Canister purge system and method for diagnosing purge valve thereof

What is this patent about?

’399 is related to the field of automotive evaporative emission control systems, specifically focusing on the diagnosis of canister purge systems. In modern vehicles, especially those with low manifold vacuum like turbocharged or hybrid engines, a dedicated pump is often required to draw fuel vapors from the storage canister and force them into the engine intake. If the control valve in this line fails to open correctly, the system cannot effectively clear the canister, leading to potential emission compliance issues or fuel tank pressure problems.

The underlying idea behind ’399 is that a failure in the purge valve—specifically a close stuck state—can be accurately detected and categorized by monitoring the pressure differential across the purge pump itself. Rather than relying on complex flow meters or indirect engine performance metrics, the invention recognizes that a blockage downstream of the pump will cause predictable, measurable deviations in both the suction side and the discharge side of the pump compared to normal operating conditions.

The claims of ’399 focus on a diagnostic method and system that utilizes a dual-sensor configuration to monitor the purge line. Specifically, the system measures an upstream pressure between the canister and the pump and a downstream pressure between the pump and the purge valve. By analyzing these two specific data points while the pump is active and the valve is commanded open, the controller can distinguish between a healthy system and one suffering from a mechanical valve failure.

In practice, the system differentiates between a total blockage and a partial restriction by comparing the measured pressures against calibrated reference values. If the downstream pressure rises above a normal threshold, it indicates a bottleneck. The system then checks the upstream pressure; if that pressure returns to near-atmospheric levels after an initial drop, it signifies a high-level close stuck state where flow is completely halted. Conversely, if the upstream suction remains low but the downstream pressure is elevated, the system identifies a partial or middle-level restriction.

This approach differs from prior solutions by providing a granular diagnosis of the valve's physical state without requiring additional hardware beyond standard pressure transducers. By correlating the pump RPM to the expected suction pressure, the invention ensures that the diagnostic logic remains accurate across varying pump speeds. This allows the vehicle's onboard diagnostics to not only detect a failure but also characterize the severity of the flow resistance, improving the reliability of emission monitoring systems.