Extended fan run-on

Abstract

The invention relates to a fan run-on control which takes into account the energy input into the combustion engine in order to calculate the required run-on time of the fan. If the characteristics of the fan are known it is possible to calculate the required fan run-on time from the integral of the energy input into the combustion engine before the combustion engine was switched off, and the current operating data and ambient data of the combustion engine. Furthermore, by comparing the energy input into the combustion engine with the cooling performance of the cooling system over a specific period of time before the engine was switched off, it is possible to predict whether or not running-on of the fan will be necessary. There is always a risk of further subsequent heating whenever the energy input into the engine has been significantly greater than the cooling performance of the system before the engine was switched off. If the opposite is true, there may sometimes be no need for the fan to run on, or the fan run-on time can be much shorter than in previously known systems.

Description

The invention relates to a method and a device for controlling a fan motor. The fan motor is preferably used in cooling systems for motor vehicles. In order to be able to determine the optimum fan run-on time after switching off the combustion engine, the energy input into the combustion engine is registered. The energy input shortly before the combustion engine was switched off and the specific fan characteristic are used to calculate the fan run-on time, which is necessary in order to prevent subsequent overheating of the combustion engine.

Run-on controls for fan motors in motor vehicles have long been known. The run-on controls hitherto disclosed operate as a function either of the temperature or the time. In the case of temperature-dependent run-on controls a temperature sensor is used to monitor the coolant temperature and if a critical temperature value is exceeded the run-on control of the fan motor is activated and the coolant circuit with an electrical coolant pump is set in operation. Time-dependent run-on controls operate with timing elements. The timing element here determines the length of the fan run-on.

The German patent specification DE 3424 580 C1 affords a broad overview of the state of the art hitherto disclosed. The German patent specification describes a cooling system which is provided with an electrically driven fan and a run-on control. The run-on control in this case operates as a function either of the temperature or the time. The cooling system comprises a second, electrically driven coolant pump, which is likewise controlled by the run-on control and which maintains the coolant flow whilst the run-on control is in operation.

Known run-on controls for fan motors have the disadvantage that they cut in regardless of the actual load condition and hence also regardless of any possible overheating of the engine. They therefore also cut in when there is no overheating of the engine whatsoever. Time-dependent fan run-on controls are always bound to cut in and temperature-dependent fan run-on controls may simply cut in, for example, because a high ambient temperature results in a high coolant temperature.

Conversely, when the engine has been run in the full-load range immediately before switching off the combustion engine, for example, it may take several minutes until the overheating of the engine makes itself felt through a temperature rise on the fan run-on temperature sensor. This delay before the fan run-on control cuts in may already be too late for temperature-sensitive microelectronic components in the motor vehicle.

The object of the invention, therefore, was to develop a fan run-on control which avoids unnecessary fan run-on times and on the other hand detects the risk of a delayed temperature rise and promptly initiates countermeasures to prevent the temperature rise.

The object is achieved by a method and a device according to the independent claims. Further preferred embodiments of the invention are contained in the dependent claims and in the exemplary embodiments.

The object is primarily achieved by means of a fan run-on control, which takes into account the energy input into the combustion engine in order to calculate the required fan run-on time. If the characteristics of the fan are known it is possible to calculate the required fan run-on time from the integral of the energy input into the combustion engine before the combustion engine was switched off, and the current operating data and ambient data of the combustion engine. Furthermore, by comparing the energy input into the combustion engine with the cooling performance of the cooling system over a specific period of time before the engine was switched off, it is possible to predict whether or not running-on of the fan will be necessary. There is always a risk of further subsequent heating whenever the energy input into the engine has been significantly greater than the currently applied cooling performance of the system before the engine was switched off. If the opposite is true, there may sometimes be no need for the fan to run on, or the fan run-on time can be much shorter than in previously known systems.

The invention primarily affords the following advantages:

The invention allows the fan run-on time to be optimally adjusted to the load condition of the engine immediately before it was switched off. This avoids unnecessary fan run-on times, and the likely effects of further subsequent heating, which owing to the thermal inertia of the cooling system would only make themselves felt after some delay, can be predicted in good time so that overheating can be promptly counteracted though increased cooling performance.

In an advantageous embodiment of the invention the energy input into the combustion engine is determined using the mass air flow as a measure of the volumetric efficiency of the combustion cylinders, and the speed of the combustion engine. This embodiment has the advantage that the necessary measured values for the volumetric efficiency and the speed of the combustion engine can be taken from existing engine management systems. Known engine management systems, which determine the volumetric efficiency of the combustion cylinders and the speed of the combustion engine, include the electronic engine management systems produced by Bosch, for example. These systems are marketed and used under the name “Motronic”. These systems are described, for example in “Automotive Handbook”, Bosch-23^rd revised edition, Braunschweig: Viehweg, 1999, pages 498-507. Other alternative operating data for calculating the energy input are the induced torque, the induced power or, especially in the case of diesel engines, the induced fuel injection quantity. These alternative operating data are likewise supplied by engine management systems.

In a further advantageous embodiment of the invention an engine-specific air mass/engine speed-dependent temperature characteristics map is determined from the signals of the engine management system in road tests using a trial vehicle. This exemplary embodiment has the practical advantage that in the case of series production vehicles this engine-specific air mass/engine speed-dependent temperature characteristics map has to be determined just once using a representative trial vehicle and that this engine-specific air mass/engine speed-dependent temperature characteristics map can then be adopted in all further series production vehicles of the same type and specifications as the trial vehicle. The engine-specific air mass/engine speed-dependent temperature characteristics map can then be used to determine the fan run-on time in each separate series production vehicle.

In a further advantageous embodiment of the invention the length of the fan run-on time is calculated through time integration of those energy inputs into the combustion engine which lie above a critical reference value in the air mass/engine speed-dependent temperature characteristics map. The time integration makes it possible to average out transient loads, which do not have any significant effect on likely further subsequent heating. Introducing a critical reference value that has likewise to be determined experimentally makes it possible to eliminate from the calculation of the fan run-on time those load conditions of the combustion engine which do not require running-on of the fan.

In a further advantageous embodiment of the invention the time integration of each of the energy inputs is performed over a predetermined time interval. The result of the integration is in this case stored by intervals. The number of integration intervals registered is limited. For example, at any one time five integration intervals of one minute each are registered and stored for the last five minutes. If the operation of the combustion engine lasts for a longer period of time, the stored interval-specific integration results are cyclically overwritten. This means that at any given time the load condition in the last five minutes before the combustion engine was switched off is recorded. This saves any excessive retention of data, which is not needed in order to calculate the fan run-on.

In a further advantageous embodiment of the invention the air mass/engine speed-dependent temperature characteristics map contains a family of characteristics for multiple temperature-critical components. Not only can the running-on of the fan thereby be related to a temperature-critical component, but the temperatures of multiple critical components can be incorporated into the calculation of the fan run-on time. This has the advantage, for example, that local irregularities in the heating up of the engine compartment of a motor vehicle can be taken into account in the calculation of the fan run-on time. Temperature-critical components which, for example, are situated in a heat sink, which does not warm up when the engine is briefly heated up, can be disregarded when calculating the fan run-on time.

Exemplary embodiments of the invention will be explained in more detail below with reference to the drawings, in which:

FIG. 1 shows a cooling system of a combustion engine having a mapped logic for controlling an electric fan motor,

FIG. 2 shows a schematic diagram, of the run-on calculation for the fan motor using operating data from the engine management system,

FIG. 3 shows an interval-specific integration diagram for calculation of the fan run-on control,

FIG. 4 shows a function diagram for averaging the interval-specific integration results,

FIG. 5 shows an experimentally determined multi-component air mass/engine speed-dependent temperature characteristics map for calculation of the fan run-on time,

FIG. 6 shows a reduced characteristics map, extracted from the characteristics map in FIG. 5, and in which all temperature measuring points not critical for the fan run-on time have been extracted by means of a limit value.

FIG. 1 shows a diagram of a typical cooling system for a six-cylinder combustion engine 1. In addition to the combustion engine, a vehicle radiator 2 and a heating system heat exchanger 3 are incorporated into the cooling system. The cooling performance of the vehicle radiator can be influenced by an electrically driven fan 4. In order to regulate the fan output the electric motor of the fan is controlled by a control unit 5. Cooled coolant is drawn from the vehicle radiator by means of the flow pipe 6 and is fed by the coolant pump 7 into the cooling pipes 8 for feeding cooling ducts (not shown further) for the combustion cylinders 9. From the combustion cylinders 9 the heated coolant is led via return pipes 10 to a three-way thermostat 11. Depending on the position of the valves in the three-way thermostat 11, the coolant passes out of the combustion engine via the radiator return pipe 12 back into the vehicle radiator or via the radiator bypass 13 and the coolant pump 7 back into the cooling pipes 8 of the combustion engine.

Depending on the position of the valves in the three-way thermostat 11 the cooling system can here be run in a manner known in the art in bypass mode, in mixed mode or on the full cooling circuit. The heating system heat exchanger 3 is connected by way of a temperature-controlled shut-off valve 14 to the high-temperature branch of the cooling system in the combustion engine. The rate of flow through the heating system heat exchanger after opening the shut-off valve 14 can be adjusted by an additional electrical coolant pump 15 and a timed shut-off valve 16 in order to regulate the heating output.

The temperature level of the coolant in the combustion engine is here set by the control unit 5, controlled by sensors. This is achieved in a manner known in the art through actuation of the control valves in the three-way thermostat 11 and by activation of the electrical fan 4, if air stream cooling is no longer sufficient.

With a sensor-controlled cooling system as described for combustion engines in motor vehicles satisfactory performances can be obtained when running. After switching off the combustion engine critical situations for temperature-sensitive components in the engine compartment of a motor vehicle can occur should the heat stored in the combustion engine no longer be dissipated due to the coolant becoming static. For this reason cooler run-on systems have already been proposed in the past. These cooler run-on systems operate, as already described as a function of the time or the temperature. In the case of purely time-dependent systems, therefore, it was in the past always necessary to provide a fan run-on, which as a rule was much too long. Temperature-dependent systems also had the disadvantage, however, that the temperature sensors, which usually measure the temperature profile of the coolant, were able to detect heating up of the combustion engine only with a considerable time delay. The delay in this case results from the thermal inertia of the system. The effect of delayed further heating after switching off the combustion engine is especially great if, for example, the combustion engine has been run for a longer period of time in the partial load range and the engine has been run up to full load only in the last few minutes before switching off the engine. In this scenario, a temperature-controlled cooling system will still be operating in the partial load range, whereas the engine has been fully fired up shortly before switching off. The engine then holds a large quantity of heat which still needs to be dissipated. Since a temperature-controlled run-on system must also cope with this scenario described above, it was necessary, in order to prevent localized overheating in the combustion engine, to set the temperature threshold for starting up of the run-on control very low. There was no facility for predicting how much energy would still have to be dissipated and for this reason it was always necessary to assume the worst case in the event of a rise in the coolant temperature being detected. This also means that in the vast majority of cases the temperature-controlled run-on control responds too often and for too long. This represents the point of departure for the invention.

According to the invention, therefore, the control unit 5 uses the calculation of the run-on time, based on the energy input into the combustion engine over a sufficient period of time immediately before switching off the engine, for controlling the run-on of the fan 4. For this purpose an engine-specific air mass/engine speed-dependent temperature characteristics map is filed in the control unit 5. By monitoring the operating data of the combustion engine, for example by reading in the operating data from the engine management system, the energy input into the combustion engine is determined from the air mass/engine speed-dependent temperature characteristics map and from this a fan run-on time is obtained. For example, the energy input into the combustion engine may be logged for the last five minutes before switching off the engine, and from the energy input over the last five minutes a time integration may be performed, the result of this integration being compared with an experimentally determined or model-based, calculated reference value. If the integration result exceeds this reference value, a fan run-on must be activated. The length of time for which the fan must run on is here determined from the difference between the integration value and the reference value. These are basically the activation characteristic curve of the fan motor, the temperature of the ambient air and the current temperature of the coolant.

With all these data an energy balance for the combustion engine and the cooling system can then be undertaken in a process computer of the control unit 5 according to the laws of thermodynamics, and the required cooling performance and hence the required run-on time of the fan can then be calculated from said energy balance.

The system of calculation is explored in more detail in FIG. 2. Here the two reference input variables, engine speed and mass air flow, are particularly relevant for the operating condition of the engine. These two reference input variables are provided by constantly updated engine controls 17 in the form of digital signals. The engine speed and the air mass are the reference input variables for that energy which is introduced into the combustion engine. The “Automotive Handbook” produced by Bosch, as already cited above, pages 498 to 507, gives a good overview of engine management systems. The energy introduced is here a measure of the energy to be dissipated by a cooling system and hence a measure of the required cooling performance and the necessary run-on time of the fan.

For determining the fan run-on, however, it is preferable to select the anticipated temperature of the engine as intensive variable to be determined, rather than the energy as extensive variable to be balanced. A calculation model which is directed towards the temperature of the combustion engine is in practice easier to analyze and improve by measuring road tests. Temperature-intensive variables can likewise be more readily adjusted to specific engines through measuring road tests. A method of calculation which is directed towards the temperature of the combustion engine can thereby be adapted to different engine variants. The adaptation is here achieved by means of software program modules 18, which use the operating data of the engine management system 17 to calculate the delayed temperature curve of the combustion engine 19. In the program modules 18 the temperature profile to be expected of the combustion engine is calculated from the operating data, engine speed and mass air flow, by means of experimentally compiled calculation equations. The calculated temperature curve is here adapted to the temperature curve actually measured through adjustment of the parameter values in the calculation equations in the program modules. The speed and mass air flow are the two most important reference input variables for the engine management and hence also for calculation of the temperature curve to be expected of the combustion engine. This predicted temperature curve is adjusted to the prevailing ambient conditions of the combustion engine by means of a correction element 20, which likewise takes the form of a software program module. The most important influencing variables among the environmental conditions are the air temperature, the temperature of the intake air, the air pressure and air humidity, the current cooling performance of the cooling system and the position of any throttle valve of the combustion engine. The temperature profile adjusted for the ambient conditions is time integrated by an integration stage 23 in the form of a so-called moving average. The integration stage 23 is explored in more detail with reference to FIG. 3. The integration result from the integration stage 23 undergoes further processing by a further program module 24 for final actuation of the fan motor 4. For this purpose the program module 24 compares the integration result from the integration stage 23 with an experimentally determined reference value 22 and calculates the required fan run-on time on the basis of the fan characteristic curve 25. The reference value 22 is here established experimentally and for the specific variant of the vehicle in question. The reference value must be established in such a way as to reliably ensure that the component having the greatest temperature sensitivity is not damaged.

FIG. 3 shows a logic flow chart for the integration stage 23. A so-called moving average is calculated. The integration stage 23 is preferably implemented as a program module, that is to say in the software. In a further preferred embodiment, however, the integration stage 23 may also be hardwired using logic elements. The term “moving average” is understood to mean a process of averaging which progresses over time and in which the averaging is in each case calculated by way of a fixed number of chronologically successive sub-averages, the sub-averages each time being cyclically recalculated and redetermined in chronological order. For example, if the sub-averages are each calculated over a period of one minute and five chronologically successive sub-averages are provided for, via which an overall average is then calculated, the overall average obtained each time is that for the last five minutes when the system was activated. Through the cyclical overwriting and recalculation of the sub-averages this average is each time updated and adjusted for the last five minutes of the activated system. This process is represented schematically in FIG. 3, as follows:

The temperature profile adjusted for the ambient conditions is each time integrated over a period of one minute by a time integration element 26, and stored. The time division is set and the integration result from the integration intervals is stored in that a cyclical cascade causes the integration to recommence once a period of one minute, for example, has elapsed, and the integration result after each minute is registered in a memory area 27. The duration of the intervals for the individual integration stages is in principle freely selectable and is defined by a time constant or a delay element 28. The cyclical storage of the integration results from the integration intervals is preferably embodied in the software in the form of a recurring loop. It is also possible, however, to provide for hard-wired switching of the integration results to the memory areas. Both embodiments are represented schematically in FIG. 3 as a cascade 29 of successive AND elements and an OR element, by means of which, among other things, the activation signal for the integration stage is also inputted. The summing of the subsequence results registered in the memory areas 27 is performed in a summation stage 33, which is preferably embodied as a software program module. An embodiment of the summation stage 33 as a hard-wired AND element 32, as represented in FIG. 3, for example, is less preferable.

FIG. 4 again shows a function diagram for the calculation of an overall average. In this case the sub-averages denoted by the FIGS. 1 to 5 are summed either by a software program or by a logic circuit to obtain an overall average. The individual sub-averages are cyclically overwritten.

FIG. 5 shows a table of measured values obtained from road tests. Fitted to the test vehicle in this case were various temperature sensors, which registered and plotted the oil temperature, the temperature of the integral carrier, the temperature of the steering rack, the temperature of the steering gaiter, the temperature of the axle half-shaft, the catalytic converter temperature and the temperature of the electronic injection system as a function of the two reference input variables, mass air flow (MAF) and engine speed (Eng-Spd).

The temperatures tabulated as a function of the two reference input variables serve the program modules 18 in FIG. 2 as reference points for the calculation of the temperature characteristics map 19. The main function of the program modules 18 is interpolation of the reference points, in order that a continuous temperature characteristics map can be calculated.

Table 1 in FIG. 5 clearly illustrates that various temperatures in the engine compartment of a motor vehicle can be used in determining the temperature characteristics map. This means that a run-on calculation according to the invention may serve not only to safeguard an isolated local temperature but also a temperature distribution or even different localized temperatures of multiple components. The fact that the program modules 18 resort to experimentally obtained reference points in order to calculate the temperature characteristics map also makes it possible to readily design the fan motor run-on control according to the invention for specific engines or for specific variants. For the various vehicle variants or the various engine variants, a test vehicle is used to determine the temperature reference points specific to each variant or each engine, and these experimentally plotted temperature reference points are fed into the program modules 18 as reference points. The fan run-on according to the invention can thereby be easily adapted to different vehicle variants.

FIG. 6 shows a further Table 2, in which the temperature reference points from Table 1 in FIG. 5 have already been evaluated with reference to a critical reference temperature. In Table 2 the mass air flow is entered in the horizontal direction and the engine speed in the vertical direction. The table values themselves contain the temperature values for the steering rack, as measured in the test results in FIG. 5. An evaluation of the temperature distribution in FIG. 5 has in fact revealed that the temperature of the rack as a function of the two reference input variables, mass air flow and engine speed, is the temperature, the level of which is most likely to lead to damage. For this reason the steering rack temperature is most suited to determining a reference temperature, as is used in FIG. 2 for the calculation of the fan run-on time. The temperature values for the steering rack in Table 1 have here been rescaled by the factor 1000 and entered in Table 2. Rescaling for the calculation of the temperature values does not constitute an essential element of the invention. Knowing the design data of the steering rack, the exceeding of a non-dimensional reference value for the temperature of 109 or 0.109 as in FIG. 6 had to be regarded as critical. These are the temperature values represented in bold type in FIG. 6. A run-on control for the fan motor is therefore to be provided for the associated operating conditions of the combustion engine in FIG. 5. In this exemplary embodiment these are the operating conditions for mass air flow and engine speed likewise shown in bold type in the table in FIG. 5. For the remaining operating conditions of the combustion engine a fan run-on may be dispensed with.

Claims

1. Method for controlling a fan motor (4), in particular for a motor vehicle, in which at least one logic element (logic) is used to evaluate operating data and ambient data of a combustion engine (1) measured by an engine management system and to calculate a fan run-on time for the fan motor, characterized in that the fan run-on time is determined from the energy input into the combustion engine.

2. The method as claimed in claim 1, characterized in that the energy input into the combustion engine (1) is determined from the mass air flow (MAF) and the speed of the combustion engine, the fuel injection quantity, the induced torque or the induced power of the combustion engine.

3. The method as claimed in claim 1, characterized in that the energy input into the combustion engine is determined from an engine-specific air mass/engine speed-dependent temperature characteristics map (19).

4. The method as claimed in claim 3, characterized in that the duration of the fan run-on time is calculated by integration of the energy inputs.

5. The method as claimed in claim 4, characterized in that the integration is each time performed over a predetermined time interval and the integration result (27) is stored by intervals, the number of retroactively recorded interval-specific integration results being limited and the recorded interval-specific integration results each time being cyclically overwritten by the currently calculated integration results.

6. The method as claimed in claim 5, characterized in that an average is formed from the interval-specific integration results (27).

7. The method as claimed in claim 1, characterized in that in addition to the energy input into the combustion engine (2), characteristics maps for the air temperature and characteristics maps for the coolant temperature for determining the currently attainable cooling performance are also introduced into the calculation for determining the duration of the fan run-on time.

8. The method as claimed in claim 3, characterized in that the air mass/engine speed-dependent temperature characteristics map (19) contains a family of characteristics for multiple temperature-critical components.

9. The method as claimed in claim 8, characterized in that the family of characteristics is corrected by correction parameters for the outside air temperature, vehicle speed, fan activation, water temperature, intake air temperature, exhaust gas temperature or radiator shutter position.

10. A device for calculating the run-on time of a fan motor (4), in particular for a motor vehicle, having at least one electronic storage medium and at last one electronic logic element (logic);

characteristics maps (19) of the operating state and operating conditions of a combustion engine being filed in the storage medium/media,

and calculations to determine the fan run-on time being performed in the electronic logic element (logic) by means of software programs or by means of logic elements, characterized in that the logic element is in communication with signal generators (17) for the volumetric efficiency of the combustion cylinders and for the speed of the combustion engine or the fuel injection quantity or the induced torque or the induced power of the combustion engine, and the fan run-on time is determined from the energy input into the combustion engine (2).

11. The device as claimed in claim 10, characterized in that at least one characteristics map (19) is an air mass/engine speed-dependent temperature characteristics map.

12. The device as claimed in claim 10, characterized in that the logic element comprises an integration stage (23) for the time integration of the energy inputs from the air mass/engine speed-dependent temperature characteristics map (19). the energy inputs from the air mass/engine speed-dependent temperature characteristics map (19).

13. The device as claimed in claim 10, characterized in that the logic element comprises a software programmed or hard-wired cyclical loop (29) for the storage of interval-specific integration results (27).

14. The device as claimed in claim 10, characterized in that the logic element comprises software programmed or hard-wired averaging (33) for all registered interval-specific integration results.

15. The device as claimed in claim 10, characterized in that the logic element is in communication with the engine management system (17) as signal generator.

16. The device as claimed in claim 1, characterized in that the logic element (logic) is integrated into an engine management system (17).

17. The device as claimed in claim 10, characterized in that the logic element (logic) contains characteristics maps of the air temperature and characteristics maps of the coolant temperature for determining the currently attainable cooling performance.

18. The device as claimed in claim 11, characterized in that the air mass/engine speed-dependent temperature characteristics map comprises a family of curves of multiple temperature-critical components in the vehicle.

19. The device as claimed in claim 18, characterized in that the family of characteristics is corrected by correction parameters for the outside air temperature, vehicle speed, fan activation, water temperature, intake air temperature, exhaust gas temperature or radiator shutter position.