Systems and methods for multiple aspirators for a constant pump rate

A system for an engine, comprising:

• an aspirator arrangement comprising at least two aspirators connected in parallel, at least two of the aspirators having different throat flow areas;
• a high pressure source fluidly coupled to a motive inlet of the aspirator arrangement, the motive inlet of the aspirator arrangement comprising a passage fluidly coupled to the high pressure source which branches into parallel flow paths, each aspirator arranged in one of the flow paths;
• a low pressure sink fluidly coupled to a mixed flow outlet of the aspirator arrangement, the mixed flow outlet of the aspirator arrangement comprising a passage fluidly coupled to the low pressure sink into which the flow paths merge upstream of the low pressure sink;
• a plurality of actively controllable valves comprising a valve in series with each aspirator of the aspirator arrangement, each valve arranged upstream of a corresponding aspirator of the aspirator arrangement in the flow path of that aspirator;
• a vacuum reservoir fluidly coupled to entraining inlets of all of the aspirators of the aspirator arrangement;
• and
• a controller with computer readable instructions for actively controlling the valves based on a desired combined motive flow rate through the aspirator arrangement and based on the throat flow areas of the aspirators.

A method for an engine, comprising:

• adjusting an opening amount of an intake throttle and a combined motive flow rate through at least two parallel valved aspirators bypassing the intake throttle based on a desired engine air flow rate;
• during a fault condition where the intake throttle is fully closed, directing all intake air flow through the aspirators and adjusting the combined motive flow rate based on the desired engine air flow rate, wherein adjusting the combined motive flow rate through the aspirators comprises adjusting a plurality of aspirator shut-off valves, the plurality of aspirator shut-off valves comprising a valve arranged in series upstream of a motive inlet of each aspirator, at least two of the aspirators having different throat flow areas, and wherein a throat flow area of a first aspirator of the at least two aspirators is half the size of a throat flow area of a second aspirator of the at least two aspirators, further comprising opening none, one, or both of first and second valves of the plurality of aspirator shut-off valves, the first and second valves arranged in series upstream of the first and second aspirators, respectively, based on the desired engine air flow rate and based on the throat flow areas of the first and second aspirators;
• and
• when the intake throttle is not in the fault condition:
• if the desired engine air flow rate is zero, opening none of the first and second valves and closing the intake throttle;
• if the desired engine air flow rate is greater than a first level and less than or equal to a second, higher level, opening the first valve and closing the second valve and closing the intake throttle;
• if the desired engine air flow rate is greater than the second level and less than or equal to a maximum combined motive flow rate through the aspirators, closing the first valve and opening the second valve and closing the intake throttle;
• and
• if the desired engine air flow rate is greater than the maximum combined motive flow rate through the aspirators, opening both of the first and second valves.