WO1997048954A1

WO1997048954A1 - Safety system for air-conditioning and refrigeration units

Info

Publication number: WO1997048954A1
Application number: PCT/AU1997/000379
Authority: WO
Inventors: Barry Allan Condon
Original assignee: Oztec Refrigerants Pty. Ltd.
Priority date: 1996-06-14
Filing date: 1997-06-16
Publication date: 1997-12-24

Abstract

A safety device (10) for an air-conditioning system has a pressure sensor (36, 136, 236) which monitors the pressure in a liquid/gas line (11, 111, 211) upstream of the expansion (Tx) value. If the pressure drops below a pre-set value due to a puncture (100), a valve (31, 131, 231) shuts off the line (11, 111, 211) to limit the escape of refrigerant gas to the passenger compartment (17) of the vehicle (15).

Description

TITLE: "SAFETY SYSTEM FOR AIR-CONDITIONING AND

REFRIGERATION UNITS BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION THIS INVENTION relates to a safety system for air

conditioning and refrigeration units.

Throughout the specification, the term "air conditioning" unit

shall be used to include a also refrigeration unit, a chiller unit, freezer unit

or the like. 2. PRIOR ART

The international concern over the depletion of the ozone

layer has resulted in agreement to progressively ban the manufacture and

sale of chlorofluorocarbons (CFCs). One consequence of this ban is that

refrigerant R12 must be phased out in its use in air conditioning systems,

including automobile air conditioners.

One proposed replacement is the refrigerant R134a,

developed by DuPont, which is a hydro fluorocarbon (HFC). As this was

the first replacement proposed, it has already received acceptance in the

market place. A new alternative has been proposed where hydrocarbons

(eg., butane, propane, or a mixture of these) has been proposed as a

refrigerant identified as "HC12a".

The proponents of refrigerant R134a have opposed the

introduction of the refrigerant HC12a arguing that the refrigerant is flammable and could cause explosion and/or fire in the passenger

compartment of an automobile if the automobile was involved in an accident and the refrigerant leaked into the passenger compartment.

The proponents of refrigerant HC12a reject this argument as

their calculations show that for a medium-sized passenger vehicle,

approximately 600 grams of the refrigerant would need to be released into

the passenger compartment (of approximately four cubic metres) to reach

the lower explosion level (LEL). As the quantity of refrigerant HC12a

required to charge an air conditioning system is 40% of the quantity

required for either refrigerant R12 or R134a, the maximum amount of

refrigerant HC12a in an automobile air conditioner is not likely to exceed

400-450 grams, which is clearly below the lower explosion level (LEL).

In their arguments, the proponents for refrigerant R134a

have been loath to acknowledge that the refrigerant R134a, eg., in an

automobile fire, breaks down to hydrogen fluoride which is odourless and

toxic at two parts per million (2ppm).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method

for preventing, or at least minimising, the amount of refrigerant which can

escape into a compartment if the air conditioning system is damaged.

It is a preferred object of the present invention to provide a

system where any gas which enters the compartment may be

automatically drawn out of the compartment or kept to a minimum should the system be damaged.

It is a further preferred object of the present invention to

provide a system which will prevent the air conditioning system from

operating if it determines that there is a leak of refrigerant from the system.

Other preferred objects of the present invention will become apparent from the following description.

In one aspect, the present invention resides in a safety

device for an air conditioning system (hereinbefore defined) of the type

having a compressor, a condensor, an expansion valve and an

evaporator; the device including:

a valve means in a liquid/gas line of the system, upstream of

the expansion (T_x) valve;

pressure sensor means to monitor the pressure in the line;

and means operable to close the valve means when the

monitored pressure in the line falls below a pre-set value.

Preferably, the valve means and the pressure sensor means

are provided in or on a single block or body provided in-line in the

liquid/gas line.

Preferably, the device is provided just downstream of the

receiver/dryer, although it may be provided in an automobile engine

compartment, adjacent the bulkhead or firewall separating the engine 7/48954 PC17AU97/00379

4 compartment from the passenger compartment.

Preferably, the valve means is urged towards the closed

position, eg., by spring means, and is only maintained open while the

pressure in the line is above the pre-set value.

The valve means may be solenoid valve, mechanical valve

or other suitable means.

Preferably, the pressure sensor means is connected to the

ignition system or compressor of the air conditioning system of the

automobile and so monitors the pressure in the line before the air conditioning system commences operation.

In one embodiment, a gas flow limiting orifice is provided

upstream of the pressure sensor means, to accelerate the response time

of the pressure sensor means by amplifying pressure differential due to

the loss of gas caused by a rupture in the line. The orifice may be

mounted between the valve means and the pressure sensor means - it is

not essential that it is be provided downstream of the valve means.

In an alternative embodiment, a low pressure activated shut-

off valve is provided upstream of the pressure sensor means and the

valve means and is normally held open when the air conditioning system

is operating normally, but is rapidly closed by the flow of gas through the

line if the line is ruptured.

An optional one-way check valve may be provided upstream

of the compressor unit (ie., interposed between the compressor and the evaporator) to prevent the leakage of refrigerant from the compressor

back towards the evaporator if the system is damaged.

Preferably, after the valve means has shut off the liquid/ gas

line, the compressor will continue to operate, until the pressure on its

downstream side exceeds a pre-set limit, to draw all or most of the

refrigerant gas, which may have escaped into the compartment, from the compartment.

In a second aspect, the present invention resides in a safety

method for air conditioning systems (as hereinbefore defined) wherein:

the pressure in the liquid/gas line is monitored and when the

pressure falls below a pre-set value, a valve means closes off the line to

prevent the escape of refrigerant from the system.

Preferably, after the valve means is closed, the compressor

is operated to draw all or most of the refrigerant, which may have escaped

into the compartment containing the evaporator, from the compartment.

Preferably, a one-way check valve is provided between the

compressor and the evaporator to prevent the escape of any refrigerant

from the compressor towards the compartment.

BRIEF DESCRIPTION OF THE DRAWINGS

To enable the invention to be fully understood, a preferred

embodiment will now be described with reference to the accompanying

drawings in which:

FIG. 1 is a schematic view of a standard automotive air conditioning system modified to incorporate the present invention;

FIG. 2 is a schematic sectional side view of one embodiment

of the safety device of the present invention;

FIG. 3 is a similar view of a second embodiment;

FIG. 4 is a part-sectional side view of the second

embodiment;

FIG. 5 is a schematic sectional side view of a third

embodiment;

FIG. 6 is a sectional side view of the valve of FIG. 5; and

FIG. 7 is an end view of the valve member of FIG. 6;

FIG. 8 is a section side view of a fourth embodiment, with

the valve closed;

FIG. 9 is a sectional side view of the valve of FIG. 8 in the

"open" position; and

FIG. 10 is an end view of the pressure sensor unit taken in

the direction of arrow Z.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1 , the safety device 10, to be hereinafter

described in more detail with reference to FIG. 2 is provided in the liquid

line 11 interconnecting the receiver/dryer 12 and the expansion valve (TJ

13, the device 10 being provided within the engine compartment 14 of the

vehicle 15. (The receiver/dryer 12 is downstream of the compressor 21 and condensor 22; the compressor 21 being drawn via engine 24 and clutch 25.)

NB: The safety device 10 may be mounted in the engine

compartment 14 on the bulkhead or firewall 16 which separates the

engine compartment 14 from the passenger compartment 17.

An optional one-way (or check) valve 18 can be provided in

the gas (suction) line 19 which interconnects the evaporator 20 (in the passenger compartment 17) with the compressor 21 (in the engine compartment 14).

Referring now to FIG. 2, the device 10 has a body 30, eg.,

machined in brass, which has suitable fittings (not shown) to enable the

device to be interposed in the liquid line 11 downstream of the

receiver/dryer 12 and upstream of the expansion valve 13.

A solenoid valve 31 has a valve member 32 operable with a

valve seat 33 to selectively control the flow of liquid through the liquid line

1 1. Current flow through a coil 34 holds the valve member 32 open

against the device of a compression spring 35.

A pressure sensor switch 36 incorporates a venturi device

37 to monitor the pressure in the liquid line 1 , a piston 38 causing a

contact plate 39 to interconnect contacts 40 and so energise the coil 34 to

open the valve member 32 while the pressure in the line 11 exceeds a

pre-set limit. One of the contacts 40 is connected to the ignition system

(IGN), so that the safety device 10 will commence operation before the air

conditioning system goes into operation. In normal operation, the pressure in the liquid line will be in

the range of 150-350 psi and the pressure in the suction line 19 will be

approximately 28-30 psi. If the liquid line should be punctured, eg., at

location 100 in FIG. 2, the release of the refrigerant will immediately

reduce the line pressure and as soon as this drops below a pre-set value,

eg., 60 psi, the electrical circuit between contacts 40 will be broken and

the coil spring 35 will close the valve member 32 on its seat 33 to prevent

the flow of refrigerant (under pressure from the compressor 21 ) through

the fluid line 11.

Meanwhile, the compressor 21 will continue to operate and

so it will tend to draw air, and some escaped refrigerant, back through the

puncture hole 100 into the liquid line 11 and through the expansion valve

13, evaporator 20 and suction line 19 and pump it under pressure to the

receiver/dryer 12. The compressor will continue to operate until the

pressure in discharge line 49 exceeds a pre-set limit and the compressor

21 will be shut off. The check valve 18 will prevent any refrigerant

downstream of the compressor 21 (eg., in the discharge line 49) from

back-flowing through the compressor to the puncture site 100. In this

way, the maximum amount of refrigerant which can escape into the

passenger compartment 17 is severely restricted; and most, if not all, of

the refrigerant will be drawn out of the passenger compartment by the

operation of the compressor 21 after the operation of the safety device 10.

Normally, when the air conditioning system is not operating, the respective pressures in the liquid line 11 , suction line 19 and

discharge line 49 equalise at, eg., 90 psi. If, however, there has been a

slow leak of refrigerant eg from the evaporator 20, and the pressure has

dropped below the pre-set value of, eg., 60 psi, then when the ignition is

5 switched on, the pressure switch 36 will not operate to connect the

contacts 40 and so the valve member 32 will remain closed, and the air

conditioning system will not operate.

The problem can only be rectified by having the puncture or

leak repaired and the air conditioning system recharged with gas.

0 Parallel with the pressure switch 36, a gas detector or

"sniffer" device could be mounted in the motor vehicle compartment, to

also cause the valve member 32 to be closed if any refrigerant is detected

in the passenger compartment.

A second embodiment will now be described with reference

to FIGS. 3 and 4, where the device 110, with solenoid valve 131 and

pressure sensor 136, modified from the first embodiment by the

incorporation of a gas limiting orifice 150.

The orifice 150 is designed to specifically accelerate the

response time of the pressure sensor 136 by amplifying the pressure

o differential between the loss of gas caused by the sudden rupture 100 and

the ability of the loss in pressure to be compensated by the compressor

12.

It may be located anywhere on the high pressure line 111 , upstream from the pressure sensor 136, and preferably between the shut-

off valve 131 and the pressure sensor 136, on the same mounting block 130 as a single unit.

When fitted, it must exclude all other means of gas flow

downstream from the orifice 150 except through the orifice 150 as it is specially designed to allow limited flow.

Orifice 150 may be described as a metallic or synthetic

washer or a solid mould 151 with a predetermined sized hole 152 drilled

through it, preferably through the centre and shall be the only means of allowing gas to flow from A to B.

The size of the hole 152 is critical to the proper function of

the orifice 150. For example, if the hole 152 is made too large, excessive

gas will flow through the hole 152 and compensate any drop in pressure

caused by the sudden rupture 100. This will delay the response time of

the pressure sensor 136. If the hole 152 is too small, there will be

unnecessary restriction to allow sufficient gas to flow to B and therefore

effect the cooling performance through the TX valve.

The hole size is preferably determined by calculating the

normal amount of gas flow through the high pressure line and on through

the TX valve. This flow must not be restricted or interfered with by the

orifice hole 150. Having calculated the flow rate and volume of gas, the

hole in the orifice 150 will preferably be drilled to the minimum size possible to restrict as much gas through the orifice 150 but at the same time sufficient to maintain normal operation through the T_x valve. The

orifice is placed upstream of the pressure sensing device 136 and

preferably (but not necessarily) downstream from the shut-off valve 131 ,

and preferably all devices shall be mounted on the one block 130 as a single unit.

In addition to the normal venturi effect, as hereinbefore

described, the orifice 150 will magnify and accelerate the response time

on the pressure sensor 136.

In the event of a rupture 100, the sudden loss of gas will

immediately reduce the pressure downstream of the orifice at B. The

effect is magnified by the continued running of the compressor extracting

any remaining gas. The specially sized hole 152 of the orifice 150 will

restrict gas flow from A to replace the drop in pressure in B. The drop in

pressure in B plus the accelerated flow through the orifice 150 will activate

the venturi 137 and activate the pressure switch 136, immediately closing the shut-off valve 131.

The combined effect of the orifice 150, pressure sensor

switch 136, venturi 137, shut-off valve 131 and the rupture 100 will result

in a quick positive response with absolute minimum gas loss prior to shut-

off. The orifice 150 will act as an additional gas limiting safety barrier if for

any reason the shut-off valve 131 fails to activate on pressure drop.

At "A", pressure is maintained by the running compressor,

even when there is a rupture 100 in the line 111 at B. At "B", in a rupture, the pressure will drop rapidly, caused by

excessive losses of gas. Because of hole size in the orifice 150,

insufficient gas flow to replace the gas loss, thus pressure will drop and

the pressure sensor switch 136 is activated to shut off the shut-off valve

131.

The orifice 150 allows only sufficient gas through hole 152 to

maintain normal operation, but it is not capable of compensating any extra loss in gas from any rupture or severe leaks.

Referring now to FIGS. 5 to 7, the device 210 has a

pressure sensor 236 upstream of the solenoid valve 231 ie the reverse of the configuration in the first and second embodiments. The solenoid valve

231 is connected to the electrical circuit for the air conditioning system

and only operates when the system is switched on.

The low pressure activated shut-off valve 270 is provided in

the body 230 of the device 210 upstream of the pressure sensor 236. An

enlarged bore 271 is provided at the upstream end of the body 230 in

communication with passage 281 therethrough. A valve member or

plunger 272 is received in the bore 271 and is restrained by a circlip 273.

A conical nose 274 on the plunger 272 is adapted to co-operate with a

valve seat 275 to selectively isolate the bore 271 from the passage 281 ; a

spring 276 biassing the plunger 272 away from the valve seat 275.

A plurality of grooves or slots 277 are provided about the

plunger 272 and are dimensional so that the gas flow about the plunger 272 and through passage 281 matches the flow through the T_x valve in normal operation.

If, however, the bore downstream of the device 210 is

ruptured, the sudden loss of pressure downstream of the valve 270 will

cause the gas pressure upstream thereof to move the plunger 272 so that

its nose 274 seats on the valve seat 275. This amplifies the pressure loss

in passage 281 and the pressure sensor 236 causes the shut-off valve

231 to close. Gradually the pressure on both sides of the plunger 272 will

equalize and it will be moved from the seat 275 by the spring 276.

However, as shut-off valve 231 is closed, no gas can escape from the

system.

This device also protects against loss of gas due to slow leaks in the system.

When the air conditioning system is switched on, the

solenoid valve 231 will initially be opened by a flow of current from the

electrical circuit of the air conditioning system. However, if the static pressure is below a preset value, eg. 60psi, the pressure sensor 236 will

close the solenoid valve 231 and the electrical supply to the compressor

will be shut off. It will be noted that the device 230 of this embodiment

provides two shut-off valves to close the system when the rupture occurs.

Referring now to the device 310 of the fourth embodiment of

FIGS. 8 to 10, the solenoid valve 331 has a body 360 connectable to the receiver/dryer 12 and to a body 380 of the pressure sensor switch 336.

A plunger 361 is slidably mounted in a bore 362 in the body

360 and is movable to selectively allow liquid to pass through passages

363 in the wall of the body 360. Small (eg., 1 mm diameter) ports 364 are

provided through a wall 363 and a steel block 365 slidably received in a

chamber 366. Small (eg. 1 mm diameter) ports 367 allow the liquid to flow

through the steel block 365 to the pressure sensor unit 370, fitted with the

pressure switch 336.

Electric coils 368, 368a surround the body 360 and a coil

spring 369 surrounds a shaft 369a connecting the plunger 361 to the steel

block 365.

The pressure sensor unit 370 has an inlet 371 connected to

a liquid reservoir 372 connected to an outlet 373 connected to line 311. A

disc 374 has a pair of angled ports 375, which discharge the liquid to

either side of a hole 376 in a table 377 connected to the pressure switch

336.

When the engine 24 is switched off, the coil spring 369

urges the steel block 365 to a position (see FIG 8) where the plunger

closes the passages 362.

Provided there has been no slow leak in the system, "start¬

up" coil 368, connected to the starter motor circuit, pulls the steel block to

cause the plunger 361 to open the passages 362 and allow the refrigerant

liquid to flow through the device 310 When the engine starts, the "hold-on" coil 368a, connected to the ignition circuit of the engine 24, holds the plunger 361 open.

(Both coils 368, 368a are wired to earth via the pressure

switch 336.)

When the engine is stopped, coil 368a releases the steel

block 365 and the plunger 361 closes the passages 362.

If a "slow" leak occurs overnight, the residual pressure in line

31 1 will be below the preset valve and pressure switch 336 will not allow the coils 368, 368a to open the switch 331.

If a major leak occurs in the system, the rapid liquid flow

through the ports 367 causes the steel block 365 to move the plunger 361

to close the passages 362 and isolate the compressor 21. The pressure

switch 336 will also switch off coil 368a.

If a slow leak occurs, the pressure drop in line 311 will be

measured by the pressure switch 336 and the coil 368a will be switched

off to cause the plunger 361 to close the passages 362.

The angled ports 375 in the disc 374 generate a venturi-like

effect adjacent the hole 376 in pressure switch tube 377 to magnify the

pressure change.

The reservoir 372 acts as a damper for liquid flow through

the device 310, when the vehicle is hot and the engine is switched on, the

Tx valve is open. The reservoir 372 provides a "rush" of liquid to the

evaporator 20 to provide quick initial cooling to possibly compensate for a momentary drop in pressure in line 311 below the preset level of pressure

switch 336.

It will be readily apparent to the skilled addressee that the

electrical pressure switch 36, 136, 236, 336 and solenoid valve 31 , 131 ,

231 can be replaced by a mechanical valving arrangement which monitors

the pressure and closes the liquid line 11 , 111 , 211 , 311 when the

pressure in the line falls below a preset value.

Various other changes and modifications may be made to

the embodiments described and illustrated without departing from the

present invention.

Claims

CLAIMS:

1. A safety device for an air conditioning system (hereinbefore

defined) of the type having a compressor, a condensor, an expansion

valve and an evaporator; the device including:

5 a valve means in a liquid/gas line of the system, upstream of

the expansion (TJ valve;

pressure sensor means to monitor the pressure in the line; and

means operable to close the valve means when the

0 monitored pressure in the line falls below a pre-set value.

2. A device as claimed in claim 1 wherein:

the valve means and the pressure sensor means are

provided in or on a single block or body provided in-line in the liquid/gas

line. 5

3. A device as claimed in claim 2 wherein:

the valve means and the pressure sensor means are

provided downstream of a receiver/dryer; or in an automobile engine

compartment, adjacent a bulkhead or firewall separating the engine compartment from the passenger compartment.

o

4. A device as claimed in any one of claims 1 to 3 wherein:

the valve means is urged towards the closed position,

optionally by spring means, and is only maintained open while the

pressure in the line is above the pre-set value.

5. A device as claimed in claim 4 wherein:

the valve means is a solenoid valve, mechanical valve or other valve means.

6. A device as claimed in any one of claims 1 to 5 wherein:

the pressure sensor means is connected to an ignition

system or compressor of the air conditioning system of an automobile and

monitors the pressure in the line before the air conditioning system

commences operation.

7. A device as claimed in any one of claims 1 to 6 wherein:

a gas flow limiting orifice is provided upstream of the pressure sensor means, to accelerate the response time of the pressure

sensor means by amplifying pressure differential due to the loss of gas caused by a rupture in the line.

8. A device as claimed in claim 7 wherein:

the orifice is mounted between the valve means and the

pressure sensor means.

9. A device as claimed in any one of claims 1 to 6 wherein:

a low pressure activated shut-off valve is provided upstream

of the pressure sensor means and the valve means, and is normally held

open when the air conditioning system is operating normally, but is rapidly

closed by the flow of gas through the line if the line is ruptured.

10. A device as claimed in any one of claims 1 to 9 wherein:

a one-way check valve is provided upstream of the compressor, between the compressor and the evaporator to prevent the

leakage of refrigerant from the compressor back towards the evaporator if

the system is damaged.

11. A device as claimed in any one of claims 1 to 10 wherein:

after the valve means has shut off the liquid/ gas line, the

compressor will continue to operate, until the pressure on its downstream

side exceeds a pre-set limit, to draw all or most of the refrigerant gas,

which may have escaped into a passenger compartment of a vehicle,

from the passenger compartment.

12. A safety method for air conditioning systems (as

hereinbefore defined) of the typing having a compressor, a condensor, n

expansion valve and an evaporator; wherein:

the pressure in a liquid/gas line is monitored and when the

pressure falls below a pre-set value, a valve means closes off the line to prevent the escape of refrigerant from the system.

13. A method as claimed in claim 12 wherein:

after the valve means is closed, the compressor is operated

to draw all or most of the refrigerant, which may have escaped into a

compartment containing the evaporator, from the compartment.

14. A method as claimed in claim 13 wherein:

a one-way check valve is provided between the compressor

and the evaporator to prevent the escape of any refrigerant from the compressor towards the compartment.