FR2661759A1 - METHOD FOR ADJUSTING FLOW RATE IN AN AIR BLOWING DEVICE AND DEVICE IMPLEMENTING THE METHOD. - Google Patents

Abstract

The invention relates to an air flow rate adjusting method at the outlet of an air blowing device comprising a fan driven by a motor and connected to an air circuit, and means for varying a parameter (Vrms) of the supply voltage of the motor in order to vary its rotation speed. It is characterized by the following steps: generating information representative of the rotation speed of said motor or fan corresponding to a known value of said parameter of the supply voltage; determining from said known value of the parameter and said information and evolution law (PCi) of the flow rate as a function of said parameter, selected amongst a plurality of such laws (PCo-PCn) previously stored and corresponding to a plurality of different head losses in said air circuit; varying said parameter (Vx) according to said determined law so as to obtain at the outlet a flow rate equal to a set flow rate (Dc). The invention also relates to a device for implementing such method.

Description

 The present invention relates generally to air blowing devices, and it relates more particularly to a new method for adjusting the air flow rate and a device implementing the method.

 When installing such a device, for example an air treatment device of the air conditioner type, on site, it is necessary in the known technique to calibrate the device according to its environment; more precisely, it is necessary to calibrate the device as a function of the pressure drops specific to the air distribution and return circuit in the room or rooms associated with the device and, where appropriate, as a function of the minimum air flows and maximums imposed by operators according to determined criteria, in particular occupancy criteria, situation, or even regulatory criteria or admissible noise level.

 The main purpose of this calibration is to determine, for each treatment device in its final environment, the law of evolution of the effective flow rate as a function of an electrical parameter of the power supply of the engine driving the fan.

 It is obvious that such on-site calibration is tedious, since it must be carried out at least once for each new device installed.

 Furthermore, as soon as a modification of the air distribution or return circuits is made, it is necessary to recalibrate due to the modification of the pressure drop which may result therefrom.

 The technique commonly used to carry out such a calibration consists in temporarily installing at the outlet of the fan a device for measuring either the effective air flow (anemometer or the like), or even differential pressure, making it possible to deduce the pressure drop in the air circuit.

 Thus all the cases, these known solutions have, in addition to the major defects exposed above, the disadvantage of requiring expensive and relatively imprecise means. In particular, in addition to the fact that a differential pressure sensor is in itself expensive, it is necessary to provide for the processing of very weak signals that it delivers electronic circuits with low noise and very high sensitivity, and therefore also expensive. In addition, this kind of sensor is fragile, and subject to fouling as well as drifts in its output signals.

 Finally, a drawback of the known solutions lies in the impossibility of taking account of the aging and fouling of the air treatment device, capable of modifying the pressure losses and therefore the flow rate, except from time to time performing a new one. calibration which of course undesirably increases operating costs.

 The present invention aims to overcome these drawbacks of the prior art and to provide an air treatment device which does not require any calibration during installation on site, this without its cost being significantly increased.

 More specifically, the present invention is based on the idea that the electric motor driving the fan is in itself able to provide at any desired time information allowing the deduction of the effective pressure drop in the distribution and supply circuits. recovery associated with the device, and therefore to control the motor as a function of this pressure drop to obtain the desired flow rate.

Thus, according to a first aspect of the present invention, there is provided a method for adjusting the air flow rate at the outlet of an air blowing device comprising at least one fan driven by an electric motor and connected to a circuit of air, and means for varying a parameter of the electric supply voltage of the motor in order to vary the speed of rotation of the latter, characterized in that it comprises the steps consisting in:
generate information representative of the speed of rotation of said motor or of the fan corresponding to a known value of said parameter of the supply voltage,
determining from said known value of the supply voltage parameter and from said information a law of evolution of the flow rate as a function of said parameter, chosen from a plurality of such laws previously stored and corresponding to a plurality of losses of different charges in said air circuit,
varying said parameter of the supply voltage according to said determined law so as to obtain at output a flow rate equal to a set flow rate.

Preferred, but not limiting, aspects of the process of the present invention are as follows:
- said parameter consists of the effective value of the motor supply voltage.

 - Said information is a pulse signal whose frequency is proportional to the speed of rotation of the motor or the fan.

 - Said plurality of laws is stored in the form of a plurality of sets of pairs of values.

 - Said plurality of laws is stored in the form of a plurality of equations.

 the step of determining the law of evolution consists in determining, among a plurality of identifiers in association with which a plurality of respective criteria are stored, the identifier whose criterion is satisfied by said parameter of the voltage of feed and said information, said identifier determining said law of evolution.

 - Said plurality of laws is stored in the form of a single equation comprising at least one variable parameter, and in that the step of determining the law of evolution consists in calculating the said parameter or parameters as a function of said known value the supply voltage parameter and said information.

according to a second essential aspect, the invention relates to an air blowing device, characterized in that it comprises in combination
a fan driven by an electric motor,
means for varying a parameter of the electric supply voltage of the motor in order to vary the speed of rotation of the latter,
means for measuring information representative of the engine rotation speed,
a memory containing a set of data representative of a plurality of laws of evolution of the effective flow rate of the fan as a function of the value of said parameter of the supply voltage, and
processing means for determining, on the basis of the knowledge of said parameter of the supply voltage and of said information at least at a given instant, the appropriate law of evolution, the means for varying said parameter of the voltage d 'power being controlled according to a set flow rate and said determined law.

Preferred, but not limiting, aspects of the device according to the present invention are as follows:
the electric motor is an asynchronous motor, said means for varying said parameter comprise a conduction angle control unit, and said parameter is the effective value of the supply voltage of the motor.

 - Said measuring means comprise a sensor chosen from the group comprising magnetoresistive sensors, Hall effect sensors and optical sensors.

 - Said memory is an interchangeable read only memory whose data correspond to a given motor-fan couple.

The invention finally relates to a device for implementing the method as defined above, characterized in that it comprises:
a fan driven by an electric motor,
means for varying a parameter of the electric supply voltage of the motor in order to vary the speed of rotation of the latter,
a sensor for generating information representative of the speed of rotation of the motor,
a memory containing said plurality of laws of evolution, and
processing means for carrying out the determination step and for controlling said means for varying the parameter of the electric voltage.

Other aspects, aims and advantages of the present invention will appear better on reading the following detailed description of a preferred embodiment thereof, given by way of nonlimiting example and made with reference to the accompanying drawing, on which
FIG. 1 is a block diagram of part of an air treatment device according to the present invention,
FIGS. 2a to 2c show three diagrams corresponding to three theoretical environments of the device, and
Figure 3 shows a diagram illustrating the principle of flow adjustment used in accordance with the present invention.

 Referring firstly to Figure 1, there is shown schematically and partially an air treatment device which comprises a fan or other blower 10 driven by an asynchronous electric motor 12. There is shown schematically a duct 16 for distributing air and an air return duct 18.

 It is well known that the no-load rotation speed (under zero load) of an asynchronous motor is determined by the frequency of the sinusoidal current which supplies it. This speed decreases linearly as the load increases.

 When such a motor is controlled at variable speed, the torque required to propel the air, under a fixed load, increases quadratically as a function of the output flow. This curve, determining the slip of the motor, is characteristic of a given motor / fan couple under given pressure drop conditions.

 The basic principle of the present invention therefore consists in determining the slip of the motor by measuring the absolute rotation speed of the motor (or any other variable which is correlated). This measurement, compared with the nominal rotation speed, gives the slip of the motor at a given instant, itself representative of the pressure drop in the air circuit to which the fan is connected.

 It is understood that it is therefore possible from this information to determine a single law of evolution of the effective flow rate at the outlet of the fan as a function for example of the effective value of the voltage which supplies the motor.

 Thus, according to the invention, the motor itself is used as the linear sensor element, the speed of rotation measured for a given effective supply voltage will make it possible to deduce the pressure drop existing downstream of the fan, and therefore to determine a law of evolution of the effective flow as a function of the effective voltage applied to the motor.

 Thus, the device represented in FIG. 1 comprises a rotation sensor 14 whose output, for example delivering a determined number of electrical pulses per revolution accomplished by the motor, is applied to a regulating plate 20. This sensor 14 can be of any appropriate type. So one can use for example a magneto-resistive sensor, a Hall effect sensor, an optical sensor, etc ...

 The plate 20 includes a computer 22 associated with a memory 24, and a speed variation module 26.

 The computer 22 receives on the one hand the output of the sensor 14, and on the other hand a set flow rate value supplied by the control unit of the air treatment device, not shown.

 The memory 24 contains, as will be seen in detail below, data representative of the evolution of the flow rate at the outlet of the fan as a function of the supply voltage of the motor, for various pressure drops in the air circuit.

 Finally, the variable speed drive 26, controlled by the computer 22, is in the present example a conduction angle control unit, of conventional design, making it possible to vary the effective supply voltage of the motor as desired.

 Referring to Figures 2a to 2c and Figure 3, we will now describe in detail a possible mode of operation of the device described above.

 We will first describe how the data loaded into memory 24 could be obtained, this data being common to any motor / fan pair with the same characteristics.

 First of all, for a given sample motor / fan couple, the pressure drop was varied in the circuit connected to the fan output.

For each given pressure drop, the effective supply voltage of the motor was varied and the effective rotation speed of the motor was measured on the one hand and the air flow rate on the other hand
Figures 2a, 2b and 2c show the variations in speed (solid lines) and flow rate (dashed lines) obtained as a function of variations in rms voltage, respectively with zero pressure drop (no load), average pressure drop and a high pressure drop (almost blocked outlet).

It is easy to understand by observing the curves of FIGS. 2a to 2c that, if one knows both the effective supply voltage and the speed of rotation of the motor, one can easily determine, only from these curves, at which pressure drop the fan is exposed. For example, if it is found that an effective voltage Va induces a speed of rotation
a, we are in the case of an average pressure drop as illustrated in FIG. 2b. (Of course, to obtain satisfactory accuracy, the tests described above are carried out for a sufficiently large number of different pressure drops).

 Data deduced from a sufficiently large number of curves of the type of those of FIGS. 2a to 2c are then permanently stored in the memory 24 associated with the computer 22, for example in a programmable read only memory. We have thus carried out once and for all, as will be seen below, the configuration of the air treatment device.

 In a first exemplary embodiment, this memorization may consist in individually identifying the different pressure drops PCi for which the measurements have been made, and in associating in the memory, in association with each of the different values PCi, a plurality of pairs of values (effective voltage, speed) corresponding to curves of the type of curves in solid lines illustrated in FIGS. 2a to 2c. In this case, there is also stored, in association with each pressure drop level PCi, a set of pairs of values (effective voltage, flow rate) corresponding to curves of the type of those in dashed lines in FIGS. 2a to 2c).

 It should be noted here that these measurements make it possible to configure all the motor / fan couples of a given type at one time. Thus, for mass production of devices all using the same type of motor and the same type of fan, these preliminary measurements will only have to be carried out once and will be valid for all the devices in the series.

 We will now describe, also with reference to FIG. 3, the operation of the device once installed on the site and equipped with its various air distribution and return ducts.

 At regular intervals, the computer 22 reads a value of rotation speed supplied by the sensor 14 and, simultaneously or practically simultaneously, reads the value of the effective voltage applied to the motor. From the data stored in memory 24, the computer 22 can then determine the level of pressure drop PCi (FIG. 3) currently caused by the air distribution and return circuit.

Knowledge of PCi then makes it possible, again as a function of a set flow rate Dc applied to the control board, to determine, again by consulting the data contained in memory 24, the effective voltage
Vx required to effectively obtain this output flow.

In the case described here where the various curves are represented in memory by a plurality of pairs of values for each value of PCi, it is possible to use conventional interpolation techniques if necessary to achieve the required precision.

 As soon as the pressure drop in the circuit varies (for example as soon as the air circuit is modified, following a new configuration of the rooms to which the air treatment device is assigned, then a new confrontation of the speed of rotation measured and the corresponding effective supply voltage with the stored data makes it possible to instantly integrate this change. Thus, in the example above, a new pressure drop identifier PCi 'is determined, which in turn will determine a new law of evolution of the flow as a function of the effective voltage applied to the motor. Thus the device of the present invention can be qualified as self-adaptive in that, without any intervention or adjustment, it adapts itself in time real to its environment, to ensure that the effective air flow at its outlet is always identical, within tolerances, to the set flow rate. e in the same way to variations in pressure losses resulting from fouling or aging of the air circuit, without it being necessary to intervene.

 Another solution for storing the data in the memory may consist in determining and storing curve equations which are as close as possible to the characteristic curves obtained experimentally. Thus, in association with an identifier PCi, a first curve of the speed as a function of the effective voltage can be memorized, and a second curve of the flow rate as a function of the effective voltage. Alternatively, a limited number of curve equations can be used, these equations having variable parameters; and it is these parameters which are then stored with regard to the respective identifiers PCi.

According to another variant, the computer can perform the following operations:
- from the RMS voltage and the corresponding speed of rotation, calculate at least one intermediate parameter using a first stored equation,
- introduce the said intermediate parameter (s) into a second stored equation, giving the flow rate as a function of the effective voltage,
- use said second equation, once configured, as the law of effective variation of the flow rate as a function of the effective voltage to control the motor with the required effective voltage as a function of the set flow rate.

 According to yet another variant, the final step consisting in adjusting the effective voltage applied to the motor to obtain the target flow rate can consist not in reading directly on the curve considered the value required for the effective voltage as a function of the target flow rate, but to read, on a different curve, the required rotation speed as a function of the set flow rate. The effective voltage is then varied, by simultaneously reading the effective speed of rotation on the sensor 14, until the required speed of rotation is reached.

The advantages of the present invention are numerous:
- The cost of a regulation system according to the invention, including the rotation sensor and the electronic part (computer and memory), is extremely low (typically a few tens of francs).

 - I1 there is no risk of drift over time, and in particular no error in the measurement of the speed of rotation.

 - No calibration process is necessary during the installation of the device on the site, this being self-adapting.

 - No flow measurement being necessary in normal operation, no inherent uncertainty in this type of measurement is encountered.

 - mass production is perfectly mastered, no adjustment being necessary. In this regard, the memories containing the data representative of the behavior of different given motor / fan couples can be physically constituted by read-only memories in integrated circuit, and it suffices during manufacture to install the integrated circuit whose data correspond to the motor / fan couple actually used.

 Of course, the present invention is in no way limited to the embodiment described above and shown in the drawings, but the person skilled in the art will know how to make any variant or modification in accordance with his spirit.

 In particular, those skilled in the art will be able to make the adaptations necessary to use the invention with motors of different type, and in particular with DC or Hall effect motors, or even with speed controls of different type. , for example with a control by variation of supply frequency using a converter.

Furthermore, the invention advantageously applies in any installation in which an electric motor driving a fan or blower must be controlled so as to obtain an output of a given real flow rate, taking into account the pressure drops which may vary in the ducts. connected to the fan. I1 may be in particular, but not limited to, an air treatment module as it is the subject of French patent No. 87 09630 in the name of the
Applicant, or any heating, air conditioning, ventilation, drying installation, etc.

 In addition, the fact that the present invention uses a speed sensor allows, almost without additional cost, the computer to also fulfill various safety functions, and in particular to detect if the engine speed does not fall below of a given threshold, risking damaging its windings.

Claims (12)

 1. A method of adjusting the air flow rate at the outlet of an air blowing device comprising at least one fan driven by an electric motor and connected to an air circuit, and means for varying a parameter of the electric supply voltage of the motor in order to vary the rotation speed of the latter, characterized in that it comprises the steps consisting in:  generate information representative of the speed of rotation of said motor or of the fan, corresponding to a known value of said parameter of the supply voltage,  determine from said known value of the parameter of the supply voltage and from said information a law of evolution of the flow as a function of said parameter, chosen from a plurality of such laws previously stored and corresponding to a plurality of losses of different charges in said air circuit,  varying said parameter of the supply voltage according to said determined law so as to obtain at output a flow rate equal to a set flow rate.  2. Method according to claim 1, characterized in that said parameter consists of the effective value of the motor supply voltage.  3. Method according to one of claims 1 and 2, characterized in that said information is a pulse signal whose frequency is proportional to the speed of rotation of the motor or the fan.  4. Method according to one of claims 1 to 3, characterized in that said plurality of laws is stored in the form of a plurality of sets of pairs of values.  5. Method according to one of claims 1 to 3, characterized in that said plurality of laws is stored in the form of a plurality of equations.  6. Method according to one of claims 4 and 5, characterized in that the step of determining the law of evolution consists in determining, among a plurality of identifiers in association with which a plurality of respective criteria are stored, the identifier whose criterion is satisfied by said parameter of the supply voltage and said information, said identifier determining said law of evolution.  7. Method according to one of claims 1 to 3, characterized in that said plurality of laws is stored in the form of a single equation comprising at least one variable parameter, and in that the step of determining the law evolution consists in calculating the said parameter or parameters as a function of said known value of the parameter of the supply voltage and of said information.  8. Air blowing device, characterized in that it comprises in combination  a fan (10) driven by an electric motor (12),  means (26) for varying a parameter of the electric supply voltage of the motor in order to vary the speed of rotation of the latter,  means (14) for measuring information representative of the engine rotation speed,  a memory (24) containing a set of data representative of a plurality of laws of evolution of the effective flow rate of the fan as a function of the value of said parameter of the supply voltage, and  processing means (22) for determining, from the knowledge of said parameter of the supply voltage and from said information at least at a given instant, the appropriate law of evolution, the means for varying said parameter of the supply voltage being controlled as a function of a set flow rate and of said determined law.  9. Device according to claim 8, characterized in that the electric motor (12) is an asynchronous motor, in that said means (26) for varying said parameter comprise a conduction angle control unit, and in that said parameter is the rms value (Veff) of the motor supply voltage.  10. Device according to one of claims 8 and 9, characterized in that said measuring means comprise a sensor (14) selected from the group comprising magneto-resistive sensors, Hall effect sensors and optical sensors.  11. Device according to one of claims 8 to 10, characterized in that said memory (24) is an interchangeable read-only memory whose data correspond to a given motor-fan couple.  12. Device for implementing the method according to one of claims 1 to 7, characterized in that it comprises:  a fan (10) driven by an electric motor (12),  means (26) for varying a parameter of the electric supply voltage of the motor in order to vary the speed of rotation of the latter,  a sensor (14) for generating information representative of the speed of rotation of the motor,  a memory (24) containing said plurality of evolution laws, and  processing means (22) for carrying out the determination step and for controlling said means for varying the parameter of the electric voltage.