Abstract:
A computer-implemented apparatus and method for inferring power steering load and for controlling airflow to an engine of a vehicle having an engine speed. A sensor which is connected to the engine senses the engine speed of the engine. An engine speed reference data table stores at least one engine reference speed, and a reference comparator module which is connected to the sensor and to the reference data table performs a comparison between the sensed engine speed and the engine reference speed. The airflow to the engine is controlled based upon the comparison.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to internal combustion engines and, more particularly, to an vehicle engine airflow compensation. 
     2. Discussion 
     A vehicle&#39;s engine experiences many loads upon itself which reduces the engine&#39;s torque output. Engine loads include activation of a power steering pump to provide power steering capability when a driver is using the vehicle&#39;s steering wheel. 
     Assistance for the engine in handling loads exists in the way of increasing the airflow to the engine. Current approaches for compensating airflow to an engine experiencing parasitic loads include using a physical component known as a pressure switch. The pressure switch is mounted directly in the power steering pump to indirectly sense a load on the engine. 
     When the pressure exceeds 400 psi fluid pressure in the pump following a steering maneuver, the physical switch activates and sets a software bit. The bit triggers an Intake Airflow Control Valve (IACV) in order to compensate for the power steering induced load on the engine at idle conditions. When fluid pressure recedes back to a predetermined set point as steering effort is reduced or stopped, the IACV resets the bit to zero. The physical component pressure switch approach suffers from such disadvantages as, but not limited to, the failure rates associated with physical components as well as the cost in order to manufacture and install a physical component in a vehicle. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the aforementioned disadvantages as well as other disadvantages. In accordance with the teachings of the present invention, a computer-implemented apparatus and method is provided for controlling airflow to an engine of a vehicle having an engine speed. A sensor which is connected to the engine senses the engine speed of the engine. An engine speed reference data table stores at least one engine reference speed, and a reference comparator module which is connected to the sensor and to the reference data table performs a comparison between the sensed engine speed and the engine reference speed. The airflow to the engine is controlled based upon the comparison. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings wherein the same referenced numeral indicates the same components: 
     FIG. 1 is a system block diagram depicting the airflow compensator module of the present invention within a vehicle&#39;s environment; 
     FIG. 2 is a block diagram depicting the components involved within the present invention for performing airflow compensation; 
     FIG. 3 is a flowchart depicting the operational steps utilized by the present invention for determining airflow compensation; 
     FIG. 4 is an x-y graph depicting the operation of the present invention for airflow compensation due to air conditioning activation; 
     FIG. 5 is an x-y graph depicting the operation of the present invention when a transmission change has occurred; 
     FIG. 6 is an x-y graph depicting the reference RPM ramping situation within the present invention when entering low idle speed; and 
     FIG. 7 is an x-y graph depicting a triggering of a PID idle response within the present invention when nearing die-out RPM levels. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, a block diagram of the engine system, in which an airflow compensation module of the present invention is implemented, is shown generally at  10 . The system  10  includes an internal combustion spark ignited engine  12 , shown in partial cross-section, which is of the type implemented in a conventional motor vehicle (not shown). Engine  12  contains a plurality of cylinders represented by cylinder  14 , with each of the cylinders having a piston, represented by piston  16 , operatively disposed therein. Each of the pistons is connected by a connecting rod  18  to a crankshaft  20 . A conventional engine cam shaft  22  is also operatively located within engine  12  for opening and/or closing an intake valve, such as valve  24  associated with the cylinder  14  for supplying a fuel/air mixture to the cylinders in a manner well known in the art during the piston intake. A manifold  25  is also operatively associated with the intake valve  24  for supplying air from outside of the engine into the cylinder  14  to provide air for the valve fuel/air mixture supply to the cylinder. 
     Engine  12  includes an intake stroke in which fuel and air mixture is input into the cylinder  14  through the intake valve  24 , a compression stroke in which the fuel/air mixture is compressed by the piston  16 , an expansion stroke in which a spark supplied by a spark plug  26  ignites the fuel/air mixture, an exhaust stroke during which gases from the burned fuel are exhausted from the cylinder through an exhaust system  28 , which includes a catalytic converter  29  having an associated catalyst  30 . 
     The preferred embodiment of the present invention is implemented in an six cylinder, four-stroke engine, but may also be implemented in a four cylinder, four-stroke engine. Moreover, it should be appreciated that the present invention may be implemented in any conventional engine system, including a two-stroke engine system or any spark ignited or diesel engine system. 
     Engine  12  experiences during its operation various loads which reduce its revolutions per minute (RPM) output. For example, operation of the vehicle steering wheel  50  activates a power steering pump  52  in order to assist the vehicle&#39;s driver in performing a steering operation. Activation of power steering pump  52  is a parasitic load upon engine  12  which acts parasitically to lower the RPM output of engine  12 . 
     The present invention&#39;s airflow compensator module  54  utilizes sensor  56  in order to sense the lower RPM output of engine  12  due to activation of power steering pump  52 . In this preferred embodiment, sensor  56  is airflow compensator module  54  which is a software-based executable program which provides opening and closing control signals to airflow valve  24  based upon comparisons of the sensed engine RPM output and various reference and threshold data tables stored within airflow compensator module  54 . 
     Since the present invention utilizes an airflow compensator module  54  which is software-based, the present invention includes more sophisticated functionality than conventional approaches which use pressure switch physical components. Accordingly, airflow compensator module  54  is able to detect other vehicle operating conditions  60  and perform different functions to suit different applications. For example, but not limited to, different vehicle operational conditions  60  include: whether the air conditioning has been activated; what the transmission state of the vehicle is (e.g., whether the vehicle&#39;s engine is in a park state or a driving state); and whether the engine fan is activated in order to cool the engine. Based upon the specific needs of the application at hand, the present invention can be set to ignore the loads imposed by vehicle operational conditions  60  and operate airflow valve  24  only upon activation of power steering pump  52 . Airflow compensation module  54  can be set to also detect one or more of the vehicle operational conditions  60  in order to adjust airflow valve  24  to provide more airflow to engine  12 . Whether airflow compensator module  54  is to adjust airflow valve  24  based upon vehicle operational conditions  60 , depends upon if devices already exist within the vehicle for adjusting airflow valve  24 . Controller  59  which utilizes a proportional-integral-derivative (PID) control approach uses the data generated from the air flow compensator module  54  in order to update its own control algorithm in controlling air flow valve  24 . 
     FIG. 2 is a block diagram which depicts the software-based components of airflow compensator module  54 . Airflow compensator module  54  includes a reference comparator module  80  which compares the engine RPM value from sensor  56  with RPM reference values stored in reference table  82 . Reference comparator module  80  utilizes different reference values from reference table  82  based upon different vehicle operational conditions  60 . For example, but not limited to, reference comparator module  80  utilizes one reference value when the vehicle is in an engine park state and a second reference value when the vehicle is in a drive state. 
     Reference comparator module  80  selects the appropriate reference value from reference table  82  and calculates the difference between the selected reference RPM value and the RPM value from sensor  56 . Reference comparator module  80  provides the ΔRPM value to flag setting determinator module  86 . 
     Flag setting determinator module  86  compares the ΔRPM value with threshold values stored in threshold table  90 . If the ΔRPM value satisfies the selected threshold value, then flag setting determinator module  86  provides a flag (or a software bit value) to valve opening determinator module  94 . 
     Valve opening determinator module  94  determines the amount of the valve opening for airflow valve  24  so that additional airflow may be provided to the engine while the power steering pump is operating. Valve opening determinator module  94  more particularly provides control signals to the stepper motor  98  of airflow valve  24  in order to indicate how much the airflow valve  24  should be opened. 
     Valve opening determinator module  94  utilizes historic RPM data stored in historic data table  102 . In the preferred embodiment of the present invention, valve opening determinator module  94  utilizes the ΔRPM values as gathered over a predetermined amount of time. Preferably, the predetermined amount of time includes the ΔRPM values gathered up to the preceding three seconds or a time factor suitable for the situation at hand. 
     Due to the various vehicle operational conditions  60 , reference comparator module  80  and flag setting determinator module  86  include modules to adjust the reference and threshold values stored respectively in the data tables  82  and  90 . For example, when the vehicle&#39;s air conditioning system is activated, reference adjustment module  106  of reference comparator module  80  lowers the normally used reference value stored in reference table  82  by a predetermined amount. 
     The following table provides reference and threshold values for various engine operating conditions used within the preferred embodiment of the present invention. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Park/ 
                   
                 Drive 
                 Offset Due 
                 Offset Due 
               
               
                   
                 Neutral 
                 Drive (High) 
                 (low) 
                 To A/C 
                 To Fan 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Reference 
                 728 
                 650 
                 543 
                 — 
                 — 
               
               
                 Idle Speed 
               
               
                 Δ Threshold 
                 80 
                  75 
                  30 
                 −100 
                 −10 
               
               
                 Absolute 
                 478 
                 — 
                 — 
                 — 
                 — 
               
               
                 RPM to 
               
               
                 Trigger PID 
               
               
                 Idle RPM 
               
               
                 Offset 
               
               
                   
               
             
          
         
       
     
     The reference values are selected according to the present requirements of the situation. Chiefly, the threshold and offset values are selected which optimize steering sensitivity and fuel economy, but can include optimization of other factors related to vehicle performance. 
     FIG. 4 depicts an example of the lowering of a reference value upon activation of the vehicle&#39;s air conditioning system. Graph  200  depicts the engine speed (RPM) as the ordinate axis versus time as the abscissa axis. Level  204  is the normal operating RPM level of the engine. If the lowering of engine speed profile  206  below threshold level  208  is due to the activation of the power steering pump, then the present invention is activated in order to provide airflow compensation. However, if the lowering of the engine speed profile  206  is due to the air conditioning system being activated, then the threshold level is lowered to threshold level  216  for the duration  212  in which the air conditioning system is activated. 
     FIG. 5 depicts an example of the delaying application of reference and threshold comparison by the present invention due to a change in transmission state. Graph  230  depicts the engine speed (RPM) as the ordinate axis versus time as the abscissa axis. RPM reference levels  238  and  234  depict the heightening of the reference value due to a transmission change from, for example, a driving idle state to a non-driving idle state. The present invention utilizes a delay  242  in order to delay application of the new heightened reference level. 
     With reference back to FIG. 2, reference and threshold adjustment modules  106  and  110  implement the threshold lowering functionality as depicted in FIG. 4 as well as the delaying functionality as depicted in FIG.  5 . 
     FIG. 3 depicts a flowchart of the processing steps of the present invention. The processing steps discussed in conjunction with FIG. 3 utilize the following variables: 
     VPSS: Virtual Power Steering switch. 
     DLRPM 2 : Delta RPM. 
     IDLSP 2 : Reference RPM for VPSS. 
     PSSTMR: Delay between exceeding LRPMz and setting VPSS bit. 
     INCTMR: Timer used for decrementing RPM during transition to VIS low idle speed. 
     SRTIMR: VPSS disable timer after start-up. 
     ACFTMR: Timer to add fan initiated offset to LRPM z . 
     VTIMER: Timer to delay IDLSP 2  update when stepping out of VIS. 
     VIS: Variable idle speed mode. 
     DRTIMR: Timer to delay IDLSP 2  update during a d/r to p/n gear transition (where d/r represents drive/reverse and p/n represents park/neutral). 
     DLRTMR: PNIDEL RPM offset timer. 
     ACTMR: Timer to add A/C initiated offset to LRPM z . 
     The processing steps discussed in conjunction with FIG. 3 utilize the following constants: 
     LRPMz: DLRPM 2  threshold (z denotes idle mode). 
     VIS 2 z: VPSS reset RPM threshold (z denotes idle mode). 
     OFFSET: RPM decrement amount during transition to VIS low speed. 
     LMTRP 0 : Offset to LRPMZ while fan offset timer ACFTMR is active. 
     PSSTIM: Delay between exceeding LRPMz and setting VPSS bit. 
     INCTIM: Loop time used for decrementing RPM during transition to VIS low idle speed. 
     SRDELY: VPSS disable time after start-up. 
     IDLSPD: Idle speed of the engine. 
     MFRPM 0 : Instantaneous RPM (i.e., sensed RPM). 
     BARAPS: Power steering barometric adjustment factor. 
     PSRPML: Power steering RPM limit. 
     CLTEMP: Engine coolant temperature. 
     PSTEMP: Power steering engine coolant temperature limit. 
     DECEL: Sensed deceleration of the vehicle. 
     IDLDEL: Start-up delta Idle RPM. 
     ACFDLO: Timer limit to add fan initiated offset LMTRPO to LRPMz. 
     VDELAY: Timer limit to delay IDLSP 2  update when stepping out of VIS. 
     DRDELY: Timer limit to delay IDLSP 2  update during a d/r to p/n gear transition. 
     PSKlz: IACV open kick tables for d/r low, d/r high and p/n (z denotes idle mode). 
     DLRLMT: MFRPM 0  low limit threshold to trigger RPM offset PNIDEL. 
     PNIDEL: RPM offset table, added to target idle speed, when MFRPM 0  exceeds DLRLMT in p/n. 
     ACOFLO: Offset to LRPMLO while A/C offset timer ACTMR is active. 
     ACOFHI: Offset to LRPMHI while A/C offset timer ACTMR is active. 
     ACOFPN: Offset to LRPMPN while A/C offset timer ACTMR is active. 
     ACTMRL: Timer limit for ACTMR to add A/C initiated offset ACOFz. 
     LOWIDL: Low Idle Status Flag. 
     With reference to FIG. 3, start indication block  150  indicates that process block  154  is to be executed. Process block  154  determines the reference idle speed of the engine. In the preferred embodiment, process block  154  utilizes the following steps in order to determine the reference idle speed: 
     a) If LOWIDL=0 and VTIMER NOT ACTIVE OR DRTIMR not active IDLSP 2 =idlspd 
     b) If LOWIDL=1 and IDLSP 2 &gt;VIS low idle speed IDLSP 2 =MFRPM 0 −(OFFSET), WHERE OFFSET is subtracted every INCTIM, until IDLSP 2 =VIS low idle speed Note: MFRPM 0  starts the decrement from the current engine speed when the LOWIDL flag is first set 
     c) If VTIMER is activated, then IDLSP 2  is held at the previous low idle speed until VTIMER=VDELAY 
     d) If DRTIMR is activated, then IDLSP 2  is held at the previous level until DRTIMR=DRDELY 
     Process block  158  determines the conditions as to whether to set or reset the flag bit. In the preferred embodiment, process block  158  utilizes the following steps: 
     a) If DLRPM 2 &gt;=LRPMz+(LMTRP 0  or ACOF z  if applicable) and VPSS  0 , then increment PSSTMR, else PSSTMR=0 
     b) If PSSTMR=PSSTIM, then VPSS=1 (i.e., to set VPSS, DLRPM 2  has to be greater than Mz for PSSTIM time). 
     c) Inhibit setting VPSS after start-up if SRDELY is active 
     d) Inhibit VIS when VPSS is set 
     e) Reset PSSTMR when VPSS is set 
     To prevent setting VPSS prematurely when the fan is engaged, an offset MTRP 0  is added to the LRPML 0  threshold in low idle speed mode for a time period ACFDL 0 . This prevents VPSS from unnecessarily triggering and canceling VIS mode. Similarly, to prevent setting VPSS prematurely from A/C on or off IACV compensation, an offset ACOF z  is added to LRP z  for a time period ACTMRL. The offset is applied before the A/C clutch is actually engaged. Process block  158  also performs the following steps: 
     a) If MFRPM 0 &gt;=VIS 2   z  and VPSS= 1 , then Reset VPSS bit. 
     Process block  162  determines the compensation by calculating the power steering kick where power steering kick refers to a step increase of air flow. In the preferred embodiment, process block  162  utilizes the following steps: 
     If VPSS bit= 1 , then 
     Power Steering Kick=PSKI z  *BARAPS when: MFRPM 0 &lt;PSRPML, CLTEMP&gt;PSTEMP, a higher priority IACV compensation is not overriding VPSS kicks, not a DECEL and not in an open to closed throttle transition. 
     Process block  166  determines the RPM offset by preferably performing the following steps: 
     If in park or neutral and 
     SRTIMR&gt;=SRDELY and 
     CLTEMP&gt;=PSTEMP then 
     a) Reset DLRTMR and hold at zero until MFRPMO&lt;DLRLMT 
     b) Once MFRPM 0 &lt;DLRLMT start to increment DLRTMR (MFRPM 0  must recover above DLRLMT for timer to continue increment) 
     c) IDLSP 2 =IDLSP 2 +[LARGEST OF PNIDEL or IDLDEL] (Where PNIDEL is indexed by DLRTMR) else (if not in P/N or other disable condition) IDLSP 2 =IDLSP 2 +IDLDEL 
     Processing for one iteration of the present invention terminates at end block  170 . 
     FIG. 6 is an x-y graph depicting the reference RPM ramping situation within the present invention. The gradual ramping down profile  320  is caused entering into variable idle speed (VIS) mode (i.e., low idle speed). Profile  320  so that the reference RPM more closely follows the actual RPM. When the low idle flag is set, the ramp rate is preferably for every unit time there is a predetermined decrease in the reference RPM. For example, for every 63 milliseconds there is a decrease in the reference RPM of 10 RPMs. It should be understood that the present invention includes using other types of ramping functions in order to decrease the reference RPM values, such as polynomial functions which can more closely follow the actual RPM. Moreover, there is a timer limit to delay IDLSP update when stepping out of VIS as shown by reference numeral  322 . 
     FIG. 7 is an x-y graph depicting a triggering of a PID idle response within the present invention. The engine reference speed is increased based upon the sensed engine speed satisfying a predetermined lower limit. RPM trace  350  is depicted at IDLSP 2  level  352  and then dropping down below the delta threshold  354  of eighty (which is 648 RPM). When RPM trace  350  drops below threshold  356  (which is DLRLMT whose value is 478 RPM), a high idle speed offset (PNIDEL) is triggered which increases by 72 RPMs the target idle speed in order to form increased target idle speed threshold  360 . This approach helps to prevent stall-out from occurring since it makes it more difficult for the RPM to drop that low again. The increased target idle speed threshold  360  is used for a predetermined time as is shown by a subsequent ramping down  362  back to the original level  352 . For the preferred embodiment, the ramping down period back to the original level is approximately 30 seconds. 
     Since preferably the vehicle&#39;s electrical system does not make coarse adjustments to electrical loads, the power steering is not compromised by activating more than one electrical load. For example, use of an alternator control system may be used to accomplish this objective. 
     It will be appreciated by those skilled in the art that various changes and modifications may be made to the embodiment discussed in the specification without departing from the spirit and scope of the invention as defined by the appended claims.