Method for comparing fuel consumption values ​​to stored energy

Abstract

Method for a vehicle comprising: - Determining a change in the square of the vehicle speed by a controller (12); - Comparing the change in the square of the vehicle speed with a first threshold value by the controller (12); - Determining a change in the vehicle's altitude by the controller (12); - Comparing the change in the vehicle's altitude with a second threshold value by the controller (12);if a positive change in the square of the vehicle speed is greater than the first threshold, and / or if a positive change in the vehicle altitude is greater than the second threshold: - Estimating a fuel conversion factor due to stored vehicle energy by the controller (12), wherein the conversion factor is determined by the controller (12) based on a difference between a fuel flow rate measured under steady-state driving conditions and a current fuel flow rate; - Compensating a measured fuel consumption value for changes in stored energy based on the estimated conversion factor by the controller (12) to obtain a compensated instantaneous fuel consumption value; and - Displaying the compensated instantaneous fuel consumption value to the driver of the vehicle.

Description

The present description relates to compensating an instantaneous fuel consumption value for stored vehicle energy.The fuel consumption of a vehicle may be indicated to a driver of the vehicle as a long term average and / or as an instantaneous fuel consumption value. The current fuel consumption value provides real-time fuel consumption data that allows the driver to adjust his / her driving style to improve fuel consumption. However, due to stored kinetic and potential energy, the displayed instantaneous fuel consumption values may have large fluctuations, e.g., zero at acceleration and infinity at deceleration, making such values useless to the driver unless they are highly filtered.An example approach to matching the mileage indication to stored energy is shown by Sim in U.S. patent application US 2011 / 0 276 260 A1. Here, an effective amount of consumed fuel is determined by measuring an actually consumed fuel amount and subtracting a fuel equivalent of both the stored energy and the consumed energy from the actually consumed fuel amount. A mileage based on the effective fuel amount is then displayed to the driver of the vehicle.However, the inventors herein have recognized potential issues with the above-mentioned approach. As an example, the above approach uses extensive on-board computations and measurements stored in the memory of the vehicle prior to delivery from a plant. For example, a conversion coefficient related to a dynamic energy storage efficiency and an electrical energy storage efficiency is integrated into the force equivalent of the stored energy. These efficiencies are measured on the test bench with energy supplied from a generator separate from the vehicle and are stored in the vehicle memory as a priori information. Furthermore, a change in the height position is measured by an inclinometer installed in the vehicle body, which can tend to produce an offset error based on the load of the vehicle. The Sim approach also involves several complicated and sophisticated calculations, including a vehicle mass calculation to determine stored kinetic and potential energy, a rotational angular velocity calculation to determine rotational velocity, and a battery power calculation to determine stored electrical energy.US 5 578 748 A discloses a method and system for calculating the effective fuel consumption of a fuel consuming engine in a vehicle. The effective fuel consumption is calculated in consideration of the chemical energy contained in the fuel and the change in the kinetic energy of the vehicle. The effective fuel consumption is also calculated with further consideration of the change in potential energy of the vehicle. The chemical energy contained in the fuel is determined by detecting the fuel mass flow. The kinetic energy is determined by detecting the change in the speed of the vehicle and the mass of the vehicle. The potential energy is determined by detecting the change in the height of the vehicle. The effective fuel consumption is indicated to the driver of the vehicle.The technical problem to be solved can be seen in eliminating or at least reducing the disadvantages of the prior art. The object is achieved by the subject matters of the independent claims.The inventors herein have recognized an approach to at least partially solve the above-mentioned problems. In an exemplary approach, a method for a vehicle is provided according to the subject matter of claim 1, which uses a conversion factor for stored energy. The method includes estimating a conversion factor for fuel based on stored vehicle energy and matching a fuel consumption value by the estimated conversion factor when the vehicle experiences a sufficient change in one or more of the square vehicle speed or the vehicle altitude. In this way, a simplified approach without too many inputs may be used to compensate for a fuel consumption value around stored energy.For example, when a vehicle is running under steady-state driving conditions, e.g., steady-speed driving, a fuel consumption value (MPG) may be calculated. Steady state driving conditions may include conditions where changes in both the quadratic vehicle speed and vehicle altitude are below a respective threshold. Under conditions where the vehicle undergoes a sufficient increase in one or both of a square vehicle speed and a vehicle attitude, a conversion factor is determined based on the fuel consumption value calculated under steady state driving conditions. Thus, the conversion factor is determined when energy is added to the vehicle system as kinetic energy, or as potential energy, or both. The conversion factor is based on an estimated fuel flow due to stored vehicle energy, which is calculated by subtracting a fuel flow rate measured during steady state driving conditions from a present fuel flow rate. As such, a difference between the additional fuel flow rate at conditions where energy is added to the system and the steady state fuel flow rate is used to determine the stored vehicle energy conversion factor. The conversion factor may be directly proportional to fuel flow due to stored vehicle energy and inversely proportional to both a change in quadratic vehicle speed and vehicle attitude. The change in vehicle attitude may be measured by an inclinometer and corrected for offset errors due to vehicle loads. The conversion factor is used to compensate a measured fuel consumption value for changes in stored energy.In this way, each time specific conditions are met, a conversion factor may be learned based on fuel flow, a change in vehicle attitude, and a change in vehicle quadratic speed, and may be stored in a memory of the controller. Similarly, fuel consumption values may be calculated during steady state driving conditions when certain conditions are met and stored in the memory of the controller. The controller may be configured to use a moving average of each of these values when performing further calculations. The correction of the fuel consumption values can be steadily improved by repeatedly learning and adjusting the conversion factor while the vehicle is being driven. Thus, labor intensive on-test efficiency calculations, a priori knowledge of fuel energy, and on-board vehicle mass calculations can be reduced by learning the conversion factor as described. Overall, a simpler methodology is provided for compensating for instantaneous fuel consumption by stored energy, which can be used across vehicles when vehicles use different fuels, engine efficiencies fluctuate, and changes in vehicle mass occur.It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages listed above or in any part of this disclosure. FIG. 1 illustrates a schematic illustration of an internal combustion engine. FIG. 2 is a schematic illustration of a vehicle instrument panel. FIG. 3 is an example flow chart for a routine that displays fuel consumption values at periodic intervals. FIGS. 4A and 4B show an example routine for calculating a compensated fuel consumption value according to the present disclosure. FIG. 5 illustrates an example flowchart for calculating a stored vehicle energy conversion factor based on input conditions being met. FIG. 6 illustrates an example flowchart for determining a steady state fuel consumption value, in accordance with the present disclosure. FIG. 7 is an exemplary relationship between fuel consumption or mileage and the stationary vehicle speed. FIG. 8 illustrates an example flowchart for a routine that calculates an offset error for values from an inclinometer. FIG. 9 shows example vehicle operation depicting driving conditions where the stored energy conversion factor and the steady state fuel consumption values may be obtained.The following description relates to systems and methods for displaying a fuel consumption value of an internal combustion engine, such as the internal combustion engine system of FIG. 1, where the fuel consumption value is compensated for by stored vehicle energy. The fuel consumption value is displayed to a driver of a vehicle on an instrument panel, such as the example instrument panel of FIG. 2 ; a controller of the vehicle may display the fuel consumption value at periodic intervals (FIG. 3 ) after compensating the values for stored vehicle energy (FIG. 4 ). Stored vehicle energy may include kinetic energy due to changes in vehicle speed and potential energy due to changes in vehicle attitude. The vehicle height may be measured using the values of an inclinometer that may be corrected for an offset error (FIG. 8 ). The compensation for stored vehicle energy may be performed using a conversion factor calculated during driving conditions where stored energy is increased (FIG. 5 ). Further, the conversion factor may be based on a steady state fuel consumption value determined during steady state driving conditions (FIG. 6 ). Fuel consumption values may have smaller variations within a certain range of steady-state vehicle speeds, as shown in FIG. 7. An example of improvements in instantaneous fuel consumption values is shown in example operation in FIG. 9.FIG. 1 is a schematic diagram showing one cylinder of the multi-cylinder internal combustion engine 10 that may be included in a propulsion system of an automobile. The engine 10 may be controlled at least in part by a control system including the controller 12 and by input of a vehicle user 132 via an input device 130. In this example, the input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Combustion chamber 30 (also known as cylinder 30) of internal combustion engine 10 may include combustion chamber walls 32 with a piston 36 positioned therein. The piston 36 may be coupled to the crankshaft 40 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. The crankshaft 40 may be coupled to at least one drive wheel (not shown) of a vehicle via an intermediate transmission system 50. Further, a starter motor may be coupled to crankshaft 40 via a flywheel (not shown) to enable cranking operation of engine 10.Combustion chamber 30 may receive intake air from intake manifold 44 via intake passage 42 and may exhaust combustion exhaust gases via exhaust manifold 48. Intake manifold 44 and exhaust manifold 48 may selectively communicate with combustion chamber 30 via respective intake valve 52 and exhaust valve 54. In some embodiments, combustion chamber 30 may include two or more intake valves and / or two or more exhaust valves.The intake valve 52 may be actuated by the controller 12 via the actuator 152. Similarly, the exhaust valve 54 may be activated by the controller 12 via the actuator 154. Under some conditions, the controller 12 may vary the signals provided to the actuators 152 and 154 to control the opening and closing of the respective intake and exhaust valves. The position of the intake valve 52 and the exhaust valve 54 may be determined by the respective valve position sensors (not shown). The valve actuators may be of the electric valve actuation type or of the cam actuation type or a combination thereof. Intake and exhaust valve timings may be controlled simultaneously or with any of the following: variable intake cam timings, variable exhaust cam timings, two independently variable cam timings, or fixed cam timings. Each cam actuation system may include one or more cams and utilize one or more of the following systems: cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) that may be operated by controller 12 to vary valve operation. For example, cylinder 30 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and / or VCT. In other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system or a variable valve timing actuator or actuation system.Fuel injector 66 is shown coupled directly to combustion chamber 30 such that fuel is injected directly thereto in proportion to the pulse width of signal FPW received from controller 12 via electronic driver stage 69. In this way, fuel injector 66 provides what is referred to as direct injection of fuel into combustion chamber 30. For example, the fuel injector may be mounted in the side of the combustion chamber or in the head of the combustion chamber. Fuel may be delivered to fuel injector 66 by a fuel system (not shown), including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chamber 30 may alternatively or additionally include a fuel injector disposed in intake manifold 44 in a configuration that provides what is known as port injection of fuel into the port upstream of combustion chamber 30.Intake passage 42 may include a throttle 64 having a throttle 61. In this particular example, the position of throttle 61 may be varied by controller 12 via a signal provided to an electric motor or actuator included in throttle 64, a configuration commonly referred to as electronic throttle control (ETC). In this way, throttle 64 may be operated to vary intake air provided to combustion chamber 30, among other engine cylinders. The position of throttle 61 may be provided to controller 12 by throttle position signal TP. Intake passage 42 may include a mass airflow sensor 120, an atmospheric pressure sensor 128, and an intake manifold pressure sensor 124 for providing respective signals MAF (mass airflow), BP (barometric pressure), and MAP (intake manifold barometric pressure) to controller 12.Ignition system 88 may provide spark to combustion chamber 30 via spark plug 92 in response to spark advance signal SA (pre-ignition) from controller 12 under selected operating modes. Although spark components are shown, in some embodiments, combustion chamber 30, or one or more other combustion chambers of engine 10, may be operated in a compression ignition mode with or without spark.Exhaust gas sensor 126 is shown coupled to exhaust manifold 48 upstream of emission control 70. Sensor 126 may be any sensor suitable for providing an indication of exhaust air-fuel ratio, such as a linear oxygen sensor or a wide band oxygen sensor (UEGO), a two-point oxygen sensor or oxygen sensor (EGO), a heated oxygen sensor (HEGO), a NOx, HC, or CO sensor. Emission control device 70 is shown disposed downstream of exhaust gas sensor 126. The device 70 may be a three-way catalyst (TWC), a nitrogen oxide trap, various other emission control devices, or combinations thereof. In some embodiments, the emission control device 70 may be periodically reset during operation of the internal combustion engine 10 by operating at least one cylinder of the internal combustion engine at a particular air-fuel ratio.Controller 12 is shown in FIG. 1 as a microcomputer including microprocessor unit 102, input / output ports 104, an electronic storage medium (or non-transitory memory) for executable programs and calibration values shown as read only memory (ROM) chip 106 in this particular example, random access memory (RAM) 108, keep alive memory (KAM) 110, and a data bus. Controller 12 may receive various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor 120, engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114, vehicle speed from vehicle speed sensor 142, grade values from inclinometer 146, profile ignition pickup (PIP) signal from Hall effect sensor 38 (or other type) coupled to crankshaft 40, and throttle position (TP) from throttle position sensor 58. Manifold pressure signal MAP from a manifold pressure sensor 124 may be used to provide an indication of vacuum or pressure in the intake manifold. An atmospheric pressure sensor 128 may provide atmospheric pressure values that may also be used to determine a grade. It should be noted that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor may provide an indication of engine torque. Further, this sensor, along with the detected engine speed, may provide an estimate of the charge induced in the cylinder (including air). In one example, the Hall sensor 38, which is also used as an engine speed sensor, may produce a predetermined number of evenly spaced pulses every revolution of the crankshaft.Storage medium read-only memory 106 may be programmed with computer readable data representing instructions executable by processor 102 to perform the methods described below, such as those of FIGS. 3, 4, 5, 6, and 8, as well as other variants that are expected but not specifically listed.As described above, FIG. 1 shows only one cylinder of a multi-cylinder internal combustion engine and that each cylinder similarly includes its own set of intake / exhaust valves, fuel injector, spark plug, etc.Referring now to FIG. 2, it shows a schematic of a dashboard display 200 as viewed by a driver of a vehicle. The instrument panel includes an instrument cluster 204 disposed behind a steering wheel (not shown). The instrument cluster 204 includes various indicators such as a fuel gauge 214, the tachometer 206, the speedometer 220, and the engine temperature gauge 216, as well as indicators and warning lights. In addition to these, an electronic display 208 shows current fuel consumption values (MPG), an approximate distance the vehicle can travel based on the fuel present, outdoor temperature, and includes an odometer display. As such, the electronic display 208 may include other values, and FIG. 2 is a non-limiting example.Example routines that may be executed by the controller 12 to determine and display a fuel consumption value compensated for stored vehicle energy will now be described with reference to FIGS. 3, 4, 5, 6, and 8. As embodied herein, the controller may estimate steady state fuel consumption when the vehicle is driving under steady state conditions. Steady state fuel consumption values may be estimated and stored multiple times during vehicle travel when specific conditions are met. During conditions including positive changes in one or more of the square vehicle speed or vehicle attitude, a conversion factor for fuel may be estimated based on stored energy using the previously measured steady state fuel consumption. The conversion factor values may be estimated and stored in memory each time the vehicle experiences a sufficient increase in the quadratic vehicle speed and / or vehicle attitude. The conversion factor may be used to first correct an observed fuel flow rate, which may then be used to calculate stored energy compensated fuel consumption. The described method provides a simple, yet reliable way of compensating for stored potential and kinetic energy without using complex calculations or measurements of vehicle mass, fuel energy, engine efficiency and the like, which may vary for different vehicles.Referring now to FIG. 3, it shows routine 300 in which it is estimated whether a specific interval has expired to calculate an updated current fuel consumption (FE) value and display it to a driver of a vehicle.At 302, it may be evaluated whether the time since the last display of a fuel consumption value is greater than or equal to a predetermined threshold t. As an example, threshold t may be one second, one-half second, five seconds, or any interval preset in a controller of the vehicle to provide instantaneous or real-time output. If the time since the last fuel consumption value is indicated is not greater than or equal to threshold t routine 300 will not update the previous fuel consumption value at 304 and may be ended.On the other hand, if it is determined in 306 that the time since the last display of the fuel consumption value is equal to or greater than threshold t a fuel consumption calculation and compensation routine may be executed as described below with reference to FIGS. 4A and 4B. At 308, the compensated instantaneous fuel consumption value may be indicated to the driver. Accordingly, routine 300 displays compensated instantaneous fuel consumption values to the driver of the vehicle at periodic intervals.Turning now further to FIGS. 4A and 4B, they show routine 400 for calculating a fuel consumption value compensated for by stored vehicle energy. Specifically, a present fuel flow rate is calculated and compensated for by stored energy, which in turn is used to determine a matched fuel consumption value (MPG).At 402, engine and vehicle operating conditions may be determined and / or measured. Engine operating conditions may include engine load, engine temperature, engine speed, torque output, etc., while vehicle operating conditions may include vehicle speed, vehicle altitude, etc. At 404, a time interval Δt since the previous calculation of the current fuel consumption value may be estimated. At 406, the time since the last calculation of the current fuel consumption value may be set as t 1, the current time may be measured as t 2 at 408, and the time difference between t 2 and t 1 may be calculated as Δt at 410.At 412, routine 400 may determine a fuel flow rate (FFR). The FFR may be synchronized in time with the measurement of vehicle speed. Typically, an estimate of fuel to be injected is determined prematurely so that the calculation of fuel flow may be a few events prior to torque transfer to the vehicle drive wheels. As a result, the fuel flow rate and vehicle speed measurements may be synchronized in time to correspond to the same amount of time for this calculation.At 414, the fuel pulse count may be retrieved from the previous fuel consumption calculation as FPC_ 1, while at 416, the current fuel pulse count may be determined as FPC_ 2. At 418, total fuel flow rate ΔF_cons may be estimated as the difference between FPC_ 2 and FPC_ 1. The FFR may then be calculated at 420 as follows: where k is a conversion factor for fuel mass per pulse and time. As a result, k may assist in converting fuel mass flow rate to gallons and time to hours.Next, at 422, a change in the quadratic vehicle speed may be determined. Stored energy in the form of kinetic energy is directly proportional to the quadratic vehicle speed. Accordingly, a change in kinetic energy is directly proportional to the change in quadratic vehicle speed over a period of time. At 424, the vehicle speed at the last fuel consumption calculation may be retrieved from the memory of the vehicle controller as Vs_ 1, and its square may be determined as (Vs_ 1) 2. At 426, the current vehicle speed may be measured as Vs_ 2, and its square may be determined as (Vs_ 2) 2. The vehicle speed can be measured in a wide variety of ways. In one example, a vehicle speed sensor coupled to the engine transmission may send signals to the vehicle controller. In another example, an average of individual wheel speeds may be used. The measurement may be in miles per hour and routine 400 may convert the vehicle speed measurement in feet per second. The controller may store these values for future computations, e.g., Vs_ 2 and (Vs_ 2) 2. At 428, a difference in the square speeds ΔVs 2 may be determined as (Vs_ 2) 2- ( Vs_ 1) 2.In one example, if the vehicle decelerates as it decelerates, the change in square speeds may be negative. In another example, if the vehicle is accelerating and gaining speed, ΔVs 2 may be positive.At 430, a change in vehicle elevation may be estimated in the unit foot. The change in vehicle attitude may be positive (if going up) or negative (if going down). Instantaneous fuel consumption values may be affected by stored potential energy that is directly proportional to vehicle altitude. For example, uncompensated fuel consumption values may experience a change of about 40% when small slopes are being driven up or down. By adjusting for changes in potential energy as the vehicle climbs or descends slopes, the fuel consumption values may become more accurate. At 432, the vehicle altitude may be retrieved as Vh_ 1 at the last fuel consumption calculation, and the current vehicle altitude Vh_ 2 may be calculated at 434 as follows: where RG_cor is an inclination value from an inclinometer corrected by an offset error due to vehicle loading. As shown above, the vehicle attitude may be determined by multiplying the corrected slope value by the distance travelled and adding the vehicle attitude determined in the last fuel consumption calculation. A grade signal or inclinometer may be corrected for an offset error by comparing altimeter grade and vehicle speed based elevations to those from an atmospheric pressure sensor, as will now be described with reference to FIG. 8.FIG. 8 illustrates a routine 800 for determining correction for values from an inclinometer. Values from an inclinometer may have a higher resolution, but may be subject to offset errors. For example, when the inclinometer is mounted on the vehicle body, the loading of the vehicle may result in an offset error, e.g., there may be a constant inclination error of 3% when the trunk of a car is heavily loaded. An atmospheric pressure sensor may provide values for vehicle attitude without offset errors, but these values may not have sufficient resolution. For example, while each altimeter may result in a 0.01 kPa change in pressure, the atmospheric pressure sensor may more accurately register changes in pressure only over a 2 to 5 meter change in elevation. Thus, the atmospheric pressure sensor may have the required accuracy without being prone to offset errors, but may suffer from lack of resolution. Routine 800 provides an example of correcting the offset error in values from an inclinometer by comparison with altitude values from an atmospheric pressure sensor after the vehicle has experienced a sufficient change in altitude.At 802, a road grade signal RG from the inclinometer may be received by the controller. In one example, RG may be a percentage value, in which case it may be converted to a ratio before proceeding with the calculation described herein. At 804, a vehicle speed Vs may be estimated or measured, and at 806, a height change rate RE may be calculated as follows: RG*Vs.At 808, the height change rate RE versus time may be integrated to obtain a total height change Ei since reset. At 810, routine 800 may determine whether the vehicle has experienced a sufficient change in elevation. The total change in elevation Eimay be compared to threshold value K. In one example, threshold K may be a height of 2 meters, while in another example, it may be 4 meters. Lack of resolution in values from the atmospheric pressure sensor can be overcome by ensuring that the vehicle has undergone sufficient change in elevation.If it is determined at 812 that the change in elevation is less than threshold K routine 800 may wait to calculate the offset correction. However, if the change in altitude is greater than threshold K then control may determine a value Eb for the change in altitude from an on-board atmospheric pressure sensor of the vehicle at 814. At 816, Eiand Ebmay be compared, and at 818, a correction factor for values from the inclinometer may be determined as Eb / Ei. This offset correction factor may be determined such that the values of the change in elevation from both the inclinometer and the atmospheric pressure sensor are the same over a significant change in elevation. Thus, an altimeter value may be corrected 820 to provide corrected slope values RG_cor as follows: RG* Eb / Ei. The correction factor may be stored in the memory of the controller.Referring now back to routine 400: At 438, a change in vehicle height position ΔVh may be determined as a difference between Vh_ 2 and Vh_ 1. Vh_ 2 may be stored in the memory of the controller for the next calculation. Next, at 440, routine 400 may retrieve a mean stored energy conversion factor SE_avg, where SE_avg is the moving mean of multiple calculations of the conversion factor during vehicle operation. The calculation of the conversion factor SE will be further carried out below with reference to FIG. 5.At 442, a fuel flow rate determined at 412 may be compensated for stored vehicle energy. At 444, a compensated fuel flow rate FFR_comp may be estimated as follows: where CK is a calibration constant. In one example, CK may be set to 1, whereas in other examples, CK may be less than 1 if less compensation is desired for the indication of current fuel consumption values.At 446, the calculated compensated fuel flow rate FFR_comp may be stored in memory and a moving average of FFR_comp may be estimated as FFR_comp_avg based on previous calculations of FFR_comp. The moving average calculation may be filtered to remove noise from measurements of vehicle speed. It should be appreciated that during most driving conditions, except for transient conditions such as transmission shift events, the compensated fuel flow rate FFR_comp may have less variation than a measured instantaneous fuel flow from the engine.At 448, the adjusted instantaneous fuel consumption value in units of miles per gallon may be calculated as follows:In this way, using a conversion factor, a measured fuel consumption value may be compensated for by stored vehicle energy resulting from changes in kinetic and potential energy. For example, the current fuel consumption value for a vehicle decelerating is displayed as an infinite value without compensation. The artificial increase in fuel consumption as the vehicle decelerates may be due to a DFSO (deceleration fuel cut) condition, where fuel flow to the engine may be cut. However, the vehicle may continue to drive due to stored vehicle energy. In this example, the conversion factor may effectively increase the present fuel flow rate, making it a positive number and thus matching the current fuel consumption value to a number less than an infinite value.In another example, if the vehicle is climbing or gaining speed, an uncompensated fuel consumption value may be less than the actual fuel consumption value. Additional fuel consumed when a vehicle is climbing an incline or experiencing acceleration may be included in or attributable to energy accumulation. In the example of an accelerating vehicle, additional fuel consumption by the engine may be due to the addition of kinetic energy compared to steady state fuel consumption. Accordingly, to compensate for the present fuel flow rate and correct the current fuel consumption value, the conversion factor may subtract an equivalent amount of fuel from the present fuel flow rate.Referring now to FIG. 5, it shows routine 500 for calculating a stored vehicle energy conversion factor SE. The conversion factor is learned when certain conditions are met, particularly when a vehicle experiences a sufficient increase in one or more of the vehicle speed or vehicle attitude, including a corresponding positive change in kinetic or potential energy. The conversion factor is based on the fuel flow due to stored energy, which is the difference between a measured fuel flow rate and a fuel flow rate during steady state driving conditions. A higher fuel consumption value is normally observed when the vehicle is driven under steady-state driving conditions. In one example, fuel consumption values less than steady-state fuel consumption values may be observed when a vehicle is going up an incline or experiencing acceleration. Lower fuel consumption values may be due to fuel flow due to the addition of potential energy or kinetic energy in this example.At 502, routine 500 may confirm that the engine has been warmed up. Fuel consumption may be higher at a cold start of the engine, for example, which may affect fuel flow calculations. Accordingly, if it is confirmed at 514 that the engine has not been warmed up, routine 500 may wait for the engine to warm up before estimating the conversion factor.At 504, it may be determined whether the present vehicle speed Vs_ 2 is greater than a minimum threshold, threshold min where threshold min is greater than zero. In one example, threshold min10 may be miles per hour (x1.6 kmh), whereas threshold min may be 20 x1.6 kmh in another example. At speeds below threshold min fuel consumed by the engine may be used to overcome rolling friction. Accordingly, if it is determined in 514 that Vs_ 2 is less than threshold min routine 500 may wait to calculate the conversion factor.However, if it is determined that the vehicle is moving at a speed above threshold min routine 500 may proceed to 506, where it may determine if braking conditions are present. During braking conditions, fuel flow may be used to overcome brake friction and stored energy may be lost as heat. Accordingly, errors may occur in all calculations for determining fuel flow rate due to stored energy when fuel flow is used to overcome friction. If it is determined that braking conditions are present, routine 500 continues to 514 where it may wait to calculate the conversion factor. In one example, the conversion factor may be determined during non-braking conditions.If no braking conditions are present, routine 500 may proceed to 508 where it may determine whether the vehicle is undergoing transmission shift events. For example, transmission shift events may cause rapid changes in engine speed that may affect fuel flow and accuracy of vehicle speed measurements. If it is determined that a transmission shift is being performed, routine 500 may wait to determine the conversion factor at 514.On the other hand, if a transmission shift is not being performed, routine 500 may proceed to 510, where it may be determined whether the vehicle is accelerating and whether the change in the quadratic vehicle speed ΔVs 2 is greater than a vehicle speed threshold, threshold V. Because the stored energy conversion factor is based on a difference between a present fuel flow rate and the fuel flow rate during steady state driving conditions, large changes in stored energy during high fuel flow conditions may make the estimate of the conversion factor more robust to small errors in steady state fuel flow rate. If the vehicle is accelerating and the positive change in Vs 2 is greater than the threshold vehicle speed, the vehicle may combust a greater amount of fuel and increase its stored energy. Because a change in kinetic energy is directly proportional to the quadratic vehicle speed, a small change in vehicle speed at higher speeds may produce a large change in kinetic energy. As a result, the conversion factor may be learned at higher vehicle speeds, rather than at low speeds.If it is determined in 512 that the vehicle speed is not increasing and that ΔVs 2 is less than threshold V routine 500 may determine whether the vehicle is going up, e.g., going up an incline, and whether the resulting change in vehicle attitude is greater than the threshold vehicle attitude, threshold h. As explained above, the conversion factor can be determined with fewer errors if the vehicle adds energy either by accelerating or by climbing an incline. Thus, if it is determined that the vehicle is not climbing and its change in elevation is not greater than threshold h routine 500 may proceed to 514 and wait for entry conditions to be met.If it is determined at 510 that the vehicle speed is increasing and the change in ΔVs 2 is positive and greater than threshold V routine 500 may proceed to 516. Similarly, if it is determined that the vehicle is climbing an incline and the change in vehicle attitude is positive and is greater than threshold h routine 500 may proceed to 516 where the average steady state fuel consumption value may be retrieved from memory. Thus, the conversion factor for fuel may be estimated based on stored vehicle energy only when the vehicle is undergoing a sufficient change in one or both of the quadratic vehicle speed or the vehicle attitude. If either the change in vehicle attitude or the change in square vehicle speed is sufficient and greater than their respective thresholds, the stored energy conversion factor may be determined.As is carried out with reference to FIG. 6, the average value MPG_SS_avg of the steady state fuel consumption may be determined when the vehicle is traveling under steady state conditions without substantial changes in vehicle acceleration or vehicle attitude. A steady state fuel consumption value may be estimated each time input conditions are met and the value may be added to previous calculations to arrive at a moving average MPG_SS_avg.At 518, a portion of fuel flow FF_str may be determined based on stored vehicle energy as follows: where FFR is present fuel flow rate, Vs_ 2 is present vehicle speed, and Vs_ 2 / MPG_SS_avg is fuel flow during steady state driving conditions.As previously discussed, the effect of errors in the calculation of MPG_SS_avg may be reduced if the present fuel flow rate FFR is higher. Thus, the stored vehicle energy conversion factor may be better determined when the vehicle experiences a positive change in vehicle speed, e.g., accelerates, and the change in square vehicle speed is greater than a threshold vehicle speed, e.g., as threshold V. The effect of errors in MPG_SS_avg may also be less if the conversion factor is calculated when the vehicle is climbing an incline, where the change in vehicle attitude is positive and the positive change is greater than a threshold vehicle attitude, such as threshold h.In another example, if the vehicle experiences deceleration or is going down an incline, the fuel flow may be slowed or shut down, thereby reducing the present fuel flow. The effect of errors in the calculation of MPG_SS_avg at steady-state conditions and, consequently, the fuel flow rate at steady-state conditions may be greater as the present fuel flow rate is less. Thus, the calculation of the conversion factor may be more sensitive to errors in the estimate of MPG_SS_avg and its corresponding steady state fuel flow rate when the present fuel flow rate is reduced.Next, at 520, the stored energy conversion factor, SE, may be determined as follows: where ΔVs 2 is the change in the quadratic vehicle speed, and ΔVh is the change in the vehicle elevation during time period Δt.The stored energy conversion factor is thus directly proportional to the fuel flow due to stored vehicle energy and inversely proportional to both a change in quadratic vehicle speed and vehicle attitude. By using the fuel flow due to stored energy to determine the conversion factor, the conversion factor is based on the steady state fuel consumption value MPG_SS and its average value. The conversion factor may thus be determined by comparing the amount of additional fuel consumed when kinetic and / or potential energy is added to the vehicle system to the amount of fuel consumed during steady state driving conditions.At 522, the calculated SE value may be stored in the memory of the vehicle controller and a moving average SE_avg may be calculated to learn a more accurate conversion factor.In this way, a conversion factor for stored vehicle energy may be calculated when specific input conditions are met, in particular when a sufficient increase in vehicle height is made and / or when a sufficient increase in quadratic vehicle speed occurs. The conversion factor may not be determined during transmission shifts and may also not be determined during vehicle braking conditions. The conversion factor is based solely on the fuel flow rate, the change in vehicle speed and the change in vehicle attitude. The fuel energy content, engine efficiency, and vehicle mass may be learned together as part of the conversion factor. Thus, additional knowledge of vehicle mass, fuel energy, or engine efficiency may not be required, and calculations of vehicle mass and engine efficiency, or a priori knowledge of fuel energy, may not be required to estimate the conversion factor, enabling easier calculation.It is understood that in the description above, the conversion factor is determined when the vehicle increases its stored energy, e.g., when it is accelerating or climbing an incline. A conversion factor may be estimated as the vehicle is travelling down an incline and / or decelerating based on a drop in fuel flow. However, this calculation may be prone to errors from the calculation of the steady state fuel flow rate.Referring now to FIG. 6, it shows routine 600 for estimating a steady state fuel consumption value based on a plurality of input conditions being met. In particular, fuel consumption values may be calculated when the vehicle is travelling under steady-state conditions, with changes in both the quadratic vehicle speed and the vehicle altitude being below the respective thresholds. Further, steady state conditions may include conditions where fuel flow and its combustion in the engine are used to maintain vehicle speed, and are not used for engine hot running, friction compensation, etc. Thus, routine 600 may be initiated only when various entry conditions are met.At 602, routine 600 may confirm that the engine has been warmed up. In one example, fuel may be consumed to warm the engine and thus is not fully utilized to maintain vehicle speed. If it is determined at 614 that the engine has not been warmed up, the steady state fuel consumption value MPG_SS may not be determined and routine 600 may wait for another opportunity.At 604, it may be determined whether the present vehicle speed Vs_ 2 is greater than a minimum threshold threshold min, but less than a maximum threshold max. In one example, threshold may be min30 miles per hour (x1.6 kmh). Alternatively, threshold min may be a speed of 35 x 1.6 kmh. If the vehicle is traveling at lower speeds, for example, those at or below threshold min the vehicle may encounter rolling friction and, as a result, the estimated fuel consumption may be lower. Further, fuel consumption measurements may be prone to errors because the torque converter may be unlocked at lower speeds. In addition, fuel measurements at lower speeds may also be sensitive to small loads from the air conditioning system and other electrical loads. On the other hand, if the vehicle is traveling at higher speeds, e.g., above threshold max fuel consumption may be lower due to drag. In one example, threshold max50 may be x1.6 kmh, whereas threshold max may be 45 x1.6 kmh in another example. Accordingly, if it is determined that the vehicle is traveling at speeds below threshold min or is traveling at speeds above threshold max routine 600 may not estimate MPG_SS and wait for the conditions to be met at 614.On the other hand, if it is determined at 606 that the vehicle speed is between threshold min and threshold max it may be confirmed whether braking conditions are present. Because braking events do not provide steady state conditions, fuel consumption values at such events may not represent steady state fuel consumption. Accordingly, if a braking event is being performed, routine 600 may proceed to 614 and may not estimate MPG_SS. However, if it is determined that a braking event is not occurring, routine 600 may proceed to 608 where it may determine whether a transmission shift is being performed. As previously mentioned with respect to FIG. 5, transmission shift events may affect the accuracy of vehicle speed measurements and fuel flow measurements. If a transmission shift is occurring, routine 600 may be deactivated at 614 and MPG_SS may not be estimated.If a transmission shift is not occurring, then at 610, routine 600 may confirm that a change in the quadratic vehicle speed ΔVs 2 is less than a threshold threshold. In an example, if the vehicle is traveling with cruise control (Cruise Control), the change in vehicle speed or the square vehicle speed may be zero. A significant increase or decrease may cause significant fuel consumption variation, resulting in errors in the calculation of MPG_SS. If it is determined that ΔVs 2 is greater than threshold, routine 600 may disable the calculation of steady state fuel consumption at 614.However, if ΔVs 2 is less than or equal to threshold, then at 612, routine 600 may determine that the change in vehicle altitude, ΔVh, is below a threshold threshold E. If the vehicle is going up or down an incline, steady state conditions may not be met. Accordingly, if ΔVh is greater than threshold E routine 600 may not calculate MPG_SS and wait for an opportunity when all input conditions are met. Thus, if one or both of a square vehicle speed change or a vehicle height position change are greater than their respective thresholds, steady state fuel consumption values may not be estimated. Steady state input conditions may be met when both the quadratic vehicle speed change and the vehicle altitude change are less than their respective thresholds.Referring back to 612: If it is determined that ΔVh is less than threshold E routine 600 may proceed to 616, where MPG_SS may be calculated as: where: Vs_ 2 is the current or present vehicle speed, and FFR is the current fuel flow rate at steady state conditions.At 618, the calculated MPG_SS is stored in the memory of the vehicle controller and a moving average MPG_SS_avg may be calculated as ROLAV(MPG_SS). The moving average may be used in compensated fuel consumption or mileage calculations.Referring now to FIG. 7, it shows an example relationship between fuel consumption in miles per gallon (MPG) and steady state speed in miles per hour (X1.6 KMH). Specifically, the map 700 shows the fuel consumption in MPG plotted along the y-axis and the steady-state speed in X1.6 KMH along the y-axis. Curve 702 shows that MPG remains relatively stable within a speed range shown by lines 711 and 713. Before line 711, at steady-state speeds less than 30 X1.6 KMH, the MPG rapidly increases from 10 MPG to ∼30 MPG, which corresponds to a decrease in fuel consumption from about 20 to about 8 L / km. Between lines 711 and 713, e.g., between steady-state speeds 30 to 50 X1.6 KMH, fuel consumption may be the highest observed and may remain between 30 and 35 MPG (approximately 8 at 7 L / km). If the steady-state speed increases beyond 50 X1.6 KMH (line 713), the fuel consumption decreases from ∼32 MPG to 20 MPG, which corresponds to a decrease in fuel consumption from about 12 to about 8 L / km.To the left of line 711, at speeds between 10 X1.6 KMH and 30 X1.6 KMH, a larger amount of fuel may be used to counteract rolling friction. To the right of line 713, as vehicle speed increases beyond 50 X1.6 KMH, the vehicle may meet sufficient drag so that fuel consumed by the engine may be used to overcome drag. However, at moderate speeds, e.g., between 30 X1.6 KMH and 50 X1.6 KMH, fuel consumption remains relatively stable because the torque converter remains locked and parasitic loads, such as those from the air conditioner or other electrical loads, may not contribute to the amount of fuel consumed. Accordingly, the steady state fuel consumption value MPG_SS may be determined when the vehicle is traveling at moderate speeds without significant acceleration / deceleration or changes in elevation.Small improvements in learning the stored energy conversion factor may be made by increasing the accuracy of MPG_SS. More accurate fuel consumption or mileage may be learned by matching a curve of steady state fuel flow versus vehicle speed Vs. In this way, a larger speed range is available for learning MPG_SS.Thus, steady state vehicle driving conditions may be used to learn a steady state fuel consumption value. If the vehicle experiences significant increases in either the quadratic vehicle speed or the vehicle altitude, a stored energy conversion factor may be determined based on the increase in fuel flow versus a steady state fuel flow. This conversion factor may then be used to adjust stored energy fuel consumption values.The conversion factor and the steady state fuel consumption values may be determined each time input conditions are met. The vehicle controller may add these values to its memory and calculate moving averages based on present data. As the number of estimated conversion factor values increases, a more accurate conversion factor may be determined that enables more reliable compensation of the fuel consumption values for stored energy.Referring now to FIG. 9, it shows a map 900 that shows example driving conditions for the vehicle when a conversion factor for stored vehicle energy, in particular kinetic energy, may be calculated. The example in map 900 shows a vehicle undergoing changes only in kinetic energy. Changes in vehicle attitude and, consequently, potential energy are nominal and are not incorporated in the example shown. Map 900 includes calculated fuel consumption at 902, calculated fuel consumption at 904 adjusted for stored energy, actual fuel flow at 908, compensated fuel flow (FFR_comp) at 906, transmission shift state at 910, brake pedal position at 912, and vehicle speed Vs at 914. All of the above are plotted against time on the x-axis.Between t 0 and t 1, a vehicle may begin to move from rest and accelerate progressively until t 1. Accordingly, between t 0 and t 1, the brake pedal may be in a released (or "off") position, and as vehicle speed increases, a vehicle controller may gradually upshift the transmission, from a lower gear (such as a first transmission gear (Gear_ 1)), to a higher gear (such as a second transmission gear (Gear_ 2), to a third transmission gear (Gear_ 3), and then to a fourth transmission gear (Gear_ 4). Thus, as the vehicle accelerates between t 0 and t 1, the actual fuel flow rate (plot 908), as measured by a fuel pulse counter, rapidly increases, indicating a greater amount of fuel consumption. Here, a portion of the fuel consumed by the vehicle may flow into increasing kinetic energy. As a result, the compensated fuel flow rate, as shown by curve 906, increases to a lower level than the actual fuel flow rate based on the calculation at 444 of FIG. 4. A stored energy conversion factor in the vehicle controller memory may be retrieved to calculate a compensated fuel flow rate. Thus, the uncompensated fuel consumption value (plot 902) between t 0 and t 1 may be less than the stored kinetic energy matched fuel consumption value (plot 904). Here, an uncompensated fuel consumption value incorrectly indicates a smaller fuel consumption value based on a higher fuel flow rate, and the compensated fuel consumption value indicates a more accurate, higher fuel consumption value based on a fuel flow rate matched around the fuel flow rate due to stored kinetic energy. Variations in the actual fuel flow and compensated fuel flow curves, such as the peaks between t 0 and t 1, may occur during transmission shifts and braking events.If the transmission gear is upshifted to fourth gear (Gear_ 4) and no further transmission shift events occur, a stored energy conversion factor may be calculated at 911. For the duration specified by 911, the vehicle continues to accelerate and add kinetic energy to the system. Further, other entry conditions for computing the conversion factor are also met, e.g., the vehicle speed is above a minimum speed to overcome rolling friction and the brake pedal is released.At t 1, the vehicle reaches a steady state speed, and between t 1 and t 2, the vehicle speed remains at a steady state level without any changes in transmission gear setting and / or brake pedal position. Furthermore, both the compensated fuel flow and the uncompensated (actual) fuel flow achieve a stable flow, wherein the fuel consumed by the internal combustion engine is largely used for maintaining the vehicle speed. Herein, steady state fuel consumption determination input conditions are met, such as steady state driving conditions, absence of transmission shift events, braking events, etc. Accordingly, at 905, steady state fuel consumption may be calculated as MPG_SS.At t 2, the brake pedal may be actuated by a driver of the vehicle. Between t 2 and t 3, the brake pedal may be applied and released twice, as shown by plot 912. Due to the brake actuation, the vehicle speed may decrease and the controller may gradually downshift the transmission from a higher gear (such as a fourth transmission gear (Gear_4)) to a lower gear (such as a third transmission gear (Gear_3) and then to a second transmission gear (Gear_2)).Due to vehicle deceleration, the actual uncompensated fuel flow (curve 908) to the engine decreases between t 2 and t 3. In response to the decrease in the actual fuel flow rate, the uncompensated fuel consumption values (curve 902) increase to higher levels, e.g., to an almost infinite value. However, the compensated fuel flow (plot 906) remains at the same level as between t 1 and t 2. Smaller compensated fuel flow variations may correspond to braking applications. During deceleration, the square vehicle speed may reduce, resulting in a negative ΔVs 2. Accordingly, based on the calculation described in FIG. 4 at 444, the compensated fuel flow rate (FFR_comp) is greater than the actual fuel flow rate. Between t2 and t3, balanced fuel consumption values are thus lower than uncompensated fuel consumption values. With each application of the brake pedal, a corresponding drop in the balanced fuel consumption values is also observed. However, once the brake pedal is released, the balanced fuel consumption values return to the levels between t1 and t2.At t 3, the brake pedal is released and the vehicle speed increases to its previous steady state value that has existed between t 1 and t 2. The controller may gradually upshift the transmission from a lower gear (such as a second transmission gear (Gear_ 2)) to a higher gear (such as a third transmission gear (Gear_ 3) and then to a fourth transmission gear (Gear_ 4)).Between t 3 and t 4, the actual fuel flow rate increases as the vehicle accelerates, but the compensated fuel flow rate remains relatively stable, except at peaks corresponding to transmission shifts. Uncompensated fuel consumption values thus decrease between t3 and t4, while fuel consumption values balanced around stored energy remain relatively stable and greater than uncompensated fuel consumption values.Once the transmission gear is in fourth gear and vehicle acceleration is sufficient to add energy to the vehicle system, the controller may calculate a stored energy conversion factor at 913. This conversion factor may be added to previous calculations and a moving average may be calculated and stored in the controller's memory.At t 4, the vehicle speed reaches a steady speed and remains at that speed between t 4 and t 5. In response to the steady state driving conditions, more steady state fuel consumption (MPG_SS) calculations may be obtained and stored in the vehicle controller memory at 907. Between t 4 and t 5, therefore, no transmission shift events and brake events occur. Further, the vehicle may be in steady state driving conditions, wherein a change in the quadratic vehicle speed may be below a threshold.At t 5, the brake pedal may be applied multiple times with a resultant decrease in vehicle speed. Further, the controller may step down the transmission from a higher gear (such as a fourth transmission gear (Gear_ 4)) to a lower gear (such as a third transmission gear (Gear_ 3), to a second transmission gear (Gear_ 2), and then to a first transmission gear (Gear_ 1). Between t 5 and t 6, as the vehicle decelerates, the actual fuel flow rate reduces, whereas the compensated fuel flow rate remains higher than the actual fuel flow rate. Between t 5 and t 6, the uncompensated fuel consumption values may increase to high figures because fuel flow is reduced. However, the matched fuel consumption values may be lower than uncompensated fuel consumption values. Finally, the transmission may be shifted to neutral and the vehicle may be deactivated at t 6. The vehicle deactivation includes a key-off condition where the engine is in a deactivation state. Thus, at t 6, the fuel flow rate, the actual and compensated, decreases to zero because the vehicle (and engine) is deactivated.Although the above example does not include changes in vehicle attitude, it should be appreciated that the conversion factor may be determined each time sufficient potential energy is added to the vehicle system and other input conditions are met.In this way, a stored energy conversion factor may be calculated based on the fuel flow rate due to stored energy. The fuel flow due to stored energy may be obtained by subtracting the fuel flow during steady state driving conditions from a present fuel flow rate. As the present fuel flow rate increases, e.g., during acceleration or while a hill is being climbed, additional fuel flow that goes beyond the steady state fuel flow may be due to energy being added to the vehicle system. The conversion factor may be further determined based on changes in vehicle attitude and changes in square vehicle speed, which may be estimated from sensor signals and / or simple calculations, respectively. As a result, fuel consumption values may be compensated for stored energy using a simple conversion factor without knowledge of fuel energy, vehicle mass, or engine efficiency, all of which may vary over time and / or vehicle-to-vehicle.It should be noted that the example control and estimation routines included herein may be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading strategies, and the like. As such, various illustrated actions, operations, and / or functions may be performed in the order illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations, and / or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations, and / or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system.It should be understood that the configurations and routines disclosed herein are exemplary in nature and that these specific embodiments are not to be considered in a limiting sense because numerous variations are possible. For example, the above technology can be applied to six-cylinder V engines (V-6), in-line four-cylinder engines (I-4), in-line six-cylinder engines (I-6), twelve-cylinder V engines (V-12), four-cylinder boxer engines, and other types of internal combustion engines. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or characteristics disclosed herein.The following claims particularly point out certain combinations and sub-combinations which are considered novel and not obvious. These claims may refer to "a" element or "a first" element, or the like. Such claims should be understood to include integration of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or characteristics may be claimed by the following of the present claims or by the presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal or different in scope from the original claims, are also considered to be within the scope of the present disclosure.

Claims

A method for a vehicle, comprising: - determining a change in a quadratic vehicle speed by a controller (12); - comparing the change in the quadratic vehicle speed with a first threshold value by the controller (12); - determining a change in a vehicle attitude by the controller (12); - comparing the change in the vehicle attitude with a second threshold value by the controller (12); if a positive change in the quadratic vehicle speed is greater than the first threshold value, and / or if a positive change in the vehicle attitude is greater than the second threshold value: - estimating a conversion factor for fuel based on stored vehicle energy by the controller (12), wherein the conversion factor is determined by the controller (12) based on a difference between a fuel flow rate measured during steady state driving conditions and a present fuel flow rate; compensating a measured fuel consumption value for changes in the stored energy based on the estimated conversion factor by the controller (12) to obtain a compensated instantaneous fuel consumption value; and displaying the compensated instantaneous fuel consumption value to the driver of the vehicle.The method of claim 1, wherein the conversion factor is directly proportional to fuel flow due to stored vehicle energy and inversely proportional to both the square vehicle speed change and the vehicle altitude change.The method of claim 1, wherein steady state driving conditions include conditions where changes in both a quadratic vehicle speed and a vehicle altitude are below their respective thresholds.The method of claim 1, wherein the compensated instantaneous fuel consumption value is displayed to the driver of the vehicle at periodic intervals.The method of claim 1, wherein stored vehicle energy is one or both of potential energy or kinetic energy, and wherein the potential energy is directly proportional to vehicle altitude and the kinetic energy is directly proportional to quadratic vehicle speed.The method of claim 1, wherein the change in vehicle attitude is estimated based on grade values from an inclinometer (146) and the vehicle speed.The method of claim 6, wherein the inclinometer slope values are corrected for offset errors by comparison with atmospheric pressure sensor (128) values.Method according to Claim 1, wherein the conversion factor for stored vehicle energy and the fuel consumption during steady-state driving conditions are determined after the internal combustion engine (10) has been warmed up.The method of claim 1, wherein the stored vehicle energy conversion factor and fuel consumption are not determined during transmission shifts during steady state driving conditions.The method of claim 1, wherein the stored vehicle energy conversion factor and fuel consumption at steady state driving conditions are not determined during vehicle braking conditions.A system in a vehicle, comprising: an internal combustion engine (10); and a controller (12) having computer readable instructions stored in non-transitory memory (106), configured to: during a first mode: determine a change in a quadratic vehicle speed; determine a change in a vehicle altitude; determine a current fuel consumption value; compare the change in the quadratic vehicle speed to a first threshold; compare the change in the vehicle altitude to a second threshold; during a second mode, if a positive change in the quadratic vehicle speed is greater than the first threshold value, and / or if a positive change in the vehicle height position is greater than the second threshold value: - determining a conversion factor for stored vehicle energy on the basis of the fuel consumption value determined in the first mode on the basis of a difference between a fuel flow rate measured during steady-state driving conditions and a present fuel flow rate; - compensating a measured fuel consumption value for changes in the stored energy on the basis of the estimated conversion factor in order to obtain a compensated present fuel consumption value; and - displaying the compensated present fuel consumption value to a driver of the vehicle.

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