Multivariable low-pressure exhaust gas recirculation control

Patent metadata

Field	Value
Publication number	US-9341127-B2
Application number	US-201414298701-A
Country	US
Kind code	B2
Filing date	Jun 6, 2014
Priority date	Jun 6, 2014
Publication date	May 17, 2016
Grant date	May 17, 2016

Abstract

Methods and systems are provided for adjusting a LP-EGR valve and an LP intake throttle to provide a desired LP-EGR flow rate while maintaining a minimum differential pressure. In one example, a method for a turbocharged engine method comprises: responsive to a differential between intake and exhaust pressure below a threshold, adjusting a LP-EGR valve while adjusting a LP intake throttle to regulate a LP-EGR flow rate and the differential to respective setpoints; and responsive to the differential above the threshold, saturating the LP-EGR valve to minimize the differential while actuating the throttle to regulate the flow rate to its setpoint. In this way, control of the LP-EGR system may be more robust to disturbances at very low differential pressures, require less actuator movement, and increase fuel economy.

First claim

The invention claimed is:

1. A method for a turbocharged engine, comprising:
responsive to a differential between intake and exhaust pressure below a threshold, adjusting a LP-EGR valve while adjusting a LP intake throttle to regulate a LP-EGR flow rate and the differential to respective setpoints; and
responsive to the differential above the threshold, one of fully opening and fully closing the LP-EGR valve to minimize the differential while actuating the throttle to regulate the flow rate to its setpoint.

2. The method of claim 1 , wherein regulating the LP-EGR flow rate to the flow rate setpoint is prioritized over regulating the differential to the differential setpoint.

3. The method of claim 1 , wherein the threshold is 5 hectopascals.

4. The method of claim 1 , wherein the flow rate setpoint is based upon engine operating conditions.

5. The method of claim 1 , wherein the differential setpoint is equivalent to the threshold.

6. The method of claim 1 , wherein the flow rate is measured downstream of the LP-EGR valve.

7. The method of claim 1 , further comprising using a pair of proportional-integral controllers and a linearization controller to control the LP intake throttle and the LP-EGR valve.

8. The method of claim 7 , wherein the linearization controller is based on a physics-based model of the LP-EGR system, the physics-based model based on assumptions of an incompressible exhaust gas and steady-state dynamics of the LP-EGR valve and the LP intake throttle.

9. The method of claim 1 , wherein the turbocharged engine includes an EGR passage, and the EGR passage couples an engine exhaust, downstream of a turbine, to an engine intake, upstream of a compressor.

10. The method of claim 9 , wherein the LP-EGR valve is positioned in the EGR passage upstream of the compressor, and wherein the LP intake throttle is positioned in an air intake passage of the engine intake upstream of the compressor.

11. A turbocharged engine method, comprising:
responsive to a differential between intake and exhaust pressure below a threshold, adjusting a LP-EGR valve while adjusting a LP intake throttle to regulate a LP-EGR flow rate and the differential respectively to a flow setpoint and a differential setpoint; and
responsive to the differential above the threshold, in a first mode, one of fully opening and fully closing the LP-EGR valve to minimize the differential while actuating the throttle to regulate the flow rate to the flow setpoint, and in a second mode, one of fully opening and fully closing the intake throttle to minimize the differential while actuating the LP-EGR valve to regulate the flow rate to the flow setpoint.

12. The method of claim 11 , wherein regulating the LP-EGR flow rate to the flow setpoint is prioritized over regulating the differential to the differential setpoint.

13. The method of claim 11 , wherein the flow rate is measured downstream of the LP-EGR valve.

14. The method of claim 11 , wherein the differential setpoint is equivalent to the threshold.

15. The method of claim 11 , wherein the threshold is 5 hectopascals.

16. The method of claim 11 , wherein the flow setpoint is based upon an engine operating condition.

17. The method of claim 11 , further comprising using a pair of proportional-integral controllers and a linearization controller to control the LP intake throttle and the LP-EGR valve.

18. The method of claim 17 , wherein the linearization controller is based on a physics-based model of the LP-EGR system, the physics-based model based on assumptions of an incompressible exhaust gas and steady-state dynamics of the LP-EGR valve and the LP intake throttle.

19. An internal combustion engine system comprising:
an engine;
a turbocharger including a compressor connected to a turbine, the compressor in communication with an intake manifold of the engine and the turbine in communication with an exhaust manifold of the engine;
a low-pressure (LP) exhaust gas recirculation (EGR) passage including an EGR valve and an intake throttle connecting the intake manifold and the exhaust manifold, said EGR valve responsive to an EGR valve control signal and said intake throttle responsive to an intake throttle control signal for regulating a flow rate into said intake manifold and a differential pressure in said LP-EGR passage;
a controller configured with instructions stored in non-transitory memory that when executed, cause the controller to:
generate a flow rate error based upon a reference flow rate and a measured flow rate;
generate a differential pressure error based upon a reference differential pressure and a measured differential pressure;
calculate a minimum and a maximum achievable flow rate;
apply the minimum and the maximum achievable flow rates as anti-windup limits to a first proportional-integral controller;
execute the first proportional-integral controller to generate an adjusted flow rate setpoint responsive to the flow rate error;
calculate a minimum and a maximum achievable differential pressure responsive to the adjusted flow rate setpoint;
apply the minimum and the maximum achievable differential pressures as anti-windup limits to a second proportional-integral controller;
execute the second proportional-integral controller to generate an adjusted differential pressure setpoint responsive to the differential pressure error;
execute a linearization controller to generate an EGR valve actuator position and a LP intake throttle actuator position responsive to the adjusted flow rate setpoint and the adjusted differential pressure setpoint; and
actuate the EGR valve to the EGR valve actuator position and the intake throttle to the LP intake throttle actuator position.

20. The system of claim 19 , wherein the linearization controller is based on a physics-based model of the LP-EGR system, the physics-based model based on assumptions of an incompressible exhaust gas and steady-state dynamics of the EGR valve actuator and the LP intake throttle actuator.

Assignees

• Ford Global Tech Llc

Inventors

• Brewbaker Thomas Alan
• Van Nieuwstadt Michiel J

Classifications

• F02D2200/0406

  Intake manifold pressure · CPC title

• F02D41/0072

  Estimating, calculating or determining the EGR rate, amount or flow (sensors in EGR systems F02M26/45) · CPC title

• F02D41/1448

  the characteristics being an exhaust gas pressure · CPC title

• F02D2041/0017

  by simultaneous control of throttle and exhaust gas recirculation · CPC title

• F02D2041/1409

  using at least a proportional, integral or derivative controller · CPC title