Method and system for vacuum generation

A method for an engine, comprising:

• determining boost pressure in at least one of an intake passage and an intake manifold;
• determining a vacuum level in a vacuum reservoir;
• when the vacuum level of the vacuum reservoir is lower than a threshold level and the boost pressure is less than or equal to a threshold pressure, opening a valve coupled upstream of an ejector to draw motive flow into the ejector from upstream of a compressor, the motive flow discharged from the ejector into an intake manifold, downstream of an intake throttle;
• and
• in response to one of the vacuum level of the vacuum reservoir being higher than the threshold level and the boost pressure being higher than the threshold pressure, closing the valve.

A system, comprising:

• an engine including an intake manifold, the intake manifold coupled to a vacuum reservoir along a first passage;
• a pressure sensor coupled to the vacuum reservoir to provide an estimate of the vacuum level at the vacuum reservoir;
• a manifold air pressure sensor that detects a boost pressure in the intake manifold
• a compressor positioned in an intake passage upstream of the intake manifold;
• an intake throttle upstream of the intake manifold and downstream of the compressor;
• an ejector positioned in a bypass passage across the compressor and intake throttle, a neck of the ejector coupled to the vacuum reservoir along a second passage, an outlet of the ejector coupled to the vacuum reservoir and the intake manifold along the first passage;
• a motive flow control valve coupled in the bypass passage upstream of an inlet of the ejector;
• a vacuum actuator coupled to the motive flow control valve, the vacuum actuator coupled to the vacuum reservoir and to an outlet of the compressor;
• and
• a controller with non-transitory computer-readable instructions for:
• operating the engine system in a first mode with the motive flow control valve open to increase motive flow through the ejector;
• and
• operating the engine system in a second mode with the motive flow control valve closed to decrease the motive flow;
• and wherein the engine system is operated in the first mode when the vacuum level in the vacuum reservoir is below a threshold level and the boost pressure is less than a threshold pressure, and wherein the engine system is operated in the second mode when the boost pressure is greater than the threshold pressure.