Patent Publication Number: US-2020282799-A1

Title: Ultra-low profile hvac apparatus for a vehicle

Description:
This application represents the national stage entry of PCT International Application No. PCT/IT2017/000249 filed Nov. 10, 2017, which is hereby incorporated herein by reference for all purposes. 
    
    
     The present disclosure relates to an ultra-low profile HVAC apparatus for a vehicle. 
     HVAC apparatuses having a large profile height usually provide more cooling power and/or a higher energy efficiency than HVAC apparatuses with a low profile height. However, the usage of a HVAC apparatus with a large profile height leads to a significant reduced valuable head height, head room and visibility from the cabin. It is also undesired to raise the roof height in order to avoid building/structure clearances issues and enlarging the vehicles aerodynamic drag. On the other hand, sufficient cooling power as well as enough fan capacity is required for cooling the vehicle&#39;s entire driver cabin and dealing with long air ducts in the vehicle. This is a demand which leads away from an ultra-low profile design. Thus, common HVAC apparatuses for mobile applications, in particular for cooling a vehicle&#39;s driver cabin, have a minimum profile height of about 120 to 180 mm. 
     Therefore, there is a strong desire to provide a HVAC apparatus having a lower profile height while providing a high efficiency as well as sufficient cooling power for cooling a vehicle&#39;s driver cabin. 
     It is the object of the present disclosure to provide a HVAC apparatus with sufficient cooling power for cooling a vehicle&#39;s driver cabin, the HVAC apparatus having a high efficiency and an ultra-low profile height. These objects are solved by the features of the independent claim. Advantageous embodiments arise from the dependent claims. 
     The described HVAC apparatus for a vehicle has a fan unit, a heat exchanger unit, and a plate-shaped housing accommodating the fan unit and the heat exchanger unit. The fan unit has a plurality of axial impellers driven by motors mounted in their centers. The heat exchanger unit forms an air duct receiving air from the fan unit. The axial impellers can have a rotational axis substantially perpendicular to the fan unit&#39;s suction direction. The fan unit&#39;s suction direction can be defined by the normal direction of the plate-shaped housing. The plate-shaped housing can be, for example, a part of a vehicle&#39;s roof construction of a separate casing small enough to fit into a vehicle&#39;s roof construction. Thus, the fan unit sucks in air from the cabin&#39;s interior, resulting in a fan unit&#39;s suction direction perpendicular to the rotational axis of the axial impellers. Further, a casing of the fan unit, for example, a support construction for fixation of the axial impellers, can be viewed as part of the plate-shaped housing. The suction air can be fresh air, cabin air, or a mixture of both. Inside of the plate-shaped housing, the suction air can be blown from the fan unit&#39;s axial impellers directly into the heat exchanger unit. This mechanical configuration allows for low profile height layouts because all relevant components of the HVAC apparatus can be arranged side by side and the fan unit&#39;s relevant profile height is also low due to the usage of a plurality of axial impellers. Further, the HVAC apparatus can be integrated in a vehicle&#39;s roof structure without thickening the roof structure. 
     Each of the plurality of axial impellers may be allocated to an outlet guide vane. Using an outlet guide vane with each of the axial impellers can improve the homogeneity of the provided air stream and can also allow a higher pressure drop in the HVAC apparatus. 
     The heat exchanger unit may comprise a heat exchanger having at least two different cooling regions with different working temperatures through which received air flows consecutively, and wherein the different working temperatures are controlled by a temperature control unit. The temperature control unit can comprise the necessary control logic for operation of the HVAC apparatus as well as components of a usual cooling circuit. The term “control logic” can refer to a mechanical object that executes a feedback control based on physical values, e.g., pressure and/or temperature. The temperature control unit can be accommodated in the plate-shaped housing. The temperature control unit can control the different working temperatures individually. In this regard, the term “individually” can mean that the working temperatures for each cooling region can change due to an (automatic) regulatory cycle for maintaining the efficiency of the heat transfer process independently from the working temperatures in other cooling regions. Providing a heat exchanger having at least two different cooling regions with different working temperatures, to which received air flows consecutively, provides for an optimized equilibrium temperature gradient between the air stream inside of the heat exchanger and a heat transfer surface of the heat exchanger. The optimized equilibrium temperature gradient increases the provided energy efficiency at a given cooling power. The optimized equilibrium temperature gradient can be a constant value over all cooling regions. Thus, the overall dimensions of the provided HVAC apparatus can be reduced while maintaining the delivered cooling power and a high efficiency. The working temperatures of the different working regions are a measure for the equilibrium temperature gradient. For example, the working temperature of a specific cooling region can be the equilibrium temperature of the heat transfer surface at a specific surface point in this cooling region. The different working temperatures decrease from cooling region to cooling region, wherein the cooling region that is initially in contact with the air stream has the highest working temperature. The provided optimization of the equilibrium temperature gradient throughout the complete heat exchanger contributes to heat exchanger layouts having an ultra-thin profile height of about 40 mm while maintaining the delivered cooling power at a high efficiency. 
     The temperature control unit may comprise at least two thermal expansion valves with different refrigerant flow rates at a given condition. The term “given condition” can refer to a sensed temperature that is used for controlling the opening/closing of the thermal expansion valve in a self-regulatory manner. In this way, different working temperatures in different cooling regions of the heat exchanger can be controlled and optimized in an easy way. Higher refrigerant flow rates provided by a thermal expansion valve lead to a reduced working temperature in the cooling region of the heat exchanger connected to this thermal expansion valve compared to another cooling region of the heat exchanger that is connected to another thermal expansion valve providing a lower refrigerant flow rate. The thermal expansion valves execute an automatic temperature driven regulatory cycle. The regulatory cycle can be modified by mechanically adjusting the valve&#39;s characteristic. This can be advantageous, for example, when using the HVAC apparatus in climate zones that have different ambient temperatures. 
     The temperature control unit may comprise at least one thermal expansion valve with a common refrigerant inlet and at least two refrigerant outlets, providing different refrigerant flow rates to the at least two different cooling regions. Similar to the previously described usage of at least two thermal expansion valves with different refrigerant flow rates at a given condition, at least some of these thermal expansion valves can be unified for simplifying the mechanical setup of the HVAC apparatus. 
     Further, the temperature control unit may comprise at least two heat pipes with different evaporation points, wherein the at least two heat pipes are connected to different cooling regions of the heat exchanger. Heat pipes are an alternative possibility for individually adjusting the working temperatures of different cooling regions for providing an optimized equilibrium temperature gradient between the surface of the heat exchanger and the air stream. The different evaporation points fulfill the same task as the different flow rates of the thermal expansion valves. However, it is not possible to modify the evaporation points for adapting the HVAC apparatus. 
     In this regard, the at least two heat pipes may be connected to a common cold reservoir. The cold reservoir can be provided by a single simple cooling circuit of the HVAC apparatus that may be at least partly integrated in the temperature control unit. 
     The at least two cooling regions may be thermally isolated from each other. A thermal isolation between the at least two cooling regions can stabilize the equilibrium temperature gradient profile within the heat exchanger because the different cooling regions do not directly interact with each other. This reduces the required control logic and simplifies the implementation of different cooling outputs of the HVAC apparatus while maintaining the desired high efficiency. 
     On the other hand, it may be possible to thermally connect the at least two cooling regions to each other which provides a more compact HVAC apparatus because the size of the heat exchanger can be further reduced. 
     An overall profile height of the HVAC apparatus may be less than or equal to 80 mm, preferably less than or equal to 60 mm, particularly less than or equal to 50 mm. The overall profile height of the HVAC apparatus is substantially defined by the profile height of the plate-shaped housing. A smaller overall profile height simplifies the integration of the HVAC apparatus in a vehicle&#39;s roof construction without thickening the roof. 
    
    
     
       The disclosure will be explained in more detail with reference to the appended drawings. In the drawings, the same merits designate identical or similar components. The actual quantity of connections and different cooling regions depicted in the figures can be freely adapted and the described embodiments are intended for understanding the basic principle of the present disclosure without restricting the number of cooling regions to a specific depicted case. 
         FIG. 1  shows a schematic top view of an unclaimed open HVAC apparatus; 
         FIG. 2  shows a schematic open side view of a heat exchanger and a connected temperature control unit; 
         FIG. 3  shows a second schematic open side view of a heat exchanger and a connected temperature control unit; 
         FIG. 4  shows a third schematic open side view of a heat exchanger and a connected temperature control unit; 
         FIG. 5  shows a schematic illustration of a vehicle using an ultra-low profile HVAC apparatus; 
         FIG. 6  shows a second schematic top view of an open HVAC apparatus; and 
         FIG. 7  shows a schematic bottom view of a HVAC apparatus. 
     
    
    
       FIG. 1  shows a schematic open top view of an unclaimed open HVAC apparatus  10 . The unclaimed HVAC apparatus  10  shown in  FIG. 1  is used to illustrate some basic aspects that are also relevant for the present disclosure. The HVAC apparatus  10  has a fan unit  14 , a heat exchanger unit  20 , and a temperature control unit  32 . The fan unit  14 , the heat exchanger unit  20 , and the temperature control unit  32  are all accommodated within a plate-shaped housing  34 . The fan unit  14  consists of an annular impeller  16  and a motor  18  which are arranged in the center of the annular impeller  16 . The annular impeller has a plurality of blades that are not shown. The heat exchanger unit  20  has two separate substantially cuboid parts that are mounted near opposite rims of the plate-shaped housing  34 . The space between the two separate substantially cuboid parts of the heat exchanger unit  20  is a central recess  56 . The fan unit  14  is mounted in the central recess  56 . The fan unit  14  generates an air stream that is equalized distributed by a plurality of air baffles  68  located in the remaining gap between the fan unit  14  and the heat exchanger unit  20 . Only two air baffles  68  are shown in the figure for simplicity reasons. The air stream enters air ducts  24  inside of the heat exchanger unit  20 . The air ducts  24  may be for example formed by heat transfer fins  60  that substantially define the internal surface of the heat exchanger unit  20 . The air stream subsequently leaves the heat exchanger unit  20  as a conditioned air stream  58  in the shown directions. 
     The heat exchanger unit  20  is connected with the temperature control unit  32 , wherein the connections provide at least two different working temperatures in different cooling regions of the heat exchanger unit  20  as will be explained later on. In the figure, the left part of the heat exchanger unit  20  has two connections with the temperature control unit  32 . The heat transfer fins  60  are thermally connecting the resulting two different cooling regions. These different cooling regions are maintained at the desired different working temperatures via the connections by the temperature control unit  32 . The connections can be formed for example by evaporators or heat pipes as will be explained later. Quite similar, the right part of the heat transfer unit  20  has three connections with the temperature control unit  32  and this part of the heat exchanger unit  20  has three different cooling regions that are maintained at three different working temperatures via the three connections to the temperature control unit  32 . The heat transfer fins  60  in these three different cooling regions of the right part of the heat transfer unit  20  are thermally isolated from each other which is indicated by the gaps between the different parts of the heat transfer fins  60 . 
     Besides the cooling function of the heat transfer unit  20 , it is possible to implement a heating function by adding an additional heating element. Such a heating element can be used to establish a so called “reheating mode” for reducing the amount of water vapor in the conditioned air. 
       FIG. 2  shows a schematic open side view of a heat exchanger  22  and a connected temperature control unit  32 . The heat exchanger  22  of the heat exchanger unit  20  has three parts providing a first cooling region  26 , a second cooling region  28 , and a third cooling region  30 . The first cooling region  26 , the second cooling region  28 , and the third cooling region  30  are connected to the temperature control unit  32 . The temperature control unit  32  comprises inter alia a first thermal expansion valve  36 , a second thermal expansion valve  38 , and a third thermal expansion valve  40 . The first thermal expansion valve  36  controls the refrigerant flow to the first cooling region  26  of the heat exchanger  22 . The second thermal expansion valve  38  controls the refrigerant flow to the second cooling region  28  of the heat exchanger  22 . The third thermal expansion valve  40  controls the refrigerant flow to the third cooling region  30  of the heat exchanger  22 . An air stream  64  provided by the fan unit  14  enters the heat exchanger  22  at its right side and leaves the heat exchanger at the left side as conditioned air  58  after subsequently flowing through the first cooling region  26 , the second cooling region  28 , and the third cooling region  30 . Thus, the air stream  64  initially enters the first cooling region  26 . The connection of the first cooling region  26  to the temperature control unit  32  is via the first thermal expansion valve  36 , which controls the amount of refrigerant flowing to this part of the heat exchanger  22 . The connection itself is a line that acts as an evaporator for the refrigerant flowing through the first thermal expansion valve  36 . 
     A temperature gradient between the air stream  64  and the surface of the heat exchanger  22  in the first cooling region  26  substantially depends on the refrigerant flow rate through the first thermal expansion valve  36 . Generally, the temperature of the air stream  64  diminishes from the right to the left as indicated by a temperature curve  62  depicted in the part of the heat exchanger  22  that corresponds to the first cooling region  26 . The temperature gradient between the air stream  64  and the surface of the heat exchanger  22  is kept almost constant. The situation is quite similar for the second cooling region  28  that is fed with refrigerant by the second thermal expansion valve  38  and the third cooling region  30  that is fed with refrigerant by the third thermal expansion valve  40 . 
     The slightly cooled air stream  64  enters the second cooling region  28  after leaving the first cooling region  26 . The second thermal expansion valve  38  provides different refrigerant flow rate compared to the first thermal expansion valve  36  that is connected to the first cooling region  26  of the heat exchanger  22 . The surface of the heat exchanger  22  in the second cooling region  28  is kept cooler than the surface of the heat exchanger  22  in the first cooling region  26 . However, the temperature gradient between the air stream  64  and the surface of the heat exchanger  22  in the second cooling region  28  is as large as the corresponding temperature gradient in the first cooling region  26  because the temperature of the air stream  64  is already reduced by the first cooling region  26 . In other words, the working temperatures are different but the temperature gradient is constant. Quite similar, the temperature of the heat exchangers surface reduces even further in the third cooling region  30  due to a different refrigerant flow rate provided by the third thermal expansion valve  40 . This leads to a constant temperature gradient throughout the heat exchanger  22 . This is an indication of an overall highly efficient cooling of the air stream  64  as the optimized temperature profile resembles a desired temperature profile of a classical counter flow heat exchanger. 
     The temperature control unit  32  comprises inter alia common components of a cooling circuit. Of course, refrigerant provided via the thermal expansion valves  36 ,  38 ,  40  to the different cooling regions  26 ,  28 ,  30  of the heat exchanger  20  evaporates and is fed back into the temperature control unit  32  to close the cooling circuit. However, this is not shown in the figure. 
       FIG. 3  shows a schematic side view of a heat exchanger  22  and a connected temperature control unit  32 . Wide parts of  FIG. 3  are identical with  FIG. 2 . However, the first cooling region  26 , the second cooling region  28 , and the third cooling region  30  are connected with the cooling circuit of the temperature control unit  32  via a single thermal expansion valve  36  having a common refrigerant inlet  42  and three separate refrigerant outlets  44 ,  46 ,  66 . Each of the three refrigerant outlets  44 ,  46 ,  66  can lead different amounts of refrigerant to the different cooling regions  26 ,  28 ,  30  of the heat exchanger  22 . In this specific embodiment shown in  FIG. 3 , working temperature of the first cooling region  26  is higher than the working temperature of the second cooling region  28 . Further, the working temperature of the second cooling region  28  is higher than the working temperature of the third cooling region  30 . Using a single thermal expansion valve  36  with a plurality of refrigerant outlets  44 ,  46 ,  66  can help to simplify the cooling circuit. 
       FIG. 4  shows a third side view of a heat exchanger  22  connected to a temperature control unit  32 . Wide parts of  FIG. 4  are identical with the previously described  FIGS. 2 and 3 . However, the temperature control unit  32  comprises a common cold reservoir  54  as part of the cooling circuit. The first cooling region  26  of the heat exchanger  22  is connected to this common cold reservoir  54  via a first heat pipe  52 . The second cooling region  28  of the heat exchanger  22  is connected to the common cold reservoir  54  via a second heat pipe  50 . The third cooling region  30  of the heat exchanger  22  is connected to the common cold reservoir  54  via a third heat pipe  48 . The first heat pipe  52 , the second heat pipe  50 , and the third heat pipe  48  have different evaporation points. In this way, the first cooling region  26 , the second cooling region  28 , and the third cooling region  30  are kept on different working temperatures. The effect of the three heat pipes  48 ,  50 ,  52  is therefore quite similar to the effect previously described in connection with the usage of thermal expansion valves in  FIGS. 2 and 3 . The temperature gradient between the air stream  64  and the surface of the heat exchanger  22  is kept almost constant. The common cold reservoir  54  is part of an ordinary cooling circuit that cools the common cold reservoir  54 . 
       FIG. 5  shows a schematic side view of a vehicle  12  using a low-profile HVAC apparatus  10  mounted on the cabin roof. The HVAC apparatus  10  uses the technical principles as herein described and has a profile height  70  that is very low, for example approximately about 40 mm. The ultra-thin profile height  70  can allow an integration of the HVAC apparatus  10  in the roof structure of the vehicle&#39;s driver cabin without thickening the roof structure. 
       FIG. 6  shows a second schematic top view of an open HVAC apparatus  10 . The shown HVAC apparatus  10  has the heat exchanger unit  20  centrally located. The fan unit  14  has two parts separated from each other. Both parts of the fan unit  14  consist of a plurality of axial impellers  16 . The upper part of the fan unit has seventeen axial impellers and the lower part has seven axial impellers. However, the exact number of axial impellers  16  is a design choice that depends on the required air stream  64 . The shown heat transfer unit has an inner wall  72  that divides the heat transfer unit in two air circuits. Both air circuits can be operated independently from each other by operating the related parts of the heat transfer unit  20  and the fan unit. The inner setup of the heat transfer unit  20  can be similar to the setups described in  FIGS. 1 to 5 . Therefore, additional remarks on internal air ducts defining the way of the air stream inside of the heat transfer unit  20  and different cooling regions are unnecessary. Each of the plurality of axial impellers  16  can have a dimension of 40×40 mm for example. Thus, the relevant overall profile height of the HVAC apparatus can be reduced down to approximately 40 mm. Each of the plurality of axial impellers  16  can be allocated to an outlet guide vane. The outlet guide vanes can be part of the axial impellers housings. The outlet guide vanes can improve the homogeneity of the provided air stream  64 . The air stream  64  is generated by the fan unit  14  and leaves the heat exchanger unit  20  as conditioned air  58 . A temperature control unit as described in connection with  FIG. 1  is not shown in  FIG. 6  for simplifying the picture. 
       FIG. 7  shows a schematic bottom view of a HVAC apparatus  10 . The shown HVAC apparatus  10  has external air ducts  74  that lead the conditioned air  58  away from the heat exchanger unit  20 . The conditioned air can leave the external air ducts  74  at provided air outlets  76 . As can be seen in  FIG. 7 , the air outlets  76  are evenly spread. In case that the shown HVAC apparatus is integrated into a vehicle&#39;s roof construction, it is possible to effectively provide conditioned air to the entire drivers cabin. Quite similar to  FIG. 6 , a temperature control unit as described in connection with  FIG. 1  is not shown in  FIG. 7  for simplifying the picture 
     The features of the disclosure disclosed in the above description, the drawings as well as in the claims may be important for a realization both individually and in any combination. 
     LIST OF NUMERALS 
     
         
           10  HVAC apparatus 
           12  vehicle 
           14  fan unit 
           16  impeller 
           18  motor 
           20  heat exchanger unit 
           22  heat exchanger 
           24  air duct 
           26  first cooling region 
           28  second cooling region 
           30  third cooling region 
           32  temperature control unit 
           34  plate-shaped housing 
           36  first thermal expansion valve 
           38  second thermal expansion valve 
           40  third thermal expansion valve 
           42  common refrigerant inlet 
           44  refrigerant outlet 
           46  refrigerant outlet 
           48  third heat pipe 
           50  second heat pipe 
           52  first heat pipe 
           54  common cold reservoir 
           56  central recess 
           58  conditioned air 
           60  heat transfer fin 
           62  temperature curve 
           64  air stream 
           66  refrigerant outlet 
           68  air baffle 
           70  profile height 
           72  wall 
           74  external air duct 
           76  air outlet