Patent Publication Number: US-2021188373-A1

Title: Reducing Aerodynamic Drag of Semi-trailer Truck

Description:
TECHNICAL FIELD 
     The disclosure relates to the field of aerodynamic drag. 
     BACKGROUND 
     It has been well-known that the aerodynamic drag is the major cause of resisting the forward movement of a semi-trailer truck and reducing the aerodynamic drag can significantly improve the fuel economy of the vehicle. 
     BRIEF SUMMARY 
     Devices and methodology for reducing the aerodynamic drag of a semi-trailer truck are disclosed. The current devices and methodology reduce the aerodynamic drag by diverting the airflow around the truck resulting in reducing the low pressure or adding pressure to the low pressure in the aerodynamic wake behind the tractor and the trailer. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The embodiments may be better understood, and numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. These drawings are used to illustrate only typical embodiments of this invention, and are not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
         FIG. 1  depicts a schematic top view of a semi-trailer truck. 
         FIG. 2  depicts a side elevational view of a semi-trailer truck. 
         FIG. 3A  depicts a sectional view of an embodiment of an air-flow deflector of the disclosure in the form of a conventional flow embodiment. 
         FIG. 3B  depicts a sectional view of an embodiment of an air-flow deflector of the disclosure in the form of a laminar flow embodiment. 
         FIG. 3C  depicts a sectional view of an embodiment of an air-flow deflector of the disclosure in the form of a flat thin piece embodiment. 
         FIG. 3D  depicts a sectional view of an embodiment of an air-flow deflector of the disclosure in the form of a curved flat thin piece embodiment. 
         FIG. 3E  depicts a sectional view of an embodiment of an air-flow deflector of the disclosure in the form of a spoon-shaped embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The description that follows includes exemplary apparatus, methods, techniques, and instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details. 
     With reference to  FIG. 1  which depicts the top view of a semi-trailer truck  5  with tractor  1  and semi-trailer/trailer  2 . When the truck is moving in the direction indicated by the arrow A, aerodynamic wake represented at gap  11  and represented at gap  12  are generated respectively behind tractor  1  and trailer  2  which are respectively due to separation of the boundary layer around the tractor  1  and the trailer  2 . As depicted in  FIG. 1 , turbulence  13  and  14  for example are generated inside the aerodynamic wake  11  and  12  respectively which create low pressure zone relative to the non-separated flow field in the boundary layer around the truck  5 . The relatively lower pressure in wake  11  and  12  is one of the main causes of the aerodynamic drag in question. Reducing the pressure drop or increasing the pressure in wake  11  and  12  is the subject of this invention. The respective boundary layer of an airfoil, an air deflector, a plate, planar surface, etc. is known to one having ordinary skill in the art of airfoils/air deflectors design. 
     The current invention uses aerodynamic foils, other forms of air deflector e.g.  3 ,  4 ,  19 ,  20 , &amp;  31  or air duct e.g.  30  to direct airflow into the aerodynamic wake  11  and  12  to increase the pressure within the wake zone. With reference to  FIG. 1 , using relatively low-drag airflow deflector, for example, laminar flow airfoils  3  and  4  to direct the airflow  7  and  8  respectively to flow into wake  11  when the truck is moving in direction A. An air duct  30  which has its air-inlet  35  between the tractor  1  windshield  37  and the top of the driver compartment  36 , for example, can be used to direct airflow  38  into wake  11  as depicted in  FIG. 2 .  FIG. 2  is the side view of the same semi-trailer truck  5  of  FIG. 1 . Air duct  30  can be in various configurations. It can be a straight air duct or with orifice or nozzle configurations. The opening of the duct  30  adjacent to wake  11  shall not consist of sharp bending edges which causes flow separation, rather it shall preferably be a gradually enlarged opening to wake  11  to minimize the flow separation thus minimizing the generation of turbulence. As depicted in  FIG. 1 , airfoil  3  and  4  are attached to the sides of the tractor  1  by means of the airfoil holders/connecting arms  15  and  16  respectively. Airfoil holders  15  and  16  can be adjustable connecting arms that provide the optimum positions of the airfoils  3  and  4  relative to the tractor  1  for the maximum deflected airflow  7  and  8  into wake  11  at any vehicle speed. It should be noted that airfoils  3  and  4  are sectional view of the airfoil  3  and  4  which are, for example, vertical panels attached to the sides  1   a  of tractor body  1  by means of the adjustable connecting arms  15  and  16  respectively. When airflow  7  and  8  are deflected into wake  11 , the aerodynamic drag is reduced due to the increase in pressure in wake  11 . The airfoils  3  and  4  can be attached on the leading corners of the trailer  2  at c and d locations respectively. 
     The airflow deflectors  19 ,  20 , &amp;  31  can also be attached on the top and bottom of the tractor  1  and the trailer  2  as depicted in  FIG. 2 . The airflow deflector  19  with its connecting arm  33  and airflow deflector  20  with its adjustable/extendable/movable connecting arm  17 , for example mounted on the top  36  of the tractor  1  and top  26  the trailer  2  respectively deflect the airflow  21  and  23  into wake  11  and  12  respectively. As an optional positioning of the deflector  20 , its end e can be extended beyond the trailing edge f of the trailer  2  when the deflector  20  is in use (i.e. operational mode). When it is not in use, the connecting arm(s)  17  pull(s) the deflector  20  back to its resting position where the deflector  20  is reclining on, abutting, or recessed in/flush with the trailer top  26  and the end e of the deflector  20  does not extend beyond the edge f of the trailer  2  (i.e. resting mode). The deflector  20  can be replaced by an air duct (similar to air duct  30 ) with various configurations such as a straight duct or an orifice or a nozzle for examples. As depicted in  FIG. 2 , the airflow deflector  31  with its adjustable/extendable/movable connecting arm  34  attached to the bottom  39  of the tractor  1  deflects the airflow  24  into wake  11 . Similarly, an airflow deflector (not shown or represented recessed) can be installed at the rear bottom edge  29  of the trailer  2  to deflect the airflow into wake  12 . 
     The air-deflectors, e.g.  3 ,  4 ,  19 ,  20 , &amp;  31 , can be a permanent fixture of the tractor  1  and trailer  2  or it can be a removable attachment to the tractor  1  and trailer  2 . If an airfoil design is used as the airflow deflector, it can be in various forms and shapes. For example, it can be a laminar flow airfoil  44  ( FIG. 3B  showing transition point  46  laminar to turbulent flow), a conventional airfoil  40  ( FIG. 3A  showing transition point  42  laminar to turbulent flow) or a straight or curved flat thin object,  48  ( FIG. 3C  showing transition point  50  laminar to turbulent flow) &amp;  52  ( FIG. 3D  showing transition point  54  laminar to turbulent flow) respectively, as depicted in  FIGS. 3A-3D . Other air-deflectors such as a spoon-shaped airflow deflector  56  as depicted in  FIG. 3E  showing transition point  58  laminar to turbulent flow may be employed. The shape and size of the airflow deflector, e.g.  3 ,  4 ,  19 ,  20 , &amp;  31 , as well as its location relative to the tractor  1  or trailer  2  are chosen to minimize the drag generated by the respective airflow deflector itself and to maximize the airflow deflection into the respective wake  11  and  12 . The adjustable/extendable connecting arms  15 ,  16 ,  17 ,  33  and  34  are designed to provide various angles of attack of the airflow deflectors, e.g.  3 ,  4 ,  19 ,  20 , &amp;  31 , which are attached to the connecting arms  15 ,  16 ,  17 ,  33  and  34  by means of hinges or the like. The said connecting arms  15 ,  16 ,  17 ,  33  and  34  are designed to pull the respective airflow deflectors  3 ,  4 ,  20 ,  19  and  31  to be closely attached to, abutting, or recessed in/flush (see  FIG. 1  representing various individual airflow deflectors recessed) with the tractor  1  or trailer  2  bodies as their resting positions when the deflectors are not in use as known to one having ordinary skill in the art. The connecting arms  15 ,  16 ,  17 ,  33  and  34  also provide various angles of attack g (one represented in  FIG. 2 , but it is to be understood that it is applicable to all deflectors) and various distances h (one represented in  FIG. 2 , but it is to be understood that it is applicable to all deflectors) between the respective deflectors  3 ,  4 ,  20 ,  19  and  31  and the truck  1  and trailer  2  bodies such that the deflectors  3 ,  4 ,  20 ,  19  and  31  generate maximum flow deflection into respective wakes  11  and  12 . The abovementioned choice of the respective angle of attack g and the respective distance h from the truck  1  and trailer  2  body can be achieved by manual means or by automatic control in which feed-back control may be used to determine the optimum parameters for the maximum air flow (volume) deflection with respect to a given truck speed and yaw angle between the truck moving direction and the head wing/wind. 
     The parameters and value for the variable distance h and the variable angle of attack g are dependent upon several factors. The distance h is such that the respective deflector  3 ,  4 ,  20 ,  19  and/or  31  shall be in the “free stream” region outside the boundary layer which is very close to the surface of the semi-trailer truck  5  body at high speed. At low vehicle speed, the respective deflector  3 ,  4 ,  20 ,  19  and/or  31  may never be in the free stream region (the use of the deflector at low vehicle speed lesser interest). The angle of attack g is dependent, at least in part, to the “drag-to-lift-ratio” which is preferably as small as possible while the respective deflector  3 ,  4 ,  20 ,  19  and/or  31  is functioning in accordance with the purpose of deflecting the volume of air flow. The deflection of flow is larger with larger angle of attack g whilst the drag-to lift-ratio increases with larger angle of attack g. Therefore selection of the optimal angle of attack g is dependent at least in part on a given semi-trailer truck  5  speed for purposes of achieving the maximum flow deflection at minimum drag-to-lift-ratio. 
     The criteria for the length and size of each aerodynamic airfoil, or other objects as airflow deflector(s)  3 ,  4 ,  20 ,  19  and  31  is determined/selected to reach the optimum airflow deflection into the wakes  11 ,  12 . For example, if the length of an airflow deflector  3 ,  4 ,  20 ,  19  and  31  is sufficiently long, such that it extends into the free stream region or near the free stream region outside the boundary layer around the tractor  1  and trailer  2 , then it shall be an effective airflow deflector  3 ,  4 ,  20 ,  19  and  31 . 
     Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.