Abstract:
A system for treating the exhaust output by an internal combustion engine includes a regeneration positioned upstream from a diesel particulate filter. The regeneration unit combusts a fuel to heat the exhaust entering the diesel particulate filter. An air pump supplies a secondary source of compressed air to the regeneration unit and is adapted to be driven by the internal combustion engine. A speed sensor is coupled to the air pump and operable to output a signal indicative of a rotational speed of an air pump component. A controller receives the speed sensor signal and determines an operating speed of the internal combustion engine based on the speed sensor signal. The controller controls the regeneration unit based on the engine operating speed.

Description:
FIELD 
       [0001]    The present disclosure generally relates to an exhaust treatment system. More particularly, a secondary air system includes an air pump and an associated speed sensor for managing the operation of a regeneration unit positioned upstream from a diesel particulate filter. 
       BACKGROUND 
       [0002]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0003]    Many personal and commercial vehicles have been constructed with an internal combustion engine for transferring power to the driven wheels of the vehicle. Older vehicles may be equipped with exhaust systems that may not meet present governmental regulatory standards or standards that are about to be imposed. When new, these vehicles may have met the emissions control regulations but these vehicles may require modification to be legally operated in the future. 
         [0004]    In one example, commercial vehicles such as buses may be equipped with a diesel fueled internal combustion engine having an exhaust system that does not include a diesel particulate filter or a regeneration unit associated with the diesel particulate filter. In addition, many of these same vehicles have relatively simple engine and driveline arrangements where an electronic engine controller is not provided. 
         [0005]    It may be desirable to retrofit certain vehicles with exhaust systems including a diesel particulate filter and a regeneration unit. Some emissions control systems require a real time indication of engine operating speed to properly manage the regeneration unit. Furthermore, operation of the regeneration unit may require a secondary supply of oxygen that may be provided by an external air pump. Accordingly, it may be desirable to provide an exhaust system including a diesel particulate filter, a regeneration unit, a secondary air supply including an air pump where the air pump is equipped with a sensor operable to output a signal indicative of the internal combustion engine speed. 
       SUMMARY 
       [0006]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0007]    A system for treating the exhaust output by an internal combustion engine includes a regeneration positioned upstream from a diesel particulate filter. The regeneration unit combusts a fuel to heat the exhaust entering the diesel particulate filter. An air pump supplies a secondary source of compressed air to the regeneration unit and is adapted to be driven by the internal combustion engine. A speed sensor is coupled to the air pump to output a signal indicative of a rotational speed of an air pump component. A controller receives the speed sensor signal and determines an operating speed of the internal combustion engine based on the speed sensor signal. The controller controls the regeneration unit based on the engine operating speed. 
         [0008]    A method of treating exhaust output by an internal combustion engine includes obtaining a signal indicative of the rotating speed of a member of an air pump driven by the internal combustion engine. An engine speed is determined based on the signal. An exhaust mass air flow rate is estimated based on the engine speed. A secondary air flow rate and a fuel rate are determined based on the estimated exhaust mass air flow rate. The secondary air flow and fuel are provided to a regeneration unit at the determined rates. The fuel in the regeneration unit is ignited to increase the temperature of exhaust flowing therethrough to regenerate a diesel particulate filter. 
         [0009]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0010]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0011]      FIG. 1  is a schematic depicting an exemplary vehicle equipped with an exhaust treatment system constructed in accordance with the teachings of the present disclosure; and 
           [0012]      FIG. 2  is a flow chart depicting a control scheme for the exhaust treatment system shown in  FIG. 1 . 
       
    
    
       [0013]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0014]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0015]    With reference  FIG. 1 , an exemplary vehicle  10  is equipped with an engine  12  and an exhaust system  16 . Exhaust system  16  includes an exhaust manifold  18 , a diesel particulate filter  20  and a regeneration unit  22 . An exhaust conduit  24  interconnects exhaust manifold  18  and regeneration unit  22 . A tail pipe  26  includes one end in receipt of gasses passing through diesel particulate filter  20  and an opposite open end allowing the treated exhaust to exit exhaust system  16 . 
         [0016]    Exhaust system  16  also includes an air pump  30  providing a supply of secondary air to an inlet  32  of regeneration unit  22 . Air pump  30  is drivingly coupled to engine  12  by a flexible drive member  34  such as a belt or chain. Alternatively, air pump  30  may be driven by engine  12  using any other power transmission device such as a gear train. A speed sensor  36  is coupled to air pump  30  and configured to output a signal  38  indicative of the rotational speed of engine  12 . 
         [0017]    A tank  42  stores a hydrocarbon such as diesel fuel. A fuel filter  46  and a fuel pump  48  are provided to transfer the hydrocarbon from fuel tank  42  to a fuel block  50 . Fuel block  50  selectively supplies fuel to a fuel line  54  terminating at inlet  32  of regeneration unit  22 . 
         [0018]    A first igniter  62  and a second igniter  64  are associated with regeneration unit  22  to ignite fuel and increase the temperature of the exhaust travelling therethrough. More particularly, first igniter  62  may be referred to as a primary igniter for combusting the fuel supplied by fuel line  54  with the secondary air provided by air pump  30 . Second igniter  64  may be operable to combust hydrocarbons present in the exhaust downstream from first igniter  62 . It should be appreciated that the regeneration unit may be equipped with only a single igniter without departing from the scope of the invention. 
         [0019]    A first pressure sensor  66  is positioned in communication with the exhaust flowing through exhaust system  16  at a position upstream from diesel particulate filter  20 . A second pressure sensor  68  is in communication with the exhaust at a position downstream from diesel particulate filter  20 . Each of first pressure sensor  66  and second pressure sensor  68  output a signal indicative of the exhaust pressure at their locations. 
         [0020]    A first temperature sensor  70  is positioned within exhaust system  16  at a location upstream from regeneration unit  22 . A second temperature sensor  72  is operable to output a signal indicative of the exhaust temperature at a position downstream from regeneration unit  22  and upstream from diesel particulate filter  20 . A third temperature sensor  74  is operable to output a signal indicative of the exhaust temperature at a location downstream from diesel particulate filter  20 . A controller  80  is in receipt of signals from first through third temperature sensors  70 ,  72 ,  74  as well as signal  38  indicating the rotational speed of engine  12 . First pressure sensor  66  and second pressure sensor  68  send signals indicating the exhaust pressure at their locations to controller  80 . 
         [0021]    Controller  80  is in communication with fuel block  50  to selectively supply fuel to fuel line  54 . An air valve  84  controls the supply of outside air to regeneration unit  22 . Controller  80  may selectively open and close air valve  84  to meter the flow rate of secondary air provided to regeneration unit  22 . Air valve  84  may be positioned upstream or downstream of air pump  30  to perform this function. 
         [0022]    The duration of regeneration may be based on engine speed, one or more pressure differentials, or some other calculation performed by controller  80 . For example, regeneration of diesel particulate filter  20  may be determined to be completed once the exhaust flowing through DPF  20  is above a predetermined temperature threshold for a predetermined amount of time. 
         [0023]    Speed sensor  36  is coupled to air pump  30  or integrally formed therewith. Speed sensor  36  may include a Hall Effect or variable reluctance type sensor. In one arrangement, the sensor target may be a toothed wheel fixed to a rotating member within air pump  30 . The sensor target may include the teeth of an existing gear already present within air pump  30 . Other arrangements including patterned shafts are contemplated as being within the scope of the present disclosure. 
         [0024]    Air pump  30  includes an input shaft  90  driven by flexible member  34 . Controller  80  is provided the geometrical relationship between the rotational speed of a crankshaft  92  of engine  12  and input shaft  90  of air pump  30 . This relationship may be as simple as the ratio of the diameters of an output pulley  94  fixed to crankshaft  92  and an input pulley  96  fixed to input shaft  90 . Regardless of the mechanical arrangement, sensor  36  is operable to output signal  38  indicative of the rotational speed of crankshaft  92 . 
         [0025]    Input shaft  90  may be driven by any other number of intermediate pulleys such as an alternator pulley, a water pump pulley, a power steering pump pulley or the like. The relationship of the intermediate pulley speed to the speed of crankshaft  92  could be taken into account to accurately provide signal  38  to controller  80 . Air pump  30  may be associated with or include a clutch  98  operable to drivingly connect and disconnect input shaft  90  from a pumping member (not shown) within air pump  30 . The pumping member may be disconnected from engine  12  to save energy and reduce wear on air pump  30  when secondary air is not required. 
         [0026]    It is contemplated that exhaust system  16  depicted in  FIG. 1  represents a modified exhaust system arranged by retrofitting an existing vehicle. In particular, an aftermarket retrofit kit including regeneration unit  22 , diesel particulate filter  20 , air pump  30 , speed sensor  36 , air valve  84 , pressure sensors  66 ,  68 , temperature sensors  70 ,  72 ,  74 , igniters  62 ,  64 , fuel block  50  and controller  80  may be used to modify a vehicle that was not originally equipped with such an exhaust aftertreatment system. A complex and costly engine controller does not need to be included with the original vehicle or the proposed exhaust aftermarket retrofit kit. Sufficient data is provided from speed sensor  36  to controller  80  to properly manage the operation of regeneration unit  22  and diesel particulate filter  20 . 
         [0027]      FIG. 2  provides a representative flow diagram related to the operation of exhaust system  16 . At block  120 , control determines whether engine  12  is running. If the engine is running, control determines the pressure differential across DPF  20  at block  122 . Controller  80  compares the pressure signal provided from first pressure sensor  66  to the signal provided from second pressure sensor  68  and calculates a pressure differential. At block  124 , control determines the amount of engine running time that has elapsed since the last DPF regeneration. Engine operating time may be determined based on the output from speed sensor  36 . 
         [0028]    At block  126 , control determines whether a regeneration of diesel particulate filter  20  is required. At this time, controller  80  determines whether the determined time since the last regeneration event is greater than a predetermined interval. If so, a regeneration is required. Controller  80  also compares the recently determined pressure differential across diesel particulate filter  20  to a threshold pressure differential. If the determined pressure differential is greater than the predetermined threshold, a regeneration event is required. As DPF  20  becomes filled with soot and other particulate matter, the pressure differential across DPF  20  increases thereby indicating a need for regeneration. 
         [0029]    At block  128 , control determines the rotating speed of crankshaft  92  of engine  12  based on signal  38  from sensor  36 . At block  130 , an exhaust mass air flow provided to regeneration unit  22  is calculated based on the previously determined engine speed. At block  132 , control determines a secondary air flow rate and a rate of fuel flow to be provided to line  54  based on the exhaust mass air flow previously determined. 
         [0030]    At block  134 , the determined air flow rate is provided by engaging clutch  98 , if present, and controlling valve  84  to provide the desired secondary air flow rate to inlet  32  of regeneration unit  22 . Controller  80  controls pump  48  and fuel block  50  to provide the determined rate of fuel supply to line  54  and inlet  32  of regeneration unit  22 . Control energizes igniters  62  and  64  at block  136 . 
         [0031]    At block  137 , control determines the average temperature of the exhaust flowing through diesel particulate filter  20 . Signals output from third temperature sensor  74  and second temperature sensor  72  may be combined and averaged to determine the average operating temperature of exhaust flowing through DPF  20 . 
         [0032]    Controller  80  may also or alternatively determine an engine load condition by evaluating speed sensor signal  38  as well as temperature signals provided by sensors  70 ,  72  and  74 . The regeneration duration may be varied based on the engine load. 
         [0033]    At block  138 , control determines whether a predetermined regeneration time at sufficient temperature has been completed. Once the regeneration has occurred at an average temperature greater than a threshold temperature for a predetermined minimum time, control continues to block  140  where the supply of fuel and secondary air to regeneration unit  22  are ceased. First igniter  62  and second igniter  64  are no longer energized. At this time, the regeneration of DPF  20  is complete. 
         [0034]    Control also provides for a modification of the regeneration process if a change in engine speed should occur during the regeneration process. At block  142 , control determines whether the engine speed has changed during regeneration by evaluating signal  38  from speed sensor  36 . If the engine speed has changed, control determines a revised mass air flow based on the engine speed signal at block  144 . At block  146 , control determines a revised secondary air flow rate and a revised fuel supply rate based on the revised exhaust mass air flow rate. At block  148 , control varies the inputs to air valve  84  and fuel block  50  to supply the revised secondary air flow rate and fuel flow rate to regeneration unit  22 . Control returns to blocks  138  and  140  as previously described to complete the regeneration process. 
         [0035]    It should be appreciated that speed sensor  36  may also be used to support a diagnostic system where signal  38  may be evaluated to confirm that a member such as input shaft  90  of air pump  30  is being rotated. Pump operation may be simply verified using this technique. Additional diagnosis may be performed to confirm proper pump operating speed and operation of clutch  98  if the rotational speed of crankshaft  92  is known from another source. Control may compare the determined crankshaft operating speed based on signal  38  to the engine operating speed supplied from the second source during a diagnostic check. 
         [0036]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.