Abstract:
Temperature control devices have become common to cool the exhaust stream from a diesel particulate filter before release into the environment. To further cool the filtered exhaust stream and to protect the temperature control device, a duct can be used to surround the inlets of the temperature control device. The duct has a head section surrounding the inlets at one end and a base section extending from the head section with a vent at the other end. Ambient air is drawn through the vent into the duct and into the inlets of the temperature control device to further cool the filtered exhaust stream.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention: 
         [0002]    The present invention relates to exhaust systems and more particularly to the reduction of exhaust gas temperature without affecting operation of pollution control elements of the exhaust system. 
         [0003]    2. Description of the Prior Art: 
         [0004]    Elevated exhaust gas temperatures from the tail pipes of diesel engine equipped motor vehicles have become a greater problem with the introduction of diesel particulate trap/filters (DPF) and the need to regenerate these filters. Diesel particulate filters remove unburned and partially burned hydrocarbons from the exhaust streams produced by diesel engines. A DPF may be periodically regenerated by raising the temperature in the filter sufficiently to accelerate the oxidation of or ignite the particulate matter trapped in the filter. This process, once initiated, further increases the temperature of the exhaust stream downstream from the filter. The increase in the temperature of the exhaust may singe passers-by, particularly where the exhaust is discharged near ground level, and add stress on exhaust pipes. 
         [0005]    The prior art frequently, though not universally, achieved exhaust gas cooling as a byproduct of cooling a component, such as a muffler, in the exhaust system. In some contemporary pollution control schemes components of the exhaust gas treatment system must run hot in order to operate or regenerate making it undesirable to reduce exhaust gas temperature ahead of the component in question or to reduce the temperature of the component itself. For example, diesel particulate filter regeneration requires maintaining the temperature of the filter during regeneration. 
         [0006]    There is thus a need to cool the exhaust gas after the exhaust leaves the filter. It remains desirable to protect pipes of the exhaust system from the high temperatures which attach to the casing housing the filter as well as reduce the danger of singing passers-by. 
         [0007]    Reducing the exhaust gas temperature after leaving the diesel particulate filter can be accomplished with a temperature control device. The temperature control device typically has inlets that allow fresh air into the device can form a venturi to mix the exhaust gas with the air. 
         [0008]    While this device works well to reduce the temperature of the exhaust, some exhaust can escape from the system if the tail pipe is clogged or plugged. Because the exhaust gasses are hot, they could potentially burn someone walking by. Furthermore, if the inlets in the device become blocked with debris or by other equipment, the temperature of the exhaust will rise above acceptable levels. 
         [0009]    Therefore, there remains a need to reduce the temperature of the exhaust gas without allowing the exhaust gas to escape out of the temperature control device, especially if the end of the exhaust pipe is plugged. There is also a need to prevent the inlets of the device from becoming blocked. In addition, there is a need to further reduce the temperature levels of the exhaust. 
       SUMMARY OF THE INVENTION 
       [0010]    According to the invention, an apparatus cools the exhaust flow from a motor vehicle exhaust system before discharge into the environment for drawing ambient air into the exhaust stream. The exhaust system includes elements providing air pollution treatment, such as catalytic converters and particulate filters for diesel vehicles. The catalytic converters and diesel particulate filters are installed in canisters or housings replacing portions of the exhaust pipe in the exhaust system. While either element can be a heat source, diesel particulate filters are subject to particularly high temperatures, which are required for regeneration of the filter. Passive cooling of the exhaust through ventilation of the exhaust system is provided by drawing ambient air into a temperature control device and into the exhaust stream without a significant reduction of the operating temperature of the pollution treatment element, particularly in the case of diesel particulate filters. Cooling is advantageously introduced to the exhaust system after the diesel particulate filter to reduce the temperature of the exhaust gas as it is returned to the exit tubing proper without affecting operation of the pollution control element. 
         [0011]    In order to further cool the filtered exhaust stream and to protect the temperature control device, a duct can be used to surround the inlets of the temperature control device, such as an exhaust diffuser. The duct has a top, a bottom, opposite first and second lateral walls between the top and bottom, a closed end, and an opposite vented end. The duct has a head section surrounding the inlets of the temperature control device and includes the closed end. The duct also has a base section with a vent. The base section extends from the head section to the vented end. 
         [0012]    Additional effects, features and advantages will be apparent in the written description that follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a perspective view of a school bus which may be equipped with an exhaust system modified to incorporate the present invention; 
           [0015]      FIG. 2  is a plan view of a vehicle equipped with an exhaust system modified to incorporate the present invention with the top of the duct removed; 
           [0016]      FIG. 3  is a perspective view of a temperature control apparatus with the top of the duct removed; 
           [0017]      FIG. 4  is a side view of a temperature control apparatus of the invention; 
           [0018]      FIG. 5  is a side view of a temperature control apparatus of the invention; 
           [0019]      FIG. 6  is a perspective view of a temperature control apparatus of the invention; 
           [0020]      FIG. 7  is a front plan view of a temperature control apparatus of the invention; 
           [0021]      FIG. 8  is a top plan view of a temperature control apparatus of the invention; 
           [0022]      FIG. 9  is a rear plan view of a temperature control apparatus of the invention; 
           [0023]      FIG. 10  is a perspective view of a temperature control apparatus of the invention installed in a motor vehicle; 
           [0024]      FIG. 11  is a partial perspective view of a temperature control apparatus of the invention along line A-A, where one of the inlets of the exhaust diffuser is aligned with the vent; 
           [0025]      FIG. 12  is a cross section of a temperature control apparatus of the invention of  FIG. 9  along line A-A, where one of the inlets of the exhaust diffuser is aligned with the vent as tested in the Example, with the magnitude and direction of the velocity indicated by the arrows and the dotted line showing the concentration of the cold flow; and 
           [0026]      FIG. 13  is a cross section of a temperature control apparatus of the invention of  FIG. 9  along line A-A, where the exhaust diffuser is rotated  45 E from the exhaust diffuser shown in  FIG. 11  as tested in the Example, with the magnitude and direction of the velocity indicated by the arrows. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Referring to the drawings and in particular referring to  FIG. 1 , a vehicle such as a school bus  100 , which is typically equipped with a diesel engine requiring use of a diesel particulate filter (DPF), is shown. In a vehicle such as school bus  100 , the tail pipe  112  of an exhaust system typically runs under the vehicle to a point of discharge  114  along the side or back of the vehicle. The point of discharge  114  is at a level where passers-by can be directly exposed to discharge of exhaust from the pipe  112 . 
         [0028]    The present invention as shown in  FIG. 2  relates to an apparatus for an exhaust system  10  which can be used for a motor vehicle  11 , such as a truck or school bus. The exhaust system  10  is installed on the motor vehicle  11  to the chassis  28  horizontally or under the vehicle  11 . 
         [0029]    The engine  12  is in fluid communication with the filter assembly  13  through entrance tubing  14  at the inlet side of the filter assembly  13 . Treated exhaust flows from the filter assembly  13  through exit tubing  16 , which can include a tailpipe, at the outlet side of the filter assembly  13 . 
         [0030]    The filter assembly  13  has a housing  22  and a diesel particulate filter  20  disposed therein. The filter assembly  10  may connect with a catalytic device  18  located between the engine  12  and the filter assembly  10 . The housing  22  has a first conduit  24  in fluid communication with the entrance tubing  14 . The opposite second conduit  26  is in fluid communication with the exit tubing  16 . 
         [0031]    A temperature control device  30  is installed in the exhaust system  10  to lower the temperature of the filtered exhaust. The temperature control device  30  is in fluid communication with the diesel particulate filter  20  to receive filtered exhaust, preferably with second conduit  26 . The temperature control device can also include exit tubing  16  in fluid communication with the outside air. The temperature control device  30  has at least one inlet and preferably multiple inlets  38 ,  39 ,  40 ,  41 , such as slits within the sidewall  34 . While four inlets are preferred in this embodiment, a different number of inlets can be used. The sidewall  34  can be angled at the inlets  38 ,  39 ,  40 ,  41 . Each inlet can be curvilinear, such as a U-shape, or V-shaped. The inlets allow ambient air into the exhaust system  10  which provides a venturi effect in the filtered exhaust stream. 
         [0032]    The temperature control device  30  can include an exhaust diffuser  32  with the inlets  38 ,  39 ,  40 ,  41  and is in fluid communication with the diesel particulate filter  20  and exit tubing  16 . The exhaust diffuser  32  has a cylindrical sidewall  34  surrounding a diffuser pipe  36 . The inlets  38 ,  39 ,  40 ,  41  can be bordered by a diffuser wall extending from the sidewall  34  to further direct the flow of air into the exhaust diffuser  32 . The diffuser wall  34  can extend outwardly and/or inwardly. 
         [0033]    The exhaust diffuser  32  can have a collar  44  engaging the second conduit  26  at an entrance end  74 . A slanted shoulder  46  extends from the collar  44  to the sidewall  34 . 
         [0034]    The exit tubing  16  can engage the sidewall  34  of the exhaust diffuser  32  opposite the collar  44  at an exit end  76 . The diffuser pipe  36  is in fluid communication with the exit tubing  16  and can narrow in diameter between the entrance end  74  and the exit end  76  of the exhaust diffuser  32 . 
         [0035]    A duct  50  surrounds the inlets  38 ,  39 ,  40 ,  41  to form a temperature control apparatus  48 . The duct  50  has a vented end  52  and an opposite closed end  54 . The duct  50  has a top  56 , a bottom  58  and opposite first and second lateral walls  60 ,  61  between the top  54  and bottom  56 . The top  56  and bottom  58  can join at the closed end  54 , and closed end edges of the top  56  and bottom  58  can extend outward to form a seam that is fastened together with adhesive, fusing, soldering, bonding, screws and other fasteners, and the like. The lateral walls  60 ,  61  can be inset from the edge of the top  54  and bottom  56 . The edges of the lateral walls  60 ,  61  can extend outward to allow easier assembly of the duct  50 , such as by fastening the top  56 , bottom  58  to the lateral walls  60 ,  61  with an adhesive or by fusing, soldering, bonding, screws and other fasteners, and the like. 
         [0036]    The duct  50  preferably has a head section  64  surrounding the inlets  38 ,  39 ,  40 ,  41  and includes the closed end  54 . A base section  62  in the duct extends from the vented end  52  to the head section  64 . The base section  62  has a vent  51 , preferably at the vented end  52 . The vent  51  allows cooler ambient air to flow into the duct  50 , through the base section  62  and into the head section  64  where the air flows to the exhaust diffuser  32 . The air can next flow through the inlets  38 ,  39 ,  30 ,  41  and mix with and cool the exhaust stream. 
         [0037]    The interior faces  80 ,  82  of the top  56  and the bottom  58  can have grooves  78  extending from the base section  62  to the closed end  54  of the head section  64 . The exterior faces of the top  56  and the bottom  58  can have ridges  79  corresponding to the grooves  78  extending from the base section  62  to the closed end  54  of the head section  64 . 
         [0038]    The distance between the top  56  and the bottom  58  of the base section  62  is can be constant and the vent  51  rectangular. The head section  64  is preferably curved. The distance between the top  56  and the bottom  58  of the head section  64  can increase from the base section  62  to a maximum distance at the exhaust diffuser  32 . More preferably, the distance between the top  56  and the bottom  58  of the head section  64  increases to a maximum distance, such as at the diameter of the exhaust diffuser  32 , then decreases until reaching the closed end  54 . 
         [0039]    The duct  50  has a first opening  84  in the first lateral wall  60  through which the second conduit  26  or collar  44  can extend. The second lateral wall  61  has a second opening  86  through which one end of the exit tubing  16  can extend. 
         [0040]    When installed in the vehicle  11  as shown in  FIG. 10 , the duct  50  preferably angles downward with the vented end  52  at the lowest point. This reduces the amount of dirt, dust, debris, water, and the like, from entering into the temperature control device  30  while allowing ambient air to flow into the duct  50  through the vent  51 . 
         [0041]    The duct  50  hangs from the chassis  28  of the vehicle  11  using at least one hanger. A first hanger  66  has arms  67  extending at least partway under the base section  62 . A second hanger  68  has arms  70  that engage the second conduit  26  and the exit tubing  16  with the head section  64  therebetween. A hanger frame can be used to attach the hangers  66 ,  68  to the chassis. Each hanger  66 ,  68  preferably has an isolator  72  to shield against bumps and shocks to the temperature control apparatus  48 . Clamps or other fastening devices can be used at either side of the duct  50  to install the hanger frame to the exhaust system. 
         [0042]    The duct  50  is easily added to the temperature control device  30  and the exhaust system  10  during assembly. The duct  50  is assembled with the temperature control device  30  to form the temperature control apparatus  48  without the second conduit  26  and exit tubing  16  or the temperature control assembly. 
       EXAMPLE 
       [0043]    The alignment of the inlets of the temperature control device in the duct was tested in the exhaust system using computational fluid dynamics with FLUENT modeling software to measure and calculate velocity, temperature and pressure. The temperature control apparatus  48  of the exhaust diffuser  32  and duct  50  was tested with one of the inlets  38  of the exhaust diffuser  32  aligned with the vent  51  of the duct  50 . A second temperature control apparatus  148  of the exhaust diffuser  32  and duct  50  was tested with the inlets of the exhaust diffuser  32  rotated  45 E from the inlets of the first temperature control apparatus  48 . This rotation aligned the sidewall  34  with the vent  51  of the duct  50 . The Tmax_exit, Tave_exit, del_P and cold air mass flow rate were calculated for both assemblies with the FLUENT software. 
         [0044]    The test had the following results for the first temperature control apparatus  48 . The Tmax_exit=459EC, Tave_exit=369EC, del_P=0.676 in. Hg. The cold air mass flow rate was 0.240 kg/s, which was 69% of the hot exhaust mass flow rate. As shown by the oval in  FIG. 12 , the cold flow was concentrated near the closed end of the duct, where the exhaust diffuser was located. The cold flow bent the hot exhaust stream to the left when measuring the static temperature at mid-plane. The asymmetry of cold flow distribution at the inlets caused a skewed hot jet of exhaust stream and a diminishing mixing efficiency. As shown in  FIG. 12 , the arrows designate the magnitude and direction of the velocity. 
         [0045]    The second temperature control apparatus  148  with the exhaust diffuser rotated  45 E had a Tmax_exit=453EC, Tave_exit=374EC, del_P=0.681 in. Hg. The cold air mass flow rate was 0.231 kg/s, which was 66% of the hot exhaust mass flow rate. The asymmetry of cold flow distribution at the inlets also caused a skewed hot jet of exhaust stream for the  45 E rotated second temperature control apparatus  148  and a diminishing mixing efficiency. As shown in  FIG. 13 , the arrows designate the magnitude and direction of the velocity. 
         [0046]    The results in the Example show the inlets of the exhaust diffuser  32  could be aligned without any particular orientation for the temperature control apparatus to work well. The preferred embodiment, as the results show, is the first apparatus  48  where one of the inlets aligns with the vent  51  in the base section  62  of the duct  50 . This alignment increased the cooling efficiency of the first temperature control apparatus  48  over the second temperature control apparatus  148 . 
         [0047]    There are a number of advantages of the using the duct and the temperature control apparatus of the invention. One advantage is that the duct increases the cooling efficiency of the temperature control device. 
         [0048]    Another advantage is that the duct directs ambient air from outside of the vehicle instead of drawing the air from under the chassis. This ambient air is cooler than the air found directly under the chassis, which is heated by the vehicle and the road. 
         [0049]    A further advantage is that the duct can limit the amount of debris, water and the like that can enter the exhaust diffuser and the temperature control device. A still further advantage is that the duct can prevent hot exhaust gasses from escaping the exhaust system when the exhaust pipe is blocked. 
         [0050]    While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.