EP2258939A2 - Method for monitoring the temperature of a glow plug - Google Patents

Abstract

The method involves calculating a mathematical model (4) from an input parameter of an output parameter (X), calculating an electrical parameter expected value (Re) and measuring the electrical parameter. The expected value of the electrical parameter is provided by the mathematical model. An independent claim is also included for a glow plug controller for executing a controlling method.

Description

The invention relates to a method for controlling the temperature of a glow plug, wherein from a setpoint temperature a desired value of a temperature-dependent electrical variable is determined and an effective voltage generated by pulse width modulation is used as a manipulated variable.

In methods for controlling or controlling the temperature of a glow plug, the electric resistance or, which is equivalent, the electrical conductivity is usually used as the setpoint. In principle, however, other temperature-dependent electrical variables, for example the inductance, can also be used instead of the electrical resistance or the electrical conductivity.

The object of the invention is to show a way how to quickly regulate the temperature of a glow plug with the engine running to a target value.

The above object is achieved by a method having the features specified in claim 1. Advantageous developments of the invention are the subject of dependent claims.

In a closed-loop control method according to the invention, a desired value of a temperature-dependent electrical variable is not compared with an actual value, as in conventional PID control methods, and the effective voltage is changed as a function of the instantaneous and possibly a preceding deviation. Instead, in a method according to the invention, a mathematical model of the glow plug is used, with which an expected value of the electrical quantity is calculated. This model is fed back with the controlled system containing the glow plug, d. H. a change in the manipulated variable is made to reach the desired setpoint temperature or the desired setpoint value as a function of the result of a comparison on the basis of the output quantity of the model and the setpoint value. The feedback required for a control therefore takes place via the output of the mathematical model at which the output variable provided by the model is provided.

By evaluating the calculated value, preferably by comparison with the measured value, an error signal is generated from which an input variable is calculated together with the value of the effective voltage for the mathematical model. From this input, the mathematical model calculates an output that specifies the expected value of the electrical quantity.

In this case, the output variable of the model can be the expected value of the electrical variable or merely predetermine the latter, so that the expected value is determined by a further calculation step from the output variable, for example by a multiplication by a constant factor. Accordingly, the comparison to be made based on the output and the setpoint may be performed by comparing values calculated from the setpoint and the output, such as voltage values, or by comparing the setpoint immediately with the expected value.

The error signal corrects any modeling errors. Without external influences, i. Therefore, after a period of time whose duration depends on the precision of the mathematical model, the calculated value finally coincides with the measured value. If faults in the candle temperature occur, this leads to a deviation of the calculated size from the measured size. Since the input of the mathematical model depends on both the calculated and measured values, such as the difference between the measured and calculated values, the mathematical model follows the glow plug, i.e., the glow plug. the calculated value approaches the measured value even when disturbances occur.

By a control method according to the invention, defects in the candle temperature can be corrected much faster than is possible with conventional control methods. In conventional PID methods, the change in the manipulated variable depends not only on the instantaneous deviation between the actual value and the setpoint, but also on previous deviations (I or D component). Disturbances, however, generally have nothing to do with previous deviations, so that the consideration of previous deviations in the treatment of disorders often does not help. On the other hand, even with a pure proportional control can not achieve good results, since the characteristic properties of a system can be detected only poorly. On the other hand, a control method according to the invention allows an efficient and rapid temperature control in the event of a fault as well as in the occurrence of disturbances.

For example, the mathematical model that calculates an expected value of electrical quantity may be formulated as a linear differential equation. In the simplest case, the mathematical model contains only two parameters that are characteristic of a given glow plug and its installation environment. The first constant is used to weight the current value of the variable to be calculated, and the second variable to weight the manipulated variable, ie the effective voltage.

In a method according to the invention, the electrical resistance or, which is synonymous, the temperature-dependent electrical variable is preferred electrical conductivity used. In this case, the electrical resistance or the electrical conductivity of the glow plug including leads can be used. Of course, however, the electrical resistance or the conductivity of the glow plug without contributions from supply lines are taken into account. Alternatively or additionally, for example, the inductance can also be used as a temperature-dependent electrical variable.

An advantageous development of the invention provides that a second error signal is generated by evaluating the calculated value, which is used to correct the setpoint value of the electrical variable, for example, the desired resistance. In this way, the influence of disturbances, which are caused by the driving operation with the engine running, treated even better. Namely, by adding a correction to the setpoint, a fault can be compensated for particularly effectively and the desired setpoint temperature can be reached particularly quickly. If, for example, the fault leads to additional heating of the glow plug, ie an increase in temperature, the desired setpoint temperature can be reached more quickly by assuming a slightly lower setpoint value when converting the setpoint value into a value of the effective voltage. In this way, the additional energy input of a disturbance can be compensated by a lower heating power. The correction of the setpoint value can be determined, for example, using a characteristic map, from which a selection is made taking into account the second error signal and the setpoint temperature or a setpoint determined from the setpoint temperature. With the second error signal so a second feedback is made.

This second feedback leads to two control loops being present per se in the method, each of which contains a controlled system containing the glow plug. A first control loop is created by the feedback of the output of the mathematical model. A second loop through the feedback of the second error signal.

The second error signal can be generated by comparing the calculated value with the measured value, for example by subtraction, so that the second error signal is proportional to the difference between the two calculated values.

However, it is also possible to determine the second error signal by using a further mathematical model of the glow plug, the input value of the further mathematical model being the value of the rms voltage applied to the glow plug, and the second error signal being used by comparing the output variables of the two models is produced. Thus, in this approach, the input of the first model depends on both the rms voltage and the measured value, while in the second model the input depends only on the rms voltage. The two mathematical models are preferably identical, that is, they perform the same arithmetic operations on an input variable.

The described use of two mathematical models surprisingly has the advantage that modeling errors have a smaller impact. This has the advantage that the quality of the control is influenced less by changing conditions, for example, use of a given glow plug in another engine or a change in the type of glow plug itself. The sometimes considerable effort, for example by appropriate attempts to determine suitable parameters for the mathematical model of the described method, can therefore be reduced.

In addition to the method described above, the present invention further relates to a glow plug control device, which performs in operation a method according to the invention. Such a glow plug control device can be realized, for example, with a memory and a control unit, for example a microprocessor, wherein a program is stored in the memory, which carries out the method according to the invention during operation. The hardware components of such a glow plug control device may be identical to the hardware of commercially available glow plug control devices.

Further details and advantages of the invention will be explained with reference to embodiments with reference to the accompanying drawings. Same and each other

Figur 1

eine schematische Darstellung eines Ausführungsbeispiels eines erfindungs- gemäßen Regelungsverfahrens; und

Figur 2

ein weiteres Ausführungsbeispiel eines erfindungsgemäßen Regelungsver- fahrens.

Corresponding elements are provided with matching reference numerals. Show it:

FIG. 1

a schematic representation of an embodiment of a control method according to the invention; and

FIG. 2

a further embodiment of a control method according to the invention.

In FIG. 1 the sequence of a method for controlling the temperature of a glow plug 1 is shown schematically. In the illustrated control method, an effective voltage U _eff generated by pulse width modulation from an on-board voltage of a vehicle is used as the manipulated variable. As a control variable, the electrical resistance R _{e of} the glow plug 1 is used in the illustrated embodiment, wherein for the control method in principle any other temperature-dependent electrical variable or a vector with multiple sizes can be used.

In the im FIG. 1 In a first step, a setpoint value R _{SolI of} the electrical resistance of the glow plug is determined, for example by means of a characteristic map 2, from the setpoint temperature T _SolI . From the setpoint value R _SolI , a value is then determined for the effective _voltage U _eff which is applied to the glow plug 1 is created. The conversion of the setpoint value R _SolI into a value for the effective _voltage U _eff can be carried out, for example, by means of a prefilter 3 or a characteristic curve.

With a mathematical model 4, an expected value R _{e of} the electrical resistance is calculated from the effective voltage U _eff applied to the glow plug 1. The mathematical model 4 can provide as output directly the expected value. However, in the illustrated embodiment, the model 4 provides an output X from which the expected value R _{e of} the electrical quantity is calculated in a further step 4a, preferably by multiplication by a constant.

By evaluating the calculated value R _e , a first error signal e ₁ (t) is generated in a method step 5. For this purpose, the calculated value R _{e is} compared with a measured value R _{m of} the resistance. For the calculation of the first error signal E ₁ (t), the calculated resistance value R _e are subtracted, for example, from the measured Widertandswert R _m, as shown in Fig. 1 indicated by the minus sign (-). The result of such difference formation may be weighted by an appropriate factor that may be empirically determined so that the first error signal e ₁ (t) is proportional to the difference between the measured resistance R _m and the calculated resistance R _e .

The input value of the mathematical model 4 is a value calculated from the value of the effective voltage U _eff and the first error signal e ₁ (t). Such a mathematical model 4, the input quantity of which depends on a comparison between a calculated and a measured value, is called Luenberger observer.

The output _quantity X of the mathematical model 4 and the setpoint value R _{SolI are} used to calculate a corrected value for the effective _voltage U _eff and to change the effective _voltage U _eff to the corrected value. If the output X is also the expected value R _e , the output can be directly compared with the setpoint R _SolI and the effective _voltage U _{eff changed} according to the result of the comparison, for example proportional to the difference. Generally speaking, it is sufficient to couple the output of the model 4 with an input of a controller, that is, to carry out a feedback of the model output.

If the output quantity X, as in the illustrated embodiment, does not coincide with the expected value R _e , a resistance value or a voltage value is first calculated from the output quantity X in a method step 6, which can be called a state regulator or feedback matrix Setpoint R _SolI or a determined from the setpoint R _SolI size, namely the current effective _voltage U _eff , is compared. According to the result of this comparison, the effective voltage U _{eff is} changed. Preferably, a voltage value is added to the instantaneous value of the effective voltage (U _eff ) which is proportional to the difference between the setpoint value R _Sol and the calculated value R _e . The comparison and the change in the effective voltage U _{eff in} dependence on the difference determined thereby are in FIG. 1 shown as process step 7.

By evaluating the calculated value R _e , a second error signal e ₂ (t) is determined, which is used to correct the setpoint R _SolI . For this purpose, the setpoint value R _SolI determined from the setpoint temperature T _{SolI is used} together with the second error signal e ₂ (t) to determine an adjusted setpoint value, for example by means of a characteristic map 8. Preferably, a correction of the setpoint value R _{SolI is} determined Calculation added to the setpoint R _SolI , as shown in FIG. 1 is indicated by the method step 9. The corrected setpoint value is subsequently converted into a value for the effective voltage U _eff , for example by means of a prefilter 3 or a characteristic curve. If appropriate, the value of the effective voltage U _eff determined in this way is adapted in method step 7 taking into account the output quantity X.

As mathematical model 4, a differential equation, in particular a linear differential equation can be used. For example, the following calculation rule can be used as model 4: dR / dt = A • R + B • U _eff (t). In general, instead of the resistance R, another electrical variable or a vector of a plurality of electrical variables can also be used as the controlled variable x , so that the mathematical model is written more generally in the form d x / dt = A • x + B • u (t) leaves, where u is the manipulated variable.

The calculation of a voltage value from the output variable X es model 4 can be determined, for example, by multiplying it by a constant whose value can be determined by trial and error.

The second error signal e ₂ (t) is in the illustrated embodiment similar to the first error signal e ₁ (t) determined by comparing the measured value with the calculated value, for example by subtraction and multiplication of the difference with a weighting factor.

The control method according to the invention comprises per se two control circuits. A first control circuit includes the glow plug 1 and the model 4, shown in the In the exemplary embodiment, this first control loop contains the glow plug 1, the method step 5, the model 4 and the method steps 6 and 7. A second control loop contains the glow plug 1 and the feedback of the second error signal.

FIG. 2 shows another embodiment of a method for controlling the temperature of a glow plug 1. This method differs from the above with reference to FIG. 1 method explained in the first place by the fact that U _eff an output X2 is calculated from the value of the voltage applied to the glow plug 1 effective voltage with a further mathematical model 10 of the glow plug. 1 The calculation rules of the two models 4, 10 can be identical. However, in the case of the second model 10, the effective voltage U _eff applied to the glow plug is used directly as the input variable, while in the first model the input variable is calculated from the first error signal e ₁ (t) and the effective voltage U _eff .

The second error signal e ₂ (t) is applied to the in FIG. 2 illustrated embodiment by comparing the output variables X, X2 of the two models 4, 10 determined, for example by subtraction, as shown in FIG. 2 is indicated. The difference can be multiplied by a constant factor to calculate the second error signal e ₂ (t). The second error signal e ₂ (t) is therefore in the second embodiment of the difference between the two output variables X, X2.

reference numeral

1

glow plug

2

map

3

prefilter

4

first model

4a

step

5

step

6

step

7

step

8th

map

9

step

10

second model

U _eff

RMS voltage

T _Solll

set temperature

R _Soll

setpoint

R _e

expected resistance

R _m

measured resistance

e ₁ (t)

first error signal

e ₂ (t)

second error signal

X

Initial size of the first model

X2

Output of the second model

Claims (15)

Method for controlling the temperature of a glow plug (1), wherein from a setpoint temperature (T _SolII ) a desired value (R _SolI ) of a temperature-dependent electrical variable is determined, and
an effective voltage (U _eff ) generated by pulse width modulation is applied to the glow plug (1),
characterized in that
using a mathematical model (4), which calculates from an input quantity an output quantity (X) provided at its output, an expected value (R _e ) of the electrical quantity is calculated,
the electrical size is measured,
by evaluating the calculated value (R _e ) a first error signal e ₁ (t) is generated,
a value calculated from the value of the effective voltage (U _eff ) and the error signal (e ₁ (t)) is used as the input variable of the mathematical model (4), wherein the mathematical model (4) calculates an output variable (X) from the input variable, which specifies the expected value (R _e ) of the electrical quantity, and
with the output quantity (X) of the mathematical model (4) a corrected value for the effective voltage (U _eff ) is calculated and the effective voltage (U _eff ) is changed to the corrected value. A method according to claim 1, characterized in that the temperature-dependent electrical variable is the electrical resistance. Method according to one of the preceding claims, characterized in that the first error signal (e ₁ (t)) is generated by a comparison of the calculated value (R _e ) with the measured value (R _m ). Method according to one of the preceding claims, characterized in that the output quantity (X) is proportional to the expected value (R _e ) of the electrical quantity. Method according to one of the preceding claims, characterized in that for calculating the corrected value for the effective voltage (U _eff ) a value calculated from the output variable (X) is compared with the desired value (R _SolI ) or a variable determined from the desired value and the effective _voltage (U _eff ) the more it changes, the greater the difference found in the comparison. Method according to one of the preceding claims, characterized in that the corrected value for the effective voltage (U _eff ) is calculated by adding to the instantaneous value of the effective voltage (U _eff ) a voltage value which corresponds to the difference between the desired value (R _SolI ) and the calculated value (R _e ) is proportional. Method according to one of the preceding claims, characterized in that by evaluating the calculated value (R _e ), a second error signal (e ₂ (t)) is generated, which is used to correct the setpoint value (R _SolI ). A method according to claim 7, characterized in that the second error signal (e ₂ (t)) by a comparison of the calculated value (R _e ) with the measured value (R _m ) is generated. Method according to Claim 8, characterized in that the second error signal (e ₂ (t)) is proportional to the difference between the calculated value (R _e ) and the measured value (R _m ). Method according to Claim 7, characterized in that a further mathematical model (10) of the glow plug (1) is used, the value of the effective voltage (U _eff ) applied to the glow plug (1) being used as the input variable of the further mathematical model (10) and the second error signal is generated by comparing the output quantities (X, X2) of the two models (4, 10). A method according to claim 10, characterized in that the second error signal (e ₂ (t)) of the difference between the two output variables (X, X2) is proportional. A method according to claim 10 or 11, characterized in that the two mathematical models (4, 10) are identical. Method according to one of claims 7 to 12, characterized in that from the second error signal (e ₂ (t)) and the desired value (R _SolI ) by means of a map, a correction of the setpoint (R _SolI ) is determined. Method according to one of the preceding claims, characterized in that the first error signal (e ₁ (t)) for the calculation of the input variable is additively linked to the value of the effective voltage (U _eff ). Glow plug control device, characterized in that the glow plug control device in operation performs a method according to any one of the preceding claims.

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