Abstract:
A method and controller for operating cruise control in a vehicle having an engine with active fuel management (AFM) is provided. Adaptive scaler values can be determined based on a cylinder deactivation signal and calibrated scaler values. Cruise control commands can be calculated based on the adaptive scaler values. A speed of the vehicle can be controlled based on the cruise control commands.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/073,796 on Jun. 19, 2008. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to internal combustion engines, and more particularly to methods and systems for operating cruise control with an active fuel management engine system. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight cylinder engine can be operated using four cylinders to improve fuel economy by reducing pumping losses. This process is generally referred to as active fuel management (AFM). Operation using all of the engine cylinders is referred to as an “activated” mode (AFM disabled). A “deactivated” mode (AFM enabled) refers to operation using less than all of the cylinders of the engine (one or more cylinders not active). 
         [0005]    In the deactivated mode, there are fewer cylinders operating. Nonetheless, there can still be adequate drive torque available to drive the vehicle driveline (such as during cruise control) and accessories (e.g., alternator, coolant pump, A/C compressor). Engine efficiency, however, is increased as a result of less engine pumping loss and higher combustion efficiency. The pumping loss experienced by the engine is mainly due to the flow restriction for flow into and out of the cylinders. The quantity of air and/or the composition/quality of gas in the cylinder can play minimum role to pumping loss during compression and expansion processes because the compression work (−) and the expansion work (+) will be traded. 
         [0006]    Cruise control systems can be provided for maintaining a vehicle at a fixed operating speed. In some instances, a vehicle can be operating in a “deactivated” mode (AFM enabled) while cruise control is engaged. As is typical however, it may be necessary for the engine control system to command a torque increase in order to maintain the fixed operating speed due to outside influences (such as encountering a hill, etc.). As a result, AFM typically would transition to a disabled state to provide the required torque (i.e., to the “activated” mode). 
       SUMMARY 
       [0007]    A method and controller for operating cruise control in a vehicle having an engine with active fuel management (AFM) is provided. Adaptive scaler values can be determined based on a cylinder deactivation signal and calibrated scaler values. Cruise control commands can be calculated based on the adaptive scaler values. A speed of the vehicle can be controlled based on the cruise control commands. 
         [0008]    According to additional features, calculating the cruise control command can include calculating a first cruise control command for the engine operating when AFM is enabled and calculating a second cruise control command for the engine operating when AFM is disabled. A vehicle speed error can be determined based on a measured vehicle speed and a desired set vehicle speed. The first cruise control command can be based on a product of the calibrated scaler values and each of a proportional, integral and derivative term associated with the first cruise control command. The controller can determine whether the engine is transitioning out of AFM and transition to the second cruise control command based on the determination. In the second cruise control command, the adaptive scaler values are 1. In one example, the adaptive scaler values can be ramped to 1. According to other features, the controller can determine whether the engine is transitioning into AFM and transition to the first cruise control command based on the determination. 
         [0009]    Further areas of applicability will become apparent from the description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0010]    The present invention will become more fully understood from the detailed description and the accompany drawings, wherein: 
           [0011]      FIG. 1  is a functional block diagram illustrating a vehicle powertrain including an active fuel management (AFM) engine control system according to the present teachings; 
           [0012]      FIG. 2  is a functional block diagram of an exemplary control module according to the present teachings; and 
           [0013]      FIG. 3  is an exemplary flowchart illustrating steps for operating the AFM engine control system of  FIG. 1  according to one example of the present teachings. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, activated refers to operation using all of the engine cylinders. Deactivated refers to operation using less than all of the cylinders of the engine (one or more cylinders not active). As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. 
         [0015]    Referring now to  FIG. 1 , a vehicle  10  can include an engine  12  that drives a transmission  14 . The transmission  14  can be either an automatic or a manual transmission that is driven by the engine  12  through a corresponding torque converter or clutch  16 . Air flows into the engine  12  through a throttle  13 . The engine  12  can include N cylinders  18 . One or more of the cylinders  18  can be selectively deactivated during engine operation. Although  FIG. 1  depicts eight cylinders (N=8), it is appreciated that the engine  12  may include additional or fewer cylinders  18 . For example, engines having 4, 5, 6, 8, 10, 12 and 16 cylinders are contemplated. Air can flow into the engine  12  through an intake manifold  20  and be combusted with fuel in the cylinders  18 . 
         [0016]    A control module  24  can communicate with the engine  12  and various inputs and sensors as discussed herein. A vehicle operator can manipulate an accelerator pedal  26  to regulate the throttle  13 . More particularly, a pedal position sensor  30  can generate a pedal position signal that is communicated to the control module  24 . The control module  24  can generate a throttle control signal based on the pedal position signal. A throttle actuator  34  can adjust the throttle  13  based on the throttle control signal to regulate air flow into the engine  12 . 
         [0017]    The vehicle operator can manipulate a brake pedal  36  to regulate vehicle braking. More particularly, a brake position sensor  38  can generate a brake pedal position signal that is communicated to the control module  24 . The control module  24  can generate a brake control signal based on the brake pedal position signal. A brake system (not shown) can adjust vehicle braking based on the brake control signal to regulate vehicle speed. 
         [0018]    An engine speed sensor  40  can generate a signal based on engine speed. An intake manifold absolute pressure (MAP) sensor  42  can generate a signal based on a pressure of the intake manifold  20 . A throttle position sensor (TPS)  44  can generate a signal based on throttle position. A vehicle speed sensor  46  can generate a signal based on a vehicle speed. 
         [0019]    The control module  24  can comprise a cruise control module  50 . In general, the cruise control module  50  can communicate with the actuator  34  for positioning the throttle  13  in relation to the difference between a commanded vehicle speed (i.e., such as from the pedal position sensor  30 ) and a measured actual vehicle speed (i.e., such as from the vehicle speed sensor  46 ). This difference commonly referred to as speed error, e(t) is represented by the following formula: 
         [0000]        e ( t )=measured vehicle speed−desired set vehicle speed   (1) 
         [0020]    The cruise control module  50  can perform mathematical processing of the speed error e(t) and other related signals. In some examples, the mathematical processing can include calculations using look-up tables that can take into account vehicle specific characteristics and time constants. The mathematical processing can comprise various combinations of proportional, integral and derivative (PID) terms. The cruise control module  50  can determine a cruise control command or gain for two different operating conditions, one with AFM “OFF” (disabled) and one with AFM “ON” (enabled). These two gains can be represented by the following formulas: 
         [0000]        AFM  “OFF” Command= Cp*e ( t )+ Ci *integral of  e ( t )+ Cd *derivative of  e ( t )   (2) 
         [0000]        AFM  “ON” Command= Kp*Cp*e ( t )+ Ki*Ci *integral of  e ( t )+ Kd*Cd *derivative of  e ( t )   (3) 
         [0000]    where Kp, Ki and Kd are calibratable scalers that can range from 0 to 1 and can be a function of vehicle speed error (e(t)). As used hereinafter, Kp, Ki and Kd are reserved collectively as “K-values”. As can be appreciated, by incorporating the K-values into the AFM “ON” command, the determination to transition out of AFM when cruise control is engaged will be delayed resulting in fuel savings. Cp, Ci and Cd are control gains, respectively, for PID. By resetting K-values to 1, for the AFM “OFF” command, normal cruise control is resumed. 
         [0021]    With reference now to  FIG. 2 , the control module  24  according to one example of the present teachings will be described. The control module  24  can include a calibration memory module  60 , a K-value determination module  62 , a cruise command module  64  and the cruise controller  50 . The calibration memory module  60  can determine calibrated K-values based on the vehicle speed error e(t). In one example, the calibrated K-values can be determined with a lookup table. The K-value determination module  62  can determine adaptive K-values based on the calibrated K-values and an AFM status signal. The cruise command module  64  can determine cruise commands (i.e., AFM “OFF” Command and AFM “ON” Command shown above) based on the adaptive K-values and a cruise status signal. The cruise controller  50  can output a cruise control signal to the throttle  13  based on the cruise commands determined by the cruise command module  64  and a vehicle speed (i.e. such as from the speed sensor  46 ). 
         [0022]    With reference now to  FIG. 3 , exemplary steps for operating cruise control in a vehicle having an engine with AFM will be described. The method is generally identified at reference numeral  70 . Control begins in step  72 . In step  74  control determines if cruise control is on. If cruise control is on, control begins using cruise commands based on the adaptive K-values in step  76 . If cruise control is not on, control loops to step  74 . In step  78  control determines if AFM is on. If AFM is on, control uses the calibrated K-values. If AFM is not on, control sets the K-values to 1 in step  82 . In step  86  control determines if the engine  12  is transitioning out of AFM. If the engine is transitioning out of AFM, control ramps the calibrated K-values to 1 in step  92 . By ramping the K-values to 1, a gradual blending can be imposed on the final cruise control (torque/throttle area) command at the transition out of AFM when cruise control is engaged. It is appreciated that such blending can be symmetric or unsymmetric (relative to a blending associated with a transition into AFM). In one example, a calibration timer T 1  can be assigned for transitions out of AFM. The blending factor can be t/T 1  where a timer t starts counting once the transition begins. In one example, a transition from AFM “ON” to AFM “OFF” can be represented by the following formula: 
         [0000]      scalers  Kx′=Kx +(1− Kx )* t/T 1   (4) 
         [0000]    where x represents p, i and d. 
         [0023]    If the engine is not transitioning out of AFM, control determines if cruise is being disabled in step  90 . If cruise is not being disabled, control loops to step  86 . If cruise is being disabled, control loops to step  100 . In step  100 , control stops using cruise commands based on the adaptive K-values. 
         [0024]    Once the K-values have been ramped to  1  in step  92 , control loops to step  94 . In step  94 , control determines if the engine  12  is entering AFM. If the engine  12  is entering AFM, control ramps the K-values from 1 to the calibrated K-values in step  98  and then loops to step  86 . By ramping the K-values to the calibrated K-values, a gradual blending can be imposed on the final cruise control (torque/throttle area) command at the transition into AFM when cruise control is engaged. In one example, a calibration timer T 2  can be assigned for transitions into AFM. The blending factor can be (1−t/T 2 ). In one example, a transition from AFM “OFF” to AFM “ON” can be represented by the following formula: 
         [0000]      scalers  Kx′=Kx +(1− Kx )*(1− t/T 2)   (5) 
         [0000]    where x represents p, i and d. 
         [0025]    If the engine  12  is not entering AFM in step  94 , control determines if cruise is being disabled in step  96 . If cruise is being disabled, control loops to step  100 . If cruise is not being disabled in step  96 , control loops to step  94 . 
         [0026]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.