System and method for estimating EGR mass flow rates

A system and method are provided for estimating an instantaneous EGR mass flow rate corresponding to a flow rate of exhaust gas through an exhaust gas recirculation (EGR) conduit fluidly coupled between an exhaust manifold and an intake manifold of an internal combustion engine with an EGR cooler positioned in-line with the EGR conduit. An operating position of the engine is monitored, and the instantaneous EGR mass flow rate is estimated at each of a plurality of fixed increments of the engine position based on EGR cooler outlet temperature, intake manifold pressure and a pressure differential across a flow restriction disposed in-line with the exhaust gas conduit between the EGR cooler and the intake manifold.

FIELD OF THE INVENTION

The present invention relates generally to internal combustion engines including an exhaust gas recirculation (EGR) system, and more specifically to systems and methods for determining the mass flow rate of exhaust gas through such an EGR system, i.e., for determining EGR mass flow rates.

BACKGROUND

When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted engine emissions, such as oxides of nitrogen, e.g., NOx. One conventional way of reducing such unwanted emissions is to direct some of the exhaust gas produced by the engine back into the air charge that will be combusted by the engine via a so-called exhaust gas recirculation (EGR) system.

In conventional EGR systems EGR mass flow rate may typically be estimated as a function of the square root of an average delta pressure across a flow restriction orifice in-line with an EGR conduit connected between the exhaust manifold and the intake manifold of the engine. Under steady state, e.g. constant, EGR flow conditions the conventional EGR flow rate estimation technique can produce accurate results. However, under transient engine operating conditions inaccuracies arise in the conventional EGR mass flow rate estimation process just described due to the pulsating nature of EGR flow under such transient operating conditions. Under such transient operating conditions, the average value of the EGR mass flow rate cannot be accurately computed from the average delta pressure value due to the inherent non-linearity associated with the square root term. It is accordingly desirable to be able to estimate instantaneous mass flow rates of exhaust gas through such an EGR system for more accurate diagnostic and/or engine control purposes.

SUMMARY

The present invention may comprise one or more of the features recited in the attached claims, and/or one or more of the following features and combinations thereof. A method is provided for estimating an instantaneous flow rate of exhaust gas through an exhaust gas recirculation (EGR) conduit fluidly coupled between an exhaust manifold and an intake manifold of an internal combustion engine, wherein the EGR conduit includes an EGR cooler disposed in-line therewith. The method may comprise monitoring an operating position of the engine, and executing the following steps at each of a plurality of fixed increments of the engine position, sampling an EGR cooler outlet temperature corresponding to a temperature of gas exiting a gas outlet of the EGR cooler, sampling a pressure differential across a flow restriction disposed in-line with the exhaust gas conduit between the EGR cooler and the intake manifold, sampling an intake manifold pressure corresponding to fluid pressure within the intake manifold, estimating the instantaneous mass flow rate of exhaust gas through the EGR conduit based on the sampled pressure differential, the EGR cooler outlet temperature and the intake manifold pressure, and storing the estimated instantaneous mass flow rate of exhaust gas in a memory unit.

The fixed increments may be selected such that the sampling of the EGR cooler outlet temperature, the pressure differential across the flow restriction and the intake manifold pressure occur at least 8-10 times faster than a firing cycle of the engine.

The method may further comprise determining an average EGR mass flow rate by averaging a number of values of the estimated instantaneous mass flow rate of exhaust gas through the EGR conduit. The method may further comprise storing the average EGR mass flow rate in the memory unit.

The method may further comprise estimating the instantaneous mass flow rate of exhaust gas through the EGR conduit based on an instantaneous EGR mass flow rate model that includes a number of model constants.

In one embodiment, the instantaneous EGR mass flow rate model may be EGRFR=[CD*AFR*sqrt[(2*ΔP*IMP/(R*COT)]/sqrt[1−(AFR/AU)2], where EGRFR is the instantaneous mass flow rate of exhaust gas through the EGR conduit, COT is the EGR cooler outlet temperature, ΔP is the pressure differential across the flow restriction, IMP is the intake manifold pressure, and CD, AFR, R and AUcomprise the number of model constants. CDmay be a charge density value, AFRmay be a cross-sectional flow area of the flow restriction, AUmay be a cross-sectional area of the EGR conduit and R may be a gas constant. In an alternative embodiment, the instantaneous EGR mass flow rate model may be EGRFR=[CD*AT*(IMP−ΔP)/sqrt(R*COT)]*[ΔP1/γ]*sqrt{[2*γ/(γ−1)]*[1−ΔP](γ-1)}, where EGRFR is the instantaneous mass flow rate of exhaust gas through the EGR conduit, COT is the EGR cooler outlet temperature, ΔP is the pressure differential across the flow restriction, IMP is the intake manifold pressure, and CD, AT, R and γ comprise the number of model constants. In this embodiment, CDmay be a charge density value, ATmay be a cross-sectional flow area of the flow restriction, R may be a gas constant and γ may be a ratio of specific heat capacity at constant pressure to specific heat capacity at constant volume for a cylinder charge.

A system for estimating an instantaneous flow rate of exhaust gas through an exhaust gas recirculation (EGR) conduit fluidly coupled between an exhaust manifold and an intake manifold of an internal combustion engine may comprise an EGR cooler disposed in-line with the EGR conduit, a temperature sensor configured to produce a temperature signal corresponding to a temperature of exhaust gas exiting the EGR cooler, a flow restriction disposed in-line with the EGR conduit between a gas outlet of the EGR cooler and the intake manifold of the engine, a differential pressure sensor fluidly configured to produce a differential pressure signal corresponding to a differential pressure across the flow restriction, a pressure sensor configured to produce a pressure signal corresponding to a pressure within the intake manifold of the engine, an engine position sensor configured to produce an engine position signal that corresponds to engine position relative to a reference position, and a control circuit including a memory having instructions stored therein that are executable by the control circuit to monitor the engine position signal and estimate at each of a plurality of fixed increments of the engine position the instantaneous mass flow rate of exhaust gas through the EGR conduit based on the temperature signal, the differential pressure signal and the pressure signal.

The instructions stored in the memory may include instructions that are executable by the control circuit to store the estimated instantaneous mass flow rate in the memory.

The instructions stored in the memory may include instructions that are executable by the control circuit to compute an average EGR mass flow rate value based on a number of most recently estimated values of the instantaneous mass flow rate of exhaust gas through the EGR conduit. The instructions stored in the memory may further include instructions that are executable by the control circuit to store the average EGR mass flow rate value in the memory.

The differential pressure sensor may be configured to sample the pressure differential across the flow restriction at a sampling rate that is at least 8-10 times faster than a firing cycle of the engine over a full range of engine rotational speeds.

In one embodiment, the instructions stored in the memory may include instructions that are executable by the control circuit to estimate the instantaneous mass flow rate of exhaust gas through the EGR conduit according to the equation EGRFR=[CD*AFR*sqrt[(2*ΔP*IMP/(R*COT)]/sqrt[1−(AFR/AU)2], where EGRFR is the instantaneous mass flow rate of exhaust gas through the EGR conduit, COT is the EGR cooler outlet temperature, ΔP is the pressure differential across the flow restriction, IMP is the intake manifold pressure, and CD, AFR, R and AUare constants. CDmay be a charge density value, AFRmay be a cross-sectional flow area of the flow restriction, AUmay be a cross-sectional area of the EGR conduit and R may be a gas constant. Alternatively, the instructions stored in the memory may include instructions that are executable by the control circuit to estimate the instantaneous mass flow rate of exhaust gas through the EGR conduit according to the equation EGRFR=[CD*AT*(IMP−ΔP)/sqrt(R*COT)]*[ΔP1/γ]*sqrt{[2*γ/(γ−1)]*[1−ΔP](γ-1)}, where EGRFR is the instantaneous mass flow rate of exhaust gas through the EGR conduit, COT is the EGR cooler outlet temperature, ΔP is the pressure differential across the flow restriction, IMP is the intake manifold pressure, and CD, AT, R and γ are constants. CDmay be a charge density value, ATmay be a cross-sectional flow area of the flow restriction, R may be a gas constant, and γ may be a ratio of specific heat capacity at constant pressure to specific heat capacity at constant volume for a cylinder charge. In either case, the constants may be stored in the memory unit, and the instructions stored in the memory may further include instructions that are executable by the control circuit to retrieve the constants from the memory unit prior to estimating the instantaneous flow rate of exhaust gas through the EGR conduit.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to one or more illustrative embodiments shown in the attached drawings and specific language will be used to describe the same.

Referring now toFIG. 1, a diagrammatic illustration of one illustrative embodiment of a system10for estimating EGR mass flow rates is shown. In the illustrated embodiment, the system10includes an internal combustion engine12having an intake manifold14fluidly coupled to an outlet16of a compressor18of a turbocharger20via an intake conduit22. The compressor16includes a compressor inlet24coupled to an intake conduit26for receiving fresh air. In some embodiments, although not shown inFIG. 1, the system10may include an intake air cooler of known construction disposed in line with intake conduit22between the turbocharger compressor18and the intake manifold14of the engine12.

The turbocharger compressor18is mechanically coupled to a turbocharger turbine30via a rotatable drive shaft28, and the turbine30includes a turbine inlet32fluidly coupled to an exhaust manifold34of engine12via an exhaust conduit36. The turbine30further includes a turbine outlet38fluidly coupled to ambient via an exhaust conduit40.

In the embodiment illustrated inFIG. 1, the system10further includes an exhaust gas recirculation (EGR) system45including an EGR cooler44disposed in-line with an EGR conduit42that is fluidly coupled at one end to the intake conduit22and an opposite end to the exhaust conduit36. The EGR system45further illustratively includes a conventional EGR valve46disposed in-line with the EGR conduit between the EGR cooler44and the intake conduit22. The EGR valve46is illustratively controllable in a conventional manner to selectively control the flow of exhaust gas through the EGR conduit42.

In the illustrated embodiment, the EGR system45further includes a flow restriction48(FR) disposed in-line with the EGR conduit42between the EGR valve46and the intake conduit22in embodiments that include the EGR valve46, or between the EGR cooler44and the intake conduit22in embodiments that do not include an EGR valve46. Alternatively, the flow restriction48may be positioned between the EGR cooler44and the EGR valve46in embodiments that include the EGR valve46. In the illustrated embodiment, the flow restriction48is provided in the form of a portion of the EGR conduit42that has a reduced, fixed cross-sectional area that is less than that of the cross-sectional area of the EGR conduit42upstream and downstream of the flow restriction48. Alternatively, the flow restriction48may be provided in the form of an orifice or other conventional exhaust gas flow reducing structure. Alternatively still, the flow restriction48may be the EGR valve46. In this embodiment, the cross-sectional flow area of the EGR valve46is less than that of the EGR conduit42, thereby restricting the flow of exhaust gas through the EGR conduit42, and the flow restriction48illustrated inFIG. 1may be omitted in this alternative embodiment.

The system10further includes a control circuit50that is generally operable to control and manage the overall operation of the engine12. The control circuit50includes a memory unit55as well as a number of inputs and outputs for interfacing with various sensors and systems coupled to the engine12. The control circuit50, is illustratively microprocessor-based, although this disclosure contemplates other embodiments in which the control circuit50may alternatively be or include a general purpose or application specific control circuit capable of operation as will be described hereinafter. In any case, the control circuit50may be a known control unit sometimes referred to as an electronic or engine control module (ECM), electronic or engine control unit (ECU) or the like. Illustratively, the memory55of the control circuit50has stored therein one or more sets of instructions that are executable by the control circuit50, as will be described in greater detail hereinafter, to estimate the mass flow rate of exhaust gas moving through the EGR conduit42.

The control circuit50includes a number of inputs for receiving signals from various sensors or sensing systems associated with system10. The control circuit50is generally operable in a conventional manner to sample the signals produced by the various sensors or sensing systems and to processes the sampled signals to determine the associated engine operating condition. For example, the system10includes an intake manifold pressure sensor52that is disposed in fluid communication with the intake manifold14and that is electrically connected to an intake manifold pressure input, IMP, of the control circuit50via a signal path54. The intake manifold pressure sensor52may be of known construction, and is operable to produce a pressure signal on the signal path54that corresponds to the pressure of a “charge” flowing into the intake manifold14. The term “charge,” for purposes of this disclosure is generally defined as the gas flowing into the intake manifold14via the conduit22that is generally made up of fresh air supplied to the intake conduit22, e.g., via the turbocharger compressor18, combined with recirculated exhaust gas supplied by the EGR conduit42. Although the intake manifold pressure sensor52is illustrated inFIG. 1as being positioned in fluid communication with the intake manifold14, the sensor52may alternatively be positioned in fluid communication with the intake conduit22downstream of the junction of the EGR conduit42and the intake conduit22. In any case, the memory55of the control circuit50includes one or more sets of conventional instructions that are executable by the control circuit50to process the intake manifold pressure signal produced by the intake manifold pressure sensor52and determine instantaneous intake manifold pressure therefrom.

The system10further includes an engine speed and position sensor56that is electrically connected to an engine speed and position input, ESP, of the control circuit50via a signal path58. The engine speed and position sensor56is conventional and is operable to produce a signal from which the rotational speed of the engine, ES, and the position of the engine, EP, relative to a reference position, can be conventionally determined by the control circuit50. The engine position, EP, may, for example, be or include an angle of the engine crankshaft (not shown), i.e., crank angle, relative to a reference crank angle, e.g., top-dead-center (TDC) of a specified one of the pistons (not shown). In one embodiment, the sensor56is a Hall effect sensor operable to sense engine speed and position by sensing passage thereby of a number of spaced-apart teeth formed on a gear or tone wheel that rotates synchronously with the engine crankshaft (not shown). In one example implementation, which should not be considered to be limiting in any way, the gear or tone wheel has a sufficient number of teeth that allows for detection by the sensor56of a tooth every 6 degrees of rotation. Alternatively, the engine speed and position sensor56may be any other known sensor operable as just described including, but not limited to, a variable reluctance sensor or the like. Alternatively still, the engine speed and position sensor56may be provided in the form of two separate sensors; one that senses only engine rotational speed and the other that senses only engine position. In any case, the memory55of the control circuit50includes one or more sets of conventional instructions that are executable by the control circuit50to process the engine speed and position signal produced by the engine speed and position sensor56and determine instantaneous engine speed and engine position therefrom.

The system10further includes an EGR cooler outlet temperature sensor60disposed in fluid communication with the EGR conduit42between the gas outlet of the EGR cooler44and the intake conduit22, and electrically connected to an EGR cooler outlet temperature input, COT, of the control circuit50via a signal path62. The intake manifold temperature sensor48may be of known construction, and is operable to produce a temperature signal on the signal path50that corresponds to the temperature of exhaust gas exiting the EGR cooler44. The memory55of the control circuit50includes one or more sets of conventional instructions that are executable by the control circuit50to process the EGR cooler outlet temperature signal produced by the EGR cooler outlet temperature sensor60and determine instantaneous EGR cooler outlet temperature therefrom.

The system10further includes a differential pressure sensor, or ΔP sensor,64having one end that is fluidly coupled via a conduit66to the EGR conduit42adjacent to the exhaust gas outlet of the flow restriction48, and that is fluidly coupled at its opposite end to the EGR conduit42adjacent to an exhaust gas inlet of the flow restriction48via a conduit68. Alternatively, the ΔP sensor64may be fluidly coupled across another flow restriction structure disposed in-line with the EGR conduit42, or across the EGR valve46in which case the flow restriction48may be omitted. In any case, the ΔP sensor64is electrically connected to a ΔP input of the control circuit42via signal a path70, and is operable to produce a differential pressure signal on the signal path70that corresponds to the pressure differential across the flow restriction48or other flow restriction structure disposed in-line with the EGR conduit48.

The ΔP sensor64is illustratively a wide bandwidth sensor that is capable of sampling the pressure differential across the flow restriction48at a rate that is high enough to capture instantaneous features of the pulsating nature of this pressure differential. The EGR flow pulses are excited by the intake and exhaust processes of the engine12. As such, the dominant feature of the EGR mass flow is a peak flow rate resulting from cylinder blowdown events that occur during the engine exhaust process. Exhaust events associated with each cylinder of the engine cause corresponding instantaneous increases in the exhaust manifold pressure which, in turn, cause corresponding pulses of high EGR flow rate.

The pulses of high EGR flow rate are periodic with respect to angular displacement of the engine crankshaft. The corresponding crank-angle periodic pressure differential signal, ΔP, has a spectral density function that varies with engine rotational speed just as the cylinder firing frequency is a function of engine rotational speed. Measurement and analysis of the ΔP signal has shown that this signal is well represented by a spectral density function which is truncated at two times the firing frequency of the engine12. From a practical standpoint, the sampling rate of the pressure differential across the flow restriction48by the ΔP sensor64is selected to be at least 8-10 times the firing frequency of the engine12. The ΔP sensor64must therefore be capable of sampling the pressure differential across the flow restriction48at a sampling rate of at least 8-10 times the firing frequency of the engine12over the entire range of possible engine rotational speeds. In one embodiment, for example, engine rotational speeds may range from near zero to 2500 RPM, although other engine rotational speed ranges are contemplated.

Using the above example of sampling the engine speed and position signal every 6 degrees of engine crank angle, it has been determined that a ΔP sensor64capable of sampling the pressure differential across the flow restriction48at the same rate provides for an adequate sampling of this pressure differential over one example engine speed range of up to about 2500 RPM. However, this should not be considered to be limiting in any way, and it will be understood that this disclosure contemplates embodiments in which the ΔP sensor64is configured to sample the pressure differential across the flow restriction48at faster or slower sampling rates. In any case, the memory55of the control circuit50includes one or more sets of conventional instructions that are executable by the control circuit50to process the pressure differential signal produced by the ΔP sensor64and determine therefrom the instantaneous pressure differential across the flow restriction48.

Referring now toFIG. 2, one illustrative embodiment of some of the functional features of the control circuit50are shown that relate to the estimation of the mass flow rate of exhaust gas through the EGR conduit42. It will be understood that the logic components shown inFIG. 2are provided only by way of example, and that other conventional logic structures and/or techniques may be used to estimate the flow rate of exhaust gas through the EGR conduit42as described herein. Illustratively, the control circuit45illustrated inFIG. 2includes an EGR mass flow rate estimation logic block80that receives as inputs the engine speed and position signal, ESP, the ΔP signal, the intake manifold pressure signal, IMP, and the EGR cooler outlet temperature signal, COT. The control circuit50further includes a model constants block82having a number of model constants stored therein. The EGR mass flow rate estimation logic illustratively includes instructions stored therein that are executable by the control circuit50to process ESP in a conventional manner to determine engine position, e.g., crank angle relative to a reference crank angle, to sample ΔP, IMP and COT at a rate determined by engine position, e.g., crank angle, and to then estimate the instantaneous EGR mass flow rate, EGRFRIas a function of the sampled ΔP, IMP and COT values.

The control circuit50further includes an instantaneous EGR mass flow rate storage location84in which any number of instantaneous EGR mass flow rate values, EGRFRI, are stored. Illustratively, the instantaneous EGR mass flow rate values, EGRFRI, are also made available to one or more other algorithms or instruction sets executed by the control circuit50. The control circuit50further includes an averaging logic block86that is configured to receive the instantaneous EGR mass flow rate values, EGRFRI, and compute an average, EGRFRAV, of the most recent M instantaneous EGR mass flow rate values, where M may be any positive integer greater than 1. Illustratively, the averaging logic block86may be configured to compute EGRFRAVaccording to any conventional linear, non-linear, adaptive, weighted or unweighted averaging technique such as, for example, but not limited to, algebraic averaging, differential averaging, running or moving averaging, or the like. In any case, the control circuit50further includes an average EGR mass flow rate storage location88in which any number of average EGR mass flow rate values, EGRFRAV, are stored. Illustratively, the one or more average EGR mass flow rate values, EGRFRAV, are also made available to one or more other algorithms or instruction sets executed by the control circuit50.

Referring now toFIG. 3, a flowchart is shown of one illustrative embodiment of the process80for estimating the flow rate of exhaust gas through the EGR conduit42. Illustratively, the process80represents the logic of the EGR mass flow rate estimation block80, and is therefore provided in the form of instructions that are stored in the memory unit55and that are executable by the control circuit50to estimate the EGR mass flow rate. The process80begins at step100where the control circuit50is operable to monitor the engine position, EP. Illustratively, the control circuit50is operable at step100to monitor EP by monitoring the engine speed and position signal, ESP, produced by the engine speed and position sensor56on the signal path58, and processing this signal in a conventional manner to determine EP. Thereafter at step102, the control circuit50is operable to determine whether the engine position, EP, is equal to a predefined reference engine position, REFP. Illustratively, REFP corresponds to a position of the engine crank shaft (not shown) at the beginning of an engine cycle, although other reference engine positions are contemplated by this disclosure. The beginning of an engine cycle may be determined from ESP in a conventional manner, or may be stored in the memory55. If, at step102, the control circuit50determines that EP is not equal to REFP, execution of the process80loops back to step100. If, on the other hand, the control circuit50determines at step102that EP=REFP, execution of the process80advances to step104. Illustratively, steps100and102will generally be executed only until the reference position, REFP, is found after engine start up. Thereafter, the flow rate of exhaust gas through the EGR conduit42will be determined at predetermined increments of engine position as will be described in more detail below.

At step104, the control circuit50is operable to sample the differential pressure signal, ΔP, on the signal path70, the intake manifold pressure signal, IMP, on the signal path54and the EGR cooler outlet temperature signal, COT, on the signal path62. Thereafter at step106, the control circuit50is operable to retrieve the model constants, MC, from the memory location82(seeFIG. 2). Thereafter at step108, the control circuit50is operable to estimate the instantaneous EGR mass flow rate, EGRFRi, as a function of ΔP, IMP, COT and MC. In one illustrative embodiment, the instantaneous EGR mass flow rate model stored in the memory55of the control circuit50and executed at step108of the algorithm 80 is given by the equation:
EGRFR=[CD*AFR*sqrt[(2*ΔP*EGD)]/sqrt[1−(AFR/AU)2]  (1),
where CDis a discharge coefficient, e.g., 0.67, AFRis the cross-sectional flow area of the flow restriction48, AUis the cross-sectional flow area of the EGR conduit42upstream of the flow restriction48, EGD is the exhaust gas density. Illustratively, the exhaust gas density is given by the equation:
EGD=IMP/(R*COT)  (2),
where R is a gas constant, e.g., R=287 J/Kg deg K. Substituting equation (2) into equation (1) yields the following equation which is illustratively executed at step108of the algorithm 80:
EGRFR=[CD*AFR*sqrt[(2*ΔP*IMP/(R*COT)]/sqrt[1−(AFR/AU)2]  (3).
In this illustrative embodiment, the model constants, MC, retrieved from the memory55at step106are CD, AFR, R and AU.

In an alternate embodiment, the instantaneous EGR mass flow rate model stored in the memory55of the control circuit50and executed at step108of the algorithm 80 is given by the equation:
EGRFR=[CD*AT*(IMP−ΔP)/sqrt(R*COT)]*[ΔP1/γ]*sqrt{[2*γ/(γ−1)]*[1−ΔP](γ-1)}  (4),
where CDis the discharge coefficient and is a stored constant, e.g., 0.67, ATis the cross-sectional flow area of the flow restriction48and is a stored constant based on the physical dimensions of the flow restriction48, R is a gas constant, e.g., R=287 J/Kg deg K and γ is the ratio of specific heat capacity at constant pressure to specific heat capacity at constant volume for the cylinder charge and is a stored constant, e.g., 1.35. In this alternate embodiment, the model constants, MC, retrieved from the memory55at step106are CD, AT, R and γ. It will be understood that this disclosure contemplates other embodiments in which the EGR flow rate estimation model includes more, fewer and/or different input parameters.

Following step108, the control circuit50is operable at step110to store the estimated instantaneous EGR mass flow rate value, EGRFRI, in the memory location84. Also following step108, the control circuit50is further operable at step112to increment the reference engine position value, REFP, by an increment value, INC. Using the example provided hereinabove, INC is illustratively 6 degrees such that the reference engine position, REFP, is set to 6 degrees advanced from the previous value of REFP. It will be understood, however, that INC may alternatively be set to other incremental angle values. In any case, the algorithm 80 loops from step112back to step100.

The algorithm 80 also advances from step108to step114where the control circuit50is operable to compute an average EGR mass flow rate value, EGRFRAV, based on the M most recent EGRFRIvalues, where M may be any positive integer greater than 1. The averaging technique used by the control circuit50at step114may illustratively be any conventional data averaging technique, non-limiting examples of which have been described hereinabove. Following step114, the control circuit50is operable at step116to store the average EGR mass flow rate value, EGRFRAV, in the memory location88.