Abstract:
A filter used to remove particulates from a diesel engine exhaust is regenerated by increasing the exhaust temperature to achieve burn off of the accumulated particulates. Regeneration of the filter is inhibited when the sensed level of fuel in a diesel fuel tank for the engine falls below a first threshold level. Optionally, filter regeneration may be initiated when the sensed fuel level is between the first threshold and a higher threshold, and the load level of particulates accumulated in said filter is above a preselected, relatively high load level. Increase of the exhaust temperature to achieve burn off may be achieved by a variety of techniques, including throttling the intake of said engine, reducing the oxygen content in the exhaust gases delivered to said engine, closing an EGR valve of said engine, or performing post injection of fuel in the engine&#39;s combustion cylinders.

Description:
TECHNICAL FIELD 
     The present invention generally relates to filters for removing particulates from the exhaust gas of diesel engines, and deals more particularly with a method of regenerating the filter only when the level in the engine&#39;s fuel tank is above a preselected value. 
     BACKGROUND OF THE INVENTION 
     Emission after-treatment devices are used to collect particulate matter from the exhaust gas of internal combustion engines. In particular, conventional emission treatment devices for diesel engines include particulate filters, oxidation catalysts and nitrous oxide (NOx) catalysts. A problem exists with particulate filters in that the particulates, which consist largely of carbon particles, tend to plug the filters, resulting in a restriction to the flow of exhaust gas. In order to periodically regenerate or purge the filter from particulates, it is known to take measures which result in an increase of the exhaust gas temperature above a predetermined level (e.g. above (450° C.) in order to incinerate the carbon particles accumulated in the filter. 
     One conventional method used to increase the exhaust gas temperature involves controlling a throttle valve in the intake manifold of the engine. In particular, it is known that by throttling/closing the throttle valve, the exhaust gas temperature may be increased. Numerous methods have been used for controlling the throttle valve. For example, in one conventional method, the intake throttle valve is controlled by utilizing the difference between a calculated target intake manifold pressure, and an actual intake manifold pressure. The target intake manifold pressure is calculated using an engine speed and engine load. The regeneration process is scheduled by engine control software based on an estimate of the particulate loading. Known techniques for raising the exhaust gas temperature result in an increase in the fuel consumption during the regeneration process. Driver dissatisfaction can result, however, if the regeneration event is initiated at a time when the vehicle&#39;s fuel tank is near empty, as when the low fuel warning lamp is illuminated. For example, the driver may observe an unexpected rapid reduction in the vehicle&#39;s remaining driving range at a critical time, or the driver may observe what appears to be poor fuel economy due to the driver&#39;s closer scrutiny of fuel mileage when the fuel tank is near empty. In an extreme case, the higher fuel consumption may result in the vehicle running out of fuel before it reaches the next refueling station. 
     Thus, there is a need for a method of regenerating diesel engine particulate filters only above low fuel levels in order to obviate the problems mentioned above. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of regenerating a diesel particulate exhaust gas filter only when the supply of fuel for the diesel engine is above a predetermined value. 
     According to one aspect of the invention, a diesel exhaust filter regeneration method is provided, comprising the steps of sensing when the level of diesel fuel in a fuel tank of a vehicle is below a first threshold level representing a relatively low fuel level; regenerating the filter; and inhibiting the regeneration of the filter when the sensed fuel level is below the threshold value. The method further optionally includes sensing when the fuel level is below the first threshold, and a second, higher threshold level; sensing when the particulate loading of the filter is between a first relatively high load level, and a second load level higher than the first load level; and, regenerating the filter when the sensed fuel level is between the first and second threshold levels, and the sensed loading level of the filter is between the first and second load levels. The filter is regenerated by determining when the loading level of particulates in the filter exceed a predetermined loading level, and increasing the temperature of the exhaust gas to at least a pre-selected exhaust temperature above which the filter is regenerated through the oxidation of the particulates. The exhaust temperature is maintained above the pre-elected temperature for a predetermined length of time corresponding to a desired level of filter regeneration. The increase in exhaust gas temperature may be achieved by a number of techniques, including throttling the engine intake by reducing the oxygen content in the exhaust gases, by closing an ERG valve of the engine or by performing pilot injection of fuel into the engine&#39;s cylinders. 
     According to another aspect of the invention, a method of controlling the regeneration of a diesel particulates in the exhaust filter for a diesel fuel engine is provided, comprising the steps of inhibiting the regeneration of the filter when the level of fuel in a fuel tank of the vehicle is below a first threshold level and a second higher threshold level, and the particulate loading of the filter is between a first, relatively high load level and a second load level higher than the first load level in which regeneration of a filter would ordinarily be necessary. 
     Accordingly, it is the primary object of the present invention to provide a method of regenerating a diesel exhaust gas particulate filter which avoids a regeneration when the fuel supply to the engine is at a relatively low level. 
     Another object of the invention is to provide a method as described above which initiates a filter regeneration event only if the filter load is above a predetermined level. 
     Another object of the invention is to provide a method of the type mentioned above which reduces the possibility of a diesel engine powered vehicle running out of fuel as the result of increased fuel consumption at low fuel levels due to the initiation of a filter regeneration event. 
     A still further object of the invention is to provide a method of the type mentioned above which reduces driver dissatisfaction as a result of the effects of particulate filter regeneration during low fuel levels. 
     These, and further objects and advantages of the present invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, which form an integral part of the specification, and are to be read in conjunction therewith, and in which like reference numerals are employed to designate identical components in the various views: 
     FIG. 1 is a combined block and diagrammatic view of an engine and related control system for carrying out the method forming the preferred embodiment of the present invention; 
     FIG. 2 is a block diagram of the control system shown in FIG. 1; and 
     FIG. 3 is a flow chart showing the steps of the method of the present invention, which may be carried out using compute software instructions. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, a vehicle generally indicated by the numeral  10  includes an internal combustion engine  12  and a microcontroller  14 . As disclosed herein, the engine  12  is a diesel engine, and includes an intake manifold  16 , and a throttle valve  18 , a throttle valve actuator  20 , a fuel injector  21 , an exhaust manifold  22 , a filter assembly  24 , a turbocharger  26 , an EGR valve  28 , a mass air flow sensor  30 , a throttle valve position sensor  32 , a pressure sensor  34 , a speed sensor  36 , an air/fuel sensor  38 , and a pressure sensors  40 ,  42 . 
     The intake manifold  16  receives compressed air from the turbocharger  26  and directs the airflow to cylinders  44  of the engine  12 . The configuration of the manifold  16  may vary based upon the number of cylinders  44 . The manifold  16  includes the throttle valve  18  disposed therein. 
     The throttle valve  18  functions to selectively restrict the amount of air flowing through the manifold  16 , to thereby control the operation of the engine  12 , and in particular to control the exhaust gas temperature of the engine  12 . When the valve  18  is throttled (e.g., moved from a full/open position to a partially closed position), the exhaust gas temperature increases. The position of the valve  18  may be controlled to increase the exhaust gas temperature above a predetermined temperature (e.g., above 450° C.), to regenerate the filter assembly  24 . The method for controlling the valve  18  to increase the exhaust gas temperature will be discussed in more detail below. The valve  18  is conventional in the art and may comprise a conventional valve capable of restricting the airflow through the manifold  16 . For example, the valve  18  may comprise a butterfly valve or the like. 
     A throttle valve actuator is provided to move the valve  18  to a specified position. The actuator  20  is conventional in the art and may comprise a pneumatically controlled actuator or a stepper motor actuator or the like. The actuator  20  may respond to electrical signals generated by the microcontroller  14  to adjust the position of the valve  18 , thereby varying the flow of air to the manifold  16 . 
     The fuel injector  21  provides fuel to one of the cylinders  44  and is conventional in the art. Although a single fuel injector  21  is illustrated for purposes of simplicity, it is understood that each of the cylinders  44  has a corresponding fuel injector  21 . The fuel injector  21  receives fuel from a fuel pump (not shown) and injects a first pre-determined amount of fuel into one of the cylinders  44  during a power stroke of the corresponding cylinder  44 . Further, the fuel injector  21  may be utilized to inject a second, pre-determined amount of fuel into one of the cylinders  44  late in the power stroke (i.e., post-injection of fuel) of the corresponding cylinder  44  to further control the exhaust gas temperature as described in further detail herein below. In particular, the microcontroller  14  may generate controls signals that cause the fuel injector  21  to inject the first and second pre-determined amounts of fuel, respectively, into one of the cylinders  44 . 
     The exhaust manifold  22  directs exhaust gas from the cylinders  44  through the turbocharger  26  to the filter assembly  24 . The configuration of manifold  22  may vary based on the number of cylinders  44  in the engine  12 . The filter assembly  24  is provided to lower the exhaust gas emissions/particles before the exhaust gas is expelled from the engine  12 . The assembly  24  may include an oxidation catalyst  46  and a particulate filter  48 . 
     The oxidation catalyst  46  functions to increase the exhaust gas temperature of the engine  12  prior to the exhaust gas entering the particulate filter  48 . In particular, the post/injection of fuel into one or more cylinders  44  results in unburned hydrocarbons being expelled from the cylinders  44  into the oxidation catalyst  46 . The oxidation of hydrocarbons in the catalyst  46  is an exothermic reaction resulting in an additional increase in the exhaust gas temperature. Accordingly, the temperature of the exhaust gas exiting the oxidation catalyst is substantially higher (e.g., up to 200° C.) than the exhaust gas entering the filter assembly  24 . Exhaust gas within the oxidation catalyst is preferably heated to at least 450° C. before being expelled into the filter  48 , thereby regenerating the filter  48 . 
     The particulate filter  48  is provided to capture particulate matter such as carbon particles in the exhaust gas. The filter  48  may be conventional in the art and may comprise a steel/wool filter, a ceramic/monolith filter, or a ceramic/coil filter or the like. As discussed above, the filter  48  must be regenerated/cleaned at certain intervals since the filter  48  may become clogged with carbon particles from the exhaust gas. Further, the filter  48  may be regenerated by throttling the valve  18  and/or post injecting fuel into the cylinders  44  to thereby increase the exhaust gas temperature above a pre-determined, incineration temperature (e.g., 450° C.) of the carbon particles. 
     The turbocharger  26  compresses the air inducted into the engine  12  and may include a compressor  50  connected to the intake manifold  16 , and a turbine  52  disposed between the exhaust manifold and the filter assembly  24 . The EGR valve  28  is provided to reduce NOx emissions from the engine  12 . The valve  28  is conventional in the art and is disposed between the intake manifold  16  and the exhaust manifold  22 . 
     The mass airflow sensor  38  generates a signal V A  indicative of the mass airflow in the intake manifold  16 . The microcontroller  14  may receive the signal V A  and derive the measured value of mass airflow MAF from the signal V A . The sensor  30  is conventional in design and is preferably disposed in an inlet  54  upstream of the intake manifold  16 . 
     The throttle valve sensor generates a signal V V  indicative of the position of the valve  18  and is conventional in design. The microcontroller  14  receives the signal V V  and derives the measured position THR M  of the valve  18  from the signal V V . In one embodiment, the measured position THR M  of the valve  18  may have a range of from 0 to 1 wherein the value 0 represents a full-open position (i.e., no throttling) of the valve  18 , and the value 1 represents a full-closed position of the valve  18 . It should be understood, however, that the position of the valve  18  may be represented in a number of alternate ways. For example, the position of the valve  18  van be represented by a percentage of the full-open or full-closed position, or by a rotation angle associated with the valve  18 . The pressure sensor  34  generates a signal V P1  indicative of the pressure within the intake manifold  16 . The microcontroller receives the signal V P1  and derives the measured value of the intake manifold pressure P from the signal V P1 . The pressure sensor  34  is conventional in design. 
     The speed sensor  36  generates a signal V N  indicative of the speed of the crankshaft of the engine  12 . As microcontroller receives a signal V N  and derives the measured value of the engine speed N from the signal V N . The speed sensor  36  is also conventional in the art. 
     The air-fuel ratio sensor  38  generates a signal V AF  indicative of the air/fuel ratio of the engine  12 . Microcontroller  14  receives the signal V AF  and derives the measured value of the air/fuel ratio AF form the signal V AF . The sensor  38  is conventional in design and is disposed between the turbine  52  and the filter assembly  24 . 
     The temperature sensor  39  generates a signal V T , indicative of the temperature at the outlet of the filter assembly  24 . Microcontroller  14  receives the signal V T  and derives the measured value of the exhaust gas temperature T of the exhaust gas entering the filter assembly  24  from the signal V T . The pressure sensors  40 ,  42  generate signals V P2 , and V P3  respectively, indicative of the pressure at the inlet and outlet, respectively of the filters  24 . A microcontroller  14  receives signals V P2 , V P3  and derives the measured values of the inlet and outlet pressures P I , and P O , from the signals V P2 , V P3 , respectively. Alternatively the pressure sensors  40 ,  42  may be replaced by a single differential pressure sensor (not shown) that generates a signal indicative of the pressure drop across the filter assembly  24 . Microcontroller  14  may determine whether a regeneration of filter  48  is required based on the difference between the inlet and outlet pressures P I , P O . 
     Microcontroller  14  controls the engine  12 , and in particular, controls the throttle valve  18 . Microcontroller  14  is conventional in the art and is electrically connected to the throttle valve actuator  20 , the fuel injector  21 , the mass air flow sensor  30 , the throttle valve position sensor  32 , the pressure sensor  34 , the speed sensor  36 , the air/fuel ratio sensor  38 , the temperature sensor  39 , and the pressure sensors  40 ,  42 . Microcontroller includes a read/only memory (ROM) (not shown) that stores a software program for implementing the method in accordance with the present invention. 
     Attention is now directed to FIG. 2 which depicts the above described control system in block diagram form. A plurality of sensors  56  acquire information from the engine  12  and exhaust gas, and relays this information to a diesel particulate filter load monitor  58 , which may comprise hardware or software forming part of the microcontroller  14 . The sensors  56  include the previously discussed sensors  30 ,  32 ,  34 ,  36 ,  38 ,  39 ,  40  and  42 . The DPF (diesel particulate filter) load monitor  58  records and stores the diesel particulate loading of the filter  48 ; this load value is essentially a particulate load recorded as a function of a pre-determined, maximum load level which corresponds to a pre-determined level of back pressure to the exhaust gas flowing through the filter assembly  24 . The load monitor  58  may optionally include an adaptive algorithm to calculate the accumulated ash in the filter  48 . It is desirable to record the amount of ash in the filter  48  because even though it does not contribute to increase exhaust backpressure, it comprises an inert material and thus does not contribute the exothermic reaction occurring during the regeneration process. The estimated DPF load is sent to both a diagnostics module  60 , and a dynamic thresholding module  62 , both of which preferably form software routines stored in the microcontroller  14 . The diagnostics module  60  also receives information from the sensor  56 , and issues a warning MIL when, for any reason, the DPF loading has exceeded a critical threshold that could cause the filter assembly  24  to melt if a regeneration event was initiated. The MIL warning may take the form of turning on a light in the driver&#39;s compartment of the vehicle. Similarly, the diagnostics module  60  may issue the same warning if the filter assembly  24  evidences signs of a catastrophic failure, as when the filter becomes clogged or begins to melt to the extent that effective filtration is no longer provided. Finally, the diagnostics module  60  sets a software flag which terminates an on-going regeneration event in the event that the filter  48  exceeds a certain critical temperature, above which the structural integrity of the filter assembly  24  is threatened. 
     The dynamic thresholding module  62  evaluates the DPF load as well as the temperature at the DPF inlet and makes a determination of when to initiate the regeneration event. When a decision is made to commence regeneration, a flag is set which is delivered to a control module  64  which functions to output a series of signals that control those components of the engine  12  required to raise the exhaust gas temperature to the threshold level necessary to produce DPF regeneration by combusting the accumulated particulates. The control module  64  is also responsive to a halt flag issued by the diagnostic module  60  which results in the termination of an on-going regeneration event. When the regeneration flag is set by the thresholding module  62 , control module  64  issues signals to the appropriate control elements of the engine  12  to raise the exhaust temperature to the level necessary to initiate DPF regeneration. For example, first a signal is issued to close the EGR valve and a VNT (if present) or a turbine bypass is set to a fixed position or alternatively to an open position. A signal is then issued by module  64  to control the actuator  20  which operates the valve  18  to throttle the intake in order to initially raise the exhaust temperature to a level necessary to ensure that the oxidation catalyst has reached the so-called light-off temperature. Subsequently, post injection into the cylinders  44  is initiated in order to provide a further increase in the temperature the inlet of the filter assembly  24 . In the event that a halt flag is issued by the diagnostics module  60 , control module  64  opens the EGR valve  28  which in turn reduces the flow of oxygen to the filter assembly  24 . When the engine&#39;s intake is severely throttled back (as much as 500 mbar), the engine&#39;s efficiency is decreased and it becomes necessary to compensate for the lack of torque. Therefore, the microcontroller  14  includes a torque compensation module  66  which comprises software that increases the amount of fuel supplied to the engine based on information derived from the sensors  56 , including boost pressure, engine speed and base fuel demand. The data output by sensors  56  and modules  58 ,  60  and  62  are typically sampled at a relatively low rate, for example once per second, whereas module  64  and  66  are sampled at a relatively high rate, for example 16 ns. 
     From the foregoing description it may be appreciated that a control system is provided for determining the particulate loading of the filter  48  and increasing the exhaust gas temperature to achieve particulate light-off when desired. As previously stated, the initiation of a filter regeneration event when the vehicle&#39;s fuel tank is relatively low can result in several undesirable events, including unnecessary alarm to the vehicle&#39;s driver or an accelerated rate of fuel consumption which causes the vehicle to run out of fuel before the vehicle reaches a refueling station. In accordance with the present invention, however, the initiation of the filter regeneration event is coordinated with both the particulate loading level of the filter, and the level of fuel remaining in the vehicle&#39;s fuel tank. 
     Referring now also to FIG. 3, he method of the present invention is preferably implemented by a software routine forming part of the microcontroller  14  (FIG. 1) which operates as follows. The routine starts at  68 , and then initially determines whether the level of fuel in the vehicle&#39;s fuel tank is less than a first relatively low threshold value which may, for example correspond to the fuel level at which a “low fuel” lamp is illuminated in the vehicle&#39;s compartment. If the vehicle&#39;s fuel level sensor determines that the current fuel level is less than the first threshold value, then an inhibit regeneration flag is set, which in turn prevents a regeneration event from being initiated. More specifically, the inhibit regeneration flag generated at step  72  would prevent the control module  64  from initiating control events that increase the exhaust gas temperature. 
     If, however, the sensed fuel level is above the first threshold as determined at step  70 , then the routine continues and a determination is made at step  76  of whether the sensed fuel level is less than a second threshold value which is greater than the first threshold value. If the answer is no, then the routine either ends at step  84  or, if engine operation is continued, the routine returns to step  70 . If, however, the fuel level sensed at step  76  is less than the second threshold value, then a determination is made at step  78  on whether the loading of the particulate filter  48  is greater than a first particulate loading level which is chosen to be slightly below the level at which the filter  48  would definitely need to be regenerated. For example, the loading threshold limit could be 90% of the maximum particulate load limit. If the sensed, current particulate loading value is greater than the pre-selected, lower loading limit, then a forced regeneration flag is issued at step  80  which in turn initiates a regeneration of that. The logic represented by steps  76 ,  78 , and  80  effectively causes a regeneration event to be initiated when the fuel level is at a relatively low level, but above the first threshold value, and the loading of the particulate filter  48  is near its maximum load value. As a result, circumstances are avoided in which a fully loaded particulate filter  48  occurs when the fuel tank is near empty. In the event that the sensed particulate loading level at step  78  is less than the pre-determined loading limit, then no action needs to be taken and the logic sequence moves to step  82 . 
     Based on the above description, it may be appreciated that the method of the present invention provides for regeneration of the filter  48  which comprises the steps of sensing when the level of fuel is below a first threshold level representing a relatively low fuel level; regenerating the filter by raising the exhaust gas temperature; and, inhibiting the regeneration process when the sensed fuel level is below the first threshold level. Furthermore, it can be appreciated that the method also includes sensing when the level of the fuel in the tank is between the first threshold level and a second, higher threshold level; sensing when the particulate loading is between a first relatively high load level, and a second load level higher than the first load level; and regenerating the filter when the sensed fuel level is between the fist and second threshold values, and the sensed filter loading is between the first and second load levels. Finally, it can be seen that the method of the present invention effectively inhibits the filter regeneration process when the sensed level of fuel in the vehicle&#39;s fuel tank is below a threshold level at which an alarm is normally issued to alert the driver of the low fuel level. 
     From the foregoing, it is apparent that the method described above not only provides for the reliable accomplishment of the objects of the invention, but does so in a particularly economical and efficient manner. It is recognized, of course, that those skilled in the art may make various modifications or additions to the preferred embodiment chosen to illustrate the invention without departing from the spirit and scope of present contribution to the art. Accordingly, it is to be understood that the protection sought and to be afforded hereby should be deemed to extend to the subject matter claimed and all equivalents thereof fairly within the scope of the invention.