AU612011B2 - Control apparatus for air-conditioning system - Google Patents

Description

COMMONWEALTH OF AUSTRAL 2 FORM

COMPLETE

PATENTS ACT 1952

SPECIFICATION

FOR OFFICE USE: Class Int.Class Application Number: Lodged: Complete Specification Lodged: Accepted: S' Published: Priority: Related Art: Name of Applicant: GEOFFREY GARNER Address of Applicant: 4 Ngarimu Street, Christchurch, Ne. Zealand S-Actual Inventor: Geoffrey Garner Address for Service: SHELSTON WATERS, 55 Clarence Street, Sydney 0 4 .Complete Specification for the Invention entitled: "CONTROL APPARATUS FOR AIR-CONDITIONING SYSTEM" The following statement is a full description of this invention, including the best method of performing it known to me:- REPRINT OF RECEIPT so006284 21 /03 1 it

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1 The present invention relates to control apparatus 2 for an air-conditioning system. The apparatus of the 3 present invention may be used in combination with any 4 of a wide range of air-conditioning systems, but it is especially useful in combination with a coach air- 6 conditioning system, and therefore will be described 7 with especial reference to this application.

8 The aim of any air-conditioning control is to 0*00 9 maintain the coach cabin temperature at a stable, com- S 10 fortable, temperature, with minimum fluctuation about 11 the desired temperature.

Oo 12 A typical coach air-conditioning system includes a 13 refrigeration unit, a heating unit, fans and a thermooO 14 stat. Air is drawn from the cabin, passes over the 000 15 thermostat, over the refrigeration unit, which cools O0 16 the air and also condenses excess moisture from the S a 17 air, and is then reheated as necessary by the h-ating 18 unit before being drawn back into the cabi! by the S 19 fans.

0 0 20 It is, of course, possible to control the cabin 21 temperature simply by turning the refrigeration unit 22 and/or the heating unit on or off, in response to the 23 temperature sensed by the thermostat, but this type of 24 control tends to over-correct for small temperature 2 1 variations, and this leads to large variations in tem- 2 perature about the desired temperature.

3 In an improved system, the temperature of the 4 heating unit is varied by varying the volume of hot water directed into the heating unit from the coach's 6 radiator. Thus, air drawn from the cabin always fol- 7 lows the same route, but the degree of heating imparted 8 to the air by the heating unit is varied. The volume o000° 9 of hot water being directed into the heating unit is controlled by a nneumatic valve located in the hoto 11 water line from the engine. The pneumatic valve is in 0 12 turn controlled by the thermostat, such that the higher 13 the temperature registered by the thermostat, the less .0 14 water the pneumatic valve allows to enter the heating 0 15 unit.

16 However, the pneumatic valve is not entirely 17 satisfactory in practice:- it tends to show an exag- 18 gerated response to the thermostat, over-correcting for 19 a temperature change, and hence producing undesirably 20 large fluctuations about the desired cabin temperature, 21 and even larger fluctuations in the temperature of the 22 air being returned to the cabin.

23 It is therefore an object of the present invention 24 to provide a control for an air-conditioning system 3

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i 0 00 eq 04q 0 0« o o 0 o o 0 o O e o 00 0 0 0 0* 0 0 0 0 0 00eo 0 0 0 O 0 000 libel 6 0 0,, BI 6 11 |iji in 1 1 II c e which overcomes the above-described drawback and is capable of providing a relatively stable cabin temperature.

The present invention provides control apparatus for an air-conditioning system which includes a refrigeration unit through which the withdrawn air passes in use, a heating unit through which said air passes in use after leaving the refrigeration unit, and a control valve located in a line for supplying hot water to said heating unit, said control apparatus including: a thermostat arranged to sense the temperature of the air before said air passes through either the refrigeration unit or the heating unit and electrically connected to electrical means for comparing the air temperature sensed by the thermostat with a predetermined reference temperature, said comparison means being arranged to switch said heating unit and/or said refrigeration unit on or off depending upon the results of said comparison; said comparison means also being arranged to pulse said control valve on and off, the pulse interval being varied by the results of said comparison.

As used herein the term "pulse interval" means the time between the beginning of one pulse and the beginning of the next pulse.

Preferably, said control valve is a solenoid valve, but it is envisaged that other types of control valve may be used.

4 S 1, I 11 a a 6666 00 0 a a4 00 0 O 9 0 6 A 6 00 64 6666 0 66 66 660 O 6 6s 6 AG A A 4 6 By way of example only, a preferred embodiment of the present invention is described in detail, with reference to the accompanying drawings, in which:- Fig. 1 is a block diagram showing the general sequence of an air-conditioning system suitable for use with the present invention; Fig. 2 is a circuit diagram of the first part of the control apparatus of the present invention; and Fig. 3 is a circuit diagram of the second part of said control system; and Fig. 4 is a block diagram showing how different portions of the control system operate over different temperature ranges.

Referring to Fig. 1, in a typical coach airconditioning system, air is drawn from the cabin and then travels past a thermostat 3. A small proportion (typically 10%) of fresh air is mixed into the air drawn from the cabin, and the mixed air then passes over the cooling coils of a refrigeration unit 4; this cools the air and also condenses any excess moisture.

Next, the air travels over the heating coil of a heating unit before being drawn back into the cabin by the fans 7.

The volume of hot water supplied to the heating coil, and hence the degree to which the air is reheated

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0 0 D 0 eSao 0Q 0 00~ 09 040 0 0 00 0e 9 0 0o 0 0 0 S) 0 when it passes over the coil, is controlled by a solenoid valve 6 located in the hot-water line from the engine; the valve in turn is controlled by the thermostat 3, as hereinafter described.

Referring to Fig. 2, the control apparatus includes the thermostat 3, which comprises a negativetemperature coefficient resistor (NTC) connected to integrated circuit I (ICI). The NTC senses the temperature of the air withdrawn from the cabin, and the ICI translates this temperature to corresponding voltage.

The ICI is capable of producing a voltage corresponding to any temperature anywhere within a 150 range:- the higher the temperature, the higher the voltage. The mid-point of the voltage ramp is pre-set (using resistor 1k) to correspond to the desired cabin temperature.

The voltage generated by ICI is one of the two controlling signals which is fed from the circuit of Fig. 2 to the circuit of Fig. 3, as hereinafter described.

ICI also is connected to integrated circuit 2 (IC2) which amplifies the central 20 portion of the ICI voltage ramp, to produce a voltage on a second voltage ramp corresponding to a 20 change in temperature; the mid-point of this ramp corresponds to the desired cabin temperature.

r~- 1 Integrated circuit 3 (IC3) is a square-wave gener- 2 ator whose basic pulse interval can be pre-set by the 3 100 k variable resistor when switch 1 (SW1) is open.

4 Said basic pulse interval is adjusted such that, when the cabin temperature is at the desired temperature, 6 and the ambient temperature also is equal to the 7 desired temperature, the control apparatus operates to 8 permit sufficient reheating of the mixed air by the 9 heating unit 5 just to balance the heat losses in said 0 10 air caused by the refrigeration unit 4. Once the pulse S 11 interval has been pre-set, SW1 is closed, and the volt- 12 age produced by IC2 is used to modulate the pulse in- 13 terval of the IC3 pulses such that, as the IC2 output S 14 voltage varies above or below the set-point, the IC3 0D0 15 pulse interval is increased or decreased. The modu- 16 lated pulse interval from IC3 is the second controlling 00 o0 17 signal which is fed from the circuit of Fig. 2 to that 18 of Fig. 3.

0 19 Referring now to Fig. 3, integrated circuit 11 20 (IC11) is connected via transistors 1 and 2 (Tl, T2) to 21 the solenoid valve 6 (Fig. The modulated pulses 22 from IC3 are fed to T2 (via terminal B) and its as- 23 sociated relay, producing a pulsed output signal from 24 terminal C, to which the solenoid valve 6 is connected.

The solenoid valve 6 therefore is pulsed on and off,

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n 9 0a 0 a 60 the length of the periods for which the solenoid valve is switched off being dependent upon the degree of modulation of the pulse interval, and hence, ultimately, upon temperature of the air leaving the cabin, as detected by thermostat 3.

This "pulsing" control gives a very fine, accurate control of the solenoid valve, very responsive to small fluctuations of temperature above or below the desired temperature. However, the control system must also cater for conditions in which the temperature of air leaving the cabin is outside the voltage ramp produced by IC2 i.e. more than 10 above or below the desired temperature.

To achieve this, the voltage produced by IC1 is applied by terminal A to integrated circuits 11, 12, 13, and 14 (IC11, TC12, IC13 and IC14 respectively).

Each of these integrated circuits act as a voltage comparator which samples the voltage from IC1 and compares it with an individual predetermined reference voltage.

These reference voltages correspond to temperatures at fixed points above or below the desired cabin temperature.

ICll1 produces a positive output when the temperature is more than 20 below the desired cabin temperature. This is applied to T2 via D11, holding it on 1 regardless of the pulsed input at terminal B, thus 2 holding the solenoid valve 6 on and producing full heat 3 until the cabin temperature sensed by thermostat 3 4 moves to within 20 of the desired temperature.

IC12 produces a positive output when the tempera- 6 ture is more than 20 above the desired cabin tempera- 7 ture. This is applied to T1, holding it on. T1 then 8 acts as a short circuit to the pulsed input and also 9 holds T2 off, thus producing no heat.

The positive output from IC12 is also applied to 11 T3, holding it on, thus producing a signal to bring the 12 refrigeration unit to maximum capacity. The refrigera- 0 13 tion unit 4 comprises a multistage compressor, and not 14 only can the compressor itself be switched on or off, oeo 15 but stages of the compressor may individually be 16 brought into or out of use. IC12 is arranged to con- 17 trol the number of compressor stages to be brought into 18 or out of use, depending upon the difference between o" o" 19 the voltage received by IC12 from IC1 and the reference *o 0 20 voltage.

21 IC13 produces a positive output when the tempera- 22 ture is more than 40 below the desired cabin tempera- 23 ture. This is applied to T4, holding it on, thus 24 producing a signal to hold the compressor off.

9 4.: 1 IC14 produces a positive output when the tempera- 2 ture is more than 40 above the desired cabin tempera- 3 ture. This is applied to T5, hulding it on, thus 4 producing a signal to turn the cabin fan 7 to maximum speed.

6 Thus, the "coarse" control of the system is 7 achieved by switching the solenoid 6 or the refrigerat- 8 ing compressor 4 on or off and/or by adding or sub- 0 9 tracting compressor stages and/or by speeding up or o 10 slowing down the fan 7, whilst the "fine" control is 11 achieved by pulsing the solenoid valve 6.

0 Oo 12 Fig. 4 shows in diagrammatic form how the various S13 overlapping controls work in the system as a whole. As *o 14 in shown in Fig. 4, the "coarse" control is effected by o o 15 IC11 to IC14 inclusive, and the "fine" control by IC3, 16 as modulated by IC2.

410 0 6 17 To avoid the problems of over-correction, IC3 can 18 control only a proportion of the full range of the S 19 solenoid valve 6 e.g. from 20% full heat-3% full heat, 0 20 as shown in Fig. 4.

21 This limiting of the control range of IC3 means 22 that the solenoid valve 6 is never required to cope 23 with fine control of small temperature fluctuations 24 over a large temperature range, and so avoids problems of over-correction. It would of course be possible to r 1 design the system so that IC2 was arranged to modulate 2 IC3 over the whole, operational temperature range, 3 rather than over the temperature range of plus or minus 1 4 10 from the desired cabin temperature. However the result of such an arrangement would be a coarse control 6 with a tendancy to over-correct, in the same manner as 7 the existing pneumatic system i.e. a small variation in 8 temperature would tend to produce an ov:r-large varia- O 9 tion in heat. At the other extreme, a control system 0 0 10 capable only of controlling the temperature within a 11 few degrees of the desired cabin temperature cannot 0 0 12 cope with start-up conditions where the initial start- 13 ing temperature may be extremely low or extremely high.

14 Up to below desired cabin temperature, IC11 is u e 0o 15 in control, and full heat can be applied. When the 16 temperature reaches -20, IC3 is in control, and a maxi- S" 17 mum of 20% of available full heat can be applied. This 18 "step" from 100% heat to 20% heat allows the hot vent 19 air to gradually decrease in temperature before the S 20 modulated temperature range of +10 of desired cabin 21 temperature is reached.

22 Similarly, if the cabin temperature is well above 1 23 the desired temperature when the control system is 24 started up, IC12 is in control, giving full refrigeration and high fan speed until the cabin temperature 11 SI ~I 1 falls to +20 of the desired temperature. At this 2 point, IC3 takes over, and a minimum of 3% of available 3 heat is applied to the air this ensures that, as the 4 cabin temperature falls, the temperature of the air coming through the cabin air-vents is not uncomfortably 6 cold.

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Claims (4)

1. 2. The control apparatus as claimed in claim I wherein said comparison means as part of said coarse temperature control also is arranged to increase or decrease the speed of said air withdrawing means. 13 j i r~ 1 3. Control apparatus as claimed in claim 1 or 2 claim 2 wherein said comparison means includes a first 3 integrated circuit arranged to produce a voltage cor- 4 responding to said sensed air temperature and electri- cally connected to means for varying the pulse interval 6 of said control valve in response to variations in said 7 voltage, so as to provide said fine temperature con- 8 trol. lot* too 9 4. Control apparatus as claimed in claim 3, 44 44a wherein said comparison means as part of said coarse S 11 temperature control also includes two further in- o4 a 12 tegrated circuits each of which is designed and ar- 13 ranged to receive the voltage produced by said first 14 integrated circuit, and to compare said voltage with a 040 S 15 predetermined reference voltage; if said comparison in- o04 16 dicates that said voltage represents a sensed air tem- o 17 perature below a first predetermined temperature, one 18 of said further integrated circuits is arranged to 19 switch on said heating unit and to maintain said heat- ing unit in operation until the sensed air temperature 21 rises to said first predetermined temperature; if said 22 comparison indicates that said voltage represents a 23 sensed air temperature above a second predetermined 24 temperature, the otier of said further integrated cir- cuits is arranged to switch off said heating unit and 14 ji i It I' 1 2 3 4 6 7 8 9 11 12 13 14 16 0 17 18 q 19 21 22 23 24 to switch said refrigeration unit to full power, and to maintain this state until the sensed air temperature falls to said second predetermined air temperature.
2. 5. Control apparatus as claimed in claim 4 when dependent upon claims 2 and 3, wherein said comparison means as part of said coarse temperature control also includes two additional integrated circuits, each of which is designed and arranged to -eceive the voltage produced by said first integrated circuit and to com- pare said voltage with a predetermined reference volt- age; if said comparison indicates that said voltage represents a sensed air temperature below a third predetermined temperature, one of said additional in- tegrated circuits is arranged to switch off said refrigeration unit until the sensed air temperature rises to said third predetermined temperature; if said comparison indicates that said voltage represents a sensed air temperature above a fourth predetermined temperature, the other of said additional integrated circuits is arranged to switch the air withdrawing means to maximum speed until the sensed air temperature falls to said fourth predetermined temperature.
3. 6. Control apparatus as claimed in claim wherein: said first predetermined temperature is below the desired temperature of the withdrawn air; L~~L 6ir 1 said second predetermined temperature is 20 above the 2 desired temperature of the withdrawn air; the third 3 predetermined temperature is 40 below the desired tem- 4 perature of the withdrawn air; and the fourth predeter- mined temperature is 40 above the desired temperature 6 of the withdrawn air. 7 7. Control apparatus as claimed in any preceding 8 claim wherein said fine temperature control is able to 9 control only part of the full range of the control 41 a 1 0 valve. 11 8. Control apparatus as claimed in claim 7 12 wherein said part of the full range is 3%-20% of the 13 full range. 14 9. An air-conditioning system in combination 1C S 15 with the control apparatus as claimed in any preceding 16 claim. S 17 30. The combination as claimed in claim 9 wherein 18 said control valve is a solenoid valve. 19 11. The combination as claimed in claim 9 or .P 20 claim 10 wherein said air withdrawing means is a fan. 21 12. The combination as claimed in any one of 22 claims 9-11 wherein said heating unit comprises a heat- 23 ing coil heated by hot water. 24 13. The combination as claimed in any one of claims 9-12 wherein said refrigeration unit comprises a 1 multi-stage compressor. 2 14. Control apparatus for an air-conditioning 3 system, substantially as hereinbefore described with 4 reference to and as shown in the accompanying drawings.
4. 15. The combination of an air-conditioning system 6 and control apparatus, substantially as hereinbefore 7 described with reference to and as shown in the accom- S panying drawings. 9 DATED this 21st Day of March, 1989 o o S 10 GEOFFREY GARNER 0 q 11 Attorney: PETER HEATHCOTE 2 Fellow Institute of Paot-;t Atom ys of Australia a 12 0a of SHELSTOil .V'iTERS 0 0 13 14 Q 16 0 4 0a 0 D 17 18 o 19 a 22 23 24 17