Abstract:
A method for actuating an electric fan motor for an internal combustion engine of a motor vehicle, comprising the steps:—determining an operating duration during which the fan motor is operated below a rotational speed which is critical with regard to pasting;—wherein if the operating duration exceeds a duration which is critical with regard to pasting, the fan motor is operated for a defined time duration at a washing rotational speed which is higher than the rotational speed which is critical with regard to pasting.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a method for operating an electric fan motor for an internal combustion engine of a motor vehicle. Furthermore, the invention relates to a control unit for carrying out such a method. 
         [0002]    Engine cooling blower devices are conventionally used to carry out coolant functions in an internal combustion engine of a motor vehicle. In this context, a direct current fan motor of the engine cooling blower device generally has a commutator with laminations via which rotor coils of the fan motor are energized by means of contact brushes. A rotational speed of the fan motor is usually predefined by an electronic control unit (ECU) of the motor vehicle in order to ensure that an engine temperature is in an acceptable region which is not critical in terms of technical safety considerations. For example, the engine cooling blower device can be used in such a way that a series of radiators which are arranged one behind the other in the engine compartment of the motor vehicle are cooled by means of the airstream of said device. 
         [0003]    When the fan motor is actuated continuously with an excessively low current or at a continuously excessively low rotational speed of the fan motor, what is referred to as “pasting” of the commutator of the fan motor can disadvantageously occur, wherein brush particles, dirt, oil etc. becomes deposited in slots between the laminations of the commutator. As a result, a greasy layer, which is frequently conductive due to coal dust of the brushes and as a result can disadvantageously bring about a reduced resistance or a short circuit between the commutator laminations, is formed. In a particularly unfavorable case, the fan motor may come to a permanent standstill and therefore fail. 
         [0004]    EP 1 871 998 discloses a method for controlling a fan motor, wherein a control unit actuates a fan motor at a specific time for a predetermined time period with a cleaning manipulated variable which is increased compared to a control manipulated variable, independently of the desired cooling power. 
       SUMMARY OF THE INVENTION 
       [0005]    The object of the present invention is to make available an improved method for operating an electric fan motor for an internal combustion engine of a motor vehicle which can very largely prevent pasting of the fan motor. 
         [0006]    The object is achieved with a method for operating an electric fan motor for an internal combustion engine of a motor vehicle, comprising:
       determining an operating duration during which the fan motor is operated below a rotational speed which is critical in terms of pasting;   wherein in the event of the operating duration exceeding a duration which is critical in terms of pasting of the fan motor, the fan motor is operated for a defined time period at a washing rotational speed which is higher than the rotational speed which is critical in terms of pasting.       
 
         [0009]    By means of the method according to the invention it is advantageously possible, taking into account threshold values for the rotational speed and operating duration of the fan motor which are critical in terms of pasting, to implement, in a reproducible fashion, an effective strategy for avoiding or eliminating pasting of the fan motor. By systematically taking into account these parameters it is therefore advantageously possible systematically to counteract pasting of the fan motor even as the pasting begins, and in this way to advantageously increase the service life of the fan motor and to reduce susceptibility of the internal combustion engine of the motor vehicle to faults. The commutator of the fan motor is then cleaned in an advantageous way compared to the known methods only when said cleaning is also actually necessary on the basis of detection of when threshold values are exceeded. Precautionary cleaning processes without genuine requirements and therefore associated wear effects and adverse commercial effects are advantageously avoided in this way. 
         [0010]    One advantageous development of the method according to the invention provides that the rotational speed which is critical in terms of pasting of the fan motor is approximately 2000 rpm (revolutions/minute). In this way a threshold of a rotational speed of the fan motor is advantageously predefined, and it is monitored when pasting of the fan motor is highly probable when said rotational speed is undershot over the long term. 
         [0011]    One preferred embodiment of the method specifies that an operating duration of the fan motor which is critical in terms of pasting is approximately one hundred hours. As a result, an operating time of the fan motor below the critical rotational speed, above which the fan motor is at a high risk of pasting, is predefined in a defined fashion. 
         [0012]    One advantageous development of the method provides that the defined time period of the operation of the fan motor at a rotational speed which is higher than the rotational speed which is critical in terms of pasting is approximately ten minutes. As a result, what is referred to as a washing time or cleaning time for the fan motor during which the fan motor has to be washed in order to substantially eliminate undesired pasting substances is defined. 
         [0013]    One preferred embodiment of the method provides that the washing rotational speed corresponds substantially to a maximum rotational speed of the fan motor. As a result, a rotational speed at which the fan motor should be operated for as long as the specified washing time, in order to substantially eliminate undesired pasting materials between the commutator laminations of the fan motor, is specified in a reproducible fashion. 
         [0014]    One advantageous development of the method provides that the method is embodied as software of a control unit of the motor vehicle. As a result, there is advantageously no need whatsoever for any modification, in terms of hardware technology, of the fan system for the internal combustion engine of the motor vehicle in order to carry out the method according to the invention. As a result, the method according to the invention can easily be implemented into an already existing control unit of the motor vehicle without large additional expenditure. 
         [0015]    One advantageous development of the method provides that the software is embodied as part of a control software package, wherein the software is processed cyclically. The resulting execution of the method according to the invention at regular intervals advantageously causes regular and systematic checking of the fan motor for pasting to be carried out. In this way, the pasting can already be systematically very largely prevented in the process of its development. 
         [0016]    One advantageous development of the method according to the invention provides that the software within the control software package has a high priority. This supports the fact that the method according to the invention is preferably carried out in a way which promotes freedom of the fan motor from interference and the fan motor can in this way carry out its envisaged cooling functionality over the long term as free of interference as possible. 
         [0017]    One advantageous development of the method according to the invention provides that the numerical values for the rotational speed and the operating duration of the fan motor which are critical in terms of pasting are determined from experimental and/or technical simulation of investigations of the fan motor. In this way, the numerical values which are respectively best suited for the rotational speed and operating duration which are critical in terms of pasting can advantageously be used on an individual basis for different fan motors. This advantageously promotes adaptability of the method to different types of fan motors. 
         [0018]    One advantageous development of the method provides that the value for the washing rotational speed is determined from experimental investigations of the fan motor. As a result, the respectively best suited washing rotational speed at which the desired cleaning effect is achieved in an optimal way when the method according to the invention is carried out can easily be determined with a high level of accuracy for any type of fan motor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention is explained below in detail with reference to three figures. The figures serve, in particular, to explain the essential principles of the method according to the invention and are not intended to be such that any concrete parameters can be obtained from them. In the drawings: 
           [0020]      FIG. 1  shows a schematic illustration of a cooling blower device for an internal combustion engine of a motor vehicle for which the method according to the invention can be used; 
           [0021]      FIG. 2  shows part of an embodiment of the method according to the invention, wherein critical threshold values are defined, monitored and evaluated; and 
           [0022]      FIG. 3  shows a further part of an embodiment of the method according to the invention, wherein, in particular, the washing or cleaning process is illustrated. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  shows a highly simplified view of a cooling blower device  100 , which is usually installed in an engine compartment of the motor vehicle (not illustrated) and is used to cool a coolant of an internal combustion engine (not illustrated) of the motor vehicle. For this purpose, the cooling blower device  100  generates an airstream which flows through a radiator (not illustrated) and as a result cools the coolant located in the radiator. 
         [0024]    The cooling blower device  100  is actuated by a control unit  10  which can be embodied, for example, as an electronic control unit (ECU). The control unit  10  is electrically connected to a fan control unit  20  (Fan Control Module, FCM) which is used to actuate an electric fan motor  30 , connected to the fan control unit  20 , of the cooling blower device  100 . For this purpose, the control unit  10  transmits, to the fan control unit  20 , a pulse-width-modulated electrical signal which converts the fan control unit  20  to a corresponding electrical voltage in order as a result to actuate the fan motor  30  in terms of rotational speed. In this way, the control unit  10  predefines a desired rotational speed to the fan motor  30  and actuates it correspondingly. 
         [0025]    The pasting effect as mentioned earlier can be undesirably produced as a result of the fan motor  30  being operated below what is referred to as a “pasting threshold” for too long a time period. It has been determined experimentally that, in particular, fan motors  30  which rotate relatively slowly over a long time period are particularly at risk of pasting. 
         [0026]    According to the invention, a method for detecting a risk of pasting and for avoiding or removing pasting is proposed. The method defines, in a form which can be reproduced in terms of numbers, the specified pasting thresholds and uses them in the method according to the invention as threshold values for a subsequent cleaning process of the commutator of the fan motor  30 . 
         [0027]    The method according to the invention can preferably be implemented as a software program in the control unit  10 , wherein the control unit  10  can be embodied as a central control unit (for example as an internal combustion engine control unit) of the motor vehicle or as a partial control unit for actuating individual functions within the motor vehicle. Any control unit which sends rotational speed requests to the fan control unit  20  can advantageously be used to carry out the method according to the invention. As a result, a high degree of flexibility during the implementation of the method according to the invention is advantageously obtained. 
         [0028]      FIG. 2  shows part of an embodiment of the method according to the invention with a schematic flowchart for determining and evaluating pasting thresholds. In one step S 1  it is checked whether a rotational speed of the fan motor  30  is below a rotational speed of the fan motor  30  which is critical in terms of pasting. A threshold value for this critical rotational speed is typically approximately two thousand revolutions per minute (2000 rpm). In the event of the specified threshold rotational speed being exceeded (branch N from step S 1 ), in a step S 2  a timing counter which detects a time period of operation of the fan motor  30  below the threshold rotational speed is not operated. 
         [0029]    Otherwise (branch Y of step S 1 ), in a step S 3  the timing counter for detecting the operating duration of the fan motor  30  below the threshold rotational speed is incremented. In a subsequent step S 4  it is checked whether the time detected by the timing counter has already reached a threshold value which is critical in terms of pasting of the fan motor  30 . A typical value for this threshold value is approximately one hundred hours. In the event of the critical operating time not yet having been reached, (branch N of step S 4 ), the sequence of the method is continued without further action. 
         [0030]    Otherwise, that is to say when the operating duration of the fan motor  30  which is running below the rotational speed of the threshold has reached or exceeded a critical value in terms of pasting, in a step S 5  a bit switch is set to “true”, as a result of which the method is informed that there is now an acute risk of pasting for the fan motor  30  or the pasting has already started.  FIG. 2  therefore shows in principle checking of conditions under which there is a risk of pasting for the fan motor  30 . The sequence of steps S 1  to S 5  of the method presented in  FIG. 2  is processed cyclically within the control unit  10 , which promotes the monitoring of the fan motor  30  for pasting in a systematic and regular way. As a result, the pasting of the fan motor  30  is advantageously already prevented as said pasting begins. 
         [0031]    In a subsequent washing or cleaning process which is illustrated in principle in  FIG. 3 , the pasting is counteracted by operation of the fan motor  30  at a very high rotational speed. 
         [0032]      FIG. 3  shows a further part of an embodiment according to the invention of a sequence of steps S 6  to S 12  which is carried out in chronological succession to the steps S 1  to S 5  (see  FIG. 2 ). In a step S 6  it is checked whether the bit switch, which informs the method of the risk of pasting of the fan motor  30 , is set to “true”. In the event of the bit switch not being set to “true” (branch N of S 6 ), the method is continued without further actions. Otherwise (branch Y of step S 6 ), in a subsequent step S 7  a timing counter for detecting a washing duration of the fan motor  30  is incremented. In a subsequent step S 8  it is checked whether the washing duration has already reached a predefined length at which cleaning of the commutator of the fan motor  30  is to be expected. The necessary washing or cleaning time for the fan motor  30  is typically approximately ten minutes, wherein the length of the washing period can depend on a washing rotational speed of the fan motor  30 . At a relatively high washing rotational speed, the washing period is correspondingly shortened, wherein a minimum value of the washing period is reached at the maximum rotational speed of the fan motor  30 . The value of ten minutes of washing time is therefore to be considered a typical value which varies depending on the washing rotational speed of the fan motor  30 , wherein the exemplary embodiment of the method which is shown in  FIG. 3  is based on a maximum washing rotational speed of the fan motor  30 . 
         [0033]    In the event of the washing time not yet having expired (branch Y of step S 8 ), in a step S 9  the washing rotational speed of the fan motor  30  is set, in the way illustrated with reference to  FIG. 1 , to a value which is above the pasting threshold. Particularly advantageously this rotational speed corresponds substantially to a maximum rotational speed of the fan motor  30 , as a result of which a washing time can be minimized. The washing time for the fan motor  30  is typically approximately ten minutes in this case. 
         [0034]    In the event of the washing time for the fan motor  30  having already expired (branch N of step S 8 ), this means that the copper commutator laminations of the fan motor  30  have substantially been cleaned completely of pasting substances owing to the centrifugal force which is generated by the rotation of the fan motor  30  at a high washing rotational speed. In a subsequent step S 10 , the timing counter for the detection of the washing time is reset to zero. In a subsequent step S 11 , the bit switch, which informs the method of the risk of pasting and initiates the washing of the fan motor  30  is reset to “incorrect”. In a subsequent step S 12 , the timing counter for detecting the operating time of the fan motor  30  below the rotational speed which is critical in terms of pasting is also reset to zero. After the ending of the processing of the step shown in  FIG. 3 , the timing counter for detecting the critical operating duration of the fan motor  30  must be operated again for approximately one hundred hours in order to initiate a next cleaning or washing procedure for the fan motor  30 . 
         [0035]    The processing of the steps S 6  to S 12 , (see  FIG. 3 ) like the processing of the steps S 1  to S 5  (see  FIG. 2 ), is carried out cyclically, as a result of which systematic cleaning of the fan motor  30 , which is as far as possible uninterrupted where necessary, is advantageously carried out. 
         [0036]    The method according to the invention is particularly advantageously carried out with a high priority within a control software package with the steps illustrated in  FIG. 2  and  FIG. 3 , which already promotes the reduction and prevention of the pasting as it begins. All the steps in  FIG. 2  are carried out here before the steps in  FIG. 3 , since the steps S 1  to S 5  in  FIG. 2  are necessary in order to determine in a defined fashion the risk of pasting during operation of the fan motor  30 , which is subsequently substantially removed by the steps S 6  to S 12 . 
         [0037]    The control unit  10  can be any electronic control unit which sends an instruction to the fan control unit  20  to rotate the fan motor  30  at a defined rotational speed. The method according to the invention is preferably implemented in a software package of the control unit  10 . 
         [0038]    Of course, the specified numerical values for the parameters and thresholds are to be understood merely as typical values for an exemplary embodiment of the method. The specified numerical values can be changed as a function of the type and operating circumstances of the fan motor  30 , wherein the values which are respectively the most suitable can be determined, for example, by means of an experimental and/or technical simulation method. By virtue of the embodiment of the method according to invention as software of a control unit  10 , the modified values can easily be used to carry out the method. As a result, the method according to the invention can advantageously easily be adapted for a multiplicity of different fan motors  30 . 
         [0039]    In summary, a method for operating an electric fan motor for an internal combustion engine of a motor vehicle is proposed which systematically provides a way of reproducibly determining and reducing/avoiding undesired pasting of the electric fan motor on the basis of the monitoring of predefined pasting threshold values. 
         [0040]    The features of the invention explained above and by means of the figures will be modified and combined with one another by a person skilled in the art in an expert fashion.