Abstract:
An electric motor or generator is used to spin the vehicle&#39;s internal combustion engine while the engine is not running, in order to draw a vacuum within the vapor control system. Vacuum bleed off is then monitored to determine if an unacceptable condition in the control system may exist. The evaporative fuel emissions test may be conducted either while the vehicle is at rest or while under way in an electric drive mode of operation.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention generally relates to emission control systems for vehicles, and deals more particularly with a method of detecting evaporative fuel emissions for a vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002]     Evaporative emission control systems are well known in internal combustion engine powered motor vehicles to prevent evaporative fuel, i.e., fuel vapor, from being emitted from the fuel tank into the atmosphere. These control systems typically include several primary components that control evaporative emission operations: vapor control valves, vapor management valves and a carbon canister for absorbing the vapors.  
         [0003]     From time to time, fuel vapors may be vented improperly, resulting in reduced engine performance and the possibility of vapor emissions into the atmosphere. A variety of on-board diagnostic systems have been devised for detecting such emissions in the evaporative emission control system so that appropriate corrective measures may be taken.  
         [0004]     Conventional emissions control may include: (1) an intake manifold of an engine connecting to a vapor control system in order to draw a vacuum on the control system, (2) sealing the vapor control system and/or, (3) bleeding-off and monitoring the resulting vacuum in the control system. With vehicles powered only by an internal combustion engine, these steps can only be performed while the engine is running. Coordinating the requirements of the engine control system and the evaporative emission control system test procedure places constraints on both systems. These problems are exacerbated in hybrid powered vehicles using both an internal combustion engine and an electric drive motor. Hybrid powered vehicles, when operating in an internal combustion (IC) mode, tend to run at relatively wide-open throttle for substantial periods in order to maximize operating efficiency. At open or near wide-open throttle, however, intake manifold pressure is lower, limiting the engine&#39;s ability to draw a vacuum in the evaporative emission control system to facilitate emissions detection.  
         [0005]     Accordingly, a need exists in the art for a method of emissions detection that can be performed effectively while the engine is not running. The present invention is intended to satisfy that need.  
       SUMMARY OF THE INVENTION  
       [0006]     A method is provided for detecting fuel vapor emissions from an internal combustion engine driven vehicle while the engine is not running. A detection test can be performed while the vehicle is not operating, or while the vehicle is powered by an alternative drive source such as an electric motor in combination with a battery fuel cell or other electric power source. In accordance with one embodiment of the present method, the method advantageously uses an onboard electric machine operated in a motor mode, to spin the non-running IC engine in order to draw a vacuum on the vapor emission control system, which is then monitored to diagnose proper operation of the vehicle emissions control system.  
         [0007]     In accordance with a first embodiment of the invention, a method is provided of detecting a fuel vapor emissions of an internal combustion, while the engine is not running. The method includes closing a first valve used for controlling the escape of fuel vapor emissions from the system, closing a throttle to prevent air from entering the engine through the throttle, opening a fuel vapor management valve to connect the engine with the control system, rotating the engine to reduce the fuel vapor pressure in the control system, then closing the vapor management valve and measuring the vapor pressure in the control system, a change in the system pressure indicating a possible unacceptable condition in the control system. The throttle is closed by moving a throttle plate to a closed position blocking airflow into the intake manifold of the engine. Rotation of the engine is performed using either an electric drive motor or an onboard generator operated as a drive motor. The detection method may be used in hybrid powered vehicles in which the electric drive motor or generator is employed as the power source to spin the IC engine during the evaporative fuel emissions test.  
         [0008]     In accordance with a second embodiment of the invention, a method is provided for detecting a evaporative fuel emissions in a fuel vapor emission control system of a hybrid powered vehicle having an internal combustion engine and an electric drive motor. The method comprises the steps of determining if the IC engine is running, closing the emission control system when the IC engine is determined not to be running, opening a fuel vapor management valve connecting the engine with the emission control system, rotating the engine to reduce the fuel vapor pressure within the emission control system, closing the fuel vapor management valve and then measuring the vapor pressure in the control system to determine whether a evaporative fuel emissions may be present.  
         [0009]     These non-limiting features, as well as other advantages of the present invention may be better understood by considering the following details of a description of a preferred embodiment of the present invention. In the course of this description, reference will frequently be made to the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a combined block and schematic diagram of a hybrid powered vehicle provided with a fuel vapor emission control system; and,  
         [0011]      FIG. 2  is a flow diagram showing the steps of the method forming the preferred embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     Referring first to  FIG. 1 , a vehicle is equipped with an evaporative, fuel vapor emission control system, generally indicated by the numeral  10 . In the illustrated embodiment, the vehicle is of the hybrid powered type, driven by an internal combustion engine  38  and an electric motor  50  which drive one or more traction wheels  44  through a set of gears  42 . The electric motor  50  is powered by energy stored in a battery  46  whose DC output is converted to AC by an inverter  48 . The electric motor  50  may be operated in a regenerative mode to generate electrical power used for recharging battery  46 . Additionally, an electrical generator  40  also produces electrical energy and is driven either directly by the engine  38  or through gear-set  42 . Generator  40  may also be operated as an electric motor capable of spinning (cranking) the IC engine  38  through either a direct drive connection or via the gear-set  42 . The above mentioned drive components are controlled by an electronic engine control (EEC)  34 , which also controls the operation of the emission control system  10 .  
         [0013]     The emission control system  10  includes a fuel tank  12  having its upper internal volume in communication with one or more evaporative canisters  16  and the intake manifold  14  of engine  38 . The fuel tank  12  provides fuel to the engine  38  and typically includes a vapor vent valve  18  as well as a rollover valve  20 . The fuel tank  12  may also include a vacuum relief valve  22 , integral with the fuel tank cap, for preventing excessive vacuum or pressure from being applied to the fuel tank  12 . The fuel tank  12  further includes a pressure transducer  24  for monitoring fuel tank pressure or vacuum and for providing a corresponding input signal to the EEC  34 . The pressure transducer  24  may be installed directly into the fuel tank  12  or remotely mounted and connected by a line to the fuel tank  12 .  
         [0014]     Evaporation canister  16  is provided for trapping and subsequently using fuel vapor dispelled from the fuel tank  12 . The evaporation canister  16  is connected to the atmosphere through a canister vent valve (CVV)  26 . A filter  28  may be provided between the CVV  26  and the atmosphere for filtering the air pulled into the evaporation canister  16 . The CVV  26  may comprise a normally open solenoid controlled by the EEC  34  via an electrical connection to the CVV  26 .  
         [0015]     A vapor management valve (VMV)  30  is coupled between the intake manifold  14  and a fuel tank  12  and the evaporation canister  16 . The VMV  30  may comprise a normally closed vacuum operated solenoid which is also energized by the EEC  34 . When the VMV  30  opens, the vacuum of the intake manifold  14  draws fuel vapor from the evaporation canister  16  for combustion in the cylinders of the engine  38 . When the EEC  34  de-energizes the VMV  30 , fuel vapors are stored in the evaporation canister  16 .  
         [0016]     The system  10  may further include a service port  32  coupled between the VMV  30  and the fuel tank  12  and the evaporation canister  16 . The service port  32  aids an operator in performing diagnostics on the emission control system  10  to identify malfunctions.  
         [0017]     In addition to controlling the CVV  26  and VMV  30 , the EEC  34  also controls a throttle plate  36  forming part of a throttle body (not shown) which in turn controls the flow of air into the intake manifold  14 .  
         [0018]     The EEC  34  may perform a series of routine diagnostic tests to determine whether the emission control system  10  is operating properly, at any of various times when the vehicle is running. These diagnostic tests may include gross evaporative fuel emissions detection and small evaporative fuel emissions detection. In accordance with the method of the present invention, however, a diagnostic test to determine the possibility of a evaporative fuel emissions in the control system  10  may be carried out while the engine  38  is not running, as would be the case when the vehicle was either being driven under the power of the electric motor  50  or when the vehicle is stationary and the IC engine  38  is turned off.  
         [0019]     The method of the present invention may be better understood by referring now also to  FIG. 2 , which shows the flow chart of the steps comprising the present method. The evaporative fuel emissions detection method is started at  52  and responds to an initiating signal produced by the EEC  34  or other on-board controller which initiates periodic diagnostic tests. A determination is initially made at  54  as to whether a evaporative fuel emissions test needs to be performed based upon current vehicle operating conditions or historical data. For example, pre-programmed instructions may dictate that a evaporative fuel emissions test be performed within ten minutes following turning on of the vehicle&#39;s ignition. If it is confirmed that a evaporative fuel emissions test is to be initiated, then the existence of a series of operating conditions are confirmed at step  56 . For example, before proceeding with the evaporative fuel emissions test, it must be confirmed that the pressure within the fuel tank  12  is within a prescribed range, that there have been no sensor or actuator failures, that the tank  12  has not been recently refueled, that the engine controls are in a closed loop mode and the vehicle is at idle conditions. Further it is confirmed that the ambient air pressure is sufficiently high, that ambient temperature is within a prescribed range, that the cumulative engine run-time is low enough and that the level of the fuel within tank  12  is within a certain range.  
         [0020]     Once the conditions in step  56  have been confirmed, a determination is made at step  58  of whether the IC engine  38  is running. If the engine  38  is running, then the EEC  34  initiates a conventional evaporative fuel emissions test of the control system  10 . However, if the engine is determined not to be running at step  58 , then the following steps of the method of the present invention are carried out to perform evaporative fuel emissions testing.  
         [0021]     First, at step  62  a determination is made as to whether the battery  46  has a state of charge (SOC) within a prescribed range. If the battery SOC is not within a prescribed range, the process returns to step  54 . However, if the battery SOC is within the prescribed range, then the process proceeds to step  64  in which both the CVV  26  and the throttle plate  36  are moved to their closed positions. With both the CVV  26  and throttle plate  36  closed, the emission control system  10  is effectively closed from the atmosphere, since atmospheric air may not pass into the system through the CVV  26  and fresh air may not pass into the intake manifold  14 .  
         [0022]     Next, at step  66 , the VMV  30  is opened, placing the engine  38  in fluid communication within the control system  10 . Then, at step  68 , the generator  40  is operated as a motor to spin or “crank” the engine  38 , causing the engine&#39;s pistons to reciprocate which in turn forces air out of the piston cylinders into an exhaust manifold (not shown). Spinning of the engine  38  therefore reduces the vapor pressure within intake manifold  14 , and thus within the lines and components comprising the emission control system  10 . The EEC  34  monitors the vapor pressure within the control system  10  and when this pressure drops to a pre-selected level representing the necessary vacuum required to perform the evaporative fuel emissions detection, the EEC  34  commands the generator  40  to stop spinning the engine  38 . If, however, the requisite vacuum level is not created within a pre-selected time period shown in step  72 , the evaporative fuel emissions detection method is terminated, and a different protocol is followed, such as the performance of a conventional, gross evaporative fuel emissions detection at step  74 .  
         [0023]     Assuming however that spinning of the engine  38  reduces the vapor pressure in the control system  10  to the pre-selected level within the prescribed time period, then the VMV  30  is closed at  76  and spinning of the engine  38  is terminated at step  78 . At this point, with the intake manifold  14  isolated from the remainder of the control system, the EEC  34  monitors the rate of vacuum bleed-off within the control system  10 . The rate of vacuum bleed-off, i.e. pressure drop in the control system is indicative of a possible evaporative fuel emissions in the system. If the pressure drop exceeds a pre-selected rate then a flag is issued within the EEC  34  which records the possibility of a vapor evaporative fuel emissions requiring corrective action.  
         [0024]     From the foregoing, it can be seen that the method of the present invention provides a very simple evaporative fuel emissions detection method which uses the IC engine  38  to produce a vacuum within the emission control system  10 , then seals the control system and subsequently monitors the ability of the system to maintain this vacuum. When used in a hybrid vehicle, advantage can be taken of the electric drive motor or generator to spin the IC engine  38  to produce the vacuum while the engine is not running. Although a generator  40  has been disclosed as being the motive means for spinning the IC engine  38 , the spinning could also be produced by power from the electric motor  20  which is transmitted as a torque through the gear-set  42  to the crankshaft of the IC engine  38 .  
         [0025]     It is to be understood that the specific methods and techniques which have been described are merely illustrative of one application of the principles of the invention. Numerous modifications may be made to the method and system as described without departing from the true spirit and scope of the invention.