METHOD AND SYSTEM FOR INDICATION OF CRANKCASE VENTILATION SYSTEM DEFECTS

Abstract

Method for an engine (10) comprising the following: during engine start-up, while a manifold air flow is below a threshold, enlargement of an intake throttle opening, and indication of a crankcase ventilation system impairment based on a temporary drop in a crankcase ventilation tube pressure after enlargement of the intake throttle opening, wherein the crankcase ventilation tube pressure is estimated by a pressure sensor (77) positioned in a crankcase ventilation tube (74), and the crankcase ventilation tube (74) is arranged between an intake duct (13) and a crankcase (28).

Description

[0001] Engines may include forced crankcase ventilation ("PCV") systems, also referred to as crankcase ventilation systems, to vent gases from the crankcase and into an engine intake manifold to ensure continuous evacuation of gases from within the crankcase and reduce interference with various engine components within the crankcase. Under certain conditions, crankcase ventilation systems may be monitored to identify violations within the system. For example, a fresh air hose (a vent tube) may become disconnected, an oil cap may become loose or missing, a dipstick may be out, and / or other seals within the crankcase ventilation system may be disrupted, resulting in interference with various components enclosed within the crankcase.

[0002] Further prior art can be found in the documents US 2010 / 0 147 270 A1, US 5 792 949 A, DE 197 57 345 B4, and DE 103 20 054 A1.

[0003] Various approaches can be used to monitor the integrity of a crankcase ventilation system. For example, diagnostic blow-through approaches can be used, where a pressure sensor located in the crankcase and a valve in a PCV fresh air line are opened, and a violation in the system can be determined based on resulting changes in crankcase pressure or vacuum. Other approaches can use a combination of pressure sensors located at different locations in the crankcase ventilation system to monitor the integrity of a crankcase ventilation system.

[0004] However, the present inventors have recognized potential problems with such approaches. As one example, even when using multiple sensors and valves, a violation in the system may not be properly diagnosed. For example, there may be conditions where the pressure or vacuum change estimated by the various pressure sensors does not have a sufficient signal-to-noise ratio to detect a crankcase violation, especially a small one. As another example, the use of multiple sensors and valves increases system cost and complexity. As yet another example, based on the location of the sensor, some combinations of pressure sensors may indicate essentially the same pressure under certain conditions, resulting in an increase in redundancy without any improvement in the accuracy of the diagnostic routine.

[0005] In one approach to at least partially address these problems, a method is provided for an engine. The method includes, during engine cranking while manifold air flow is below a threshold, increasing the throttle opening and indicating a crankcase ventilation system degradation based on a change in crankcase vent tube pressure after the throttle opening. In this way, a signal used to detect a crankcase violation can be enhanced, allowing even small violations to be better detected.

[0006] In one example, a crankcase ventilation system may include a crankcase vent tube coupled between an air intake passage and a crankcase. A pressure sensor (or flow sensor) may be disposed within the crankcase vent tube to provide an estimate of the flow or pressure of air flowing through the vent tube. During engine cranking, before fuel is injected into an engine cylinder and while air flow through the vent tube is low, a controller may determine whether sufficient intake manifold vacuum exists to perform a crankcase ventilation system violation diagnosis. If the intake manifold vacuum is insufficient (e.g., the manifold vacuum is below a threshold), the controller may increase the opening of an intake throttle to increase the intake manifold vacuum.Alternatively, the control module may open (or increase the opening of) a PCV valve coupled between the crankcase and the engine intake manifold to increase manifold vacuum. For example, the PCV valve or throttle may be held open to maintain manifold vacuum at a threshold level for the duration of the diagnostic test.

[0007] Once a sufficient vacuum has been created, the controller may determine the crankcase ventilation system degradation based on characteristics (e.g., amplitude) of a transient drop in pressure sensed by the crankcase vent tube pressure sensor after throttle opening during engine cranking. For example, in response to an amplitude of the transient drop being less than a threshold (e.g., a substantially negligible transient drop in crankcase vent tube pressure), a controller may conclude that flow through the vent tube is interrupted due to a breach in the integrity of the crankcase ventilation system (e.g., due to a disconnection of the crankcase vent tube).Additionally, or alternatively, while maintaining intake manifold vacuum, the control module may determine a crankcase system violation based on differences between an estimated flow rate through the crankcase ventilation tube relative to an expected flow rate through the crankcase ventilation tube. After determining the crankcase system violation, a mitigating action may be taken, such as setting an appropriate diagnostic code during a limit on engine speed or load, to delay the depletion of lubricant from the violated crankcase and the siphoning of lubricant through the crankcase into the engine components.

[0008] In this way, changes to a throttle and / or PCV valve can be advantageously used to improve intake manifold vacuum during engine cranking, thereby improving the accuracy of crankcase violation detection. By using existing crankcase ventilation system sensors to diagnose crankcase violation during cranking, the number of sensors and valves used in a crankcase ventilation monitoring system can be reduced, providing benefits of reduced cost and complexity. Additionally, the approach allows the crankcase ventilation system to remain active during a diagnostic procedure.

[0009] It should be understood that the Summary above is provided to introduce, in simplified form, a selection of concepts further described in the Detailed Description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is clearly defined by the claims that follow the Detailed Description. Furthermore, the claimed subject matter is not limited to implementations that resolve any of the disadvantages identified above or in any part of this disclosure. Fig. 1 shows an engine part view according to the disclosure. Fig. 2A-B show a high level flow chart for indicating degradation of one or more components of a crankcase ventilation system based on changes in crankcase ventilation tube pressure during cranking and / or engine running. Fig. 3-4 illustrate exemplary methods for indicating a crankcase ventilation system violation and a crankcase ventilation system violation location based on a transient drop in crankcase vent tube pressure during engine cranking and changes in crankcase vent tube pressure relative to changes in manifold airflow during engine running. Fig. 5 shows an example method for indicating PCV valve degradation based on changes in crankcase vent tube airflow during the low manifold airflow condition. Fig. 6 shows an exemplary method for indicating a blockage of an air intake filter based on the output of a pressure sensor located in the crankcase ventilation tube. Fig. Figures 7 through 8 show exemplary changes in crankcase vent tube pressure that can be used to indicate a crankcase injury and to identify a location of the injury. Fig. 9 shows an example map for indicating air filter blockage based on changes in crankcase vent tube pressure relative to changing manifold air flow. Fig. Figure 10 shows example changes in crankcase ventilation tube pressure that may be used to indicate PCV valve degradation.

[0010] The following description relates to systems and methods for monitoring the integrity of a crankcase ventilation system in an engine crankcase ventilation system, such as the system of Fig. 1. The output of one or more pressure or flow sensors, such as a pressure sensor located in a crankcase ventilation tube of the crankcase ventilation system, may be used to identify a crankcase system violation, a location of the violation, a PCV valve impairment, and an air filter blockage. An engine control unit may be configured to execute various routines, such as the routines of Fig. 2A to B and 3 to 6, to indicate degradation of the crankcase ventilation system based on changes in crankcase vent tube pressure (or air flow) during engine cranking, as well as changes in crankcase vent tube pressure relative to changes in manifold air flow during engine running. The crankcase vent tube pressure sensor may be configured to indicate static pressure or dynamic pressure. Furthermore, it may be disposed within a venturi tube (a constricted portion of the vent tube) and thus be sensitive to either pressure or flow rate, or both.For example, the control module may determine a crankcase system violation based on characteristics of a transient drop in crankcase vent tube pressure and then further determine a violation based on both the transient drop and changes in crankcase vent tube vacuum during engine running (. Fig. 3, Fig. 4, Fig. 7 and Fig. 8) identify a location and origin of the violation. As another example, the control module may determine PCV valve impairment based on deviations of an expected crankcase ventilation tube pressure / airflow profile relative to an actual pressure / airflow profile ( Fig. 5 and Fig. 10). In addition, the control unit may detect an air filter blockage (or intake hose collapse) based on deviations of a vent tube pressure level from a reference pressure during high manifold airflow conditions, with the reference pressure (and an associated offset) being learned during low manifold airflow conditions ( Fig. 6 and Fig. 9). Using the same sensor to identify degradation in different system components provides device reduction benefits without compromising detection accuracy.

[0011] With reference to Fig. 1 shows an exemplary system configuration of a multi-cylinder internal combustion engine, generally depicted at 10, which may be included in a propulsion system of a motor vehicle. The engine 10 may be controlled at least in part by a control system including a controller 12 and by input from a vehicle operator 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP.

[0012] The engine 10 may include a lower portion of the engine block, indicated generally at 26, which may include a crankcase 28 enclosing a crankshaft 30 with an oil pan 32 disposed below the crankshaft. An oil filler port 29 may be disposed within the crankcase 28 so that oil may be supplied to the oil pan 32. The oil filler port 29 may include an oil cap 33 to seal the oil port 29 when the engine is operating. A dipstick tube 37 may also be disposed within the crankcase 28 and may include a dipstick 35 for measuring an oil level in the oil pan 32. In addition, the crankcase 28 may include several other openings for servicing components within the crankcase 28. These openings in the crankcase 28 may be kept closed during engine operation so that a crankcase ventilation system (described below) may operate during engine operation.

[0013] The upper portion of the engine block 26 may include a combustion chamber (i.e., a cylinder) 34. The combustion chamber 34 may include combustion chamber walls 36 with a piston 38 disposed therein. The piston 38 may be coupled to the crankshaft 30 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. The combustion chamber 34 may receive fuel from a fuel injector 45 (configured herein as a direct fuel injector) and intake air from an intake manifold 42 disposed downstream of a throttle 44. The engine block 26 may also include an engine coolant temperature (ECT) sensor 46 that inputs to an engine control module 12 (described in more detail below).

[0014] A throttle 44 may be arranged in the engine intake to control the airflow entering the intake manifold 42, and may be preceded upstream by a compressor 50, for example, followed by a charge air cooler 52. An air filter 54 may be arranged upstream of the compressor 50 and may filter fresh air entering an intake passage 13. The intake air may enter the combustion chamber 34 via a cam-actuated intake valve system 40. Similarly, combusted exhaust gas may exit the combustion chamber 34 via a cam-actuated exhaust valve system 41. In an alternative embodiment, the intake valve system and / or the exhaust valve system may be electrically actuated.

[0015] Combustion exhaust gases exit the combustion chamber 34 via an exhaust passage 60 located upstream of a turbine 62. An exhaust gas sensor 64 may be located upstream of the turbine 62 along the exhaust passage 60. The turbine 62 may be equipped with a wastegate (not shown) bypassing it. The sensor 64 may be any suitable sensor for providing an indication of the exhaust gas air / fuel ratio, such as a linear oxygen sensor or UEGO (Universal or Widerange Exhaust Gas Oxygen), a dual-state oxygen sensor or EGO, a HEGO (Heated EGO), a NO x -, HC, or CO sensor. The exhaust gas sensor 64 can be connected to the control unit 12.

[0016] In the example of Fig. 1, a positive crankcase ventilation (PCV) system 16 is coupled to the engine intake so that gases in the crankcase can be vented from the crankcase in a controlled manner. During non-boosting conditions (when manifold pressure (MAP) is less than barometric pressure (BP)), the crankcase ventilation system 16 draws air into the crankcase 28 via a vent hole or crankcase vent tube 74. A first side 101 of the crankcase vent tube 74 may be mechanically coupled or connected to the fresh air intake passage 13 upstream of the compressor 50. In some examples, the first side 101 of the crankcase vent tube 74 may be coupled (as shown) downstream of the air cleaner 54 to the intake passage 13. In other examples, the crankcase ventilation tube may be coupled to the intake passage 13 upstream of the air filter 54.A second, opposite, side 102 of the crankcase ventilation tube 74 may be mechanically coupled or connected to the crankcase 28 via an oil separator 81.

[0017] The crankcase ventilation tube 74 further includes a sensor 77 coupled thereto to provide an estimate of the air flowing through the crankcase ventilation tube 74 (e.g., flow rate, pressure, etc.). In one embodiment, the crankcase ventilation tube sensor 77 may be a pressure sensor. When configured as a pressure sensor, the sensor 77 may be an absolute pressure sensor or a relative pressure sensor. In an alternative embodiment, the sensor 77 may be a flow sensor or flowmeter. In yet another embodiment, the sensor 77 may be configured as a venturi tube. In some embodiments, in addition to a pressure or flow sensor 77, the crankcase ventilation tube may optionally include a venturi tube 75 for sensing the flow therethrough.In still other embodiments, pressure sensor 77 may be coupled to a throat of a venturi tube 75 to estimate a pressure drop across the venturi tube. One or more additional pressure and / or flow sensors may be coupled to the crankcase ventilation system at alternating locations. For example, a barometric pressure (BP) sensor 57 may be coupled to the intake passage 13 upstream of the air cleaner 54 to provide an estimate of barometric pressure. In an example where the crankcase ventilation tube sensor 77 is configured as a relative sensor, the BP sensor 57 may be used in conjunction with the relative pressure sensor 77. In some embodiments, a pressure sensor (not shown) may be coupled to the intake passage 13 downstream of the air cleaner 54 and upstream of the compressor 50 to provide an estimate of compressor inlet pressure (CIP).However, because the crankcase ventilation tube pressure sensor 77 can provide an accurate estimate of compressor inlet pressure during conditions of increased engine airflow (such as during engine start-up), the need for a dedicated CIP sensor may be reduced. Furthermore, a pressure sensor 59 may be coupled downstream of the compressor 50 to provide an estimate of throttle inlet pressure (TIP). Any of the above-mentioned pressure sensors may be absolute pressure sensors or gauge sensors.

[0018] The PCV system 16 also vents gases from the crankcase and into the intake manifold 42 via a conduit 76 (also referred to herein as PCV conduit 76). In some examples, the PCV conduit 76 may include a one-way PCV valve 78 (i.e., a passive valve that tends to seal when flow is in the opposite direction) to ensure continuous venting of crankcase gases from within the crankcase 28 before connecting to the intake manifold 42. In one embodiment, the PCV valve may change its flow restriction in response to a decrease in pressure across it (or the flow rate through it). However, in other examples, the conduit 76 may not include a one-way PCV valve. In still other examples, the PCV valve may be an electronically controlled valve controlled by the controller 12.It will be appreciated that PCV flow, as used herein, refers to the flow of gases through conduit 76 from the crankcase to the intake manifold. Similarly, PCV backflow, as used herein, refers to the flow of gases through conduit 76 from the intake manifold to the crankcase. PCV backflow may occur when intake manifold pressure is higher than crankcase pressure (i.e., during engine operation with boost). In some examples, PCV system 16 may be equipped with a check valve to prevent PCV backflow. It will be appreciated that while the depicted example shows PCV valve 78 as a passive valve, this is not to be construed as limiting, and in alternative embodiments, PCV valve 78 may be an electronically controlled valve (e.g.,a valve controlled by a powertrain control module (PCM), where a controller can command a signal to change a position of the valve from an open position (or a high-flow position) to a closed position (or a low-flow position), or vice versa, or any position therebetween.

[0019] The gases in the crankcase 28 may consist of unburned fuel, unburned air, and fully or partially combusted gases. A lubricant mist may also be present. Therefore, various oil separators may be included in the crankcase ventilation system 16 to reduce the escape of oil mist from the crankcase through the PCV system. For example, the PCV line 76 may include a unidirectional oil separator 80 that filters oil from vapors exiting the crankcase 28 before they re-enter the intake manifold 42. Another oil separator 81 may be disposed in the line 74 to remove oil from the stream of gases exiting the crankcases during boosted operation. Additionally, the PCV line 76 may also include a vacuum sensor 82 coupled to the PCV system.In other embodiments, a MAP or manifold vacuum (ManVac) sensor may be disposed in the intake manifold 42.

[0020] The present inventors have recognized that by locating the pressure sensor 77 in the crankcase vent tube 74, a violation of the integrity of the crankcase system can be detected not only under high engine airflow conditions, but also under low engine airflow conditions, based on a pulldown of the vacuum in the vent tube. At the same time, the crankcase vent tube pressure sensor 77 can also detect crankcase pulsations. This allows for a deterioration of the crankcase system to be more accurately identified, while also allowing a location of a violation of the crankcase system to be reliably determined.As such, since the pressure sensor in the vent tube is used to infer or estimate the presence of air flow through the vent tube, the pressure sensor can also be used as (or interchanged with) a flow meter or gauge. Consequently, in some embodiments, a crankcase system violation can also be identified using a flow meter or venturi in the crankcase vent tube. Since flow through the crankcase vent tube is also affected by the opening / closing of the PCV valve 78, the same crankcase vent tube sensor can also advantageously be used to diagnose PCV valve degradation.Furthermore, since the crankcase ventilation pressure sensor will sense the compressor inlet pressure under engine running conditions when the engine air flow is increased, the need for a CIP sensor can be reduced. Furthermore, since the flow through the crankcase ventilation tube is also affected by the clogging condition of the air filter 54, the same crankcase ventilation tube sensor can also be advantageously used to diagnose air filter clogging. In this way, by using an existing crankcase ventilation tube pressure or air flow sensor of an engine system to diagnose various engine components, such as a PCV valve, an intake air filter, as well as for diagnosing a crankcase ventilation system failure, advantages of hardware and software reduction in the engine system can be achieved.

[0021] The control unit 12 is in Fig. 1 as a microcomputer including a microprocessor unit 108, input / output ports 110, an electronic storage medium for executable programs and calibration values, shown in this particular example as a read-only memory chip 112, random access memory 114, battery-powered memory 116, and a data bus. The controller 12 may receive various signals from sensors coupled to the engine 10, including measurements of the intake mass air flow (MAF) from a mass air flow sensor 58, the engine coolant temperature (ECT) from the temperature sensor 46, the PCV pressure from the vacuum sensor 82, the exhaust air / fuel ratio from the exhaust gas sensor 64, the crankcase ventilation tube pressure sensor 77, the BP sensor 57, the CIP sensor 58, the TIP sensor 59, etc. Further, the controller 12 may monitor and adjust the position of various actuators based on the input received from the various sensors.These actuators may include, for example, the throttle 44, intake and exhaust valve systems 40, 41, and the PCV valve 78. The read-only memory 112 of the storage medium may be programmed with computer-readable data representing instructions executable by the processor 108 to perform the methods described below, as well as other variations contemplated but not specifically listed. Example methods and routines are described herein with reference to FIG. Fig. 2A to 6.

[0022] In this way, the system enables Fig. 1 various methods for diagnosing engine components coupled to a crankcase ventilation system based on at least one estimated crankcase vent tube pressure. In one embodiment, a method is enabled for an engine that includes indicating a crankcase ventilation system impairment based on characteristics of a transient drop in crankcase vent tube pressure during engine cranking. In another embodiment, an engine method is enabled that includes indicating a location of a crankcase ventilation system violation based on both a transient drop in crankcase vent tube pressure during cranking and a change in crankcase vent tube pressure during steady-state engine airflow.In yet another embodiment, an engine method is enabled that includes, during engine start-up, while manifold airflow is less than a threshold, increasing throttle opening and indicating degradation of the crankcase ventilation system based on a change in crankcase vent tube pressure subsequent to the throttle opening. In yet another embodiment, a method for an engine is enabled that includes indicating degradation of the intake air filter based on a pressure sensor in a crankcase vent tube. In another embodiment, a method for an engine is enabled that includes indicating degradation of a valve coupled between a crankcase and an intake manifold based on characteristics of a transient drop in crankcase vent tube pressure during engine start-up.

[0023] Now Fig. Turning to FIGS. 2A-B, a method 200 is illustrated for indicating degradation of one or more engine components, including crankcase ventilation system components and intake air filters, based on changes in crankcase ventilation pressure (or air flow) during engine start-up and running. By using the same sensor to detect degradation in multiple engine components, cost and component reduction benefits are achieved.

[0024] At 202, an engine start from a standstill may be confirmed. For example, it may be confirmed that the engine has been completely stopped for a period of time and the engine is started from the complete standstill state. After confirmation, at 204, the engine may be started by cranking the engine with the assistance of a starter motor. Next, at 206, it may be determined whether the intake manifold vacuum is higher than a threshold. If not, at 208, an actuator may be adjusted to increase the intake manifold vacuum up to the threshold. In one example, the actuator being adjusted may be an intake throttle, wherein adjusting includes increasing an opening of the throttle.In another example, the actuator being adjusted may be a PCV valve coupled between the crankcase and the intake manifold, where adjusting includes opening the PCV valve (if the valve is a switching valve) or increasing an opening of the PCV valve (if the valve is a duty cycle valve).

[0025] In itself, the PCV valve can respond to both the pressure drop across it and the air flow rate through it. Specifically, when it is in a low restriction position, the flow rate through the crankcase ventilation tube (CVT) is high. In comparison, when it is in the high restriction position (sound-limited volume flow), the flow rate through the CVT is fixed (neglecting the relatively small blow-by component at high ManVac). When manifold vacuum becomes essentially sufficient to drive flow (e.g., 5 kPa), but not high enough to begin causing restriction in the PCV valve (e.g., 25 kPa), a very high CVT flow rate occurs. This high flow rate can be detected as a pressure drop in the CVT pressure sensor.The presence of this drop confirms proper PCV operation and the absence of crankcase injury.

[0026] Once the intake manifold vacuum is at the threshold, from 206 to 208, the routine proceeds to 210, where, while the engine is cranking and maintaining the vacuum at or above the threshold vacuum level, a crankcase vent tube pressure (and / or air flow) is monitored. This includes monitoring a crankcase vent tube pressure sensor output during engine cranking, while the engine speed is below a threshold speed, and before fuel is injected into any cylinder.

[0027] As such, during engine start-up, intake manifold vacuum may be low, such that the PCV valve position of the crankcase ventilation system is open (e.g., the PCV valve may be fully open or at a position with maximum effective area). This causes a large flow of air to be drawn through the intake air filter, then through the crankcase ventilation tube, and then through the crankcase, into the intake manifold. This flow through the crankcase ventilation tube toward the intake manifold may be detected by a flow meter or venturi tube as a temporary increase in air flow at the crankcase ventilation tube, or by a pressure sensor as a temporary decrease in crankcase ventilation tube pressure (or a temporary increase in crankcase ventilation tube vacuum).As engine speed increases following cranking and manifold vacuum increases, airflow through the crankcase vent tube into the intake manifold may decrease. Consequently, at 212, the routine includes estimating characteristics of a transient drop in crankcase vent tube pressure during cranking. The estimated characteristics include, for example, an amplitude of the transient drop, a timing of the drop (e.g., relative to engine speed or piston position), a duration of the drop, etc.

[0028] Next, at 214, the routine includes determining and indicating a crankcase ventilation system impairment based on one or more characteristics of the temporary drop in crankcase vent tube pressure during engine cranking. As discussed above, during engine cranking, when manifold vacuum is lower, an increased airflow from the air cleaner through the crankcase vent tube toward the intake manifold may be detected as a temporary drop in crankcase vent tube pressure (or a temporary increase in vent tube vacuum or airflow). However, this temporary drop may be influenced by the presence of a crankcase system violation (e.g., if the vent tube is disconnected) as well as the position of the PCV valve (e.g., the PCV valve is stuck open or stuck closed). Consequently, as with Fig. 3 to 4, a violation of the integrity of the crankcase ventilation system and a location of the violation may be indicated based on at least an amplitude of the transient drop in crankcase ventilation tube pressure. For example, a violation of the crankcase ventilation system may be determined in response to the amplitude of the transient drop being less than a threshold during cranking.

[0029] Following detection of a crankcase system violation, the routine proceeds to 216, where a PCV valve impairment is determined based on the characteristics of the transient pressure change at the crankcase vent tube. As with Fig. 5, this includes indicating PCV valve degradation based on an estimated crankcase vent tube pressure profile that differs from an expected profile during engine cranking. It will be appreciated that while the routine indicates that PCV valve degradation is detected after a crankcase system violation is diagnosed, the diagnoses may be performed in parallel in alternative embodiments.

[0030] After diagnosing a crankcase system violation and PCV valve degradation during engine cranking, the routine includes, at 218, injecting fuel into the engine cylinders and initiating an initial cylinder combustion event. During engine cranking, the intake manifold air flow may be lower, and as engine speed increases (e.g., up to an idle speed), the intake manifold air flow may gradually increase. Thereafter, the controller may resume cylinder combustion events to allow engine run-up. At 220, it may be confirmed that the intake manifold air flow (or engine inlet air flow) is higher than a threshold air flow. As such, once the engine is at or above an idle speed, the manifold air flow as well as the crankcase vent tube pressure may be at steady-state levels.Specifically, engine speed (along with throttle position) affects intake manifold pump-out characteristics during cranking and run-up, thereby affecting PCV valve position.

[0031] At 222, the routine includes monitoring steady-state manifold air flow and steady-state crankcase vent tube pressure. Thereafter, at 224 and 226, the routine includes determining a degradation of the crankcase ventilation system and a degradation of an intake air filter based on the estimated change in steady-state crankcase vent tube pressure. As described in Fig. 3 to 4, this includes, at 224, indicating a deterioration of the crankcase system based on a change (e.g., a decrease) in steady-state crankcase vent tube pressure relative to a change (e.g., an increase) in steady-state manifold air flow during engine operation. As described in Fig. 5, indicating air cleaner degradation includes, at 226, indicating a degree of air cleaner clogging based on a rate of change (e.g., a rate of decrease) in steady-state crankcase vent tube pressure during engine running. As further explained herein, detection of air cleaner clogging / tube collapse is performed during engine running because the diagnosis has greater sensitivity at higher engine air flow rates. It will be appreciated that while the routine shows air cleaner degradation being determined in parallel with diagnosing a crankcase system violation, in alternative embodiments, the diagnoses may be performed sequentially.

[0032] At 228, after all diagnostic routines have been performed, one or more diagnostic codes may be set to indicate deterioration of the affected engine component. For example, different diagnostic codes may be set to indicate an air filter blockage, a crankcase system violation (including different codes indicating the location / nature of the violation), and a PCV valve violation. At 230, the routine includes performing a mitigation action based on the indication and the diagnostic code that was set.

[0033] In one example, the control unit may also record a number of crankcase violation detections to determine whether a threshold number of violation detections has been reached. For example, the diagnostic routines of Fig. 2A to B may be repeated multiple times during a given engine operating period, including from key-on to key-off, as well as continuously during key-off. If the routine indicates a crankcase violation, the controller may record each instance of a violation detection for that engine operating period and execute a notification routine once a threshold number of detections has been reached. The threshold may be one violation detection in some embodiments. In other embodiments, to avoid false positive tests, the threshold may be multiple violation detections, such as two, five, ten, etc.Once the threshold number of injury detections is reached, a message can be displayed to the vehicle operator, such as activating a Malfunction Indication Light (MIL), to notify the vehicle operator of the detected crankcase injury. The operator can also be prompted to check for possible injury locations (e.g., a loose or missing oil cap, or a misaligned / loose dipstick). Alternatively, the likely location of an injury (as in . Fig. 4, explained in more detail below).

[0034] Mitigation actions may also include adjusting one or more operating parameters to prevent additional engine damage during engine operation with a damaged crankcase, PCV valve, or clogged filter. For example, mitigation actions may include acting to delay the draining of lubricant from the crankcase if the crankcase is indicated to be damaged. Other example mitigation actions include reducing air intake into the engine, limiting engine speed or torque, limiting an amount of fuel injection delivered to the engine, limiting throttle opening, limiting an amount of boost, shutting down the turbocharger, and / or various other actions intended to limit the draining of engine lubricant from the damaged crankcase.In some embodiments, the mitigation action taken may be one of a plurality of mitigation actions taken when a crankcase breach is detected. As yet another example, the plurality of mitigation actions may include adding lubricant to the crankcase or pumping lubricant from a sub-reservoir and into the crankcase.

[0035] In one example, in response to the crankcase ventilation tube being disconnected, engine operation with boost (i.e., where MAP > BP) may be limited or interrupted. In another example, in response to an oil cap becoming loose or an oil dipstick becoming out of position, an engine speed may be limited. Limiting an engine speed may reduce oil slinging because slinging oil over the oil cap / dipstick is more likely at high engine speeds than at low engine speeds. As yet another example, in response to a PCV valve being stuck closed, no failure mode action may be taken because the blowby gas (and any entrained oil mist) is simply directed to the compressor inlet and subsequently combusted.In an alternative example, a controller may limit engine speed by a greater amount in response to an indication that the crankcase ventilation tube is disconnected, while limiting engine speed by a lesser amount in response to an indication of PCV valve degradation.

[0036] Now Fig. Turning to FIG. 3, a method 300 is shown for indicating crankcase ventilation system degradation based on characteristics of a transient drop in crankcase vent tube pressure during engine start-up. The method further enables crankcase ventilation system degradation to be determined based on a change in crankcase vent tube pressure relative to a change in manifold airflow during engine running conditions.

[0037] The routine of Fig. 3 operates on the principle that if the drop occurs (i.e., if there is high CVT flow while a PCV valve is in a low-throttle position), then the integrity of the PCV system can be confirmed (except for a disconnect at the first side 101). A disconnect at the first side 101 can be easily detected in vehicles equipped with a MAF sensor. For vehicles without MAF sensors, the disconnect at the first side 101 is detectable by the absence of a pressure drop with high engine air flow at the MAF sensor 58 or the CVT pressure sensor 77.

[0038] At 302, the routine includes estimating a crankcase vent tube pressure during engine cranking and monitoring a transient drop in the crankcase vent tube pressure during engine cranking. The crankcase vent tube pressure may be estimated or inferred by a pressure sensor, a flow sensor, or a venturi coupled into the crankcase vent tube. As used herein, estimating the crankcase vent tube pressure during engine cranking includes prior to a first combustion event from standstill, that is, prior to fuel injection to any engine cylinder. When the flow rate through the CVT is low, the CVT pressure sensor is essentially a static pressure sensor. It senses both the steady-state flow pressure drop due to flow across the air cleaner and crankcase pressure pulsations.Tube separations and crankcase damage affect the pulsation amplitude. At 304, an amplitude of the temporary drop may be detected and compared relative to a threshold amplitude. In one example, the threshold amplitude may be based on manifold vacuum during engine cranking. Herein, the threshold may be increased as the expected flow through the PCV valve changes. That is, under some conditions, the threshold amplitude may increase with increasing manifold vacuum, and under other conditions, the threshold amplitude may decrease with increasing manifold vacuum.

[0039] If the amplitude of the transient drop is lower than the threshold, then the routine determines and indicates a crankcase ventilation system impairment at 314. That is, a system violation may be detected in response to insufficient airflow through the crankcase ventilation tube during cranking. Indicating a crankcase ventilation system impairment includes indicating that the crankcase ventilation tube is disconnected. For example, the crankcase ventilation tube may have been disconnected at a first side where the vent tube is mechanically coupled to the air intake duct (upstream of a compressor) or at a second, opposite side where the vent tube is mechanically coupled to the engine crankcase via an oil separator. As with Fig. 4, the controller may be configured to execute an additional routine to identify the location and nature of the violation (e.g., the location of the vent tube disconnection) based on both the temporary drop in crankcase vent tube pressure during engine cranking (when engine airflow is lower) and a steady-state change in crankcase vent tube pressure relative to a steady-state change in manifold airflow during engine running conditions (when engine airflow is higher). In this way, a controller may indicate a disconnection of a crankcase vent tube from an engine crankcase ventilation system based on changes in airflow through the crankcase vent tube during engine cranking and running.

[0040] Returning to 304, if the amplitude of the transient drop is not less than the threshold, it may be possible that there is no crankcase system violation. To confirm this, the routine proceeds to further determine a crankcase system violation during engine running conditions after engine cranking. Specifically, at 306, it may be confirmed that manifold vacuum is higher than a threshold. That is, it may be confirmed that the engine has passed through the engine cranking condition and is running at or above a defined engine speed (e.g., at or above an engine idle speed) if the engine airflow rate (inferred or measured) is higher.After confirming that the manifold air flow is higher than the threshold, the routine includes monitoring, at 308, a change in steady-state crankcase vent tube pressure relative to a change in steady-state manifold air flow. Specifically, as the engine is running and engine speed increases, the steady-state manifold air flow may gradually increase. Concurrently, in the absence of any violation, the crankcase vent tube pressure may be expected to gradually decrease (i.e., a measure of negative pressure created in the crankcase vent tube may increase due to increased air flow through the crankcase vent tube).

[0041] At 310, it may be determined whether, during engine operation, the decrease in steady-state crankcase ventilation (CVT) tube pressure is proportional to the increase in steady-state manifold air flow. That is, it may be determined whether there is more than a threshold amount of negative pressure created at the crankcase ventilation tube during engine operation at a high engine air flow. If, during engine operation, the change in steady-state crankcase ventilation (CVT) tube pressure is proportional to the steady-state manifold air flow, it may be determined at 312 that there is no degradation or violation of the crankcase ventilation system.If the change is not proportional, then the routine proceeds to 314 to indicate a crankcase ventilation system impairment (e.g., the crankcase ventilation tube is disconnected) based on a decrease in crankcase vent tube pressure not being proportional to an increase in manifold airflow over a period of time while the engine speed is at or above a threshold speed. For example, a crankcase violation is determined in response to reduced or no vacuum generation in the crankcase vent tube at higher engine airflows.As used herein, determining whether the decrease in steady-state crankcase ventilation (CVT) tube pressure is proportional to the increase in steady-state manifold air flow during engine running may include determining whether their ratio deviates from a threshold ratio or whether their absolute difference is greater than a threshold difference.

[0042] A control unit may indicate a crankcase ventilation system violation at 314 by setting a diagnostic code. Further, in response to the indication, one or more mitigation actions may be performed. These may include, for example, limiting engine speed and load to reduce / delay the evacuation of lubricant from the crankcase and the drawing of lubricant into engine components. Example illustrations used to identify a crankcase system violation are shown herein at Fig. 7 to 8 illustrated.

[0043] Now Fig. 4, method 400 illustrates a routine that may be executed to determine a location of a crankcase system violation based on both a temporary drop in crankcase vent tube pressure during engine cranking and a change in crankcase vent tube vacuum during and after engine start-up.

[0044] At 402, it can be confirmed that the amplitude of the transient drop in crankcase ventilation tube pressure during start-up is less than a threshold. As with Fig. As further explained in Figure 3, during engine start-up, when the engine air flow is lower, a higher air flow through the crankcase vent tube may be perceived (in the absence of injury), which is detected by the crankcase vent tube pressure sensor as a temporary drop in vent tube pressure (or a temporary increase in vent tube vacuum). If an injury is present, the amplitude of the temporary drop may be reduced.

[0045] After confirmation, at 404, it may be determined whether a ratio of the decrease in steady-state crankcase ventilation (CVT) tube pressure during engine running (i.e., after engine start-up, while engine speed is higher than a threshold) to the increase in steady-state manifold airflow during engine running is less than a threshold ratio. Alternatively, it may be determined whether the absolute difference between them is greater than a threshold difference. Therefore, it may be determined whether vacuum generation at the vent tube during higher engine airflows is at or above a threshold level.

[0046] In yet another embodiment, if a temporary drop is observed, it may be determined that the PCV system has not degraded, and the controller may then check for a disconnect at the first side 101. This may be done by looking for a faulty MAF reading and a pressure drop at the MAP sensor that is too small at high engine airflow rates. Alternatively, the first side disconnect may be identified based on a pressure drop at the CVT pressure sensor 77 that is too small at high engine airflow rates. Detection of pulsations at the CVT pressure sensor 77 may also be used.

[0047] In response to the transient drop in crankcase vent tube pressure during cranking being less than a threshold amplitude and the decrease in steady-state crankcase vent tube pressure during the steady-state increase in manifold air flow during engine running being less than a threshold rate, a crankcase ventilation system violation may be determined at 406 on a first side of the crankcase vent tube. For example, in response to a muted transient drop in crankcase vent tube pressure during engine cranking and substantially no crankcase vent tube vacuum (zero vacuum) being generated during engine run-up, a violation may be determined on the first side of the vent tube.Specifically, the crankcase ventilation system breach may be determined to be due to the crankcase ventilation tube being severed at a first side where it is mechanically connected to an air intake duct. Exemplary images used to identify a crankcase system breach at the first side are shown in FIG. Fig. 7 illustrated.

[0048] In comparison, in response to the transient drop in crankcase vent tube pressure during cranking being less than a threshold amplitude and the decrease in steady-state crankcase vent tube pressure during the steady-state increase in manifold air flow during engine running being greater than a threshold rate, a crankcase ventilation system violation may be determined at 408 at a second side of the crankcase vent tube. For example, in response to a muted transient drop in crankcase vent tube pressure during engine cranking and a reduced crankcase vent tube vacuum being generated during engine run-up, a violation is determined at the second side of the vent tube.Specifically, it may be determined that there is a crankcase system injury on a second, opposite, side of the crankcase vent tube, where it is mechanically connected to the crankcase. Thus, a crankcase system injury on the second side may include a separation of the crankcase vent tube from the crankcase on the second side, a loosening of a crankcase oil filler cap, a loosening of a crankcase oil dipstick, or a blockage of the crankcase vent tube on the second side.

[0049] To differentiate between the different second-side crankcase system violations, the routine then proceeds to 410, where an opening size of the violation is determined. In one example, an opening size of the violation may also be determined. At 412, it may be determined if the opening size is greater than a threshold size. If so, then at 414, based on the opening size being greater than the threshold, a crankcase oil filler cap looseness may be determined. Otherwise, at 416, it may be determined that the second-side violation is due to a separation of the crankcase vent tube from the crankcase at the second side, a loosening of the crankcase oil dipstick, or a blockage of the crankcase vent tube at the second side.Example images used to identify a second side crankcase system violation are shown herein at . Fig. 7 to 8 illustrated.

[0050] As such, when the PCV valve is in the low-restriction (fully open) position, high airflow rates typically result in the crankcase ventilation tube. The PCV valve may be in this position due to standard pneumatic control, active PCM control, or a PCV valve malfunction. This high airflow rate should be detected as a pressure drop or flow rate increase at the crankcase ventilation tube pressure / flow rate sensor. In one example, manifold vacuum can be calculated and used to infer PCV valve position. If the crankcase is compromised (cover off, dipstick out of position, or crankcase ventilation tube separated from the crankcase), then the high airflow rate while the PCV valve is open will not be detected.For example, the pressure drop either does not occur or is noticeably reduced. The amplitude of the pressure drop or the magnitude of the crankcase ventilation tube airflow rate also decreases as the area (opening area or opening size) of the breach increases. Oil cap loss and hose separation will likely completely eliminate the drop. Some reduced drop may also occur with an out-of-position dipstick.

[0051] After determining a location and nature of a crankcase system violation at 406, 414, and 416, the routine proceeds to 418 to indicate the location and nature of the crankcase system violation by setting a diagnostic code. Thus, a different diagnostic code may be set based on whether a violation is detected on the first side or the second side of the crankcase vent tube, and further based on the nature of the violation on the second side. At 420, an MIL may be illuminated and / or a message may be set to inform the vehicle operator of the nature and location of the crankcase system violation.At 422, one or more engine operating parameters may be adjusted to temporarily limit engine power to reduce leakage of lubricant from the damaged crankcase ventilation system and aspiration of lubricant into engine components (which may degrade engine operation).

[0052] Thus, if the crankcase ventilation tube is disconnected at the engine main air line (i.e., at the compressor inlet, also referred to herein as the first side), the high airflow velocity while the PCV valve is fully open may still be detected. In one example, an engine control system may limit engine boost in response to an indication of a violation located on the first side of the crankcase ventilation tube or a violation located on the second side of the crankcase ventilation tube. For example, engine boost operation may be interrupted.

[0053] Now Fig. 7, is used in the Fig. An example of a diagnosis of damage to the integrity of the crankcase system is shown. In detail, the Fig. Characteristics of a transient drop in crankcase ventilation (CVT) tube pressure during cranking in the respective upper graphs (graphs 702, 712, 722) and characteristics of a decrease in crankcase ventilation tube pressure with increasing manifold air flow during engine running (steady-state conditions) in the respective lower graphs (graphs 704, 714, 724). The upper graphs in the figures are plotted over time during engine operation, while the lower graphs in the figures are plotted against the engine air flow rate (as shown) along the x-axis.

[0054] As previously discussed, the crankcase ventilation tube installation configuration and the specific position of the crankcase ventilation tube sensor within the tube cause the crankcase ventilation tube to experience negative pressure at high engine airflow rates. Consequently, if the sensor detects negative pressure, it can be determined that there is no damage and that the ventilation tube is properly secured. However, if negative pressure is not detected, a violation of the integrity of the crankcase system is determined.For example, a separation of the vent tube on one side (a first side where it connects to the air intake duct, or a second side where it connects to the crankcase) can result in reduced vacuum at high engine flow rates (with the degree of vacuum reduction differing depending on whether the injury is on the first or second side). Furthermore, if it is separated on the second side, crankcase pulsations cannot be sensed.

[0055] The Fig. shows a first example, where the amplitude of the transient drop in CVT pressure (plot 702) is greater than a threshold, indicating sufficient airflow through the vent tube during engine cranking. Furthermore, during engine running, a steady-state decrease in CVT pressure is proportional to a steady-state increase in manifold airflow (plot 704). In other words, as engine airflow increases, a smaller but gradual flow passes through the vent tube, and a corresponding negative pressure is created and sensed by a pressure or flow sensor in the crankcase ventilation tube.

[0056] The Fig. shows a second example, where the amplitude of the transient drop in CVT pressure (plot 712) is less than the threshold amount, indicating insufficient airflow through the vent tube during engine cranking. Furthermore, during engine running, a steady-state decrease in CVT pressure is not proportional to a steady-state increase in manifold airflow, but the decrease is still greater than a threshold rate (plot 714). Specifically, during high engine airflow conditions (compared to the vacuum created in the absence of a violation, as shown at plot 704), a reduced vacuum is sensed by a pressure or flow sensor in the crankcase vent tube.Herein, in response to the transient drop in crankcase vent tube pressure during cranking being less than the threshold amplitude and the decrease in crankcase vent tube pressure during the steady-state increase in manifold air flow being greater than the threshold rate, a crankcase ventilation system violation is indicated at the second side of the crankcase vent tube. The second side corresponds to a side where the crankcase vent tube is mechanically coupled to the crankcase. As in . Fig. 8, various injuries to the crankcase system on the second side can be distinguished based on the characteristics of crankcase ventilation tube pressure and flow.

[0057] The Fig. shows a third example, where the amplitude of the transient drop in CVT pressure (plot 722) is less than the threshold amount (in the depicted example, less than the amplitude of plot 702 but greater than the amplitude of plot 712), indicating insufficient airflow through the vent tube during engine cranking. Furthermore, during engine running, a steady-state decrease in CVT pressure is not proportional to a steady-state increase in manifold airflow, where the decrease is less than a threshold rate (plot 724). Specifically, during high engine airflow conditions (compared to the vacuum created in the absence of a violation, as shown at plot 704), essentially no vacuum (zero vacuum) is sensed by a pressure or flow sensor in the crankcase vent tube.Herein, in response to the transient drop in crankcase vent tube pressure at start-up being less than the threshold amplitude and the decrease in crankcase vent tube pressure during the increase in manifold air flow at steady-state being less than the threshold rate, a violation of the crankcase ventilation system is indicated at the first side of the crankcase vent tube. The first side corresponds to a side where the crankcase vent tube is mechanically coupled to the air intake passage. For example, it may be indicated that the violation at the first side is due to the crankcase vent tube being disconnected from the air intake passage at the first side.

[0058] Now Fig. 8, is used in the Fig. An exemplary injury diagnosis of the integrity of the crankcase system is shown to distinguish between different conditions that can lead to an injury identified on the second side of the crankcase ventilation tube. In detail, the Fig. Characteristics of a transient drop in crankcase ventilation (CVT) tube pressure during cranking in the respective upper plots (plots 802, 812, 822) and characteristics of a decrease in crankcase ventilation (CVT) tube pressure with increasing manifold air flow during engine running (steady-state conditions) in the respective lower plots (plots 804, 814, 824). All upper plots are plotted over time of engine operation along the x-axis, while all lower plots are plotted over engine air flow rates along the x-axis.

[0059] The Fig. shows a first example of a crankcase system violation at the second side of the crankcase vent tube caused by a crankcase oil filler cap becoming loose. Herein, an amplitude of the temporary drop in CVT pressure (plot 802) is less than the threshold amount, indicating insufficient airflow through the vent tube during engine cranking. Furthermore, during engine running, a steady-state decrease in CVT pressure is not proportional to a steady-state increase in manifold airflow. Specifically, after a threshold level of engine airflow (plot 804), no vacuum is sensed by a pressure or flow sensor in the crankcase vent tube. Herein, a missing oil cap condition is further indicated based on an opening size of the violation being greater than a threshold amount.

[0060] The Fig. shows a second example of a crankcase system violation at the second side of the crankcase vent tube caused by a crankcase oil dipstick being displaced. Herein, an amplitude of the transient drop in CVT pressure (plot 812) is less than the threshold amount, indicating insufficient airflow through the vent tube during engine cranking. Furthermore, during engine running, a steady-state decrease in CVT pressure is not proportional to a steady-state increase in manifold airflow (plot 814). Specifically, during high engine airflow conditions, no vacuum is sensed by a pressure or flow sensor in the crankcase vent tube. Herein, a missing dipstick condition is further indicated based on an orifice size of the violation being less than a threshold amount.

[0061] It will be appreciated that in embodiments where the crankcase ventilation tube includes a venturi tube with a coupled pressure sensor, in response to an oil cap becoming loose or a dipstick becoming out of position, a large resulting airflow through the venturi tube may be sensed by the coupled pressure sensor as a deep vacuum. Thus, the vacuum created due to an oil cap becoming loose may be greater than the vacuum created due to the dipstick being out of position.

[0062] The Fig. shows a third example of a crankcase system violation at the second side of the crankcase vent tube caused by the crankcase vent tube being blocked or clogged at the second side. Herein, an amplitude of the transient drop in CVT pressure (chart 822) is less than the threshold amount, indicating insufficient airflow through the vent tube during engine cranking. Also, during engine running, a steady-state increase in CVT pressure is observed during a steady-state increase in manifold airflow. Specifically, during high engine airflow conditions, a high (positive) pressure is sensed by a pressure or flow sensor in the crankcase vent tube. In response to these conditions, a blockage of the crankcase vent tube at the second side (which is coupled to the crankcase) is detected.

[0063] In this way, an existing sensor used to monitor the crankcase ventilation system can advantageously be used to also reliably identify a location and nature of a violation of the integrity of the crankcase system.

[0064] Now Fig. Turning to Figure 5, an exemplary method 500 is shown for indicating degradation of a PCV valve (i.e., a valve coupled into a positive crankcase ventilation line between a crankcase and an intake manifold) based on changes in crankcase ventilation tube pressure and / or air flow rate during engine cranking. As such, the routine may be Fig. 5 after confirming whether a crankcase injury has been identified based on the characteristics of the temporary waste.

[0065] This is how the procedure of Fig. 5 the PCV flow characteristics during engine operation (or during a maintenance procedure), provided that both the pressure drop across the PCV valve (ManVac) and the flow rate through the valve (CVT flow rate) are measured by the CVT pressure sensor. In some embodiments of Fig. 5, the method can easily verify the CVT flow rates for given ManVacs. There, at the most restricted PCV valve position, the CVT flow rate will be essentially low, thus being in the noise range. At the least restricted flow rate position, the flow rate will be significant (i.e., a temporary drop will be evident).

[0066] At 502, the routine includes confirming that the engine intake air flow is lower than a threshold flow. In one example, the engine intake air flow may be lower than the threshold flow during engine cranking and early run-up when the engine speed is less than a threshold speed and before a threshold number of combustion events have occurred. Next, at 504, it may be confirmed that the manifold vacuum is lower than a threshold vacuum level. For example, it may be confirmed that the manifold vacuum is lower than 40 kPa. If the manifold vacuum is not lower than the threshold, then at 505, an actuator may be adjusted to ensure a desired manifold vacuum level. For example, a throttle opening may be adjusted so as to maintain the manifold vacuum below the threshold vacuum level.In principle, since the throttle opening is linked to a flow rate through a PCV valve, the throttle opening can be adjusted to ensure a manifold vacuum level (e.g. 13 kPa) so that maximum flow through the PCV valve is ensured.

[0067] The routine of Fig. 5 uses the output of a crankcase vent tube pressure sensor to estimate PCV valve degradation. Specifically, a relative sensor in the crankcase vent tube may advantageously be used as a flowmeter to sense changes in the air flow rate in the crankcase vent tube. However, such a pressure sensor may correlate any negative pressure in the crankcase vent tube as a flow. In other words, flow through the crankcase vent tube may be sensed as a negative pressure at the crankcase vent tube pressure sensor, and likewise, negative pressure in the crankcase vent tube may be sensed as a negative pressure at the crankcase vent tube pressure sensor.Consequently, by performing the diagnostic routine when the engine intake air flow is lower than a threshold flow, a crankcase vent tube pressure sensor output is set only during conditions when the engine intake air flow itself does not cause a vacuum to be sensed. Likewise, by performing the diagnostic routine when a manifold vacuum is lower than a threshold vacuum level, a crankcase vent tube pressure sensor output is set only during conditions when the manifold vacuum itself does not cause a vacuum to be sensed. Furthermore, during conditions when the engine intake air flow is low and the manifold vacuum is low (i.e., during engine cranking and early run-up), an air flow velocity through the crankcase vent tube is expected to be high.Consequently, by performing diagnostics during these conditions, PCV valve diagnostics based on changes in crankcase ventilation tube airflow are only enabled when there is sufficient airflow through the ventilation tube for a reliable diagnosis.

[0068] At 506, the routine includes determining an expected crankcase vent tube pressure and / or airflow profile based on the current engine intake airflow and manifold vacuum levels. The expected profiles may include an expected vent tube pressure and an expected vent tube flow rate for a given engine speed. At 508, the routine includes estimating an actual crankcase vent tube pressure and / or airflow profile based on the output of the crankcase vent tube pressure sensor. It will be appreciated that in alternative embodiments, the estimated profile may be based on the output of a dedicated crankcase vent tube flow sensor or a pressure sensor coupled to the throat of a crankcase vent tube venturi.The estimated profiles may include a measured and / or inferred vent tube pressure and a measured and / or inferred vent tube flow rate for the given engine speed.

[0069] Typically, during engine cranking and subsequent run-up, the PCV valve is initially in a more open position (e.g., a maximum open position when manifold vacuum is lower and the throttle opening is small). During these conditions, airflow through the crankcase ventilation tube is substantially higher and can be estimated by the crankcase ventilation tube pressure / flow sensor as a temporary increase in vent tube airflow or a temporary increase in vent tube pressure. Thereafter, when engine speed is above a threshold and manifold vacuum is higher, the PCV valve may be in a second, less open, position (e.g., a position with a smaller fixed opening allowing lower flow).For example, in the second position, flow through the PCV valve may be directed to a silenced hole. During these conditions, air flow through the crankcase ventilation tube decreases and stabilizes at a steady-state value, which can also be estimated by the crankcase ventilation tube pressure / flow sensor. If a PCV valve becomes stuck open, crankcase ventilation tube air flow may continue to increase under higher manifold vacuum conditions instead of decreasing and stabilizing at the steady-state value. Likewise, if the PCV valve becomes stuck in the small-opening position during cranking, crankcase ventilation tube air flow may not increase to the expected values ​​during lower manifold vacuum conditions.Consequently, by comparing the characteristic changes in an expected flow / pressure profile of a crankcase vent tube pressure with the actual changes in a crankcase vent tube flow / pressure profile as estimated by a crankcase vent tube pressure / flow sensor, PCV valve degradation can be identified.

[0070] Accordingly, at 510, the measured or estimated crankcase vent tube pressure profile and / or airflow profile may be compared to the expected crankcase vent tube pressure profile and / or airflow profile, and a determination may be made as to whether an absolute difference between the profiles is greater than a threshold. That is, a determination may be made as to whether the expected and actual crankcase vent tube pressure values ​​or flow rates differ by more than a threshold amount. If not, then the routine determines at 512 that there is no PCV valve degradation.

[0071] If there is a deviation, then at 514 it is determined that the PCV valve may be degraded, and the routine may proceed to determine the nature of the degradation based on the estimated crankcase vent tube pressure and / or flow rate profiles. Specifically, at 516 it may be determined whether the estimated crankcase vent tube pressure or air flow rate is greater than the expected crankcase vent tube pressure (or air flow rate) by more than the threshold amount. Alternatively, it may be determined whether an estimated amplitude of a transient drop in crankcase vent tube pressure is greater than an expected amplitude (or threshold amplitude).If so, at 518, it may be determined that the estimated crankcase vent tube pressure / airflow profile is greater than the expected profile (or that the amplitude of the temporary drop in crankcase vent tube pressure is greater than an expected amplitude) due to the PCV valve being stuck open. The control module may indicate this by setting an appropriate diagnostic code.

[0072] If the estimated crankcase vent tube pressure or air flow rate is not greater than the expected crankcase vent tube pressure (or air flow rate), then it may be confirmed that the estimated crankcase vent tube pressure or air flow rate is less than the expected crankcase vent tube pressure (or air flow rate) by more than the threshold amount. Alternatively, it may be determined whether an estimated amplitude of a transient drop in crankcase vent tube pressure is less than an expected amplitude (or threshold amplitude). After confirmation, it may be determined at 522 whether a crankcase injury condition has already been detected. As described above with reference to Fig. 2A to B, a violation of the integrity of the crankcase ventilation system before initiating the PCV valve diagnostic routine can Fig. 5. As stated with reference to Fig. 3 to 4, a violation of the integrity of the crankcase ventilation system and a location of the violation can be determined based on characteristics of a temporary drop in crankcase ventilation tube pressure during engine start-up and a change in steady-state crankcase ventilation tube pressure relative to a change in steady-state manifold air flow during engine running.

[0073] For example, if there is a breach in the integrity of the crankcase system, there may be a change in one or more of the crankcase vent tube pressure and flow rate, both of which can affect the output of the crankcase vent tube pressure / flow sensor and the resulting profile during engine cranking and run-up. Furthermore, the profile is influenced by the location of the crankcase breach. For example, crankcase system breaches that occur on the second side of the crankcase vent tube (i.e., the side of the crankcase vent tube coupled to the crankcase) may cause the crankcase vent tube flow rate to be significantly reduced due to the breach causing a short circuit at the expected flow rate.Additionally, the crankcase vent tube pressure sensor may no longer indicate a vacuum at high engine airflow rates (compared to the vacuum indicated in the absence of a breach at high engine airflow rates). Second-side vent tube breaches that may cause these effects include, for example, separation of the vent tube from the crankcase at the second side, a crankcase oil filler cap becoming loose, or a crankcase oil dipstick becoming displaced.As another example, crankcase system injuries that occur on the first side of the crankcase vent tube (that is, the side of the crankcase vent tube coupled to the air intake duct) may cause the crankcase vent tube flow rate to remain substantially unaffected, but the crankcase vent tube pressure sensor may no longer display a negative pressure at high engine air flow rates (compared to the negative pressure displayed at high engine air flow rates in the absence of an injury). Injuries on the first side of the vent tube that may cause these effects include, for example, the separation of the vent tube from the air intake duct on the first side.

[0074] Accordingly, if no crankcase violation was previously detected, the routine determines at 524 that the estimated crankcase vent tube pressure / airflow profile is less than the expected profile (or that the amplitude of the transient drop in crankcase vent tube pressure is less than an expected amplitude) due to the PCV valve being stuck in a low-flow open position (e.g., a small orifice position or a closed position). The controller may indicate this by setting an appropriate diagnostic code. For example, the diagnostic code set to indicate PCV valve impairment due to the valve being stuck open (at 518) may be different from the diagnostic code set to indicate PCV valve impairment due to the valve being stuck closed (at 524).If a crankcase violation was previously detected, the control module may determine at 526 that the PCV valve may be functional and unaffected.

[0075] It will be appreciated that in some embodiments, in addition to confirming at 522 whether a crankcase system violation has been detected, it may also be determined whether an air intake filter has been diagnosed, and if so, a degree of air filter clogging may be included in the PCV valve diagnosis. As with Fig. 10, if air filter clogging is confirmed, then at 524, the deviation between the expected profile and the estimated profile may be due to the air filter being clogged, rather than the PCV valve being stuck in the low-flow position. The controller may distinguish between these conditions based on the (known) degree of filter clogging relative to the observed deviation between the estimated and expected crankcase vent tube flow velocity profiles. For example, if the deviation is greater than the expected consideration for the degree of filter clogging, a crankcase system violation may be determined.

[0076] In this way, PCV valve degradation can be detected based on changes in air flow velocity through a crankcase ventilation tube, as estimated by a crankcase ventilation tube pressure or flow sensor, during engine cranking. Based on deviations of an expected flow profile from an estimated flow profile, PCV valve degradation due to a stuck open valve can be better distinguished from degradation due to a stuck closed valve.By performing the PCV valve diagnostic routine after completing a crankcase system diagnostic routine, changes in crankcase vent tube pressure or flow caused by a crankcase system violation on either a crankcase side or an air intake port side of the crankcase vent tube can be included to enable reliable PCV valve diagnosis. Specifically, changes in crankcase vent tube air flow due to a crankcase system violation (e.g., due to a disconnected vent tube or a displaced oil filler cap) can be better differentiated from those due to a compromised PCV valve.

[0077] In one example, in response to the PCV valve being stuck open (or in the high-flow position), engine boost may be limited so that MAP is below BP. As such, a stuck open PCV valve will result in crankcase gases and oil mist being blown into the compressor inlet. This creates the potential for rapid oil consumption, which can be mitigated by limiting (or stopping) boost. In comparison, a stuck closed PCV valve essentially results in a stale crankcase ventilation system. Over the long term, this leads to engine sludge buildup in the oiled sections of the engine. Consequently, mitigation action may not be necessary. Alternatively, in response to the PCV valve being stuck closed (or in the low-flow position), engine speed may be reduced.

[0078] It will be seen that while the routine of Fig. 5 is depicted as being executed while an engine is being started, in alternative embodiments, such as in embodiments where the engine is coupled into a hybrid vehicle system, or in engine start-stop systems where the engine is configured to be selectively shut down in response to idle stop conditions, the routine of Fig. 5 may also be executed during key-off conditions (i.e., where a vehicle operator has turned an ignition key to an off position). For example, during a key-off condition, a control module may close an intake throttle and perform a vacuum decay test with the PCV valve in any given position. PCV valve degradation may then be determined based on a rate of vacuum decay from the crankcase ventilation tube.

[0079] An example PCV valve diagnosis is shown at Fig. from Fig. 10. In detail, the Fig. Changes in crankcase vent tube airflow velocity along the y-axis and changes in manifold vacuum along the x-axis. Plots 1002 through 1008 depict example changes in vent tube flow velocity versus manifold vacuum used to diagnose a PCV valve.

[0080] Diagram 1002 depicts a first illustration of an expected change in the crankcase ventilation tube air flow rate during engine cranking and run-up. As previously detailed, during engine cranking, when manifold vacuum is low (and throttle opening is small), the PCV valve may be in an open position, causing a large amount of air to be directed from an intake air filter, through the crankcase ventilation tube, across the crankcase, into the intake manifold. As a result, at low manifold vacuum levels (e.g., at or around 13 kPa), a considerably high velocity of air flow through the crankcase ventilation tube is observed. Thereafter, as the engine progresses from cranking into run-up, throttle opening may increase, PCV valve opening may decrease (e.g.,to a fixed smaller opening position or a low flow position), manifold vacuum may increase (e.g., above 13 kPa), and air flow into and through the crankcase ventilation tube may decrease, causing a decrease and eventual stabilization of the crankcase ventilation tube air flow rate.

[0081] Plot 1004 shows a second illustration of an estimated change in crankcase vent tube airflow rate during engine cranking and run-up in the presence of a stuck open PCV valve. Herein, as the engine progresses from cranking to run-up, the PCV valve opening does not decrease as expected due to the PCV valve being stuck open. Consequently, as manifold vacuum increases, airflow into and through the crankcase vent tube may continue to increase, causing the estimated crankcase vent tube airflow rate and profile (plot 1004) to be higher than the expected airflow rate and profile (plot 1002).

[0082] Plot 1006 shows a third illustration of an estimated change in crankcase vent tube airflow rate during engine cranking and run-up in the presence of a stuck-open PCV valve. Here, the PCV valve may not be able to open to the fully open position during engine cranking, causing a significantly smaller amount of air to be directed from the intake air filter, through the crankcase vent tube, across the crankcase, and into the intake manifold. As a result, at low manifold vacuum levels, a significantly smaller velocity of airflow through the crankcase vent tube is observed, causing the estimated crankcase vent tube airflow rate and profile (plot 1006) to be lower than the expected airflow rate and profile (plot 1002).

[0083] Plot 1008 shows a fourth illustration of an estimated change in crankcase vent tube airflow rate during engine cranking and run-up in the presence of a functional PCV valve and a fully clogged air cleaner. Herein, as with plot 1006, during engine cranking, even though the PCV valve is open, airflow from the intake air cleaner, through the crankcase vent tube, across the crankcase, into the intake manifold may be reduced due to the clogged air cleaner. As a result, at low manifold vacuum levels, a significantly lower velocity of airflow through the crankcase vent tube is observed, causing the estimated crankcase vent tube airflow rate and profile (plot 1006) to be lower than the expected airflow rate and profile (plot 1002).

[0084] In one example, plot 1002 is observed if the PCV valve is unaffected, plot 1004 is observed if the PCV valve is stuck in a low restriction position, plot 1006 is observed if the PCV valve is stuck in a high restriction position, and plot 1008 is observed if the air cleaner is clogged or stuck closed.

[0085] It will be seen that, while the example of Fig. 10 illustrates the detection of PCV valve degradation based on deviations in an estimated vent tube airflow velocity profile from an expected airflow velocity profile. In an alternative example, it may be detected (or illustrated as) by deviations in an estimated vent tube vacuum profile from an expected vacuum profile. In this way, an existing sensor used to monitor the crankcase ventilation system may be advantageously used to reliably diagnose a PCV valve.

[0086] Now Fig. 6, an exemplary method 600 is shown for indicating intake air filter degradation based on a crankcase vent tube pressure estimated by a pressure sensor in the crankcase vent tube. As such, the routine of Fig. 6 as a part of the routine of Fig. 2A to B are carried out.

[0087] At 602, the routine includes confirming whether the manifold air flow is lower than a first threshold. By confirming that the manifold air flow is lower than the first threshold, it may be confirmed that a sensor offset is calculated during low engine flow conditions (such as while there is no engine flow) to reduce noise interference in the calculation resulting from the engine flow. Next, at 604, a crankcase vent tube pressure during the low manifold air flow conditions may be estimated by a pressure sensor disposed in the crankcase vent tube. The pressure sensor in the crankcase vent tube may be, for example, an absolute pressure sensor or a gauge pressure sensor. In embodiments where the pressure sensor is an absolute pressure sensor, it may or may not be coupled to a barometric pressure sensor.In embodiments where the pressure sensor is a relative sensor, an absolute air pressure sensor (e.g., the BP sensor 57 of . Fig. 1) be coupled to it (e.g. additionally present outside the filtered volume) or used in conjunction.

[0088] At 606, the routine includes calculating a sensor offset. Specifically, the algorithm used zeros the relative pressure sensor during low engine flow conditions or learns a sensor offset based on the barometric pressure reading from the BP sensor during low engine flow conditions. In this manner, the controller learns or infers the barometric pressure from the crankcase vent tube pressure sensor and can either use the output of the crankcase vent tube pressure sensor itself at low engine flow as the barometric pressure or can use the output to ensure a common and calibrated reference to a separately measured barometric pressure. In one example, the barometric pressure can be separately measured from a dedicated barometric pressure sensor coupled to the intake passage (e.g.,upstream of the air cleaner), or from a compressor inlet pressure (CIP) sensor located in the inlet upstream of the compressor and downstream of the air cleaner. However, using the existing crankcase vent tube pressure sensor to estimate BP reduces the need for a BP sensor or a CIP sensor.

[0089] In one example, the pressure sensor in the crankcase ventilation tube is a first pressure sensor, and the offset is determined based on a second pressure sensor (e.g., a BP sensor) coupled downstream of the air cleaner and upstream of the compressor. Specifically, the offset may be based on the output of the first pressure sensor relative to the output of the second pressure sensor during low manifold airflow conditions. For example, if the first pressure sensor is an absolute pressure sensor without a BP sensor, the output of the first pressure sensor may be used to infer the BP. As another example, if the first pressure sensor is an absolute pressure sensor with a BP sensor, the difference between the outputs of the first pressure sensor and the coupled BP sensor may be used to infer the BP and determine a sensor offset.As yet another example, if the first pressure sensor is a gauge pressure sensor, the difference of the first pressure sensor from a zero reading can be used to infer the BP and calculate a sensor offset.

[0090] The calculated offset can then be stored in the ECU's memory as a reference pressure. The stored offset can then be recalled and applied during subsequent higher engine flow conditions to detect air filter blockage, as discussed in more detail below.

[0091] Next, at 608, it may be determined whether the engine airflow (or another signal associated with engine airflow rate) is higher than a second threshold. By confirming that the engine airflow is higher than the second threshold, it may be determined that an air filter blockage is estimated during higher engine flow conditions when the impact of an air filter blockage on crankcase vent tube pressure is greater, thus improving detection accuracy. If the engine airflow is not higher than the second threshold, the routine may wait until desired engine airflow levels are reached to perform the air filter blockage diagnostic. At 610, after confirming that the manifold airflow levels are higher than the second threshold, it may be confirmed that the sensor offset has been updated.This may include confirming that the sensor offset learned during the lower engine flow conditions immediately preceding the higher engine flow conditions has been stored in the ECU (e.g., a lookup table has been updated with the most recently learned sensor offset).

[0092] At 612, after confirming that the offset has been updated, the sensor output(s) may be adjusted based on the updated offset. This includes adjusting the output of the crankcase ventilation tube pressure sensor with the updated offset. At 614, it may be determined whether the deviation between the adjusted sensor output and an estimated / inferred BP is greater than a threshold. In one example, the deviation may be based on the difference between the sensors. In another example, the deviation is based on a relationship between the sensor outputs. If the difference is not greater than the threshold amount, then at 616, it may be determined that the air filter is clean and not clogged. In comparison, if the difference is greater than the threshold amount, then at 618, an air filter blockage may be indicated.A degree of air filter clogging can be determined based on the difference between the adjusted sensor output and the BP (e.g., relative to the threshold value).

[0093] In an alternative example, a deviation between the crankcase ventilation tube pressure reading at high air flow (which is essentially equal to CIP) and the reference pressure estimated at low air flow can be calculated. A reference air filter differential pressure can then be retrieved from a lookup table. The control module can then compensate the reference air filter differential pressure for actual conditions and calculate a clogging factor from the ratio of Delta CIP to the compensated reference differential pressure.That is, the controller may estimate an instantaneous air filter clogging factor based on a ratio of the difference between the crankcase vent tube pressures estimated during high and low airflow conditions relative to a reference air filter drop, with a correction factor for non-standard temperature and pressure (STP). In one example, the STP conditions include 103 kPa and 100°F (38°C). As an example, the controller may estimate the clogging factor using the following equation: Instantaneous clogging factor = BP offset − CVP sensor reading F (air flow at conditions) ∗ F (air flow) where the clogging factor is determined with reference to standard conditions (STP).

[0094] At 620, the control module may set a diagnostic code to indicate an air filter restriction. As such, the diagnostic code to indicate an air filter restriction may be different from a diagnostic code used to indicate a crankcase ventilation system violation / deterioration. The control module may also illuminate a MIL to alert the vehicle operator to service the air filter. The control module may also limit engine power to reduce compressor overspeed and overheating, which may be caused by a clogged air filter.

[0095] In this way, by indicating air filter degradation based on crankcase ventilation tube pressure, monitoring of both crankcase system integrity and air filter clogging can be performed using a single set of sensors already present in the crankcase ventilation tube.

[0096] An example of an air filter blockage diagnosis is shown in the Fig. from Fig. 9. In detail, the Fig. Changes in crankcase vent tube pressure along the y-axis and changes in manifold airflow along the x-axis. Graphs 902 through 906 depict example changes in vent tube pressure versus manifold airflow used to indicate an intake air filter condition.

[0097] During low engine airflow conditions, such as before the manifold airflow is at a first threshold AF1, an offset for the crankcase vent tube pressure sensor may be detected. For example, if the crankcase vent tube pressure sensor is an absolute pressure sensor, the barometric pressure may be inferred based on the output of the crankcase vent pressure sensor or due to an offset between the vent tube pressure sensor and a coupled BP sensor. With reference to Fig. P1 (which extends as a dashed line across the figure) reflects the inferred reference BP when the crankcase ventilation tube pressure sensor is an absolute pressure sensor. In an alternative example, the crankcase ventilation tube pressure sensor may be a gauge pressure sensor, wherein an offset of the pressure sensor reading from a zero reading is detected such that P1 on the Fig. reflects a balanced reference zero pressure.

[0098] During medium manifold airflow conditions, that is, when the manifold airflow is higher than the first threshold AF1 but lower than a second threshold AF2, no offset can be learned or applied. Thereafter, when high manifold airflow conditions are reached, such as when the manifold airflow is higher than the second threshold AF2, the learned offset can be applied to determine an air filter clogging factor.

[0099] Plot 902 shows deviations in crankcase vent tube pressure from reference P1, as estimated by a crankcase vent tube pressure sensor, relative to changes in manifold air flow in the absence of air filter blockage (i.e., a clean air filter). Plot 904 shows a corresponding deviation in crankcase vent tube pressure from P1 relative to manifold air flow when the air filter is partially blocked. Plot 906 shows changes in crankcase vent tube pressure relative to manifold air flow when the air filter is dirty and substantially blocked. As can be seen by comparing plots 902 to 906, as the air filter blockage factor increases, a deviation in pressure from reference P1 increases. A controller can determine the degree of filter blockage based on the degree of deviation.In this way, an existing sensor used to monitor the crankcase ventilation system can advantageously be used to reliably diagnose an air filter blockage.

[0100] In this way, by placing a pressure sensor within a crankcase vent tube, changes in pressure and air flow through the vent tube can be monitored while housing the sensor in a cost-effective manner. By correlating the estimated changes in vent tube pressure in the crankcase with expected values, crankcase system integrity, air filter degradation, and PCV valve degradation can be reliably indicated. By relying on characteristics of crankcase vent tube pressure and flow data during engine start-up and engine running, violations in the crankcase ventilation system located on one side of the vent tube coupled to an air intake passage can be better differentiated from those occurring on one side of the vent tube coupled to a crankcase.By making adjustments to a throttle and / or PCV valve to increase intake manifold vacuum during engine cranking, the accuracy of crankcase violation detection can be improved. By also using the crankcase ventilation system pressure sensor to identify air filter restriction and PCV valve violation, the need for additional sensors and valves to monitor air filter and PCV valve violation can be reduced, providing the benefits of reduced cost and complexity without reducing the accuracy of violation detection. Furthermore, an engine crankcase ventilation system can remain active during diagnostic procedures.

[0101] It will be appreciated that the configurations and methods disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered limiting, as numerous variations are possible. For example, the above technology can be applied to V6, R4, R6, V12, horizontally opposed four, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and / or characteristics disclosed herein.

Claims

[1] A method for an engine (10) comprising: during engine start-up while a manifold air flow is below a threshold, increasing an intake throttle opening, and indicating a crankcase ventilation system degradation based on a temporary drop in a crankcase vent tube pressure after increasing the intake throttle opening, wherein the crankcase vent tube pressure is estimated by a pressure sensor (77) positioned in a crankcase vent tube (74), and the crankcase vent tube (74) is arranged between an intake passage (13) and a crankcase (28). [2] The method of claim 1, wherein indicating based on the transient drop in crankcase vent tube pressure includes indicating based on the transient drop in crankcase vent tube pressure after increasing the intake throttle opening with an amplitude less than a threshold amplitude. [3] The method of claim 1, wherein increasing the intake throttle opening includes increasing the intake throttle opening to provide a threshold intake manifold vacuum. [4] The method of claim 1, wherein increasing the intake throttle opening includes fully opening the intake throttle (44). [5] The method of claim 1, further comprising indicating degradation of a valve (78) coupled between an intake manifold (42) of the engine (10) and the crankcase (28) based on a crankcase vent tube pressure profile after increasing the intake throttle opening. [6] The method of claim 5, wherein indicating includes indicating degradation of the valve (78) based on an estimated crankcase vent tube pressure profile deviating from an expected crankcase vent tube pressure profile during cranking. [7] The method of claim 6, wherein the indicating further includes indicating that the valve (78) is stuck in a high flow position based on the estimated crankcase vent tube pressure profile being higher than the expected vent tube pressure profile during cranking, and indicating that the valve (78) is stuck in a low flow position based on the estimated crankcase vent tube pressure profile being lower than the expected vent tube pressure profile during cranking. [8] The method of claim 7, further comprising indicating that the valve (78) is stuck in the high flow position by setting a first diagnostic code and indicating that the valve (78) is stuck in the low flow position by setting a second, different diagnostic code. [9] The method of claim 8, further comprising indicating the crankcase ventilation system impairment by setting a third diagnostic code different from the first and second diagnostic codes. [10] The method of claim 8, further comprising limiting engine boost in response to the indication that the valve (78) is stuck in the high flow position. [11] A method for an engine crankcase ventilation system comprising: Adjusting an actuator to increase an intake manifold vacuum to a threshold level and, while the vacuum is maintained at the threshold level by means of the actuator, indicating a crankcase ventilation system degradation based on a temporary drop in a crankcase vent tube pressure, wherein the crankcase vent tube pressure is estimated by a pressure sensor (77) positioned in a crankcase vent tube (74), and the crankcase vent tube (74) is arranged between an intake passage (13) and a crankcase (28). [12] The method of claim 11, wherein the indicating is based on the temporary drop in crankcase vent tube pressure during engine start-up. [13] The method of claim 12, wherein the actuator is an intake throttle (44), and wherein adjusting the actuator includes increasing an opening of the intake throttle (44). [14] The method of claim 12, wherein the actuator is a PCV valve (78) coupled between an intake manifold (42) and the crankcase (28), and wherein adjusting the actuator includes opening the PCV valve. [15] The method of claim 12, wherein indicating whether an amplitude of the transient drop in crankcase ventilation tube pressure during engine cranking is below a threshold includes indicating the crankcase ventilation system degradation. [16] The method of claim 15, wherein indicating the crankcase ventilation system impairment includes indicating that the crankcase ventilation tube (74) is disconnected from the intake passage (13) or the crankcase (28). [17] Engine crankcase ventilation system comprising: an engine (10) including an intake duct (13) and a crankcase (28), a crankcase ventilation tube (74) mechanically connected to the intake duct (13) upstream of a compressor (50), the crankcase ventilation tube (74) also being mechanically connected to the crankcase (28) via an oil separator (81), the crankcase ventilation tube (74) being arranged outside the engine (10), a sensor (77) coupled to the crankcase ventilation tube (74) for estimating a ventilation tube air flow and a control system with computer-readable instructions for the following: during engine start-up, when the manifold air flow is below a threshold flow, adjusting an actuator to raise an intake manifold vacuum to a threshold level, and while maintaining the vacuum at the threshold level, indicating a crankcase ventilation system degradation based on differences between the estimated flow and an expected flow through the crankcase ventilation tube (74). [18] The system of claim 17, wherein the actuator is an intake throttle (44) or a PCV valve (78) coupled between an intake manifold (42) and the crankcase (28), and wherein adjusting the actuator includes increasing an opening of the intake throttle (44) or the PCV valve. [19] The system of claim 18, wherein the expected flow through the crankcase ventilation tube (74) is based on an engine speed and an intake manifold vacuum level, and wherein the estimated flow is based on an output of the sensor coupled into the crankcase ventilation tube (74), the sensor (77) including a pressure sensor, a flow meter, and a venturi tube (75). [20] The system of claim 19, wherein the control system further comprises instructions for: setting a diagnostic code to indicate crankcase ventilation system impairment, and limiting engine speed and load in response to the indication.

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