METHOD FOR CONTROLLING THE TEMPERATURE OF GLOW PLUGS

Abstract

A method for controlling the temperature of glow plugs of a combustion engine is described, wherein all glow plugs are heated up for an engine start by the input of electrical energy according to a profile which is uniformly specified for all glow plugs of the engine, a change in resistance R is ascertained for each of the glow plugs for at least one specified time span, and a target resistance value is calculated for each glow plug from the associated change in resistance R, this value being expected for the glow plug when it has reached its target temperature, and the target resistance value is used to control the temperature of the glow plug to the target temperature.

Claims

1. A method for controlling the temperature of glow plugs of a combustion engine, comprising: heating up all glow plugs of the combustion engine for an engine start by inputting electrical energy according to a profile which is uniformly specified for all of the glow plugs of the engine; ascertaining a change in resistance R for each of the glow plugs for at least one specified time interval; and calculating a target resistance value for each glow plug from the associated change in resistance R, the target resistance value being a value that is expected for the respective glow plug when a target temperature is reached; and for each glow plug, using the target resistance value to control the temperature of the glow plug to the target temperature.

2. The method according to claim 1, wherein the change in resistance R is ascertained from measured values which are measured within a time span in which the engine has not yet been started.

3. The method according to claim 1, wherein the change in resistance R is ascertained from measured values which are measured during the first 800 milliseconds after the start of heating up.

4. The method according to claim 1, wherein the target resistance value is calculated using a formula in which the target resistance value is assumed to be proportional to the change in resistance R.

5. The method according to claim 1, wherein the profile is a power profile.

6. The method according to claim 1, wherein a value for the change in resistance R is ascertained for each glow plug for several time intervals.

7. The method according to claim 6, wherein the power profile is chosen to result in an approximately linear change in resistance R of the glow plug.

8. The method according to claim 6, wherein a total value is obtained from the several time intervals.

9. The method according to claim 6, wherein the time intervals lie within the first 800 milliseconds after the start of the heating-up process.

10. The method according to claim 6, wherein the time intervals overlap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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:

[0015] FIG. 1 shows the resistance R of different ceramic glow plugs as a function of time during heating up with a power profile which is uniform for all glow plugs and indicated by the line provided with an arrow; and

[0016] FIG. 2 shows the resistance R.sub.end reached by different ceramic glow plugs at the end of the heating-up process versus the change in resistance R during the heating-up process.

DESCRIPTION

[0017] 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.

[0018] FIG. 1 shows the resistance R in m as a function of time during heating-up with a power profile which is uniformly specified for all glow plugs. The power profile as a function of time is also shown in FIG. 1 by a line, which is associated with an arrow pointing towards the right ordinate axis on which the power P is given in watts. The power fed into the glow plugs according to this power profile is diminishing in monotonous fashion. In the embodiment shown the power profile can be divided roughly into three sections in which the applied power drops linearly at different rates. Heating-up of the glow plugs may also be effected using alternative power profiles, for example power profiles where the power is changed in steps and remains constant over an extended period of time.

[0019] Independently of the power profile used there is an approximately linear correlation between the resistance R.sub.end obtained at the end of the heating-up process and the change in resistance R during the heating-up process or a specified part of the heating-up period. These facts are schematically shown in FIG. 2, in which the resistance R.sub.end in reached at the end of the heating-up process is plotted versus the change in resistance R in m/s. FIG. 2 thus shows that there is a linear correlation between a change in resistance R which occurs during heating-up of a glow plug for an engine start in a pre-set time interval and the resistance R.sub.end of the glow plug at the end of a heating-up process, i.e., the resistance at its target temperature.

[0020] By heating-up all glow plugs of an engine for an engine start by the input of an electrical power profile uniformly specified for all glow plugs of the engine and ascertaining a change in resistance R for each of the glow plugs for at least one specified time span, a target resistance value can thus be calculated from the change in resistance R, which is expected for each glow plug when it has reached its target temperature. The target resistance value calculated in this way can therefore be used for controlling the temperature of the glow plug to the target temperature.

[0021] 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.