Patent Application
20240336109
The present application claims the benefit of and priority to German Patent Application No. 10 2023 108 913.7, filed Apr. 6, 2023, the entire contents of which are incorporated herein for all purposes by reference.
The invention relates to a device for reducing noises in motor vehicle air conditioning units. The device according to the invention is provided in particular to reduce low-frequency noises below the frequency of 1000 Hz in motor vehicle air conditioning units.
For motor vehicle air conditioning units, radial fans are often used to generate the air flows necessary for vehicle ventilation. The basic structure of a radial fan comprises a fan housing having an axial air inlet opening, a fan screw, and an air outlet opening, which is usually oriented radially. Inside the fan housing there is a driven fan wheel, with which air is drawn in via the axial air inlet opening. The drawn-in air passes through the screw-shaped flow channel of the fan screw via the fan tongue to the air outlet opening. The design of the axial air inlet opening is conceivably realised simply with an axial cut-out, which is usually situated in the region of the driven fan wheel. The simple structural and functional design of the region in front of the axial air inlet and a low pressure loss downstream of the fan screw do not require any particular measures to conduct air into the fan wheel, and therefore, despite a comparatively simply designed fan tongue, only a small amount of air passes from the fan screw through the blades of the fan wheel back into the air inlet opening. However, this is different in newer motor vehicle air conditioning units, since the region of the axial air inlet is assigned more and more functions, which result in changed air flows owing to adaptations to the installation space. Reduced installation spaces mean that mechanical elements of flaps for air layering are moved closer to the air inlet and thus into the region of influence of air flows. Furthermore, the fan not only has to be supplied with fresh air or recirculation air; additional functions are required such as partial recirculation air with or without dynamic pressure compensation and devices for avoiding an overflow of fresh air into the recirculation air flow. The increased complexity of the air inlet in the intake region leads to changed characteristics of the air flowing into the fan. Air flows which lead past mechanical elements of the flaps or past the flaps themselves can cause vortices, which is associated with an undesirable generation of noise. Furthermore, higher pressure losses arise in the interior of the air conditioning unit downstream of the fan screw owing to increasingly smaller installation spaces and higher demands on the components installed there, such as filters and heat exchangers, which is likewise associated with an undesirable generation of noise.
Particular challenges are associated with the development of motor vehicle air conditioning units for electric vehicles, since air conditioning units represent a considerable source of noise in electric vehicles, owing to the lack of a combustion engine. In addition to the increased demands in terms of the acoustics of motor vehicle air conditioning units, the conditions under which the acoustic specifications must be met are becoming more and more difficult. These include, for example, higher pressure losses, for example of heat exchangers or filters with a higher efficiency. Furthermore, smaller and smaller installation spaces are available.
The said influences result in undesirable acoustic phenomena such as buzzing, for example, in particular in the frequency range below 1000 Hz. Measures such as using insulation materials cannot achieve the desired success in this frequency range. Therefore, the approach is taken of avoiding the occurrence of noise emissions in particular in the range of frequencies below 1000 Hz.
The object of the invention thus consists in proposing a device with which air flow-induced noises of a motor vehicle air conditioning unit, in particular a radial fan of a motor vehicle air conditioning unit, are reduced. It should be possible with the device to counteract the generation of noises at frequencies below 1000 Hz.
The object is achieved by subject matter having the features shown and described herein.
The device according to the invention for reducing noise is intended for motor vehicle air conditioning units in which an air flow is generated with a radial fan. A radial fan within the meaning of the invention comprises a fan housing with a spiral or screw-shaped inner contour which forms a spiral flow channel, wherein a drivable fan wheel is arranged in the interior of the fan housing. Axially in relation to the rotational axis of the fan wheel, the fan housing has an air inlet opening within an air inlet opening plane. The air inlet opening plane is understood as a plane of the fan housing in which the axial air inlet opening is formed. In the fan housing interior, a flow channel leads along the spiral inner contour via a fan tongue to an air outlet opening of the fan housing. Air is drawn in via the axial air inlet opening using the driven fan wheel. The drawn-in air is conveyed from the fan interior via the fan tongue to an air outlet opening. The air to be drawn in can be provided from a flow channel with a flow path which leads transversely over the air inlet opening plane and the axial air inlet opening. The flow channel can be supplied with fresh air from one side, wherein the opposite side is connected to a flow path for recirculation air. A recirculation air flap for changing flow paths of the air drawn in from the flow channel is pivotable at least in some areas over the axial air inlet opening. The recirculation air flap allows fresh air operation in a first position and recirculation air operation in a second position. The design of the inside of the recirculation air flap allows an air flow to be deflected in the direction of the axial air inlet opening in the first position or in the second position.
The device according to the invention for reducing noise has at least one air flow limiting element which projects laterally on the outer circumference of the axial air inlet opening vertically out of the air inlet opening plane of the fan housing. The at least one air flow limiting element has a surface which limits or blocks a flow path next to the axial air inlet opening. The arrangement of the at least one air flow limiting element next to the axial air inlet opening results in a reduction in the cross section of the flow channel leading transversely over the axial air inlet opening. The arrangement of the at least one air flow limiting element at right angles to the air inlet opening plane next to the opening cross section of the axial air inlet opening prevents air flows next to the opening cross section of the axial air inlet opening over the air inlet opening plane. Advantageously, a flow of air past the axial air inlet opening of the fan screw into a rear region of the axial air inlet opening is thereby prevented or limited, as a result of which undesirable vortices above the fan wheel or below the recirculation air flap are avoided. The drawn-in air can flow more uniformly through a front region of the axial air inlet opening into the fan wheel.
In addition to the arrangement of the at least one air flow limiting element, the device has at least two plate-shaped air guiding elements, which are arranged on the inside of the recirculation air flap in mutually spaced parallel planes at right angles to the recirculation air flap pivot axis. Owing to the plate-shaped air guiding elements arranged in parallel and spaced apart on the inside of the recirculation air flap, a recirculation of the air flowing in an upper part of the axial air inlet opening in front of the recirculation air flap above the fan wheel is reduced. The air which flows across the axial air inlet opening above the at least one air flow limiting element can thus flow more uniformly into the fan wheel, as a result of which less low-frequency noise is generated.
Furthermore, in combination with the arrangement of the at least one air flow limiting element and the at least two plate-shaped air guiding elements on the inside of the recirculation air flap, the device according to the invention has an air flow guiding element which is arranged on the fan tongue and extends radially from the fan tongue at a distance from the fan wheel into the spiral flow channel. The air flow guiding element forms a barrier in some regions between the fan wheel and the spiral flow channel. Owing to the arrangement of the air flow guiding element, the flow channel inside the radial fan is extended in the direction of the air outlet opening. In this way, the proportion of air which flows from the radial fan through the blades of the fan wheel back into the axial air inlet opening is reduced. In other words, the risk of conveyed air flowing back into the region of influence of the fan wheel is reduced. In air conditioning units which have comparatively high counterpressures, the design of the fan tongue with the air flow guiding element results in the advantageous effect that less air passes out of the screw-shaped flow channel through the blades of the fan wheel back into the axial air inlet opening. The resistance of the conveyed air is thus reduced in the direction of the air outlet opening via which the air passes into a diffuser adjoining the radial fan. The reduction of the backflow and the simultaneously improved filling of the diffuser in turn result in more favourable flow characteristics, which advantageously contribute to a reduction in the generation of noise, in particular in the low-frequency range.
An arrangement of the at least one air flow limiting element and the at least two plate-shaped air guiding elements on the inside of the recirculation air flap already results in a successful reduction in undesirable air flow noise so that a reduction in noise for motor vehicle air conditioning units can be achieved. It has also been found that, as a result of the combined arrangement of the at least one air flow limiting element, the at least two plate-shaped air guiding elements on the inside of the recirculation air flap, and the air flow guiding element on the fan tongue, a particularly good reduction in the generation of noise in the low-frequency range, i.e., at frequencies below 1000 Hz, is achieved.
The at least one air flow limiting element can be arranged in front of the recirculation air flap in the direction of flow of fresh air drawn in. In this case, the air flow limiting element is situated outside a pivot region of the recirculation air flap in a front region of the axial air inlet opening. A height of the air flow limiting element projecting vertically out of the air inlet opening plane of the fan housing can be lower than the height of the flow channel which extends transversely to the axial air inlet opening and from which the fresh air is provided. The height of the air flow limiting element projecting vertically out of the air inlet opening plane of the fan housing can be lower than the highest position of the recirculation air flap above the air inlet opening plane. In other words, the height of the at least one air flow limiting element above the air inlet opening plane is smaller than the highest position of the recirculation air flap above the air inlet opening plane. Preferably, the geometry of the at least one air flow limiting element ensures that at least some of the supplied air can flow at a distance over the air inlet opening plane next to the opening cross section of the axial air inlet opening. This portion of the air flowing past at a distance over the axial air inlet opening passes into the region of influence of the recirculation air flap. Since the at least one air flow limiting element does not extend over the entire height of the flow channel running transversely to the axial air inlet opening, the flow of the air flowing over the air inlet opening plane above the highest position of the air flow limiting element is influenced only slightly or not at all.
The at least one air flow limiting element can be designed in one part or as an integral component of the radial fan housing. In this case, the at least one air flow limiting element extends vertically out of the air inlet opening plane of the fan housing as a plate-shaped element with its surface which forms a barrier for air flows next to the opening cross section of the axial air inlet opening. The surface of the at least one air flow limiting element is preferably oriented transversely to the air flow. It can also be provided for the surface of the air flow limiting element to be slightly inclined in a direction of flow in order to allow air flows to be diverted in a desired direction.
It can also be provided for the air flow limiting element to be designed as a part of an air inlet housing in which the recirculation air flap and at least one further flap as a fresh air flap can be accommodated. The air inlet housing in the form of an independent housing part can be connected to the radial fan housing such that the air flow limiting element is situated laterally at the outer circumference of the axial air inlet opening.
According to a preferred embodiment of the device according to the invention, two air flow limiting elements are arranged laterally opposite one another on the outer circumference of the axial air inlet opening, wherein the air flow limiting elements arranged opposite one another can have sloping sides leading away from one another on their facing narrow sides so that the opening cross section of the flow channel leading transversely over the axial air inlet opening is enlarged between the opposing narrow sides of the air flow limiting elements in the vertical direction leading away from the air inlet opening plane.
According to a further advantageous embodiment of the device according to the invention, that a plurality of the plate-shaped air guiding elements can be arranged on the inside of the recirculation air flap, the plate-shaped air guiding elements being evenly spaced apart. A uniform air flow and deflection into the axial air inlet opening can thus be brought about in a simple manner.
The plate-shaped air guiding elements can be designed as integral components of the recirculation air flap. In this case, the plate-shaped air guiding elements can have a right-angled triangle shape.
The air flow guiding element can have a recess tapering in the direction of the air outlet opening. According to one embodiment, the air flow guiding element can be designed as an integral component of the radial fan housing in the form of an extension of the fan tongue. According to a further embodiment, the air flow guiding element can be formed in two parts from an upper air flow guiding element and a lower air flow guiding element, the upper air flow guiding element and the lower air flow guiding element being arranged axially opposite one another. The opposing elements then form the geometry of the recess together. The upper air flow guiding element and/or the lower air flow guiding element can have a tip pointing into the spiral flow channel with a radius which corresponds to 0.25 times to 0.75 times the radius of the fan tongue. The radius at the tip of the air flow guiding elements is thus smaller than the radius of the fan tongue.
Furthermore, it can be provided for the upper air flow guiding element and/or the lower air flow guiding element on the fan tongue to have an axial height which corresponds to 0.35 times to 0.75 times the axial height of the fan wheel. In this case, an axial height of the tip of the upper air flow guiding element and/or of the lower air flow guiding element pointing into the spiral flow channel can correspond to a maximum of 0.7 times the axial height of the upper air flow guiding element and/or of the lower air flow guiding element at the fan tongue. It can also be provided for a contour of the tip of the upper air flow guiding element and/or of the lower air flow guiding element to have no radius.
The axial height of the upper air flow guiding element and/or of the lower air flow guiding element increases from the tip in the direction of flow. The radial width of the upper air flow guiding element and/or of the lower air flow guiding element can also increase in the direction of flow. The increase in the width can be limited to the side of the relevant air flow guiding element facing the spiral flow channel. The surfaces of the upper air flow guiding element and/or of the lower air flow guiding element can have a concave or convex contour oriented in the direction of flow.
The air flow guiding element or the upper air flow guiding element and/or the lower air flow guiding element can have a wrap angle related to the fan wheel in the range of 47° and 67°.
Further details, features and advantages of embodiments of the invention can be found in the description of exemplary embodiments below with reference to the associated drawings. In the drawings:
Recurring features are labelled with the same reference signs in the figures.
The further flap 9 is arranged pivotably inside the flow channel for fresh air.
At the tip 13.1.1, the upper air flow guiding element 13.1 has a radius D which corresponds to 0.25 times to 0.75 times the radius formed on the side 13.1.2 facing the fan tongue 6. The radius E corresponds to the radius at the fan tongue 6. The radius D at the tip 13.1.1 is thus smaller than the radius of the fan tongue 6.
The upper air flow guiding element 13.1 has a wrap angle C related to the fan wheel 3 in the range of 47° and 67°.
The radial width of the upper air flow guiding element 13.1 increases in the direction of flow, i.e., from the tip 13.1.1 in the direction of the side 13.1.2 facing the fan tongue 6.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2023 108 913.7 | Apr 2023 | DE | national |
