Method for the detection of a glow plug replacement

Abstract

A method for detecting glow plug replacement or an aging glow plug. The glow plugs are heated and monitored. When a threshold value is reached for a first glow plug, a first value of a temperature-dependent variable is measured for all other glow plugs and is stored as reference values associated with the first glow plug. This process is repeated until reference values associated with each glow plug have been determined and stored for each glow plug. The process is repeated to determine a set of comparative values. The comparative values are compared with the reference values. A deviation of a comparative from a reference value of less than a specified tolerance value is considered an agreement. The inventive process concludes which of the glow plugs of the engine are unaltered and which have a resistance-temperature characteristic that has been altered to an extent indicating replacement, aging or a defect.

Claims

1. A method for detecting a glow plug replacement or an aging of a glow plug, comprising: (a) supplying a uniformly specified electrical power to each of the glow plugs of an engine for a predetermined amount of time to heat all glow plugs; (b) monitoring each glow plug to assess whether a temperature-dependent variable of each said glow plug reaches a threshold value; (c) when the threshold value has been reached for a first glow plug, a first value of the temperature-dependent variable is measured substantially simultaneously for all the other glow plugs of the engine, and the first measured values are stored as a first set of reference values associated with the first glow plug; (d) when the threshold value has been reached for a second glow plug, a second value of the temperature-dependent variable is measured simultaneously for all the other glow plugs of the engine, and the second measured values are stored as a second set of reference values associated with the second glow plug; (e) continuing the monitoring until the temperature-dependent variable has reached the threshold value for all of the glow plug, and a set of reference values associated with each glow plug has been determined and stored for each glow plug, or the specified period of time has elapsed; (f) after the set of reference values has been determined in step (e) for each glow plug, determining a set of comparative values for each glow plug during a subsequent heating process repeating steps (a)-(e) and storing the values thus determined as a set of comparative values; (g) for each glow plug, comparing the set of comparative values with the set of reference values, wherein each comparative value is compared with the corresponding reference value; (h) considering a deviation of a comparative value from a reference value by less than a specified tolerance value as an agreement; and (i) using step (h) to conclude which of the glow plugs of the engine are unaltered and which have a resistance-temperature characteristic that has been altered to an extent indicating replacement, aging or a defect.

2. The method according to claim 1, wherein a conclusion is drawn that all the glow plugs have been replaced when, for the first glow plug, no agreement was established in the comparison between the set of comparative values and the set of reference values for all the other glow plugs, and, for the second glow plug no agreement was established in the comparison between the set of comparative values and the set of reference values for all the other glow plugs.

3. The method according to claim 1, wherein a conclusion is drawn that the first glow plug has been replaced, has aged or is defective when, for the first glow plug, no agreement has been established in the comparison between the set of comparative values and the set of reference values for all the other glow plugs and for the second glow plug, agreement has been established in the comparison between the set of comparative values and the set of reference values for all the other glow plugs apart from the first glow plug.

4. The method according to claim 1, wherein the sets of reference data and the sets of comparative data are each corrected linearly by an amount by which the measured value at the i.sup.th glow plug deviates from the threshold value in the i.sup.th set of reference values, or the i.sup.th set of comparative values, wherein i is a whole number whose value is between 1 up to the number of glow plugs of the engine.

5. The method according to claim 1, wherein during heating, the electrical variable is measured simultaneously on all glow plugs, at time intervals that become shorter as heating progresses.

6. The method according to claim 1, wherein during heating the electrical variable is measured simultaneously on all glow plugs at constant time intervals.

7. The method according to claim 1, wherein a glow plug is also detected as defective when the temperature-dependent electrical variable measured on said glow plug does not reach the threshold value within the specified period of time.

8. The method according to claim 1, wherein a glow plug replacement is detected by the fact that no agreement is found in a majority of comparisons.

9. The method according to claim 1, wherein additional sets of reference values and associated sets of comparative values are also determined with a second threshold value, and the agreements determined during comparisons are statistically evaluated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 shows a flow chart, which illustrates how the sets of reference and comparative value are determined.

DESCRIPTION

(3) The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following 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.

(4) FIG. 1 illustrates an example of embodiment of a method with which a set of reference values is determined for each of the glow plugs of an engine. The engine has N glow plugs, where N is an integer greater than 2.

(5) The method illustrated in FIG. 1 is carried out while all the glow plugs of the engine are heated in the same way, that is to say, that each glow plug is supplied at a uniformly specified power. The uniformly specified power is supplied to the glow plugs for a specified period of time, which can be 2 seconds, for example. The method ends with the expiry of the specified period of time.

(6) In the embodiment shown, the electrical resistance R is used as the temperature-dependent variable of the glow plugs. However, any other temperature-dependent electrical variable can be used instead.

(7) While the glow plugs are heating up, the electrical resistance of each individual glow plug is continuously measured. The measurements are carried out simultaneously on all the glow plugs of the engine, or at least at such short intervals from one another that the temperature of the glow plugs changes only insignificantly during this time. The measurements can, for example, be carried out in successive cycles of a microprocessor. The results of these measurements are in each case stored in a buffer memory, for example as a set of measured values (R.sub.1, R.sub.2, . . . , R.sub.N), and can be overwritten with the results from a later measurement.

(8) For each of the measured resistances a check is then made as to whether it has reached a given threshold value C, i.e., a check is made as to whether R.sub.i is ≥C, wherein all integers from 1 to N are to be used for i in sequence.

(9) If this condition is met for one of the glow plugs, e.g., the second glow plug, a check is made as to whether a set of reference values has already been stored for the glow plug in question. If this is not the case, the measured values R.sub.1, R.sub.2, . . . , R.sub.N stored in the buffer memory are stored as a set of reference values for the glow plug in question. If the threshold value for one of the glow plugs has not yet been reached, or a set of reference values for the glow plug in question already exists, monitoring of the resistance of this glow plug nevertheless continues, since measured values of the resistance of this glow plug may still be required for sets of reference values of the other glow plugs.

(10) As a rule, a set of reference values is generated and stored for each of the glow plugs using the method as described. Only if a glow plug is defective can the case occur in which the threshold value C for the glow plug in question is not reached within the specified heating time. In this case, the defective glow plug must be replaced and execution of the method repeated so that a set of reference values is available for each glow plug.

(11) If there is a set of reference values for each glow plug, that is to say, if each glow plug has functioned as a lead plug, a set of comparative values is generated for each glow plug of the engine in order to detect a glow plug replacement during subsequent heating by an application of the method illustrated in FIG. 1.

(12) If a set of reference values and a set of comparative values are available for each glow plug, for each glow plug i, the set of comparative values V.sub.i belonging to the latter is compared with the set of reference values S.sub.i belonging to the latter. For i, any whole number from 1 to N must be used, where N is the number of glow plugs in the engine.

(13) A set of comparative values V.sub.i (R.sub.1, R.sub.2, . . . , R.sub.N) is compared with a set of reference values S.sub.i (R.sub.1, R.sub.2, . . . , R.sub.N) by comparing each of the resistance values R.sub.j of the set of comparative values with the corresponding resistance value R.sub.j of the set of reference values, where j is an integer less than N. The value R.sub.1 of the set of comparative values V.sub.i measured on the first glow plug is compared with the value R.sub.1 of the set of reference values V.sub.i measured on the first glow plug, the value R.sub.2 of the set of comparative values V.sub.i measured on the second glow plug is compared with the value R.sub.2 of the set of reference values V.sub.i measured on the second glow plug, and so on. In such a comparison, a deviation of a comparative value from a reference value by less than a specified tolerance value is considered to be an agreement.

(14) In what follows, this comparison is explained using a concrete example for a four-cylinder engine. Assuming the following sets of reference values S.sub.i are available for this engine:

(15) S.sub.1=(403 mΩ, 380 mΩ, 383 mΩ, 394 mΩ)

(16) S.sub.2=(430 mΩ, 405 mΩ, 409 mΩ, 419 mΩ)

(17) S.sub.3=(423 mΩ, 399 mΩ, 402 mΩ, 412 mΩ)

(18) S.sub.4=(413 mΩ, 392 mΩ, 394 mΩ, 405 mΩ)

(19) In these sets of reference data, the first resistance was measured on the glow plug of the first cylinder, the second resistance was measured on the glow plug of the second cylinder, the third resistance was measured on the glow plug of the third cylinder and the fourth resistance was measured on the glow plug of the fourth cylinder. The threshold value C used to determine this set of reference values was 400 mΩ. As conditioned by the clock rate of a microprocessor with which the measured values were recorded, it was in general not possible to measure a set of values immediately when the threshold value C was reached; a measurement could only be carried out on each glow plug with a slight time delay after the threshold value had been exceeded. The value R.sub.i of the set of comparative values V.sub.i and of the set of reference values S.sub.i therefore lies slightly above the threshold value (R.sub.1 in set V.sub.1 or S.sub.1, R.sub.2 in set V.sub.2 or S.sub.2, R.sub.3 in set V.sub.3 or S.sub.3, and R.sub.4 in set V.sub.4 or S.sub.4).

(20) The following sets of comparative data are also available for this engine:

(21) V.sub.1=(400 mΩ, 378 mΩ, 380 mΩ, 392 mΩ)

(22) V.sub.2=(430 mΩ, 406 mΩ, 410 mΩ, 420 mΩ)

(23) V.sub.3=(424 mΩ, 399 mΩ, 403 mΩ, 413 mΩ)

(24) V.sub.4=(410 mΩ, 390 mΩ, 392 mΩ, 401 mΩ)

(25) The sets of comparative values are respectively compared with the sets of reference values belonging to them, by comparing these value-by-value, i.e., values are respectively compared with one another, which have been measured for glow plugs of the same cylinder. The comparison of S.sub.1 with V.sub.1 is calculated as S.sub.1-V.sub.1. A comparison of each set of comparative values V.sub.i with the corresponding set of reference values S.sub.i yields the following result:

(26) S.sub.1-V.sub.1=(403 mΩ-400 mΩ), (380 mΩ-378 mΩ), (383 mΩ-380 mΩ), (394 mΩ-392 mΩ)

(27) S.sub.2-V.sub.2=(430 mΩ-430 mΩ), (405 mΩ-406 mΩ), (409 mΩ-410 mΩ), (419 mΩ-420 mΩ)

(28) S.sub.3-V.sub.3=(423 mΩ-424 mΩ), (399 mΩ-399 mΩ), (402 mΩ-403 mΩ), (412 mΩ-413 mΩ)

(29) S.sub.4-V.sub.4=(413 mΩ-410 mΩ), (392 mΩ-390 mΩ), (394 mΩ-392 mΩ), (405 mΩ-401 mΩ)

(30) From calculations of the terms in brackets there ensues:

(31) S.sub.1-V.sub.1=3 mΩ, −2 mΩ, 3 mΩ, 2 mΩ

(32) S.sub.2-V.sub.2=0 mΩ, −1 mΩ, −1 mΩ, −1 mΩ

(33) S.sub.3-V.sub.3=−1 mΩ, 0 mΩ, −1 mΩ, −3 mΩ

(34) S.sub.4-V.sub.4=3 mΩ, 2 mΩ, −2 mΩ, 4 mΩ

(35) If a deviation of a comparative value from a reference value by less than a specified tolerance value of 2 mΩ is still considered to be an agreement, the result is as follows, where 1 is an agreement and 0 is a deviation:

(36) For S.sub.1-V.sub.1 the result is (0, 1, 0, 1)

(37) For S.sub.2-V.sub.2 the result is (1, 1, 1, 1)

(38) For S.sub.3-V.sub.3 the result is (1, 1, 1, 0)

(39) For S.sub.4-V.sub.4 the result is (0, 1, 1, 0)

(40) This evaluation can be improved if one takes into account that the value R.sub.i of the set of comparative values V.sub.i and of the set of reference values S.sub.i lies slightly above the threshold value, and makes a corresponding linear correction.

(41) In the set of reference values S.sub.1, the reference value R.sub.1 is 403 mΩ, that is to say, it is 3 mΩ too high. The result can therefore be improved by reducing all reference values of the set of reference values S.sub.1 by 3 mΩ, In the set of reference values S.sub.2, the reference value R.sub.2 is 405 mΩ, that is to say, it is 5 mΩ too high. The result can therefore be improved by reducing all reference values of the set of reference values S.sub.2 by 5 mΩ, In the set of reference values S.sub.3, the reference value R.sub.3 is 402 mΩ, that is to say, it is 2 mΩ too high. The result can therefore be improved by reducing all reference values of the set of reference values S.sub.3 by 2 mΩ In the set of reference values S.sub.4, the reference value R.sub.4 is 405 mΩ, that is to say, it is 5 mΩ too high. The result can therefore be improved by reducing all reference values of the set of reference values S.sub.4 by 5 mΩ.

(42) The sets of comparative values must then also be corrected accordingly. In the set of comparative values V.sub.1, the comparative value R.sub.1 is 400 mΩ, that is to say, it is exactly correct, so that any correction of this set is unnecessary. In the set of comparative values V.sub.2, the comparative value R.sub.2 is 406 mΩ, that is to say, it is 6 mΩ too high. The result can therefore be improved by reducing all comparative values of the set of comparative values V.sub.2 by 6 mΩ, In the set of comparative values V.sub.3, the comparative value R.sub.3 is 403 mΩ, that is to say, it is 3 mΩ too high. The result can therefore be improved by reducing all comparative values of the set of comparative values V.sub.3 by 3 mΩ. In the set of comparative values V4, the comparative value R.sub.4 is 401 mΩ, that is to say, it is 1 mΩ too high. The result can therefore be improved by reducing all comparative values of the set of comparative values V.sub.4 by 1 mΩ.

(43) Taking these corrections into account, the comparison therefore ensues as:

(44) (S.sub.1-3 mΩ)-(V.sub.1-0 mΩ)=(403 mΩ-3 mΩ-400 mΩ), (380 mΩ-3 mΩ-378 mΩ), (383 mΩ-3 mΩ-380 mΩ), (394 mΩ-3 mΩ-392 mΩ)=0 mΩ, −1 mΩ, 0 mΩ, −1 mΩ

(45) (S.sub.2-5 mΩ)-(V.sub.2-6 mΩ)=(430 mΩ-5 mΩ-430 mΩ+6 mΩ), (405 mΩ-5 mΩ-406 mΩ+6 mΩ), (409 mΩ-5 mΩ-410 mΩ+6 mΩ), (419 mΩ-5 mΩ-420 mΩ+6 mΩ)=1 mΩ, 0 mΩ, 0 mΩ, 0 mΩ

(46) (S.sub.3-2 mΩ)-(V.sub.3-3 mΩ)=(423 mΩ-2 mΩ-424 mΩ+3 mΩ), (399 mΩ-2 mΩ-399 mΩ+3 mΩ), (402 mΩ-2 mΩ-403 mΩ+3 mΩ), (412 mΩ-2 mΩ-413 mΩ+3 mΩ)=0 mΩ, 1 mΩ, 0 mΩ, 0 mΩ

(47) (S.sub.4-5 mΩ)-(V.sub.4-1 mΩ)=(413 mΩ-5 mΩ-410 mΩ+1 mΩ), (392 mΩ-5 mΩ-390 mΩ+1 mΩ), (394 mΩ-5 mΩ-392 mΩ+1 mΩ), (405 mΩ-5 mΩ-401 mΩ+1 mΩ)=1 mΩ, 2 mΩ, 2 mΩ, 0 mΩ

(48) If a deviation of a comparative value from a reference value by less than a specified tolerance value of 2 mΩ is still considered to be an agreement, the following result is obtained, where 1 indicates an agreement, and 0 a deviation:

(49) For S.sub.1-V.sub.1 the result is (1, 1, 1, 1)

(50) For S.sub.2-V.sub.2 the result is (1, 1, 1, 1)

(51) For S.sub.3-V.sub.3 the result is (1, 1, 1, 1)

(52) For S.sub.4-V.sub.4 the result is (1, 1, 1, 1)

(53) It can therefore be detected that no glow plug replacement has taken place and thus all resistance-temperature characteristics are still valid.

(54) If, in the above example, (only) the second glow plug has been replaced, the following sets of comparative values are obtained, for example:

(55) V.sub.1=(400 mΩ, 410 mΩ, 380 mΩ, 392 mΩ)

(56) V.sub.2=(464 mΩ, 403 mΩ, 441 mΩ, 449 mΩ)

(57) V.sub.3=(424 mΩ, 431 mΩ, 403 mΩ, 413 mΩ)

(58) V.sub.4=(410 mΩ, 433 mΩ, 392 mΩ, 401 mΩ)

(59) Comparison with the sets of reference data for the previous example of embodiment shows that:

(60) S.sub.1-V.sub.1=(403 mΩ-400 mΩ), (380 mΩ-410 mΩ), (383 mΩ-380 mΩ), (394 mΩ-392 mΩ)

(61) S.sub.2-V.sub.2=(430 mΩ-464 mΩ), (405 mΩ-403 mΩ), (409 mΩ-441 mΩ), (419 mΩ-449 mΩ)

(62) S.sub.3-V.sub.3=(423 mΩ-424 mΩ), (399 mΩ-431 mΩ), (402 mΩ-403 mΩ), (412 mΩ-413 mΩ)

(63) S.sub.4-V.sub.4=(413 mΩ-410 mΩ), (392 mΩ-433 mΩ), (394 mΩ-392 mΩ), (405 mΩ-401 mΩ)

(64) From calculations of the terms in brackets there ensues:

(65) S.sub.1-V.sub.1=3 mΩ, −20 mΩ, 3 mΩ, 2 mΩ

(66) S.sub.2-V.sub.2=−34 mΩ, 2 mΩ, −32 mΩ, −30 mΩ

(67) S.sub.3-V.sub.3=−1 mΩ, −32 mΩ, −1 mΩ, −3 mΩ

(68) S.sub.4-V.sub.4=3 mΩ, −41 mΩ, −2 mΩ, 4 mΩ

(69) If a deviation of a comparative value from a reference value by less than a specified tolerance value of 2 mΩ is still considered to be an agreement, the following result is obtained, where 1 indicates an agreement, and 0 a deviation:

(70) For S.sub.1-V.sub.1 the result is (0, 0, 0, 1)

(71) For S.sub.2-V.sub.2 the result is (0, 1, 0, 0)

(72) For S.sub.3-V.sub.3 the result is (1, 0, 1, 0)

(73) For S.sub.4-V.sub.4 the result is (0, 0, 1, 0)

(74) If one takes into account that the value R.sub.i of the set of reference values V.sub.i and the set of reference values S.sub.i is slightly above the threshold value, and makes the corrections described above, the result of the comparison is as follows:

(75) (S.sub.1-3 mΩ)-(V.sub.1-0 mΩ)=(403 mΩ-3 mΩ-400 mΩ), (380 mΩ-3 mΩ-410 mΩ), (383 mΩ-3 mΩ-380 mΩ), (394 mΩ-3 mΩ-392 mΩ)=0 mΩ,−27 mΩ, 0 mΩ,−1 mΩ

(76) (S.sub.2-5 mΩ)-(V.sub.2-3 mΩ)=(430 mΩ-5 mΩ-464 mΩ+3 mΩ), (405 mΩ-5 mΩ-403 mΩ+3 mΩ), (409 mΩ-5 mΩ-441 mΩ+3 mΩ), (419 mΩ-5 mΩ-449 mΩ+3 mΩ)=−36 mΩ, 0 mΩ,−34 mΩ,−32 mΩ

(77) (S.sub.3-2 mΩ)-(V.sub.3-3 mΩ)=(423 mΩ-2 mΩ-424 mΩ+3 mΩ), (399 mΩ-2 mΩ-431 mΩ+3 mΩ), (402 mΩ-2 mΩ-403 mΩ+3 mΩ), (412 mΩ-2 mΩ-413 mΩ+3 mΩ)=0 mΩ, −31 mΩ, 0 mΩ, 0 mΩ

(78) (S.sub.4-5 mΩ)-(V.sub.4-6 mΩ)=(413 mΩ-5 mΩ-410 mΩ+1 mΩ), (392 mΩ-5 mΩ-433 mΩ+1 mΩ), (394 mΩ-5 mΩ-392 mΩ+1 mΩ), (405 mΩ-5 mΩ-401 mΩ+1 mΩ)=−1 mΩ, −45 mΩ, 2 mΩ, 0 mΩ

(79) If a deviation of a comparative value from a reference value by less than a specified tolerance value of 2 mΩ is still considered to be an agreement, the following result is obtained, where 1 indicates an agreement, and 0 a deviation:

(80) For S.sub.1-V.sub.1 the result is (1, 0, 1, 1)

(81) For S.sub.2-V.sub.2 the result is (0, 1, 0, 0)

(82) For S.sub.3-V.sub.3 the result is (0, 0, 1, 0)

(83) For S.sub.4-V.sub.4 the result is (0, 0, 0, 1)

(84) For the first set, the first comparative value is always anticipated to be in agreement with the first reference value, as the values in question were measured when the threshold value C was reached. Similarly, for the second set, an agreement between the first comparative value and the second reference value is always to be anticipated. Generally speaking, for the i.sup.th set an agreement between the i.sup.th comparative value and the i.sup.th reference value is always to be anticipated, as the values in question were measured when the threshold value C was reached. Here i is an integer for which all numbers from 1 up to the number of glow plugs of the engine are to be used one after another.

(85) The above comparison thus shows agreement in a comparison between the second set of comparative values and the second set of reference values only with regard to the second glow plug, and no agreement for all the other glow plugs. The comparison of the other sets of comparative values with the sets of reference values associated with them, on the other hand, shows no agreement only for the second glow plug, and agreement for all the other glow plugs. This comparison result thus proves that only the second glow plug was replaced, and the other glow plugs of the engine are unchanged.

(86) If the result of a comparison does not give a clear result, a statistical evaluation can be undertaken. In order to increase the amount of data available for this purpose, the determination of reference and comparative values can be performed with a plurality of threshold values, for example with a first threshold value of 400 mΩ and a second threshold value of 500 mΩ, The evaluation then takes place in the manner described, with the sets of reference and comparative values of the first threshold value firstly being processed separately, and the sets of reference and comparative values of the second threshold value firstly being processed separately. The results of the comparisons are then amalgamated and statistically evaluated together.

(87) Once it has been established through application of the inventive method that some or all the glow plugs of the engine have been replaced, specific control parameters must be determined for the glow plugs that have been replaced, such as a resistance-temperature characteristic. For example, the resistance-temperature characteristic of a glow plug can be determined by heating it under controlled conditions for a longer period of time, for example 2 minutes at a constant power rating, e.g., 33 W, with the engine switched off. The temperature reached in thermodynamic equilibrium under these circumstances then depends essentially only on the heat capacity of the glow plug and the cooling due to heat dissipation via the engine, so that the final temperature then reached is known. The advantage is that this time-consuming re-characterization does not have to be carried out for all the glow plugs of the engine, but only for those glow plugs which, due to replacement, aging or defect, have such a severely altered resistance-temperature characteristic that a resistance-temperature characteristic stored for the engine cylinder in question has become unusable.

(88) 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.