Abstract:
Apparatus and method for reducing fan noise in a personal computer having at least one fan with a direct current motor. The fan is disposed within and ventilates a zone. Operative voltage is applied to the motor through a controller from a power supply. Thermo-sensors in the zone measure the temperature in the zone. A table coupled to the controller lists for each temperature value an optimum rotational rate for the fan, the optimal value being the minimal value of rotation rate for the fan to provide a sufficient ventilating of the zone at this corresponding temperature. The thermo-sensor when actual temperature in the zone is changed during operation, inputs this condition to the controller, which modifies the voltage, applied to the motor, to provide the assigned optimal rotation rate. The fan noise increases with increasing rotational rate, and thus minimizing the fan rotation rate for the current temperature in the ventilating zone reduces the noise generated by the fan, and reducing voltage supplied to the fan conserves energy.

Description:
FIELD OF THE INVENTION 
     The present invention relates to control of variable speed fans utilized in computer type systems. 
     BACKGROUND OF THE INVENTION 
     Fans are standard components in many commercial computers, workstations, notebook and desktop personal computer systems, and in many other electronic and mechanical systems. Fans remove heat generated due to operation of integrated circuits and other components in such systems. 
     The use of fans often presents certain disadvantages in various systems. For example, fan is a source of objectionable acoustic vibrations, the noise generated by the fan being a monotone non-decreasing function of the rotational rate of the motor. Also, fan often has a service life that is less than the service life of the equipment it protects, and generally a fan service life expectancy is the shorter the higher is operation rotation rate of the fan. 
     Additionally, fans require large operating currents, the current requirements increasing with the fan rotational rate. Such usage of large currents creates problems for low power, “green” personal computer systems. 
     The present invention employs simple and novel methods and apparatus for overcoming these disadvantages. 
     SUMMARY OF THE INVENTION 
     In accordance with the principles of this invention, the noise generated by at least one fan with a direct current motor, which is disposed within and ventilates a zone of a personal computer, is found to be a function of the rotational rate of the motor. In order to reduce the noise, it is necessary to reduce this rotational rate. To this end, a thermo-sensor is positioned within the zone adjacent the fan to measure the actual temperature thereof. 
     A controller is connected between the fan motor and a direct voltage power supply of the computer. The controller receives a first input from the sensor thereby reading the temperature in the zone and also receives an input voltage from the supply. The computer has a data file which contains for said fan a table which lists for each temperature an optimal rotational rate and also specifies a maximum allowable temperature value and recommended corresponding rotational rate value for said motor. When the actual temperature in the zone is changed during operation, the controller modifies the voltage fed to the motor in such manner as to provide the assigned optimal rotation rate. 
     In order to optimize the fan cooling efficiency at a given temperature, a tachometer can be integrated with the fan to measure the actual rotational rate thereof. The tachometer provides a second input to the controller thereby providing optimal reaction of the controller to variations in zone temperature. 
     The data file can also list first, second and third chosen modes of operation identifying respectively, suspension of normal computer operation, emergency deactuation of the computer, and generation of warning message to be received by the user. Each mode is initiated by a corresponding one of first, second and third specific listed commands when the current temperature exceeds the specified maximum. In the event that the actual temperature is not reduced below the maximum value, the controller actuates a selected one of first second and hird modes of operation in response-to a corresponding one of the first, second and third listed commands. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram of system including a fan control method and apparatus in accordance with the invention applicable for fan without built-in tachometer. 
     FIG. 2 shows a block diagram of system including a fan control method and apparatus in accordance with the invention applicable for fan provided with built-in tachometer. 
     FIG. 3 shows a circuit diagram of a fan power controller in accordance with the invention applicable for fan without built-in tachometer. 
     FIG. 4 shows a circuit diagram of a fan power controller in accordance with the invention applicable for fan provided with built-in tachometer. 
     FIG. 5 shows a flowchart of fan power control in accordance with the invention. 
     FIG. 6 A and B, show graphs of fan speed control during continuous mode operation in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring first to FIG.  1 . In a PC (or another system) there are one or more zones  132 ,  134 ,  136  to be cooled (in a modern PC the zones usually are power supply unit and main processor, and, in some cases, the chassis). Each of the zones is ventilated by an individual fan powered by a direct current motor; e.g., fan  102  takes care of zone  132 . Each of the zones is additionally supplied with an individual thermo-sensor (e.g., thermo-sensor  106  in zone  132 ) installed in the zone to measure its current temperature. The fans are power-supplied not directly from PC power supply unit  110 , but via controller  108 , which is able to modify the voltage supplied to each of the fans independently. During operation, controller  108  receives input signals from each of the thermo-sensors thereby reading the temperature in each of the zones. The actual temperature is compared with a discrete temperature values from a table stored in data storage  112  and accessed by the controller. The table lists for each corresponding zone temperature value a minimal rotational rate for providing the necessary ventilation of the corresponding zone at this temperature value and also specifies a maximum allowable temperature value and recommended corresponding rotational rate value for each of the motors. The controller when the actual temperature in any one of the zones is changed during operation, modifies the voltage supplied to this motor in such manner as to provide the assigned optimal rotation rate. 
     FIG. 2 shows a block diagram of system including a fan control method and apparatus in accordance with the invention applicable for fan provided with built-in tachometer. In contrast to block diagram shown in FIG. 1, in this case each of fans in ventilated zones  132 ,  134 , and  138  is equipped with a built-in tachometer (e.g., tachometer  204  is adjusted to fan  102 , ventilating zone  132 ). Controller  108  receives additional, as compared with the case of FIG. 1, signals from the tachometers thereby reading the actual rotation rate of each of the fan motors. Data storage  112  in this case contains, for each of the zones, a table with a series of temperature values for corresponding zone and corresponding optimal rotation rates of the fan in the zone. In operation, controller compares current temperature reading for each of the zones with discrete temperature values in the table, and modifies the voltage supplied to the fan motor in such a way as to make the fan rotation rate reading provided by the fan tachometer to be equal to the rotation rate value, which corresponds to the nearest temperature value superior to the actual measured temperature in the zone. 
     FIG. 3 shows a circuit diagram of fan controller and adjacent software applicable for use without a tachometer. 
     Controller  108  contains micro code  305 , which ensures interaction of elements of the apparatus. Input/output interface with system bus  312  provides signal exchange between the controller and software component  332  (e.g., via  12 C interface). After the system is started up, initializing module  309  generates signal that actuate hardware detection block  301 , which enables system to adapt itself for current PC configuration with the allowance made for actually installed or removed fans and thermo-sensors. Signal from module  309  also initializes the fans acceleration with short-run energizing the fan motors by 100% nominal voltage (the acceleration regime is necessary for the fans to be set to motion, because initially supplied low voltage may fail to start the motors). 
     Readings from the thermo-sensors installed in ventilated zones of the PC come to signal processing block  303  (analog-to-digit converter). The results are compared in block  310  with temperature values from table stored in data storage  112 , the data being read with the help of reading module  307 . 
     The control over fan rotation rates is performed by fan speed control module  316 . Signals from the module are transferred to controller  108  via interface  312 . In accordance with the signals, block  302  (digit-to-analog converter) generates corresponding DC voltages supplied to the fans. When voltage supplied to a fan is altered to be brought into agreement with tabulated voltage value for current temperature in the corresponding zone, timer  315  sets a time delay (a pause) which is necessary for the fan rotation rate to stabilize at a new level. 
     The system is provided with user&#39;s interface  317 , which displays current values of temperatures in ventilated zones of the PC and rotation rates of corresponding fans. The interface may be also used to alternate the content of data storage  112  (that is, the tables of temperature values and corresponding fan supply voltages for each of the ventilated zones); the data are written to the file with the help of data writing module  311 . 
     FIG. 4 shows a circuit diagram of fan controller and adjacent software in accordance with the invention applicable for fans provided with built-in tachometer. 
     This system is designed to operate with ventilating fans provided with built-in tachometers. The availability of the tachometers (as well as fans and thermo sensors) is checked by hardware detection block  301 , which enables system to adapt itself for current PC configuration. Controller  108  receives additional, as compared with the case of the system shown in FIG. 3, signals from the tachometers thereby reading the actual rotation rate of each of the fan motors. The signals arrive to micro code  305  via block of accumulating counters  404  (analog-to-digit converters). 
     Data storage  112  in this case contains, for each of the zones, a table with a series of temperature values for the zone and corresponding optimal rotation rates of the fan ventilating the zone. In operation, block  310  compares current temperature reading for each of the zones with discrete temperature values in the table, and fan speed control module  316  modifies the voltage supplied to the fan motor in such a way as to make the fan rotation rate reading provided by the fan tachometer to be equal to the rotation rate value, which corresponds to the nearest temperature value superior to the actual measured temperature in the zone. Fan speed comparison module  406  exerts control over the voltage modulation by checking the current rotation rate of the fan motor against the value read from the corresponding table in data storage  112  with the help of data reading module  307 . 
     The systems features may be expanded to include protection of PC components against accidental overheating. Additional system health monitoring module  413  constantly compares, for each of the PC zones, current temperature reading, derived from controller  108  via interface  312 , with maximal allowable temperature for the zone read from data storage  112  with the help of data reading module  307 . When the current temperature in a zone exceeds the specified maximum, system health monitoring module  413  passes control to PC control signals generation block  414 . In accordance with preset mode of system operation in case of the PC component (zone) overheating, block  414  generates a warning message to be received by the user via user&#39;s interface  312 , or issues a command to emergency deactivate the PC or to suspend its normal operation. Mode of system operation is specified in data file stored in module  112 , the mode may be chosen by PC user and written to the file with the help of user&#39;s interface  312  and data writing module  311 . 
     FIG. 5 shows a flowchart of fan power control in accordance with the invention. When the program is started up, it is loaded to the PC operation memory and initialized (block  501 ). After initialization, the program checks actual configuration of the cooling system (availability of thermo-sensors and fans, and the presence of build-in tachometers); the procedure is realized by block  502 . When the checking procedure is completed, fans motors starting-up routine is executed, the starting pulse being delivered to the fans by block  503 . 
     The next step is reading operation information from data storage; the function is being conducted by block  504 . The information to be read includes, for each of ventilated zones, a table of discreet temperature values and corresponding optimal fan rotation rates. An example of such a table (for a PC power supply unit) is presented below in Table 1: 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Initial table of “temperature-rate” dependence for one of 
               
               
                 ventilated zones (a PC power supply unit) 
               
             
          
           
               
                 Temperature, C.° 
                 Fan rotation rate, rpm 
               
               
                   
               
             
          
           
               
                 24 
                 0 
                   
               
               
                 25 
                 800 
               
               
                 35 
                 1200 
               
               
                 40 
                 2400 
               
               
                 50 
                 4000 
                 (max) 
               
               
                   
               
             
          
         
       
     
     In addition to a —“temperature—rate” table, the operation information include maximal allowable temperature value for the zone, and modes of system operation in case of the PC component (zone) overheating. 
     the system operation can be watched by operator with the help of user&#39;s interface, which is data-supplied from block  505 . The block is the first in the main operation cycle of the program, which incorporates also blocks  506 - 512 . 
     Block  506  sets the necessary time interval between separate readings of current data and provides a time delay to ensure fan rotation rate stabilization after a change is made in voltage supplied to the fan. Block  507  reads discreet temperature values from data file, and  509  compares actual temperature readings fed by thermo-sensor with the tabulated values. It is just the block, which perfumes the function of fan rotation rate control. 
     In case of stable operation regime, when actual temperature inside the zone remains in the same interval between tabulated temperature values and the fan rotation rate is equal to the corresponding (tabulated) optimal value (±10%), the algorithm is being closed by block  505 . Otherwise, if the actual temperature reading is found to exceed the upper value of the initial temperature interval, (or to drop below the lower value of the interval), the fan rotation rate should be increased (decreased) to be brought to agreement with a new optimal (tabulated value). The decision on necessary modulation (increase or decrease) of rotation rate and, therefore, fan-supplied voltage is derived by block  510 , and than control transition to block  511  or block  512 , correspondingly. After a modification is done, control returns to block  508 ; it makes it possible to determine, if the carried out modification of voltage supplied to the fan is sufficient for optimization the fan rotation rate. An example of the fan speed control system operation is demonstrated by graphs shown in FIG. 6, A, and B. The graphs corresponds to the case of PC power supply unit ventilation, the initial“temperature—rate” table being presented in Table 1. 
     The starting moment for the diagrams corresponds to the moment when fan starting up routine is completed (about a minute after the system operation begins). The initial temperature inside the zone (PC power supply unit) is below 25° C., as is seen in FIG. 6A, so the zone does not needs ventilation (fan rotation rate is zero during the period, see FIG.  6 B). In 10 min the zone is warmed up (the temperature exceeds 25° C. in FIG.  6 A), and the fan is started; its rotation rate is being increased for about  5  min, as seen in FIG. 6B, to become equal to the optimal value of 800 rpm for the temperature regime (in accordance with Table 1). 
     The temperature of the zone continues to increase and exceeds the next tabulated value of 35° C. (see Table 1) by the moment T=30 min in FIG.  6 A. As a response, the algorithm brings the fan rotation rate to the new optimal value of 1200 rpm, specified by Table 1, as seen in FIG.  6 B. In 5 minutes increasing in the zone temperature is terminated (the delay determined by thermal capacity of elements of the PC power supply unit), the temperature decreases and comes to the level of 35° C. (FIG.  6 A). 
     While the invention has been described with particular reference to the drawings and detailed description, the protection solicited is to be limited only by the terms of the claims which follow.