Method for determining a dilution of recirculated gases in a split exhaust engine

Patent metadata

Field	Value
Publication number	US-10731580-B2
Application number	US-201815926940-A
Country	US
Kind code	B2
Filing date	Mar 20, 2018
Priority date	Mar 20, 2018
Publication date	Aug 4, 2020
Grant date	Aug 4, 2020

Abstract

Methods and systems are provided for determining a dilution of recirculated gases, including blowthrough air, combusted exhaust gas, and fuel vapor, in a split exhaust engine. In one example, the dilution rate may be calculated using a feedforward model that includes determining a pressure differential across a region in an intake passage, mapped engine parameters such as gas temperature, and exhaust valve timing. Engine operations such as spark advance and fuel injection may be adjusted according to the modeled rate to reduce engine knock and improve combustion efficiency.

First claim

The invention claimed is:

1. A method, comprising:
determining a dilution rate of gas recirculated from a first set of exhaust valves to an intake passage based on a corrected temperature of the gas and on a timing of the first set of exhaust valves while flowing exhaust gas from a second set of exhaust valves to a turbocharger turbine and not to the intake passage, where each cylinder includes one valve from each of the first and second sets of exhaust valves, and wherein determining the dilution rate based on the corrected temperature of the gas includes multiplying a temperature correction with a temperature of a manifold coupling the first set of exhaust valves to the intake passage to determine the corrected temperature; and
adjusting one or more of fuel injection to engine cylinders and spark timing based on the determined dilution rate.

2. The method of claim 1 , wherein the temperature correction accounts for heat transfer across a region between a temperature sensor where the temperature of the manifold is measured and a region immediately upstream of a turbocharger compressor.

3. The method of claim 1 , wherein determining the dilution rate of gas recirculated from the first set of exhaust valves to the intake passage includes determining the dilution rate of gas recirculated from the first set of exhaust valves to the intake passage, upstream of a turbocharger compressor.

4. The method of claim 1 , wherein determining the dilution rate of gas recirculated from the first set of exhaust valves to the intake passage is further based on a differential pressure across an exhaust gas recirculation (EGR) valve positioned in an EGR passage and across a venturi positioned between the EGR valve and an inlet to a turbocharger compressor, the EGR passage coupled between the intake passage, upstream of the turbocharger compressor and a scavenge exhaust manifold, the scavenge exhaust manifold coupled exclusively to the first set of exhaust valves.

5. The method of claim 4 , wherein determining the dilution rate of gas recirculated from the first set of exhaust valves to the intake passage is further based on engine speed, engine load, and an estimate of a temperature of the recirculated exhaust gas at an outlet of the venturi.

6. The method of claim 5 , further comprising determining the estimate of the temperature of the recirculated gas based on engine speed, engine load, and a correction factor for temperature loss from the exhaust gases to the exhaust valves.

7. The method of claim 1 , further comprising opening the first set of exhaust valves at a different timing in an engine cycle than the second set of exhaust valves.

8. The method of claim 1 , wherein the gas recirculated from the first set of exhaust valves includes a portion of each of burnt combustion gases, fresh blowthrough air, and unburnt fuel.

9. The method of claim 1 , further comprising combusting air and fuel in each engine cylinder and then: first, flowing a first portion of combusted gases to the turbocharger turbine disposed in an exhaust passage via the second set of exhaust valves; second, flowing a second portion of combusted gases to the intake passage via the first set of exhaust valves; and third, flowing fresh blowthrough air to the intake passage via the first set of exhaust valves.

10. The method of claim 9 , further comprising not flowing fresh blowthrough air to a turbocharger compressor, and further comprising flowing a portion of the second portion of combusted gases to the exhaust passage, downstream of the turbocharger turbine.

11. A method, comprising:
flowing gases from a first set of exhaust valves to a compressor disposed in an intake passage and flowing combusted exhaust gases from a second set of exhaust valves to a turbine disposed in an exhaust passage and not to the intake passage, where each cylinder of a plurality of engine cylinders includes one valve of the first set of exhaust valves and one valve of the second set of exhaust valves;
determining a dilution rate of the gases flowing from the first set of exhaust valves to the compressor based on a timing of the first set of exhaust valves and a differential pressure across an exhaust gas recirculation (EGR) valve and across a venturi, the EGR valve positioned in an EGR passage coupled between the first set of exhaust valves and the intake passage, upstream of the compressor, and the venturi arranged in the intake passage downstream of where the EGR passage couples to the intake passage; and
adjusting one or more of fuel injection to the plurality of engine cylinders and spark timing based on the determined dilution rate.

12. The method of claim 11 , wherein the gases from the first set of exhaust valves include a combination of combusted exhaust gases and fresh, blowthrough air, where an amount of fresh, blowthrough air is based on a valve opening overlap period between the first set of exhaust valves and intake valves of each cylinder, and wherein the combusted exhaust gases from the second set of exhaust valves do not contain fresh, blowthrough air.

13. The method of claim 11 , wherein the determined dilution rate is further based on engine speed and engine load.

14. The method of claim 13 , wherein the determined dilution rate is further based on a temperature of the gases flowing from the first set of exhaust valves to the compressor, where the temperature is a mapped temperature that is based on engine speed, engine load, and a temperature correction that is based on a maximum and a minimum EGR temperature according to a range of EGR flow during engine operation.

15. The method of claim 14 , further comprising opening the first set of exhaust valves at a different timing in an engine cycle than the second set of exhaust valves.

16. A system for an engine, comprising:
a first set of exhaust valves exclusively coupled to a first exhaust manifold, the first exhaust manifold coupled to an intake passage, upstream of a turbocharger compressor, via an exhaust gas recirculation (EGR) passage, the EGR passage including an EGR valve;
a second set of exhaust valves exclusively coupled to a second exhaust manifold coupled to an exhaust passage, upstream of a turbocharger turbine disposed in the exhaust passage;
a plurality of engine cylinders, each including one of the first set of exhaust valves and one of the second set of exhaust valves; and
a controller including memory with instructions stored thereon for:
determining a dilution rate of gas flowing from the first set of exhaust valves to the turbocharger compressor via the EGR passage based on a corrected temperature of the gas and on a cam timing of the first set of exhaust valves, wherein determining the dilution rate based on the corrected temperature of the gas includes multiplying a temperature correction with a temperature of a manifold coupling the first set of exhaust valves to the intake passage to determine the corrected temperature; and
adjusting spark timing and fuel injection to the plurality of engine cylinders based on the determined dilution rate.

17. The system of claim 16 , wherein the first set of exhaust valves opens at a different timing than the second set of exhaust valves and wherein there is a valve overlap period between the first set of exhaust valves and intake valves of the plurality of engine cylinders, where the one exhaust valve of the first set of exhaust valves and intake valves of each cylinder are both open while the second set of exhaust valves are closed.

18. The system of claim 16 , further comprising a bypass passage coupled

Assignees

• Ford Global Tech Llc

Inventors

• Surnilla Gopichandra
• Clark Timothy
• Ulrey Joseph
• Hakeem Mohannad

Classifications

• F02M26/07

  Mixed pressure loops, i.e. wherein recirculated exhaust gas is either taken out upstream of the turbine and reintroduced upstream of the compressor, or is taken out downstream of the turbine and reintroduced downstream of the compressor · CPC title

• F02D2041/0067

  Determining the EGR temperature · CPC title

• F02D41/0077

  Control of the EGR valve or actuator, e.g. duty cycle, closed loop control of position (EGR valve position sensor F02M26/48) · CPC title

• F02M26/04

  with a single turbocharger · CPC title

• F02D13/0261

  Controlling the valve overlap · CPC title