Patent Grant
7310959
This application claims the priority of German Patent Application No. 103 48 133.8, filed on Oct. 16, 2003, the subject matter of which, in its entirety, is incorporated herein by reference.
The invention relates to a method for controlling the power of a fan motor and to a control program with which the power of the fan motor is controlled. The method and control program are suitable in particular for actuating fan motors such as are used with fans in cooling systems for internal combustion engines. The control program determines here the power of the fan using characteristic curves of the fan motor and using the operating parameters of the cooling system and using predefined reference variables which predefine a temperature level to be set. However, the method and control program here are not restricted in any way to cooling systems in motor vehicles but rather can always be used wherever the aim is to set various temperature levels using a fan motor.
A method of the generic type and a control program of the generic type are known from German Patent Application DE 197 28 814 A1. Various temperature levels are to be set in a cooling system for an internal combustion engine of a motor vehicle. The temperature levels which are to be set here are the reference variables for a fan control which determines the necessary power of the fan using a control program. The power of fan is determined here from the operating parameters of the cooling system, the predefined reference variable. Also from characteristic diagrams and characteristic curves of the fan motor. The operation of the fan is interrupted here until the coolant in the cooling system has reached and exceeded a minimum temperature. The intention here is to ensure that the internal combustion engine reaches the operating temperature as quickly as possible and that a cooling effect of the fan cannot occur prematurely. Once the fan function has been enabled, the control program adapts the power of the fan to the temperature level to be set. In particular two temperature levels of 90 degrees Celsius and of 108 degrees Celsius to which the power of the fan is to be adapted are provided here.
The abovementioned control of the power is thus an efficient method for reaching as quickly as possible the temperature levels which are predefined as reference variables. However, disadvantages result if the intention is to change over from a high temperature level to a low temperature level. The changing of the temperature level is in fact predefined by the changing of the reference variable for the control of the power. This reference variable changes here from 108 degrees Celsius to 95 degrees Celsius. For the control of the power of the fan motor this means that owing to the large temperature difference when the reference variable is changed from a high value to a low value it detects a large temperature difference with respect to the current actual temperature which is to be compensated as quickly as possible. This means that the fan motor whines at maximum power. This has the advantage that the lower temperature level is reached as quickly as possible, but is generally neither desirable nor necessary. The whining of the fan motor therefore leads to noise pollution and to unnecessary consumption of energy.
This is where the invention comes into play. The object of the invention is in fact to prevent whining of the fan motor when the temperature level to be set changes from a high value to a low value.
This object is achieved using a method as claimed in claim 1 and using a control program as claimed in claim 11. Advantageous refinements of the method according to the invention and of the control program according to the invention are contained in the subclaims and in the description of the exemplary embodiments.
The solution applies mainly to a power control process in which the power of the fan is determined from the characteristic curves of the fan motor, the operating parameters of the cooling system and the reference variables which are predefined in the form of temperature levels. The various temperature levels which are to be set have various associated characteristic curves for the actuation of the fan motor. If the reference variable for the control changes, this also means a change in the characteristic curves for actuating the fan motor. In order to prevent whining of the fan motor, the operation of the fan motor is kept constant for a settable minimum waiting time when the reference variable for the control of the fan changes. During this minimum waiting time, the operating parameters of the cooling system can, if appropriate, be adapted by means of other control mechanisms which are independent of the fan to the new reference variable to such an extent that it is no longer necessary to take measures with respect to the whining of the fan motor.
In one advantageous refinement of the invention, the starting up of the fan motor is damped using a filter which is connected into the circuit for actuating the fan motor. As a result, a slow startup of the fan is made possible even if large temperature differences with respect to the current actual temperatures of the system to be cooled occur when the temperature level to be set changes. This filter preferably has what is referred to as a PT1 characteristic.
Further advantageous refinements of the invention include the possibility of adapting the minimum waiting time until the fan motor starts and the method of a possibly necessary fan startup to the system conditions in a selective fashion. For this purpose, for example, the minimum waiting time can be shortened as a function of the thermal loading of the system to be cooled or the filter characteristics with which the starting up of the fan motor is influenced can be changed selectively so that the fan accelerates to higher power levels more quickly. When the system to be cooled and the ambient conditions are monitored by sensor, the chronological duration of the effectiveness of an adapted filter setting can be reduced if the ambient conditions change too strongly in comparison with what would still be appropriate for the selected filter settings. For this purpose, for example, the minimum waiting time for the interruption of the fan motor is set as a function of the temperature level to be set or the current operating parameters. Likewise, the filter settings are set as a function of the current operating parameters.
The invention is particularly suitable for use in cooling systems of internal combustion engines. In this case, relevant operating parameters according to which the filter settings and the minimum waiting time are selected are the current engine load of the internal combustion engine and the intake air temperature of the internal combustion engine.
The invention is explained in more detail using the example of a cooling system for an internal combustion engine without restricting the general applicability. In this regard, reference is made to the following drawings, in which:
Fan motors are usually used as a protection against overheating of a system to be cooled. The system to be cooled usually has here a primary temperature control in addition to the control of the fan. The temperature in the cooling system is preferably controlled using this primary temperature control. In particular in internal combustion engines, thermostats with which closed cooling circuits are switched over are used for the primary temperature control. Thermostats operate here in a significantly more energy-efficient fashion than fan motors and also have the advantage that the energy present in the system is retained better in the system by them. Fan motors have the disadvantage here that they use up a lot of energy merely for the purpose of taking energy out of an existing system. However, it is better to leave the energy in the system and to attempt to be able to obtain as much effective power as possible from it. The temperature control in a cooling system is therefore preferably carried out with an energy-efficient primary control, while the fan motor and the fan control are merely used as an additional protection if a reliable temperature control can no longer be maintained using the primary control. For this reason, in particular in motor vehicles, the fan is as far as possible not to be used for temperature control in the cooling system. However, in known fan controls from the prior art, problems occur here if, as already stated at the beginning, the temperature level in a cooling system is to be reduced from a high level to a lower temperature level. These problems are illustrated in
In
The fan control according to the invention is suitable in particular here for use in a cooling system for an internal combustion engine.
Depending on the position of the valves in the three-way thermostat 11, the cooling system can be operated here in a manner known per se in the short-circuit mode, in the mixed mode or in the large cooling circuit. The heating heat exchanger 3 is connected to the high temperature branch of the cooling system in the internal combustion engine via a temperature-controlled shut-off valve 14. The throughput rate through the heating heat exchanger after the shut-off valve 14 has been opened can be controlled in order to control the heating power, using an additional coolant pump 15 and a clocked shut-off valve 16.
The actuation of the activation elements at the valves of the three-way thermostat 11 is set here by the control device 5. The control device contains a logic component Logic in the form of a microelectronic computing unit. The control device is preferably formed by the control device in the motor electronics or is a component in the control device of the motor electronics. Here, the three-way thermostat 11 and the fan motor 4 are actuated using the control device 5. The actuation of the heating element of the three-way thermostat 11 is carried out here in a manner known per se. The three-way thermostat 11 is here the actuating element for the primary control mentioned at the beginning, which is also implemented as a control program for actuating the heating element in the three-way thermostat 11 in the control device 5. By suitably actuating the three-way thermostat 11 it is possible to set and control in particular three different temperature levels of 80 degrees Celsius, 90 degrees Celsius, and 105 degrees Celsius, in the cooling system for the internal combustion engine. The temperature levels are set here predominantly in a load-controlled fashion. This means that, of the requirements made of the engine, the temperature which is suitable for the current requirement is set in the cooling system from the operating modes of the internal combustion engine which can usually be tapped in the electronics of a modern internal combustion engine in the form of digital signal values. The most important influencing variable is here the engine load which is determined in particular from the engine speed, the sucked-in quantity of air or the fuel quantity injected into the combustion cylinders. If a satisfactory temperature control is no longer successful with the three-way thermostat 11 alone, the fan can be used for additional cooling. The fan motor 4 is also actuated here with the control device 5. The power of the fan motors is usually controlled with a pulse width modulation. For this purpose, the necessary cooling power is calculated from the operating parameters of the cooling system by a control program and when the currently necessary cooling power is known, the sampling ratio of the pulse width modulation with which the required cooling power can be provided is determined from the fan characteristic curves. The most important influencing variables for determining the suitable fan power are here the current engine load, the cooling water setpoint temperature, the cooling water actual temperature, the intake air temperature and the fan characteristic curves. If various temperature levels are to be set using the cooling system, various fan characteristic curves Khigh, Klow can be used for the various temperature levels.
According to the invention, the control program is then extended for the actuation of the fan motor to the effect that when the temperature level in the cooling system drops, the fan motor is prevented from starting up at least for a minimum waiting time and if it is still necessary to start up the fan after the minimum waiting time, the startup of the fan is attenuated in such a way that the working point of the fan control on the fan characteristic curve can be approached asymptotically. This is possible according to the invention with a control program such as is described in more detail below with respect to
If the cooling water setpoint temperature which is predefined by the engine management system changes, the process described above is carried out for the new cooling water setpoint temperature using the program module 31 to select a new fan characteristic curve. The program module 31 switches, as it were, from a characteristic curve Khigh for the high cooling water setpoint temperature to a characteristic curve Klow for a lower cooling water setpoint temperature. Furthermore, the cooling water actual temperature is permanently monitored, so that a working point for the fan motor can also be found on the new fan characteristic curve Klow and set. The changing of the cooling water setpoint temperature and the changing of the associated characteristic curve are evaluated in terms of programming using a subroutine 33. Checking is carried out to determine whether the cooling water setpoint temperature has changed from a high prescribed temperature value to a lower prescribed temperature value. If this is the case, a further program module, designated as Timer 1, is activated. In
After the minimum waiting time which is determined by the Timer 1 has expired, the low characteristic curve Klow, or to be more precise the activation signal—calculated on the basis of the low characteristic curve—to the fan motor, is enabled. The high characteristic curve Khigh is not switched and remains continuously active. The enabling of the characteristic curve is represented symbolically in
The attenuation of the fan startup is carried out with a settable digital filter 32 with which the actuation signal to the electronic system of the fan motor is filtered. The filter ensures the actuation signal present at the input end of the filter is transmitted to the filter output with a filter characteristic curve which approaches the input value asymptotically. The filter is preferably a filter with what is referred to as a PT1 characteristic. These filters are defined by a filter characteristic curve with an exponential profile, the time constant of the exponential function indicating after what time the output signal has reached 66 percent of the value of the input signal. By selecting the time constant of the exponential function it is possible for these filters to be adapted in terms of their effect and set. The invention also makes use of this by embodying the filter constant of the filter 32 in such a way that it can be exchanged using a subroutine 35. A time constant of 5 seconds and a time constant of 60 seconds are provided here. The switching over of the time constants of the filter is triggered by the program module Timer 2 by activating a selection process 35. The selection process is illustrated in
The duration of the filter settings of the abovementioned filter 32 is set using the program module Timer 2. The program module Timer 2 is used here mainly for resetting the time constants of the filter 32 from a high time constant to a lower time constant. In the exemplary embodiment of
However, particular circumstances apply if there is a risk of overheating owing to an excessively high damping effect of the filter 32. This risk may be present if the filter settings permit only a slow fan startup. For this reason, a protective function is implemented using the program module Timer 2, said function permitting the time period of the filter settings to be shortened. For this purpose, the intake air temperature of the internal combustion engine and the current engine load of the internal combustion engine are also read out of the engine control device using the program module Timer 2 by monitoring the corresponding characteristic variables. If the intake air temperature exceeds the value of 50 degrees Celsius or if the engine load is above a value of 90 percent of the maximum possible engine load, the time constant of the filter 32 is reset immediately to the lower value of 5 seconds. As a result, if there is a risk of overloading, the fan can accelerate more quickly to its maximum power. The fan is in fact active more quickly with a shorter time constant of filter 32.
The interaction between the individual program modules as described in
With the primary control, after the end of the minimum waiting time Δt1 the cooling water actual temperature should generally have dropped below the activation threshold for the fan motor. This activation threshold is 95 degrees Celsius in the exemplary embodiment under discussion here. If the cooling water temperature has not dropped below this activation threshold, the fan is activated with an attenuated startup after the expiry of the minimum waiting time Δt1 at the time T1. The attenuation of the fan startup has the effect that the actuation signal for the PWM modulation of the fan approaches the working point on the fan characteristic curve asymptotically. This profile is illustrated in exemplary impression in the sixth diagram in
It will be appreciated that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 103 48 133 | Oct 2003 | DE | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4806832 | Muller | Feb 1989 | A |
| 6101987 | Saur et al. | Aug 2000 | A |
| 6291956 | Ku | Sep 2001 | B1 |
| Number | Date | Country |
|---|---|---|
| 197 28 814 | Jan 1999 | DE |
| Number | Date | Country | |
|---|---|---|---|
| 20050081542 A1 | Apr 2005 | US |
