or the heat loss P.sub.out can be calculated, and/or other overload conditions derived from these variables are evaluated. The equations 1-3 discussed later can be used here.

[0027] The initial temperature Tstart of the component 56 could be used in equations 1 and 3 for a time tstart, for instance. The following overload condition could then be evaluated, for example:

[00001]$i^2*R>\frac{T_{\mathrm{start}}-T_{\mathrm{amb}}}{\mathrm{Rt}}$ [0028] wherein R: electrical resistance of the component 56 Rt: thermal resistance of the component 56, e.g. in K/W or:

[00002]$i^2*R_{20}\left(1+\left(T\left(t\right)-20\right)*\right)>\frac{T_{\mathrm{start}}-T_{\mathrm{amb}}}{\mathrm{Rt}}$ [0029] if the temperature dependence of the electrical resistance R is taken into account.

[0030] If this is not the case (no overload operation), a jump (arrow 14) to step 10 takes place. If this is the case (arrow 16), the time t.sub.overload to overloading is calculated in a step 18. In such a case then, an overload state or an impending overload is identified. This is followed in a step 20 with an overload operation. The variable t.sub.overload is passed on or reported so that an optimum emergency measure can be selected. The method then jumps to step 10 again (arrow 22).

[0031] FIG. 2 shows a highly simplified schematic illustration of a vehicle electrical system which is labeled overall with the reference number 50. This vehicle electrical system 50 includes a first vehicle electrical system channel 52 and a second vehicle electrical system channel 54. A component 56, the operation of which is being monitored, is shown in the second vehicle electrical system channel 54. For this purpose, an arrangement 58 is provided, to which a first unit 60, for example a first temperature sensor 60, for acquiring a component temperature 62, a second unit 64, for example a second temperature sensor, for acquiring an ambient temperature 66, and a current measuring device 68 for measuring a current 70 flowing through the component 56 are assigned. The component 56 can be an electronic switch (for example a MOSFET) that, for instance, protects a safety-relevant consumer (for example an electrical brake or steering system) or safety-relevant branches of the vehicle electrical system. In the event of an impending fault, such as overload, overvoltage, etc., the safety-relevant consumer can be switched off by the component 56. In the event of a fault in a non-safety-relevant branch of the vehicle electrical system, the component 56 could also be used to disconnect the safety-relevant branch of the vehicle electrical system, in which safety-relevant consumers are supplied, for instance, from the faulty branch of the vehicle electrical system.

[0032] The unit 60 can be implemented with a temperature sensor or, for example, also using a thermal model of the component 56. The component temperature 62 can be inferred from certain operating variables of the component 56. It is therefore immaterial whether the component temperature 62 is measured directly or determined in some other way.

[0033] It is also possible that only an initial temperature Tstart of the component temperature 62 is acquired.

[0034] From the acquired variables, namely the component temperature 62, the ambient temperature 66 and the current 70, the arrangement 58 calculates a time or period of time 72 to overloading of the component 56 as described in more detail in the following. An overload operation of at least the second vehicle electrical system channel 54 or the entire vehicle electrical system 50 is initiated depending on this calculation by selecting and then also implementing an emergency measure. This can lead to the second vehicle electrical system channel 54 or even the entire vehicle electrical system 50 being switched off. A switch, for example a MOSFET, is typically used for this purpose.

[0035] The method is based on the fact that current flowing through an electronic component produces heat. This heat in turn produces heat in the element or in the component 56 as a function of its thermal capacity or heat capacity Ct. This also causes a flow of heat P.sub.out from the component 56 if the ambient temperature 66 or T.sub.amb lower than the component temperature 62 or T itself. If this heat capacity Ct and the maximum permissible temperature at the component 56 before it is destroyed by heat are known, it is possible to calculate the time (or period of time 72 to overloading of the component 56) in which the current 70 or i can still flow to carry out a safety maneuver in an emergency.

[0036] However, this prediction is only valid if the current 70 or i remains constant. If a higher-level control unit takes over an emergency measure, it is expedient, for example in the event of an overload of an ABS channel (ABS: anti-lock braking system) and an emergency braking measure, to not only use the measured current 70 or i for the calculation of the remaining time (or period of time 72 to overloading of the component 56), but to instead use the measured current 70 or i plus an expected current increase resulting from the emergency measure, such as the measured current plus a nominal current, or carry out two separate calculations for an optimistic and a pessimistic time prediction.

[0037] The needed input variables are the current 70 or i, the component temperature 62 and the ambient temperature 66 or T.sub.amb, for example.

[0038] The following variables contribute to ascertaining the period of time 72 to overloading of the component 56:

[0039] The heat loss P.sub.out (for example in W) of the component 56 due to the ambient temperature 66 (for example in degrees Celsius) or T.sub.amb has to first be described or possibly calculated using the following equation:

[00003]$\begin{array}{cc}{P}_{\mathrm{out}}=\frac{\left(T\left(t\right)-T_{\mathrm{amb}}\right)}{\mathrm{Rt}}& \mathrm{Eq}.1\end{array}$ [0040] wherein T(t): the temporal progression of the component temperature 62 (for example in degrees Celsius), and [0041] Rt: thermal resistance of the component 56, e.g. in K/W=C/W.

[0042] As an alternative to calculating P.sub.out at the beginning of an overload period or a potential overload period, a specific initial temperature T.sub.start of the component 62 could be used.

[0043] The heat input P.sub.in (for example in W) caused by the current 70 or i (for example in A) into the component 62 with its electrical resistance R (for example in ohms) can be described or calculated as follows:

[00004]$\begin{array}{cc}{P}_{\mathrm{in}}=i^2*R& \mathrm{Eq}.2\end{array}$

[0044] If the electrical or ohmic resistance R of the component 62 is temperature-dependent, this may need to be taken into account as well:

[00005]$\begin{array}{cc}{P}_{\mathrm{in}}=i^2*R_{20}\left(1+\left(T\left(t\right)-20\right)*\right)& \mathrm{Eq}.3\end{array}$ [0045] wherein R20: electrical resistance R of the component 56 at 20 C. Temperature factor, in ohms/K

[0046] The thermal differential equation for component 56 is also known:

[00006]$\begin{array}{cc}\frac{\mathrm{dT}\left(t\right)}{\mathrm{dt}}=\frac{\left(P_{\mathrm{in}}-P_{\mathrm{out}}\right)}{\mathrm{Ct}}& \mathrm{Eq}.4\end{array}$ [0047] wherein Ct: heat capacity of the component 56, e.g. in J/K Using equations 1 and 3, this then results in:

[00007]$\begin{array}{cc}\frac{\mathrm{dT}\left(t\right)}{\mathrm{dt}}+T\left(t\right)*{\mathrm{Rt}}_{\mathrm{inv}}*{\mathrm{Ct}}_{\mathrm{inv}}-T_{\mathrm{amb}}*{\mathrm{Rt}}_{\mathrm{inv}}*{\mathrm{Ct}}_{\mathrm{inv}}-i^2*R_{20}\left(1+\left(T\left(t\right)-20\right)*\right)*{\mathrm{Ct}}_{\mathrm{inv}}=0& \mathrm{Eq}.5\end{array}$ [0048] And finally by solving the differential equation and solving for time and taking into account the condition T (t.sub.overload)=T(end)

[00008]$\begin{array}{cc}{t}_{\mathrm{overload}}=\frac{\ln \left(\frac{R_{20}{T}_{\mathrm{end}}{i}^2-20R_{20}{i}^2+R_{20}{i}^2-{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{end}}+{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{amb}}}{\begin{array}{c}{R}_{20}{T}_{\mathrm{start}}{i}^2-20R_{20}{i}^2+\\ R_{20}{i}^2-{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{start}}+{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{amb}}\end{array}}\right)}{{\mathrm{Ct}}_{\mathrm{inv}}\left(R_{20}{i}^2-{\mathrm{Rt}}_{\mathrm{inv}}\right)}& \mathrm{Eq}.6\end{array}$ [0049] P.sub.in: heat input [0050] P.sub.out: heat loss [0051] T.sub.amb: ambient temperature 66 [0052] R.sub.20: electrical resistance at 20 C. [0053] R.sub.tinv: inverted thermal resistance R.sub.tinv=1/Rt [0054] C.sub.tinv: inverted thermal capacity Ct.sub.inv=1/Ct [0055] a: temperature correction factor for the electrical resistance per degree Celsius [0056] t.sub.overload: the period of time 72 to overloading of the component 56 [0057] T.sub.start: initial temperature of the component 56

[0058] If the temperature dependence of the component 56 is not taken into account, the formula is simplified at a temperature correction factor equal to zero to:

[00009]$\begin{array}{cc}{t}_{\mathrm{overload}}=\frac{\ln \left(\frac{R_{20}{i}^2-{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{end}}+{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{amb}}}{R_{20}{i}^2-{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{start}}+{\mathrm{Rt}}_{\mathrm{inv}}{T}_{\mathrm{amb}}}\right)}{{\mathrm{Ct}}_{\mathrm{inv}}\left(-{\mathrm{Rt}}_{\mathrm{inv}}\right)}& \mathrm{Eq}.7\end{array}$

[0059] The presented method is in particular suitable to be used in conjunction with Powernet Guardians to thus increase the availability of vehicle electrical system channels.