METHOD FOR REGULATING THE SURFACE TEMPERATURE OF A GLOW PLUG

Abstract

A method for regulating the surface temperature of a glow plug is described, wherein the electrical resistance of the glow plug is continuously measured and used to regulate the surface temperature of the glow plug to a target temperature or a target resistance corresponding to the target temperature by means of a resistance temperature characteristic. According to this disclosure, it is provided that the resistance temperature characteristic used for the temperature regulation is adjusted as a function of the present motor operating state.

Claims

1. A method for regulating the surface temperature of a glow plug, comprising: continuously measuring the electrical resistance of the glow plug; using the continuously measured resistance and a resistance temperature characteristic to regulate the surface temperature of the glow plug to a target temperature or a target resistance corresponding to the target temperature; and adjusting the resistance temperature characteristic as a function of the present motor operating state.

2. The method according to claim 1, wherein the motor operating state is defined by the rotational speed and/or its load state.

3. The method according to claim 1, wherein: the adjustment is made by a glow plug control device, the electrical power or voltage required to maintain a second target resistance is compared with an expected value that is required to maintain the second target resistance at a defined reference motor operating state, and, from the magnitude of a deviation thereby determined, the magnitude of the adjustment to be made of the target resistance corresponding to the current target temperature is inferred.

4. The method according to claim 3, wherein the adjustment is made with a characteristic diagram.

5. The method according to claim 3, wherein the defined reference motor operating state is an idling state.

6. A method for regulating the surface temperature of a glow plug, comprising: continuously measuring the electrical resistance of the glow plug; using the continuously measured electrical resistance and a resistance temperature characteristic to regulate the surface temperature of the glow plug to a target temperature or a target resistance corresponding to the target temperature; and adjusting the resistance temperature characteristic used for the temperature regulation as a function of the present motor operating state, wherein the adjustment is made by a glow plug control device; wherein the electrical power or voltage required to maintain a second target resistance is compared with an expected value that is required to maintain the second target resistance at a defined reference motor operating state, and, from the magnitude of a deviation thereby determined, the magnitude of the adjustment to be made of the target resistance corresponding to the current target temperature is inferred.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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:

[0018] FIG. 1 is a bar graph that indicates the resistance R in m for various surface temperatures of a glow plug respectively for different load states of the motor;

[0019] FIG. 2 is a table that indicates, by example, the electric resistance, in m, of the glow plug belonging to the respective surface temperature at various load states of the motor for various surface temperatures of a glow plug; and

[0020] FIG. 3 is a table that indicates, by example, various surface temperatures of a glow plug, the effective voltages required to maintain the respective surface temperature in V at different load states of the motor.

DESCRIPTION

[0021] 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.

[0022] In FIG. 1, the electric resistance for a glow plug is specified as a bar graph in m for surface temperatures of 900 C., 1,000 C., 1,100 C., 1,200 C. and 1,250 C. at different load states of the motor, namely respectively from left to right for 0%, 25%, 50%, 75% and 100% motor load. FIG. 1 clearly shows that the resistance of a glow plug can change by about 20% at a constant surface temperature as a function of the motor operating state. In this context, it should be noted that glow plugs react differently to changes of the motor operating state, depending on the type. The example of FIG. 1 therefore does not indicate any generally valid changes of the resistance of a glow plug as a function of the motor operating state, but rather merely illustrates that the motor operating state influences the resistance. The magnitude of the influence of the motor operating state on the resistance of the glow plug is different for each glow plug type and each glow plug model. The corresponding data for an adjustment of the resistance temperature characteristic to the motor operating state should therefore be determined separately for each glow plug model.

[0023] FIG. 2 shows the data illustrated in FIG. 1 in the form of a table, wherein the entries in the table indicate the resistance of the glow plug in m for the different load states of the motor and the different surface temperatures. It can clearly be seen therein that the greater the resistance of the glow plug, which resistance belongs to a given surface temperature, the greater the load state of the motor.

[0024] FIG. 3 correspondingly shows a table which indicates the voltage in volts required to maintain a surface temperature of the glow plug for various load states of the motor. In this case, FIG. 3 clearly shows that the voltage which has to be applied to the glow plug in order to maintain a given surface temperature, for example, a surface temperature of 1,200 C., increases with increasing load state of the motor.

[0025] The figures explained above make it clear that, for a precise regulation of the surface temperature by closed-loop control, the present motor operating state must be taken into account, that is, the resistance temperature characteristic used for closed-loop control of the temperature must be adjusted as a function of the present motor operating state.

[0026] The glow plug control device could make this adjustment by the motor control device or a corresponding sensor communicating the present motor operating state to it. However, the related effort can be avoided by the glow plug control device monitoring the power or voltage that is required to maintain the resistance associated with a given target temperature according to the resistance temperature characteristic used.

[0027] For temperature regulation, i.e., closed-loop control, the glow plug control device in this case initially uses a resistance temperature characteristic which was determined for a defined reference state of the motor, for example, for a motor load of 0%. If the glow plug control device is then to maintain a target temperature of, for example, 1,200 C., the glow plug control device will first regulate the resistance of the glow plug to a value of 1,161 m, since this is the resistance value which, according to FIG. 2, is associated with the target temperature of 1,200 C. at the reference motor operating state, for example, a motor load of 0%. If the motor load is higher than 0%, that is, 75%, for example, the resistance value of 1,161 m corresponds only to a temperature value of about 1,150 C., which can be determined by interpolation of the values of the corresponding column of FIG. 2.

[0028] At a motor load of 75%, however, a value of about 8.8 V belongs to a temperature value of about 1,150 C., which can be seen by interpolation of the corresponding column of FIG. 3. Instead of the expected 6.52 V, the glow plug control device thus recognizes that approximately 8.8 V are required to maintain the resistance of 1,161 m. With a characteristic diagram on the basis of the data shown in FIGS. 2 and 3, the glow plug control device can determine therefrom the load state of the motor and determine the electrical resistance belonging to the target temperature at this load state and regulate this, thus, for example, to 1,210 m instead of to 1,161 m. The glow plug control device thus adjusts the resistance temperature characteristic used for the temperature regulation as a function of the present motor operating state and thus achieves a substantially more precise control of the surface temperature.

[0029] 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.