WO2013030562A1

WO2013030562A1 - System for calibrating egr pressure sensing systems

Info

Publication number: WO2013030562A1
Application number: PCT/GB2012/052105
Authority: WO
Inventors: Adam Jonathan STUBBS
Original assignee: Perkins Engines Co Ltd
Current assignee: Perkins Engines Co Ltd
Priority date: 2011-08-26
Filing date: 2012-08-28
Publication date: 2013-03-07
Anticipated expiration: 2014-02-26
Also published as: GB201401435D0; GB2509620A; GB2509620B

Abstract

A method of controlling EGR in an engine system comprises the steps of determining a differential pressure across an EGR valve (26) using an EGR pressure sensing system (28,30), comparing the determined differential pressure across an EGR valve (26) to an expected differential pressure across the EGR valve (26), and calibrating the EGR pressure sensing system (28,30) based on the comparison while the engine system is in operation.

Description

SYSTEM FOR CALIBRATING EGR PRESSURE SENSING SYSTEMS

Technical Field

The present disclosure relates generally to an engine system, and more particularly, to a system for calibrating an exhaust gas recirculation pressure sensor system. Background

Exhaust gas recirculation (EGR) is a known technique for use in internal combustion engines (petrol or diesel) wherein a portion of an engine's exhaust gas is recirculated back to the engine cylinders. EGR may be used to reduce emissions of oxides of nitrogen including NO and N0₂.

A typical EGR system may include a conduit, or other structure, fluidly connecting a portion of the exhaust path of an engine with a portion of the air intake system of the engine, thereby forming an EGR path. Different amounts of exhaust gas recirculation may be desirable under different engine operating conditions and, in order to regulate the amount of exhaust gas recirculation, such systems typically employ an EGR valve that is disposed at some point in the EGR path to control the flow rate through the EGR system.

A model is typically used to estimate the flow rate through the EGR valve based on the exhaust gas temperature, the degree of opening of the EGR valve, and the pressure drop across the EGR valve (i.e. a differential of the pressure upstream and downstream of the valve). It is desirable to obtain an accurate measurement of the pressure drop across the EGR valve in order to calculate a good estimate of the EGR flow rate.

Pressure sensors are known to drift over time, therefore the pressure sensors in the EGR system need to be calibrated. The pressure sensors are typically calibrated at shut down of the engine.

Brief Description of the Drawings Fig. 1 is a pictorial illustration of an exemplary disclosed engine system;

Fig. 2 is a flowchart depicting an exemplary disclosed method performed by the engine system of Fig. 1; and Fig. 3 is a graphical illustration of the operation of an exemplary disclosed method performed by the engine system of Fig. 1.

Detailed Description

Referring to Fig. 1, there is shown an engine system 10 according to one embodiment. Engine system 10 may include an engine 11 having an engine block 12 that at least partially defines a plurality of cylinders 14. It is contemplated that engine system 10 may include any number of cylinders 14 and that cylinders 14 may be in an "in-line" configuration, a "V" configuration, or any other conventional configuration.

An exhaust system 16 may be associated with engine system 10 and may be configured to receive exhaust gas resulting from the combustion of air and fuel from engine block 12. Exhaust system 16 may include an exhaust manifold 18, EGR system 20, an open crankcase ventilation (OCV) filter 22; a turbine of a turbocharger 13, and an exhaust back pressure regulator 15.

EGR system 20 may include an EGR cooler 24, an EGR valve 26, an EGR valve intake pressure sensor 28, and EGR valve outlet pressure sensor 30, and an EGR temperature sensor 32. Alternatively, EGR valve intake pressure sensor 28 and EGR valve outlet pressure sensor 30 may be combined in the form of an EGR differential pressure sensor, or any other type of EGR pressure sensing system. EGR valve 26 may take different forms, such as a selectively controllable, variable position valve.

Engine system 10 also includes a controller 34. Controller 34 may embody a single microprocessor or multiple microprocessors that control an operation of EGR valve 26 in response to various engine system parameters. Numerous commercially available

microprocessors can be configured to perform the functions of controller 34. It should be appreciated that controller 34 could readily employ a general power system microprocessor capable of controlling numerous power system functions and modes of operation. For example, controller 34 may include hardware and software to receive and manipulate a multitude of engine system data, and transmit data to the engine system. For example, controller 34 may determine a fuel injection quantity to be supplied to the cylinders 14 based on a desired fuel quantity received at controller 34. Relevant to this disclosure, controller 34 may receive a coolant temperature sensor signal (not shown). Various known circuits may be associated with controller 34, including power supply circuitry, signal-conditioning circuitry, solenoid driver circuitry, communication circuitry, and other appropriate circuitry.

In one embodiment, a timer 35 may be associated with controller 34. In response to a command from controller 34, timer 35 may track an elapsed time. Controller 34 may also be connected to an engine speed sensor 36 configured to detect a speed of engine 11.

Engine system 10 also includes an intake system 40 including a compressor of turbocharger 13, an air-to-air after cooler (ATAAC) and an intake manifold 44 that delivers intake air to engine block 12. Intake system 40 may also be configured to receive and deliver EGR gas from EGR system 20 to the plurality of cylinders 14.

Fig. 2 illustrates an exemplary method performed by controller 34. Fig. 2 will be discussed in more detail in the following section to further illustrate the disclosed concepts.

Industrial Applicability

The disclosed control system may be applicable to any engine where EGR mass flow measurement accuracy is desired. The disclosed system may provide real-time calibration to EGR mass flow while an engine system is running.

Turning to Fig. 2, there is shown a flowchart 200 illustrating an engine control process according to one embodiment. The process of flowchart 200 may start at Control Block 220.

At Control block 220, conditions are checked to determine whether the calibration process should be initiated. One such condition includes whether engine 11 has been running for greater than a threshold amount of time since either the last successful calibration, or since engine 11 started. This time period may be tracked by timer 35. The threshold time period may be selected as 30 minutes in the case that a successful calibration has taken place since an engine start. It should be noted, however, that any selected time period may alternatively be used.

Initiation of the calibration may further require that the speed of engine 11 be above a threshold speed and a coolant temperature be above a coolant temperature threshold. For example, the engine speed threshold may be 500 rpm. It should be noted, however, that any selected engine speed may alternatively be used. The process may further require that both engine speed and coolant temperature be above their respective thresholds for greater than a threshold amount of time. Initiation of the calibration may also require that an EGR temperature be between a high EGR temperature threshold and a low EGR temperature threshold. Initiation of the calibration may still further require that the engine 11 is operating in a specified range. For example, calibration may be initiated only if engine speed and fuel delivery are within an acceptable range. This calibration condition helps to assure that engine to engine variability in pressure differential is within acceptable ranges. Alternatively, EGR valve 26 may be opened for calibration purposes if instructed to by an operator.

If at least one of the conditions is not met, the process will not proceed. The process will continue to check these conditions until met, or will wait a specified time and try again. If all of the conditions are met, the calibration process will proceed to block 225 where the controller 34 sends a signal to EGR valve 26 to open fully.

If it is sensed that EGR valve 26 has not opened to more than 95 percent of its opening capacity, the control strategy will abort at Control Block 290 to protect stuck or failed valves. It should be noted, however, that the process may abort to Control Block 290 at any time after a request is made to open EGR valve 26 for calibration if it is sensed that EGR valve 26 is not opened to at least 95%. It should also be noted that any alternative opening capacity of EGR valve 26 may be selected as the abort threshold. If the valve is functioning properly (opening at more than 95%), the process may proceed to Control Block 240 where controller 34 receives signals from EGR valve intake pressure sensor 28 and EGR valve outlet pressure sensor 30. The sensed pressure difference (or differential pressure) between intake pressure sensor 28 and outlet pressure sensor 30 may be determined by controller 34, or received directly by controller if a differential pressure sensor is used. After EGR valve 26 has been opened for a predetermined threshold amount of time, such as about 200 milliseconds, the pressure differential may be determined. The collection of EGR pressure sensor data may take place over a predetermined capture window. For example, a capture window may be set to a period of about 1000 ms (1 second), and differential pressure may be measured at defined intervals of about 15-20 ms during the capture window. Alternatively the differential pressure may be measured at defined crank shaft positions. It should be noted, however, that the capture window and/or intervals can be set to any selected amounts of time. Once a number of instantaneous measurements have been taken, an average of the differential pressures may be determined and EGR valve 26 may be closed or return to normal operating conditions.

From Control Block 240, the process may proceed to a checking step at Control

Block 250. At Control Block 250, controller 34 may determine if the calibration process should be aborted to Control Block 290. The calibration process may be aborted if the engine speed deviates beyond a predetermined threshold amount during the capture period. For example, the engine speed threshold amount may be 10 rpm, or may alternatively be any selected threshold amount. Further, the calibration process may be aborted if the fuel injection rate deviates beyond a predetermined threshold amount during the capture period. For example, the fuel injection rate threshold may be 10 cubic mm per stroke, or may alternatively be any selected fuel injection rate. The calibration process may also be aborted if the differential pressure deviates beyond a predetermined threshold amount during the capture period. Alternatively, the threshold may be any selected value according to any selected differential pressure deviation and rpm value.

Further, the calibration process may be aborted if the differential pressure exceeds a

predetermined threshold. For example, the differential pressure threshold may be selected to be 36 kPa. It should be noted, however, that any selected differential pressure threshold may alternatively be used. Still further, the calibration process may be aborted if it is detected that at least one of the EGR pressure sensors 28 or 30 has faulted during the operation. Additionally, the calibration process may abort if the controller is set to a mode having a higher priority while EGR valve 26 is opened. For example, a low temperature regeneration mode may have a higher priority than a calibration mode. The calibration process may also be aborted if exhaust back pressure regulator 15 is in any position other than fully open, or if its position sensor is faulted. While the flowchart of Fig. 2 shows determining calibration abort after the opening of the EGR valve 26 and measuring the differential pressure in the capture window, it is understood that the system may check the abort conditions and abort the calibration process to Control Block 290 at any time after a request is made to open EGR valve 26 for calibration.

If no faults are detected at Control Block 250, the process may proceed to Control Block 260 where the measured differential pressure is compared to an expected differential pressure. As noted above, this measured differential pressure may be an average of the differential pressures determined during the capture window. Controller 34 may determine an expected differential pressure by referencing a differential pressure model stored within the memory of controller 34. The differential pressure model may include a collection of data in the form of tables, and/or equations. In particular, the differential pressure model may represent an empirical-based prediction of the differential pressure between EGR pressure sensors 28 and 30 at different engine system conditions. These engine system conditions may include one or more of engine speed, fuel injection quantity (or load), DPF soot load, barometric pressure, and EGR temperature. In one embodiment, the model may identify expected differential pressures based on engine speed, and fuel injection quantity (or load).

If the measured differential pressure determined at Control Block 240 is equal to or within an acceptable range of the expected differential pressure determined from the differential pressure model, the process may return to Control Block 220 via return line 265. If the measured differential pressure is not equal to or within a range of the expected differential pressure, the process may proceed to Control Block 270 where a calibration value is set and stored in the memory of controller 34. It is understood that engine system 10 is in operation when engine 11 is receiving fuel that is combusted in cylinders 14.

For example, at certain engine system parameters, the differential pressure across a fully open EGR valve may be expected to be zero, as indicated by the differential pressure model. If the differential pressure determined from EGR pressure sensors 28, 30 is not zero, or not within an acceptable range of zero, then a calibration value is set by controller 34 as the difference between the expected differential pressure and the measured differential pressure. This set calibration value may then be applied to calibrate future differential pressure values from EGR pressure sensors 28 and 30. Controller 34 may use the set calibration value until a subsequent calibration process is performed and a new calibration value is determined and stored in controller 34. Once the calibration is set at Control Block 270, the process may return to Control Block 220 via return line 275.

According to one embodiment, the currently set calibration value is reset when the engine system 10 is shut down. Still further, the calibration value may be erased at shut down of the engine system 10 and replaced with a separate calibration value determined by a separate calibration process performed by controller 34 after the shutdown of engine system 10.

As noted above, the calibration process may be aborted to Control Block 290 based on determinations at either Control Block 230 or Control Block 250. Once aborted, the process may proceed to Control Block 280 where timer 35 tracks the amount of time since the process was aborted. Once the timer exceeds a threshold time, such as about 10 minutes, the process may return to Control Block 220 to be restarted. It should be noted, however, that any amount of time may alternatively be selected as the abort threshold amount.

Turning to Fig. 3, there is shown a graph 300 depicting operation of the engine control calibration process according to an embodiment of this disclosure. In this embodiment, the calibration process discussed above may set new calibration values at a plurality of intervals 302. Time periods 310, 320, 330, and 340 represent periods of time between the setting of new calibration values. A calibration value of zero may be represented by the dotted line at 304. A calibration value set by controller 34 may be represented by line 306. For example, the time period 310 may represent a time before a first EGR calibration has occurred, and therefore, a calibration value in controller 34 may be zero. The time period 320 may represent a time period after a first calibration value has been determined and set in controller 34. This calibration value is then applied to the differential pressure values determined by EGR pressure sensors 28, 30 over period 320. Similarly, a time period 330 may represent a period after a subsequent calibration value has been set, and this new calibration value is applied to the detected differential pressure values from EGR pressure sensors 28, 30. In the disclosed embodiment, a time period 340 may represent a period after a calibration process where the expected differential pressure is approximately equal to the measured differential pressure, and the calibration value is set to zero and no calibration is applied to the differential pressure values from EGR pressure sensors 28, 30.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed calibration system without departing from the scope of the disclosure. Other embodiments of the calibration system will be apparent to those skilled in the art from consideration of the specification and practice of the calibration system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

Claims

1. A method of controlling EGR in an engine system, comprising the steps of:

(a) determining a differential pressure across an EGR valve using an EGR pressure sensing system;

(b) comparing the determined differential pressure across the EGR valve to an expected differential pressure across the EGR valve; and

(c) calibrating the EGR pressure sensing system based on the comparison while the engine system is in operation.

2. A method of controlling EGR in an engine system according to claim 1, further comprising the step of fully opening an EGR valve for a calibration capture period prior to step (a).

3. A method of controlling EGR in an engine system according to claim 2, wherein step (a) is determined during the calibration capture period.

4. A method of controlling EGR in an engine system according to claim 3, wherein the differential pressure is measured at defined intervals during the calibration capture period and an average of the differential pressures is calculated.

5. A method of controlling EGR in an engine system according to claim 1, wherein in step (a) the differential pressure is measured at defined crank shaft positions.

6. A method of controlling EGR in an engine system according to claim 2 or claim 3, further comprising the step of determining an engine speed and a fuel injection quantity during the calibration capture period.

7. A method of controlling EGR in an engine system according to any one of the preceding claims, wherein in step (b) the expected differential pressure is determined from a model based on at least the engine speed and fuel injection quantity.

8. A method of controlling EGR in an engine system according to any one of the preceding claims, wherein the calibration of step (c) comprises adjusting future differential pressure determinations based on a calibration value calculated based on a difference between the determined differential pressure and the expected differential pressure.

9. A method of controlling EGR in an engine system, comprising:

fully opening an EGR valve for a calibration capture period;

determining a differential pressure across the EGR valve during the calibration capture period using an EGR pressure sensing system;

determining an engine speed and a fuel injection quantity during the calibration capture period;

comparing the determined differential pressure across the EGR valve to an expected differential pressure across the EGR valve, the expected differential pressure determined from a model based on at least the engine speed and fuel injection quantity; and

adjusting future differential pressure determinations based on a calibration value calculated based on a difference between the determined differential pressure and the expected differential pressure.

10. A method of controlling EGR in an engine system according to any one of the preceding claims, wherein the differential pressure is determined using an EGR valve intake pressure sensor and an EGR valve outlet pressure sensor.

11. A method of controlling EGR in an engine system according to any one of claims 1 to 6, wherein the differential pressure is determined using an EGR differential pressure sensor.

12. A method of controlling EGR in an engine system according to any one of the preceding claims, further comprising the step of checking engine conditions to determine whether the calibration process should be initiated/aborted.

13. A method of controlling EGR in an engine system according to any one of the preceding claims, further comprising the step of aborting the control strategy if the EGR valve has not opened to more than a threshold percentage of its opening capacity.

14. A method of controlling EGR in an engine system according to any one of the preceding claims, wherein the pressure differential is determined after the EGR valve has been opened for a predetermined threshold amount of time.

15. A method of controlling EGR in an engine system according to any one of the preceding claims, wherein the method is carried out at a time when the differential pressure across the fully open EGR valve is expected to be zero.