Air conditioning device for a motor vehicle

Abstract

Air conditioning device for a motor vehicle, comprising an evaporator (10) designed as an air / refrigerant heat exchanger, which is internally permeable with refrigerant and externally with an airflow (14) of a predetermined airflow rate, comprising two evaporator sections (11, 12) arranged adjacent to one another and sequentially permeable by the same airflow (14), each having a plurality of horizontally extending, parallel fins (24, 26) around which the airflow can flow and which are arranged at a distance (Δ) from one another which, measured in the direction of the airflow, is 10 mm to 30 mm, preferably 10 mm to 20 mm, particularly preferably 12 mm to 17 mm, wherein in the free space (16) resulting from the distance (Δ) between the evaporator sections (11, 12) a12) a frame- or semi-frame-shaped insulating layer (18) made of a metal foam with a thermal conductivity of less than 200 W / (m*K) is arranged at the edges.

Description

[0001] The invention relates to an air conditioning device for a motor vehicle.

[0002] The central subject matter of DE 10 2014 207 278 A1 is an air conditioning device for motor vehicles with a two-part evaporator. The two-part evaporator has two evaporator sections connected in series on the air side. This means that both evaporator sections are successively subjected to the same airflow, which is thereby cooled and dehumidified before being blown into the passenger compartment of the vehicle as air conditioning airflow. The special feature of the air conditioning device disclosed in the aforementioned document is that the evaporator section on the airflow outlet side operates at temperatures below 0°C, while the evaporator section on the airflow inlet side operates at temperatures above 0°C. As a result, the airflow undergoes pre-cooling as it passes through the airflow inlet-side evaporator section, hereinafter referred to as the first evaporator section, which is associated with significant dehumidification.As the airflow passes through the evaporator section on the outlet side, referred to below as the second evaporator section, it experiences a further, significant cooling below the freezing point of water. However, the risk of ice formation on the second evaporator section is considerably reduced by the dehumidification that occurred previously in the first evaporator section. This leads to a considerable delay in the inevitable clogging of the second evaporator section with ice. Consequently, the number and frequency of so-called defrosting intervals, during which the second evaporator section is operated at temperatures above 0°C, resulting in temporary discomfort in the passenger compartment, can be significantly reduced compared to air conditioning systems with only one evaporator section.

[0003] Especially at high humidity, dehumidification in the first evaporator section is associated with the formation of considerable amounts of condensation. If this liquid water were to come into contact with the surface of the second evaporator section, which has cooled below 0°C, it would freeze there, quickly leading to clogging of the second evaporator section. Three pathways for water transport from the first to the second evaporator section are of practical importance: firstly, large droplets running down the back of the first evaporator section can contact the front of the second evaporator section. Secondly, it is conceivable that running water could accumulate in an open channel or tray between the two evaporator sections. Finally, there is a risk that water droplets on the first evaporator section could be carried by the airflow to the second evaporator section.This can of course be taken into account by establishing a considerable distance between the first and second evaporator sections. This approach is implemented, for example, in DE 697 29 836 T2. However, given the notoriously critical space constraints in automotive engineering, this is not a suitable solution.

[0004] WO 2007 / 037 670 A1 and US 2014 / 0262 181 A1 disclose heat exchanger sections connected in series on the air side, which are mechanically and thermally connected to each other by common fins extending from the air-inlet front surface of the first heat exchanger section to the air-outlet rear surface of the second heat exchanger section. This thermal coupling makes it impossible—even hypothetically assuming the use of such a heat exchanger as an evaporator—to effectively implement the concept of pre-dehumidification followed by extreme cooling described above. Furthermore, the transport of condensate from the first to the second heat exchanger section is not prevented, as the water can flow across the fins from one section to the other. A similar situation exists with DE 600 31 932 T2.

[0005] German patent DE 10 2007 056 473 A1 discloses an evaporator connected to a thermal storage unit and designed as an air / refrigerant heat exchanger. A similar aspect is addressed in DE 10 2006 011 327 A1.

[0006] US Patent 2012 / 0 103 582 A1 discloses a heat exchanger with two vertical tubes, between which horizontal transverse tubes extend, between which in turn microstructured fins are arranged to optimize heat transfer between a fluid flowing in the transverse tubes and air flowing perpendicularly through the heat exchanger.

[0007] A similar concept, providing for different microstructures, is disclosed in US 2009 / 0 308 585 A1.

[0008] US patent 2014 / 0 144 605 A1 discloses a heat exchanger that is sealed in a housing by means of a specially shaped gasket. Similar aspects are addressed in DE 102 42 899 A1.

[0009] DE 690 19 633 T2 discloses an air / refrigerant heat exchanger used as a condenser in a motor vehicle air conditioning system, which has two condenser sections arranged one behind the other in the direction of airflow and through which the same airflow flows sequentially, and which are arranged at a distance of approximately 10 mm from each other in the direction of airflow. The icing problem described above does not occur with the condenser, which is supplied with hot, gaseous refrigerant.

[0010] The object of the present invention is to propose measures that prevent or at least reduce condensate transport from the first to the second evaporator section, taking into account tight installation space restrictions.

[0011] This problem is solved by a device according to claim 1, i.e.An air conditioning device for a motor vehicle, comprising an evaporator designed as an air / refrigerant heat exchanger, which is internally permeable with refrigerant and externally with an airflow of predetermined airflow intensity, comprising two evaporator sections arranged adjacent to each other and traversed successively by the same airflow, each having a plurality of horizontally extending, parallel fins around which the airflow can flow and which are arranged at a distance from each other which, measured in the direction of the airflow, is 10 mm to 30 mm, preferably 10 mm to 20 mm, particularly preferably 12 mm to 17 mm, wherein in the free space resulting from the distance between the evaporator sections a frame- or partial-frame-shaped insulating layer made of a metal foam with a thermal conductivity of less than 200 W / (m*K) is arranged, connecting the evaporator sections at their edges.

[0012] Preferred embodiments of the invention are the subject of the dependent patent claims.

[0013] The specific selection of the distance values ​​according to the invention between the two evaporator sections represents a technically and economically sound compromise between the requirement of a sufficiently large distance to prevent significant water transport between the two evaporator sections on the one hand, and the notoriously limited installation space on the other. Surprisingly, it has been found that the aforementioned specific distance values ​​are already sufficient to almost completely prevent droplet flight from the first to the second evaporator section at the airflow rates typically used in automotive air conditioning systems. At the same time, the distances according to the invention are also sufficient to ensure the drainage of condensate from the first evaporator section without contact with the second evaporator section.

[0014] Further features of the invention, which will be discussed in more detail below, support the prevention of liquid transport between the evaporator sections, which makes it possible to fully utilize the spacing interval proposed according to the invention towards its lower limit.

[0015] According to the invention, a frame- or semi-frame-shaped insulating layer is arranged in the space between the evaporator sections, connecting them at their edges. For stability reasons, it will generally be necessary for the two evaporator sections to be mechanically connected. Such mechanical connections carry the risk of creating thermal bridges. Such a thermal bridge could result in certain areas of the first evaporator section being locally excessively cooled. Consequently, any condensate forming in these areas would also be cooled, which could lead to freezing on the first evaporator section or to particularly rapid freezing of the pre-cooled water upon contact with the second evaporator section.The introduction of the aforementioned insulating layer, which according to the invention is made of a metal foam with poor thermal conductivity, in particular with a thermal conductivity of less than 200 W / (m*K), counteracts the formation of such thermal bridges. A partial frame-like design has proven particularly advantageous, as it does not impede water drainage in the base area of ​​the two evaporator sections.

[0016] Additionally, it can be provided that connecting webs are arranged at specific points in the free space between the evaporator sections. These webs provide additional stabilization. With a suitable, small cross-section, e.g., no more than 5 mm, this can be achieved. 2For each web, the thermal bridging effect can be limited to a tolerable level. The choice of material for the webs, preferably made of a rigid, poorly thermally conductive plastic material, especially with a thermal conductivity of less than 200 W / (m*K), can also be used as a measure to reduce the thermal bridging effect.

[0017] According to another, additionally usable approach, a further development of the invention provides that a grid or mesh is arranged in the free space between the evaporator sections created by the spacing. This grid or mesh serves to collect airborne droplets, which can then quickly run off its surface. The grid or mesh is preferably arranged in a region of the free space where the cooling effect of the second evaporator section does not yet ensure sustained temperatures below 0°C, so that airborne droplets cannot freeze onto the grid or mesh.

[0018] According to a further feature of the invention, the two evaporator sections each have, as is quite common and known to those skilled in the art, a plurality of horizontally extending, parallel fins around which the airflow flows. These fins serve to increase the interaction surface with the airflow and are common in air / refrigerant heat exchangers.

[0019] In a preferred embodiment of the invention, the fins of the airflow-inlet-side evaporator section each have a first fin section aligned parallel to the airflow direction and arranged on the airflow-inlet side, and a second fin section angled downwards and arranged on the airflow-outlet side. In other words, the fins are bent downwards in their rear region, so that the airflow passing through the first evaporator section is deflected downwards, the angle of which depends on the deflection angle. In this way, any entrained condensate droplets are also blown obliquely downwards into the space between the evaporator sections. This reduces their horizontal trajectory, thereby reducing the risk of them reaching the second evaporator section.

[0020] With regard to the horizontal extent of the fins parallel to the respective evaporator section, a straight path can be chosen. However, with regard to reducing liquid transfer, it has surprisingly proven advantageous if the fins of at least one evaporator section, preferably the first evaporator section, have a sinusoidal wave pattern in their horizontal direction parallel to the respective evaporator section.

[0021] Preferably, the vertical distance between the fins of the airflow-inlet evaporator section is smaller than the vertical distance between the fins of the airflow-outlet evaporator section. This ensures particularly intensive interaction between the airflow and the first evaporator section, resulting in intensive pre-cooling and, in particular, maximum dehumidification of the airflow. Conversely, the fin spacing in the second evaporator section is chosen to be larger, so that the spaces there are less likely to become clogged with any ice that may have formed. Both of these measures contribute to reducing the number and frequency of required defrosting intervals for the second evaporator section.

[0022] Preferably, the fins of at least one evaporator section have vertical openings with air guide vanes inclined to the respective fin plane. Such air guide vanes are known to those skilled in the art as louvers. Surprisingly, it has proven particularly efficient with regard to preventing liquid transfer if the air guide vanes (louvers) have an angle of inclination of 20° to 40°, preferably 25° to 30°, and most preferably 28° to 32°.

[0023] Regarding the refrigerant-side connection of the two evaporator sections, various configurations are conceivable. In one embodiment of the invention, the evaporator sections are connected in series with respect to the refrigerant.

[0024] Further features and advantages of the invention will become apparent from the following detailed description and the drawings.

[0025] They show: Fig. 1: a schematic representation of an arrangement of two evaporator sections of an air conditioning device not according to the invention, Fig. 2: a schematic representation of an arrangement of two evaporator sections of an air conditioning device according to the invention, Fig. 3: a schematic representation of an arrangement of two evaporator sections of an air conditioning device not according to the invention, Fig. 4: a schematic representation of an arrangement of two evaporator sections of an air conditioning device not according to the invention, Fig. 5: a schematic representation of a first preferred embodiment of the fins of the first evaporator section, Fig. 6: a schematic representation of a second preferred embodiment of the fins of the first evaporator section, Fig. 7: a schematic representation of a preferred embodiment of the fins of both evaporator sections.

[0026] Identical reference symbols in the figures indicate identical or analogous elements.

[0027] Fig. Figure 1 shows a highly schematic representation of an evaporator 10 of an air conditioning system for a motor vehicle (not shown). The evaporator 10 comprises two evaporator sections 11 and 12, which are internally permeated by a refrigerant flow (not shown) and externally by a shared airflow 14. During operation of the air conditioning system, the airflow 14 first flows through the first evaporator section 11 and then through the second evaporator section 12, which is arranged parallel to the first evaporator section 11. Accordingly, the first evaporator section 11 is also referred to here as the airflow-inlet evaporator section, and the second evaporator section 12 as the airflow-outlet evaporator section. On the refrigerant side, both evaporator sections 11 and 12 can be connected in series or controlled independently of each other.Each of the evaporator sections 11, 12 is designed as an air / refrigerant heat exchanger. The airflow 14 passing through the evaporator 10 undergoes pre-cooling and dehumidification as it passes through the first evaporator section 11, and further cooling as it passes through the second evaporator section 12. In the preferred control configuration of the air conditioning device, the second evaporator section 12 is operated at temperatures below 0°C, while the first evaporator section 11 is operated at temperatures above 0°C. The evaporator sections 11, 12 are spaced apart from each other at a distance Δ, such that a free space 16 of a corresponding width extends between them. The distance Δ, or the width of the free space 16, is preferably approximately 15 mm.

[0028] At the in Fig. In the embodiment shown in Figure 2, which is to be understood as an exploded view, a partially frame-shaped insulating layer 18 is inserted into the free space 16. In the final assembly state, the insulating layer 18 rests against the edges of the facing surfaces of the evaporator sections 11, 12. The insulating layer has a thickness that corresponds to the width of the free space 16, or the distance Δ between the two evaporator sections 11, 12. In the embodiment of Fig. 2. The insulating layer surrounds the opposing evaporator surfaces only laterally and above, so that the space 16 is open at the bottom to ensure unobstructed drainage of condensate. Of course, it is also possible to design the insulating layer 16 as a full frame and to provide suitable drainage channels.

[0029] In the evaporator arrangement of Fig. 3. The two evaporator sections 11, 12 are mechanically connected to each other via narrow connecting webs 20. Both the dimensions of the connecting webs 20 and their material are preferably selected such that the formation of thermal bridges between the evaporator sections 11, 12 is largely prevented.

[0030] In the evaporator arrangement of Fig. 4 A grid or mesh 22 is inserted into the free space 16, which extends parallel to the evaporator sections 11, 12 and catches condensate droplets that are carried along with the airflow 14 from the first evaporator section 11 and thus prevents them from passing to the second evaporator section.

[0031] As explained at the beginning, the evaporator sections 11 and 12 are designed as air / refrigerant heat exchangers, which are generally known to those skilled in the art. Such air / refrigerant heat exchangers typically have a finned structure to increase the interaction surface with the airflow 14. Fig. Figures 5-7 show preferred lamella shapes ( Fig. 5 and Fig. 6) or a preferred lamella configuration ( Fig. 7).

[0032] Fig. Figure 5 shows a highly schematic representation of two adjacent lamellae 24 of the airflow-inlet side of the evaporator section 11. The lamellae 24 essentially consist of an airflow-inlet lamella section 241 and an airflow-outlet lamella section 242. The former will also be referred to here as the front lamella section 241 and the latter as the rear lamella section 242. The front lamella section 241 is oriented essentially parallel to the direction of airflow 14. In contrast, the rear lamella section 242 is angled slightly downwards. In the illustrated embodiment, the angle is approximately 30°. This leads to a deflection of the airflow 14 in the rear lamella area, so that the air flows obliquely downwards into the free space 16 between the evaporator sections 11 and 12, thereby reducing the travel distance of any entrained condensate droplets.

[0033] In the embodiment of Fig. 6. The louvers 24 have additional vertical openings 243 in their front louver section 241, which are reinforced with air guide vanes, so-called louvers 244. This design serves to guide the airflow 14 in a wave-like manner in order to increase the interaction area with the louvers 24.

[0034] Fig. Figure 7 shows a preferred configuration of the fins 24 of the first evaporator section 11 and the fins 26 of the second evaporator section 12. Regardless of the specific shape of the fins 24, 26, the following applies: Fig. Figure 7 clearly shows that the vertical fin spacing between the fins 24 of the airflow inlet-side evaporator section 11 is smaller than the vertical fin spacing of the fins 26 of the airflow outlet-side evaporator section. This delays the clogging of the airflow outlet-side evaporator section 12 due to ice formation between the fins 26.

[0035] Of course, the embodiments discussed in the specific description and shown in the figures represent only illustrative examples of the present invention. In light of this disclosure, a wide range of variations is available to those skilled in the art. In particular, they will recognize that the embodiments shown in the figures represent different measures that can be used individually or in combination. Reference symbol list 10 evaporators 11 First evaporator section (airflow inlet side) 12 Second evaporator section (airflow outlet side) 14 Airflow 16 Free space between 11 and 12 18 Insulating layer 20 Bridge 22 Net or grid 24 lamellae of 11 241 Front louver section of 24 (airflow inlet side) 242 Rear louver section of 24 (airflow outlet side) 243 Breakthrough in 241 244 Air guide flag (Louver) 26 lamellae of 12 Δ distance

Claims

[1] Air conditioning device for a motor vehicle, comprising an evaporator (10) designed as an air / refrigerant heat exchanger, which is internally permeable with refrigerant and externally with an airflow (14) of a predetermined airflow rate, comprising two evaporator sections (11, 12) arranged adjacent to one another and permeable to the same airflow (14) in succession, each having a plurality of horizontally extending, parallel fins (24, 26) around which the airflow can flow and which are arranged at a distance (Δ) from one another which, measured in the direction of the airflow, is 10 mm to 30 mm, preferably 10 mm to 20 mm, particularly preferably 12 mm to 17 mm, wherein in the free space (16) resulting from the distance (Δ) between the evaporator sections (11, 12) a12) a frame- or semi-frame-shaped insulating layer (18) made of a metal foam with a thermal conductivity of less than 200 W / (m*K) is arranged at the edges. [2] Air conditioning device according to any one of the preceding claims, characterized by , that in the free space (16) resulting from the distance (Δ) between the evaporator sections (11, 12) the evaporator sections (11, 12) are arranged ribs (20) connecting them at points. [3] Air conditioning device according to claim 2, characterized by , that the struts (20) are made of a rigid plastic material with a thermal conductivity of less than 200 W / (m*K). [4] Air conditioning device according to any one of the preceding claims, characterized by , that a grid or mesh (22) is arranged in the free space (16) between the evaporator sections (11, 12) resulting from the distance (Δ). [5] Air conditioning device according to any one of the preceding claims, characterized by , that the fins (24) of the airflow inlet-side evaporator section (11) each have a first fin section (241) aligned parallel to the airflow direction and arranged on the airflow inlet side and a second fin section (242) angled downwards and arranged on the airflow outlet side. [6] Air conditioning device according to any one of the preceding claims, characterized by that the fins of at least one evaporator section run in a sinusoidally wavy pattern parallel to the respective evaporator section in their horizontal extension direction. [7] Air conditioning device according to any one of the preceding claims, characterized by , that the distance between the fins (24) of the airflow inlet side evaporator section (11) is smaller than the distance between the fins (26) of the airflow outlet side evaporator section (12). [8] Air conditioning device according to any one of the preceding claims, characterized by , that the fins (24) of at least one evaporator section (11) have vertical openings (243) with air guide vanes (244) inclined to the respective fin plane. [9] Air conditioning device according to claim 8, characterized by that the air guide vanes (244) have an angle of attack of 20° to 40°, preferably 25° to 35°, particularly preferably 28° to 32°. [10] Air conditioning device according to any one of the preceding claims, characterized by , that the evaporator sections (11, 12) are connected in series in terms of refrigerant technology.

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