Method and system for supplying fuel to a power engine

Abstract

Methods for supplying fuel to a power engine, comprising: Receiving fuel data from a control unit; Estimating fuel compressibility from fuel data through instructions in the control unit; and Adjusting the output of a fuel pump via the controller in response to the estimated fuel compressibility, wherein adjusting the output of the fuel pump includes increasing a voltage or a quantity of current supplied to the fuel pump in response to the estimated fuel compressibility being greater than a threshold compressibility.

Description

Background / Brief description

[0001] Port-injected engines receive fuel pumped from a fuel tank via a fuel pump. The fuel pump supplies fuel to a fuel rail, and fuel injectors coupled to the fuel rail inject fuel into engine intake ports. Fuel can be delivered to the engine from the fuel rail as a liquid, a gas, or a mixture of a gas and a liquid, depending on a condition of the fuel in the fuel rail. However, injecting fuel in a liquid state may be more desirable because the amount of fuel injected is easier to control. Injecting liquid fuel can be ensured by increasing the fuel pressure above the fuel vapor pressure. The fuel pressure can be increased by supplying additional power to the fuel pump.However, increasing the amount of energy supplied to the fuel pump may reduce the vehicle's fuel economy, since energy to operate the fuel pump is derived from an alternator coupled to the vehicle's engine. Furthermore, the pressure at which fuel can be delivered to the engine in a liquid state may vary with fuel composition and fuel temperature. Consequently, it may be difficult to provide fuel to an engine in a liquid state without delivering it at a pressure that increases the vehicle's fuel consumption more than desired.

[0002] DE 196 33 156 A1 describes an engine in which fuel compressibility is estimated from fuel data. DE 10 2008 017 160 B3 and US Pat. No. 5,975,056 A also disclose similar methods.

[0003] According to the invention, a method according to claim 1 and a system according to claim 6 are proposed. Advantageous embodiments of the invention are specified in the dependent claims and the following description.

[0004] The present inventors have recognized the above limitations and have developed a method for delivering fuel to an engine, comprising: receiving fuel data from a controller, estimating fuel compressibility from the fuel data through instructions in the controller, and adjusting the output of a fuel pump via the controller in response to the estimated fuel compressibility.

[0005] By adjusting the output of a fuel pump in response to fuel compressibility, it may be possible to provide the technical result of supplying liquid fuel to an engine while simultaneously reducing the power supplied to a fuel pump. In particular, fuel compressibility may be a basis for regulating the fuel pressure supplied to the engine such that liquid fuel can be provided to the engine while minimizing fuel pump energy consumption. The output of the fuel pump may be increased or decreased in response to fuel compressibility.Consequently, even if fuel properties that affect the state of an injected fuel are unknown, fuel can be injected into the engine in a liquid state while simultaneously minimizing fuel pump energy consumption.

[0006] The present description can provide several advantages. In particular, the approach can provide the delivery of liquid fuel to an engine at reduced fuel pump outlet pressures. The reduced pressure is particularly useful for extending the dynamic range of the injector so that low fuel injection masses can be accurately accounted for. The low fuel injection mass is important under idle conditions during fuel vapor purge operation. This effect does not reduce the ability to provide standard pressure (or higher pressure) at high engine speed when the injection window is short. High engine speed is a less common condition, and therefore high pressure during this condition does not significantly affect fuel economy.Furthermore, the method provides adjustment of the fuel pressure delivered to an engine without knowledge of the fuel type or fuel vapor pressure. Furthermore, the approach provides control of the energy delivered to a fuel pump without knowledge of the fuel vapor pressure or fuel temperature.

[0007] The above advantages and other advantages and features of the present description will be readily apparent from the following detailed description, considered alone or in conjunction with the accompanying drawings.

[0008] It should be understood that the above summary is provided to introduce, in simplified form, a selection of concepts further described in the detailed description. It is not intended to reveal critical or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any disadvantages identified above or in any part of this disclosure. Short description of the characters Fig. 1 shows a schematic representation of a power machine; Fig. 2 shows a diagram of an exemplary manner of determining fuel compressibility; Fig. 3 shows a diagram of an exemplary manner of determining a desired fuel pressure in response to fuel compressibility; and Fig. 4 shows a flowchart of an exemplary method of supplying fuel to an engine. Detailed description

[0009] This description relates to the supply of fuel to an engine such that liquid fuel is injected into the engine while simultaneously reducing fuel pump energy consumption. In one example, fuel is supplied via a fuel system as shown in Fig. 1 of an engine. The compressibility of a fuel can be determined as shown in Fig. 2 for adjusting the output of a fuel pump. A desired fuel pump output pressure can be determined by determining a fuel pump pressure, wherein the fuel compressibility is determined as shown in Fig. 3 increases. A method for adjusting the output of a fuel pump in response to fuel compressibility is described in Fig. 4 shown.

[0010] With reference to Fig. 1, the internal combustion engine 10, which comprises several cylinders, one of which is in Fig. 1, is controlled by the electronic engine control 12. The engine 10 includes a combustion chamber 30 and cylinder walls 32 with a piston 36 positioned therein and connected to a crankshaft 40. The combustion chamber 30 is shown communicating with an intake manifold 44 and an exhaust manifold 48, respectively, via an intake valve 52 and an exhaust valve 54. Each intake and exhaust valve may be actuated by an intake cam 51 and an exhaust cam 53. Alternatively, one or more of the intake and exhaust valves may be actuated by an electromechanically controlled valve spool and armature assembly. The phase of the intake cam 51 and the exhaust cam 53 with respect to the crankshaft 40 may be adjusted by cam phase actuators 59 and 69. The position of the intake cam 51 can be determined by the intake cam sensor 55.The position of the exhaust cam 53 can be determined by the exhaust cam sensor 57.

[0011] Fuel injector 66 is shown positioned to inject fuel into port 38 of cylinder 30, known to those skilled in the art as port injection. Fuel injector 66 delivers liquid fuel in proportion to the pulse width from controller 12. Fuel is supplied to fuel injector 66 by a fuel system including a fuel tank 140, a fuel pump 142, a fuel line 141, and a fuel rail 145. Operating power is supplied to fuel injector 66 and fuel pump 142 from controller 12. Also shown, intake manifold 44 is in communication with an optional electronic throttle 62 that adjusts a position of throttle plate 64 to control airflow from air intake 42.

[0012] A distributorless ignition system 88 provides an ignition spark to the combustion chamber 30 via a spark plug 92 in response to the controller 12. The ignition system 88 may provide a single or multiple sparks to each cylinder during each cylinder cycle. Furthermore, the timing of the spark delivered via the ignition system 88 may be advanced or retarded relative to the crankshaft timing in response to engine operating conditions.

[0013] A wideband universal exhaust gas oxygen (UEGO) sensor 126 is illustrated coupled to the exhaust manifold 48 upstream of an exhaust aftertreatment device 70. Alternatively, a dual-state oxygen sensor may be employed in place of the UEGO sensor 126. In some examples, the exhaust aftertreatment device 70 is a particulate filter and / or a three-way catalyst. In other examples, the exhaust aftertreatment device 70 is solely a three-way catalyst.

[0014] The control 12 is in Fig. 1 as a conventional microcomputer including a microprocessor unit 102, input / output (I / O) ports 104, a read-only memory (ROM) 106, a random access memory (RAM) 108, a retained memory (RAM) 110, and a conventional data bus.In the illustration, in addition to the signals previously discussed, the controller 12 receives various signals from sensors coupled to the engine 10, including engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; a position sensor 134 coupled to an accelerator pedal 130 for sensing the accelerator pedal position (PP) set by foot 132; fuel pressure from fuel pressure sensor 121; an engine position sensor from a Hall effect sensor 118 that senses the position of the crankshaft 40; a measurement of air mass entering the engine from sensor 120 (e.g., a hot wire air flow sensor); and a measurement of throttle position from sensor 58. Barometric pressure may also be sensed for processing by the controller 12 (sensor not shown).In a preferred aspect of the present description, the engine position sensor 118 generates a predetermined number of evenly spaced pulses during each revolution of the crankshaft from which the engine speed (RPM) can be determined.

[0015] In some examples, the engine may be coupled to an electric motor / battery system in a hybrid vehicle. The hybrid vehicle may include a parallel configuration, a series configuration, or a variation or combination thereof. Furthermore, in some examples, other engine configurations may be employed, for example, a diesel engine.

[0016] During operation, each cylinder in the engine 10 typically experiences a four-stroke cycle: the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. During the intake stroke, the exhaust valve 54 generally closes and the intake valve 52 opens. Air is introduced into the combustion chamber 30 via the intake manifold 44, and the piston 36 moves to the bottom of the cylinder to increase the volume within the combustion chamber 30. The position where the piston 36 is near the bottom of the cylinder and at the end of its stroke (e.g., when the combustion chamber 30 is at its largest volume) is typically referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, the intake valve 52 and the exhaust valve 54 are closed. The piston 36 moves toward the cylinder head to compress the air in the combustion chamber 30.The point at which the piston 36 is at the end of its stroke and closest to the cylinder head (for example, when the combustion chamber 30 is at its smallest volume) is generally referred to by those skilled in the art as top dead center (tdc). In a process referred to below as injection, fuel is fed into the combustion chamber. In a process referred to below as ignition, the injected fuel is ignited by known ignition means, such as the spark plug 92, resulting in combustion. During the power stroke, the expanding gases push the piston 36 back to bdc. The crankshaft 40 converts piston movement into torque of the rotating shaft.

[0017] Finally, during the exhaust stroke, the exhaust valve 54 opens to release the combusted air-fuel mixture to the exhaust manifold 48, and the piston returns to TDC. It should be noted that the above is described merely as an example, and that the timing of intake and exhaust valve opening and / or closing may vary to provide positive or negative valve overlap, late intake valve closing, or various other examples.

[0018] Thus, the system of Fig. 1 provides a system for controlling an engine, comprising: an engine; a fuel pump supplying fuel to the engine; a controller including executable instructions stored in non-volatile memory for adjusting output of the fuel pump in response to compressibility of fuel supplied to the engine. The system includes wherein compressibility of the fuel supplied to the engine is based on an injected fuel mass divided by a change in fuel rail pressure. The system further includes a fuel rail coupled to the engine and the fuel injector, and a pressure sensor coupled to the fuel rail.

[0019] In some examples, the system further includes additional instructions for estimating the compressibility of the fuel delivered to the engine based on an output of the pressure sensor. The system further includes additional instructions for determining a desired fuel pressure in response to the compressibility of the fuel delivered to the engine. The system further includes additional instructions for estimating the compressibility of the fuel delivered to the engine in response to a change in fuel temperature or a refill of a fuel tank.

[0020] Now on Fig. Referring to Figure 2, a simulated exemplary diagram of one way of determining fuel compressibility is shown. The values ​​shown in the diagram of Fig. The sequence shown in Figure 2 can be obtained by the method of Fig. 4. The vertical markers T0-T6 represent time points of interest in the sequence.

[0021] The first diagram from the top of Fig. 2 represents the voltage supplied to a fuel pump. The vertical axis represents the fuel pump voltage, and the fuel pump voltage increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time decreases from the left side of Fig. 2 to the right of Fig. 2 to.

[0022] The second diagram from the top in Fig. 2 represents the fuel pressure in a fuel rail supplying fuel to one or more engine cylinders. The vertical axis represents the fuel pressure in the fuel rail, and the fuel pressure increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time decreases from the left side of Fig. 2 to the right of Fig. 2. Fuel is supplied to the engine throughout the entire Fig. 2 shown sequence at the same rate.

[0023] At time T0, the fuel pump is commanded to the off state, as indicated by the low fuel pump voltage, and fuel pressure in the fuel rail decreases. Fuel pressure in the fuel rail decreases in response to the injection of fuel into the engine cylinders to operate the engine.

[0024] At time T1, the fuel pump is activated, as indicated by the higher fuel pump voltage. The fuel pump is activated in response to a request to determine the compressibility of the fuel injected into the engine. The fuel pressure in the fuel rail increases in response to the fuel pump activation.

[0025] At time T2, the fuel pump is deactivated, as indicated by the transition from a higher fuel pump voltage to a lower fuel pump voltage. The fuel pump is deactivated to determine the compressibility of the fuel injected into the engine. Even after the fuel pump is deactivated and no longer supplies fuel to the fuel rail, fuel is injected into engine cylinders (not shown).

[0026] Between time T2 and time T3, fuel is injected into the operating engine, and fuel pressure begins to decrease because the fuel pump is not operating and is replenishing fuel in the fuel rail. Fuel pressure decreases at a constant rate because a constant fuel rate is injected into the engine. If the same curve were plotted as fuel pressure versus fuel volume consumed, the pressure would decrease in a constant line regardless of the fuel rate, as long as the fuel compressibility remained constant. Thus, this calculation can be performed even with varying fuel injection rates.

[0027] At time T3, counting of the accumulated amount of fuel injected into the engine begins. The mass (or volume) of fuel injected into the engine can be determined based on the time a fuel injector opens to inject fuel and a transfer function that provides fuel quantity versus fuel pressure and the time the injector is open. Furthermore, the fuel pressure is determined so that fuel pressure drop in the fuel rail can be determined. Sampling the fuel pressure at multiples or sub-multiples of the injection frequency can reduce compressibility noise (d / dt V / d / dt P). A large volume change with a small pressure change indicates high compressibility. When the fluid is at vapor pressure, it theoretically has infinite compressibility.If the fuel storage tank were completely rigid and the fluid were completely liquid, the compressibility is also theoretically directly proportional to the inverse of the bulk modulus.

[0028] At time T4, counting of the accumulated amount of fuel injected into the engine is stopped, and the fuel rail pressure is determined. The total actual mass (or total actual volume) of fuel injected into the engine is divided by the fuel rail pressure difference between time T3 and time T4 to determine the compressibility of the fuel injected into the engine. The fuel pressure drop is shown by marker 204. The time period the fuel mass is injected into the engine is accumulated, as shown by marker 202.

[0029] Between time T4 and time T5, fuel continues to be injected into the engine while the fuel pump is off.

[0030] At time T5, the fuel pump is activated, as indicated by the higher fuel pump voltage. The fuel pump is activated in response to a request to resupply fuel to the fuel rail. The fuel pressure in the fuel rail increases in response to the fuel pump activation.

[0031] At time T6, the fuel pump is deactivated, as indicated by the transition from a higher fuel pump voltage to a lower fuel pump voltage. The fuel pump is deactivated to reduce fuel pump operation after the fuel pressure in the fuel rail reaches a setpoint. Fuel continues to be injected into the fuel cylinders.

[0032] In this way, the compressibility of the fuel supplied to an engine can be determined while the engine is operating and a vehicle is traveling along a road. Furthermore, when the engine is operating at higher loads, fuel compressibility can often be determined without interfering with engine operation, since smaller amounts of fuel are supplied to the engine under low-load engine conditions.

[0033] Now on Fig. Referring to Figure 3, a simulated sequence for determining a desired fuel pressure in response to fuel compressibility is shown. The sequence of Fig. 3 can be done by the procedure of Fig. 4 that by instructions from the controller 12 in the system of Fig. 1. The vertical markers T10-T14 represent points in time that are of interest in the sequence. Fuel is supplied to the engine during the entire Fig. 3 shown sequence at the same rate. The three diagrams of Fig. 3 are time-adjusted and take place at the same time.

[0034] The first diagram from the top in Fig. Figure 3 plots the fuel pressure in a fuel rail supplying fuel to an engine versus time. The vertical axis represents the fuel pressure, and the fuel pressure increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time decreases from the left side of Fig. 3 to the right of Fig. 3 to.

[0035] The second diagram from the top in Fig. Figure 3 shows the compressibility of the fuel in the fuel rail supplying fuel to an engine versus time. The vertical axis represents the compressibility of the fuel in the fuel rail, and the compressibility increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time decreases from the left side of Fig. 3 to the right of Fig. 3. The horizontal line 305 represents a fuel compressibility threshold. The fuel pump should be operated to keep the fuel compressibility below the threshold 305.

[0036] The third diagram from the top of Fig. Figure 3 represents the fuel injection rate (e.g., cc / second) versus time. The vertical axis represents the fuel injection rate, and the fuel injection rate increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time decreases from the left side of Fig. 3 to the right of Fig. 3 to.

[0037] At time T10, the fuel pressure in the fuel rail is at a lower level. Fuel is injected into the engine during the sequence, but is not shown. The fuel pump is also deactivated (not shown). Fuel compressibility increases, and the fuel injection rate is at a constant rate.

[0038] At time T11, the fuel pump is activated in response to fuel compressibility reaching threshold 305, and fuel pressure in the fuel rail increases in response to fuel pump activation. The fuel pump is activated to ensure that the fuel in the fuel rail is in a liquid state rather than a partially gaseous (vaporous) state. Between time T11 and time T12, when the fuel pump is activated, compressibility is not calculated.

[0039] At time T12, the fuel pump is deactivated. The fuel pump may be deactivated at a predetermined time after its activation or in response to the fuel rail pressure reaching a desired pressure. Fuel continues to be injected into the engine at a constant rate after the fuel pump (not shown) is deactivated, and fuel compressibility is determined to be at a lower value.

[0040] Between time T12 and time T13, the fuel pressure in the fuel rail decreases while fuel is injected into the engine (not shown). In some examples, the compressibility of the fuel may be determined between time T12 and time T13, as shown in Fig. 2. In this example, the fuel compressibility remains nearly constant, and the fuel injection rate remains constant.

[0041] At time T13, the rate of change of fuel pressure (e.g., slope) in the fuel rail decreases. The rate of change of fuel pressure decreases as the fuel vapor pressure floor is reached and fuel compressibility begins to increase. Some fuel in the fuel rail may be in a gaseous state. Horizontal line 304 represents fuel rail pressure, with the slope, or rate of decrease, of fuel rail pressure being reduced in response to encountering the fuel vapor pressure floor. Operation with a pressure in the fuel rail indicated by horizontal line 302 may be desirable. Horizontal line 302 is equal to the fuel rail pressure of horizontal line 304 plus an offset. In this example, the offset is the pressure between horizontal line 304 and horizontal line 302.Thus, the fuel pump may be controlled to maintain fuel pressure in the fuel rail at the elevation indicated by horizontal line 302 to deliver liquid fuel to the engine and reduce the energy supplied to the fuel pump. Fuel pump energy may be reduced when the fuel rail pressure is at the elevation indicated by horizontal line 302, since operating the fuel rail at pressures higher than the elevation of line 302 increases fuel pump energy consumption. The fuel pressure offset between horizontal line 304 and horizontal line 302 provides a confidence interval that fuel in the fuel rail is not entering a gaseous state. The fuel injection rate remains constant.

[0042] Between time T13 and time T14, fuel continues to be injected into the engine while the fuel pump is off. The pressure in the fuel rail decreases at a slower rate or with a smaller gradient compared to between time T12 and time T13, although fuel is injected into the engine at the same rate. However, fuel compressibility steadily increases, even with the fuel injection rate remaining constant.

[0043] At time T14, the fuel pump is reactivated to increase the fuel pressure in the fuel rail in response to the fuel compressibility reaching threshold 305. The fuel injection rate remains constant, and the fuel compressibility calculation ceases. The sequence may be repeated multiple times to confirm a pressure in the fuel rail at which the fuel vapor pressure floor is reached.

[0044] In this way, a control pressure can be determined to adjust the fuel pump output. The control pressure is a pressure that provides liquid fuel to the engine while delivering a smaller amount of energy to a fuel pump supplying fuel to the fuel rail and the engine. Alternatively, a measured pressure can be associated with a voltage, duty cycle, current, or power, and the voltage, duty cycle, current, or power would be the new control setting after a margin is added.

[0045] Now on Fig. Referring to Figure 4, a flowchart of an exemplary method for supplying fuel to an engine is shown. At least a portion of the method of Fig. 4 can be integrated into the system of Fig. 1 as executable instructions. Furthermore, parts of the method can be Fig. 4 via a controller that receives data from sensors and controls actuators in the physical world. The method of Fig. 4 is active when a vehicle's engine is running. The fuel compressibility test can be prevented if the fuel injection rate is high. At high injection rates, one could select an a priori pressure or an electrical energy level of the lift pump.

[0046] At 402, method 400 judges whether the compressibility of the fuel injected into the engine has been determined. It may be desirable to determine the compressibility of a fuel because the compressibility of the fuel increases to a higher value when the fuel is at least partially in a gaseous state. The compressibility of the fuel is at a lower value when the fuel is solely in a liquid state. In one example, a bit in memory may be set to a value of one if the compressibility of a fuel is known and a value of zero if the compressibility of the fuel is not known. If method 400 judges that the compressibility of the fuel is known, the answer is yes, and method 400 proceeds to 430; otherwise, the answer is no, and method 400 proceeds to 404.The idea here is to raise the fuel pressure high enough to where you know in advance that the fuel pressure is well above the vapor pressure, and to determine the compressibility in this state. Although we refer to compressibility as a property of the fuel alone, it is actually also a property of the mechanical structure containing the fuel, because the container itself is not completely rigid.

[0047] At 404, a fuel pump supplying fuel to a fuel rail and an engine is operated at full or rated capacity to provide a higher fuel rail pressure. The fuel pump may be activated for a predetermined period of time or until a threshold pressure in the engine fuel rail is reached. After the fuel pump has operated for the predetermined period of time or until the threshold pressure in the fuel rail is reached, method 400 proceeds to 406.

[0048] At 406, method 400 deactivates the fuel pump. The fuel pump stops providing fuel to the fuel rail when the fuel pump is deactivated. The fuel pump may be deactivated by stopping the flow of electrical power to the fuel pump. After deactivating the fuel pump, method 400 proceeds to 408.

[0049] At 408, method 400 injects fuel into the engine. Fuel is injected into the engine at a constant rate so that each cylinder receives substantially the same amount of fuel (e.g., within ± 5%). Method 400 proceeds to 410.

[0050] At 410, method 400 totals the mass (or volume) of fuel delivered to the engine via the fuel rail. The fuel is injected over multiple engine cycles, and pressure in the fuel rail decreases in response to no fuel being delivered to the fuel rail via the fuel pump and fuel being injected into the engine cylinders. The mass (or volume) of fuel injected into the engine cylinders may be totaled for a predetermined period of time or until a predetermined drop in fuel rail pressure is observed.In one example, the mass (or volume) of fuel injected into the engine cylinders may be determined by indexing a fuel injector transfer function, which outputs a fuel rail pressure given by the fuel mass, and the time the fuel injector was open. Method 400 proceeds to 412.

[0051] At 412, method 400 determines a fuel rail pressure drop in response to the injection of fuel into a running engine and a fuel pump off state. The fuel rail pressure drop is determined from a time at which summing of an injected fuel mass begins to a time at which summing of an injected fuel mass ends. Method 400 proceeds to 414.

[0052] At 414, method 400 determines the compressibility of the fuel injected into the engine. The compressibility of the fuel is determined by dividing the total mass (volume) of injected fuel, as determined at 410, by the change in fuel rail fuel pressure determined at 412. Furthermore, method 400 indicates that the fuel compressibility is known by setting a bit in memory to a value of one. Fig. 2 is an example of the sequence described from 404 to 414. In some examples, the sequence from 404 may be repeated multiple times, and an average fuel compressibility may be taken to determine the compressibility of the fuel. After determining the fuel compressibility, method 400 proceeds to 416.

[0053] At 418, method 400 assesses whether it is desirable to determine a fuel rail pressure at which fuel compressibility increases to indicate that at least a portion of the fuel in the fuel rail is in a gaseous state. It may be desirable to determine the fuel rail pressure at which fuel compressibility increases to indicate the vapor pressure floor of the fuel when the engine is operating at lower loads, where the engine may be operated without large changes in engine torque or engine air-fuel ratio. Thus, when the engine is operating within a predetermined speed and torque range, the fuel rail pressure at which fuel compressibility increases may be determined.If method 400 judges that it is desired to determine a pressure of fuel in the fuel rail at which fuel compressibility increases, the answer is yes and method 400 proceeds to 420; otherwise, the answer is no and method 400 proceeds to 418.

[0054] At 420, method 400 continues to inject fuel into the engine with the fuel pump off to determine a desired fuel pressure to be provided to the fuel rail via the fuel pump. Method 400 determines a slope, or rate of change, of the fuel rail pressure versus the injected fuel mass. Fuel compressibility is low when the fuel is in a liquid state and higher when it is in a gaseous or at least partially gaseous state. A change in the slope, or rate of change, of the fuel rail pressure relative to the injected fuel mass from a higher value to a lower value may indicate a change in the compressibility of a fuel, as in Fig. 3. The engine can be operated under constant conditions (for example, a constant injected fuel mass, a constant speed, and a constant torque) if the change in the gradient of the fuel pressure is determined against the injected fuel mass. The fuel pressure at which the gradient or rate of change of the fuel pressure changes is determined as in Fig. 3 and stored in memory. The fuel pressure in the fuel rail at which the fuel pressure gradient changes indicates a fuel vapor pressure floor. In one example, a predetermined offset value is added to the fuel pressure in the fuel rail at which the fuel pressure gradient changes to determine a desired fuel pressure in the fuel rail to ensure the injection of liquid fuel and reduce the energy consumed by the fuel pump providing fuel to the fuel rail. The sequence is described in Fig. 3. After determining the desired fuel rail pressure, method 400 ends. The desired fuel rail pressure may be a basis for controlling fuel pump output. Furthermore, a bit value in memory may be changed to a value of one to indicate that a fuel control pressure is determined.

[0055] At 418, method 400 adjusts the fuel compressibility value determined at 414 by a predetermined factor (e.g., 1.4). The resulting value is a desired fuel compressibility, and the desired fuel compressibility may be the basis for controlling the output of the fuel pump supplying fuel to the fuel rail. After determining the desired fuel compressibility, method 400 exits.

[0056] The next time method 400 is executed, the desired fuel rail fuel pressure or the desired fuel compressibility may be a basis for controlling the output of the fuel pump supplying fuel to the fuel rail and the engine.

[0057] At 430, method 400 assesses whether a fuel control pressure for fuel in the fuel rail has been determined based on the compressibility of the fuel in the fuel rail. In one example, if a value of a variable in memory is one, then the answer is yes, and method 400 proceeds to 436; otherwise, the answer is no, and method 400 proceeds to 432. The variable may be set to a value of one at 420.

[0058] At 432, method 400 adjusts the fuel pressure to provide fuel in the fuel rail with a desired fuel compressibility value. The desired fuel compressibility value may be obtained from 418. In one example, the fuel pressure is set to a maximum value and decreased in predetermined increments until the desired fuel compressibility value is provided. Fuel compressibility may be determined as described at 404-414 each time the pressure of the fuel in the fuel rail is incrementally decreased to determine if fuel in the fuel rail has the desired compressibility. If the fuel pressure in the fuel rail is at a level that provides the desired compressibility, method 400 proceeds to 434.

[0059] At 434, method 400 stores a fuel pressure of the fuel in the fuel rail that provides the desired fuel compressibility in memory. The stored fuel pressure value is a desired fuel pressure for controlling the fuel pressure in the fuel rail. After storing the desired fuel pressure in memory, method 400 proceeds to 436.

[0060] At 436, method 400 judges whether a fuel tank refill has occurred or whether a fuel temperature change has occurred at the fuel rail. Method 400 may judge that a fuel refill has occurred if a fuel tank sensor indicates an increase in fuel stored in a fuel tank. Method 400 may judge that a fuel temperature change has occurred based on engine temperature or a measured temperature of the fuel in the fuel rail. If method 400 judges that a fuel refill has occurred or that there is a fuel temperature change at the fuel rail, the answer is yes, and method 400 proceeds to 450; otherwise, the answer is no, and method 400 proceeds to 438.

[0061] At 450, method 400 indicates that the desired fuel compressibility is unknown, so that a new fuel compressibility value may be determined at 404-414. After setting a value of a bit in memory to zero to indicate that the fuel compressibility is unknown, method 400 exits.

[0062] At 438, method 400 judges whether the fuel pressure in the fuel rail is greater than (>) the desired fuel pressure plus a predetermined offset value. If so, the answer is yes, and method 400 proceeds to 460; otherwise, the answer is no, and method 400 proceeds to 440.

[0063] At 460, method 400 decreases the fuel pump output by reducing the voltage and / or current supplied to the fuel pump. The fuel pump output may be decreased proportionally to a difference between the desired fuel pressure and the actual fuel pressure. After adjusting the fuel pressure, method 400 exits.

[0064] At 440, method 400 judges whether the fuel pressure in the fuel rail is less than (<) the desired fuel pressure minus a predetermined offset value. If so, the answer is yes, and method 400 proceeds to 442; otherwise, the answer is no, and method 400 proceeds to exit after no adjustments have been made to the fuel pump output.

[0065] At 442, method 400 increases the fuel pump output by increasing the voltage and / or current supplied to the fuel pump. The fuel pump output may be increased proportionally to a difference between the desired fuel pressure and the actual fuel pressure. After adjusting the fuel pressure, method 400 exits.

[0066] In this way, the fuel pressure in a fuel rail can be adjusted in response to the compressibility of the fuel supplied to an engine. The fuel rail pressure is adjusted to provide liquid fuel to the engine while reducing fuel pump energy consumption.

[0067] Thus, the procedure of Fig. 4 provides a method for delivering fuel to an engine, comprising: receiving fuel data from a controller, estimating fuel compressibility from the fuel data through instructions in the controller, and adjusting output of a fuel pump via the controller in response to the estimated fuel compressibility. The method includes where estimating fuel compressibility comprises dividing a mass of fuel injected into the engine by a pressure drop in a fuel rail. Further, the method includes where the fuel data comprises fuel pressure in a fuel rail. The method includes where the fuel data comprises an estimate of the mass of fuel injected.

[0068] In some examples, the method includes adjusting the output of the fuel pump comprising increasing a voltage or an amount of current supplied to the fuel pump in response to the estimated fuel compressibility being greater than a compressibility threshold. The method includes adjusting the output of the fuel pump comprising decreasing a voltage or an amount of current supplied to the fuel pump in response to the estimated fuel compressibility being less than a threshold compressibility.

[0069] Furthermore, the procedure of Fig.4 provides a method for supplying fuel to an engine, comprising: injecting fuel into an engine while a fuel pump supplying fuel to the engine is stopped; receiving fuel data from a controller while the fuel pump is stopped; providing a desired fuel pressure in response to a change in a slope of the fuel pressure from the fuel data; and adjusting, via the controller, the output of a fuel pump in response to the desired fuel pressure. The method includes wherein the change in slope is indicative of a fuel vapor pressure.

[0070] The method further includes where the desired fuel pressure is greater than a fuel pressure at which the slope changes. In some examples, the method includes where the change in slope is a decrease in the slope. The method further includes revising the desired fuel pressure in response to a change in fuel temperature or refilling of a fuel tank. The method includes where the received fuel data includes fuel pressure. The method includes adjusting the output of the fuel pump to provide the desired fuel pressure. The method includes injecting fuel into the engine while the fuel pump supplying fuel to the engine is stopped in response to a change in fuel temperature or refilling of the fuel tank.

[0071] It should be noted that the example control and estimation routines included herein may be used with various engine and / or vehicle system configurations. Further, the methods described herein may be a combination of actions performed by a controller in the physical world and instructions in the controller. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be performed by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The particular routines described herein may represent one or more of a number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like.Thus, various illustrated acts, 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 exemplary embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may be performed repeatedly depending on the particular strategy employed.Furthermore, the described acts, operations, and / or functions may graphically represent code to be programmed into the non-transitory memory of the computer-readable storage medium in the engine control system, wherein the described acts are performed by execution of the instructions in a system including the various engine hardware components in combination with the electronic controller.

[0072] This concludes the description. A reading of it by one skilled in the art would reveal many changes and modifications without departing from the spirit and scope of the description. For example, I3, I4, I5, V6, V8, V10, and V12 engines powered by natural gas, gasoline, diesel, or alternative fuel configurations could advantageously utilize the present description.

[0073] The following claims particularly point out certain combinations and subcombinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims should be construed as encompassing the inclusion of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by presenting new claims in this or a related application. Such claims, whether their scope is broader, narrower, the same, or different with respect to the original claims, are also considered to be included within the subject matter of the present disclosure.

Claims

[1] A method of supplying fuel to an engine, comprising: Receiving fuel data from a controller; Estimating fuel compressibility from fuel data through instructions in the controller; and Adjusting the output of a fuel pump via the controller in response to the estimated fuel compressibility, wherein adjusting the output of the fuel pump comprises increasing a voltage or an amount of current supplied to the fuel pump in response to the estimated fuel compressibility being greater than a threshold compressibility. [2] The method of claim 1, wherein estimating fuel compressibility comprises dividing a mass of fuel injected into the engine by a pressure drop in a fuel rail. [3] The method of claim 1, wherein the fuel data includes fuel pressure in a fuel rail. [4] The method of claim 1, wherein the fuel data comprises an estimate of the injected fuel mass. [5] The method of claim 1, wherein adjusting the output of the fuel pump comprises decreasing a voltage or an amount of current supplied to the fuel pump in response to the estimated fuel compressibility being less than a threshold compressibility. [6] A system for controlling a prime mover, comprising: a power machine; a fuel pump supplying fuel to the engine; a controller including executable instructions stored in the non-volatile memory for adjusting the output of the fuel pump in response to compressibility of fuel supplied to the engine, wherein the compressibility of the fuel supplied to the engine is based on an injected fuel mass divided by a change in fuel rail pressure, and configured to perform a method according to any preceding claim. [7] The system of claim 6, further comprising a fuel rail coupled to the engine and the fuel injector, and a pressure sensor coupled to the fuel rail. [8] The system of claim 7, further comprising additional instructions for estimating the compressibility of the fuel supplied to the engine based on an output of the pressure sensor. [9] The system of claim 6, further comprising additional instructions for determining a desired fuel pressure in response to the compressibility of the fuel supplied to the engine. [10] The system of claim 9, further comprising additional instructions for estimating the compressibility of the fuel supplied to the engine in response to a change in fuel temperature or a refill of a fuel tank.

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