Abstract:
A control system for a hybrid vehicle including an engine with cylinder deactivation comprises an engine time off module that determines an engine time off value. A re-purge determining module estimates a re-purge time required to purge a hydraulic control system of the engine of air before initiating cylinder deactivation. The re-purge time is estimated based on the engine time off value and an engine temperature.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/992,386, filed on Dec. 5, 2007. The disclosure of the above application is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates to engine control systems, and more particularly to engine control systems for hybrid vehicles with cylinder deactivation. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Both active fuel management (AFM) or cylinder deactivation and hybrid propulsion systems may be used to improve fuel economy in vehicles. Cylinder deactivation involves deactivating one or more cylinders of an engine during low load conditions to reduce pumping losses. 
     Hybrid propulsion systems typically include a first torque generator, such as an internal combustion engine (ICE), and a second torque generator, such as an electric machine (EM). Each can provide torque to a driveline to propel a vehicle. Various configurations of hybrid powertrains can be used, including a strong hybrid powertrain, a mild hybrid powertrain and/or other hybrid types. In a strong hybrid powertrain, the EM can drive the driveline directly, without transferring torque through a component of the ICE. 
     In a mild hybrid configuration, the EM is coupled with the ICE, such as through the front end accessory drive. Torque generated by the EM is transferred to the driveline through the ICE. An exemplary mild hybrid powertrain includes a belt alternator starter (BAS) system. In the BAS system, the EM is coupled to the ICE via a traditional belt and pulley configuration, which drives other accessory components including, but not limited to, pumps and compressors. 
     When coupled together, these technologies are capable of providing further fuel savings. One hybrid propulsion efficiency improvement is the engine start-stop feature. During periods where a conventional engine would be idling, the hybrid system stops the engine to increase fuel savings. When the system senses that the driver is about to request the vehicle to accelerate, the hybrid system restarts the engine and may assist the engine in the subsequent vehicle acceleration. 
     In a system that combines cylinder deactivation with hybrid propulsion, there are times where it is advantageous to deactivate engine cylinders soon after the restart of a hybrid start-stop sequence. Some systems with cylinder deactivation require a time period to completely purge a hydraulic control system of air before cylinder deactivation can occur. For example, a lifter oil manifold assembly (LOMA) and its associated passages in the cylinder block may need to be purged. Current approaches use a predetermined fixed period to allow the purge to occur. 
     The predetermined fixed period assumes a worst-case condition where the engine off-time completely drains the engine oil galleries of oil. In a non-hybrid vehicle, this delay is not a fuel economy detriment. However in a hybrid vehicle with cylinder deactivation, this delay in deactivating cylinders may be a significant loss in fuel saving opportunity. 
     SUMMARY 
     A control system for a hybrid vehicle including an engine with cylinder deactivation comprises an engine time off module that determines an engine time off value. A re-purge determining module estimates a re-purge time required to purge a hydraulic control system of the engine of air before initiating cylinder deactivation. The re-purge time is estimated based on the engine time off value and an engine temperature. 
     A method for operating a hybrid vehicle including an engine with cylinder deactivation includes determining an engine time off value; and estimating a re-purge time required to purge a hydraulic control system of the engine of air before initiating cylinder deactivation, wherein the re-purge time is estimated based on the engine time off value and an engine temperature. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a functional block diagram illustrating variable displacement components of an exemplary variable displacement and hybrid engine system; 
         FIG. 2  is a functional block diagram illustrating hybrid components of the engine of  FIG. 1 ; 
         FIG. 3  illustrates the exemplary variable displacement components of  FIG. 1  in further detail; 
         FIG. 4  illustrates an exemplary control module in further detail; and 
         FIG. 5  is a flowchart illustrating an exemplary method for operating the engine system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify the same 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 and/or device 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. 
     According to the present disclosure, drain-back and re-purge time of the LOMA are characterized at various engine temperatures. Partial drain-back may result in shorter re-purge times. This information can then be used in hybrid vehicle with cylinder deactivation to allow cylinder deactivation earlier. For example, the conventional fixed time period may be set equal to 30 seconds after restart. The present disclosure shortens the time period using physical LOMA/oil gallery drain-back and purge characteristics, engine off time, and engine temperature to determine the delay period. 
     In some implementations, at engine restart, a period that the crankshaft has been stopped and a period that the crankshaft has been rotating are used to index a LOMA re-purge time table to determine an appropriate cylinder deactivation delay. For system protection, this control approach may be enabled when hybrid start-stop is enabled. In other words, this reduced delay may or may not be used during an initial cold start. 
     Referring now to  FIG. 1 , a vehicle  10  includes an engine  12  that drives a transmission  14 . The transmission  14  can include, but is not limited to, a manual transmission, an automatic transmission, a continuously variable transmission (CVT) and an automated manual transmission (AMT). The transmission  14  is driven by the engine  12  through a corresponding torque converter or clutch  16 . The transmission  14  is electronically controlled by a control module  24 . 
     Air flows into the engine  12  through a throttle  13 . The engine  12  includes N cylinders  18 . One or more select cylinders  18 ′ may be selectively deactivated during engine operation. Although  FIG. 1  depicts eight cylinders (N=8), 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 flows into the engine  12  through an intake manifold  20  and is combusted with fuel in the cylinders  18 . The engine also includes a lifter oil manifold assembly (LOMA)  22  that deactivates selected ones of the cylinders  18 ′, as described in further detail below. 
     A control module  24  communicates with the engine  12  and various inputs and sensors as discussed herein. A vehicle operator manipulates an accelerator pedal  26  to regulate the throttle  13 . More particularly, a pedal position sensor  28  generates a pedal position signal that is communicated to the control module  24 . The control module  24  generates a throttle control signal based on the pedal position signal. A throttle actuator (not shown) adjusts the throttle  13  based on the throttle control signal to regulate air flow into the engine  12 . 
     The vehicle operator manipulates a brake pedal  30  to regulate vehicle braking. More particularly, a brake position sensor  32  generates a brake pedal position signal that is communicated to the control module  24 . The control module  24  generates a brake control signal based on the brake pedal position signal. A brake system (not shown) adjusts vehicle braking based on the brake control signal to regulate vehicle speed. 
     An engine speed sensor  34  generates a signal based on engine speed. An intake manifold absolute pressure (MAP) sensor  36  generates a signal based on a pressure of the intake manifold  20 . A throttle position sensor (TPS)  38  generates a signal based on throttle position. 
     During low engine load, the control module  24  may transition the engine  12  to the deactivated mode. In an exemplary embodiment, N/2 cylinders  18 ′ (i.e. half of the cylinders N) are deactivated, although any number of cylinders may be deactivated. Upon deactivation of the select cylinders  18 ′, the control module  24  increases the power output of the remaining or activated cylinders  18 . Inlet and exhaust ports (not shown) of the deactivated cylinders  18 ′ are closed to reduce pumping losses. 
     The engine load may be determined based on the intake MAP, cylinder mode and engine speed. More particularly, if the MAP is below a threshold for a given engine revolutions per minute (RPM), the engine load may be deemed light and the engine  12  may be transitioned to the deactivated mode. If the MAP is above the threshold for the given RPM, the engine load may be deemed heavy and the engine  12  is operated in the activated mode. The control module  24  controls the LOMA  22  as discussed in further detail below. 
     Referring now to  FIG. 2 , the engine  12  and electric machine  64  are coupled via a belt-alternator-starter (BAS) system  68 . More specifically, the electric machine  14  operates as a starter (i.e., motor) and an alternator (i.e., generator) and is coupled to the engine  12  through a belt and pulley system. The engine  12  and the electric machine  64  include pulleys  70 ,  72 , respectively, that are coupled for rotation by a belt  74 . The pulley  70  is coupled for rotation with a crankshaft  76  of the engine  12 . While a mild hybrid configuration is shown, a strong hybrid may also be used. 
     In one mode, the engine  12  drives the electric machine  64  to generate power used to recharge an energy storage device (ESD)  78 . In another mode, the electric machine  64  drives the engine  12  using energy from the ESD  78 . An AC/DC converter  79  may be used between ESD and the electric machine  64 . The ESD  78  can include, but is not limited to, a battery or a super-capacitor. Alternatively, the BAS system  68  can be replaced with a flywheel-alternator-starter (FAS) system (not shown), which includes an electric machine operably disposed between the engine and the transmission or a chain or gear system that is implemented between the electric machine  64  and the crankshaft  76 . 
     During periods where low drive torque is needed to drive the vehicle (i.e., a hybrid engine off mode), drive torque may be provided by the electric machine  64 . When in the hybrid engine off mode, fuel and spark are cut-off to the cylinders of the engine. Further, opening and closing cycles of the intake and exhaust valves can be prevented to inhibit air flow processing within the cylinders. 
     Referring now to  FIG. 3 , an intake valvetrain  140  of the engine  12  includes an intake valve  142 , a rocker  144  and a pushrod  146  associated with each cylinder  18 . The engine  12  includes a rotatably driven camshaft  148  having a plurality of valve cams  150  disposed there along. A cam surface  152  of the valve cams  150  engage the lifters  154  to cyclically open and close intake ports  153  within which the intake valves  142  are positioned. The intake valve  142  is biased to a closed position by a biasing member (not shown) such as a spring. As a result, the biasing force is transferred through the rocker  144  to the pushrod  146 , and from the pushrod  146  to the lifter  154 , causing the lifter  154  to press against the cam surface  152 . 
     As the camshaft  148  rotates, the valve cam  150  induces linear motion of the corresponding lifter  154 . The lifter  154  induces linear motion in the corresponding pushrod  146 . As the pushrod  146  moves outward, the rocker  144  pivots about an axis (A). Pivoting of the rocker  144  induces movement of the intake valve  142  toward an open position, thereby opening the intake port  153 . The biasing force induces the intake valve  142  to the closed position as the camshaft  148  continues to rotate. In this manner, the intake port  153  is cyclically opened to enable air intake. 
     Although the intake valvetrain  140  of the engine  12  is illustrated in  FIG. 3 , the engine  12  may also include an exhaust valvetrain (not shown) that operates in a similar manner. More specifically, the exhaust valvetrain includes an exhaust valve, a rocker and a pushrod associated with each cylinder  18 . Rotation of the camshaft  148  induces reciprocal motion of the exhaust valves to open and close associated exhaust ports, as similarly described above for the intake valvetrain. 
     The LOMA  22  provides pressurized fluid to a plurality of lifters  154  and includes solenoids  156  (shown schematically) associated with select cylinders  18 ′ as shown in  FIG. 1 . The select cylinders  18 ′ are those that are deactivated when operating the engine  12  in the deactivated mode. The lifters  154  are disposed within the intake and exhaust valvetrains to provide an interface between the cams  150  and the pushrods  146 . In general, there are two lifters  154  provided for each select cylinder  18 ′ (one lifter for the intake valve  142  and one lifter for the exhaust valve). It is anticipated, however, that more lifters  154  can be associated with each select cylinder  18 ′ (i.e., multiple inlet or exhaust valves per cylinder  18 ′). The LOMA  22  may include a pressure sensor  158  that generates a pressure signal indicating a pressure of a hydraulic fluid supply to the LOMA  22 . One or more pressure sensors  158  may be implemented. 
     Each lifter  154  associated with the select cylinders  18 ′ is hydraulically actuated between first and second modes. The first and second modes respectively correspond to the activated and deactivated modes. In the first mode, the lifter  154  provides a mechanical connection between the cam  150  and the pushrod  146 . In this manner, the cam  150  induces linear motion of the lifter  154 , which is transferred to the pushrod  146 . In the second mode, the lifter  154  functions as a buffer to provide a mechanical disconnect between the cam  150  and the pushrod  146 . Although the cam  150  induces linear motion of the lifter  154 , the linear motion is not transferred to the pushrod  146 . 
     The solenoids  156  selectively enable hydraulic fluid flow to the lifters  154  to switch the lifters  154  between the first and second modes. Although there is generally one solenoid  156  associated with each select cylinder  18 ′ (i.e., one solenoid for two lifters), it is anticipated that more or fewer solenoids  156  can be implemented. Each solenoid  156  actuates an associated valve  160  (shown schematically) between open and closed positions. In the closed position, the valve  160  inhibits pressurized hydraulic fluid flow to the corresponding lifters  154 . In the open position, the valve  160  enables pressurized fluid flow to the corresponding lifters  154  via a fluid passage  162 . The pressurized hydraulic fluid flow is provided to the LOMA  22  from a pressurized hydraulic fluid source. 
     Referring now to  FIG. 4 , an exemplary implementation of the control module  24  is shown in further detail. The control module  24  includes an engine time off module  180  that determines an engine time off. An engine temperature  182  and the engine time off are input to a re-purge determining module  186 . The re-purge determining module  186  estimates a re-purge time based on the engine time off and the engine temperature. The re-purge determining module  186  may employ a mathematical relationship or a lookup table. A cylinder deactivation enable module  188  receives the re-purge time and a crankshaft rotating time from a crankshaft rotating time module  184  and selectively enables a cylinder deactivation control module  190 . The cylinder deactivation control module  190  controls cylinder deactivation. 
     Referring now to  FIG. 5 , exemplary steps of a method for operating the engine system of  FIGS. 1-3  are shown. In step  200 , control optionally determines whether a cold start timer delay has timed out. In step  204 , control determines whether a propulsion system is in a start-stop mode. If step  204  is true, control continues with step  208  and control determines whether the engine is in a restart mode. If step  208  is false, control returns to step  204 . If step  208  is true, control reads the engine temperature in step  212 . In step  216 , control reads the engine time off. In step  220 , control reads an expected re-purge time from a lookup table or calculates the expected purge time using a mathematical relationship that is based on the engine time off and the engine temperature. 
     In step  228 , control determines whether the crankshaft rotating time is longer than the expected LOMA re-purge time. If step  228  is true, control continues with step  232  and allows the cylinder deactivation function. If step  228  is false, control returns to step  224 . Control also continues with step  232  from step  204  when step  204  is false.