GB2260785A

GB2260785A - Apparatus for controlling the conditioned air output of an air conditioner

Info

Publication number: GB2260785A
Application number: GB9122434A
Authority: GB
Inventors: Tien-Cheng Hu; Jam-Shyng Shin
Original assignee: Industrial Technology Research Institute ITRI
Current assignee: Industrial Technology Research Institute ITRI
Priority date: 1991-10-23
Filing date: 1991-10-23
Publication date: 1993-04-28
Also published as: GB9122434D0

Abstract

Disclosed is an apparatus for controlling the rotational speed of an electric fan which is employed for propelling the conditioned air out of an air conditioner in accordance with the difference between a desired preset temperature level 10 and the temperature of the conditioned environment 20. The apparatus generates an error signal by means 30 corresponding to the temperature difference and uses subsequently the error signal for controlling the rotational speed of a DC motor 50 which is employed for driving the electric fan. A pulse-width modulation (PWM) method is employed for the controlling of the DC motor. <IMAGE>

Description

TITLE: APPARATUS FOR CONTROLLING ThE CONDITIONED AIR OUTPUT OF AN AIR CONDITIONER BACKGROUND OF ThE INVENTION The present invention relates to an apparatus for controlling the conditioned air output of an air conditioner. In particular, the apparatus is capable of controlling the rotational speed of an electric fan which is employed for propelling the conditioned air out of the air conditioner depending on the temperature of the conditioned environment.

The air conditioning system installed in an automobile generally employs an electric fan arranged at an air outlet thereof for blowing out the conditioned air. The faster the electric fan rotates, the great amount of conditioned air blown out of the air condition system and thus the sooner the conditioned environment reaches a lower temperature.

Therefore, the temperature inside the interior of the automobile can be adjusted by controlling the rotational speed of the electric fan.

A prior air conditioning system presets a number of ranges for the temperature. A number of devices, each of which is coupled to the electric fan, are then separately provided for controlling the temperature of the conditioned interior of the automobile within a particular preset range assigned thereto. Each of the devices is capable of controlling the ON and OFF mode of the electric fan depending on the temperature of the conditioned interior of the automobile. If the temperature is detected to be equal to or lower than a predetermined lower value, the device will turn off the electric fan. As a result, the temperature will gradually rise. And once the temperature has risen to a value equal to or higher than a predetermined upper value, the device will turn on the electric fan again.

Using the above method, the temperature within the interior of the automobile may be fluctuated constantly within the predetermined upper and lower levels, thereby causing unacceptable conditioning effects. Therefore, there often exists a need for a controller of the electric fan which would be capable of maintaining the temperature of the conditioned environment at a substantially constant level.

SUMMARY OF THE INVENTION It is therefore a primary object of the present invention to provide an apparatus for controlling the rotational speed of the electrical fan such that the conditioned environment can be maintained at a constant temperature value In accordance with the above object, there is provided an apparatus which is capable of adjusting the output of the conditioned air by controlling the rotational speed of the electric fan employed for blowing out the conditioned air.

The controlling of the electric fan is performed in accordance with the temperature of the conditioned environment. A user can select a predetermined temperature level and preset it into the apparatus. The apparatus will accordingly compare the temperature of the conditioned environment with the predetermined temperature level and use the error signal to control the rotational speed of the electric fan.

The electric fan is mostly driven by a DC motor.

Therefore, a pulse-width modulation method (PWM) is utilized for controlling the power delivered to the DC motor in the preferred embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention can be more fully understood by reading the subsequent detailed description of the preferred embodiments with references made to the accompanying figures, wherein: FIG. 1 is a block diagram of the apparatus in accordance with the present invention; FIG. 2 is a schematic circuit diagram of a preferred embodiment of the apparatus according to the present invention; FIG. 3 is a plot of resistance versus temperature for a thermistor utilized in the preferred embodiment of the apparatus according to the present invention; and FIGs. 4A-4D show the waveforms of several square pulse sequences which are used for controlling the power delivery to a DC motor employed for driving an electric fan of an air conditioner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown a block diagram used for depicting the concept of the present invention. As shown, an apparatus in accordance with the present invention for controlling the rotational speed of an electric fan 51 employed for blowing out the conditioned air of an air conditioner includes a desired temperature presetting device 10 which allows a user to preset a temperature level for the air conditioned environment he/she desires. A first signal will be generated by the desired temperature presetting device 10, the value of which is in proportion to the preset temperature level. A temperature detector 20 is employed for detecting the current temperature of the conditioned environment and will proportionally output a second signal.

The first signal and the second signal are compared by a comparator 30 which will output an error signal in proportion to the difference thereof. The error signal is subsequently fed into a power controller 40 to control the power delivered to a DC motor 50 employed for driving the electric fan 51.

A preferred embodiment of the present invention which will carry out the functions of the blocks of FIG 1 will be described with reference made to FIGs. 2-4.

As shown in FIG. 2, two resistors 11, 13 connected in series with a variable resistor 12 are arranged as the desired temperature presetting device 10. The resistance of the variable resistor 12 can be adjusted to change the voltage VA input to a comparator 30 which consists of an operational amplifier 31 coupled with a resistor 32 and a capacitor 33.

A resistor 22 is connected in series with a thermistor 21 to form the conditioned environment temperature detector 20. The thermistor 21 is a device whose resistance is dependent on the temperature. Referring to FIG. 3, there is shown a plot of resistance versus temperature for the thermistor 21 utilized in the preferred embodiment of the present invention. As shown, the resistance of the thermistor 21 becomes smaller as the temperature increases. When the temperature changes, the resistance value of the thermistor 21 also changes, and whereby the voltage VB input to the comparator 30 is also varied.

Accordingly, for the desired temperature presetting device 10, since the value of VA is linearly in correspondence to the resistance values of the variable resistor 12, the resistors 11 and 13 are designed in such a way that a certain value of the voltage VA corresponds to a certain temperature level. For the conditioned environment temperature detector 20, the resistance value of the resistor 22 is designed in accordance with the characteristic curve of FIG. 3 such that the corresponding relationship of the voltage VB to a temperature level is the same as that of the voltage VA.

The output of the comparator 30 is an analog voltage Vout which will be referred to as the error signal. The magnitude of the error signal Vout is in proportion to the difference between VA and VB, or in other words, the difference between the desired temperature setting and the actual temperature of the conditioned environment.

The error signal Vout is subsequently converted by an A/D converter 41 into a digital signal with a binary value substantially in proportion to the magnitude of Volt.

The electric fan 51 for blowing out the conditioned air is mostly driven by a DC motor 50. Therefore, the preferred embodiment of the present invention utilizes a pulse-width modulation (PWM) method for controlling the DC power delivered to the DC motor 50. The circuit configuration using the PWM method comprises a transistor (e.g. a bipolar junction transistor) 46 coupled between the DC power source (designated by V ) and the DC motor 50. When a sequence of periodic square pulses is sent to the base 461 of the transistor 46, the DC current from the DC power source will be delivered intermittently to the DC motor 50. Thus, the power delivered to the DC motor 50 can be modulated either by changing either the width of the square pulses, or by changing the frequency of the same.

In the preferred embodiment, the frequency of the periodic pulses will be maintained constant. Therefore, when the electric fan 51 needs to be rotated faster, pulses with wider widths should be sent to the gate 461 of the transistur46; and if on the other hand the electric fan 51 needs to be rotated more slowly, pulses with narrower widths are sent there.

Referring to FIG. 4A, there is shown a pulse sequence in which each of the pulses is with a width of W1 which is about 30% of the period T. Therefore, if the pulse sequence of FIG. 2 is sent to the transistor 46, the DC power source would deliver 30% of its full power to the DC motor 50. If the DC motor 50 needs more power, the width W1 can be increase to W2 or W3 as shown in FIGs. 4B and 4C. If the DC motor 50 needs full power from the DC power source, a DC current as shown in FIG. 4D would be sent to the gate of the transistor 46. A transistor 44 is often used for amplifying the generally low-levelled pulses to a high-levelled one such that they are able to drive the transistor 46.

A square pulse generator 42 is operatively coupled between the transistor 46 and the output of the A/D converter 41. The square pulse generator 42 is capable of generating a sequence of pulses, the width of each of the pulses being in proportion to the error voltage Vout It may be provided, for example, by a microprocessor CPU.

If the temperature of the conditioned environment is detected to be lower than the desired temperature, i.e. the error voltage is negative, the square pulse generator 42 will output a pulse sequence with the width of each of the pulses thereof in proportion to the error voltage such that an appropriate amount of DC power would be delivered from the DC power source V+ via the transistor 46 to the DC motor 50.

On the other hand, if the temperature of the conditioned environment is detected to be higher than the desired temperature, i.e. the error voltage is positive, the square pulse generator 42 will output nothing such that no DC power can be delivered from the DC power source V+ via the transistor 46 to the DC motor 50.

If the error voltage exceeds a threshold value, i.e. if the temperature of the conditioned environment is detected to be far higher than the desired temperature, the square pulse generator 42 will output a DC current as shown in FIG. 4D so as to rotate the electric- fan 51 in full power.

The present invention has been described hitherto with an exemplary preferred embodiment. However, it is to be understood that the scope of the present invention need not to be limited to the disclosed preferred embodiment. On the contrary, it is intended to cover various modifications and similar arrangements within the scope defined in the following appended claims and the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. For example, a MOSFET may be substituted for the transistor 46.

Claims

What is claimed is:

1 An apparatus for controlling the conditioned air output for an air conditioner depending on the temperature of the conditioned environment, the apparatus controlling the rotational speed of an electric fan, the electric fan being driven by a motor, the apparatus comprising: means tor presetting a desired temperature, said presetting means being capable of producing a first signal in proportion to the desired temperature; means for detecting the temperature of the conditioned environment, said detecting means being capable of producing a second signal in proportion to the temperature of the conditioned environment; comparing means, responsive to the first signal and the second signal, for producing a third signal in proportion to the difference of the first signal and the second signal; and means, responsive to the third signal, for driving the motor with a power delivered thereto in accordance with the third signal.

2 An apparatus according to Claim 1, wherein said desired temperature presetting means comprises: a variable resistor; and at least one resistor coupled to said variable resistor; wherein the change of the resistance of said variable resistor occasions a voltage change which is taken as the first signal.

3 An apparatus according to Claim 1, wherein said temperature detecting means comprises: a thermister; and a resistor coupled to said thermister; wherein the temperature change would cause a change in the resistance of said thermister and a voltage change thereby occasioned is taken as the second signal.

4. An apparatus substantially as described with to Figures 1 and 2 of the accompanying drawings.

4 An apparatus according to Claim 1, wherein the motor is a DC motor which is controlled by said driving means with a pulse width modulation (PWM) method.

5 An apparatus substantially as described referring to and as shown in the accompanying drawings.

6. An automobile air conditioner comprising means for controlling a fan speed by sensing the ambient temperature.

Amendments to the claims have been filed as follows CLAIMS 1. An apparatus for controlling the conditioned air output for an air conditioner depending on the temperature of the conditioned environment, the apparatus controlling the rotational speed of an electric fan, the electric fan being driven by a DC motor, the apparatus comprising:: means for presetting a desired temperature, said presetting means being capable of producing a first signal in proportion to the desired temperature; means for detecting the temperature of the conditioned environment, said detecting means being capable of producing a second signal in proportion to the temperature of the conditioned environment; comparing means, responsive to the first signal and the second signal, for producing a third signal in proportion to the difference between the first signal and the second signal; pulse width modulating means, responsive to the third signal, for producing a fourth signal, the fourth signal being a sequence of periodic square pulses having a pulse width proportion to the magnitude of the third signal; power supply means for supplying the DC motor; and control means, responsive to the fourth signal, for controlling the DC motor by regulating the amount of DC power delivered to the DC motor in accordance with the pulse width of the fourth signal.

2. An apparatus as claimed in Claim 1, wherein said desired temperature presetting means comprises: a variable resistor; and at least one resistor coupled to said variable resistor; wherein the change of the resistance of said variable resistor occasions a voltage change which is taken as the first signal.

3. An apparatus as claimed in Claim 1 or 2, wherein said temperature detecting means comprises: a thermistor; and a resistor coupled to said thermistor; wherein temperature change in the conditioned environment causes change in the resistance of said thermistor, and a voltage change thereby occasioned is taken as the second signal.