Title of Invention	A CONTROL SYSTEM AND A METHOD FOR DETECTING A HYDRAULIC SYSTEM LEAK IN A VEHICLE POWERTRAIN
Abstract	The invention relates to a control system for detecting a hydraulic system leak in a vehicle powertrain (10), comprising : a filtering module (302) that outputs filtered pressure values by filtering a pressure signal (Psupply) output by a pressure sensor (58) to remove high frequency content (Psupply) from said pressure signal (Psupply), wherein said pressure sensor (58) senses pressures of a fluid within a gallery of a hydraulic system of said vehicle powertrain; a pressure reading module (304) that determines a first pressure reading based on a first one of said filtered pressure values output before a valve (62) of said hydraulic system (22) is actuated and that determines a second pressure reading based on a second one of said filtered pressure values output after said valve (62) is actuated; and a comparison module (306) that calculates a pressure ratio of said first and second pressure readings and that signals a fault condition indicative of said hydraulic system leak based on a relationship between said pressure ratio and a pressure threshold, characterized in that said valve controls an active fuel management event of an engine (12) of said vehicle powertrain (10), said active fuel management event comprises deactivating a set of cylinders of said engine (12), and said first one of said filtered pressure values is output before said active fuel management event and said second one of said filtered pressure values is output after said active fuel management event.

Title of Invention

A CONTROL SYSTEM AND A METHOD FOR DETECTING A HYDRAULIC SYSTEM LEAK IN A VEHICLE POWERTRAIN

Abstract

The invention relates to a control system for detecting a hydraulic system leak in a vehicle powertrain (10), comprising : a filtering module (302) that outputs filtered pressure values by filtering a pressure signal (Psupply) output by a pressure sensor (58) to remove high frequency content (Psupply) from said pressure signal (Psupply), wherein said pressure sensor (58) senses pressures of a fluid within a gallery of a hydraulic system of said vehicle powertrain; a pressure reading module (304) that determines a first pressure reading based on a first one of said filtered pressure values output before a valve (62) of said hydraulic system (22) is actuated and that determines a second pressure reading based on a second one of said filtered pressure values output after said valve (62) is actuated; and a comparison module (306) that calculates a pressure ratio of said first and second pressure readings and that signals a fault condition indicative of said hydraulic system leak based on a relationship between said pressure ratio and a pressure threshold, characterized in that said valve controls an active fuel management event of an engine (12) of said vehicle powertrain (10), said active fuel management event comprises deactivating a set of cylinders of said engine (12), and said first one of said filtered pressure values is output before said active fuel management event and said second one of said filtered pressure values is output after said active fuel management event.

Full Text	FIELD OF THE INVENTION The present disclosure relates to internal combustion engines, and more particularly to engine control systems that detect hydraulic fluid leaks in hydraulic systems. BACKGROUND OF THE INVENTION Some internal combustion engines include engine control system that deactivate cylinders under specific low load operating conditions. 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. Conversely, operation using less than all of the cylinders of the engine (i.e. one or more cylinders are not active) is referred to as a "deactivated" mode. In the deactivated mode, there are fewer firing cylinders. As a result, there is less drive torque available to drive the vehicle driveline and accessories (e.g. alternator, coolant pump, A/C compressor). However, engine efficiency is increased as a result of decreased air pumping losses due to the deactivated cylinders not taking in and compressing fresh intake air. A lifter oil manifold assembly (LOMA) is implemented to activate and deactivate select cylinders of the engine. The LOMA includes a series of solenoids associated with corresponding cylinders. The solenoids are selectively energized to enable hydraulic fluid flow to the lifters to inhibit valve lifter operation, thereby deactivating the corresponding cylinders. The LOMA can experience significant oil leakage caused by faulty assemblies, hydraulic solenoid valves, and/or LOMA gaskets. Hydraulic leaks can slow the dynamic response of the LOMA subsystems and cause engine damage due to mistimed AFM valve lifter events. SUMMARY OF THE INVENTION A control system and method for detecting a hyudraulic system leak in an engine includes a pressure sensor that senses a first pressure reading of a hydraulic fluid supply at a first time and a second pressure reading of said hydraulic fluid supply at a second time. A comparison module calculates a pressure ratio based on the first and second pressure readings and signals a fault condition based on a relationship between the pressure ratio and a pressure threshold. In other features, a pressure reading module determines the first pressure reading before a mode change of the engine and determines the second pressure reading after the mode change of the engine. The comparison module signals the fault condition when the pressure ratio one of falls below the pressure threshold the comparison module stores said fault condition as a fault code. In other features, a filtering module removes high frequency content from the first pressure reading and the second pressure reading. A pressure reading module determines the first pressure reading before an active fuel management event of the engine and determines the second pressure reading after the active fuel management event of the engine. The active fuel management event includes deactivating a set of cylinders of the engine. A pressure reading module determines the first pressure reading before actuating a valve of the engine and determines the second pressure reading after actuating the valve of the engine. A control system for detecting a hydraulic system leak in an engine includes a pressure sensor that senses pressure of a hydraulic fluid supply, a pressure reading that determines a first pressure reading of the hydraulic fluid supply at a first time and a second pressure reading of the hydraulic fluid supply at a second time, and a comparison module that calculates a pressure ratio based on the first and second pressure readings and that signals a fault condition based on a relationship between the pressure ratio and a pressure ratio threshold. In other features, the comparison module signals the fault condition when the pressure ratio falls below the pressure threshold and rises above the pressure threshold. The reading module determines the first pressure reading before actuating a valve of the engine and determines the second pressure reading after actuating the valve of the engine. The pressure reading module determines , the first pressure reading before an active fuel management event of the engine and determines the second pressure reading after the active fuel management event of the engine. Further areas of applicability will become apparent from t he 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. BRIEF DESCRIPTION OF ACCOMPANYING 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. Figure 1 is a functional block diagram illustrating a vehicle powertrain including an active fuel management (AFM) engine control system according to the present invention; Figure 2 is a partial cross-sectional view of the AFM engine illustrating a lifter oil manifold assembly (LOMA) and an intake valvetrain; Figure 3 is a functional block diagram illustrating an exemplary module that executes the leak detection control system of the present invention; Figure 4 is a flowchart illustrating the leak detection control system of the present invention; Figure 5A is a graph illustrating an exemplary pressure reading signal generated according to the present invention; and Figure 5B is a graph illustrating an exemplary pressure reading signal generated according to the present invention. DETAILED DESCRIPTION OF THE INVENTION 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. Referring now to figure 1, a vehicle 10 includes an engine 12 that drives a transmission 14. The transmission 14 is 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 includes N cylinders 18. One or more select cylinders 18 may be selectively deactivated during engine operation. Although figure 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 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 the select cylinders 18, as described in further detail below. \|8©2tL A controller 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 controller 24. The controller 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. [0022] 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 controller 24 The controller 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 EQJE3}- When the engine 12 enters an operating point to enable the deactivated mode, the controller 24 transitions 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 controller 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 J9824] The engine load is determined based on the intake MAP, cylinder mode and engine speed. More particularly, if the MAP is- below a threshold level for. a given engine revolutions per minute (RPM), the engine load is deemed light and the engine 12 could possibly be operated in the _ deactivated mode. If the MAP is above the threshold level for the given RPMr the engine load is deemed heavy.and the engine 12 is operated in the activated mode. The controller 24 controls the LOMA 22 based on the solenoid control, as discussed in further detail below. ^ \Qtf25fr Referring now to FIG 2, an intake valvetrain 40 of the engine 12 includes an intake valve 42, a rocker 44 and a pushrod 46 associated with each cylinder 18. The engine 12 includes a rotatably driven camshaft 48 having a plurality of valve cams 50 disposed therealong A cam surface 52 of the valve cams 50 engage the lifters 54 to cyclically open and close intake ports 53 within which the intake valves 42 are positioned The intake valve 42 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 44 to the pushrod 46, and from the pushrod 46 to the lifter 54, causing the lifter 54 to press against the cam surface 52 [Q£26J^ As the camshaft 48 is caused to rotate, the valve cam 50 induces linear motion of the corresponding lifter 54 The lifter 54 induces linear motion in the corresponding pushrod 46 As the pushrod 46 is induced to move outward, the rocker 44 is caused to pivot about an axis (A) Pivoting of the rocker 44 induces movement of the intake valve 42 toward an open position, thereby opening the intake port 53 The biasing force induces the intake valve 42 to the closed position as the camshaft 48 continues to rotate In this manner, the intake port 53 is cyclically opened to enable air intake _J0fl22J Although the intake valvetrain 40 of the engine 12 is illustrated in FIG. 2, it is 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 18. Rotation of the camshaft 48 induces reciprocal motion of the exhaust valves to open and close associated exhaust ports, as similarly described above for the intake valvetrain. -fO©?8J-. The LOMA 22 provides pressurized fluid to a plurality of lifters 54 and includes solenoids 56 (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 54 are disposed within the intake and exhaust valvetrams to provide an interface between the cams 50 and the pushrods 46 In general, there are two lifters 54 provided for each select cylinder 18' (one lifter for the intake valve 42 and one lifter for the exhaust valve) It is anticipated, however, that more lifters 54 can be associated with each select cylinder 18' (i e , multiple inlet or exhaust valves per cylinder 18') The LOMA 22 further requires a pressure sensor 58 that generates a pressure signal indicating a pressure of a hydraulic fluid supply to the LOMA 22 It is anticipated that one or more pressure sensors 58 can be implemented t0®2%}-^ Each lifter 54 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 54 provides a mechanical connection between the cam 50 and the pushrod 46 In this manner, the cam 50 induces linear motion of the lifter 54, which is transferred to the pushrod 46 In the second mode, the lifter 54 functions as a buffer to provide a mechanical disconnect between the cam 50 and the pushrod 46 Although the cam 50 induces linear motion of the lifter 54, the linear motion is not transferred to the pushrod 46 _f£032]r The solenoids 56 selectively enable hydraulic fluid flow to the lifters 54 to switch the lifters 54 between the first and second modes. Although there is generally one solenoid 56 associated with each select cylinder 18' (i.e., one solenoid for two lifters), it is anticipated that more or fewer solenoids 56 can be implemented Each solenoid 56 actuates an associated valve 60 (shown schematically) between open and closed positions. In the closed position, the valve 60 inhibits pressurized hydraulic fluid flow to the corresponding lifters 54. In the open position, the valve 60 enables pressurized fluid flow to the corresponding lifters 54 via a fluid passage 62. The pressurized hydraulic fluid flow is provided to the LOMA 22 from a pressurized hydraulic fluid source. •fgtp?}' Although not illustrated, a brief description of an exemplary solenoid is provided herein to provide a better understanding of the present invention. The solenoids 56 generally include an electromagnetic coil and a plunger that is disposed coaxially within the coil The plunger provides a mechanical interface between the solenoid 56 and a mechanical element, such as the valve 60 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 56 is energized by supplying current to the coil, which induces 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 60 in its closed position to inhibit pressurized hydraulic fluid flow to the corresponding lifters In the second position, the plunger actuates the valve 60 to its open position to enable pressurized hydraulic fluid flow to the corresponding lifters fO032§s The detection control system of the present invention determines the occurrence of a hydraulic system leak at or downstream of the LOMA solenoid(s). In an exemplary embodiment, the hydraulic system leak can occur at, but is not limited, a LOMA gasket (not shown) More specifically, the detection control system of the present invention determines that a hydraulic system leak has occurred based on pressure readings of the LOMA hydraulic fluid supply preceding and following a commanded active fuel management (AFM) event (i.e. deactivation of select cylinders 18'). It is anticipated, however that the current invention can be implemented to detect leaks in other hydraulic systems in which hydraulic fluid flow restrictions remain substantially constant over the operation of the system. XOgSSfr In various embodiments, the fluid pressure sensor 58 can be positioned in other fixed engine fluid passages or galleries including, but not limited to, a hydraulic lash adjuster fluid gallery (not shown). Additionally, in various embodiments, rather than sensing pressure readings prior to and after an AFM event, pressure readings can be taken before and after switching among other various operating modes (i e changing actuation modes of a valve) For example, such embodiments include, but are not limited to, two- step variable valve actuation systems. ■{9033] Referring now to FIG 3, the controller 24 includes a filter module 302 that receives as inputs, hydraulic fluid pressure signals (PSUppiy) provided by the pressure sensor 58 The filter module 302 contains low pass filtering components to remove high frequency content of the PSupPiy signal 4fifl3S] The leak detection system 300 includes a pressure reading module 304 that determines a first pressure reading of the hydraulic fluid supplied to the LOMA 22 prior to an AFM valve 62 opening event and a second pressure reading after the AFM valve 62 opening event In the present implementation, the pressure reading module 304 determines the first pressure reading before the controller 24 energizes the LOMA solenoid(s) The pressure reading module 304 determines the second pressure reading after a period of time after the first pressure reading in which all commanded cylinders 18' should be deactivated, and the pressure of the hydraulic fluid supplied to the LOMA 22 should have recovered to substantially the same pressure as before the controller 24 switched the solenoid 56 A comparison module 306 calculates a pressure ratio of the second pressure reading to the first pressure reading The comparison module 306 then compares the calculated pressure ratio to a pressure threshold. If the pressure ratio is below the pressure threshold, the comparison module 306 generates a fault control - signal indicating that a hydraulic system leak exists at and/or downstream of the valve 62. f0ft3GJ-, Referring now to FIG. 4 a method 400 for determining the presence of a hydraulic system leak in the leak detection system 300 will be described in more detail. Control begins the method 400 at step 402. In step 404, control determines whether to switch the solenoid 56 (i.e , from the de- energized state to the energized state) which will switch the engine 12 to the deactivated mode. If the engine 12 is not to be switched, control returns to step 404. In step 406, control determines a first pressure reading of the hydraulic fluid supply before delivering the hydraulic fluid supply to the lifter 54 ffHJ^SL. In step 408, control determines a second pressure reading of the hydraulic fluid supply In the present implementation, control waits a period of time before determining the second pressure reading In step 410, control calculates a pressure ratio of the second pressure reading to the first pressure reading taken in step 406 In step 412, control determines whether the pressure ratio is less than a pressure threshold If the pressure ratio is above or equal to the pressure threshold, control determines that no leak exists at the LOMA 22 and sets a no fault condition in step 416 If the pressure ratio is below the pressure threshold, control determines that a leak has been detected and sets a fault condition in step 414 The method 400 ends in step 418 In an exemplary embodiment, the conditions can be stored as a fault indicator code Additionally, the fault indication code can be requested by a service technician during a diagnosis of the engine 12 [O05SJ Referring now to FIG. 5A and 5B, the pressure ratio of the second pressure reading relative to the first pressure reading is determined based on test data using an equivalent LOMA system. More specifically, the pressure readings of the hydraulic fluid supply are monitored over time. The horizontal axis represents time given in seconds and the vertical axis represents pressure given in pounds per square inch (PSI) [&ES&\ FIG. 5A and FIG 5B illustrate simulations of the pressure readings of the hydraulic fluid supply provided to the LOMA 22 before and after the engine 12 is switched to deactivation mode In FIG. 5A, point A is approximately equal to 44 5 PSI and point B is approximately equal to 43 5 PSI resulting in a pressure ratio of 0 978 In an exemplary embodiment, the pressure threshold could be set at 0.90. Since the pressure ratio exceeds the exemplary pressure threshold, the leak detection control system indicates that no hydraulic system leak has occurred It should be appreciated that other values for the pressure threshold are anticipated tgPRJT FIG 5B illustrates a simulation in which the leak detection control system of the present invention would signal a system leak Point A' is approximately equal to 44 1 PSI and point B' is approximately equal to 38 4 PSI resulting in a pressure ratio of 0 870 The pressure ratio falls below exemplary pressure threshold indicating a hydraulic system leak within the LOMA 22 f064tj_ 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 WE CLAIM : 1. A control system for detecting a hydraulic system leak in a vehicle powertrain (10), comprising : a filtering module (302) that outputs filtered pressure values by filtering a pressure signal (P supply) output by a pressure sensor (58) to remove high frequency content (Psupply) from said pressure signal (Psupply), wherein said pressure sensor (58) senses pressures of a fluid within a gallery of a hydraulic system of said vehicle powertrain; a pressure reading module (304) that determines a first pressure reading based on a first one of said filtered pressure values output before a valve (62) of said hydraulic system (22) is actuated and that determines a second pressure reading based on a second one of said filtered pressure values output after said valve (62) is actuated; and a comparison module (306) that calculates a pressure ratio of said first and second pressure readings and that signals a fault condition indicative of said hydraulic system leak based on a relationship between said pressure ratio and a pressure threshold, characterized in that said valve controls an active fuel management event of an engine (12) of said vehicle powertrain (10), said active fuel management event comprises deactivating a set of cylinders of said engine (12), and said first one of said filtered pressure values is output before said active fuel management event and said second one of said filtered pressure values is output after said active fuel management event. 2. The control system as claimed in claim 1 wherein said pressure ratio is said second pressure ratio is said second pressure reading divided by said first pressure reading and wherein said comparison module signals said fault condition when said pressure ratio falls below said pressure threshold. 3. The control system as claimed in claim 1 wherein said comparison module stores said fault condition as a fault code. 4. A method for detecting a hydraulic system leak in a vehicle powertrain, comprising: outputting filtered pressure values by filtering a pressure signal output by a pressure sensor to remove high frequency content from said pressure signal, wherein said pressure sensor senses pressures of a fluid within a gallery of a hydraulic system of said vehicle powertrain; determining a first pressure reading based on a first one of said filtered pressure values output before a valve of said hydraulic system is actuated; determining a second pressure reading based on a second one of said filtered pressure values output after said valve is actuated; and calculating a pressure ratio of said first and second pressure readings and signaling a fault condition indicative of said hydraulic system leak based, on a relationship between said pressure ratio and a pressure threshold, wherein said valve controls an active fuel management event of an engine of said vehicle powertrain, said active fuel management event comprises deactivating a set of cylinders of said engine, and said first one of said filtered pressure values is output before said active fuel management event and said second one of said filtered pressure values is output after said active fuel management event. 5. The method as claimed in claim 4, comprising signaling said fault condition when said pressure ratio falls below said pressure threshold, wherein said pressure ratio is said second pressure reading divided by said first pressure reading. 6. The method as claimed in claim 4, wherein said fault condition is stored as a fault code. 7. A control system for detecting a hydraulic system leak in a vehicle powertrain comprising : a pressure sensor that senses pressures of a fluid within a gallery of a hydraulic system of said vehicle powertrain and outputs a pressure signal based on said pressures; a filtering module that outputs filtered pressure values by filtering said pressure signal to remove high frequency content from said pressure signal; a pressure reading module that determines a first pressure reading based on a first one of said filtered pressure values output before a valve of said hydraulic system is actuated and a second pressure reading based on a second one of said filtered pressure values output after said valve is actuated; and a comparison module that calculates a pressure ratio of said first and second pressure readings and that signals a fault condition of said hydraulic system leak based on a relationship between said pressure ratio and a pressure threshold, wherein said valve controls an active fuel management event of an engine of said vehicle powertrain, said active fuel management event comprises deactivating a set of cylinders of said engine, and said first one of said filtered pressure values is output before said active fuel management event and said second one of said filtered pressure values is output after said active fuel management event. 8. The control system as claimed in claim 7, wherein said pressure ratio is said second pressure reading divided by said first pressure reading and wherein said comparison module signals said fault condition when said pressure ratio falls below said pressure threshold. ABSTRACT TITLE : "A control system and a method for detecting a hydraulic system leak in a vehicle powertrain" The invention relates to a control system for detecting a hydraulic system leak in a vehicle powertrain (10), comprising : a filtering module (302) that outputs filtered pressure values by filtering a pressure signal (Psupply) output by a pressure sensor (58) to remove high frequency content (Psupply) from said pressure signal (Psupply), wherein said pressure sensor (58) senses pressures of a fluid within a gallery of a hydraulic system of said vehicle powertrain; a pressure reading module (304) that determines a first pressure reading based on a first one of said filtered pressure values output before a valve (62) of said hydraulic system (22) is actuated and that determines a second pressure reading based on a second one of said filtered pressure values output after said valve (62) is actuated; and a comparison module (306) that calculates a pressure ratio of said first and second pressure readings and that signals a fault condition indicative of said hydraulic system leak based on a relationship between said pressure ratio and a pressure threshold, characterized in that said valve controls an active fuel management event of an engine (12) of said vehicle powertrain (10), said active fuel management event comprises deactivating a set of cylinders of said engine (12), and said first one of said filtered pressure values is output before said active fuel management event and said second one of said filtered pressure values is output after said active fuel management event.

Full Text

FIELD OF THE INVENTION
The present disclosure relates to internal combustion engines, and more
particularly to engine control systems that detect hydraulic fluid leaks in
hydraulic systems.
BACKGROUND OF THE INVENTION
Some internal combustion engines include engine control system that deactivate
cylinders under specific low load operating conditions. 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. Conversely, operation using less than all of the cylinders of
the engine (i.e. one or more cylinders are not active) is referred to as a
"deactivated" mode.

In the deactivated mode, there are fewer firing cylinders. As a result, there is
less drive torque available to drive the vehicle driveline and accessories (e.g.
alternator, coolant pump, A/C compressor). However, engine efficiency is
increased as a result of decreased air pumping losses due to the deactivated
cylinders not taking in and compressing fresh intake air.
A lifter oil manifold assembly (LOMA) is implemented to activate and deactivate
select cylinders of the engine. The LOMA includes a series of solenoids
associated with corresponding cylinders. The solenoids are selectively energized
to enable hydraulic fluid flow to the lifters to inhibit valve lifter operation, thereby
deactivating the corresponding cylinders.

The LOMA can experience significant oil leakage caused by faulty assemblies,
hydraulic solenoid valves, and/or LOMA gaskets. Hydraulic leaks can slow the
dynamic response of the LOMA subsystems and cause engine damage due to
mistimed AFM valve lifter events.
SUMMARY OF THE INVENTION
A control system and method for detecting a hyudraulic system leak in an engine
includes a pressure sensor that senses a first pressure reading of a hydraulic
fluid supply at a first time and a second pressure reading of said hydraulic fluid
supply at a second time. A comparison module calculates a pressure ratio based
on the first and second pressure readings and signals a fault condition based on
a relationship between the pressure ratio and a pressure threshold.
In other features, a pressure reading module determines the first pressure
reading before a mode change of the engine and determines the second
pressure reading after the mode change of the engine. The comparison module
signals the fault condition when the pressure ratio one of falls below the
pressure threshold the comparison module stores said fault condition as a fault
code.
In other features, a filtering module removes high frequency content from the
first pressure reading and the second pressure reading. A pressure reading
module determines the first pressure reading before an active fuel management
event of the engine and determines the second pressure reading after the active
fuel management event of the engine. The active fuel management event
includes deactivating a set of cylinders of the engine. A pressure reading module

determines the first pressure reading before actuating a valve of the engine and
determines the second pressure reading after actuating the valve of the engine.
A control system for detecting a hydraulic system leak in an engine includes a
pressure sensor that senses pressure of a hydraulic fluid supply, a pressure
reading that determines a first pressure reading of the hydraulic fluid supply at a
first time and a second pressure reading of the hydraulic fluid supply at a
second time, and a comparison module that calculates a pressure ratio based on
the first and second pressure readings and that signals a fault condition based on
a relationship between the pressure ratio and a pressure ratio threshold.
In other features, the comparison module signals the fault condition when the
pressure ratio falls below the pressure threshold and rises above the pressure
threshold. The reading module determines the first pressure reading before
actuating a valve of the engine and determines the second pressure reading
after actuating the valve of the engine. The pressure reading module determines ,
the first pressure reading before an active fuel management event of the engine
and determines the second pressure reading after the active fuel management
event of the engine.
Further areas of applicability will become apparent from t he 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.
BRIEF DESCRIPTION OF ACCOMPANYING 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.

Figure 1 is a functional block diagram illustrating a vehicle powertrain including
an active fuel management (AFM) engine control system according to the
present invention;
Figure 2 is a partial cross-sectional view of the AFM engine illustrating a lifter oil
manifold assembly (LOMA) and an intake valvetrain;
Figure 3 is a functional block diagram illustrating an exemplary module that
executes the leak detection control system of the present invention;
Figure 4 is a flowchart illustrating the leak detection control system of the
present invention;
Figure 5A is a graph illustrating an exemplary pressure reading signal generated
according to the present invention; and
Figure 5B is a graph illustrating an exemplary pressure reading signal generated
according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
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.
Referring now to figure 1, a vehicle 10 includes an engine 12 that drives a
transmission 14. The transmission 14 is 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 includes N cylinders 18. One or more select cylinders 18 may be
selectively deactivated during engine operation. Although figure 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 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 the select cylinders 18, as
described in further detail below.

|8©2tL A controller 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 controller 24. The controller 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.
[0022] 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 controller
24 The controller 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
EQJE3}- When the engine 12 enters an operating point to enable the
deactivated mode, the controller 24 transitions 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 controller 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

J9824] The engine load is determined based on the intake MAP,
cylinder mode and engine speed. More particularly, if the MAP is- below a
threshold level for. a given engine revolutions per minute (RPM), the engine
load is deemed light and the engine 12 could possibly be operated in the
_ deactivated mode. If the MAP is above the threshold level for the given RPMr
the engine load is deemed heavy.and the engine 12 is operated in the
activated mode. The controller 24 controls the LOMA 22 based on the
solenoid control, as discussed in further detail below.
^ \Qtf25fr Referring now to FIG 2, an intake valvetrain 40 of the engine
12 includes an intake valve 42, a rocker 44 and a pushrod 46 associated with
each cylinder 18. The engine 12 includes a rotatably driven camshaft 48
having a plurality of valve cams 50 disposed therealong A cam surface 52 of
the valve cams 50 engage the lifters 54 to cyclically open and close intake
ports 53 within which the intake valves 42 are positioned The intake valve 42
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 44 to
the pushrod 46, and from the pushrod 46 to the lifter 54, causing the lifter 54
to press against the cam surface 52
[Q£26J^ As the camshaft 48 is caused to rotate, the valve cam 50
induces linear motion of the corresponding lifter 54 The lifter 54 induces
linear motion in the corresponding pushrod 46 As the pushrod 46 is induced
to move outward, the rocker 44 is caused to pivot about an axis (A) Pivoting
of the rocker 44 induces movement of the intake valve 42 toward an open
position, thereby opening the intake port 53 The biasing force induces the
intake valve 42 to the closed position as the camshaft 48 continues to rotate
In this manner, the intake port 53 is cyclically opened to enable air intake

_J0fl22J Although the intake valvetrain 40 of the engine 12 is
illustrated in FIG. 2, it is 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 18. Rotation of the camshaft 48
induces reciprocal motion of the exhaust valves to open and close associated
exhaust ports, as similarly described above for the intake valvetrain.
-fO©?8J-. The LOMA 22 provides pressurized fluid to a plurality of
lifters 54 and includes solenoids 56 (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 54 are disposed within the intake and exhaust valvetrams to
provide an interface between the cams 50 and the pushrods 46 In general,
there are two lifters 54 provided for each select cylinder 18' (one lifter for the
intake valve 42 and one lifter for the exhaust valve) It is anticipated,
however, that more lifters 54 can be associated with each select cylinder 18'
(i e , multiple inlet or exhaust valves per cylinder 18') The LOMA 22 further
requires a pressure sensor 58 that generates a pressure signal indicating a
pressure of a hydraulic fluid supply to the LOMA 22 It is anticipated that one
or more pressure sensors 58 can be implemented
t0®2%}-^ Each lifter 54 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 54 provides a mechanical connection between the
cam 50 and the pushrod 46 In this manner, the cam 50 induces linear motion
of the lifter 54, which is transferred to the pushrod 46 In the second mode,
the lifter 54 functions as a buffer to provide a mechanical disconnect between
the cam 50 and the pushrod 46 Although the cam 50 induces linear motion
of the lifter 54, the linear motion is not transferred to the pushrod 46

_f£032]r The solenoids 56 selectively enable hydraulic fluid flow to the
lifters 54 to switch the lifters 54 between the first and second modes.
Although there is generally one solenoid 56 associated with each select
cylinder 18' (i.e., one solenoid for two lifters), it is anticipated that more or
fewer solenoids 56 can be implemented Each solenoid 56 actuates an
associated valve 60 (shown schematically) between open and closed
positions. In the closed position, the valve 60 inhibits pressurized hydraulic
fluid flow to the corresponding lifters 54. In the open position, the valve 60
enables pressurized fluid flow to the corresponding lifters 54 via a fluid
passage 62. The pressurized hydraulic fluid flow is provided to the LOMA 22
from a pressurized hydraulic fluid source.
•fgtp?}' Although not illustrated, a brief description of an exemplary
solenoid is provided herein to provide a better understanding of the present
invention. The solenoids 56 generally include an electromagnetic coil and a
plunger that is disposed coaxially within the coil The plunger provides a
mechanical interface between the solenoid 56 and a mechanical element,
such as the valve 60 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 56 is
energized by supplying current to the coil, which induces 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
60 in its closed position to inhibit pressurized hydraulic fluid flow to the
corresponding lifters In the second position, the plunger actuates the valve
60 to its open position to enable pressurized hydraulic fluid flow to the
corresponding lifters
fO032§s The detection control system of the present invention
determines the occurrence of a hydraulic system leak at or downstream of the
LOMA solenoid(s). In an exemplary embodiment, the hydraulic system leak
can occur at, but is not limited, a LOMA gasket (not shown) More
specifically, the detection control system of the present invention determines

that a hydraulic system leak has occurred based on pressure readings of the
LOMA hydraulic fluid supply preceding and following a commanded active fuel
management (AFM) event (i.e. deactivation of select cylinders 18'). It is
anticipated, however that the current invention can be implemented to detect
leaks in other hydraulic systems in which hydraulic fluid flow restrictions
remain substantially constant over the operation of the system.
XOgSSfr In various embodiments, the fluid pressure sensor 58 can be
positioned in other fixed engine fluid passages or galleries including, but not
limited to, a hydraulic lash adjuster fluid gallery (not shown). Additionally, in
various embodiments, rather than sensing pressure readings prior to and after
an AFM event, pressure readings can be taken before and after switching
among other various operating modes (i e changing actuation modes of a
valve) For example, such embodiments include, but are not limited to, two-
step variable valve actuation systems.
■{9033] Referring now to FIG 3, the controller 24 includes a filter
module 302 that receives as inputs, hydraulic fluid pressure signals (PSUppiy)
provided by the pressure sensor 58 The filter module 302 contains low pass
filtering components to remove high frequency content of the PSupPiy signal
4fifl3S] The leak detection system 300 includes a pressure reading
module 304 that determines a first pressure reading of the hydraulic fluid
supplied to the LOMA 22 prior to an AFM valve 62 opening event and a
second pressure reading after the AFM valve 62 opening event In the
present implementation, the pressure reading module 304 determines the first
pressure reading before the controller 24 energizes the LOMA solenoid(s)
The pressure reading module 304 determines the second pressure reading
after a period of time after the first pressure reading in which all commanded
cylinders 18' should be deactivated, and the pressure of the hydraulic fluid
supplied to the LOMA 22 should have recovered to substantially the same
pressure as before the controller 24 switched the solenoid 56 A comparison
module 306 calculates a pressure ratio of the second pressure reading to the
first pressure reading The comparison module 306 then compares the

calculated pressure ratio to a pressure threshold. If the pressure ratio is below
the pressure threshold, the comparison module 306 generates a fault control -
signal indicating that a hydraulic system leak exists at and/or downstream of
the valve 62.
f0ft3GJ-, Referring now to FIG. 4 a method 400 for determining the
presence of a hydraulic system leak in the leak detection system 300 will be
described in more detail. Control begins the method 400 at step 402. In step
404, control determines whether to switch the solenoid 56 (i.e , from the de-
energized state to the energized state) which will switch the engine 12 to the
deactivated mode. If the engine 12 is not to be switched, control returns to
step 404. In step 406, control determines a first pressure reading of the
hydraulic fluid supply before delivering the hydraulic fluid supply to the lifter
54
ffHJ^SL. In step 408, control determines a second pressure reading of
the hydraulic fluid supply In the present implementation, control waits a
period of time before determining the second pressure reading In step 410,
control calculates a pressure ratio of the second pressure reading to the first
pressure reading taken in step 406 In step 412, control determines whether
the pressure ratio is less than a pressure threshold If the pressure ratio is
above or equal to the pressure threshold, control determines that no leak
exists at the LOMA 22 and sets a no fault condition in step 416 If the
pressure ratio is below the pressure threshold, control determines that a leak
has been detected and sets a fault condition in step 414 The method 400
ends in step 418 In an exemplary embodiment, the conditions can be stored
as a fault indicator code Additionally, the fault indication code can be
requested by a service technician during a diagnosis of the engine 12

[O05SJ Referring now to FIG. 5A and 5B, the pressure ratio of the
second pressure reading relative to the first pressure reading is determined
based on test data using an equivalent LOMA system. More specifically, the
pressure readings of the hydraulic fluid supply are monitored over time. The
horizontal axis represents time given in seconds and the vertical axis
represents pressure given in pounds per square inch (PSI)
[&ES&\ FIG. 5A and FIG 5B illustrate simulations of the pressure
readings of the hydraulic fluid supply provided to the LOMA 22 before and
after the engine 12 is switched to deactivation mode In FIG. 5A, point A is
approximately equal to 44 5 PSI and point B is approximately equal to 43 5
PSI resulting in a pressure ratio of 0 978 In an exemplary embodiment, the
pressure threshold could be set at 0.90. Since the pressure ratio exceeds the
exemplary pressure threshold, the leak detection control system indicates that
no hydraulic system leak has occurred It should be appreciated that other
values for the pressure threshold are anticipated
tgPRJT FIG 5B illustrates a simulation in which the leak detection
control system of the present invention would signal a system leak Point A' is
approximately equal to 44 1 PSI and point B' is approximately equal to 38 4
PSI resulting in a pressure ratio of 0 870 The pressure ratio falls below
exemplary pressure threshold indicating a hydraulic system leak within the
LOMA 22
f064tj_ 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

WE CLAIM :
1. A control system for detecting a hydraulic system leak in a vehicle
powertrain (10), comprising :
a filtering module (302) that outputs filtered pressure values by
filtering a pressure signal (P supply) output by a pressure sensor (58)
to remove high frequency content (Psupply) from said pressure signal
(Psupply), wherein said pressure sensor (58) senses pressures of a
fluid within a gallery of a hydraulic system of said vehicle powertrain;
a pressure reading module (304) that determines a first pressure
reading based on a first one of said filtered pressure values output
before a valve (62) of said hydraulic system (22) is actuated and that
determines a second pressure reading based on a second one of said
filtered pressure values output after said valve (62) is actuated; and
a comparison module (306) that calculates a pressure ratio of said first
and second pressure readings and that signals a fault condition
indicative of said hydraulic system leak based on a relationship
between said pressure ratio and a pressure threshold,
characterized in that said valve controls an active fuel management
event of an engine (12) of said vehicle powertrain (10), said active fuel
management event comprises deactivating a set of cylinders of said
engine (12), and said first one of said filtered pressure values is output
before said active fuel management event and said second one of said
filtered pressure values is output after said active fuel management
event.

2. The control system as claimed in claim 1 wherein said pressure ratio is
said second pressure ratio is said second pressure reading divided by
said first pressure reading and wherein said comparison module
signals said fault condition when said pressure ratio falls below said
pressure threshold.
3. The control system as claimed in claim 1 wherein said comparison
module stores said fault condition as a fault code.
4. A method for detecting a hydraulic system leak in a vehicle powertrain,
comprising:
outputting filtered pressure values by filtering a pressure signal output
by a pressure sensor to remove high frequency content from said
pressure signal, wherein said pressure sensor senses pressures of a
fluid within a gallery of a hydraulic system of said vehicle powertrain;
determining a first pressure reading based on a first one of said
filtered pressure values output before a valve of said hydraulic system
is actuated;
determining a second pressure reading based on a second one of said
filtered pressure values output after said valve is actuated; and
calculating a pressure ratio of said first and second pressure readings
and signaling a fault condition indicative of said hydraulic system leak
based, on a relationship between said pressure ratio and a pressure
threshold,
wherein said valve controls an active fuel management event of an
engine of said vehicle powertrain, said active fuel management event
comprises deactivating a set of cylinders of said engine, and said first

one of said filtered pressure values is output before said active fuel
management event and said second one of said filtered pressure
values is output after said active fuel management event.
5. The method as claimed in claim 4, comprising signaling said fault
condition when said pressure ratio falls below said pressure threshold,
wherein said pressure ratio is said second pressure reading divided by
said first pressure reading.
6. The method as claimed in claim 4, wherein said fault condition is
stored as a fault code.
7. A control system for detecting a hydraulic system leak in a vehicle
powertrain comprising :
a pressure sensor that senses pressures of a fluid within a gallery of a
hydraulic system of said vehicle powertrain and outputs a pressure
signal based on said pressures;
a filtering module that outputs filtered pressure values by filtering said
pressure signal to remove high frequency content from said pressure
signal;
a pressure reading module that determines a first pressure reading
based on a first one of said filtered pressure values output before a
valve of said hydraulic system is actuated and a second pressure
reading based on a second one of said filtered pressure values output
after said valve is actuated; and

a comparison module that calculates a pressure ratio of said first and
second pressure readings and that signals a fault condition of said
hydraulic system leak based on a relationship between said pressure
ratio and a pressure threshold,
wherein said valve controls an active fuel management event of an
engine of said vehicle powertrain, said active fuel management event
comprises deactivating a set of cylinders of said engine, and said first
one of said filtered pressure values is output before said active fuel
management event and said second one of said filtered pressure
values is output after said active fuel management event.
8. The control system as claimed in claim 7, wherein said pressure ratio is
said second pressure reading divided by said first pressure reading and
wherein said comparison module signals said fault condition when said
pressure ratio falls below said pressure threshold.

ABSTRACT

TITLE : "A control system and a method for detecting a hydraulic
system leak in a vehicle powertrain"
The invention relates to a control system for detecting a hydraulic system
leak in a vehicle powertrain (10), comprising : a filtering module (302) that
outputs filtered pressure values by filtering a pressure signal (Psupply) output
by a pressure sensor (58) to remove high frequency content (Psupply) from
said pressure signal (Psupply), wherein said pressure sensor (58) senses
pressures of a fluid within a gallery of a hydraulic system of said vehicle
powertrain; a pressure reading module (304) that determines a first pressure
reading based on a first one of said filtered pressure values output before a
valve (62) of said hydraulic system (22) is actuated and that determines a
second pressure reading based on a second one of said filtered pressure
values output after said valve (62) is actuated; and a comparison module
(306) that calculates a pressure ratio of said first and second pressure
readings and that signals a fault condition indicative of said hydraulic system
leak based on a relationship between said pressure ratio and a pressure
threshold, characterized in that said valve controls an active fuel
management event of an engine (12) of said vehicle powertrain (10), said
active fuel management event comprises deactivating a set of cylinders of
said engine (12), and said first one of said filtered pressure values is output
before said active fuel management event and said second one of said
filtered pressure values is output after said active fuel management event.

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Patent Number

270267

Indian Patent Application Number

283/KOL/2008

PG Journal Number

50/2015

Publication Date

11-Dec-2015

Grant Date

07-Dec-2015

Date of Filing

18-Feb-2008

Name of Patentee

GM GLOBAL TECHNOLOGY OPERATIONS, INC.

Applicant Address

300 GM RENAISSANCE CENTER DETROIT, MICHIGAN

Inventors:

#	Inventor's Name	Inventor's Address
1	MIKE M. MC DONALD	50053 MIDDLE RIVER MACOMB, MICHIGAN 48044-1208
2	WILLAIM C. ALBERTSON	44472 RIVERGATE DRIVE CLINTON TOWNSHIP, MICHIGAN 48038

PCT International Classification Number

G01M3/02

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/685,718	2007-03-13	U.S.A.