Engines may include crankcase ventilation systems to vent gases out of the crankcase and into an engine intake manifold to provide continual evacuation of gases from inside the crankcase in order to reduce degradation of various engine components in the crankcase. During certain conditions, such as during OBD routines, crankcase ventilation systems may be monitored to identify breaches in the system. For example, a fresh air hose (also referred to as breather tube or crankcase vent tube) may become disconnected, an oil cap may be off or loose, a dipstick may be out, and/or other seals in the crankcase ventilation system may be broken resulting in degradation of various components included in the crankcase.
Various approaches may be used to monitor crankcase ventilation system integrity. For example, diagnostic blow-by approaches may be used wherein a pressure sensor used in the crankcase and a valve in a PCV fresh air hose are opened and a breach in the system is determined based on resulting changes in crankcase pressure or vacuum. Another example approach, shown by Pursifull et al. in US 2014/0081549, relies on a crankcase vent hose pressure sensor to detect disconnection of the vent tube/hose. Specifically, a measured pressure drop in the hose is correlated with air flow rate through an air induction system throttle, and the correlation is used to diagnose crankcase vent tube (CVT) disconnection. Still other approaches may use a combination of pressure sensors positioned at different locations in the crankcase ventilation system to monitor crankcase ventilation system integrity.
However, the inventors herein have recognized potential issues with such approaches. As one example, the system of Pursifull et al. requires large air intake system flow rates (e.g., higher than 12 lbm/min) to robustly detect a vent tube disconnected at the air induction system end. As such, for some power-to-weight ratio vehicles, it may be difficult to achieve the required high air flows during standard OBD demonstration cycles. As a result, the vehicle may be unable to complete the crankcase vent tube diagnostic required for meeting federal emissions standards. As another example, the system of Pursifull relies on seeing a transient dip in crankcase vent tube pressure during engine cranking and run-up to diagnose that the vent tube is connected at the crankcase end. The transient dip is generated due to the PCV valve opening during increased intake manifold vacuum creation at the engine run-up. However, variation in engine run-ups can cause variations in the transient dip. In some circumstances, the PCV valve may not open enough for the pressure sensor in the vent tube to detect the transient dip. As such, these events can lead to misdetection of a disconnected hose.
Further still, the various approaches may necessitate additional hardware to perform the monitoring, such as additional sensors and valves, thereby increasing costs and complexity. As another example, based on the location of the sensor, some combinations of pressure sensors may read substantially the same pressure under certain conditions, leading to an increase in redundancy without an increase in the accuracy of the diagnostic routine.
In one approach, to at least partially address these issues, a method for an engine is provided. The method comprises indicating crankcase ventilation system breach based on an integrated value of an error in change of actual crankcase vent tube pressure over a duration of transient engine airflow relative to an integrated value of an error in change of expected crankcase vent tube pressure over the duration. In this way, disconnection of the crankcase vent tube (CVT) on the air intake side (or clean side) may be reliably determined during an OBD cycle.
As an example, during transient engine airflow conditions when airflow is at or above a threshold flow (e.g., at or above 5 lbm/min), actual CVT pressure readings may be collected and monitored. The actual CVT pressure readings may be estimated by a pressure sensor (or flow sensor or venturi) connected in the CVT. In addition, expected CVT pressure readings corresponding to each collected actual CVT reading may be estimated based on engine operating conditions such as engine airflow and barometric pressure. The slope of each collected actual CVT reading may be compared to the slope of the corresponding estimated CVT reading. If the slopes do not match due to slopes of differing signs (e.g., one is increasing while the other is decreasing, or vice versa), the collected actual CVT reading may be rejected and not used for integration. In addition, if the engine airflow transiently falls below the threshold flow, actual CVT readings collected during the below threshold flow condition may also be rejected and not used for integration analysis. As such, while the actual CVT readings are being collected, the expected CVT readings may be integrated until a threshold value is reached. The threshold value may be indicative of a minimum amount of airflow having passed through the tube for reliable integration analysis to be performed. Thus, when the integrated value of the expected CVT readings reach the threshold value, further collection of actual CVT readings is discontinued and the actual readings (not including the rejected readings) are integrated. The integrated actual value is then adjusted with a gain factor and a noise floor to improve the weighting contribution of the CVT pressure sensor. A ratio of the integrated value of the actual readings to the integrated value of the expected readings is determined, the ratio normalized and clipped (e.g., between 0 and 1). In response to the ratio being lower than a threshold, e.g., closer to 0, it may be determined that the CVT is disconnected on the air intake side (the clean side). Accordingly, a diagnostic code may be set and engine operation may be adjusted to compensate for the disconnected CVT. For example, engine boost may be limited. If the ratio is higher than the threshold, e.g., closer to 1, it may be determined that the CVT is connected on the air intake side and no crankcase breach is indicated.
In this way, crankcase ventilation system breaches may be better identified. Further, breaches at the AIS end (the clean side) of the crankcase vent tube/hose may be better distinguished from breaches at the crankcase end. By integrating CVT pressure readings collected over a duration of steady-state engine airflow, crankcase ventilation system breaches at the air intake system (AIS) end of the CVT may be robustly identified even at lower air mass regions (e.g., above 5 lbm/min). As such, this allows the breach detection to be reliably completed both while the vehicle is travelling on the road, as well as during OBD cycles. By using the existing sensors to diagnose crankcase system degradation, the number of sensors and valves employed in a crankcase ventilation monitoring system may potentially be reduced, providing cost and complexity reduction benefits. Further, the approach allows the crankcase ventilation system to remain active during a diagnostic procedure.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It if is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.