Abstract:
A fault detection system for detecting a fault in a lifter oil manifold assembly (LOMA) of a displacement on demand engine that is operable during transition from activated and deactivated modes includes a first fluid circuit of the LOMA that selectively provides pressurized fluid to regulate operation of the engine between activated and deactivated modes. The fault detection system further includes a sensor that is responsive to fluid pressure of the LOMA and that generates a pressure signal based thereon. A control module outputs a control signal to switch operation of the engine between the activated and deactivated modes. The control module further determines a pressure differential based on a first pressure prior to switching between the modes and a second pressure after switching between the modes.

Description:
FIELD OF THE INVENTION 
     The present invention relates to internal combustion engines, and more particularly to engine control systems for displacement on demand engines. 
     BACKGROUND OF THE INVENTION 
     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 displacement on demand (DOD). Operation using all of the engine cylinders is referred to as an activated mode. A deactivated mode refers to operation using less than all of the cylinders of the engine (i.e., one or more cylinders not active). 
     In the deactivated mode, there are fewer cylinders operating. As a result, there is less drive torque available to drive the vehicle driveline and accessories (e.g., alternator, coolant pump, A/C compressor). Engine efficiency, however, is increased as a result of decreased fuel consumption (i.e., no fuel supplied to the deactivated cylinders). Because the deactivated cylinders do not compress fresh air, pumping losses are also reduced. 
     A lifter oil manifold assembly (LOMA) is implemented to activate and deactivate select cylinders of the engine. The LOMA includes lifters and solenoids associated with corresponding cylinders. The solenoids are selectively energized to enable hydraulic fluid flow to the lifters to disable cylinder operation, thereby deactivating the corresponding cylinders. It is possible that one or more of the solenoids could seize or become slow to actuate and cause the system to operate improperly. As a result, the LOMA may need to be replaced. 
     SUMMARY OF THE INVENTION 
     Accordingly, a fault detection system for detecting a fault in a lifter oil manifold assembly (LOMA) of a displacement on demand engine that is operable in activated and deactivated modes includes a first fluid circuit of the LOMA that selectively provides pressurized fluid to regulate operation of the engine between activated and deactivated modes. The fault detection system further includes a sensor that is responsive to fluid pressure of the LOMA and that generates a pressure signal based thereon. A control module outputs a control signal to switch operation of the engine between the activated and deactivated modes. The control module further determines a pressure differential based on a first pressure prior to switching between the modes and a second pressure after switching between the modes. 
     In one feature, the control module determines a PASS/FAIL status event of the first fluid circuit based on the pressure differential and a predetermined pressure differential range. 
     In another feature, the pressure differential range is defined by an upper pressure differential value and a lower pressure differential value. 
     In another feature, the control module indicates a FAIL status event of the first fluid circuit when the pressure differential is lower than the lower pressure differential value. 
     In still another feature, the control module indicates a FAIL status event of the first fluid circuit when the pressure differential is greater than the upper pressure differential value. 
     In yet other features, the first fluid circuit includes a solenoid that selectively enables a flow of pressurized fluid to a lifter associated with a cylinder of the engine. The control module calculates the pressure differential based on a first pressure prior to the solenoid enabling the flow of pressurized fluid pressure and a second pressure subsequent to the solenoid enabling the flow of pressurized fluid. 
     In still another feature, the control module detects a faulty fluid circuit when the number of FAIL status events exceeds a predetermined FAIL status range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram illustrating a vehicle powertrain including a displacement on demand (DOD) engine control system according to the present invention; 
         FIG. 2  is a partial cross-sectional view of the DOD engine including a lifter oil manifold assembly (LOMA) and an intake valvetrain; 
         FIG. 3  is partial plan view illustrating a LOMA; 
         FIGS. 4A and 4B  are graphs illustrating the oil pressure of the LOMA sampled over a period of time before and after operating the engine in activated and deactivated modes, according to the present invention; 
         FIG. 5  is a graphical representation of an X out of Y counter according to the present invention; and 
         FIG. 6  is a flowchart illustrating steps of a method for detecting faults in a LOMA. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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, and/or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an engine system  10  includes an engine  12  and a transmission  14 . The transmission  14  can be an automatic or a manual transmission that is driven by the engine through a corresponding torque converter or clutch  16 . 
     A throttle  18  that regulates air flow into an intake manifold  20 . The intake manifold  20  delivers air into cylinders  22  where it is mixed with fuel and is combusted to drive pistons (not shown). One or more cylinders  22 ′ may be selectively deactivated during engine operation. Although  FIG. 1  depicts 8 cylinders, it can be appreciated that the engine  12  may include additional or fewer cylinders. For example, engines having 4, 5, 6, 8, 10, 12 and 16 cylinders are contemplated. A lifter oil manifold assembly (LOMA)  24  is implemented in the engine  12  and deactivates select cylinders  22 ′, as discussed further below. Furthermore, the engine system  10  includes an engine speed sensor  25 , an intake manifold absolute pressure (MAP) sensor  26  and a throttle position sensor (TPS)  27 . The engine speed sensor  25  generates a signal indicative of engine speed. The MAP sensor generates a signal indicating a pressure of the intake manifold  20 . The TPS  27  generates a signal indicative of a position of the throttle  18 . A control module  28  communicates with the engine  12  and the various sensors and actuators to selectively deactivate cylinders  22 ′, as discussed below. 
     A vehicle operator manipulates an accelerator pedal (not shown) to regulate the throttle  18 . The control module  28  outputs a throttle control signal based on the position of the accelerator pedal. A throttle actuator (not shown) adjusts the throttle  18  based on the throttle control signal to regulate air flow into the engine  12   
     When predetermined conditions occur, the control module  28  can operate the engine  12  in the deactivated mode. In an exemplary embodiment, N/2 cylinders  22 ′ are deactivated, although one or more cylinders  22 ′ may be deactivated. When the selected cylinders  22 ′ are deactivated, the control module  28  increases the power output of the activated cylinders  22 . The inlet and exhaust ports (not shown) of the deactivated cylinders  22 ′ are closed to reduce fuel consumption and pumping losses. 
     The engine load can be determined based on the intake MAP, cylinder mode and engine speed. More particularly, if the MAP is below a predetermined threshold value for a given RPM, the engine load is deemed light and the engine  12  can possibly be operated in the deactivated mode. If the MAP is above the threshold value for the given RPM, the engine load is deemed heavy and the engine  12  is operated in the activated mode. 
     Referring now to  FIG. 2 , an intake valvetrain  29  of the engine  12  includes an intake valve  30 , a rocker  32  and a pushrod  34  associated with each cylinder  22 ′. The engine  12  includes a rotatably driven camshaft  36  having a plurality of valve cams  38  disposed therealong. A cam surface  40  of the cams  38  engage the pushrods  34  to cyclically open and close intake ports  42  within which the intake valves  30  are positioned. The intake valve  30  is biased to a closed position by a biasing member (not illustrated) such as a spring. As a result, the biasing force is transferred through the rocker  32  to the pushrod  34  causing the pushrod  34  to press against the cam surface  40 . 
     As the camshaft  36  rotates, the cam  38  induces linear motion of the corresponding pushrod  34 . As the pushrod moves outward, the rocker  32  is caused to pivot about an axis (A). Pivoting of the rocker  32  induces movement of the intake valve  30  toward an open position, thereby opening the intake port  42 . The biasing force induces the intake valve  30  to a closed position as the camshaft  36  continues to rotate. In this manner, the intake port  42  is cyclically opened to enable air intake. 
     Although the intake valvetrain  29  of the engine  12  is illustrated in  FIG. 2 , it can be appreciated that the engine  12  also includes 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  22 ′. Rotation of the camshaft  36  induces reciprocal motion of the exhaust valves to open and close associated exhaust ports, as similarly described above for the intake valvetrain  29 . 
     The LOMA  24  directs a supply of hydraulic fluid to a plurality of fluid circuits. Typically, a single fluid circuit is associated with each set of cylinder valves. A single fluid circuit includes a solenoid  50  and at least one lifter  52 . The solenoid  50  regulates the pressure of hydraulic fluid to the lifter  52  associated with select cylinders  22 ′, as discussed further below. The selected cylinders  22 ′ are those that are deactivated when operating the engine  12  in the deactivated mode. The lifters  52  are disposed within the intake and exhaust valvetrains to provide an interface between the cams  38  and the pushrods  34 . Typically, there are two lifters  52  provided for each select cylinder  22 ′ (one lifter  52  for the intake valve  30  and one lifter for the exhaust valve). It can be appreciated, however, that additional lifters  52  can be associated with each select cylinder  22 ′ (i.e., multiple inlet or exhaust valves per cylinder  22 ′). The LOMA  24  further includes one or more pressure sensors  54  that communicate with the control module  28  and that generate a pressure signal indicating a pressure of the hydraulic fluid to the LOMA  24 . 
     Referring now to  FIG. 3 , the LOMA  24  is schematically illustrated. A single fluid circuit  48  includes a solenoid  50 , a pair of lifters  52  and a valve  56 . The fluid circuit  48  further includes a counter  60  that communicates with the control module and is incremented when the fluid circuit  48  experiences a fault, as discussed further below. 
     The solenoid  50  communicates with the control module  28  and selectively actuates the valve  56  coupled thereto between open and closed positions. Although one solenoid  50  is shown with each select cylinder  22 ′ (i.e., one solenoid for two lifters), additional or fewer solenoids  50  can be implemented. The position of the valve  56  regulates the flow of hydraulic fluid delivered to the lifter  52 . In the closed position, the valve  56  inhibits pressurized hydraulic fluid flow to the corresponding lifter  52 . In the open position, the valve  56  delivers pressurized fluid flow to the corresponding lifter  52  through a fluid passage (not shown). The lifter  52  is hydraulically actuated between first and second modes based on a supply of hydraulic fluid. The first and second modes respectively correspond to the activated and deactivated modes of the engine  12 , respectively. 
     Although not illustrated, a brief description of an exemplary solenoid  50  is provided herein to provide a better understanding of the present invention. The solenoids  50  typically include an electromagnetic coil, a plunger and a mechanical interface, such as the valve  56 . The plunger (not shown) is disposed coaxially within the coil and provides a mechanical interface between the solenoid  50  and the valve  56 . The plunger is biased to a first position relative to the coil by a biasing force. The biasing force can be imparted by a biasing member, such as a spring, or by a pressurized fluid. The solenoid  50  is energized by supplying electrical current to the coil, which induces a magnetic force along the coil axis. The magnetic force induces linear movement of the plunger to a second position. In the first position, the plunger holds the valve in its closed position to inhibit pressurized hydraulic fluid flow to the corresponding lifters. In the second position, the plunger actuates the valve  56  to its open position to enable pressurized hydraulic fluid flow to the corresponding lifters. 
     When the control module  28  initiates the deactivated mode of engine  12  operation, hydraulic fluid flows throughout the LOMA  24  and is directed to each of the corresponding lifters  52 . 
     The control module  28  includes a diagnostic system that determines the operation of the LOMA  24  based on the fluid pressure and faults associated with corresponding fluid circuits. The control module  28  receives a pressure signal and determines a PASS/FAIL status of a fluid circuit  48  based on a pressure differential and a predetermined pressure differential range. More specifically, a first pressure value (P PRE ) is stored prior to energizing a specific solenoid  50  corresponding to a specific fluid circuit  48  (C N ). The control module  28  will select the first solenoid to be energized based upon the instantaneous position of the engine at the time it makes the decision to transition the engine to the deactivated mode. Since the instantaneous position of the engine at the transition time can be thought of as a random function, the first solenoid to get energized can be considered a random function. The random selection ensures that each fluid circuit  48  is evaluated during a driving scenario. Subsequent to energizing the first solenoid  50 , the control module  28  determines the time when the fluid pressure of the LOMA  24  will decrease due to opening the solenoid valve  56 . The control module  28  retrieves a programmed time parameter (t DEAC     —     SOL     —     RESPONSE ) and calculates a time when the fluid pressure will be at a minimum (t MIN ). At t MIN , the control module  28  stores a second pressure value (P POST ). The parameter t DEAC     —     SOL     —     RESPONSE  is discussed in greater detail in commonly assigned US Published Patent Application No. 20020189575, which is hereby incorporated by reference in its entirety. 
     The control module  28  further determines a pressure differential (ΔP) based on P PRE  and P POST  and compares the result to a predetermined pressure differential range (P RANGE ). P RANGE  is defined as having a predetermined upper pressure value (P H ) and a predetermined lower pressure value (P L ). When ΔP exceeds P H , or when ΔP is less than P L , the control module  28  indicates a FAIL status event by incrementing the counter  60  associated with the corresponding fluid circuit  48 . Although the counters  60  are shown externally, the counters  60  may be implemented within the control module  28 . 
     Referring now to  FIGS. 4A and 4B , exemplary graphs illustrating the oil pressure of the LOMA  24  sampled over a period of time before and after operating the engine  12  in activated and deactivated modes are shown.  FIG. 4A  shows an actual oil pressure signal appearing at the oil pressure sensor  54  when the fist electrohydraulic circuit  48  is energized. The oil pressure sensor  54  measures the oil pressure of the LOMA  24  and outputs an analogue signal to the control module  28 . The analogue oil pressure signal is filtered to remove noise prior to being converted to a digital signal. The digital oil pressure signal is further scaled and numerically converted into engineering units of measurement. 
       FIG. 4B  shows the oil pressure signal after being filtered and digitally converted. Reading A could be taken at time=0.04 seconds. Reading B could be taken at time=0.07 sec. The drop in pressure is due to oil flow into the solenoid valve  56 . The pressure differential between these readings could be calculated to make a fault/no fault decision. Only the first fluid circuit  48  that is energized is analyzed because later fluid circuits will have large amounts of hydraulic noise in the pressure signal which may cause inaccurate measurements. 
     Referring now to  FIG. 5 , a graphical representation of an X out of Y counter is illustrated. The counters  60  are characterized according to three predefined FAIL status event ranges. The first FAIL status event range (RANGE FAULT ) has an upper threshold equal to a first predetermined value and a lower threshold equal to a second predetermined threshold. The second FAIL status event range (RANGE POS     —     FAULT ) has an upper threshold equal to a third predetermined value and a lower threshold equal to a forth predetermined value. The third FAIL status event range (RANGE NO     —     FAULT ) has an upper threshold equal to a fifth predetermined value and a lower threshold equal to zero. Furthermore, the values defining RANGE POS     —     FAULT  are greater then the values defining RANGE NO     —     FAULT . The values defining RANGE FAULT  are greater than the values defining RANGE POS     —     FAULT  and RANGE NO     —     FAULT . 
     A fluid circuit  48  is characterized as faulty when the number of fail status events recorded by the counter  60  exceeds RANGE POS     —     FAULT . A fluid circuit  48  is characterized as having a possible fault when the number of fail status events corresponding to the fluid circuit equals a value that falls within RANGE POS     —     FAULT . Finally, a fluid circuit  48  is characterized as having no fault when the number of fail status events corresponding to the fluid circuit  48  equals a value that falls within RANGE NO     —     FAULT . 
     The control module  28  can further determine whether a specific fluid circuit (C N ) is faulty based on FAIL status events recorded by the counters  60  and the three predetermined FAIL status ranges. When C N  is characterized as faulty, the remaining counters  60  are analyzed. If the number of fail status events recorded by the remaining counters  60  are within RANGE NO     —     FAULT , and they are filled with readings, then the control module  28  determines that the fault is specific to C N . The fault may include, but is not limited to, a seized solenoid  50  and/or a seized lifter pin. However, when a plurality of fluid circuits are characterized as faulty, then a problem exists that is not specific to a single fluid circuit  48 . For example, a blocked fluid passage upstream from the fluid circuits may deliver an insufficient supply of hydraulic fluid that causes a low pressure differential signal. 
     Referring now to  FIG. 6 , a flowchart illustrates the steps executed by the LOMA diagnostic control. In step  400 , control randomly selects the solenoid  50  associated with C N  to energize. In step  402 , control determines P PRE  prior to energizing the solenoid  50 . Control energizes the solenoid  50  associated with C N  in step  404 . In step  406 , control determines t P     —     MIN  based on a predetermined time parameter (t DEAC     —     SOL     —     RESPONSE ). Control determines P POST  at t P     —     MIN  in step  408 . In step  410 , control calculates ΔP based on P PRE  and P POST . 
     In step  412 , control determines whether ΔP is within P RANGE . When ΔP is within P RANGE , control sets a PASS status in step  414 , delivers that PASS reading to the associated X out of Y counter and control ends. When ΔP is not within P RANGE , control delivers a FAIL reading to the associated X out of Y counter  60  corresponding to C N  in step  416 , and proceeds to determine whether the fault is specific to C N . In step  418 , control determines whether the FAIL status event total associated with C N  exceeds RANGE POS     —     FAULT . When the FAIL status event total does not exceed RANGE POS     —     FAULT , control determines that the fault is not specific to C N  in step  424 . Otherwise, control determines whether the remaining X out of Y counters are filled with readings in step  419 , When the remaining X out of Y counters are not filled with readings, control proceeds to step  424  because it cannot be determined if the fault is specific to circuit C N . 
     When, in step  419 , control determines all of the other counters are filled with readings, control will proceed to check if the FAIL status event totals associated with the remaining fluid circuits are within RANGE NO     —     FAULT  in step  420 . If the remaining fluid circuits have fault counts within RANGE NO     —     FAULT , then control determines that the fault is specific to C N  in step  422  and control ends. Otherwise, control determines there is no fault specific to C N  in step  424  and control ends. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention 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.