Abstract:
The present invention provides an electric blower that performs: measuring an amount of airflow against a fan rotation speed of the blower with a load magnitude detected previously; determining an empirical formula to calculate a fan rotation speed to discharge an amount of target airflow in response to the magnitude of a load of the blower according to the data obtained from the above measurement repeated a plurality of times varying the magnitude of the load on the blower; operating, firstly in practice, the blower to detect the magnitude of the load of the blower, then to calculate the fan rotation speed to discharge the amount of target airflow using the empirical formula; and then changing the blower operation to the fan rotation speed given by the calculation.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to an electric blower for use in an air conditioner or the like coupled to a duct to supply an airflow necessary to a refrigerating cycle or the like in response to the duct condition.  
       BACKGROUND ART  
       [0002]     There has been the kind of conventional electric blower that, observing always a fan rotation speed and the PWM (Pulse Width Modulation) signal for an electric motor to calculate the amount of airflow to compare the calculated amount of airflow with an amount of target airflow, corrects the control signal sent to the electric motor if there is a difference between the two, which is so-called a feedback control method. The technology is disclosed for instance in Japanese Patent Unexamined Publication No. H07-301450 (hereafter referred to as patent document 1).  
         [0003]      FIG. 3  shows a process flowchart of a conventional electric blower described in patent-document  1 . As shown in  FIG. 3 , the control process of the conventional electric blower comprises; step  135  to recognize the amount of target airflow; step  140  to calculate the amount of airflow by using the PWM signal sent to the electric motor at present and the fan rotational speed; steps  145  and  150  to compare the calculated amount of airflow with the amount of target airflow; steps  155  and  165  to correct the PWM signal according to the comparison results; and step  160  to send the corrected PWM signal to the motor controller, repeating from step  135  to step  160  constantly.  
         [0004]     However, owing to pulsations occurring inevitably in the airflow of electric blowers, conventional electric blowers cannot continue to operate stably matching the amount of target airflow with the calculated amount of airflow, but is operated always fluctuated in the rotation speed. Moreover, elements having big inertia such as the electric motor and fan included in the feedback control system could cause overshooting or depending on conditions the pulsation could be amplified to cause an unstable rotation speed fluctuating largely  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention aims at providing an electric blower to solve the above-mentioned drawbacks, which can operate stably keeping an amount of target airflow in response to conditions of duct.  
         [0006]     To solve the above-mentioned drawbacks the electric blower of the present invention includes an electric motor, a blower with a fan driven to rotate by the electric motor, and a controller to control the electric motor. The controller comprises: a load-detector to detect output data on the magnitude of the load; a rotation-speed-calculator to calculate output data on the fan rotation speed required for the blower to discharge the amount of target airflow according to the magnitude of the load of the fan output from the load-detector and the given amount of target airflow; a rotation-speed-selector to switch over the rotation speed from the load-detection-rotation-speed determined previously to the rotation speed required for the blower to discharge the amount of target airflow according to the data output from the rotation speed calculator; and a timing-device to determine the operation timing for the load-detector, rotation-speed-calculator and rotation-speed-selector respectively.  
         [0007]     The configuration can perform a stable operation for the controlled airflow without amplifying the pulsation in the rotation speed, because the timing device is allowed to work according to need such as before the operation starts or when a load condition varies to detect the duct condition beforehand and can operate the blower at a rotation speed capable of discharging the amount of target airflow in response to the duct condition detected. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  illustrates a block diagram of the electric blower used in exemplary embodiment 1 of the present invention.  
         [0009]      FIG. 2  illustrates a characteristic showing a relation between the amount of airflow and rotation speed of the electric blower used in exemplary embodiment 1 of the present invention.  
         [0010]      FIG. 3  illustrates a flowchart of a conventional electric blower. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     Exemplary Embodiment 1  
       [0011]     Generally, an amount of airflow is proportional to a rotation speed of a fan included in a duct when the duct condition is determined and the duct condition affects relative gradients or the like. If, therefore, the duct condition is detected somehow the relation between the amount of airflow and rotation speed can be determined. The duct condition is detectable as a load of the blower and the load of the blower is detectable as an output force of an electric motor as well. Moreover, because the output force of the electric motor is proportional to the product of the rotation speed and torque of the fan, the duct condition can be detected from the torque of the electric motor when the rotation speed is kept constant. In case of a DC motor, whose torque is proportional to the input current, the torque can be detected by measuring the motor input current. Therefore, the duct conditions can be detected by measuring the motor input current.  
         [0012]     The present invention is to detect the duct condition according to a value showing the magnitude of the load of the blower (hereafter referred to as a blower-load-variable) obtained from the input current of the electric motor operating at a predetermined rotation speed. To measure the blower-load-variable, the blower must operate at a predetermined rotation speed.  
         [0013]     Namely, through the operation to detect the load by measuring the input current of the electric motor operating at a predetermined rotation speed, the duct condition is detected as a blower-load-variable. A fan rotation speed to discharge the amount of target airflow in response to the duct condition is calculated according to an empirical formula having been obtained from the characteristics of the blower. Subsequently, controlling the motor to rotate the fan at the given rotation speed can realize an operation for a stable airflow without doing any constant feedback control.  
         [0014]     Now, exemplary embodiment of the present invention is described with reference to the drawings. The present invention is not limited to the exemplary embodiment only.  
         [0015]      FIG. 1  is a block diagram of the electric blower used in exemplary embodiment  1  of the present invention. In  FIG. 1 , electric blower  1  of the present invention includes electric motor  25 , blower  20  and controller  10 .  
         [0016]     Electric motor  25  supplies a driving force necessary to rotate blower  20 . A DC brush-less motor is employed in the exemplary embodiment. The driving shaft of electric motor  25  is coupled to blower  20  directly.  
         [0017]     Blower  20  flows air through duct system  15  forming an air-path. A sirocco fan is used in the blower of the exemplary embodiment.  
         [0018]     Controller  10  includes variable-motor-controller  30 , airflow-controller  35  and system-controller  40 .  
         [0019]     Variable-motor-controller  30  controls the rotation speed of the electric motor, in response to control-signal Fo produced in airflow-controller  35 . Additionally, variable-motor-controller  30  detects the motor rotation speed, and sends it to airflow-controller  35  as motor-rotation-speed-signal Rm.  
         [0020]     Airflow-controller  35  includes timing-device  100 , load-detector  105 , rotation-speed-calculator  110 , rotation-speed-selector  120  and control signal feeder  90 .  
         [0021]     Timing-device  100  allows to start load-detector  105  at a prescribed timing.  
         [0022]     Load-detector  105 , receiving signals from timing-device  100 , outputs load-detection-rotation-signal Fra to drive electric motor  25  at a load detection rotation speed. Load-detector  105 , additionally, outputs blower-load-variable Tra according to the electric motor input current Im measured at this time.  
         [0023]     System-controller  40 , varying the operation capacity of a variable compressor (not shown) in response to an air-conditioning capacity required, sends rotation-speed-calculator  110  information on an amount of airflow, as target airflow Q, corresponding to the varied compressor capacity.  
         [0024]     Rotation-speed-calculator  110  calculates the fan rotation speed for the fan to discharge the amount of target airflow Q by substituting blower-load-variable Tra output from load-detector  105  and the amount of target airflow Q sent from system controller  40  into formula (a) described later. The fan-rotation-speed is then output as fan-rotation-speed-signal Fr.  
         [0025]     Rotation-speed-selector  120  switches over rotation-speed-signal Fs input into control signal feeder  90  from load-detection-rotation-signal Fra to fan-rotation-speed-signal Fr according to fan-rotation-speed-signal Fr output from rotation-speed-calculator  110 .  
         [0026]     Control-signal-feeder  90  sends rotation-speed-control-signal Fo to variable-motor-controller  30  so that rotation-speed-signal Fs from rotation-speed-selector  120  matches with motor-rotation-speed-signal Rm from variable-motor-controller  30 .  
         [0027]     Formula (a) is determined according to the following procedure.  
         [0028]     (1) The blower load condition is detected to determine the blower-load-variable by measuring the input current of the electric motor driving the blower at a predetermined rotation speed.  
         [0029]     (2) The fan rotation speed is varied leaving the blower-load-variable kept constant, and then the amount of airflow of the blower is measured in each varied fan rotation speed.  
         [0030]     (3) The empirical formula is determined as formula (a) from the relationship between the amount of airflow of the blower and the fan rotation speed in the above experiment by using the least-square method.  
         [0031]     An input current value of the electric motor can be directly used as the blower-load-variable, or other value determined unambiguously from the input current value of the electric motor such as the ratio of the electric motor input current to the rated current may also be used as the variable.  
         [0032]     Duct system  15  is a conduit tube used to deliver airflow for certain regions to be conditioned. Duct system  15  is for instance installed in a building to supply conditioned airflow to rooms requiring the air. The static air pressure in duct system  15  is affected by form and length of the duct, damper  45 , filter  50  and heat exchanger  55 .  
         [0033]     Now, the work and function of electric blower  1  with aforementioned configuration is described.  
         [0034]     A command from timing device  100  starts electric motor  25  at a predetermined rotation speed, which rotates blower  20 . When blower  20  reaches a stable rotation speed, rotation-speed-calculator  110  measures blower-load-variable Tra output from load-detector  105 . Blower-load-variable Tra thus measured is what reflects the duct conditions determined by the static air pressure in duct system  15 , the form and length of the duct, filter  50  and heat exchanger  55 .  
         [0035]      FIG. 2  illustrates characteristic curves showing relations between the amount of airflow and rotation speed of the blower from the aforementioned formula (a). The amount of airflow of the blower is proportional to the fan rotation speed, and the values of blower-load-variable Tra (Tra 1  to Tra 4 ) affect the gradient of lines as shown in  FIG. 2 .  
         [0036]     For example, the rotation speed Fr is given by the following formula (a), using blower-load-variable Tra and amount of target airflow Q at a load detection rotation speed of 600 r/min. 
 
 Fr=− 642.75+6.0837  Tra+ 19598.1/ Tra+ (−121.96+1.819  Tra+ 4134.1/ Tra ) Q  
 
 Where 
        Fr: rotation speed in r/min     Tra: blower-load-variable     Q: amount of airflow        
 
         [0040]     With stored data of measured blower-load-variable Tra, rotation speed Fr for the amount of target airflow Q can be calculated by substituting the amount of target airflow signal Q sent from system controller  40  into the above formula (a). The amount of target airflow is supplied to the duct when control signal Fo corresponding to the rotation speed is sent to variable motor controller  30 .  
         [0041]     The aforementioned configuration can adjust the airflow to an amount of target airflow in response to the coupled duct conditions stably, because blower  20  operates at a rotation speed corresponding to the amount of target airflow required for a duct condition detected previously.  
         [0042]     Load-detector  105 , rotation-speed-calculator  110  and rotation-speed-selector  120  could start sequentially, and any case such as sequential starting following output from the precedent elements or sequential starting by control means such as timing device or the like could perform the aim of the present invention.  
         [0043]     Timing-device  100  may be a type that starts together with electric blower  1 . In a newly installed air-conditioner, the type of timing device  100  can detect duct conditions automatically at the start of electric blower  1  instead of having to detect the duct conditions separately. For example, when an operation switch is turned on to operate a compressor (not shown), the load detection operation starts automatically to detect the duct condition by measuring blower-load-variable Tra previously.  
         [0044]     Moreover, timing device  100  may be a type that detects the duct condition regularly. For example, by starting a load detection operation at 12 o&#39;clock every day to measure blower-load-variable Tra and to store the data until 12 o&#39;clock next day, the blower can respond to a change of duct conditions in the case of increase in resistance to the airflow owing to a pile of dust on filter  50  in duct system  15 .  
         [0045]     Additionally, timing device  100  may be a type that operates at the change of airflow condition in duct system  15 , and then starts operation of load detector  105 . The configuration can detect open/shut condition of dampers installed in branches coupled to the duct.  
         [0046]     As described above, the electric blower of the present invention can discharge an amount of target airflow in response to the duct condition and is useful for duct type air conditioners or the like accordingly.