Methods and systems for fuel rail pressure relief

Abstract

Procedure comprising: during a warmed-up engine idle condition, Maintaining direct injection nozzles (252) in a deactivated state until a direct injection fuel rail pressure is reduced by a high pressure pump relief valve (272), and then further reducing the direct injection fuel rail pressure by intermittently activating the direct injection nozzles (252).

Description

Area

[0001] The present application generally relates to systems and methods for adjusting the operation of fuel injectors of an internal combustion engine to reduce injector click noise. State of the art / brief description

[0002] Engines may be configured to deliver fuel to an engine cylinder using port fuel injection and / or direct fuel injection. Port-to-port direct fuel injection (PFDI) engines are capable of effectively utilizing both fuel injection systems. For example, at high engine loads, fuel may be injected directly into an engine cylinder via a direct fuel injector, utilizing the load-cooling properties of direct fuel injection (DI). At lower engine loads and during engine start-up, fuel may be injected into an intake port of the engine cylinder via a port fuel injector, reducing particulate emissions. During still other conditions, a portion of the fuel may be delivered to the cylinder via the port fuel injector, while the remainder of the fuel is delivered to the cylinder via the direct fuel injector.

[0003] During periods of engine operation where direct fuel injection is disabled and no fuel is released from the direct injector (for example, during conditions where only port fuel injection is scheduled), fuel trapped within the DI fuel rail may expand due to high temperatures. This can result in a pressure buildup in the DI fuel rails as well as increased injector peak temperatures. If the DI deactivation period is long, the pressure buildup can be significant. Prolonged exposure to such high pressure conditions can cause damage to fuel system components.To counteract this, while direct injection is disabled, a small amount of fuel may be released intermittently from the direct injection injectors to relieve excess pressure in the direct injection fuel rail and reduce the injector peak temperature.

[0004] However, the inventors have identified potential problems with the above-mentioned approach. As one example, activating the direct fuel injectors for DI fuel rail pressure relief creates a high impact force that is transmitted from the injectors to the engine cylinder heads. This creates a clicking noise in the vehicle that can be annoying to the vehicle driver. The higher the rail pressure, the louder the clicking noise that is generated. Additionally, if port fuel injection is used during engine idle, when engine noise is low, there may not be enough engine noise to mask the clicking noise, making the clicking noise more audible and annoying to the driver. Additionally, the high pressure transmitted from the direct-injected fuel to the cylinder heads can damage the cylinder head, resulting in warranty issues.

[0005] In one example, the above-mentioned problems may be at least partially addressed by a method for an engine, comprising: during a warm-up engine idle condition, maintaining the direct injection fuel injectors deactivated until a direct injection fuel rail pressure is reduced by a high-pressure pump relief valve, and then further reducing the direct injection fuel rail pressure by intermittently activating the direct injection fuel injectors. In this way, pressure at the direct injection fuel rail may be relieved with reduced clicking noise.

[0006] As one example, an engine may be configured with both port and direct fuel injection. Fuel may be delivered to the port fuel rail by a low-pressure lift pump. Pressurized fuel may then be delivered to the direct fuel rail via a high-pressure pump (HPP), which receives fuel from the low-pressure lift pump (LPP). During warm-up idle conditions, fuel may be delivered to the engine only via port fuel injection, and the direct fuel injectors may be deactivated. Pressure may therefore build up from fuel trapped at the direct fuel rail, resulting in increased pressure experienced by the HPP.A controller may determine a required pressure relief amount based at least on a duration of direct injector deactivation (or a duration of PFI-only operation) and further based on engine operating conditions. The DI rail pressure may then be relieved while the direct injectors are maintained deactivated. As a first step, while the rail pressure exceeds a first threshold pressure corresponding to a high pressure (HP) pump relief pressure, a pump relief valve coupled to the HPP may intermittently open (e.g., automatically via mechanical actuation) to maintain the rail pressure at the first threshold pressure.If further pressure relief is required, such as when a DI deactivation duration exceeds a threshold duration, the direct injectors can be activated intermittently to deliver a small fuel pulse to the cylinders. By relieving at least some pressure via the pump unloading valve, the additional pressure relief required via the direct injectors (if necessary) can result in a smaller number of fuel pulses, as well as fuel pulses with a smaller pulse width, than would be required if only direct injection were used for pressure relief.Due to the smaller size and smaller number of fuel pulses, as well as the lower fuel rail pressure at which the injectors are activated, the impact force transmitted from the injector to the engine cylinder heads can be significantly lower (e.g., negligible), resulting in a reduced occurrence of annoying clicking noise. Additionally, damage to fuel system components is reduced.

[0007] In this way, pressure can be relieved from a DI fuel rail and associated HPP with less generation of objectionable noise, such as clicking. By allowing DI fuel rail pressure to be reduced below a HPP relief threshold via actuation of the pump unloading valve, the direct injectors can be kept deactivated for a longer duration, reducing the occurrence of clicking. Even when the direct injectors are activated for pressure relief, since a lower degree of pressure relief is required across the injectors due to the pressure relief provided via the pump unloading valve, the amount of objectionable noise generated can be significantly lower or negligible.Therefore, the lower-volume clicking noise can be low enough to be masked by engine noise, making it inaudible (or annoying) to the driver. By reducing the impact force on the cylinder head from direct injection, component life is also extended, reducing warranty issues.

[0008] DE 10 2006 000 333 A1 describes a fuel injection control system for common-rail diesel internal combustion engines. DE 10 2014 007 880 A1 presents a method for reducing pressure in the high-pressure system of a fuel injection system during load changes, in which minute amounts of fuel are injected via the injectors. DE 100 58 674 A1 discloses a method for regulating the fuel pressure in an internal combustion engine, in which a control signal interrupts the fuel delivery into the fuel manifold as soon as a specified limit is exceeded.

[0009] It should be understood that the above summary is provided to introduce, in a simplified form, a selection of concepts 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 solely by the claims following the detailed description. Short description of the drawings Fig. 1 schematically illustrates an exemplary embodiment of a cylinder of an internal combustion engine. Fig. 2 depicts an exemplary embodiment of a fuel system configured for schematic port fuel injection and direct fuel injection, both associated with the engine of Fig. 1 can be used. Fig. 3 shows a flowchart illustrating a method that may be implemented to relieve direct injection fuel rail pressure with reduced clicking noise. Fig. 4 shows an example operation of the fuel system to reduce direct injection fuel rail pressure. Fig. Figure 5A shows an example bar chart comparing click noise levels produced by different DI fuel rail pressure relief methods. Fig. Figure 5B shows an example table comparing click noise levels produced by different DI fuel rail pressure relief methods. Fig. Figure 6 shows example plots of DI fuel rail pressure relief using various techniques. Detailed description

[0010] The following description relates to systems and methods for adjusting the operation of fuel injectors of an internal combustion engine to reduce injector click noise. An exemplary embodiment of a cylinder in an internal combustion engine equipped with both a direct fuel injector and a port fuel injector is described in Fig. 1 given. Fig. 2 depicts a fuel system connected to the engine of the Fig. 1 can be used. Fuel under pressure may then be delivered to a direct injection fuel rail in the fuel system via a high-pressure pump that receives fuel from a low-pressure lift pump. During certain engine operating conditions, fuel may only be delivered to the engine via port fuel injection, and the direct injectors may be deactivated. During an extended period of deactivation of the direct injectors, pressure may build up in the direct injection (DI) fuel rail. A method for relieving DI fuel rail pressure with reduced direct injector click noise is described with reference to Fig. 3. A pressure relief valve coupled to the high pressure pump can, for example, be used together with intermittent DI, as shown in Fig. 4 shown. The Fig. 5A-5B show an example bar chart and table comparing click noise levels produced by different methods (such as DI pump relief valve pressure release) for DI fuel rail pressure relief. Fig. Figure 6 shows example plots of DI fuel rail pressure relief using such techniques.

[0011] Regarding the terminology used throughout this detailed description, a high-pressure pump or direct injection pump may be abbreviated as HPP. Similarly, a low-pressure pump or lift pump may be abbreviated as LPP. Port fuel injection may be abbreviated as PFI, while direct injection may be abbreviated as DI. Furthermore, fuel rail pressure, or the value of fuel pressure in a fuel rail, may be abbreviated as FRP.

[0012] Fig. 1 depicts an example of a combustion chamber or cylinder of an internal combustion engine 10. The engine 10 may be controlled at least in part by a control system including a controller 12 and by input from a vehicle operator 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The cylinder (also referred to herein as "the combustion chamber") 14 of the engine 10 may include combustion chamber walls 136 with a piston 138 positioned therein. The piston 138 may be coupled to the crankshaft 140 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. The crankshaft 140 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system.Furthermore, a starter motor (not shown) may be coupled to the crankshaft 140 via a flywheel to enable starting operation of the engine 10.

[0013] Cylinder 14 may receive intake air via a series of intake air passages 142, 144, and 146. Intake air passage 146 may communicate with other cylinders of engine 10 in addition to cylinder 14. In some examples, one or more of the intake passages may include a boosting device, such as a turbocharger or a supercharger. For example, Fig. 1 shows the engine 10 configured with a turbocharger having a compressor 174 disposed between intake passages 142 and 144, and an exhaust turbine 176 disposed along the exhaust passage 148. The compressor 174 may be at least partially powered by the exhaust turbine 176 via a shaft 180, wherein the boosting device is configured as a turbocharger. However, in other examples, such as when the engine 10 is provided with a supercharger, the exhaust turbine 176 may optionally be omitted, wherein the compressor 174 may be driven by a mechanical input from an engine or the engine. A throttle 162 having a throttle valve 164 may be provided along an intake passage of the engine to vary the flow rate and / or pressure of intake air supplied to the engine cylinders. The throttle 162 can, for example, as in Fig. 1, may be positioned downstream of the compressor 174, or alternatively it may be provided upstream of the compressor 174.

[0014] Exhaust passage 148 may receive exhaust gases from other cylinders of engine 10 in addition to cylinder 14. Exhaust gas sensor 128 is shown coupled to exhaust passage 148 upstream of emissions control device 178. Sensor 128 may be selected from various suitable sensors, such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a dual-state oxygen sensor or an EGO (as shown), a HEGO (heated EGO), a NOx, an HC, or a CO sensor to provide an indication of the exhaust air / fuel ratio. Emissions control device 178 may be a three-way catalyst (TWC), a NOx trap, various other emissions control devices, or combinations thereof.

[0015] Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown including at least one intake poppet valve 150 and at least one exhaust poppet valve 156 located at an upper portion of cylinder 14. In some examples, each cylinder of engine 10, including cylinder 14, may include at least two intake poppet valves and at least two exhaust poppet valves located at an upper portion of the cylinder.

[0016] The intake valve 150 may be controlled by the controller 12 via the actuator 152. Similarly, the exhaust valve 156 may be controlled by the controller 12 via the actuator 154. During certain 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 150 and the exhaust valve 156 may be determined by respective valve position sensors (not shown). The valve actuators may be of the electric valve actuation type or the cam actuation type, or a combination thereof.Intake and exhaust valve timing may occur simultaneously, or any of variable intake cam timing, variable exhaust cam timing, dual independent variable cam timing, or fixed cam timing may be used. Each cam actuation system may include one or more cams and may utilize cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (VVL) systems that may be actuated by controller 12 to vary valve operation. For example, cylinder 14 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 examples, 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.

[0017] Cylinder 14 may have a compression ratio that is the ratio of volumes when piston 138 is at bottom dead center or top dead center. In one example, the compression ratio is in the range of 9:1 to 10:1. However, in some examples where different fuels are used, the compression ratio may be increased. This may occur, for example, when using higher octane fuels or fuels with higher latent heat of vaporization. The compression ratio may also be increased if direct injection is used due to its effect on engine knock.

[0018] In some examples, each cylinder of engine 10 may include a spark plug 192 for initiating combustion. Ignition system 190 may provide an ignition spark to combustion chamber 14 via spark plug 192 in response to spark advance signal SA from controller 12 during selected operating modes. However, in some embodiments, spark plug 192 may be omitted, for example, when engine 10 is capable of initiating combustion through auto-ignition or by injecting fuel, as may be the case with some diesel engines.

[0019] In some examples, each cylinder of engine 10 may be configured with one or more fuel injectors to deliver fuel to the cylinders. As a non-limiting example, cylinder 14 is shown having two fuel injectors 166 and 170. Fuel injectors 166 and 170 may be configured to deliver fuel received from fuel system 8. As described with reference to Fig. 2 and Fig. 3, the fuel system 8 may include one or more fuel tanks, fuel pumps, and fuel rails. The fuel injector 166 is shown coupled directly to the cylinder 14 to inject fuel directly therein in proportion to the pulse width of a signal FPW-1 received from the controller 12 via an electronic driver 168. In this manner, the fuel injector 166 provides so-called direct injection (hereinafter referred to as "DI") of fuel into the combustion cylinder 14. Although Fig. 1 shows the injector 166 positioned on one side of the cylinder 14, it may alternatively be positioned above the piston, such as near the position of the spark plug 192. Such a position may improve mixing and combustion when the engine is operating on an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be positioned overhead and near the intake valve to improve mixing. Fuel may be supplied to the fuel injector 166 from a fuel tank of the fuel system 8 via a high-pressure fuel pump and a fuel rail. The fuel tank may further include a pressure transducer that provides a signal to the controller 12.

[0020] Fuel injector 170 is shown disposed in intake passage 146 rather than in cylinder 14 in a configuration that provides what is known as port fuel injection (hereinafter referred to as "PFI") into the intake manifold opening upstream of cylinder 14. Fuel injector 170 may inject fuel received from fuel system 8 in proportion to the pulse width of signal FPW-2 received from controller 12 via electronic driver 171. Note that a single driver 168 or 171 may be used for both fuel injection systems, or multiple drivers, for example, driver 168 for fuel injector 166 and driver 171 for fuel injector 170, may be used as shown.

[0021] In an alternative example, each of fuel injectors 166 and 170 may be configured as a direct fuel injector for injecting fuel directly into cylinder 14. In yet another example, each of fuel injectors 166 and 170 may be configured as a port fuel injector for injecting fuel upstream of intake valve 150. In still other examples, cylinder 14 may have only a single fuel injector configured to receive different fuels from the fuel systems in varying relative amounts as a fuel mixture, and further configured to inject this fuel mixture either directly into the cylinder as a direct fuel injector or upstream of the intake valves as a port fuel injector.It should therefore be understood that the fuel systems described herein are not intended to be limited by the particular fuel injector configurations described herein by way of example.

[0022] Fuel may be delivered to the cylinder by both injectors during a single cylinder cycle. For example, each injector may deliver a portion of a total fuel injection combusted in cylinder 14. Further, the distribution and / or relative amount of fuel delivered by each injector may vary with operating conditions, such as engine load, knock, and exhaust temperature, as described below.

[0023] The manifold-injected fuel may be delivered during an intake-valve open event, a intake-valve closed event (e.g., substantially prior to the intake stroke), and during both open and closed intake-valve operation. Likewise, direct-injected fuel may be delivered, for example, during an intake stroke, as well as partially during a previous exhaust stroke, during the intake stroke, and partially during the compression stroke. Even for a single combustion event, injected fuel may therefore be injected at different times by the port and direct injector. Furthermore, for a single combustion event, multiple injections of the delivered fuel may be performed per cycle. The multiple injections may be performed during the compression stroke, intake stroke, or any suitable combination thereof.

[0024] Fuel injectors 166 and 170 may have different characteristics. These include size differences; for example, one injector may have a larger injection opening than the other. Other differences include, but are not limited to, different injection angles, different operating temperatures, different target areas, different injection timing, different injection characteristics, different positions, etc. Furthermore, different effects may be achieved depending on the distribution ratio of the injected fuel to injectors 166 and 170.

[0025] The fuel tanks in the fuel system 8 may contain fuels of different fuel types, such as fuels with different fuel qualities and different fuel compositions. The differences may include different alcohol contents, different water contents, different octane numbers, different latent heats, different fuel blends, and / or combinations thereof, etc. An example of fuels with different latent heats could include gasoline as a first fuel type with a lower latent heat of vaporization and ethanol as a second fuel type with a higher latent heat of vaporization.In another example, the engine may use gasoline as a first fuel type and an alcohol-containing fuel blend, such as E85 (which consists of approximately 85% ethanol and 15% gasoline) or M85 (which consists of approximately 85% methanol and 15% gasoline), as a second fuel type. Other technically feasible substances include water, methanol, a mixture of alcohol and water, a mixture of methanol and water, a mixture of alcohols, etc.

[0026] In yet another example, both fuels may be alcohol blends with a varying alcohol composition, where the first fuel type may be a gasoline-alcohol blend with a lower alcohol concentration, such as E10 (containing approximately 10% ethanol), while the second fuel type may be a gasoline-alcohol blend with a higher alcohol concentration, such as E85 (containing approximately 85% ethanol). In addition, the first and second fuels may also differ in other fuel qualities, such as a difference in temperature, viscosity, octane number, etc. Furthermore, the fuel properties of one or both fuel tanks may vary frequently, for example, due to daily variations in tank refilling.

[0027] The control device 12 is in Fig. 1 as a microcomputer having a microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs and calibration values, shown as a non-volatile read-only memory chip 110 in this particular example for storing executable instructions, random access memory 112, latch 114, and a data bus.Controller 12 may receive various signals from sensors coupled to engine 10 in addition to the signals discussed above, including induced mass air flow (MAF) measurements from mass air flow sensor 122, engine coolant temperature (ECT) from temperature sensor 116 coupled to cooling jacket 118, a profile ignition pickup (PIP) signal from Hall effect sensor 120 (or other sensor type) coupled to crankshaft 140, throttle position (TP) from a throttle position sensor, and an absolute manifold pressure (MAP) signal from sensor 124. Engine speed signal RPM may be generated by controller 12 from the PIP signal.The intake manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of intake manifold vacuum or pressure. Controller 12 receives signals from the various sensors of the . Fig. 1 and uses the various actuators of the Fig. 1 for adjusting the machine operation based on the received signals and instructions stored in a memory of the control device.

[0028] As described above, Fig. 1 only a single cylinder of a multi-cylinder engine. Therefore, each cylinder may similarly have its own set of intake / exhaust valves, fuel injector(s), spark plug, etc. It is understood that the engine 10 may have any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Further, each of these cylinders may include some or all of the various described components described in Fig. 1 in relation to the cylinder 14.

[0029] Fig. 2 schematically shows an embodiment 200 of a fuel system, such as the fuel system 8 of the Fig. 1. The fuel system 200 is operable to supply fuel to an engine, such as the engine 10 of the Fig. 1, supply fuel. The fuel system 200 may be controlled by a controller to perform some or all of the steps described with reference to the method of Fig. 3 described actions.

[0030] The fuel system 200 includes a fuel storage tank 210 for storing fuel on board the vehicle, a low-pressure fuel pump (LPP) 212 (also referred to herein as fuel lift pump 212), and a high-pressure fuel pump (HPP) 214 (also referred to herein as fuel injection pump 214). Fuel may be provided to the fuel tank 210 via the fuel fill passage 204. In one example, the LPP 212 may be an electrically operated low-pressure fuel pump disposed at least partially within the fuel tank 210. The LPP 212 may be controlled by a controller 222 (e.g., controller 12 of the Fig. 1) to provide fuel via fuel passage 218 to HPP 214. LPP 212 may be configured as a so-called fuel lift pump. As one example, LPP 212 may be a turbine pump (e.g., a centrifugal pump) having an electric (e.g., direct current (DC)) pump motor, wherein the pressure rise across the pump and / or the volumetric flow through the pump may be controlled by varying the electrical power provided to the pump motor, thereby increasing or decreasing the motor speed. For example, if the controller decreases the electrical power provided to lift pump 212, the volumetric flow and / or pressure rise across the lift pump may also be decreased. The volumetric flow and / or pressure rise across the pump may be increased by increasing the electrical power provided to lift pump 212.As one example, the electrical power supplied to the low-pressure pump motor may be obtained from an alternator or other energy storage device onboard the vehicle (not shown), allowing the control system to control the electrical load used to power the low-pressure pump. Therefore, by varying the voltage and / or current supplied to the low-pressure fuel pump, the flow rate and pressure of the fuel supplied at the inlet of the high-pressure fuel pump 214 are adjusted.

[0031] The LPP 212 may be fluidly coupled to a filter 217, which removes small contaminants contained in the fuel that could potentially damage fuel-handling components. A check valve 213, which can facilitate fuel delivery and maintain fuel line pressure, may be fluidly positioned upstream of the filter 217. With the check valve 213 upstream of the filter 217, the flexibility of the low-pressure passage 218 can be increased, as the filter may have a large physical volume. Additionally, a pressure relief valve 219 may be used to limit the fuel pressure in the low-pressure passage 218 (for example, in the outlet of the lift pump 212). The pressure relief valve 219 may comprise a ball-and-spring mechanism that seats and seals, for example, at a predetermined pressure differential.The pressure differential setpoint at which the pressure relief valve 219 may open according to its configuration may take on various suitable values; in one non-limiting example, the setpoint may be 6.4 bar or 5 bar(g). An orifice 223 may be used to allow air and / or fuel vapor to be vented from the lift pump 212. This vent at orifice 223 may also be used to drive a jet pump used to transfer fuel from one location to another within the tank 210. In one example, an orifice check valve (not shown) may be placed in series with the orifice 223. In some embodiments, the fuel system 8 may include one or more (e.g., a series of) check valves fluidly coupled to the low-pressure fuel pump 212 to prevent fuel from leaking back upstream of the valves.In this context, upstream flow refers to fuel flow flowing from the fuel rails 250, 260 to the LPP 212, while downstream flow refers to a nominal fuel flow direction from the LPP to the HPP 214 and on to the fuel rails.

[0032] Fuel delivered from the LPP 212 may be supplied at a lower pressure to a fuel passage 218 leading to an inlet 203 of the HPP 214. The HPP 214 may then deliver fuel to a first fuel rail 250 coupled to one or more fuel injectors of a first group of direct fuel injectors 252 (also referred to herein as a first injector group). Fuel delivered from the LPP 212 may also be supplied to a second fuel rail 260 coupled to one or more fuel injectors of a second group of port fuel injectors 262 (also referred to herein as a second injector group). The HPP 214 is operable to raise the pressure of the fuel delivered to the first fuel rail above the lift pump pressure, wherein the first fuel rail is coupled to the direct injector group operating at a high pressure.Therefore, high pressure DI can be enabled while PFI operates at a lower pressure.

[0033] Although both the first fuel rail 250 and the second fuel rail 260 are shown delivering fuel to four fuel injectors of the respective injector group 252, 262, it should be understood that each fuel rail 250, 260 can deliver fuel to any suitable number of fuel injectors. In one example, the first fuel rail 250 can deliver fuel to one fuel injector of the first injector group 252 for each cylinder of the engine, while the second fuel rail 260 can deliver fuel to one fuel injector of the second injector group 262 for each cylinder of the engine. The controller 222 can individually actuate each of the port injectors 262 via a port injector driver 237 and actuate each of the direct injectors 252 via a direct injector driver 238.The controller 222, the drivers 237, 238, and other suitable engine system controls may comprise a control system. Although the drivers 237, 238 are shown external to the controller 222, it should be understood that in other examples, the controller 222 may include the drivers 237, 238 or may be configured to provide the functionality of the drivers 237, 238. The controller 222 may include additional components not shown, such as those included in the controller 12 of FIG. Fig. 1 are included.

[0034] The HPP 214 may be an engine-driven positive displacement pump. As a non-limiting example, the HPP 214 may be a BOSCH HDP5 high-pressure pump, which uses an electromagnetically actuated control valve (e.g., a fuel volume regulator, a solenoid valve, etc.) to vary the effective pumping volume of each pump stroke. The HPP's output check valve is mechanically controlled, not electronically, by an external control device. The HPP 214, unlike the engine-driven LPP 212, may be mechanically driven by the engine. The HPP 214 includes a pump piston 228, a pump compression chamber 205 (also called compression chamber herein), and a stepper chamber 227. The pump piston 228 receives a mechanical input from the engine crankshaft or camshaft via the cam lobe 230, thereby operating the HPP according to the principle of a cam-driven single-cylinder pump. A sensor (in Fig. 2 not shown) may be positioned near the cam 230 to enable the determination of the angular position of the cam (for example, between 0 and 360 degrees), which may be relayed to the controller 222.

[0035] A lift pump fuel pressure sensor 231 may be positioned along the fuel passage 218 between the lift pump 212 and the high-pressure fuel pump 214. In this configuration, the readings from the sensor 231 may be interpreted as indications of the fuel pressure of the lift pump 212 (e.g., the lift pump fuel outlet pressure) and / or the high-pressure fuel pump inlet pressure. The readings from the sensor 231 may be used to evaluate the operation of various components in the fuel system 200, determine whether enough fuel pressure is being provided to the high-pressure fuel pump 214 so that the high-pressure fuel pump receives liquid fuel and not fuel vapor, and / or minimize the average electrical power supplied to the lift pump 212.

[0036] The first fuel rail 250 includes a first fuel rail pressure sensor 248 for providing an indication of direct injection fuel rail pressure to the controller 222. Likewise, the second fuel rail 260 includes a second fuel rail pressure sensor 258 for providing an indication of port injection fuel rail pressure to the controller 222. An engine speed sensor 233 may be used to provide an indication of engine speed to the controller 222. The indication of engine speed may be used to identify the speed of the high-pressure fuel pump 214, since the pump 214 is mechanically driven by the engine 202, for example, via the crankshaft or the camshaft.

[0037] The first fuel rail 250 is coupled along the fuel passage 278 to an outlet 208 of the HPP 214. A check valve 274 and a pressure relief valve (also called a pump relief valve) 272 may be positioned between the outlet 208 of the HPP 214 and the first (DI) fuel rail 250. The pump relief valve 272 may be coupled to a bypass channel 279 of the fuel passage 278. The outlet check valve 274 opens to allow fuel to flow from the high-pressure pump outlet 208 into a fuel rail only when a pressure at the outlet of the direct injection fuel pump 214 (e.g., a compression chamber outlet pressure) is higher than the fuel rail pressure. The pump relief valve 272 may limit the pressure in the fuel passage 278 downstream of the HPP 214 and upstream of the first fuel rail 250.For example, the pump relief valve 272 may limit the pressure in the fuel passage 278 to 200 bar. The pump relief valve 272 allows fuel flow out of the DI fuel rail 250 to the pump outlet 208 when the fuel rail pressure is higher than a predetermined pressure. The valves 244 and 242 act together to maintain the low-pressure fuel rail 260 pressurized to a predetermined low pressure. The pressure relief valve 242 helps limit the pressure that may build up in the fuel rail 260 due to thermal expansion of the fuel.

[0038] Based on engine operating conditions, fuel may be delivered from one or more of port fuel injectors 262 and direct fuel injectors 252. For example, during high load conditions, fuel may be delivered to a cylinder on a given engine cycle only via direct injection while the port fuel injectors 262 are deactivated. In another example, during medium load conditions, fuel may be delivered to a cylinder on a given engine cycle via both direct and port fuel injection. In yet another example, during low load conditions, engine start-up, and warm idle conditions, fuel may be delivered to a cylinder on a given engine cycle only via port fuel injection, with the direct fuel injectors 252 deactivated.Because fuel injection from the direct injectors results in injector cooling, after a period of inactivity, pressure may build up from the fuel trapped at the DI fuel rail 250, resulting in increased pressure at both the DI fuel rail 250 and the HPP 214. Additionally, temperatures at the direct injector tip may increase. Under such circumstances, the pressure of the DI fuel rail 250 must be relieved to prevent damage to fuel system components.However, if the DI injectors 252 are activated at this stage to inject fuel into the engine, the common rail pressure may be lowered due to the high common rail pressure when the DI injectors 252 are activated, and an impact force may be transmitted from the injectors 252 to the engine cylinder head, causing a clicking noise that may be unacceptable to the driver. As described herein with reference to FIG. Fig. 3, to reduce the clicking noise during the reduction of the DI fuel rail 250 pressure, the pump relief valve 272 may be opened (e.g., automatically via mechanical actuation, each time the rail pressure exceeds the HPP relief pressure) to maintain the rail pressure at or below the HPP relief pressure 214. If further pressure relief is required, such as when a duration of DI deactivation is longer than a threshold duration, the direct fuel injector 252 may be intermittently activated to deliver a smaller fuel pulse to the cylinders at a lower frequency.

[0039] In this way, by relieving at least some of the DI fuel rail 250 pressure via the pump relief valve 272, the additional pressure relief required via the direct injectors can be accomplished using a smaller number of fuel pulses with a narrower pulse width than would be required if only direct injection were used for pressure relief. Due to the smaller size and number of fuel pulses, as well as the lower absolute pressure at which the injectors are activated, the impact force transmitted from the injectors to the engine cylinder heads can be significantly lower, resulting in a reduction in annoying clicking noise. Damage to fuel system components can also be reduced.

[0040] It should be noted that the high pressure pump 214 of the Fig. 2 is shown as an illustrative example of a possible configuration for a high-pressure pump. Components used in Fig. 2 may be removed and / or modified, while additional components not shown here may be added to the pump 214 while still maintaining the ability to deliver high pressure fuel to a direct injection fuel rail and a port injection fuel rail.

[0041] Controller 12 may also control the operation of each of fuel pumps 212 and 214 to adjust an amount, pressure, flow rate, etc., of fuel delivered to the engine. For example, controller 12 may vary a pressure setting, pump stroke amount, pump duty cycle command, and / or fuel flow rate of the fuel pumps to deliver fuel to different locations in the fuel system. A driver (not shown) electronically coupled to controller 222 may be used to send a control signal to the low-pressure pump, as needed, to adjust the output (e.g., speed, flow output, and / or pressure) of the low-pressure pump.

[0042] The Fig. 1 and Fig. 2 show example configurations of the fuel system with relative positioning of the various components. If they are shown directly touching or directly coupled to one another, such elements may, in at least one example, be said to be directly touching or directly coupled, respectively. Likewise, elements shown as contiguous or adjacent to one another may, in at least one example, be contiguous or adjacent to one another, respectively. As one example, components that are in surface contact with one another may be said to be in surface contact with one another. As another example, elements that are positioned only with a gap between one another and no other components may, in at least one example, be said to be such.

[0043] Fig. 3 illustrates an exemplary method 300 for relieving direct injection rail pressure with reduced injector click noise. Instructions for performing method 300 and the remainder of the methods included herein may be executed by a controller based on instructions stored in a memory of the controller and in conjunction with signals received from engine system sensors, such as those described above with reference to Fig. 1 and Fig. 2. The controller may use engine actuators of the engine system according to the methods described below to adjust engine operation.

[0044] At 302, engine operating conditions may be determined by the controller. The engine operating conditions may include engine load, engine temperature, engine speed, operator torque demand, etc. Depending on the estimated operating conditions, a variety of engine parameters may be determined. For example, at 304, fuel injection scheduling may be established. This includes determining an amount of fuel to be delivered to a cylinder (e.g., based on torque demand) and injection timing. Furthermore, a fuel injection mode best suited to the current engine operating conditions may be selected.In one example, at high engine loads, direct injection (DI) of fuel into an engine cylinder via a direct fuel injector may be selected to utilize the load cooling characteristics of DI, allowing the engine cylinders to operate at higher compression ratios without risking undesirable engine knock. If direct injection is selected, the controller may determine whether to deliver the fuel as a single injection or divided into multiple injections, and whether to deliver the injection(s) in an intake stroke and / or a compression stroke. In another example, at lower engine loads (low engine speed) and during engine start-up operations (particularly during cold starts), port fuel injection (PFI) of fuel into an intake port of the engine cylinder via a port fuel injector may be selected to reduce particulate emissions.If port fuel injection is selected, the controller may determine whether to deliver fuel during a closed intake valve event or an open intake valve event. Other conditions may exist where a portion of the fuel is delivered to the cylinder via the fuel injector, while the remainder of the fuel is delivered to the cylinder via the direct fuel injector. Determining fuel injection scheduling may also include determining, for each injector, a fuel injector pulse width and a duration between injection pulses based on estimated engine operating conditions.

[0045] At 306, the routine includes determining whether only port fuel injection has been requested based on the current engine operating parameters. For example, only PFI may be requested during low engine load and low engine temperature conditions, as well as during engine start-ups. If it is determined that PFI is not currently requested, the routine may include determining at 308 whether only direct injection has been requested. For example, DI may be desirable during high engine load and / or high engine temperature conditions. If it is determined that only DI is requested, fuel may be injected into the engine at 310 via the direct injectors (such as the direct injectors 252 in Fig. 1). The controller may adjust an injection pulse width of the direct injectors to deliver fuel through the direct injectors according to the specified fuel delivery schedule.

[0046] If it is determined that only PFI and only DI are undesirable for fueling, the routine may determine at 312 whether both DI and PFI are requested for fuel injection. If it is determined that both direct injection and port injection have been requested, the controller may send a signal to actuators coupled to the direct injector and the port injector at 314 to initiate fueling based on a predetermined fueling schedule. Each injector may deliver a portion of a total fuel injection combusted in the cylinder. As shown in Fig. 2, the distribution and / or relative proportion of fuel delivered by each injector may vary based on operating conditions such as engine load, knock, exhaust gas temperature, etc.

[0047] Returning to 306, if it is determined that only PFI is desired, the controller may, at 316, provide the specified pulse width to the port injector (such as port injectors 262 in Fig. 1) to initiate fuel injection. Additionally, the controller may deactivate the direct injectors at 318.

[0048] Therefore, when direct injection is disabled, fuel cannot be delivered through the direct injection fuel rail (such as the DI fuel rail 250 in Fig. 2) to the cylinders and the direct fuel injectors. Consequently, any fuel trapped within the DI fuel rail may expand due to high temperatures. This can result in a pressure buildup at the DI fuel rail. Since fuel injection results in injector cooling, the lack of direct injection also results in elevated injector peak temperatures. Therefore, if the direct injectors are kept deactivated for an extended period, the pressure buildup in the fuel rail can be significant and cause damage to various fuel system components.

[0049] At 320, while the direct injectors are deactivated, a pressure at the DI fuel rail may be estimated (e.g., predicted or modeled) by the controller. In one example, the expected pressure may be based on the duration of DI deactivation and the DI fuel rail temperature. The longer the duration of DI deactivation and / or the higher the fuel rail temperature, the higher the expected fuel rail pressure. The DI fuel rail pressure may also be based on input from a fuel rail pressure sensor (such as the DI fuel rail pressure sensor 248 in Fig. 2). In an alternative example, the expected DI fuel rail pressure can be modeled based on a duration of operation in port injection mode only.

[0050] A pump relief valve (such as valve 272 in Fig. 2) may be coupled to a bypass passage of the fuel passage between the high-pressure pump (HPP) and the direct injection fuel rail, and this valve may ensure that the DI fuel rail pressure does not rise above a pressure relief threshold of the HPP. At 322, if the DI fuel rail pressure exceeds the HPP pressure relief threshold (e.g., a first threshold), the pump relief valve coupled to the HPP may open to maintain the rail pressure at the first threshold pressure. In one example, the valve may be a mechanical valve that automatically opens each time the fuel rail pressure in the DI fuel rail exceeds the first threshold to release fuel into the fuel passage via the bypass passage.The valve may also be automatically closed once the fuel rail pressure in the DI fuel rail reaches or falls below the first threshold. In alternative examples, the valve may be electrically opened and closed in response to the fuel rail pressure. Opening the valve allows for a reduction in the fuel rail pressure and a lower injector peak temperature of the direct injectors.

[0051] During extended fuel system operation with DI deactivation and elevated DI fuel rail temperature, further pressure relief in the DI fuel rail may be desired to prevent any damage to fuel system components. At 324, the routine includes determining whether a further reduction in pressure is required, for example, to a second threshold below the first threshold. In one example, the second threshold corresponds to a lower pressure in the DI fuel rail while avoiding fuel component damage. As an example, further pressure reduction may be requested if the direct injectors have been deactivated for an extended period of time and / or if the temperature of the HPP is higher than a threshold temperature (for example, if the HPP temperature exceeds 100°C).

[0052] If it is determined that further reduction of pressure below the HPP pressure relief threshold (first threshold) is desired (for example, if the HPP temperature is higher than a threshold), the controller may send a signal to activate the DI injectors at 326. If the HPP temperature is higher than the threshold, activation of the DI (HPP fuel pump and direct injectors) is requested to prevent fuel vapors from entering the HPP chamber, thereby increasing the durability of the HPP. Once DI injectors are activated, at 328 the DI injectors may be used to inject fuel into the engine to provide the requested additional pressure relief to the second, lower threshold.For example, the controller may control a duty cycle to the injectors to inject fuel with a plurality of narrow pulse width fuel injection pulses, with the pulses delivered at a lower frequency. Therefore, if only direct injection was used to provide all of the pressure relief (e.g., to the first threshold and then the lower threshold), as when the injectors were activated at 322, a high impact force would be transferred from the injectors to the engine cylinder heads. This force may have generated a clicking noise in the vehicle that may be annoying to the vehicle driver. The higher the rail pressure, the louder the clicking noise generated. Also, during DI, the operation of an engine cooling fan may completely mask any annoying noise generated by the DI injectors.By using the pump relief valve, the DI fuel rail pressure can therefore be limited to a specified pressure relief limit without causing annoying clicks. In this way, by relieving at least some pressure via the pump relief valve (down to the first threshold), the additional pressure relief requested via the direct injectors can require a smaller number of fuel pulses and fuel pulses with smaller pulse widths than would be required if only direct injection was used for pressure relief. Due to the smaller size and number of fuel pulses, as well as the lower absolute pressure at which the injectors are activated, the impact force transmitted from the injectors to the engine cylinder heads can be significantly lower, resulting in a reduced occurrence (also with lower volume) of annoying clicks.

[0053] At 330, fueling from the port fuel injectors may be adjusted to account for intermittent fuel injection from the DI injectors. Because additional fuel is injected from the DI injectors during DI fuel rail depressurization, fuel scheduling for the PFI injectors may need to be adjusted to maintain the amount of fuel delivered to the cylinders and also to maintain the combustion air-fuel ratio at the target air-fuel ratio (e.g., at or around stoichiometry). For example, in response to fuel injection via the direct fuel injector, a corresponding reduction in the amount of fuel at the port fuel injector may be performed.

[0054] In this way, primarily by using the pump relief valve combined with intermittent DI, the DI fuel rail pressure can be relieved with reduced clicking noise and reduced damage to fuel system components.

[0055] Fig. 4 shows an exemplary operating sequence 400 illustrating engine operation with a fuel system (for example, with the fuel system 200 shown in Fig. 2), and relieving direct injection (DI) fuel rail pressure with reduced clicking noise. The method demonstrates the use of a pump unloading valve with intermittent activation of the DI injectors to relieve DI fuel rail pressure with reduced clicking noise. The horizontal axis (x-axis) indicates time, and the vertical markers t1-t5 identify significant points in time during fuel system operation.

[0056] The first plot, line 402, from the top, shows the variation in engine load over time. The second plot, line 404, shows the pressure in the DI fuel rail. The dotted lines 405, 406, and 407 show significant pressure values ​​of the DI rail pressure. Pressure differential values ​​ΔP 1 and ΔP 2show differences in DI fuel rail pressure compared to the significant pressure values ​​mentioned above. In the third plot, lines 408 and 409 show direct injection operating modes. DI can be either active or deactivated. Similarly, the fourth plot, line 410, shows the port fuel injection operating mode. PFI can be either active or deactivated. The fifth plot, line 412, shows the state (open or closed) of a pump relief valve. The pump relief valve is a spill valve that can be automatically (mechanically) opened to reduce DI fuel rail pressure when the pressure exceeds a threshold. The sixth plot, line 414, shows the variation of a pressure relief index over time. During DI deactivation, pressure builds in the DI fuel rail.A pressure relief index can therefore be formulated to quantify the pressure buildup in the DI fuel rail. As the fuel rail pressure increases, the pressure relief index can be increased, indicating the need for more pressure relief. Dotted lines 415 and 416 show the upper and lower thresholds for the pressure relief index, respectively. The seventh and final plotter representation has lines 417 and 418, which show the tick knock indices (TKI) of a click noise generated upon intermittent activation of the DI during high DI rail pressure conditions, at two different frequencies. TKI is used here as a measurement to quantify periodic impulsiveness, which in this case is the injector click noise.

[0057] Before time t1, the engine load may be high, and fuel may be injected into the engine via DI. During this period, based on engine operating conditions, DI alone may be used for fuel injection, and port fuel injection (PFI) may be kept in a deactivated state. Due to the use of DI, the pressure in the DI fuel rail may not build significantly during this time, and the pressure relief index is low. Due to the low DI fuel rail pressure, the pump relief valve may remain in a closed position. While the DI is operating with low DI fuel rail pressure, no clicking noise is generated during this time.

[0058] At time t1, engine speed may increase to a range where only PFI is desired for engine operation. The direct injectors may thus be deactivated, and PFI may be activated to deliver fuel to the engine. Between time t1 and time t2, while DI is maintained in deactivated mode, fuel trapped within the DI fuel rail may expand due to high temperatures at the fuel rail and injector, resulting in a pressure buildup in the DI fuel rail. The DI fuel rail pressure visibly increases gradually during this period. However, between t1 and t2, the fuel rail pressure remains below a high pressure pump (HPP) pressure relief threshold (here, a first threshold, indicated by dotted line 406).The pump relief valve therefore remains in the closed position.

[0059] At time t2, the DI fuel rail pressure increases above the first threshold 406, causing the pump unload valve to open to allow fuel to spill over and release enough pressure to return the DI fuel rail pressure to or below the first threshold. This process is repeated a number of times between time t2 and time t3. Each time the DI fuel rail pressure exceeds the first threshold, the pump unload valve is opened to reduce the pressure to a value below the first threshold. In this way, without requiring DI activation, the DI fuel rail pressure can be maintained within the first threshold.

[0060] If only DI was used to address the rail pressure issue, larger amounts of fuel may have needed to be released from the direct fuel injectors more frequently to relieve excess pressure in the DI fuel rail. Plotter representation 408 shows example fuel pulses that may have needed to be delivered for DI fuel rail pressure relief if only direct injection was used. In the example shown, DI pulses with a pulse width W1 are injected with an interval I1. Due to a higher impact force transmitted from the direct fuel injectors to the engine cylinder heads during the pressure relief injection, a high-volume clicking noise may be generated in the vehicle, as indicated at 417.Specifically, due to a larger difference (ΔP1) between a pressure at which pressure relief injection is initiated (indicated by line 405) and a pressure at which pressure relief injection ends (indicated by lower threshold 407), a louder clicking noise is generated. Specifically, the clicking noise (as represented by TKI 417) would be proportional to the pressure differential ΔP1. Therefore, by allowing the pump unload valve to encounter the fuel rail pressure while keeping DI deactivated, the DI fuel rail pressure can be maintained within a specified pressure relief limit without the annoying clicking noise.

[0061] Between times t2 and t3, as the period of DI inactivity increases, the pressure relief index may increase, and additional pressure relief may be required. Additionally, control of the direct injector peak temperature may be required. Even if the pump relief valve vents excess pressure above the first threshold, the prolonged presence of relatively high pressure (at the first threshold) in the fuel rail may cause an increase in the pressure relief index. At time t3, based on the pressure relief index reaching an upper threshold 415, a further reduction in the DI fuel rail pressure below the first threshold (to the second threshold) may be desired to reduce any potential damage to the fuel system components.Between times t3 and t4, DI may be activated intermittently, and small, lower-frequency fuel pulses may be delivered to the engine via the DI injectors. Specifically, in the illustrated example, DI pulses with a pulse width W2 (less than pulse width W1) are injected at an interval I2 (greater than interval I1), as can be seen when comparing the direct injection at t3-t4 with the hypothetical injection at t2-t3.

[0062] In this way, the remainder (below the first threshold) of the built-up DI fuel rail pressure may be relieved until the DI fuel rail pressure reaches the second threshold 407. The reduction in the pressure relief index is directly proportional to the increase in DI fuel rail pressure from the first threshold to the second threshold. Intermittent fuel injection using DI may continue until the pressure relief index reaches a lower threshold 416.

[0063] Because some of the built-up pressure has already been relieved by using the pump relief valve, the additional pressure relief requested via the direct injectors results in fewer clicks. Specifically, due to a smaller difference (ΔP2) between a pressure at which the pressure relief injection is initiated (indicated by line 407) and a pressure at which the pressure relief injection ends (indicated by lower threshold 407), a quieter click is generated, as indicated by TKI 418. Specifically, the click (as represented by TKI 418) would have been proportional to the smaller pressure differential ΔP2.Additionally, due to the smaller size and number of fuel pulses, as well as the lower absolute pressure at which the injectors are activated, the impact force transmitted from the injectors to the engine cylinder heads can be significantly lower, resulting in reduced damage to fuel system components.

[0064] Between times t3 and t4, when the DI injectors are periodically activated, the PFI injectors may continue to be maintained in the active mode, but the fuel injection scheduling for PFI may be adjusted taking into account the injection of fuel by the DI injectors.

[0065] Due to the intermittent activation of DI, the DI fuel rail pressure may be at the second threshold at t4. At this time, DI is no longer required, and the DI injectors are deactivated again. Between times t4 and t5, fuel injection via the PFI injectors may continue. The DI fuel rail pressure and depressurization index are low during this period without any further depressurization requirement. At time t5, the engine load may increase, and consequently, DI may be desired instead of PFI. Therefore, at this time, PFI may be deactivated, and DI may be activated to deliver fuel to the combustion chamber.In this way, pressure can be effectively relieved from a DI fuel rail, reducing any possibility of damage to the fuel rail components and producing less annoying clicking noise.

[0066] Fig. 5A shows an example bar chart 500 comparing click noise levels generated using different direct injection (DI) fuel rail pressure relief techniques. As described in detail in connection with the Fig. 3 and Fig. As explained in Section 4, pressure can build up in the DI injector fuel rail during extended periods of DI injector inactivity (when fueling is performed via port fuel injection). Such pressure buildup can cause damage to various fuel system components.

[0067] In one example, to relieve DI fuel rail pressure while direct injection is disabled, small amounts of fuel may be intermittently released from the direct injection injectors to relieve excess pressure in the direct injection fuel rail and reduce peak temperature. This method of DI fuel rail pressure relief is called maintenance mode (MM). Activating the direct injection (DI) injector for rail pressure relief creates a high impact force that is transferred from the injectors to the engine cylinder heads, creating a clicking noise in the vehicle that may be annoying to the driver of the vehicle. The volume of the clicking noise heard at different parts of the vehicle when pressure relief is performed in maintenance mode is shown in bar graph 500.The different parts of the vehicle include the steering wheel, the driver's side door, the passenger side wheel, and the front of the vehicle. The targets of the clicking noise at each vehicle part are shown by the dotted lines 502. As can be seen from the bar graph, by using the above-mentioned pressure relief (MM) method, the level of the clicking noise is significantly higher than the targets.

[0068] In another example, while the common rail pressure exceeds a first threshold pressure corresponding to a high-pressure pump relief pressure, a pump relief valve coupled to the HPP may intermittently open (e.g., automatically via mechanical actuation) to maintain the common rail pressure at the first threshold pressure. If further pressure relief is required, the direct fuel injectors may only be intermittently activated to deliver a small pulse of fuel to the cylinders. By relieving at least some pressure via the pump relief valve, the additional pressure relief required via the direct fuel injectors may require a smaller number of fuel pulses, as well as fuel pulses with smaller pulse widths, than would be required if only direct injection was used for pressure relief.Due to the smaller size and number of fuel pulses, as well as the lower absolute pressure at which the injectors are activated, the impact force transmitted from the injectors to the engine cylinder heads can be significantly lower, resulting in a reduced occurrence of annoying clicking noise. This method of reducing DI fuel rail pressure can be called Pressure Relief Valve (PRV) mode. As can be seen from the bar graph, by using the second pressure relief method (PRV mode), the level of clicking noise detected at all vehicle components is lower than the target volume. Therefore, using PRV mode can ensure that DI fuel rail pressure is effectively reduced with less clicking noise.

[0069] Fig. Figure 5B shows the data presented in the bar chart of the Fig. 5A, in tabular form 510. This table shows the absolute click noise levels collected at various vehicle parts during operation in the service mode and pressure relief valve mode. A difference between the target click noise level and the detected noise level is also provided. It can be seen that the best match of the target noise levels occurs during operation in the pressure relief valve mode. The quieter click noise heard in the pressure relief valve mode may be quiet enough to be masked by the engine noise, making it inaudible (or annoying) to the driver.

[0070] Fig. 6 shows two example plots of direct injection (DI) fuel rail pressure relief using two different techniques. Plot 610 shows DI fuel rail pressure relief using the pressure relief valve mode, as shown in Fig. 5, and the plotter representation 620 shows the DI fuel rail pressure relief using the maintenance mode as in Fig. 5. On plots 610 and 620, the x-axes show time, the first y-axis shows the DI fuel rail pressure amplitude (in psi), and the second y-axis shows the electrical current amplitude (in A). On plot 610, line 602 shows the variation in DI fuel rail pressure over time, and line 604 shows that the electrical current amplitude remains constant at zero over time (no electrical current flows through the DI injectors). On plot 620, line 606 shows the variation in DI fuel rail pressure over time, and line 608 shows the change in electrical current amplitude over time (DI activation).

[0071] Current may be supplied to activate the DI. During the period in which the DI is maintained in the deactivated mode, no current flows through the DI injectors. As seen in plotter representation 610, the fuel rail pressure is maintained at a threshold corresponding to the fuel system high-pressure pump (HPP) pressure relief limit (first threshold) without requiring DI activation. During extended periods of DI deactivation, the DI fuel rail pressure may tend to rise above the first threshold (due to fuel trapped in the fuel rail under high temperature conditions), which may cause potential damage to fuel system components.In the pressure relief valve mode, as the DI fuel rail pressure rises above the first threshold, an HPP relief valve may open intermittently to relieve some DI fuel rail pressure to reduce the pressure below the first threshold. In this way, the DI fuel rail pressure may be maintained at a desirable level below the first threshold without requiring activation of the DI injectors. If further pressure relief below the threshold is desired, only the DI injectors may be activated intermittently to relieve the remaining pressure.

[0072] Details relating to this procedure have been discussed in detail with reference to Fig. 3 described.

[0073] In the maintenance mode (as shown on plotter representation 620), while the DI fuel rail pressure rises above a threshold, instead of intermittently venting via the pump unloading valve, the DI injectors are activated to reduce the DI fuel rail pressure. Electrical current is supplied to the injectors to activate them periodically or opportunistically to reduce the DI fuel rail pressure. However, with this method, because the fuel rail pressure is not reduced using the pump unloading valve, more frequent pulses (also with a higher pulse width) of the DI may be required to reduce the built-up pressure. Due to such DI activation events, increased clicking noise may occur in the engine, which may be annoying to the operator.Additionally, due to the high pressure level in the DI fuel rail, the impact force from the DI injectors to the cylinder heads (the cause of the clicking noise) may be higher, increasing the possibility of damage to fuel system components.

[0074] In this way, in the pressure relief valve mode, by limiting the need for DI activation, the transfer of impact force from the DI injectors to the cylinder heads can be limited, thereby reducing the annoying clicking noise and reducing any potential damage to the fuel system components.

[0075] One example includes, during a warm-up engine idle condition, maintaining the direct injection fuel rail pressure deactivated until a direct injection fuel rail pressure is reduced via a high pressure pump relief valve, and then further reducing the direct injection fuel rail pressure via intermittent activation of the direct injection fuel injectors. In the preceding example, the warm idle conditions additionally or optionally include operating the engine below a threshold speed and supplying fuel to the engine only via the port fuel injector. In any or all of the preceding examples, the direct injection fuel injectors are additionally or optionally maintained deactivated until the direct injection fuel rail pressure is at or below a first threshold pressure.In any or all of the preceding examples, the first threshold pressure is additionally or optionally a pressure setting of the high pressure pump relief valve. In any or all of the preceding examples, intermittently activating the direct injector is additionally or optionally based on an elapsed duration that the direct injectors were deactivated. In any or all of the preceding examples, further decreasing additionally or optionally comprises intermittently injecting fuel via the direct injectors until the fuel rail pressure decreases to a second threshold that is lower than the first threshold. In any or all of the preceding examples, a fuel pulse width and the intermittent injection interval are additionally or optionally based on a pressure difference between the first and second thresholds.Any or all of the preceding examples further additionally or optionally include deactivating the direct injector when the direct injection fuel rail pressure has reached the second threshold. In any or all of the preceding examples, the high-pressure pump relief valve is additionally or optionally a mechanically actuated valve. Any or all of the preceding examples further additionally or optionally include adjusting fuel delivery via the port injector based on the intermittent injection via the direct injector.

[0076] Another exemplary method for an engine exhaust system includes delivering fuel to an engine cylinder via a port fuel injector while maintaining a direct fuel injector deactivated; during a first condition, reducing pressure at the fuel rail of the direct fuel injector by opening a pump relief valve while maintaining the direct fuel injector deactivated; and during a second condition, first reducing pressure at the fuel rail of the direct fuel injector by opening the pump relief valve while maintaining the direct fuel injector deactivated, and then further reducing the pressure by intermittently activating the direct fuel injector.In the preceding example, additionally or optionally, during the first state, the direct injector was deactivated for a shorter duration before the pump relief valve is opened, and during the second state, the direct injectors were deactivated for a longer duration before the pump relief valve is opened. In any or all of the preceding examples, additionally or optionally, during the first state, a pressure relief index is lower, and during the second state, the pressure relief index is higher, where the pressure relief index is a measure of a need for fuel rail pressure relief based on a duration of direct injection deactivation and engine operating conditions.

[0077] Any or all of the preceding examples further additionally or optionally include, during a third condition, reducing the pressure by intermittently activating the direct injector while maintaining the pump relief valve closed. In any or all of the preceding examples, intermittently activating the direct injector during the second condition additionally or optionally comprises fuel injection at a first pulse width and a first frequency, and intermittently activating the direct injector during the third condition comprises fuel injection at a second pulse width and a second frequency, wherein the second pulse width is greater than the first pulse width and the second frequency is higher than the first frequency.Any or all of the preceding examples further additionally or optionally include adjusting fuel delivery via port injection based on intermittent fuel delivery during the first, second, and third states via direct injection.

[0078] In yet another example, a fuel system includes a first fuel rail coupled to a direct fuel injector, a second fuel rail coupled to a port fuel injector, a high-pressure pump coupled to a fuel line leading to the first fuel rail, a fuel tank, a low-pressure fuel pump coupled to the fuel tank, a pump relief valve coupled upstream of the high-pressure fuel pump, between the high-pressure fuel pump and the first fuel rail, the pump relief valve configured to maintain a specified fuel pressure in the first fuel rail, and a controller that provides non-transitory instructions to intermittently activate direct injection only if further pressure relief below the specified fuel pressure is requested.In the preceding example, the pump relief valve is additionally or optionally a mechanical valve or an electrically actuated valve. In any or all of the preceding examples, intermittently enabling direct injection additionally or optionally includes enabling fuel injection via direct injection for a certain duration while maintaining port fuel injection active. Any or all of the preceding examples further additionally or optionally include adjusting port fuel injection based on intermittent activation of direct injection. In this manner, built-up pressure in a DI fuel rail may be relieved with reduced occurrence of an annoying clicking noise. By allowing DI fuel rail pressure to be reduced below a relief threshold of the HPP by actuating the pump relief valve,The direct injectors can be deactivated for a longer duration, reducing the occurrence of clicking. By reducing the pressure to a level below the relief threshold by actuating the pump relief valve, even when the direct injectors are activated for pressure relief, a lower degree of pressure relief is required across the injectors, so the amount of objectionable noise generated can be significantly lower or even negligible. By reducing the activation frequency of the DI injectors, the impact force on the cylinder head from the DI injectors is also reduced, thereby reducing any risk of component damage and warranty-related issues.

[0079] In this way, built-up pressure in a DI fuel rail can be relieved with reduced occurrence of an annoying clicking noise. By allowing DI fuel rail pressure to be reduced below a relief threshold of the HPP by actuating the pump unloading valve, the direct injectors can be kept deactivated for a longer duration, reducing the occurrence of clicking. By reducing pressure to a level below the relief threshold by actuating the pump unloading valve, even when the direct injectors are activated for pressure relief, a lower degree of pressure relief across the injectors is required, so the amount of annoying noise generated can be significantly lower or even negligible.By reducing the activation frequency of the DI injectors, the impact force on the cylinder head from the DI injectors is also reduced, thereby reducing any risk of component damage and warranty-related issues.

[0080] It should be appreciated 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 and may be executed by the control system comprising the controller combined with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Therefore, various actions, operations, and / or functions may be performed in the illustrated order, 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 performed repeatedly depending on the particular strategy employed. Furthermore, 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, wherein the described actions are performed by executing the instructions in a system including the various engine hardware components in combination with the electronic control device.

[0081] 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 limiting, as numerous variations are possible. For example, the above technology may be applied to V-6, I-4, I-6, V-12, horizontally opposed four, and other engine types. 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.

[0082] 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 understood to encompass 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 broader, narrower, the same, or different in scope from the original claims, are also considered to be encompassed within the subject matter of the present disclosure.

Claims

[1] Procedure comprising: during a warmed-up engine idle condition, Maintaining direct injection nozzles (252) in a deactivated state until a direct injection fuel rail pressure is reduced by a high pressure pump relief valve (272), and then further reducing the direct injection fuel rail pressure by intermittently activating the direct injection nozzles (252). [2] The method of claim 1, wherein the warmed-up idle condition comprises operating the engine (10) below a threshold speed and supplying fuel to the engine (10) only via a port fuel injector (262). [3] The method of claim 1, wherein the direct injection injectors (252) are maintained deactivated until the direct injection fuel rail pressure is at or below a first threshold pressure. [4] The method of claim 3, wherein the first threshold pressure is a pressure setting of the high pressure pump relief valve (272). [5] The method of claim 1, wherein the intermittent activation of the direct injector (252) is based on an elapsed duration in which the direct injectors (252) were deactivated. [6] The method of claim 1, wherein further decreasing comprises intermittently injecting fuel via the direct injectors (252) until the fuel rail pressure decreases to a second threshold pressure that is lower than the first threshold pressure. [7] The method of claim 6, wherein a fuel pulse width and an interval of intermittent injection are based on a pressure difference between the first and second threshold values. [8] The method of claim 6, further comprising deactivating the direct injection injector (252) when the direct injection fuel rail pressure has reached the second threshold pressure. [9] The method of claim 1, wherein the high pressure pump relief valve (272) is a mechanically actuated valve. [10] The method of claim 6, further comprising adjusting fuel delivery via the port injector (262) based on the intermittent injection via the direct injector (252). [11] Procedure comprising: Delivering fuel to an engine cylinder via a port fuel injector (262) while maintaining a direct fuel injector (252) deactivated during a first condition, reducing pressure at a fuel rail (250) of the direct fuel injector (252) by opening a pump relief valve (272) while maintaining the direct fuel injector (252) deactivated, and during a second condition, first reducing the pressure at the fuel rail (250) of the direct injector (252) by opening the pump relief valve (272) while keeping the direct injector (252) deactivated, and then further reducing the pressure by intermittently activating the direct injector (252). [12] The method of claim 11, wherein during the first state, the direct injector (252) was deactivated for a shorter duration before the pump unloading valve (272) is opened, and during the second state, the direct injector (252) was deactivated for a longer duration before the pump unloading valve (272) is opened. [13] The method of claim 11, wherein during the first condition, a pressure relief index is lower and during the second condition, the pressure relief index is higher, the pressure relief index being a measure of a need for fuel rail pressure relief based on a duration of direct injection deactivation and engine operating conditions. [14] The method of claim 11, further comprising, during a third condition, reducing the pressure by intermittently activating the direct injector (252) while maintaining the pump relief valve (272) closed. [15] The method of claim 14, wherein intermittently activating the direct injector (252) during the second state comprises fuel injection at a first pulse width and a first frequency, and intermittently activating the direct injector (252) during the third state comprises fuel injection at a second pulse width and a second frequency, the second pulse width being greater than the first pulse width and the second frequency being higher than the first frequency. [16] The method of claim 14, further comprising adjusting fuel delivery via port injection based on intermittent fuel delivery during the first, second, and third direct injection states. [17] Fuel system comprising: a first fuel rail coupled to a direct injection nozzle (252), a second fuel rail coupled to a port injector (262), a high-pressure pump (214) coupled to a fuel line leading to the first fuel rail (250), a fuel tank, a low-pressure fuel pump coupled to the fuel tank, a pump relief valve (272) coupled upstream of the high-pressure fuel pump (214) between the high-pressure fuel pump (214) and the first fuel rail (250), the pump relief valve (272) being configured to maintain a predetermined fuel pressure in the first fuel rail (250), and a control device (12) having non-volatile instructions for intermittently activating direct injection only if further pressure relief below the specified fuel pressure is required. [18] The fuel system of claim 17, wherein the pump relief valve (272) is a mechanical valve or an electrically actuated valve. [19] The fuel system of claim 17, wherein intermittently enabling direct injection comprises enabling fuel injection via direct injection for a predetermined duration while maintaining port fuel injection active. [20] The fuel system of claim 17, further comprising adjusting port injection based on intermittent activation of direct injection.

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