Abstract:
A motor vehicle operator interface and control algorithm convey diesel particulate filter regeneration status to the operator. The algorithm also allows new control over heretofore automatic regeneration, through limiting the inhibit function. The DPF after-treatment operator interface provides multiple status indications to the operator. In a preferred embodiment this is effected using a switched indicator lamp.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The invention relates to operator control over diesel engine exhaust particulate filter regeneration. 
   2. Description of the Problem 
   Electronic engine control systems are known which provide processor-based engine controllers that process data from various sources to develop control data for controlling certain functions of the engine. The interaction of such control systems with more general vehicle control networks, typically controller area networks (CAN), is also known. The state of development in the art is represented by the development by the Society of Automotive Engineers of several standards, most particularly the SAE J1939 standard governing vehicle control networks. The SAE J1939 standard seeks to assure, among other things, the seamless interaction of different manufacturers&#39; engine controllers over such networks with other controllers. 
   The context of the present invention is the handling of diesel particulate filter (DPF) regeneration. DPF&#39;s trap Diesel Particulate Matter (DPM) includes soot or carbon, the soluble organic fraction (SOF), and ash (i.e. lube oil additives etc.). The trapping of those constituents by a DPF prevents what was once seen as black smoke billowing from a vehicle&#39;s exhaust pipe. The organic constituents of trapped DPM, i.e. carbon and SOF, are oxidized within the DPF at appropriate times and under appropriate conditions to form CO 2  and H 2 O, which can then pass through and exit the exhaust pipe to atmosphere. The ash collects within the DPF over time, progressively aging the DPF by gradually reducing its trapping efficiency. 
   DPF regeneration is typically handled by the engine controller. The reasons for locating control in the engine controller stem from the fact that regeneration requires the combustion or oxidation of the carbon rich particles which have built up in the DPF. One way to regenerate a DPF involves raising the temperature in the filter to the ignition temperature of a substantial portion of the particles and supplying enough oxygen (the conventional oxidizer) or NO 2  (a possible oxidizer) to the filter to support combustion. While there are several techniques used to start such combustion, most involve changing physical attributes or chemical mix of the exhaust stream into the DPF. Among the quantities that can be controlled are: temperature of the stream; the quantity of oxygen in the stream; and the amount of supplemental fuel in the stream (the supplemental fuel can have a lower combustion initiation temperature). All of these conditions can be affected by manipulating engine operation. 
   The rate at which trapped carbon is oxidized to CO 2  is controlled not only by the concentration of NO 2  or O 2  but also by temperature. Specifically, there are three important temperature variables for a DPF. The first is the oxidation catalyst&#39;s “light off” temperature, below which catalyst activity is too low to oxidize HC. That temperature is typically around 180-200 degrees Celsius. The second controls the conversion of NO to NO 2 . This NO conversion temperature spans a range of temperatures having both a lower bound and an upper bound, which are defined as the minimum temperature and the maximum temperature at which 40% or greater NO conversion is achieved. The conversion temperature window defined by those two bounds extends from approximately 250 degrees C. to approximately 450 degrees C. The third temperature variable is related to the rate at which carbon is oxidized in the filter. Reference sources in relevant literature call that temperature the “Balance Point Temperature” (or BPT). It is the temperature at which the rate of oxidation of particulate, also sometimes referred to as the rate of DPF regeneration, is equal to the rate of accumulation of particulate. The BPT is one of the variables that is especially important in determining the ability of a DPF to enable a diesel engine to meet expected tailpipe emissions laws and/or regulations. 
   A typical diesel engine comprises fuel injectors for injecting fuel into the engine cylinders under control of an engine control system. The engine control system controls the duration, timing, quantity and potentially the charge shape of each pulse. These factors can be varied to control completeness of combustion, the quantity of oxygen in the exhaust, the amount of unburned fuel in the exhaust and the temperature of the exhaust. In a turbocharged diesel engine, the electronic engine control system also exercises control over turbocharger boost to vary the amount of oxygen being delivered. 
   Typically, a diesel engine runs relatively lean and relatively cool compared to a gasoline engine. That factor makes natural achievement of BPT problematic. Therefore, a manufacturer of a DPF for a diesel engine should strive for a design that minimizes BPT, and a diesel engine manufacturer should strive to develop engine control strategies for raising the exhaust gas temperature to temperatures in excess of BPT whenever the amount of trapped particulates exceeds some threshold that has been predetermined in a suitably appropriate manner, such as by experimentation. Using an engine control to raise exhaust gas temperature in this way is a type of regeneration. 
   Investigation of several methods for initiating a forced regeneration of a DPF has disclosed that retarding the start of main fuel injections seems to be the most effective way to elevate exhaust gas temperature. That method is able to increase the exhaust gas temperature sufficiently to elevate the catalyst&#39;s temperature above catalyst “light off” temperature and provide excess HC that can be oxidized by the catalyst. Such HC oxidation provides the necessary heat to raise the temperature in the DPF above the BPT. 
   The diesel trucking industry is developing operator interfaces for their respective 2007 EPA-mandated Diesel Particulate Filter (DPF) aftertreatment systems. These interfaces may control two basic aftertreatment operations: allow a particulate trap regeneration, and inhibit a particulate trap regeneration. Operator interfaces for such systems have typically provided only a Particulate Trap Warning lamp, and a High Exhaust Temperature System Warning lamp. 
   U.S. Pat. No. 6,497,095 discussed circumstances under which automatic initiation of regeneration might be inhibited. That patent provided for such inhibition in response to low fuel reserves, a consequence of the fact that most regeneration methods involve increased fuel flow. 
   SUMMARY OF THE INVENTION 
   The present invention is implemented using contemporary vehicle control systems, and in the preferred embodiment is implemented using a controller area network conforming to the SAE J1939 standard. The algorithm of the present invention supplements this preexisting feature of contemporary vehicle control architecture to provide an operator interface conveying DPF regeneration status to the operator. The algorithm also allows new control allowing-inhibiting over heretofore automatic regeneration. 
   The DPF after-treatment operator interface provides multiple status indications to the operator. In a preferred embodiment this is effected using a switched indicator lamp. In the preferred embodiment a slow blinking switch indicates that particulate trap regeneration is prevented by an interlock, or the engine software is unavailable or incorrect. A fast blinking switch indicator lamp conveys that the J1939 link has been lost (loss of message communication to the engine). A continuously illuminated lamp solid switch indicator shows that particulate trap regeneration is occurring. When the solid switch indicator transitions from solid to off, the regeneration has finished. The algorithm of the present invention inhibits particulate trap regeneration under certain conditions. The inhibit signal is only allowed during a window delimited by a top and bottom vehicle speed. For example: an operator may choose to inhibit the regeneration during low speeds, but when the operator increases the vehicle speed, the inhibit function will cease (allowing the engine to initiate automatic regeneration), and the operator will be notified by the inhibit switch indicator slow blinking. The operator is also notified when the communication to the engine is lost by the fast flash of the inhibit switch indicator. The operator is notified when an inhibit is successful. 
   SAE J1939 documentation specifies that the inhibit function takes precedence over the request for regeneration function. We have developed an algorithm that meets this requirement, while allowing the operator to intuitively choose the after-treatment function using a “last-in, first out” algorithm. 
   Additional effects, features and advantages will be apparent in the written description that follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a general schematic diagram of an exemplary diesel engine having an engine controller which provides engine operation supporting forced regeneration of a diesel particulate filter in accordance with principles of the present invention. 
       FIG. 2  is a semi-schematic drawing of a particulate filter. 
       FIG. 3  is a semi-schematic drawing of another particulate filter. 
       FIG. 4  is a high level schematic of a vehicle controller area network. 
       FIG. 5  is a state diagram illustrating the principles of the invention. 
       FIG. 6  is a state diagram illustrating the principles of the invention. 
       FIG. 7  is a state diagram illustrating the principles of the invention. 
       FIG. 8  is a state diagram illustrating the principles of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a schematic diagram of an exemplary diesel engine  20  for powering a motor vehicle. Engine  20  has a processor-based engine control system/engine controller  22  that processes data from various sources to control various aspects of engine operation. The data processed by engine controller  22  may originate at external sources, such as sensors or received over a network bus, and/or be generated internally. 
   Engine controller  22  includes an injector driver module  24  for controlling the operation of electric-actuated fuel injectors  26  that inject fuel into combustion chambers in the engine cylinder block  28 . A respective fuel injector  26  is associated with each cylinder and comprises a body that is mounted on the engine and has a nozzle through which fuel is injected into the corresponding engine cylinder. A processor of engine control system  22  can process data sufficiently fast to calculate, in real time, the timing and duration of injector actuation to set both the timing and the amount of fueling. 
   Engine  20  further comprises an intake system having an intake manifold  30  mounted on block  28 . An intercooler  32  and a compressor  34  of a turbocharger  36  are upstream of manifold  30 . Compressor  34  draws air through intercooler  32  to create charge air that enters each engine cylinder from manifold  30  via a corresponding intake valve that opens and closes at proper times during engine cycles. 
   Engine  20  exhausts combustion by product under pressure to an exhaust system for eventual release, after treatment, to the atmosphere. The exhaust system comprises an exhaust manifold  38  mounted on block  28 . Exhaust gases pass from each cylinder into manifold  38  via a respective exhaust valve that opens and closes at proper times during the composition cycle. The exhaust system further includes an exhaust turbine  40  and a diesel particulate filter  42 . 
   Turbocharging of engine  20  is accomplished by turbocharger  36  that further comprises a turbine  40  in the exhaust system and coupled via a shaft to compressor  34  in an intake system. Hot exhaust gases acting on turbine  40  cause the turbine to operate compressor  34  to develop the charge air that provides boost for engine  20 . 
   The exhaust system further comprises a diesel particulate filter or trap DPF  42  downstream of turbine  40  for treating exhaust gas before it passes into the atmosphere through an exhaust pipe  44 . The DPF shown in  FIG. 2  is representative of the “Continuously Regenerating Trap”. It comprises an oxidation catalyst  46  disposed upstream of a non-catalyzed DPF  48 . DPF  48  physically traps a high percentage of DPM in exhaust gas passing through it, preventing the trapped DPM from passing into the atmosphere. Oxidation catalyst  46  oxidizes hydrocarbons (HC) in the incoming exhaust gas to CO2 and H2O and converts NO to NO2. The NO2 is then used to reduce the carbon particulate trapped in DPF  48 . 
   The DPF  42  shown in  FIG. 3  is representative of another type of DPF (or CSF) having an additional CeO 2  catalyst that makes it less dependent on NO 2  for oxidizing trapped particulate. It has a single substrate  50  that combines an oxidation catalyst with a trap, thereby eliminating the need for a separate upstream oxidation catalyst as in the DPF  42  shown in  FIG. 2 . As exhaust gases are passing through substrate  50 , DPM is being trapped, and the oxidation catalyst is oxidizing hydrocarbons (HC) and converting NO to NO 2 , with the NO 2  being used to oxidize the trapped carbon. 
   Control of regeneration of the illustrated DPF  42  is implemented through the engine controller, in part responsive to data received over a controller area network (CAN)  101  from diverse controllers attached to a system bus  18  forming the backbone of the CAN  101 . Referring to  FIG. 4  it may be seen that engine controller  22  is coupled to receive from a series of sensors, data relating to variables required for initiating and controlling filter regeneration. The sensors provide throttle position  120 , DPF temperature  121  (which may be exhaust temperature), DPF inlet pressure (related to soot loading)  122 , exhaust mass flow  123 , engine speed (tachometer)  125  (typically a cam shaft rotational position sensor which is required for determining injection timing), and soot load information  126 . The engine controller  22  provides through the injection controller  24  injection timing, duration and shape ( 124 A-C). Changes in injection, particularly timing (such as injection occurring after peak pressure or post ignition injection) can be used to increase exhaust temperature or insert unburned fuel into the exhaust stream and thereby support DPF regeneration. As described above, operating conditions of the turbosupercharger  36  may also be varied. The particular method of regeneration used is not an essential part of the invention other than it is put into effect by the engine controller  22 . 
   The need for regeneration is determined by the soot load. Typically a surrogate is used for soot load such as DPF inlet pressure  122 , which is related to exhaust back pressure independent of changes in engine output. Circumstances under which regeneration is possible, or allowed, may be determined from a variety of sources. Engine operating conditions, as provided by the throttle position, engine speed (i.e. tachometer signal) or engine temperature may all be relevant depending upon the regeneration method used. However, vehicle operating conditions may also be relevant. Engine controller  22  is supplied with CAN messages over network bus  18  relating to vehicle operating conditions. For example, an anti-lock brake system (ABS) controller  122  may supply vehicle speed as determined from the wheel speed sensors  123 . The same value may also come from a transmission controller  16  which generates a speed signal from a transmission tachometer  17  (the output from the tachometer  17  may also be supplied directly to the engine controller  22 ). On automatic transmission equipped vehicles the transmission controller  16  also provides indication of which gear the vehicle is in. If the vehicle is equipped for power take off (PTO) operation, indication that PTO operation has been invoked may be provided indirectly from a PTO controller  80  over a private bus  118  connecting the PTO controller to an electrical system controller  30  (ESC) which places the signal onto the public J1939 network bus  18 . Operator inputs relating to regeneration control are typically received by engine controller  22  from a gauge cluster controller  14 , though they could be connected to the network bus  18  through instrument and switch bank controller  12 . ESC  30  is connected directly to a series of switches (or switch ladders) possibly affecting regeneration including a clutch pedal position switch  140 , an ignition position switch  141 , a park brake position switch  142  and a speed control ladder network  143 . 
   Operator control over regeneration is implemented through an interface  25  connected to a gauge and cluster controller  14  (or, alternatively to an instrument and switch bank controller  12 ). Interface  25  provides at least two switches, including a regeneration inhibit switch  701  and a parked regeneration switch (or “forced regeneration switch”)  601  along with indicator lights  60 ,  50 , associated with each switch. The controllers communicate with other vehicle controllers over bus  18 . 
     FIGS. 5-8  graph the state machines implementing the algorithm of the invention. The algorithms determine when DPF regeneration is in progress, or when a DPF regeneration has been inhibited, and alert the operator to system conditions. As seen in  FIG. 5  from state machine  500 , the state machine is entered from start  502  by the ignition  141  being in the “ON” condition and the engine running, which is known to the engine controller  22 . At the highest level of abstraction there are three states  504 ,  506 ,  508 : (1) Regeneration automatically controlled by the engine controller  22 ; (2) Regeneration inhibited by the engine controller  22 ; and (3) Request to force regeneration accepted by the engine controller  22 . The interlock conditions mentioned in the various transition condition definitions relate to other vehicle conditions being met under which regeneration is allowed. 
   Several CAN messages are identified in the State machines. They include:
         SPN  3695  Particulate Trap Regeneration Inhibit Switch       

   This signal indicates the state of the switch (Regeneration Inhibit Switch  701 ) that inhibits particulate trap regeneration. When this message assumes a not active value regeneration is allowed to occur normally.
         SPN  3696  Particulate Trap Regeneration Force Switch (Parked Regen)   This signal indicates the state of the switch available to the operator to force particulate trap regeneration.   SPN  3697  Particulate Trap Lamp Command   SPN  3700  Particulate Trap Active Regeneration Status   This signal indicates if regeneration is occurring.   SPN  3702  Particulate Trap Active Regeneration Inhibited Status   This message indicates the reason for regeneration not being initiated or terminated prior to completion.   SPN  3703  Particulate Trap Active Regeneration Inhibited Due to Inhibit Switch       

   Beginning with the default automatic regeneration control state  504  entered on engine-start it is seen that transitions are allowed to either of the other two major states. The regeneration inhibited state  506  follows occurrence of a regeneration inhibit request by the operator entered through the regeneration interface  25 , provided that various interlocks are met (transition conditions  510 ). The regeneration inhibited state  506  is maintained only if the transition conditions  510  are met. Once they are not met (condition  511 ) the state returns to automatic control state  504 . 
   Next, transition  512  from automatic regeneration state  504  to the park regeneration request accepted state  508  occurs when a parked regeneration of the DPF is requested by an operator and another set of interlocks is met (transition conditions  512 ). A return transition from state  508  to state  504  occurs under transition conditions  513 . Condition set  513  is essentially the negative of transition conditions  512  or completion of regeneration. 
   It is also possible for transitions to occur directly between states  506  and  508 . Transition from the regeneration inhibited state  506  to the parked regeneration accepted state  508  occurs when conditions  515  are met, which are basically the same conditions as condition set  512 . The transition path from the parked regeneration request state accepted state  508  back to the regeneration inhibited state  506  occurs upon the inhibit regeneration request condition  516  occurring upon entry of such a request by an operator. 
   Referring to  FIGS. 6 and 7 , indicators  50 ,  60  are used to indicate operating status of a diesel particulate filter by changes in flash rates of the indicators. In the preferred embodiment a slow blinking switch indicates that particulate trap regeneration is prevented by an interlock, or the engine software is unavailable or incorrect. A fast blinking switch indicator  50  conveys that the J1939 link has been lost (loss of message communication to the engine), that is, an error condition. A continuously illuminated lamp indicator  50  shows that particulate trap regeneration is occurring. When the solid switch indicator  50  transitions from solid to off, the regeneration has finished. The inhibit signal is only allowed during a window delimited by a top and bottom vehicle speed. For example: an operator may choose to inhibit the regeneration during low speeds, but when the operator increases the vehicle speed, the inhibit function will cease (allowing the engine to initiate automatic regeneration), and the operator will be notified by slow blinking of the indicator  60 . The operator is also notified when the communication to the engine is lost by the fast flash of the inhibit switch indicator  60 . The operator is notified when a request to inhibit regeneration is successful. 
     FIG. 6  illustrates a state machine  600  for illumination control of the back lit indicator  50  of a parked regeneration request switch  601  installed in the operator interface  25 . The parked regeneration request switch  601  is a three position mono-stable switch where Up equals ON, Down equals OFF (Cancel) and center is NEUTRAL. Switch  601  is stable in the center position. With movement of the ignition switch  141  to the one state entry to the state machine  600  from an ignition off state  602  to an indicator  50  off state  604  occurs. 
   From state  604  three transitions are possible, to an Indicator  50  flashing “fast” state  616 , to an Indicator  50  flashing “slow” state  610  and to another Indicator  50  flashing “slow” state  606 . Indicator  50  flashing “slow” state  606  corresponds to a ready condition for initiating DPF regeneration and occurs only following the Indicator OFF state  604  following simultaneous occurrence of four conditions  620 : (1) the CAN message (SPN  3696 =01) is present indicating the operator has requested forcing regeneration; (2) the Parked Regeneration Switch  601  has been at least momentarily closed ON (or UP); (3) the Inhibit switch  701  has not been closed ON or UP; and (4) Regeneration is needed as indicated by the engine controller  22 . The CAN SPN  3696  message value is set in response to operator use of the parked regeneration switch as defined below with reference to  FIG. 8 . 
   From state  606  various intervening conditions may occur which prevent transition to the indicator ON state  608 . These factors include closure of the Inhibit switch  701  and engine controller  22  unavailability or failure of a selected CAN message to set to the appropriate value (SPN  3702 =01, i.e. inhibited). Obviously then a state transition from “slow” flashing (state  606 ) to a state  608  of constant illumination of indicator  50  occurs under the conditions  626  when all interlocks have been met, the Parking Regeneration Switch has not been closed down or OFF and the inhibit switch  701  has not been closed up or ON and the ignition has not been turned OFF. Additionally, the operator is enabled to over ride the inhibit switch  701  by a subsequent activation of the Parking Regeneration switch  601 . Accordingly, the transition from state  606  to state  608  also occurs, notwithstanding the fact that the inhibition switch has been closed UP, if the Regeneration switch is also closed ON or up contemporaneously or afterward. 
   The remaining two transitions from the Indicator  50  “slow” flashing state  606  are in essence aborts. The state returns to Indicator  50  OFF when condition set  622  is met. Condition set  622  provides SPN  3696 =00, i.e. not active) and that the conditions for transition to state  608  are not met. Alternatively, if either the parked regeneration switch is depressed downwardly or OFF, or the ignition  141  is turned OFF, then the state transits to Indicator OFF state  604 . The state returns to Indicator  50  flashing “slow” state  612  under condition set  624 , that is where an intervening actuation of the inhibit switch  701  has occurred (without an override by subsequent depression of the Parked Regeneration Switch  701 ). 
   Five transitions from the Indicator  500 N state  608  exist. These transitions include a transition to the Indicator  50  flashing “slow” state  610 , a transition to Indicator  50  flashing “slow” state  612 , transition back to Indicator  50  OFF state  604 , and transitions to the error states, Indicator  50  flashing “fast” states  616  and  618 . Condition set  630  defines when the transition from state  608  to state  604  occurs. One such condition is simply turning the ignition  141  off. The transition also occurs upon a concurrent combination of events including transmission of the SPN  3696 =00 message and all engine interlocks being met and the inhibit switch  701  not being UP. 
   Error conditions (SPN  3696 =10)  628  can arise with the Regeneration switch  601  being UP or it being not UP. If the Regeneration switch  601  is not UP when a fault condition arises a transition from state  608  to the Indicator  50  flashing fast state  618  occurs. If the Regeneration switch  601  is UP the transition to Indicator  50  flashing “fast” state  616  occurs. The reason for two error states relates only to the exit conditions from the states. As long as the Parked Regeneration switch  601  is held UP, flashing of the indicator  50  continues. When the switch in longer up flashing discontinues after a five second time out. Hence a transition from state  616  to state  618  is provided upon release of the parked Regeneration switch from the UP position. Indicator  50  flashing “fast” is reached from the Indicator OFF state  604  under an identical set of conditions  632  to those by it is reached from the Indicator on continuously state  608 . 
   Indicator  50  “slow” flashing states  610 ,  612  will now be described. These states may be reached under conditions where regeneration would be allowed, but is not needed, among other events. The difference between states  610 ,  612  is only the exit condition between from the states. Exit from state  612  is only to the Indicator OFF state  604  and occurs after a time out event. Exit from state  610  is only to “slow” flashing state  612  and occurs upon release of the Parked Regeneration switch  601  from its “UP” position. A transition path is provided from the Indicator OFF state  604  to the Indicator  50  “slow” flashing state  610  based on the condition set  636  which outlines two subsets of events for the transition. Both subsets include that the no error condition has occurred relating to the regeneration request (SPN  3696  . . . 10). Then, if the Parked Regeneration switch  601  is UP and regeneration is not needed the transition occurs. Alternatively, if the Parked Regeneration switch  601  is UP and the Inhibit Switch  701  is UP the transition to state  610  occurs. 
   Transition paths are provided from state  608  (Indicator  50  on continuously) to either “slow” flashing state  610 ,  612 . Either transition requires that the engine controller  22  indicate software unavailability. Then either the inhibit switch  701  must be UP or the engine interlock conditions must fail. These conditions are sufficient to provide transition from state  608  to either slow flashing state  610 ,  612 . Determination of which one depends upon the position of the parked regeneration switch  601 . If UP the transition is to slow flashing state  610 . If DOWN the transition is to slow flashing state  612 . 
   Referring now to  FIG. 7 , as before, the default OFF state  702  of the inhibition indicator lamp  60  is assumed upon ignition  1410 N. The Regeneration Inhibit switch  701  is preferably a three position mono-stable unit akin to the parking regeneration switch, though it is possible to use a two position bistable switch. An ON state of the indicator lamp  60  is delayed after an inhibit request, an accordingly no direct transition from OFF state  702  to ON state  704  is provided. Instead, an intermediate delay state  706  is provided which is reached from OFF state  702  when the Inhibit switch  701  is UP and the Parked Regeneration switch  601  is not UP and there is no error. Condition set  712  described the circumstances under which the state will transition from delay state  706  back to OFF state  702  after a 10 second delay. The first subset of conditions corresponds to no error occurring and the inhibit switch  701  being moved affirmatively to the down position. A second subset of conditions corresponds to the inhibit switch not being UP and the parked regeneration switch being UP. A third subset occurs with an engine controller message that it is not inhibited by the inhibit switch and the inhibit switch is not UP. Delay state  706  allows up to 10 seconds to satisfy the conditions to move to ON state  704 . 
   A transition from ten second delay state  706  to the inhibit light illuminated state  704  occurs as soon as the transition conditions  714  are met. Transition condition  714  are that there is no error, the inhibit switch is not down and either that the parked regeneration switch is UP or both the inhibit switch and parked regeneration switches are UP, and that engine controller acknowledge that regeneration is inhibited and finally that the ignition not be off. A transition from the delay state  706  or the ON state  704  to an error state  708  follows breakdown in CAN communication or an invalid switch position. 
   A second transition from the ON state  704  is possible back to the OFF state  702 . The condition set  710  describes these circumstances which include: (1) engine OFF; or, (2) there is no error and either the inhibit switch is down or there is a message that the engine controller is not inhibited by the inhibit switch, OR, the inhibit switch in not UP and the parked regeneration switch is UP. 
   Finally, state transitions are possible between the OFF state  702  and the error state  708 . Error state  708  is reached from OFF state  702  upon occurrence of condition set  716 , essentially loss of CAN network communication or the occurrence of invalid switch positions. Transition to the OFF state  702  from error state  708  occurs upon restoration (or indication) of good CAN communications with all switch positions being valid, or upon turning the ignition OFF. 
   Referring to  FIG. 8 , a state machine defining the value of CAN message SPN  3696  (forced regeneration). As before, the default is termed the OFF state  802 , which here corresponds to a message value of “00”. The SPN  3696  value is reset in response to actuation of the Parked Regeneration switch  601  and expiration of a delay. Reset of the value begins with the transition from the OFF state  802  to a Two minute delay state  804 . The conditions for this transition are that the parked regeneration switch be UP, the inhibit switch not be UP and that regeneration is needed. 
   A state transition back to the OFF state  802  from delay state  804  is possible. The condition set  810  defines the conditions giving rise to this transition, which occurs if there is no error and the following logical relationship holds true:
         the delay period (here two minutes since the regeneration request) and [the Parked Regeneration Switch is down or (the Inhibit switch is UP AND the Parked Regeneration Switch is not UP) OR the Ignition is OFF].       

   A transition from the two minute delay state  804  to ON state (SPN  3696 =01) occurs when condition set  812  is met. Condition set  812  provides:
         There is no error AND the Engine controller  22  reports all interlocks have been met AND [the Inhibit Switch is not UP OR (the Inhibit Switch is UP and the Parked Regeneration switch is UP)] AND the Ignition Switch is not OFF and the Park Brake  142  is set.       

   A transition from the ON state  806  to OFF state  802  occurs upon meeting the requirements of condition set  814 . Condition set  814  provides:
         That there is no error AND [the Ignition is OFF OR the Parked Regeneration Switch  601  is DOWN OR (the Inhibit Switch  701  is UP AND Parked Regeneration Switch is not UP) OR Regeneration is complete (SPN=3700 transitions from 01 to 00) OR there is an Engine controller  22  message that all interlocks for regeneration have not been met (SPN  3702 =01) OR (the vehicle is reported as a selected model and the park brake has not been set)].       

   The error state follows occurrence of condition sets  818 ,  816 , which are substantively identical. Basically, condition sets  818 ,  816  are that there has been a loss of CAN communication or an invalid switch position has been detected. The Error state  808  can only be exited to the OFF state  802 . This occurs upon reestablishment of good CAN communications with no invalid switch positions, or upon the ignition being turned off. 
   Using SAE J1939 messaging, indication can be given the operator of the status of DPF regeneration whenever the ignition is on. The operator&#39;s required actions are reduced by the simplicity of interface. Other methods utilize a high-temperature exhaust warning indicator to alert the operator to the ongoing DPF regeneration, whereas the algorithm of the present invention determines the status and reports it in the switch indicator of the parked regeneration request switch. Failed interlocks, for example, are reported as a slow blink, while a critical error is reported as a fast blink. A unblinking light means serves as acknowledgment of the requested operation and indicates execution of the operation. Through the interface of the invention, in cooperation with existing an existing controller area network and supplemental programming, operators are given the ability to intervene in DPF regeneration. 
   While the invention is shown in only a few 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.