Abstract:
A control system and method for a hydraulic system (HS) that controls a fluid supply in an engine includes a timer module determines the response time of the HS to perform at least one of: increasing the pressure of the fluid supply above a predetermined threshold following the state change command and decreasing said pressure of said fluid supply below said predetermined threshold following said state change command. An update module updates the desired time of the HS based on the response time of the HS.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to internal combustion engines, and more particularly to a system for controlling the response time of a hydraulic system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Intake valves control entry of an air/fuel mixture into cylinders of an internal combustion engine. Exhaust valves control gases exiting the cylinders of an internal combustion engine. Camshaft lobes (or “cam lobes”) on a camshaft push against the valves to open the valves as the camshaft rotates. Springs on the valves return the valves to a closed position. The timing, duration and degree of the opening, or “valve lift,” of the valves can impact performance. 
         [0003]    As the camshaft rotates, the cam lobes open and close the intake and exhaust valves in time with the motion of the piston. There is a direct relationship between the shape of the cam lobes and the way that the engine performs at different speeds and loads. When running at low speeds, the cam lobes should ideally be shaped to open the intake valve as the piston starts moving downward in the intake stroke. Generally, the intake valve should close as the piston reaches the bottom of its stroke and then the exhaust valve opens. The exhaust valve closes as the piston completes the exhaust stroke at the top of its stroke. 
         [0004]    At higher engine speeds, however, this configuration for the cam lobes does not work as well. If, for example, the engine is running at 4,000 RPM, the valves are opening and closing 33 times every second. At this speed, the piston is moving very quickly. The air/fuel mixture rushing into the cylinder is also moving very quickly. When the intake valve opens and the piston starts the intake stroke, the air/fuel mixture in the intake runner starts to accelerate and move into the cylinder. By the time that the piston reaches the bottom of its intake stroke, the air/fuel mixture is moving at a high speed. If the intake valve is shut quickly, all of the air/fuel flow stops and does not enter the cylinder. By leaving the intake valve open longer, the momentum of the fast-moving air/fuel mixture continues flowing into the cylinder as the piston starts its compression stroke. The faster the engine turns, the faster the air/fuel mixture moves and the longer the intake valve should stay open. The valve should also be opened to a greater lift value at higher speeds and higher loads. This parameter, called “valve lift,” is governed by the cam lobe profile. A fixed cam lobe profile which always lifts the valve the same amount does not work well at all engine speeds and loads. Fixed cam lobe profiles tend to compromise engine performance at both idle and at high loads. 
         [0005]    Variable valve actuation (VVA) technology improves fuel economy, engine efficiency, and/or performance by modifying the valve event lift, timing, and duration as a function of engine operating conditions. Two-step VVA systems enable two discrete valve events on the intake and/or exhaust valves. The engine control module (ECM) selects the optimal valve event profile that is best utilized for each engine operating condition. 
         [0006]    An issue in the development and application of the two-step VVA system is the response time variability of a Control Valve (CV) and VVA hydraulic control system. A limited amount of time is available for switching two-step Switching Roller Finger Followers (SRFF) between engaging in one valve event and the corresponding part of the next valve event of another engine cylinder controlled by the same CV. If the CV causes a fluid pressure change in the lifter fluid gallery to occur too soon relative to the critical part of a valve lift curve, the SRFF arm lock pin may only partially engage and then disengage after the valve has started lifting. This unscheduled disengagement is called a “Critical Shift” and may cause the engine valve to drop uncontrollably from the high-lift valve event to the low-lift valve event, or on to the valve seat. After a number of such events, the SRFF arm or the valve may show signs of accelerated wear or damage. 
         [0007]    Several factors can affect hydraulic system variation including but not limited to engine oil aeration, duration of engine operation, wear upon the components of the engine, degradation of fluid quality over time, engine temperature, and/or fluid viscosity. These factors increase hydraulic system variations among engines and contribute to the accelerated wear and damage to the engine components. 
       SUMMARY OF THE INVENTION 
       [0008]    A control system and method for a hydraulic system (HS) that controls a fluid supply in an engine includes a timer module determines a response time of the HS to perform at least one of: increasing a pressure of the fluid supply above a predetermined threshold following a state change command and decreasing the pressure of the fluid supply below the predetermined threshold following the state change command. An update module updates the desired time of the HS based on the response time of the HS. 
         [0009]    In other features, a pressure sensor senses the pressure of the fluid supply. A control valve (CV) controls the fluid supply. A command module selectively generates and transmits the state change command to the CV when the engine requires a mode change and the engine is operating within a predetermined operating range. 
         [0010]    In still other features, the timer module stores a first time when the command module transmits the state change command to the CV and stores a second time when a comparison module detects that the pressure of the fluid supply has at least one of: exceeded the predetermined threshold and fallen below said predetermined threshold. The response time of the HS is based on a difference between the first time and the second time 
         [0011]    In still other features the desired time of the HS is indexed in a look-up table that is a function of predetermined engine operating conditions. The update module updates the desired time to equal the response time when the response time exceeds a predetermined time range about the desired time for the predetermined operating condition. Engine operating condition is based on at least one of: engine speed, engine voltage, engine temperature, and fluid temperature. 
         [0012]    A control system for controlling a hydraulic system (HS) in an engine includes a pressure sensor that senses pressure of a fluid supply. A control valve (CV) of the HS controls the fluid supply. A control module communicates with the pressure sensor. The control module selectively generates and transmits a state change command to the CV. The control module determines a response time of the HS to at least one of: increase the pressure of the fluid supply above a predetermined threshold following the state change command and decrease the pressure of the fluid supply below the predetermined threshold following the state change command. The control module updates a desired time of the HS based on the response time of the HS. 
         [0013]    In other features, the control module selectively generates and transmits the state change command to the CV when the engine requires a mode change and the engine is operating within a predetermined operating range. The control module stores a first time upon generating said state change command and stores a second time upon detecting the pressure of the fluid supply has at least one of: exceeded a predetermined threshold and fallen below the predetermined threshold. The response time of the HS is based on a difference between the first time and the second time. The desired time of the HS is indexed in a look-up table that is a function of predetermined engine operating conditions. 
         [0014]    In still other features the control module updates the desired time to equal the response time when the response time exceeds a predetermined time range of said desired time for said engine operating point. Engine operating points are based on at least one of: engine speed, engine voltage, engine temperature, and fluid temperature. 
         [0015]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0017]      FIG. 1  illustrates an exemplary vehicle including an engine control module (ECM) that communicates with engine sensors and controls the control valve (CV) of a switching roller finger follower (SRFF) mechanism; 
           [0018]      FIG. 2  is a three-dimensional view of the SRFF mechanism; 
           [0019]      FIG. 3  is a cross-sectional view through the SRFF mechanism; 
           [0020]      FIG. 4  is a functional block diagram of a control system for controlling the response time of a hydraulic system according to the present invention; 
           [0021]      FIG. 5  is a flow chart illustrating the exemplary steps executed by a control system for controlling the response time of a hydraulic system according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    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, 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. 
         [0023]    Referring to  FIG. 1 , an exemplary vehicle  10  includes an engine  12 , a transmission  14 , and an engine control module (ECM)  16 . The operation of a two-step switching roller finger follower (SRFF) mechanism  28  is controlled by a control valve (CV)  30  that controls a fluid supply (not shown) to a hydraulic lash adjuster  29 . The ECM  16  monitors the operation of the vehicle  10  using various engine sensors. The ECM  16  communicates with a fluid pressure sensor  18 , an engine speed sensor  22 , an engine voltage sensor  24 , and an engine temperature sensor  26 . The fluid pressure sensor  18  generates a signal indicating the fluid pressure within a hydraulic lash adjuster  29  fluid gallery (not shown), and the engine speed sensor  22  generates a signal indicating engine speed (RPM). In various embodiments, the fluid pressure sensor  18  can be positioned in other fixed engine fluid galleries including but not limited to a cam phaser gallery (not shown). The engine voltage sensor  24  generates a signal indicating the operating voltage of the engine electric system, and the engine temperature sensor  26  generates a signal indicating the operating temperature of the engine. The ECM  16  includes memory  20  that stores a look-up table  50 , as depicted in  FIG. 4 , for utilization in commanding the CV  30  to switch the operating mode of the SRFF mechanism  28 . In various embodiments, rather than switching among operating modes of the SRFF mechanism  28 , specific operating modes of the SRFF  28  may be commanded to be deactivated from operation. Such embodiments are known in the art and include but are not limited to Valve Deactivation systems. 
         [0024]    Referring now to  FIGS. 2 and 3 , a switching roller finger follower (SRFF) mechanism  28  is schematically depicted. It is appreciated that the SRFF mechanism  28  is merely exemplary in nature. The SRFF mechanism  28  includes an inner arm assembly  150  and an outer arm assembly  152  which are pivotably joined by a pivoting pin  154 . The inner arm assembly  150  includes a low-lift contact  156  which interfaces with a low-lift cam lobe (not shown) of a camshaft (not shown). The outer arm assembly  152  includes a pair of high-lift contacts  158   a ,  158   b  as depicted in  FIG. 2 , that are configured for contact with a pair of high-lift cams lobes (not shown) of the camshaft and are positioned on either side of the low-lift contact  156 . The inner arm assembly  150  defines a cavity  160  in which a portion of a hydraulic lash adjuster (not shown) can be inserted and about which the inner arm assembly  150  may also pivot. 
         [0025]    As depicted in  FIG. 3 , a locking pin housing  162  contains locking pins  164   a ,  164   b . The locking pins  164   a ,  164   b  restrict the independent movement of the outer arm assembly  152  from the inner arm assembly  150  about the pivoting pin  154  when the locking pins  164   a ,  164   b  are in an engaged position. The end faces  165   a ,  165   b  of locking pins  164   a ,  164   b , respectively exist in fluid communication with a source of fluid pressure  166  such as a fluid supply (not shown). The fluid supply is fed from the hydraulic lash adjuster (not shown) to the locking pin housing  162  through a fluid supply hole  168 . 
         [0026]    The fluid supply from the hydraulic lash adjuster is controlled by a solenoid or CV, as depicted in  FIG. 1  at  30 . At predetermined engine operating ranges, the ECM, as depicted in  FIG. 1  at  16 , can cause the CV  30  to switch the fluid supply of the hydraulic lash adjuster from a lower pressure (P 1 ) (not shown) to a higher pressure (P 2 ) (not shown) within the locking pin housing  162 . When fluid pressure (P 2 ) is sufficiently high, the pressure exerted on the locking pins  164   a ,  164   b  is sufficient to overcome the resistance provided by the springs  170   a ,  170   b  resulting in the locking pins  164   a ,  164   b  being extended from their retracted position (shown) to an engaged position (not shown). While the locking pins  164   a ,  164   b  are in an engaged position, the outer arm assembly  152  is locked to the inner arm assembly  150  and causes the valve (not shown) to follow the high lift cam (not shown) that interfaces with the high-lift contacts  158   a ,  158   b.    
         [0027]      FIG. 3  depicts the SRFF mechanism  28  configured to operate in low-lift mode. In “normal” (fluid pressure supply at P 1 ) operation, or “low-lift” mode, the low lift cam lobe causes the inner arm assembly  150  to pivot to a second position in accordance with the low-lift cam&#39;s prescribed geometry and thereby open a valve (not shown) a first predetermined amount. In various embodiments, a different low mode lift profile may exist for each of the adjacent valves in any given cylinder. The pressure inside the locking pin housing  162  is sufficiently low such that the locking pins  164   a ,  165   b  remain in the retracted position. The low pressure fluid supply (P 1 ), which enters the inner arm assembly  150  at the cavity  160  and is fed through the hydraulic lash adjuster, is of insufficient pressure to compress the spring  170  and cause the locking pins  164   a ,  164   b  to engage in order to lock the inner arm assembly  150  for motion dependent on the outer arm assembly  152 . In this condition, the valve (not shown) moves due to the low lift cam (not shown) interfacing with the low-lift contact on the inner arm ( 150 ). 
         [0028]    In a high-lift mode (not shown), the ECM  16  instructs the CV  30  to increase the fluid pressure in the locking pin housing  162  to a higher pressure state (P 2 ) sufficiently such that the locking pins  164   a ,  164   b  compress the springs  170   a ,  170   b , respectively and is in an engaged position resulting in the outer arm assembly  152  being locked to the inner, low lift arm  150  and thus prevented to independently pivot about the pivoting pin  154 . The outer arm assembly  152  pivots to a third position in accordance with the high-lift cam lobe geometry causing the valve to open to a second predetermined amount greater than the first predetermined amount. The present invention recognizes that in various embodiments, switching the fluid supply from P 1  to P 2  can cause the locking pins  164   a ,  164   b  to retract and therefore disengage the outer arm assembly  152  from the inner arm assembly  150  and prevent the valve (not shown) from following the high lift cam (not shown) that interfaces with the high-lift contacts  158 . 
         [0029]    Additionally, the present invention envisions further embodiments that may require maintaining a fluid supply at a pressure state of P 2  in which P 2  represents “normal” operation of the SRFF mechanism  28 . In such embodiments, the ECM  16  instructs the CV  30  to decrease the fluid pressure in the locking pin housing  162  to a lower pressure state (P 1 ) in order to engage or disengage the locking pins  164   a ,  164   b . The present invention further envisions an embodiment having a single locking pin  164  serve to engage the outer arm assembly  152 . 
         [0030]    Referring now to  FIG. 4 , a hydraulic control system  32  includes monitoring and transmitting signals received from engine sensors including but not limited to the engine speed sensor  22 , the engine voltage sensor  24 , and the engine temperature sensor  26 . A two-step change flag  34  indicates that the engine requires a change in the lift mode of the SRFF mechanism  28  to maintain appropriate engine operation. A SRFF positioning module  38  monitors the two-step change flag  34  and compares the measured engine operating speed, RPM op , received from the engine speed sensor  22  to a predetermined RPM range. If the value of RPM op  is within the predetermined RPM range and the two-step change flag  34  is set, the SRFF positioning module  38  enables the CV command module  40 . 
         [0031]    The command module  40  commands the CV  30  to change its state of operation by generating and transmitting a state change command to the CV  30 . In accordance with the state change command, the CV  30  switches the fluid supply provided to the locking pin housing  162  via the hydraulic lash adjuster from a low pressure state (P 1 ) to a higher pressure state (P 2 ). When the command module  40  commands the CV  30  to change its state, a timer module  42  stores the clock time of this command as T a . A comparison module  44  monitors the fluid pressure sensor  18  and compares the pressure within the fluid gallery of the hydraulic lash adjuster  29  to a predetermined pressure threshold. When the comparison module  44  detects a signal from the fluid pressure sensor  18  that the pressure exerted by the fluid supply within the fluid gallery of the hydraulic lash adjuster  29  has exceeded or fallen below a predetermined threshold, the timer module  42  stores this second clock time as T b . The timer module  42  then calculates the time difference between T a  and T b  as the time response, T act , of the CV  30  to the change of state command. 
         [0032]    An update module  46  receives signals from the engine speed sensor  22 , the engine voltage sensor  24 , and the engine temperature sensor  26  indicating the engine operating condition. The update module  46  then retrieves a desired time, T des , of the CV  30  from a lookup table  50  that corresponds to the engine operating condition sensed by the update module  46 . The update module  46  compares the value of T act  to T des . If the value of T act  has exceeded a predetermined time range about T des , the update module  46  assigns a new value to T des  by setting T des  equal to T act  and stores the new value T des  in the look-up table  50  as a function of the engine operating condition. 
         [0033]    Referring now to  FIG. 5 , the hydraulic control system  32  will be described in further detail. In step  100 , if the engine  12  is turned on, the ECM  16  will be operational and proceed to step  102 . If the engine is not turned on, the ECM  16  will not be operational and the hydraulic control system  32  will not be initiated. In step  102 , the SRFF positioning module  38  determines whether the engine is operating within a predetermined RPM range. The predetermined RPM range is an engine and mechanism specific range. If the engine operating speed, RPM op , is not within the predetermined RPM range, the process ends. 
         [0034]    If the RPM op  is within the predetermined RPM range, the SRFF positioning module  38 , in step  104 , determines whether a two-step change flag  34  is set indicating that the engine requires a change in the lift mode of SRFF mechanism  28 . If a position change of the SRFF mechanism  28  is not required and the two-step change flag  34  is not set, the process ends. If the two-step change flag  34  is set, the SRFF positioning module  38  enables the command module  40 . In step  106 , the command module  40  generates and transmits a state change command directing the CV  30  to change its state of operation by switching the fluid supply provided to the locking pin housing  162  from either a low pressure state (P 1 ) to a higher pressure state (P 2 ) or from P 2  to P 1 . Additionally in step  106 , the timer module  42  stores the time of the sate change command as a first time, T a . 
         [0035]    In step  108 , when the comparison module  44  detects that the pressure exerted by the change in fluid supply has either exceeded or fallen below a predetermined pressure threshold within the locking pin housing  162 , the timer module  42  stores the corresponding time as a second time, T b . In step  110 , the timer module  42  calculates the time difference between T a  and T b  as T act . The response time of the hydraulic control system  32  is based on T act . In step  112 , the update module  46  determines the engine operating condition by monitoring the engine speed sensor  22 , the engine voltage sensor  24 , and the engine temperature sensor  26 . 
         [0036]    In step  114 , the update module  46  retrieves a desired time of the hydraulic control system  32 , T des , from a look-up table  50  that corresponds to engine operating condition in step  112 . In step  116 , the update module  46  compares the value T act  t to T des . If the update module  46  determines that T act  is within a predetermined time range, about T des , the process ends. If the update module  46  determines that T act  t has exceeded the predetermined time range about T des , the update module  46  assigns a new value to T des  by setting T des  equal to T act  in step  118 . In step  120 , the look-up table  50  stores the value T des  as a function of the engine operating point read in step  112 . The process ends in step  122 . Important to note is that the applicability of the present invention is not limited to embodiments that employ SRFF technology but is additionally applicable to valve train technologies that utilize a CV to control the activation of a hydraulic system to regulate valve events. Such valve train technologies include but are not limited to Displacement on Demand technologies and other related VVA technologies. 
         [0037]    Additionally, the scope of the invention is not limited to embodiments that solely implement engine component or system control valves. The current invention is applicable to various systems that employ valve control operations including but not limited to transmission torque converters, clutches and brakes. 
         [0038]    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.