The invention relates to an air supply device for a vehicle air conditioning system.

Such air supply devices are always connected to a vehicle inner space in order to supply fresh air from outside the vehicle to the inner space and/or to circulate the air in the inner space. Furthermore, there are generally provided air conditioning components which can heat and/or cool the fresh air or circulation as required.

In the meantime, these air conditioning components are in most cases part of a vehicle air conditioning system, also referred to as an HVAC unit, which enables the ventilation, heating and air conditioning of a vehicle . The air supply device generally comprises a ventilator fan, which can draw in air and can supply the drawn-in air to the vehicle air conditioning system and blow it into the inner space of the vehicle. From the prior art there are known air supply devices in which a leaf protection grid is arranged in a suction channel of the ventilator fan in order to keep away foliage and other large objects and to prevent blockage of or damage to the ventilator fan. Such leaf protection grids are generally coarse-mesh injection- molded components of plastics materials having mesh widths of approximately 4 mm.

Furthermore, in the conventional air supply devices, there is generally provided an air filter which prevents or at least reduces a contamination of the vehicle inner space by harmful substances. In most cases, this air filter is arranged upstream of the ventilator fan in order, for example, to filter out sand particles which could damage a ventilator impeller of the ventilator fan.

However, it has been found that, with such air supply devices, an evaporator of the vehicle air conditioning system, which evaporator is arranged downstream of the ventilator fan, is subject to rapid corrosion.

An object of the invention is to provide a robust, durable air supply device, which reliably prevents or at least reduces damage to the air conditioning system and contamination of the vehicle inner space by harmful substances from the environment and which further has a long service-life, with acceptable flow resistance.

This object is achieved according to the invention by an air supply device for a vehicle air conditioning system having a ventilator fan which can draw in air and supply it to the vehicle air conditioning system, a first air filter which is arranged upstream of the ventilator fan, and a second air filter which is arranged downstream of the ventilator fan. The invention is based on the recognition that protection of the ventilator fan and the vehicle air conditioning system can best be carried out by means of two separate air filters which are arranged in series. The two air filters can be adapted to their respective requirements with little complexity. Thus, the first air filter is in particular a fairly large-pored particulate filter, whereas the second air filter is preferably a fairly fine-pored dust filter. For this reason, the two separate air filters become clogged substantially more slowly than a single air filter, which has a positive effect on the service-life.

In an embodiment of the air supply device, the first air filter has a pore size of a maximum of 0.5 mm. In particular, the maximum pore size is selected in such a manner that sand particles which could damage the ventilator fan in the event of impact thereof with a ventilator impeller, are to a large extent retained, but the smallest particles, such as dust or fine dust, are substantially allowed through in order to prevent rapid clogging of the first air filter and to increase the service-life thereof.

In a particularly preferred manner, the first air filter is a fabric filter having a mesh width of a maximum of 0.5 mm, in particular a maximum of 0.2 mm. Such fabric filters can be produced in a cost-effective manner and are particularly suitable as coarse filters for retaining sand.

Furthermore, the first air filter and the second air filter may have identical dimensions. Consequently, even with different filter media, identical filter frames or filter housings can be used, which reduces the production complexity of the air supply device.

In another embodiment of the air supply device, the first air filter and/or the second air filter has/have a coating for the adsorption of gases, in particular an activated carbon coating. Such coatings may, for example, adsorb harmful gaseous substances, but also fine dusts, pollen, bacteria or noxious odors. For this reason, in particular the finer-pored second air filter has the coating for adsorption of gases.

In order to achieve a desired capacity for the adsorption of harmful gaseous substances, a specific quantity of coating material is required. So that the flow resistance of the second air filter does not increase excessively as a result of the coating, the coating material is preferably divided between the first air filter and the second air filter. In this manner, the first air filter which is arranged upstream of the ventilator fan already contributes to the adsorption of harmful gaseous substances. In a particularly preferred manner, the coating material is divided in such a manner that the first air filter and the second air filter become clogged in a substantially uniform manner. Accordingly, the two air filters have a similar service-life and can be replaced at the same time after a predeterminable maintenance period. In another embodiment of the air supply device, the second air filter is arranged in a suction channel for fresh air and surrounding air so that the ventilator fan can draw in fresh air and/or surrounding air via the first air filter. When passing through the air filter, the drawn-in air flow is homogenized, which has a noise-damping effect. If both the fresh air and the surrounding air are drawn in via the first air filter, this consequently leads to extremely low-noise operation of the air supply device, regardless of whether fresh air, surrounding air or mixed air operation is involved.

In an alternative variant of the air supply device, the first air filter is arranged in a suction channel for fresh air so that the ventilator fan can draw in fresh air via the first air filter, the suction channel for fresh air having downstream of the first air filter a recirculation opening via which the ventilator fan can draw in surrounding air. Since the surrounding air does not pass through the first air filter in this instance, the air supply device has a lower flow resistance in surrounding air or mixed air operation, which ultimately leads to more energy efficient operation of the ventilator fan. Since the surrounding air further flows through the second air filter, and it is further possible to assume a lower contaminant load of the surrounding air, this reduced filtering of the surrounding air only has an insignificant effect on the quality of the air supplied to the vehicle inner space.

In another embodiment of the air supply device, the ventilator fan has a ventilator impeller which can be rotated about a rotation axis, the first air filter being arranged in a state axially offset from the ventilator fan. Compared with a radially offset arrangement, this axially offset arrangement, depending on the specific structural space requirements, can simplify the axial air supply to the ventilator fan.

Other features and advantages of the invention will be appreciated from the following description of preferred embodiments, with reference to the drawings, in which:

- Figure 1 is a schematic cross-section through an air supply device according to the invention in accordance with a first embodiment;

- Figure 2 is a schematic cross-section through an air supply device according to the invention in accordance with a second embodiment; and

- Figure 3 is a schematic cross-section through an air supply device according to the invention in accordance with a third embodiment.

Figures 1 to 3 each show an air supply device 10 for a vehicle air conditioning system 12 which is also referred to as an HVAC unit and which allows ventilation, heating and air conditioning of a vehicle inner space.

The air supply device 10 may optionally be constructed as a completely pre-assembled unit and comprises a ventilator fan 14 which can draw in air 16, 18 and supply it to the vehicle air conditioning system 12, a first air filter 20, which is arranged upstream of the ventilator fan 14 and which is constructed as a particulate filter, and a second air filter 22, which is arranged downstream of the ventilator fan 14 and is constructed as a dust filter.

In place of the vehicle air conditioning system 12 the Figures illustrate only an evaporator 24 which is arranged in an air channel 26 of the air supply device 10 downstream of the second air filter 22. The general structure and the operating principle of vehicle air conditioning systems 12 are already generally known from the prior art, for which reason more detailed reference will not be made to this below.

The ventilator fan 14 of the air supply device 10 comprises a ventilator motor 28 and a ventilator impeller 30 which is driven thereby and can be rotated about a rotation axis A and which, for reasons of service-life, is produced from metal, in particular from copper. When the ventilator impeller 30 is rotated, the air 16, 18 is axially drawn in by the ventilator fan 14 and blown radially into the air channel 26.

In order to prevent damage to the ventilator impeller 30 for example, by sand particles which strike the ventilator impeller 30 when the air 16, 18 is drawn in, the first air filter 20 which is constructed as a particulate filter, is arranged upstream of the ventilator fan 14 and has a pore size of a maximum of 0.5 mm, preferably a maximum of 0.2 mm.

According to Figures 1 to 3, the first air filter 20 is a fabric filter having a mesh width of a maximum of 0.1 mm. The maximum mesh width of the first air filter 20 is always a compromise since it is intended, on the one hand, to be fine enough to substantially prevent damage of the ventilator impeller 30 as a result of fine sand particles, but, on the other hand, is intended to be coarse enough to prevent rapid clogging of the first air filter 20 and to ensure a satisfactory service- life.

Generally, a pore size of the first air filter 20 is substantially larger than a pore size of the second air filter 22 in order to achieve substantially identical service-lives and replacement intervals for the air filters 20, 22. The second air filter 22 is in this instance a fine dust filter, which removes, for example, pollen or soot particles from the air 16, 18 which flows through it.

Furthermore, the second air filter 22 retains fine metal particles which become disengaged from the metal ventilator impeller 30 during operation of the air supply device 10 and can lead to contact corrosion of the downstream evaporator 24 of the vehicle air conditioning system 12. The metal particles are produced, for example, by means of oxygen corrosion of the ventilator impeller 30 or an impact of (sand) particles carried in the air 16, 18 on the ventilator impeller 30.

According to the illustrated embodiments, the second air filter 22 is constructed as a so-called combi- filter which can both retain solid particles and adsorb gases. A corresponding coating for adsorption of gases, in particular an activated carbon coating, is schematically indicated in Figures 1 to 3 and given the reference numeral 32. Apart from the adsorption of harmful gaseous substances, an activated carbon coating may in particular also retain fine dust or noxious odors . In order to achieve a desired capacity for adsorption of harmful gaseous substances, a specific quantity of coating material is required. In the embodiments according to Figures 1 to 3, the necessary quantity of the coating material is divided between both air filters 20, 22. The first air filter 20 thus also receives a coating 32 for the adsorption of gases, in particular an activated carbon coating, and is consequently also constructed as a combi-filter . Accordingly, the quantity of coating material to be applied to the second air filter 22 can be reduced, which leads to a reduced flow resistance of the second air filter 22 and consequently to particularly energy- efficient operation of the air supply device 10. The adsorption of harmful gaseous substances is carried out in this instance both by the first air filter 20 and by the second air filter 22.

In a preferred construction variant of the air supply device 10, the first air filter 20 and the second air filter 22 have identical dimensions. This reduces the production complexity of the air supply device 10 since, for both air filters 20, 22 in spite of different filter media, identical filter frames or filter housings can be used.

Figure 1 shows a first embodiment of the air supply device 10, in which the first air filter 20 is arranged in a suction channel 34 for fresh air 16 and surrounding air 18 so that the ventilator fan 14 can draw in both fresh air 16 and surrounding air 18 via the first air filter 20.

In this instance, the first air filter 20 is arranged in a state radially offset from the ventilator fan 14 with respect to the rotation axis A of the ventilator impeller 30.

In contrast, Figure 2 shows an alternative, second embodiment of the air supply device 10, in which the first air filter 20 is arranged in a suction channel 36 for fresh air 16 so that the ventilator fan 14 can draw in exclusively fresh air 16 via the first air filter 20, the suction channel 36 for fresh air 16 having downstream of the first air filter 20 a recirculation opening 38 via which the ventilator fan 14 can draw in surrounding air 18.

Figure 3 shows a third embodiment of the air supply device 10, which differs from the air supply device 10 according to Figure 1 only in that the first air filter 20 is not arranged in a radially offset manner, but instead axially offset with respect to the ventilator fan 14.

This facilitates, with respect to the air supply device 10 according to Figure 1, the axial air supply to the ventilator fan 14, the respective structural space requirements generally being decisive for the specific construction of the air supply device 10.