FAN SYSTEM AND METHOD FOR CONTROLLING A FAN MOTOR

Abstract

In a fan system for an internal combustion engine of a motor vehicle, having an electrical fan motor with a commutator, and having a control unit which detects a fault in the fan motor and switches said motor to a voltage-free state if the motor current reaches a predetermined load-dependent switch-off value, the invention proposes that the control unit controls the fan motor with at least a virtually maximum power for a predetermined period of time if the motor current reaches a load-dependent switching value which is lower than the associated switch-off value by a predetermined amount. As a result, the fan motor is not switched off in an undesirable manner if only contamination, but not blocking, is present.

Description

BACKGROUND OF THE INVENTION

The invention relates to a fan system for carrying out controlled cooling for an internal combustion engine of a motor vehicle, having an electrical fan motor which has a commutator, and having a control unit for controlling the fan motor, the control unit being configured in such a manner that it detects a fault in the fan motor, in particular a power consumption which is increased in comparison with the stipulation, and switches said motor to a voltage-free state if the motor current reaches a predetermined load-dependent switch-off value. The invention also relates to a method for controlling a fan motor.

A fan system of the generic type with blocking detection via the current/voltage characteristic curve is known, for example, from DE 103 26 785 A1.

Cooling systems for modern motor vehicle drives are provided with powerful fan motors which drive a fan wheel or cause the latter to rotate in order to be able to provide the heat exchangers of the cooling system with a sufficiently high air mass flow even at a standstill, that is to say when the motor vehicle is stationary, or in the case of only low vehicle speeds. The fan motors usually used are DC motors whose rotor provided with coils is supplied with electrical energy via a commutator with a brush arrangement. According to the prior art, such fan motors are controlled using a relay circuit, which has up to three series resistors and implements different loads or rotational speeds of the fan, or using power electronics which generate periodic pulse-width-modulated control signals, the duty ratio of which can be varied, for the purpose of virtually infinitely variable control. Although fan motors generally have to be designed for a high maximum required cooling power, the motors are loaded only with a considerably lower power and thus with a lower current for a large part of the total operating time during normal operation.

Faults may occur during operation of the fan motor, which faults cause, in particular, blocking or sluggishness of the fan motor. Since further energization of the DC motor in such a situation may result in the control electronics and the fan motor being damaged as a result of overheating, an attempt is usually made to detect blocking of the DC motor in good time in order to interrupt the flow of current through the DC motor if blocking is detected. In modern fan systems, the required rotational speed monitoring is not carried out with the aid of a relatively complicated rotational speed sensor, but rather an attempt is made to detect the rotational speed only on the basis of evaluation of a power consumption of the DC motor. It is assumed that the blocked DC motor has a considerably higher power consumption than would be the case when a motor under load is operating correctly. However, the current/voltage characteristic curve of the fan motor is dependent on further factors, for example the temperature of the fan motor, its supply voltage, manufacturing tolerances and the vehicle speed. On account of such influences and inaccurate detection of the current, the power consumption of the DC motor may vary by a factor of greater than one, generally at least a factor of two in the case of powerful DC motors, in the same operating state.

However, problems arise with the known detection of fan system blocking if the motor current is increased, for example on account of wear, in particular pasting of the commutator, and thus results in unwanted switching-off of the fan motor by the control device. Such “pasting”, in which coal dust, dirt, oil and so on settles in the slots between the contact laminations of the commutator, the pasting often being conductive as a result of the coal dust and/or the commutator abrasion and thus causing a short circuit between the laminations, regularly occurs on account of the fan motor being permanently controlled with an excessively low current or an excessively low rotational speed.

In the case of a fan system without blocking detection, known from DE 10 2005 016 452 A1, it is known practice to control the fan motor with a greatly increased power at a predetermined time, that is to say irrespective of the actual power consumption, in order to avoid or reduce pasting so that the pasting is either expelled from the fan motor or is burnt away.

SUMMARY OF THE INVENTION

In a fan system whose power consumption is monitored in order to detect faults, the object of the invention is therefore to avoid or reduce unwanted switching-off of the fan motor, in particular on account of pasting of the commutator.

In the fan system according to the invention, the control unit is configured in such a manner that it controls the fan motor with at least a virtually maximum power for a predetermined period of time if the motor current reaches a load-dependent switching value which is lower than the associated switch-off value by a predetermined amount.

The fan system of the present invention has the advantage that, when pasting begins or becomes greater, as a result of which its power consumption approaches the switch-off threshold, the fan motor is switched on, thus cleaning the fan motor and preventing undesirable switch-off, since, on account of the cleaning, the power consumption is moved away from the switch-off threshold if only pasting and not blocking was present. It is also advantageous, in particular, that the fan motor is not switched on independently of the requirements at arbitrary times but rather if more or less great actual pasting is present according to the power consumption.

According to a first development of the invention, the switching values are each approximately 10% lower than the associated switch-off values, which provides advantages, in particular, with respect to a resolution which is not too complex when detecting the current. In particular, there is no need for any additional outlay on hardware.

According to one advantageous development of the invention, the predetermined period of time is less than 60 seconds, preferably approximately 10 seconds. On the one hand, this generally suffices to clean the commutator slots and, on the other hand, the load on the fan motor, whose power consumption is increased in comparison with normal full load on account of the pasting, is kept low.

In another development of the invention which is considered to be particularly advantageous, the switch-off values and/or the switching values are each stored in the form of a characteristic curve in the control unit. This makes it possible for the required information to be acquired and used in a simpler and more precise manner than proposed, for example, in the generic prior art mentioned at the outset.

Another aspect of the present invention provides a method for controlling a fan motor for an internal combustion engine of a motor vehicle. In this case, an item of information relating to the current through the fan motor is determined, and a fault in the fan motor is detected and the fan motor is switched off if the motor current reaches a predetermined load-dependent switch-off value. Furthermore, the fan motor is controlled with at least a virtually maximum power for a predetermined period of time if the motor current reaches a load-dependent switching value which is lower than the associated switch-off value by a predetermined amount.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail below using exemplary embodiments. In the drawing:

FIG. 1 shows a schematic block diagram of a fan system according to the invention for an internal combustion engine,

FIG. 2 shows a schematic illustration of a commutator of the fan motor, and

FIG. 3 shows a current characteristic curve diagram for an exemplary fan motor.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a block diagram of a fan system 1 for an internal combustion engine (not shown) in a motor vehicle. The fan system 1 has a blower with a fan motor 2. The fan motor 2 is electrically connected to a control unit 3 which controls the fan motor 2 in an infinitely variable manner according to the blower requirement of the motor management system and further acquired information, in particular the temperature and the supply voltage U_bat of the fan, in a suitable manner with a manipulated variable, usually a voltage. The fan motor 2 has a commutator (not illustrated here).

Such a commutator 4 is schematically illustrated in FIG. 2. The commutator 4 to which, for example, eight contact laminations 5 are fitted is seen, which contact laminations are arranged in an electrically insulated manner on a shaft 6 of the fan motor 2. The contact laminations 5 are electrically connected to rotor coils of the fan motor 2. Slots which electrically insulate the contact laminations 5 with respect to one another are situated between the contact laminations 5. Contact is made with the laminations 5 with the aid of so-called brushes 7 which are pressed onto the laminations 5 with a spring force, with the result that there is continuous contact. An electrical current passes to the rotor coils of the fan motor 2 via the brushes 7. During operation of the motor, the brushes 7 slide on the laminations 5 and cause, for example, abrasion which preferably settles as dust in the slots between the laminations 5. Since other materials in the immediate surroundings also settle in the slots, a “paste” which is substantially conductive forms. The fan motor 2 is shown, by way of example, for a two-pole motor with two carbon brushes. Four-pole motors with two or four brushes or six-pole motors with two or four or six brushes are also possible.

A characteristic curve of the motor current I_motor, which depicts the fan current requirement dependent on the blower requirement during “normal operation”, is illustrated in the lower region of the current characteristic curve diagram according to FIG. 3. All of the characteristic curves in FIG. 3 apply, by way of example, to a constant temperature or other factors which are kept constant. A current switch-off characteristic curve I_switch-off which can be seen in the upper region of FIG. 3 is stored in the control unit 3 as a function of the motor voltage, supply voltage, temperature, time etc. If the switch-off value dependent on the respective blower requirement (motor voltage) is reached on the characteristic curve I_switch-off, the fan motor 2 is switched to a voltage-free state. Since these switch-off values would also be reached, without a fault or blocking, when only more or less great pasting of the commutator 4 is present, the fan motor 2 would be switched off in an unwanted manner by the control unit 3 in these cases. In order to avoid this, a second switching characteristic curve I_switch_2 is stored in the control unit 3, again as a function of the motor voltage, supply voltage, temperature, time etc. However, the respective switching value on the characteristic curve I_switch_2 is lower than the associated value in the switch-off characteristic curve I_switch-off. A value which is lower by approximately 10%, for example, is useful, in particular with regard to a resolution which can be achieved with acceptable outlay when detecting the current. When this switching characteristic curve I_switch_2 is reached, the DC motor 2 is fully controlled for a time to be stipulated, for example 10 seconds, if there is a blower requirement from the motor management system. As a result of this full control, particles in the commutator slots are removed and operation of the fan motor which is still fault-free is ensured.

The fan motor 2 may also be switched on for a longer period of time if the motor and the control device are designed for a correspondingly lasting increased power consumption. While switching on the fan motor 2, the upper limit I_switch-off continues to remain in force and is not reached if only pasting and not blocking is present.

Claims

1. A fan system for carrying out controlled cooling for an internal combustion engine of a motor vehicle, having an electrical fan motor which has a commutator, and having a control unit for controlling the fan motor, the control unit being configured in such a manner that it detects a fault in the fan motor and switches said motor to a voltage-free state if the motor current reaches a predetermined load-dependent switch-off value, characterized in that the control unit controls the fan motor with at least a virtually maximum power for a predetermined period of time if the motor current reaches a load-dependent switching value which is lower than the associated switch-off value by a predetermined amount.

2. The fan system according to claim 1, characterized in that the switching values are each 5 to 20% lower than the associated switch-off values.

3. The fan system according to claim 2, characterized in that the switching values are each approximately 10% lower than the associated switch-off values.

4. The fan system according to claim 1, characterized in that the predetermined period of time is less than 60 seconds, preferably approximately 10 seconds.

5. The fan system according to claim 1, characterized in that the switch-off values and/or the switching values are each stored in the form of a characteristic curve in the control unit.

6. A method for controlling a DC fan motor for an internal combustion engine of a motor vehicle, an item of information relating to the current through the fan motor being determined, and a fault in the fan motor being detected and the fan motor being switched off if the motor current reaches a predetermined load-dependent switch-off value, characterized in that the fan motor is controlled with at least a virtually maximum power for a predetermined period of time if the motor current reaches a load-dependent switching value which is lower than the associated switch-off value by a predetermined amount.

7. The method according to claim 6, characterized in that the switching values are each selected to be 5 to 20%, in particular approximately 10%, lower than the associated switch-off values.