초록

A method for reducing imbalance between multiple compressors supplying air to an engine is disclosed. In one embodiment, engine boost pressure is limited by choking flow through a compressor. The method may reduce compressor surge during some operating conditions.

대표청구항 ▼

1. A method of operating an engine having an intake manifold communicating with first and second compressors arranged in separate intake passages, the method comprising: adjusting a boost pressure provided to the engine by the first and the second compressors in response to a total volumetric flow r

1. A method of operating an engine having an intake manifold communicating with first and second compressors arranged in separate intake passages, the method comprising: adjusting a boost pressure provided to the engine by the first and the second compressors in response to a total volumetric flow rate of air consumed by the engine, said first and second compressors cooperating to provide the total volumetric flow rate; andadjusting a volumetric flow rate of the first compressor and a volumetric flow rate of the second compressor via at least one actuator in response to a compressor surge threshold so that one of the first and second compressors operates closer to a choked flow condition than the other of the first and second compressors operates to a surge condition. 2. The method of claim 1, where said adjusting the boost pressure includes limiting the boost pressure in response to the total volumetric flow rate of air consumed by the engine, and where during an imbalanced flow condition between the first and second compressors, a flow through the first compressor is greater than a flow through the second compressor, and where a compressor choked flow condition further limits reduction of flow through the second compressor, the method further comprising: increasing the total volumetric flow rate of air consumed by the engine by increasing a gear ratio of a transmission; and increasing a boost pressure limit via adjusting a position of a wastegate in response to said increasing of the transmission gear ratio, and where an output shaft of the engine is coupled to a vehicle drive wheel via the transmission. 3. The method of claim 2, wherein said adjusting the total volumetric flow rate of air consumed by the engine includes increasing the total volumetric flow rate of air consumed by the engine by increasing the gear ratio; and increasing the boost pressure limit in response to the increased gear ratio. 4. The method of claim 1, wherein the total volumetric flow rate of air through the engine includes a total volumetric flow rate of intake air. 5. The method of claim 1, wherein the first compressor is fixedly coupled to a first turbine arranged in a first exhaust stream of the engine and the second compressor is fixedly coupled to a second turbine arranged in a second exhaust stream of the engine; and further comprising limiting the boost pressure provided to the engine by adjusting a volumetric flow rate of the first exhaust stream provided to the first turbine and adjusting a volumetric flow rate of the second exhaust stream provided to the second turbine. 6. The method of claim 5, wherein the volumetric flow rate of the first exhaust stream provided to the first turbine is adjusted by adjusting an opening of a first wastegate arranged in a first bypass passage of the first turbine; and wherein the volumetric flow rate of the second exhaust stream provided to the second turbine is adjusted by adjusting an opening of a second wastegate arranged in a second bypass passage of the second turbine. 7. The method of claim 1, further comprising adjusting the total volumetric flow rate of air consumed by the engine by adjusting an opening of a throttle arranged along an intake passage of the engine common to the first and second compressors; and increasing a boost pressure limit in response to the opening of the throttle. 8. The method of claim 7, wherein the boost pressure limit is increased by adjusting a first vacuum pressure provided to a first wastegate actuator arranged along a first turbine bypass passage of the engine and by adjusting a second vacuum pressure provided to a second wastegate actuator arranged along a second turbine bypass passage of the engine. 9. A method of operating a twin turbocharged engine including an internal combustion engine receiving intake air from a common ambient air supply via a first compressor of a first turbocharger and a second compressor of a second turbocharger, said first compressor rotationally coupled with a first exhaust turbine arranged in a first branch of an exhaust system and said second compressor rotationally coupled with a second exhaust turbine arranged in a separate second branch of the exhaust system, the method comprising: in response to a first imbalanced flow condition between the first and second compressors while operating the twin turbocharged engine at a higher volumetric flow rate of intake air, adjusting volumetric flow rates of the first and second compressors such that when the volumetric flow rate of the first compressor increases, the volumetric flow rate of the first compressor reaches a choked flow region of the first compressor before the volumetric flow rate of the second compressor surges to compensate for the volumetric flow rate of the first compressor by opening bypass wastegates of the first and the second turbine to limit a boost pressure provided to the twin turbocharged engine by the first and second compressors to a first level; andin response to a second imbalanced flow condition between the first and second compressors while operating the twin turbocharged engine at a lower volumetric flow rate of intake air, adjusting volumetric flow of the first and second compressors such that when a flow rate of the first compressor increases, the flow rate of the first compressor reaches a choked flow region of the first compressor before the second compressor surges to compensate for the flow rate of the first compressor by selectively opening the bypass wastegates of the first and second turbines to limit the boost pressure provided by the twin turbocharged engine by the first and second compressors to a second level. 10. The method of claim 9, further comprising adjusting a throttle arranged along an intake passage of the twin turbocharged engine common to both the first and second compressors to adjust a volumetric flow rate of air consumed by the internal combustion engine. 11. The method of claim 9, further comprising adjusting a gear ratio of a transmission to adjust a volumetric flow rate of intake air. 12. The method of claim 9, wherein limiting the boost pressure includes providing a first vacuum pressure to a flexible diaphragm of an actuator of each of the bypass wastegates, and wherein limiting the boost pressure to the first level includes providing a second vacuum pressure to the flexible diaphragm of each actuator of the bypass wastegates, said first vacuum pressure different than said second vacuum pressure. 13. A vehicle propulsion system, comprising: an engine having a plurality of cylinders;a common air intake manifold communicating with the plurality of cylinders;a first air intake passage having a first end communicating with the common air intake manifold;a first compression device arranged along the first air intake passage;a second air intake passage having a first end communicating with the common air intake manifold;a second compression device arranged along the second air intake passage, said first and second compression devices receiving intake air from a common air supply;an anti-surge valve arranged along the first air intake passage; anda control system including a computer program stored in a non-transitory medium including executable instructions to: adjust the anti-surge valve in response to a surge threshold to increase volumetric flow rates of the first and second compression devices such that when the volumetric flow rate of the first compression device increases, the volumetric flow rate of the first compression device reaches a choked flow condition before the volumetric flow rate of the second compression device surges to compensate for the volumetric flow rate of the first compression device to provide a total volumetric engine flow delivered to the engine. 14. The vehicle propulsion system of claim 13, wherein a second end of the first air intake passage and a second end of the second air intake passage are joined at a first end of a common intake passage, said common intake passage having a second end communicating with an ambient air supply. 15. The vehicle propulsion system of claim 13, further comprising a throttle arranged along a common intake passage coupling the first end of the first air intake passage and the first end of the second air intake passage to the common air intake manifold; and wherein the control system is further configured to adjust an opening of the throttle to adjust a volumetric flow rate of air consumed by the engine. 16. The vehicle propulsion system of claim 13, further comprising a vehicle drive wheel and a transmission, wherein an output shaft of the engine is coupled to the vehicle drive wheel via the transmission, and wherein the control system is further configured to increase a volumetric flow rate of air consumed by the engine by increasing a gear ratio of the transmission in response to an indication of compressor surge; and wherein the control system is further configured to increase a level of boost pressure in response to said increase of the transmission gear ratio. 17. The vehicle propulsion system of claim 13, where the anti-surge valve is configured to communicatively couple the first air intake passage downstream of the first compression device to a second end of the first intake air passage and to communicatively couple the second air intake passage downstream of the second compression device to a second end of the second intake air passage; and wherein the control system includes further instructions to increase a volumetric flow rate of air flowing through the first and second compression devices without substantially increasing a volumetric flow rate of air consumed by the engine by selectively opening the anti-surge valve. 18. The vehicle propulsion system of claim 13, further comprising a first exhaust passage coupled to a first portion of the plurality of engine cylinders; a second exhaust passage coupled to a second portion of the plurality of engine cylinders; a first turbine arranged along the first exhaust passage and rotationally coupled with the first compression device; a second turbine arranged along the second exhaust passage and rotationally coupled with the second compression device; and wherein the control system includes additional instructions to limit a first volumetric flow rate of exhaust gases provided to the first turbine and a second volumetric flow rate of exhaust gases provided to the second turbine to limit a level of boost pressure provided to the common intake manifold of the engine. 19. The vehicle propulsion system of claim 18, further comprising a first bypass passage bypassing the first turbine; a first wastegate arranged along the first bypass passage; a second bypass passage bypassing the second turbine; a second wastegate arranged along the second bypass passage; and wherein the control system includes additional instructions to limit the first volumetric flow rate by increasing an opening of the first wastegate and instructions to limit the second volumetric flow rate by increasing an opening of the second wastegate. 20. The vehicle propulsion system of claim 18, further comprising a differential pressure sensor configured to provide an indication of pressure difference between the first exhaust passage upstream of the first turbine and the second exhaust passage upstream of the second turbine; and wherein the control system is further configured to reduce a pressure difference indicated by the differential pressure sensor by adjusting a first vacuum pressure provided to an actuator of a first wastegate relative to a second vacuum pressure provided to an actuator of a second wastegate.