Abstract:
A vehicle has an engine, an exhaust aftertreatment system, an electric machine, and a controller configured to, in response to an actual engine torque output being less than an inferred engine torque, shut down the engine. A vehicle has an engine, an exhaust aftertreatment system, an electric machine, and a controller configured to, in response to an actual engine torque output being less than a first threshold and a torque request to the engine being greater than a second threshold, set a diagnostic code. A method includes receiving an actual engine torque output, receiving an engine torque request, and shutting down the engine when the actual engine torque output is less than a first threshold and the engine torque request is greater than a second threshold for a predetermined time period to limit temperature increase of a catalyst.

Description:
TECHNICAL FIELD 
       [0001]    Various embodiments relate to monitoring engine conditions to limit a temperature increase in a catalyst or to detect restricted airflow in an exhaust aftertreatment system in a vehicle, including a hybrid electric vehicle (HEV). 
       BACKGROUND 
       [0002]    Vehicles with engines require engine exhaust aftertreatment systems to remove unwanted chemicals from the exhaust flow and meet emissions requirements. The engine exhaust aftertreatment system may be a catalytic converter. In the case of a three-way catalytic converter, various amounts of carbon monoxide, unburned hydrocarbons and nitrous oxides are removed from the engine exhaust flow before it exits the vehicle to the environment. Unburned hydrocarbons may include unburned fuel and partially burned fuel. If high levels of unburned hydrocarbons are permitted to reach the catalytic converter, the catalytic converter temperature may increase due to chemical reactions between the unburned hydrocarbons and oxygen caused by the catalyst material. These chemical reactions release heat. The temperature rise in the catalytic converter may lead to catalyst degradation or damage, with the potential for catalyst meltdown, restricted exhaust flow, and catalyst deactivation. 
         [0003]    Hybrid vehicles may have electric motors configured to rotate the engine without combustion occurring. This hybrid architecture may allow high levels of unburned hydrocarbons reaching the catalytic converter if the electric motor is rotating the engine while the engine is misfiring, stalling, or complete combustion is otherwise not occurring within a cylinder. 
         [0004]    A system and method needs to be provided to monitor the engine and exhaust to detect and/or prevent large amounts of unburned hydrocarbons from reaching the catalytic converter, or to provide a diagnostic code when it does occur. 
       SUMMARY 
       [0005]    In an embodiment, a vehicle is provided with an engine, an exhaust aftertreatment system having a catalyst, an electric machine, and at least one controller. The at least one controller is configured to, in response to an actual engine torque output being less than an inferred engine torque output for a predetermined time period, shut down the engine to limit temperature increase of the catalyst. 
         [0006]    In another embodiment, a vehicle is provided with an engine, an exhaust aftertreatment system, an electric machine, and at least one controller. The at least one controller is configured to, in response to an actual engine torque output being less than a first threshold and a torque request to the engine being greater than a second threshold for a predetermined time period, set a diagnostic code to indicate restricted air flow in the aftertreatment system. 
         [0007]    In yet another embodiment, a method for controlling an engine is provided. Data indicative of an actual engine torque output is received from an electric machine configured to control the speed of the engine. Data indicative of an engine torque request is received. The engine is shut down when the actual engine torque output is less than a first threshold and the engine torque request is greater than a second threshold for a predetermined time period to limit temperature increase of a catalyst in an engine aftertreatment system 
         [0008]    Various embodiments according to the present disclosure have associated advantages. For example, torque may be used to determine whether the engine is operating or stalling/misfiring with unburned hydrocarbons being motored to the catalytic converter to detect conditions that may degrade or damage the catalyst and preserve the catalyst. Alternatively, the algorithm may detect conditions showing that the catalyst is degraded or damaged, and an appropriate diagnostic code may be set for a service technician. Detection may be difficult, as the vehicle may continue to meet emissions regulations as the flow over the remaining degraded or damaged catalyst surface area is restricted. Previous monitors were unable to operate unless the catalyst was inactive, could not diagnose low engine power complaints caused by restricted flow through the catalytic converter, and could not detect a throttle stuck in a closed position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic diagram of a hybrid vehicle capable of implementing various embodiments of the present disclosure; 
           [0010]      FIG. 2  is a flowchart depicting an algorithm for detecting a stall condition for a catalyst monitor according to an embodiment; and 
           [0011]      FIG. 3  is a flowchart depicting an algorithm for detecting a partially blocked exhaust path from a damaged catalyst for a catalyst monitor according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    As required, detailed embodiments of the present disclosure are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary and may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the claimed subject matter. 
         [0013]    In  FIG. 1 , an embodiment of a hybrid electric vehicle (HEV) is shown that may be used with the diagnostic of the present disclosure. Of course,  FIG. 1  represents only one type of HEV architecture, and is not intended to be limiting. The present disclosure may be applied to any suitable HEV. Furthermore, the present disclosure may be applied to any conventional vehicle that includes a start motor or other device for rotating the crankshaft when the engine is not operating. 
         [0014]    Engine  20  is a primary power source in the HEV configuration of  FIG. 1 . A secondary power source is a combination of a generator  40 , an electric motor  42 , and a battery and battery control module  44 . The components of the combination are electrically coupled by an electrical high voltage bus. In some embodiments, the battery  44  is additionally rechargeable in a plug-in hybrid electric vehicle (PHEV) configuration using a receptacle  45  connected to the battery  44 , possibly through a battery charger/converter unit. The receptacle  45  may be connected to the power grid or other outside electrical power source to charge the battery  44 . 
         [0015]    The powertrain includes a transmission  46 , which comprises a planetary gear unit  48 , the generator  40  and the motor  42 , as well as torque transfer counter shaft gearing  50 . The planetary gear unit  48  comprises a ring gear, a sun gear, a planetary carrier and planet gears rotatably supported on the planetary carrier for engagement with the ring gear and the sun gear. A power output gear element of the gearing  50 , is driveably connected to a differential-and-axle assembly  52 , which distributes power to vehicle traction wheels  54 . In other embodiment, other transmission  46  architectures may be used as are known in the art. 
         [0016]    An overall controller for the operating modes of the powertrain may be implemented by a vehicle system controller (VSC)  56 , electronic control unit (ECU), or controller, that receives various inputs including driver inputs at  58  and  60 . The input at  58  is an accelerator pedal position sensor signal (APPS) and the input at  60  is driver selection for “park,” “reverse,” “neutral” or “drive range” (PRND). 
         [0017]    The engine  20  has an exhaust  22 , which flows through an aftertreatment system  24  containing a catalyst, such as a catalytic converter or the like, and to the environment. The catalytic converter  24  contains a substrate which supports a catalyst material as is known in the art. The catalyst material chemically reacts with the exhaust to reduce emissions of unburned hydrocarbons, carbon monoxide, and nitrous oxides. 
         [0018]    If the engine  20  stalls, misfires or otherwise has incomplete combustion while being rotated, such as when being spun by the generator  40 , an unburned fuel and air mixture flows through the exhaust  22  and to the catalytic converter  24 . The temperature in the catalytic converter  24  can rise to the point where the catalyst may melt if the unburned hydrocarbon level is sufficiently high and conditions in the catalytic converter  24  and vehicle are met, i.e. high catalyst temperature. Additionally, if catalyst melting occurs in the catalytic converter  24 , an increased back pressure on the engine  20  from exhaust flow restriction may reduce the engine power output. Catalyst degradation, melting, or damage may undetectable using emissions sensors, as the restricted flow over the remaining catalyst material often meets vehicle emissions regulations. 
         [0019]    A flow chart illustrating an embodiment of a diagnostic or monitor using algorithm  70  is shown in  FIG. 2 . The algorithm  70  may detect an engine stall based on actual engine torque, inferred engine torque, and requested engine torque to detect and/or prevent conditions that may damage the catalyst. The algorithm  70  may be implemented by the VSC  56  and use sensor data available to the VSC  56 . In one embodiment, algorithm  70  detects conditions that may lead to catalyst damage and operates the vehicle to prevent damage. 
         [0020]    The algorithm  70  starts at  72 . The controller  56  determines if the engine  20  is being commanded to run or operate at  74 . This does not mean that the engine  20  is actually operating and combusting, for example, the engine  20  could be commanded to run but be stalled or misfiring, and not operating correctly. 
         [0021]    The algorithm  70  then determines if various entry conditions are met at  76 . For example, entry conditions may include the engine  20  not being in secondary idle where the engine is operating in speed control and a torque measurement would not be valid. Another entry condition is the engine  20  not operating in spark retard above a specified torque ratio, i.e. above 50%. Another entry condition is the engine  20  operating without any fuel injectors being cut or disabled, such as when an injector needs replacement, is above a specified temperature, or when an ignition coil needs replacement. Another entry conditions is that the engine  20  is synchronized. When the engine  20  is unsynchronized, the engine  20  position is unknown and needs to be resynchronized, and the entry condition will not be met. All or some of these entry conditions need to be satisfied for algorithm  70  at  76 , although the list is not inclusive and other entry conditions as are known in the art may be required. 
         [0022]    If the entry conditions are satisfied at  76 , the algorithm  70  then determines the inferred torque produced by the engine  20  at  78 . The inferred torque is the amount of torque that the engine  20  is expected to produce based on the operating conditions of the engine  20 . The inferred torque may be determined as is known in the art, for example as a function of the amount of fuel and air flowing into the engine  20 , or using an engine  20  map. The VSC  56  may use measurements from fuel sensors, air sensors, or other engine  20  sensors as required to determine the inferred torque. In one embodiment, the controller  56  maps the inferred torque for the engine  20  from the air and fuel flowing to the engine, the amount of spark retard commanded for the engine, and the speed of the engine. Alternatively, the inferred torque may be available from a controller area network (CAN) in communication with the VSC  56 . 
         [0023]    The algorithm  70  then determines a threshold, T1, from a calibration table at  80 . The calibration table may provide the threshold, T1, as a function of the inferred torque and the engine coolant temperature. A lower engine coolant temperature may desensitize T1. 
         [0024]    The algorithm  70  then measures the actual torque produced by the engine  20  at  82 . In one embodiment, the actual engine torque output may be mapped using generator  40  current, generator  40  speed, and engine  20  speed in the HEV as disclosed above. Other measurements may also be used to map the actual engine torque output, such as the outer ring speed of the planetary gear unit  48 . The actual engine torque output may also be measured using a torque sensor. Other vehicle sensors and vehicle components may be used to determine the actual engine  20  torque output based on the system architecture. The actual engine torque output may be available from the CAN. 
         [0025]    The algorithm  70  compares the actual torque produced by the engine  20  to T1 for a specified time at  84 . For example, the time may be on the order of one second and be a sustained time. In one embodiment, T1 is on the order of approximately 25-30% of the inferred torque value, meaning that the actual torque output of the engine  20  is much less than what it should be producing based on the inferred torque determined from the engine map. If the actual torque is greater than T1 at  84 , the algorithm  70  proceeds to  86  where it determines the requested torque. The requested torque is the torque that the engine  20  is being commanded to produce, and may be available from the CAN. The requested torque is set as the minimum of either the instantaneous (fast) torque or the long term (slow) torque at  86 . Fast torque is based on the spark path in the engine  20 , and will be reduced for example using spark retard. Slow torque is based on the air path in the engine  20 , and will be reduced for example by restricting the air flow. 
         [0026]    At  88 , the actual torque is compared to a second threshold, T2, and the requested torque from  86  is compared to a third threshold, T3, for a specified time period. In an embodiment, the thresholds, T2, T3, are set values or constants. In one example, T2 is −1 Nm, T3 is 59 Nm, and the time period is forty five seconds sustained. Of course, other values may be used in other embodiments of the disclosure. 
         [0027]    If the actual torque is less than T2 and the requested torque is greater than T3 for the specified time at  88 , the algorithm  70  proceeds to  90 . Alternatively, the algorithm  70  proceeds from  84  to  90  if the actual torque is less than T1 at  84 . At  90 , the algorithm  70  increments a stall counter based on one of four stall criteria. The stall criteria include: the engine starting while the catalyst is cold, the engine starting while the catalyst is hot, the engine stalling while the catalyst is cold, and the engine stalling while the catalyst is hot. Whether the catalyst is hot or cold is based on a temperature measurement of the catalyst and set temperature ranges for the catalyst. Each stall criteria has a different maximum count value that is associated with the stall counter. For example, the starting cold criteria will have a higher maximum stall count value than the starting hot criteria because the engine  20  may be restarted a larger number of times before unburned hydrocarbons cause the catalytic converter to heat to the point where the catalyst may melt. In one embodiment, the stall criteria is based on the catalyst temperature and the engine start condition, i.e. whether the engine was in a start sequence or had been operating for a time. 
         [0028]    At  92 , the stall counter is compared to the maximum count value for that stall criteria. If the stall counter is greater than the maximum count value at  92 , the algorithm  70  sets a diagnostic code at  94 . The algorithm  70  may also cause the controller  56  to send a command to shut down the engine  20  at this time in order to protect the catalyst from potential damage. In some embodiments, the diagnostic code at  94  may cause the vehicle to enter a limited mode of operation, such as a service mode, and may provide a service indicator to the user. 
         [0029]    If the stall counter is less than the maximum count value at  92 , the engine  20  is commanded to restart the combustion process while the vehicle is operating at  96 , and the algorithm  70  then proceeds back to  72 . 
         [0030]    Referring to  88 , if the actual torque is greater than T2 and/or the requested torque is less than T3 for the specified time, the algorithm  70  proceeds to  98 . At  98 , the algorithm  70  determines if a specified time period has elapsed with no stalls. In one embodiment, the time is thirty seconds. If the specified time has elapsed with no stalls at  98 , the stall counter is cleared at  100  and the algorithm  70  returns to  71 . If the time has not elapsed without stalls at  98 , the algorithm  70  returns to  72 . 
         [0031]      FIG. 3  illustrates a flow chart of an embodiment of a diagnostic or monitor using algorithm  110 . The algorithm  110  may be used to detect a zone where the engine  20  is operating between normal operation/combustion and complete stall to detect and/or prevent conditions that may degrade or damage the catalyst due to unburned hydrocarbons. The algorithm  110  may be implemented by the VSC  56  in conjunction with or independent of algorithm  70  as shown in  FIG. 2 . In one embodiment, algorithm  110  detects conditions that may confirm existing catalyst degradation or damage where engine power output is limited due to a restricted exhaust flow. For steps similar to those shown in  FIG. 2 , refer to the discussion above with respect to  FIG. 2 . 
         [0032]    The algorithm  110  starts at  112 . The controller  56  determines if the engine  20  is being commanded to run or operate at  114 . The algorithm  110  then determines if various entry conditions are met at  116 . For example, entry conditions may include the engine  20  not being in secondary idle such that the engine is operating in speed control and a torque measurement is not valid, the engine  20  not operating in spark retard above a specified torque ratio, i.e. above 50%, the engine  20  operating without any fuel injectors being cut or disabled, and that the engine is synchronized. All or some of these entry conditions need to be satisfied for algorithm  110  at  116 , although the list is not inclusive and other entry conditions as are known in the art may be required. 
         [0033]    If the entry conditions are satisfied at  116 , the algorithm  110  then determines the inferred torque produced by the engine  20  at  118 . 
         [0034]    The algorithm  70  then determines a threshold, T4, from a calibration table at  120 . The threshold, T4, may be a function of the inferred torque and the engine coolant temperature. The algorithm  110  then measures the actual torque produced by the engine  20  at  122 . 
         [0035]    The algorithm  110  compares the actual torque produced by the engine  20  to T4. If the actual torque is greater than T4 at  124 , the algorithm  110  proceeds to  126  where it determines the requested torque. The requested torque is the torque that the engine  20  is being commanded to produce. The requested torque is set as the minimum of either the instantaneous (fast) torque or the long term (slow) torque at  126 . 
         [0036]    At  128 , the actual torque is compared to a threshold, T5, and the requested torque from  126  is compared to a threshold, T6. In an embodiment, the thresholds, T5, T6, may be set values or constants. In one example, T5 is 5 Nm, −1 Nm, or −100 Nm, and T6 is 59 Nm. Of course, other values may be used in other embodiments. 
         [0037]    If the actual torque is less than T5 and the requested torque is greater than T6 at  128 , the algorithm  110  proceeds to  130 . Alternatively, the algorithm  110  proceeds from  124  to  130  if the actual torque is less than T4 at  124 . In one embodiment, T4 is on the order of approximately 50% of the inferred torque. At  130 , the algorithm  110  increments a timer. At  132 , the timer is compared to a predetermined time value. In one embodiment, the time value is forty five seconds. If the timer is greater than the time value at  132 , the algorithm  110  sets a diagnostic code at  134 . If the timer is less than the time value at  132 , the algorithm proceeds back to  112 . 
         [0038]    If the actual torque is greater than T5 and/or the requested torque is less than T6 for the specified time at  128 , the algorithm  110  proceeds to  136 . At  136 , the algorithm  110  decrements or clears the timer, and the algorithm  110  returns to  112 . 
         [0039]    Various embodiments according to the present disclosure have associated advantages. For example, torque may be used to determine whether the engine is operating or stalling/misfiring with unburned hydrocarbons being motored to the catalytic converter. This allows for detection of conditions that may degrade or damage the catalyst to preserve the catalyst. Alternatively, the algorithm may detect conditions showing that the catalyst is degraded or damaged, and an appropriate diagnostic code may be set for a service technician. Detection may be difficult, as the vehicle may continue to meet emissions regulations as flow over the remaining degraded or damaged catalyst surface area is restricted. Previous monitors were unable to operate unless the catalyst was inactive, could not diagnose low engine power complaints caused by restricted flow through the catalytic converter, and could not detect a throttle stuck in a closed position. 
         [0040]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of that are not explicitly illustrated or described. Where one or more embodiments have been described as providing advantages or being preferred over other embodiments and/or over prior art with respect to one or more desired characteristics, one of ordinary skill in the art will recognize that compromises may be made among various features to achieve desired system attributes, which may depend on the specific application or implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, any embodiments described as being less desirable relative to other embodiments with respect to one or more characteristics are not outside the scope of the claimed subject matter.