Abstract:
A method and device for raising the temperature of exhaust gas from an engine by increasing parasitic loading on the engine without significantly increasing engine speed. This may be accomplished by increasing a demand on a hydraulic fan powered by a variable displacement hydraulic pump and meeting the demand by adjusting the displacement for the variable displacement hydraulic pump.

Description:
FIELD OF THE INVENTION 
     This invention relates to internal combustion engines and, more particularly, to a system and method for regenerating particulate filters used to filter particulates from exhaust gases of these engines. 
     BACKGROUND OF THE INVENTION 
     In diesel and lean burn engines, particulate matter such as, for example, soot is present in exhaust gas from the engine at higher levels than normal gasoline engines. Under these conditions, i.e., higher levels of soot, manufacturers generally choose particulate filters to capture particulate matter. Particulate filters used to remove particulate matter from the exhaust gases of diesel engines are commonly called diesel particulate filters. Accumulated particulate matter such as soot within the filter may eventually reach an undesirable level and may, at this point, cause an undesirable drop in pressure across the diesel particulate filter. Undesirable levels of particulate matter in the DPF may necessitate a regeneration of the filter which may be, generally accomplished with an increase in temperature of exhaust gases to around 600° C. and above just prior to the exhaust gases entering the diesel particulate filter. At these temperatures, the exhaust gas may react with the soot, creating an exothermic reaction to oxidize or burn the soot away which increases the temperatures within the filter, enhancing the burning of the soot, as the soot is burned away. 
     One method of achieving regeneration temperatures is to increase the idle speed of the engine. However, there are times when such an option is not available or practical such as, for example, when vehicle operations demand a lower engine speed than that required for regeneration when exhaust gas temperature is dependent upon elevated engine speeds. 
     SUMMARY OF THE INVENTION 
     One example of a vehicle operation that may require lower engine speeds than required for regeneration is a motor grader performing a fine grading operation. In such an operation it may be desirable to regenerate the diesel particulate filter (hereinafter referenced as “DPF”) with no increase in engine speed or with minimal increase in engine speed as the desired engine speed for fine motor grading is usually substantially lower than engine speeds required for regeneration when engine exhaust temperature is more directly dependent upon engine speed. 
     The invention includes a method of increasing parasitic load on the engine to increase exhaust gas temperature to a level sufficient to achieve regeneration without a concomitant increase in engine speed. To achieve the increase in parasitic load, a speed of a hydraulic fan for the cooling system of the machine may be increased beyond that required for the cooling needs of the machine. The desired fan speed may be a function of the current engine speed with the desired fan speed being higher at lower engine speeds and lower exhaust gas. In the event that the fan speed required for cooling is higher than the fan speed required for regeneration, the desired fan speed may be based upon cooling requirements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exemplary illustration of a vehicle in which the invention may be used; 
         FIG. 2  illustrates an engine, fan and exhaust system in which the invention may be used; and 
         FIG. 3  is a flowchart illustrating an exemplary embodiment of the workings of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is an exemplary illustration of a vehicle (motor grader  10 ) which, during vehicle operations, generally demands lower engine speeds than that required to raise exhaust gas temperatures to a level sufficient for DPF regeneration, and, thus, may benefit from use of the invention. Indeed, in such vehicles, the operation of fine grading may require very low engine speeds. Thus, when such vehicles are fine grading, an increase in engine speed to effect a required increase in exhaust gas temperature is not a practical option. 
       FIG. 2  is an exemplary illustration of an exhaust system  100  utilizing the invention. It includes a diesel engine  20 , a fuel dosing injector  21 , an engine exhaust  22 , a diesel oxidation catalyst (“DOC”)  23 , a DPF  24 , a tailpipe  25 , an engine control unit  26 , a vehicle control unit  27 , a fan  28  having a hydraulic fan motor  28   a  and fan blades  28   b , and a fan power source, i.e., a variable displacement hydraulic pump  29 , an exhaust gas temperature detector  30 , and a transmission  31  to which the hydraulic pump  29  is operably connected. 
     As illustrated in  FIG. 2 , the exhaust gas temperature detector  30  is placed such that it measures the temperature of the exhaust gas prior to the exhaust gas coming into contact with the DOC  23 . As illustrated, the exhaust gas emerges from the engine  20  then moves along the exhaust gas line  22  to the fuel dosing injector  21  and the temperature detector  30  where, if the exhaust gas temperature is equal to or greater than a minimum, predetermined value of, for example, 275° C., a predetermined amount of fuel based upon local exhaust gas temperature is injected into the exhaust gas. This mixture is then burned at the DOC  23  to increase the gas temperature to a level sufficient for regeneration of the DPF  24 , a temperature of, for example, 600° C. At exhaust gas temperatures of around 600° C. and above, the exhaust gas may react with the soot in the DPF  24 , creating an exothermic reaction increasing the temperatures within the DPF  24  as the soot is burned away. This creates even higher temperatures within the DPF  24  to enhance the regeneration process. 
     The ECU  26  shown in  FIG. 2  may determine the need for regeneration of the DPF  24  by monitoring engine operation and exhaust gas temperatures over time and calculating the soot accumulated from a lookup table which includes values for first conditions under which soot is accumulated and values for second conditions under which soot is oxidized as well as values for amounts of soot accumulated or oxidized under first and second conditions over time. First conditions include conditions under which the temperatures of the exhaust gas fall under a predetermined value and second conditions include those in which the temperatures of the exhaust gas equal to or exceed the predetermined value. Thus, the calculated soot accumulated may be a function of a total of calculated soot accumulations over times during which conditions were suitable for given amounts of soot accumulation minus a total of calculated soot oxidized over times during which conditions were suitable for given amounts of soot oxidized. Regardless of the method used, the ECU  26 , in this exemplary embodiment, determines the need for DPF regeneration and signals the VCU  27  that a regeneration of the DPF  24  is in progress. Once the VCU  27  receives the signal it begins to make fan speed adjustments as necessary. 
     The ECU  26  may signal the VCU  27  that a regeneration of the DPF  24  is in progress once the ECU  26  determines that the soot level is at a predetermined level and the vehicle is under working operations. The predetermined soot level may vary from vehicle to vehicle and may be set to different values by different designers but, for this particular embodiment, its value may be experimentally determined and may be associated with a slight decline in engine efficiency. The VCU  27 , upon receiving the signal that a regeneration is in progress from the ECU  26 , begins adjusting exhaust gas temperature by adjusting fan speed via displacement adjustment of the variable displacement hydraulic pump  29 . In doing so, the VCU  27  uses a lookup table to find a predetermined value for a hydraulic fan speed suitable for increasing the temperature of the exhaust gas to a level sufficient for regeneration, i.e., for increasing the temperature of the exhaust gas to a value greater than 275° C. in this particular embodiment prior to contact with the DOC  23 . The lookup table may be a cross reference of pump displacements and predetermined fan speeds for regeneration of the DPF  24 . It may also include a cross reference between predetermined fan speeds and current engine speeds as the predetermined fan speed may be a function of engine speed. The lookup table may be empirically or theoretically developed. Once the predetermined fan speed is found or calculated, the VCU  27  may, via use of the lookup table, determine a required pump displacement for the predetermined fan speed. The VCU  27  may then send a signal to the variable displacement hydraulic pump  29  to set pump displacement to the required pump displacement for achieving the predetermined hydraulic fan speed for the hydraulic fan  28 . The VCU  27  may monitor the fan speed, via signals from fan speed sensor  29   a , incrementally adjusting the pump displacement until the speed of the hydraulic fan  28  is approximately equal to the requisite fan speed. The VCU  27  may continue to maintain the requisite predetermined hydraulic fan speed until either the ECU  26  determines and signals the VCU  27  that regeneration of the DPF  24  is complete and no longer in progress, or the fan speed for the cooling needs of the machine exceeds the predetermined fan speed. Increasing pump displacement to achieve a required fan speed may result in an increased load on the engine  20  with a consequential rise in exhaust gas temperature and little or no change in engine speed. This is especially beneficial for machinery requiring low engine speeds for work operations. 
       FIG. 3  illustrates an exemplary embodiment of the workings of the invention via a flowchart  40 . As illustrated, if the ECU  26  signals a DPF regeneration via fan speed adjustment at  110 , the VCU  27  determines at  120  the predetermined, i.e., the required fan speed required for DPF regeneration, i.e., for raising the current exhaust gas temperature to the exhaust gas temperature required to effect regeneration, i.e., at least 275° C. in this embodiment. This may be accomplished by using the cross reference between predetermined fan speeds and engine speeds in the lookup table. The VCU  27 , then, at  130  determines if the current unadjusted fan speed is less than the required fan speed. If the current fan speed is less than the required fan speed, the VCU brings the fan to the required fan speed by adjusting the displacement of the variable displacement hydraulic pump  29  at  140 . If, at any time, the current fan speed is greater than or equal to the required fan speed at  130 , the VCU  27  makes no adjustment to the displacement, i.e., the current fan speed is not adjusted. In this embodiment, the process of displacement for the sake of regeneration stops when the signal for regeneration from the ECU  26  ceases, either due to a determination by the ECU  26  that the regeneration of the DPF  24  is complete or for some other reason, e.g., the ignition is turned off. 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.