METHOD FOR REGULATING THE TEMPERATURE OF A GLOW PLUG

Abstract

Described is a method for regulating the temperature of a glow plug of an internal combustion engine, wherein a target resistance is determined from a target temperature by means of a resistance temperature characteristic of the glow plug and the actual resistance of the glow plug is regulated to the target resistance, the glow plug is heated to determine the resistance temperature characteristic of the glow plug, and thereby determining a resistance gradient and an electrical resistance of the glow plug is measured before the heating or at a defined time during the heating, using both the measured resistance and the resistance gradient, the resistance temperature characteristic is determined.

Claims

1. A method for regulating the temperature of a glow plug of an internal combustion engine, comprising: (a) determining a resistance temperature characteristic of the glow plug by: (i) heating the glow plug and at the same time determining a resistance gradient; (ii) measuring the electrical resistance of the glow plug before the hearing or at a defined time during the heating; and (iii) using both the measured resistance and the resistance gradient to determine the resistance temperature characteristic; (b) determining a target resistance from a target temperature by means of the resistance temperature characteristic; and (c) regulating the actual resistance of the glow plug to the target resistance.

2. The method according to claim 1, wherein the electrical resistance of the glow plug is measured as a cold resistance at the beginning of the heating.

3. The method according to claim 1, wherein the resistance temperature characteristic is determined by means of a given resistance temperature characteristic, which is adapted using the measured resistance and the resistance gradient.

4. The method according to claim 3, comprising: for determining the resistance temperature characteristic, a reference heating behavior of a reference glow plug is used and the measured resistance is compared with a resistance of the reference glow plug, which were measured at the same time in the reference heating behavior relative to the beginning of the heating behavior, and a first correction value is determined from the difference of these two resistances, with which correction value the given resistance temperature characteristic is adapted; the resistance gradient determined with the heating of the glow plug is compared with a resistance gradient of the reference glow plug, which is calculated from two resistances which were measured at the same times in the reference heating behavior relative to the beginning of the heating behavior, and a second correction value is determined from the deviation of these resistance gradients; and the resistance temperature characteristic of the glow plug is determined from the given resistance temperature characteristic, the first correction value and the second correction value.

5. The method according to claim 3, comprising: comparing the measured resistance with a corresponding resistance which was determined from the given resistance temperature characteristic, and a first correction value is determined from the difference of these two resistances, with which value the given resistance temperature characteristic is adapted; comparing the resistance gradient determined with the heating of the glow plug with a resistance gradient of the given resistance temperature characteristic or the resistance temperature characteristic corrected using the first correction value, and determining a second correction value from the deviation; and determining the resistance temperature characteristic of the glow plug from the given resistance temperature characteristic, the first correction value and the second correction value.

6. The method according to claim 4, wherein the first correction value is used additively to adapt the given resistance temperature characteristic.

7. The method according to claim 4, wherein the second correction value is used to adapt the steepness of the given resistance temperature characteristic.

8. The method according to claim 1, wherein the resistance gradient is determined by feeding a predetermined energy into the glow plug in a predetermined period of time and determining the difference between the electrical resistance of the glow plug at the end and at the beginning of this period of time.

9. The method according to claim 8, wherein the predetermined period of time is at least 400 ms.

10. The method according to claim 8, wherein the predetermined period of time is at least 500 ms.

11. The method according to claim 8, wherein the predetermined period of time is at least 700 ms.

12. The method according to claim 8, wherein the predetermined period of time is not more than 1000 ms.

13. The method according to claim 8, wherein the predetermined period of time is not more than 900 ms.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0017] FIG. 1 shows the resistance profile of various ceramic glow plugs of the same type with the heating;

[0018] FIG. 2 shows temperature profiles which were determined from the resistance profiles shown in FIG. 1 by means of a standard resistance temperature characteristic; and

[0019] FIG. 3 shows temperature profiles which were determined from the resistance profiles shown in FIG. 1 by means of a resistance temperature characteristic determined according to the invention.

DESCRIPTION

[0020] The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure.

[0021] In FIG. 1, typical examples of resistance profiles of ceramic glow plugs of the same type are shown in a heating process with identical power profile. The upper line indicates resistance R as a function of time t for a glow plug at the upper edge of the tolerance or specification range, the lower line resistance R as a function of time t for a glow plug at the bottom edge of the tolerance or specification range and the middle line resistance R as a function of time t for a glow plug from the middle of the tolerance or specification range. In particular, the glow plug from the middle of the tolerance range with the middle line can be considered as a reference glow plug, which shows a reference heating behavior.

[0022] In FIG. 1, it can be clearly seen that the resistances scatter in a range of about 200 m. The cold resistance of the ceramic glow plugs at the beginning of the heating process in this case is between 200 m and 400 m the resistance at the end of the heating process, for example, between about 1100 m and 1300 m.

[0023] The resistance temperature characteristic of glow plugs can be typically described as a linear function of the form T(R)=a.Math.R+b, wherein T is the temperature of the glow plug, R the electrical resistance of the glow plug, a and b are constants that must be determined for the respective glow plug.

[0024] A reference resistance temperature characteristic indicates the resistance temperature characteristic of a reference glow plug, e.g., an average glow plug of one type, such as, perhaps, a glow plug which is in the middle of the manufacturing tolerance or specification range. FIG. 2 shows, by way of example, temperature profiles in C. over time t, which were calculated from the resistance profiles shown in FIG. 1 by means of such a reference resistance temperature characteristic. As can be seen, the final temperatures determined in this way scatter about 100 K, so that a corresponding inaccuracy arises in the temperature regulation on the basis of the reference resistance temperature characteristic.

[0025] FIG. 3 shows temperature profiles in C. over time t in seconds which were calculated from the resistance profiles shown in FIG. 1, using resistance temperature profiles which were determined as described below by adaptation from a given reference resistance temperature characteristic. It can be seen that the scattering of the calculated temperatures can be considerably reduced in this way, so that a much more precise temperature regulation is possible.

[0026] In order to adapt the given reference resistance temperature characteristic, the resistance profile which results for the glow plugs of FIG. 1 is considered in each case, if these are heated with a defined heating profile, thus, for example, a defined electric power is fed into the glow plugs for a defined period of time. The temperature increase accompanying a defined heating profile of an average glow plug of one type, for example, a reference glow plug, is referred to as a reference heating behavior.

[0027] In a method according to this disclosure, for example, the electrical resistance can be measured at the beginning of the heating process. If the engine has not previously been in operation for a sufficiently long time, this can be the cold resistance. In addition, the gradient of the electrical resistance is determined, for example, by feeding a predetermined energy into the glow plug in a predetermined period of time and determining the difference between the electrical resistance of the glow plug at the end and at the beginning of this period of time. For this purpose, for example, the difference in the electrical resistance at a time t1 and a time t2 can be determined and this difference can be divided by the value t2t1. The difference between the times t2 and t1 may be 400 ms or more, for example 500 ms or more, in particular 600 ms or more. The time t1 may mark the beginning of the heating process or after the beginning of the heating process, for example, 50 ms later. The time t2 is preferably at most 1000 ms, for example, not more than 900 ms after the beginning of the heating process.

[0028] In FIG. 1, the middle line may be regarded as a resistance profile of a reference glow plug, for example, an average glow plug having resistance values in the middle of a production-related tolerance range. The electrical resistance of the glow plug to be regulated at time t0, i.e., R(t0), is compared with the resistance of a reference glow plug at the corresponding time, i.e., the resistance at time t0 with a reference heating behavior. From the difference d1 determined thereby, a first correction value can be obtained which is added to a given resistance temperature characteristic in order to adapt it to the present plug. When the given resistance temperature characteristic has the form T(R)=a.Math.R+b, the resistance temperature characteristic adapted to the first correction value thus has the form T(R)=a.Math.R+b+d1. In this approach, the time t0 may indicate the beginning of the heating operation or may be anywhere between t1 and t2, so that t1t0t2. These times t0, t1, t2 may be fixed times or be defined by boundary conditions, such as an amount of energy supplied. The time t0 can also be associated, for example, with a specific heating phase, that is, also before the time t1.

[0029] A second correction value is determined by comparing the resistance gradient determined for the times t1 and t2 with the resistance gradient of a reference glow plug in the reference heating behavior. A second correction value d2 can be obtained from the difference between these two resistance gradients, for example, the difference of the resistance gradients can be used directly as a second correction value.

[0030] This second correction value can also be used additively. When the given resistance temperature characteristic has the form T(R)=a.Math.R+b, the resistance temperature characteristic adapted with the first correction value and the second correction value thus has the form T(R)=a.Math.R+b+d1+d2.

[0031] Alternatively, the second correction value d2 may also be used multiplicatively to correct the steepness of the resistance temperature characteristic, such as in the form T(R)=(a+d2).Math.R+b+d1.

[0032] While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.