The present invention relates to an improved ioniser for an air purifying device.

Ionisers are sometimes used in air filtration systems. Such ionisers use high voltage to ionise air molecules and any particulates entrained therein. These particles are then attracted to an electrostatic precipitator and thereby removed from the air stream.

WO 98/50162 (Blue Air) discloses a simple system whereby air particles are ionised by an ioniser such that the particles are attracted to a fibrous precipitation (capture) device.

EP-A-0 646 416 (Trion) discloses an electrostatic filter system with a positive and negative ion source. The device is switched from a positive to a negative polarity at intervals with a time relay and is set at 60 seconds negative and 30 seconds positive.

JP H 03 135455 (Nippon Denso Co) discloses an air cleaner comprising a bipolar inoiser and wherein the ioniser switches polarity after a time period set at from one hour to one week.

JP H 2018 041575 (Maxell Holdings) discloses an air cleaner comprising a bipolar inoiser and wherein the ioniser switches polarity after a time period set at either 30 minutes or a minute.

Despite the prior art there remains a need for improved ionisers for air purifying devices which are able to manage their performance over time such that they use the filters more efficiently. This provides for a more efficient device which works more efficiently over the average lifespan of a filter and also permits the user to replace the filters less regularly.

Accordingly, and in a first aspect, the present invention provides for an ioniser for an air purifying device wherein the ioniser comprises a corona discharge tip and is capable of alternately generating positive corona discharge and a negative corona discharge, wherein the ioniser comprises a voltage source, a switch for switching from a first polarity to a second polarity or vice versa during use and a timer for timing the time interval between switching from a first polarity to a second polarity and wherein the switch is activated to switch the polarity after a period of from 0.2 to 20 seconds. Through using ions of a different charge, we have surprisingly found that performance of the device is dramatically improved in many regards. In particular, we have surprisingly found that a filter is more efficiently used when the fibre dipole is repeatedly switched during use for from 0.2 to 20 seconds between switching. Repeatedly alternating the current orientation in the corona discharge means that the dipole arrangement in the precipitating fibres is also alternated. The consequence of this is that a greater proportion of the filter gets used, thereby increasing the time before a new filter is required.

The ioniser alternates between a positive ion generating state and a negative ion generating state when in use. This permits the generation of positive ions for a determined period of time and then generation of oppositely charged ions for a determined period of time. The corona discharge tip generates a corona field of charge determined by the polarity of the voltage source. The voltage source preferably generates a voltage at from -20 to 20 kV, more preferably from -10 to 10 kV and most preferably from -7 to 7 kV during use.

The ioniser comprises at least one discharge electrode and at least one ground electrode. The different polarities of ioniser can be achieved either by two ionisers with opposite polarities working alternatively, or with one ioniser capable of switching between two polarities.

Where there is just one discharge electrode and just one ground electrode, each electrode would need to function as both emitter and collector alternately. Preferably, such a device would also comprise a switch means for switching between the two generating states.

The discharge electrode receives a voltage from a voltage supply and is capable of producing a corona discharge. A discharge electrode is often referred to as a corona tip and may take any of various forms, a brush, a tip or a blade being particularly preferable.

Preferably, the device comprises a first ionising device for generating positive ions in an air stream and a second ionising device for generating negative ions in an air stream.

Preferably, the device comprises a sensor for determining the optimal time for switching from one polarity to the other and a means for doing so. The sensor may be a time sensor, a particle size sensor, a fan speed sensor or other such sensor which measures some aspect of performance of the filter device. Where the sensor is a particle size sensor, and the sensor senses the size of particles in the air purifier or ambient air and then adjusts the time intervals between switching between the positive and negative ionisation discharging periods. For example, when ambient air is highly polluted, i.e. there is a high concentration of particulate matter in the airflow, the time intervals would be modified accordingly to ensure the most efficient use of energy to clean the airflow.

Preferably, the sensor is a timer for timing the period in either of the two ion generating states.

The ioniser of the invention can be employed in a standalone air purifying device or incorporated into a vehicle or dwelling structure.

For example, where the device is incorporated into a vehicle it is intended that the air purifying system that the ioniser operates within is part of the vehicle's air conditioning system.

Alternatively, the ioniser is part of a standalone air purifying device wherein the device comprises a fan and a filter together with the ioniser and is housed and powered.

Preferably, and when employed as part of a standalone air purifying device, the ioniser is disposed after the fan and before the filter in an airflow direction.

Preferably, and where the sensor is time sensor, it is preferred that the time between switching from one polarity to the other and back again is from 0.2 seconds to 20 seconds and especially preferably from 0.5 to 10 seconds. The most preferred time is from 1.5 to 5 seconds. Preferably, the time period for each polarity is substantially the same.

The device according to the invention also comprises all the necessary means to perform its role within an air purifier. For example, it will comprise a power source sufficient to power a fan and preferably an additional power source for the ionising chamber. Where the ionising chamber comprises two separate corona discharge electrodes it is preferred that each corona discharge electrode has its own power source.

The device also comprises a fan for displacing the air from the exterior of the device through the ionising chamber and through the filtration media.

The filtration media is standard in the art and consists of any of the known means for air filtration. The device may comprise any of a number of sensors to sense performance of the device versus the conditions of the air.

In a second aspect there is provided a device is finally housed in a suitable housing which preferably keeps all the components out of sight and reach of the consumer. Air purifying device comprising an ioniser according to any preceding claim, a fan and a filter and wherein the ioniser is disposed after the fan and before the filter in an airflow direction.

In a third aspect there is provide a vehicle comprising an ioniser according to the first aspect of the invention.

In a fourth aspect there is provided an inhabitable dwelling comprising a dwelling structure and an air purifier according to the second aspect of the invention and wherein the air purifier forms part of the dwelling structure and is disposed in the structure such that the device in use is able to use air outside the dwelling and filter it as it enters the dwelling.

Embodiments of the invention will now be described with reference to the following non-limiting examples and figures.

Figures 1 and 2 are schematics of the basic components of an embodiment according to the invention.

Figure 1 shows a filter (1 ) and a corona discharge tip (2) between a pair of collecting electrodes (3). The corona discharge electrode receives an appropriate voltage from a voltage generator (4) such that air displaced by the fan (10) flows through the ion stream (9) and any particles entrained in the airflow are similarly charged. The airflow (5) passes through the filter medium (1 ) and is cleansed.

The voltage supply is also in communication with a switch (7) which reverses the polarity of the corona discharge from the corona discharge tip (4) as and when determined. This particular embodiment also has a particle size sensor (9) which senses the size of particles in the air stream (5) and which thus determines the frequency the polarity reversal of the corona discharge.

Figure 2 shows a similar system except that this embodiment has two corona discharge electrodes (4a and 4b) and two sets of collecting electrodes (5a and 5b). In this embodiment, corona discharge electrode (4a) generates a corona discharge (9a) of opposite polarity to corona discharge electrode (4b), seen in (9b). Each corona discharge electrode (4a and 4b) is powered by an appropriate voltage source (7a and 7b) and each is in in electrical communication with a means for switching between one corona discharge and the other such that only one is generated at any one time. Figure 3 shows the decrease in CADR (Clean Air Delivery Rate) in long-term use in a Blue Air Classic 400.

The figure shows the reduction of CADR overtime comparing a single polarity ioniser and a dual polarity ioniser.

Clearly shown is that using a dual ionising system, the CADR reduction over time is significantly lower.