METHOD AND DEVICE FOR DETERMINING THE SURFACE TEMPERATURE OF A GLOW CURRANT IN A COMBUSTION ENGINE

Description

State of the art

[0001] The invention relates to a method for determining a surface temperature of a glow plug in an internal combustion engine, in which a physical parameter is used to determine the surface temperature, and to a device for carrying out the method.

[0002] Glow plugs, which are used in internal combustion engines to ignite a fuel-air mixture, have a heater that preheats the cold glow plug to a temperature high enough to ignite the fuel-air mixture. However, the temperature distribution from the heater across the entire glow plug is very inhomogeneous, resulting in temperature differences between the temperature of the heater located inside the glow plug and the temperature on the glow plug's surface.

[0003] Since the glow plug protrudes into the combustion chamber of the internal combustion engine, the surface of the glow plug is always cooled by the fuel-air mixture that flows past the glow plug during dynamic operation of the internal combustion engine, so that the surface of the glow plug never reaches the temperature of the heater inside the glow plug.

[0004] If the glow plug temperature is to be controlled, this is done based on the resistance of a heater inside the glow plug, from which the actual temperature control value is determined. The higher the temperature of the heater, which is designed as a current-carrying wire, the greater the resistance. Due to the resulting temperature difference, the quality of the glow plug temperature control is insufficient, as it is not based on a temperature that actually occurs on the glow plug's surface.

[0005] DE 10 2009 047 650 A1 discloses a method for determining the temperature of a glow plug in an internal combustion engine. In this method, a temperature difference between the temperature of the glow plug at a location outside the heater and the temperature at the heater of the glow plug is determined depending on the operating parameters of the internal combustion engine. This approach is very computationally intensive and requires significant development effort.

[0006] Another method for determining the temperature of a glow plug in an internal combustion engine is known from DE 10 2006 060 632 A1. Disclosure of the invention

[0007] The invention is based on the object of specifying a method and a device for determining a surface temperature of a glow plug in an internal combustion engine, in which an exact surface temperature can be determined with reduced computational and development effort.

[0008] According to the invention, the object is achieved by the features of the appended claims 1 or 8.

[0009] Advantageously, at least one of the at least two physical parameters for determining the surface temperature of the glow plug is measured on the glow plug during its operation. Since the current operating state of the glow plug is incorporated into the determination of the surface temperature via its current physical parameters, the accuracy of the surface temperature determined in this way is improved.

[0010] In one embodiment, at least one of the two physical parameters of the glow plug is calculated from at least one other physical parameter measured on the glow plug during its operation. This ensures at all times that the calculated physical parameter is directly related to the current operating state of the glow plug, thereby determining precise surface temperatures derived from the actual operating parameters of the glow plug.

[0011] Furthermore, the at least one calculated physical parameter is stored in a characteristic map, with this at least one physical parameter being read from the characteristic map to calculate the surface temperature of the glow plug. This indirect determination of the surface temperature allows a one-time determination of the characteristic map for the glow plug in use, whereby this characteristic map can be used at any time during operation of the glow plug to determine the surface temperature.

[0012] In a further development, at least two physical parameters are used: a resistance of the glow plug, a power consumed by the glow plug, an effective current of the glow plug, and / or a voltage of the glow plug. By selecting two of these physical parameters, the surface temperature of the glow plug can be determined easily and reliably.

[0013] In one variant, the resistance of the glow plug and / or the power consumed by the glow plug are calculated from the measured current and voltage of the glow plug. Thus, only two physical quantities need to be measured on the glow plug, from which further physical parameters of the glow plug can be determined. This significantly reduces the measurement effort.

[0014] In a further embodiment, the determined surface temperature is corrected using a correction factor, which depends in particular on at least one operating parameter of the internal combustion engine. The correction of the surface temperature takes into account the fact that the glow plug cools down during operation of the internal combustion engine. The discrepancy, which arises because the surface temperature no longer has a linear relationship to the temperature of the heater arranged inside the glow plug, is compensated for by the correction factor.

[0015] Preferably, the operating parameters used are a speed and / or an injection quantity and / or an air mass and / or a boost pressure of the air mass of the combustion engine. Taking these operating parameters of the combustion engine into account enables a precise correction of the surface temperature, as they reflect the actual ambient conditions of the glow plug in the combustion engine. Since these operating parameters are also detected for the evaluation of other combustion engine situations, no additional hardware effort is required to obtain this measurement data.

[0016] In a further development, the determined surface temperature of the glow plug is used as the actual temperature for temperature control of the glow plug. This temperature control is particularly advantageous during transient operation of the glow plug. Due to this highly accurate determination of the surface temperature, the quality of the control is improved.

[0017] A further development of the invention relates to a device for determining the surface temperature of a glow plug in an internal combustion engine, in which a physical parameter is used to determine the surface temperature. In order to determine an accurate surface temperature with reduced computational and development effort, means are available which use at least two physical parameters of the glow plug alone to determine the surface temperature of the glow plug. This has the advantage that the surface temperature can be determined in a particularly simple yet accurate manner. Under the changing operating conditions of the internal combustion engine and the resulting changing properties of the glow plug, the surface temperature is easily determined using a device already present in the motor vehicle.

[0018] Advantageously, a control unit is connected to a glow plug extending into a combustion chamber of the internal combustion engine, with the control unit determining the at least two physical parameters. The surface temperature thus determined very precisely by the control unit can be evaluated for temperature control or regulation of the glow plug.

[0019] The invention permits numerous embodiments. One of these will be explained in more detail with reference to the figures shown in the drawing.

[0020] It shows: Figure 1: Schematic diagram of the arrangement of a glow plug in an internal combustion engine Figure 2: Schematic flow diagram for determining the surface temperature of a glow plug

[0021] Cold combustion engines, especially diesel engines, require starting assistance at ambient temperatures below 40°C to ignite the fuel-air mixture introduced into the diesel engine. Glow systems are used as starting assistance. These consist of glow plugs, a glow time control unit, and glow software stored in an engine control unit.

[0022] Figure 1 shows such a glow system 1. A glow plug 2 protrudes into the combustion chamber 3 of the diesel engine 4. The glow plug 2 is connected, on the one hand, to the glow plug control unit 5 and, on the other hand, to an on-board voltage supply 6, which controls the glow plug 2 with a nominal voltage of, for example, 11 volts. The glow plug control unit 5 is connected to the engine control unit 7, which in turn is connected to the diesel engine 4.

[0023] To ignite the fuel-air mixture, glow plug 2 is preheated by applying an overvoltage in a push phase lasting 1 to 2 seconds. The electrical energy thus supplied to glow plug 2 is converted into heat by a heater (not shown) of glow plug 2. This causes the temperature at the tip of glow plug 2 to rise sharply. The heating output of the heater is adjusted to the requirements of the respective diesel engine 4 via the electronic glow time control unit 5.

[0024] The fuel-air mixture is directed past the hot tip of glow plug 2, thereby heating up. At the same time, the tip of glow plug 2 cools down. Combined with intake air heating during the compressor stroke of diesel engine 4, the ignition temperature of the fuel-air mixture is reached.

[0025] For applications of the combustion processes taking place in the diesel engine 4, it is necessary to know the exact surface temperature T of the glow plug 2. The determination of the surface temperature T should be carried out using the flow chart in Figure 2 explained. In block 101, a current and a voltage are measured at glow plug 2. From this current and voltage, the resistance R of glow plug 2 and the power P currently absorbed by the glow plug are calculated in block 102. These calculated values, resistance R of glow plug 2 and the power P currently absorbed by glow plug 2, are stored in a characteristic map in block 103. From this calculated resistance R of glow plug 2 and the power P currently absorbed by glow plug 2, the surface temperature T is calculated. The mathematical relationship is: T Kerze = T Kerze R Kerze P Kerze

[0026] In block 104, the surface temperature T candle calculated in block 103 is corrected, since the glow plug 2 cools down during operation of the diesel engine 4 and the surface temperature T candle is no longer linearly related to the heater temperature during engine operation. The following relationship thus results in the determination of the surface temperature T candle: T Kerze = T Kerze R Kerze P Kerze + ΔT q , n , m Luft , … . The surface temperature T of glow plug 2 is corrected depending on, for example, the engine speed n, the intake air volume m air, or the boost pressure T of the air mass. These operating parameters of the diesel engine 4 improve the accuracy of the surface temperature T of glow plug 2.

[0027] This procedure allows for a simpler and more reliable determination of the surface temperature T of glow plug 2 without significant computational effort. Correcting the surface temperature T of glow plug 2 using engine speed n, intake air flow m air , injection quantity q, etc. is only necessary in exceptional cases, since determining the surface temperature T of glow plug 2 using at least two physical parameters of glow plug 2 alone is already very accurate.

[0028] The determination of the surface temperature T plug of glow plug 2 is not limited to the combination of resistance R plug of glow plug 2 and the power P plug currently absorbed by glow plug 2. A variety of other combinations are conceivable, such as resistance R plug of glow plug 2 and voltage of glow plug 2 or resistance R plug of glow plug 2 and current of glow plug 2. The crucial point is that the physical quantities used to determine the surface temperature T plug of glow plug 2 are exclusively attributable to the respective operating state of glow plug 2 itself.

Claims

1. Method for determining a surface temperature of a sheathed-element glow plug in an internal combustion engine, in which method a physical parameter (RKerze, PKerze) is used for ascertaining the surface temperature (TKerze), wherein at least two physical parameters (RKerze, PKerze) only of the sheathed-element glow plug (2) are used for determining the surface temperature (TKerze) of the sheathed-element glow plug (2), characterized in that a resistance (RKerze) of the sheathed-element glow plug (2) and a power (PKerze) drawn by the sheathed-element glow plug (2) or a resistance (RKerze) of the sheathed-element glow plug (2) and a root mean square current of the sheathed-element glow plug (2) or a resistance (RKerze) of the sheathed-element glow plug (2) and a voltage of the sheathed-element glow plug (2) are used as at least two physical parameters and in that the at least two physical parameters are used as input signals for a characteristic map for determining the surface temperature in the operation of the sheathed-element glow plug.

2. Method according to Claim 1, characterized in that at least one of the at least two physical parameters (RKerze, PKerze) for determining the surface temperature (TKerze) of the sheathed-element glow plug (2) is measured at the sheathed-element glow plug (2) during its operation.

3. Method according to Claim 1, characterized in that at least one of the two physical parameters (RKerze, PKerze) of the sheathed-element glow plug (2) is calculated from at least one further physical parameter that is measured at the sheathed-element glow plug (2) during its operation.

4. Method according to Claim 1, characterized in that the resistance (RKerze) of the sheathed-element glow plug (2) and / or the power (PKerze) drawn by the sheathed-element glow plug (2) is calculated from the measured current and the measured voltage of the sheathed-element glow plug (2).

5. Method according to at least one of the preceding claims, characterized in that the ascertained surface temperature (TKerze) is corrected with a correction factor (ΔT) which in particular depends on at least one operating parameter (n, q, mLuft) of the internal combustion engine (4).

6. Method according to Claim 5, characterized in that an engine speed (n) and / or an injection quantity (q) and / or an air mass (mLuft) and / or a charging pressure of the air mass of the internal combustion engine (4) is used as an operating parameter.

7. Method according to at least one of the preceding claims, characterized in that the ascertained surface temperature (TKerze) of the sheathed-element glow plug (2) is used as the actual temperature for a temperature control of the sheathed-element glow plug (2).

8. Device for determining a surface temperature of a sheathed-element glow plug in an internal combustion engine, in which device a physical parameter (RKerze, PKerze) is used for ascertaining the surface temperature (TKerze), wherein there are means (5, 7) which use at least two physical parameters (RKerze, PKerze) only of the sheathed-element glow plug (2) for determining the surface temperature (TKerze) of the sheathed-element glow plug (2), characterized in that the means use a resistance (RKerze) of the sheathed-element glow plug (2) and a power (PKerze) drawn by the sheathed-element glow plug (2) or a resistance (RKerze) of the sheathed-element glow plug (2) and a root mean square current of the sheathed-element glow plug (2) or a resistance (RKerze) of the sheathed-element glow plug (2) and a voltage of the sheathed-element glow plug (2) as at least two physical parameters and in that the means use the at least two physical parameters as input signals for a characteristic map for determining the surface temperature in the operation of the sheathed-element glow plug.

9. Device according to Claim 8, characterized in that a control unit (5, 7) is connected to a sheathed-element glow plug (2) projecting into a combustion chamber (3) of the internal combustion engine (4), wherein the control unit (5, 7) determines the at least two physical parameters (RKerze, PKerze).