EP0931595A1

EP0931595A1 - A device for spraying a liquid

Info

Publication number: EP0931595A1
Application number: EP98400152A
Authority: EP
Inventors: Georges Fonzes; Michel Gschwind; Jean Lauretti
Original assignee: IMRA Europe SAS
Current assignee: IMRA Europe SAS
Priority date: 1998-01-26
Filing date: 1998-01-26
Publication date: 1999-07-28

Abstract

The invention relates to a device for spraying a liquid, the device comprising at least one vessel, a transducer placed in the vessel, and a feed circuit for filling said vessel with the liquid to be sprayed. It includes a sensor (14) organized to deliver a signal representative of a given state of operation of the feed circuit, and control means (13) for interrupting the operation of the transducer (4) when said signal crosses a predetermined threshold.

Description

The present invention relates to a spray device for spraying a liquid, the device comprising at least one vessel, a transducer placed in the vessel, and a feed circuit for filling the vessel with the liquid to be sprayed.
Such a device is described, for example, in French patent of invention No. 2 721 839.
The liquid present in the vessel, as renewed by the feed circuit, participates in cooling the transducer and in removing the mechanical energy generated thereby.
The invention seeks in particular to avoid the transducer overheating if the supply of liquid in the vessel is insufficient.
It achieves this by the fact that the spray device includes a sensor organized to deliver a signal representative of a given state of operation of the feed circuit, and control means for interrupting the operation of the transducer when said signal crosses a predetermined threshold.
In particular, it is possible to deliver a signal representing the flow of liquid in the feed circuit.
In a particular embodiment of the invention, a pressure sensor is used, which has the advantage of being relatively insensitive to variations in the inclination of the spray device.
When the feed circuit includes a pump, the pressure sensor is placed, for example, downstream from the pump and upstream from the vessel, and the control means interrupt the operation of the transducer when the pressure measured by the sensor drops below a predetermined value.
Because of the invention, it is easy to detect a failure of the feed circuit due, for example, to the pump stopping, to a leak from the pipework connecting the pump to the vessel or to its own feed tank, or indeed to said tank being empty.
This ensures that the transducer does not operate with an insufficient quantity of liquid in the vessel.
It may also be advantageous to improve the efficiency of the spray device, i.e. the ratio of the quantity of liquid sprayed in the form of droplets having a predetermined size to the quantity of liquid injected into the vessel by the feed circuit.
This is achieved by ensuring that at least a fraction of the liquid that is to be sprayed is injected into the vessel with a non-zero axial component towards the open end of the vessel.
With this particular embodiment, the turbulence of the liquid in the vessel is reduced and a flow of liquid at the outlet from the vessel is obtained which is much more laminar than is the case in above-mentioned French patent 2 721 839 where the liquid to be sprayed is injected into the vessel in a purely radial direction.
Because the liquid flow towards the open end of the vessel is less turbulent, the resulting droplets are more uniform in size, and the spray device is more efficient.
Also preferably, a fraction of the liquid injected into the vessel is directed onto the transducer, thereby cleaning it and cooling it.
It is also advantageous to feed electrical power to the transducer by using all or part of the vessel as an electrical contact.
This serves to simplify making electrical connections with the transducer.
It can also be advantageous to feed the vessel from a tank that is completely full of the liquid to be sprayed.
This embodiment makes it possible to control more accurately the characteristics of the jet of liquid leaving the vessel, and to improve the effectiveness of the spray device.
Also, by using a tank that is completely full, it is possible to reduce variations in the flow rate of the liquid feeding the vessel as a function of the inclination of the tank, or as a function of variations in pump operating rate.
It has also been found that this reduces the risk of bubbles being present in the liquid feeding the vessel.
In an embodiment, the tank completely full of liquid to be sprayed, referred to as the "downstream" tank below, is fed by a pump which takes the liquid from another tank, referred to as the "upstream" tank, with the upstream tank being only partially full.
In an embodiment, the downstream tank overflows into the upstream tank via an overflow orifice situated in a high portion of the downstream tank so as to maintain a column of liquid above the orifice(s) through which the liquid for spraying is extracted from the downstream tank.
Depending on the height of this liquid column, the pressure of the liquid feeding the vessel(s) used for spraying the liquid increases or decreases.
In another particular embodiment, instead of using an overflow orifice, a pressure-relief valve or the like is used to regulate the pressure in the downstream tank, the liquid leaving via said valve flowing into the upstream tank, which may be connected via an electrically controlled valve to a liquid feed pipe for initial filling and periodically delivering a quantity of liquid that is to replace the liquid which has been sprayed.
The liquid which leaves the vessel(s) without being sprayed is advantageously recycled via the upstream tank by flowing over a sloping wall until it reaches it.
In this embodiment having upstream and downstream tanks, it is particularly advantageous for the purpose of detecting anomalous operation of the spray device to make use of a differential pressure sensor which is suitable for delivering a signal representative of the pressure difference between the upstream tank and the downstream tank.
Thus, using a single sensor, it is possible to detect various kinds of anomalous operation, and in particular the situation in which there is an insufficient quantity of liquid in the upstream tank, the situation in which said tank needs to be topped up again to compensate for loss of liquid, and the situation where either the upstream tank contains too much liquid or the downstream tank is leaking or the pump is faulty.
The use of a differential pressure sensor makes it possible to detect anomalous operation of the spray device very quickly because of the particularly short response time of this type of sensor.
It is also relatively easy to make such a sensor leakproof.
In another embodiment having upstream and downstream tanks, it is also advantageous to use a pressure sensor for measuring the pressure in the downstream tank.
Naturally the various above-described embodiment features can be implemented in combination or separately, for their specific advantages.
To make the invention easier to understand, there follows a description of various embodiments given as non-limiting examples and made with reference to the accompanying drawings, in which:

Figures 1 to 5 are diagrams of five spray devices; and
Figure 6 is a diagram of a spray head.

The spray device 1 shown diagrammatically in Figure 1 comprises a tank 2 containing a supply of liquid to be sprayed, e.g. water, and a spray head including an elongate vessel 3 with a piezoelectric transducer 4 of known type placed in the bottom thereof.
The cross-section of the vessel 3 tapers progressively going away from the transducer 4 to an opening 5.
The inside surface 6 of the vessel 3 is in the form of a paraboloid of revolution to focus the ultrasound emitted by the transducer 4 into the vicinity of the opening 5.
The vessel 3 receives liquid taken from the tank 2 via a feed circuit 7 including a pump 8 which is connected to the tank 2 via an intake duct 9 and to the vessel 3 via an injection duct 10.
The transducer 4 is excited by an electrical amplifier 1 which receives the high frequency signal delivered by a signal generator 12.
An electronic switch 13 makes it possible to interrupt the connection between the signal generator 12 and the amplifier 11.
In the example described, the electronic switch 13 is connected to a pressure sensor 14 disposed so as to deliver a signal representative of the pressure of liquid in the injection duct 10.
By way of example, the pressure sensor 14 may be of a conventional membrane type.
While the spray device 1 is operating properly, liquid is continuously injected by the pump 8 into the vessel 3, at an absolute pressure lying in the range 102,000 Pa and 120,000 Pa in the embodiment described, i.e. at a pressure increase lying in the range 2000 Pa to 20,000 Pa.
A jet of liquid is formed leaving the opening 5 of the vessel 3. The role of the transducer 4 is to act on said jet of liquid to cause fine droplets of liquid to be formed. The ultrasound waves emitted by the transducer are concentrated by the surface 16 into the vicinity of the opening 5, and when concentrated in this way, these waves cause a mist made up of fine droplets to be emitted from the jet of liquid, in conventional manner.
Reference may usefully be made to French patent 2 721 839 which describes a configuration enabling the mist formed in this way to be removed by means of a fan, e.g. for humidifying a vehicle cabin.
In the event of the pump 8 failing, for example, then the pressure of liquid injected into the vessel 3 drops.
This pressure drop is immediately detected by the pressure sensor 14 and the electronic switch 13 is organized to interrupt the connection between the signal generator 12 and the amplifier 11 when the pressure measured by the pressure sensor 14 drops below a predetermined threshold, e.g. set at 102,000 Pa, i.e. at about 2000 Pa above atmospheric pressure.
This avoids damaging the transducer 4 which is no longer being properly cooled by renewal of the liquid in the vessel 3.
It is thus possible to counter the risk of the transducer 4 being damaged in the event of a failure in the circuit feeding liquid to be sprayed, and to do so at relatively low cost and with a high degree of reliability.
As in the embodiment described, the pressure sensor is preferably located so as to be swept continuously by a flow of liquid, thereby making clogging unlikely.
The pressure sensor also has the advantage of being capable of being used in any position, which is advantageous when the spray device 1 is fitted to a vehicle.
Naturally, the embodiment described above is not limiting.
Thus, without going beyond the ambit of the invention, it is possible to place the pressure sensor elsewhere on the liquid feed circuit, e.g. upstream from the pump 8.
Under such circumstances, the electronic switch 13 is organized to interrupt the operation of the transducer 4 when the pressure upstream from the pump 8 exceeds a predetermined value, representative of the fact that the pump is no longer taking in liquid properly from the tank 2.
It is also possible to place the pressure sensor so that it delivers a signal representative of the pressure of the liquid at the outlet from the injection duct 10.
It is also possible to place the pressure sensor in the tank 2 so that it delivers a signal representative of the pressure of the liquid at the inlet to the intake duct 9, for example.
Also, without going beyond the ambit of the present invention, it is possible to use a sensor other than a pressure sensor, e.g. to measure the flow rate of the liquid in the feed duct and to cause the transducer 4 to be stopped in the event of the pump failing.
Any known flow measuring device can be used for this purpose.
Figure 2 shows a spray device 1' constituting a variant embodiment of the invention.
The device 1' differs from the above-described device 1 in the nature of the sensor 14' used to replace the pressure sensor 14 for detecting an anomaly in the liquid feed circuit to the transducer 4, and by the presence in the feed circuit of a heat exchanger 15 through which the liquid sent to the transducer passes so as to cool one or more electronic components, e.g. certain components of the amplifier 11.
The sensor 14' may be constituted, for example, by a flow meter delivering a signal representative of the flow rate of the liquid in the injection duct 10, with the electronic switch 13 being organized in such a manner as to interrupt the connection between the signal generator 12 and the amplifier 11 in the event of the flow rate dropping below a predetermined value.
In the embodiments described above, the electronic switch 13 is placed between the generator 12 and the amplifier 11.
In a variant, the electronic switch could be placed between the amplifier 11 and the transducer 4.
Figure 3 shows a third embodiment of the spray device 1''.
This device 1'' has two tanks separated by a common partition, the liquid to be sprayed being pumped by a pump 22 from a first tank 20, referred to below as the "upstream" tank, and delivered into a second tank 21, referred to below as the "downstream" tank.
The pump 22 is immersed in the downstream tank 21 which is completely filled with the liquid and which has, at its top portion 25, a narrow section and an overflow orifice 24, with liquid flowing under gravity from said orifice 24 into the upstream tank 20.
In the example described, the spray device has two spray heads with respective feeds of liquid to be sprayed via ducts 26 and 27 both opening out into the downstream tank 21.
The overflow orifice 24 is higher than the orifices through which the ducts 26 and 27 open out into the downstream tank, so the pressure of the liquid at the inlets of these ducts therefore depends on the height of the top portion 25 of the downstream tank 21.
A sloping wall 28 is provided to collect non-sprayed liquid leaving the spray head vessels 3 and to guide that liquid via a passage (not shown) through the upper portion 25 of the downstream tank 21 into the upstream tank 20.
A pressure sensor 30 is mounted in the outlet duct of the pump 22 to detect anomalous operation, like the pressure sensors 14 and 14' of the previous embodiments.
The spray device 1'' shown in Figure 3 has the advantages of enabling the spray heads to operate regardless of the inclination of the device and of reducing the risk of bubbles of air being present in the ducts feeding the spray heads.
In addition, regulating the pressure by means of an overflow leading back into the upstream tank 20 enables the spray device 1'' to be relatively insensitive to variations in the operating rate of the pump 22.
In a variant that is not shown, the upper portion 25 of the downstream tank 21 and the overflow orifice 24 are replaced by a pressure-relief valve which opens when the pressure of the liquid in the downstream tank 21 exceeds a predetermined value.
Figure 4 shows a spray device 1''' constituting a fourth embodiment of the invention.
In this device 1''', pressure regulation in the downstream tank, given reference 31, is provided by a valve 32.
When the valve 32 opens, the liquid contained in the downstream tank 31 drops into the upstream tank, given reference 33 in this case.
The downstream tank 31 communicates via feed ducts 34 and 35 with respective spray heads.
A sloping wall 36 is provided to collect the liquid that is not sprayed by the spray heads and to return it to the upstream tank 33.
Figure 4 shows an electrically controlled valve 37 connected to a source of liquid for automatically filling the upstream tank 33.
A pump 38 immersed in the downstream tank 31 enables liquid to be taken from the upstream tank 33 and to be delivered into the downstream tank 31, as in the preceding embodiment.
The upstream and downstream tanks 33 and 31 are separated by a common partition 42.
A differential pressure sensor 40 is mounted through said partition 42 to deliver an electric signal representative of the pressure difference at the bottoms of said tanks.
This single sensor 40 makes it possible to detect and identify various kinds of operating anomaly.
More particularly, the sensor 40 delivers a voltage V which can cross three levels V1, V2, and V3 where V1 > V2 > V3.
When the voltage delivered by the sensor 40 is greater than V1, that means that the height of liquid in the upstream tank 33 is less than a height h₁ which is slightly greater than the height of the intake orifice of the pump 38.
Control means are provided to trigger an alarm under such circumstances to warn that the content of the upstream tank 33 is too low.
When the voltage V lies between V2 and V1, that means the height of liquid in the upstream tank 33 lies in the range h₁ to h₂, with the valve 32 being slightly higher than h₂.
Control means are provided to open the electrically controlled valve 37 when the voltage V lies between V1 and V2 to cause the upstream tank 33 to be filled.
This filling ceases when the liquid level reaches the height h₂, i.e. when the voltage V crosses the threshold V2.
When the voltage V is greater than V3 and less than V2, that means that the height of liquid in the first tank 33 lies in the range h₂ to h₃, the value h₃ being slightly lower than the maximum height liquid can reach in the upstream tank 33. There is a risk of the upstream tank 33 overflowing or there is a leak in the downstream tank 31.
If the voltage V is less than V3, that may mean that the pump 38 is not operating properly.
Control means (not shown) are provided to trigger an alarm under such circumstances.
It will be understood that in this embodiment, using a single differential pressure sensor and associated control means, it is possible to obtain a considerable amount of information, concerning the operating state of the spray device.
Figure 5 shows a fifth embodiment of a spray device implementing the invention.
In this device, the pressure in the downstream tank, referenced 71, is regulated by a pressure sensor 70 placed at the base of the top wall 72 of the downstream tank 71.
This pressure sensor 70 delivers information representative of the height h of liquid above it, i.e. the difference in height between itself and the top end of the jet emitted by the vessel 3.
When the liquid level in the upstream tank, referenced 73, decreases, then the height h of the jet also decreases.
The pressure sensor 70 thus serves to deliver a signal representative to some extent of the height of liquid in the upstream tank.
When the height h has decreased by the quantity dh₁, or dh₂, that means the level of liquid in the upstream tank has decreased by an amount dh₁' or dh₂,, respectively, and for a predetermined value of dh₁', the control means (not shown) to which the sensor 70 is connected cause the electrically controlled valve 37 to open and the upstream tank to be filled up to a reference level, i.e. until the height h of the jet at the outlet from the vessel 3 as measured by the sensor 70 has returned to a predetermined value.
The threshold dh₂ is selected to be representative of abnormal operation of the device, and under circumstances, the control means to which the sensor 70 is connected cause the pump 38 feeding the transducer placed in the vessel 3 to be stopped.
Figure 6 shows a particularly advantageous way of implementing the spray head, referenced 50 in this figure, comprising a vessel 51 having an axis X, and a transducer 52.
In the spray heads described above, as in the prior art, the liquid is injected into the vessel in a purely radial direction, whereas in the embodiment of Figure 6, at least a fraction of the liquid to be sprayed is injected into the vessel 51 with a non-zero axial component towards the open end 53 thereof.
This makes it possible to improve the efficiency of the device, i.e. the ratio of the quantity of liquid sprayed in the form of droplets of predetermined size to the total quantity of liquid injected into the vessel by the feed means.
This improved performance of the spray head is explained by the fact that the flow of liquid towards the open end 53 of the vessel 51 is less turbulent, thereby giving rise to greater uniformity in the size of the droplets which are formed.
The vessel 51 is fed from an annular cavity 54 which receives the liquid via a duct 55.
The annular cavity 54 communicates with the inside of the vessel 51 via an annular passage 56 that slopes obliquely towards the axis X of the vessel and towards its open end 53, and which is defined both top and bottom by conical surfaces.
The liquid passing through the annular passage 56 is directed towards the opening 53 which tends to make the flow along the wall of the vessel 51 laminar while the spray device is in operation.
The diameter d of the opening 53 is selected so that the jet of water formed solely by the pressure of liquid coming into the vessel 51 when the transducer is not operating is substantially the same as the acoustic fountain that would be generated by the soundwaves emitted by the transducer on their own if the liquid present in the vessel were static.
In the example described, the diameter d of the opening 53 is 5.6 mm, the inside diameter D of the vessel 51 at its base is 18 mm and the length l of the vessel 51 is 38 mm.
The energy efficiency of spraying is increased because the energy of the waves is used for the most part to break the water up into droplets, the jet of water being already formed by the pressure of the liquid injected into the vessel 51.
The action of the ultrasound emitted by the transducer 52 on the jet of water leaving the vessel 51 is to cause a mist to be formed that is made up of droplets of relatively uniform size.
In the example described, the cavity 54 is formed by assembling together a top piece 58 and a bottom piece 59.
The bottom and top pieces 59 and 58 have circularly cylindrical walls about the axis X, which radially define the cavity 54.
The cylindrical wall 60 of the bottom part 59 has a radial hole 57 passing therethrough which opens out slightly above the transducer 52 and which directs a fraction of the liquid coming from the duct 55 into the cavity 54 onto the transducer 52, thereby cooling it.
The electrical power supply to the transducer 52 is advantageously provided using the vessel 51 and the bottom and top parts 59 and 58 that include metal portions to convey electricity.
In the example shown, the transducer has a contact 63 on its outside face which is connected to an electrical power supply wire 64.
Electric current return is provided by a wire 67 connected to a contact 66 situated on the outside surface of the vessel 51 and via a portion of the transducer 52 in contact with the bottom part 59.

Claims

A spray device for spraying a liquid, the device comprising at least one vessel, a transducer placed in the vessel, and a feed circuit for feeding the vessel with the liquid to be sprayed, the device being characterized by the fact that it includes a sensor (14; 14'; 30; 40) organized to deliver a signal representative of a given state of operation of the feed circuit, and control means (13) for interrupting the operation of the transducer (4) when said signal crosses a predetermined threshold.
A device according to claim 1, characterized by the fact that said sensor is a sensor suitable for delivering a signal representative of liquid flow, preferably a pressure sensor (14; 30).
A device according to claim 2, characterized by the fact that said feed circuit (7) includes a pump (8), and by the fact that said pressure sensor (14; 30) is placed downstream from the pump and upstream from the vessel (3), said control means (13) interrupting operation of the transducer (4) when the pressure measured by the pressure sensor (14) drops below a predetermined threshold.
A device according to claim 1 or 2, characterized by the fact that the vessel is fed from a tank (21, 31) that is completely filled with liquid to be sprayed.
A device according to the preceding claim,
characterized by the fact that said tank entirely filled with liquid to be sprayed, referred to as the "downstream" tank, is fed by a pump (22; 38) which takes the liquid from another tank (20; 33) referred to as the "upstream" tank.
A device according to the preceding claim,
characterized by the fact that the downstream tank (21) overflows into the upstream tank (20) via an overflow orifice (24) situated in a high portion (25) of the downstream tank (21).
A device according to claim 5, characterized by the fact that the downstream tank (31) is fitted with a pressure-relief valve (32) or the like enabling the pressure therein to be regulated.
A device according to any one of claims 5 to 7, characterized by the fact that it includes a differential pressure sensor (40) suitable for delivering a signal representative of the pressure difference between the upstream tank (33) and the downstream tank (31).
A device according to any one of claims 5 to 8, characterized by the fact that it includes a pressure sensor (70) placed in said downstream tank.
A device according to any preceding claim,
characterized by the fact that the liquid to be sprayed is injected into the vessel (5) with a non-zero axial component towards its open end (53).
A device according to any preceding claim,
characterized by the fact that the vessel (3) is fed with liquid to be sprayed at a pressure lying in the range 102,000 Pa to 120,000 Pa.
A device according to any preceding claim,
characterized by the fact that it includes a heat exchanger (15) through which the liquid flowing in the feed circuit passes to cool one or more electronic components (11).
A device according to any preceding claim, characterized by the fact that the electrical power supply to the transducer (52) is provided by using all or part of the vessel (51) as an electrical contact.