Direct injection fuel pump

Methods and systems are provided for a direct injection fuel pump. The methods and system control pressure within a compression chamber so as to improve fuel pump lubrication.

BACKGROUND AND SUMMARY

A vehicle's fuel systems may supply fuel to an engine in varying amounts during the course of vehicle operation. During some conditions, fuel is not injected to the engine but fuel pressure in a fuel rail supplying fuel to the engine is maintained so that combustion can be reinitiated. For example, during vehicle deceleration fuel flow to one or more engine cylinders may be stopped by deactivating fuel injectors. If the engine torque demand is increased after fuel flow to the one or more cylinders ceases, fuel injection is reactivated and the engine resumes providing positive torque to the vehicle driveline. However, if the engine is supplied fuel via direct fuel injectors and a high pressure fuel pump, the high pressure pump may degrade when fuel flow through the high pressure pump is stopped while the fuel injectors are deactivated. Specifically, the lubrication and cooling of the pump may be reduced while the high pressure pump is not operated, thereby leading to pump degradation.

The inventors herein have recognized the above-mentioned issue may be at least partly addressed by a method of operating a direct injection fuel pump, comprising: regulating a pressure in a compression chamber of the direct injection fuel pump to a single pressure during a direct injection fuel pump compression stroke, the pressure greater than an the pressure on the low pressure side of the piston. This pressure may be the output pressure of a low pressure pump supplying fuel to the direct injection fuel pump.

By regulating pressure in the compression chamber of a direct injection fuel pump it may be possible to lubricate the direct injection fuel pump's cylinder and piston when flow out of the direct injection fuel pump to fuel injectors is stopped. Specifically, a fuel pressure differential across the direct injection fuel pump's piston may be provided that allows fuel to flow into the piston/bore clearance and lubricate an area. Further, pressure in the compression chamber is less than pressure in the fuel rail so there is no flow from the direct injection fuel pump to the fuel rail. In this way, the piston may continue to reciprocate within the direct injection fuel pump with a low rate of degradation and without supplying fuel to the engine.

The present description may provide several advantages. Specifically, the approach may improve fuel pump lubrication and reduce fuel pump degradation. Additionally, pressure in the compression chamber can be regulated to a higher pressure than low pressure fuel pump pressure so that engine operation may be improved during conditions of direct injection fuel pump degradation. Further, the approach may be applied at low cost and complexity. Further still, the approach may reduce fuel pump noise since a solenoid activated check valve at an inlet of the direct injection fuel pump may be deactivated when fuel flow to the engine is stopped.

DETAILED DESCRIPTION

The following disclosure relates to methods and systems for operating a direct injection fuel pump, such as the system ofFIGS. 2 and 3. The fuel system may be configured to deliver one or more different fuel types to a combustion engine, such as the engine ofFIG. 1. Alternatively, the fuel system may supply a single type of fuel as shown in the system ofFIG. 3. A direct injection fuel pump with integrated pressure relief and check valves as shown inFIG. 4may be incorporated into the systems ofFIGS. 2 and 3. Alternatively, the pressure relief valves and check valves may be external to the direct injection fuel pump. In some examples, the direct injection fuel pump may further include an accumulator as shown inFIG. 5to further enhance direct injection fuel pump operation. The direct injection fuel pumps may operate as shown ifFIGS. 6-8when fuel is not being supplied to the engine while the engine is rotating.FIG. 9shows a method for operating a direct injection fuel pump in the systems ofFIGS. 2 and 3to provide the sequences shown inFIGS. 7 and 8.

FIG. 1depicts an example of a combustion chamber or cylinder of internal combustion engine10. Engine10may be controlled at least partially by a control system including controller12and by input from a vehicle operator130via an input device132. In this example, input device132includes an accelerator pedal and a pedal position sensor134for generating a proportional pedal position signal PP. Cylinder (herein also “combustion chamber’)14of engine10may include combustion chamber walls136with piston138positioned therein. Piston138may be coupled to crankshaft140so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft140may be coupled to at least one drive wheel of the passenger vehicle via a transmission system. Further, a starter motor (not shown) may be coupled to crankshaft140via a flywheel to enable a starting operation of engine10.

Cylinder14can receive intake air via a series of intake air passages142,144, and146. Intake air passage146can communicate with other cylinders of engine10in addition to cylinder14. 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. 1shows engine10configured with a turbocharger including a compressor174arranged between intake passages142and144, and an exhaust turbine176arranged along exhaust passage148. Compressor174may be at least partially powered by exhaust turbine176via a shaft180where the boosting device is configured as a turbocharger. However, in other examples, such as where engine10is provided with a supercharger, exhaust turbine176may be optionally omitted, where compressor174may be powered by mechanical input from a motor or the engine. A throttle162including a throttle plate164may be provided along an intake passage of the engine for varying the flow rate and/or pressure of intake air provided to the engine cylinders. For example, throttle162may be positioned downstream of compressor174as shown inFIG. 1, or alternatively may be provided upstream of compressor174.

Exhaust passage148can receive exhaust gases from other cylinders of engine10in addition to cylinder14. Exhaust gas sensor128is shown coupled to exhaust passage148upstream of emission control device178. Sensor128may be selected from among various suitable sensors for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), a NOx, HC, or CO sensor, for example. Emission control device178may be a three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof.

Each cylinder of engine10may include one or more intake valves and one or more exhaust valves. For example, cylinder14is shown including at least one intake poppet valve150and at least one exhaust poppet valve156located at an upper region of cylinder14. In some examples, each cylinder of engine10, including cylinder14, may include at least two intake poppet valves and at least two exhaust poppet valves located at an upper region of the cylinder.

Intake valve150may be controlled by controller12via actuator152. Similarly, exhaust valve156may be controlled by controller12via actuator154. During some conditions, controller12may vary the signals provided to actuators152and154to control the opening and closing of the respective intake and exhaust valves. The position of intake valve150and exhaust valve156may be determined by respective valve position sensors (not shown). The valve actuators may be of the electric valve actuation type or cam actuation type, or a combination thereof. The intake and exhaust valve timing may be controlled concurrently or any of a possibility 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 one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems that may be operated by controller12to vary valve operation. For example, cylinder14may 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.

In some examples, each cylinder of engine10may be configured with one or more fuel injectors for providing fuel thereto. As a non-limiting example, cylinder14is shown including two fuel injectors166and170. Fuel injectors166and170may be configured to deliver fuel received from fuel system8. As elaborated with reference toFIGS. 2 and 3, fuel system8may include one or more fuel tanks, fuel pumps, and fuel rails. Fuel injector166is shown coupled directly to cylinder14for injecting fuel directly therein in proportion to the pulse width of signal FPW-1 received from controller12via electronic driver168. In this manner, fuel injector166provides what is known as direct injection (hereafter referred to as “DI”) of fuel into combustion cylinder14. WhileFIG. 1shows injector166positioned to one side of cylinder14, it may alternatively be located overhead of the piston, such as near the position of spark plug192. Such a position may improve mixing and combustion when operating the engine with an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located overhead and near the intake valve to improve mixing. Fuel may be delivered to fuel injector166from a fuel tank of fuel system8via a high pressure fuel pump, and a fuel rail. Further, the fuel tank may have a pressure transducer providing a signal to controller12.

Fuel injector170is shown arranged in intake passage146, rather than in cylinder14, in a configuration that provides what is known as port injection of fuel (hereafter referred to as “PFI”) into the intake port upstream of cylinder14. Fuel injector170may inject fuel, received from fuel system8, in proportion to the pulse width of signal FPW-2 received from controller12via electronic driver171. Note that a single driver168or171may be used for both fuel injection systems, or multiple drivers, for example driver168for fuel injector166and driver171for fuel injector170, may be used, as depicted.

In an alternate example, each of fuel injectors166and170may be configured as direct fuel injectors for injecting fuel directly into cylinder14. In still another example, each of fuel injectors166and170may be configured as port fuel injectors for injecting fuel upstream of intake valve150. In yet other examples, cylinder14may include only a single fuel injector that is configured to receive different fuels from the fuel systems in varying relative amounts as a fuel mixture, and is 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. As such, it should be appreciated that the fuel systems described herein should not be limited by the particular fuel injector configurations described herein by way of example.

Fuel may be delivered by both injectors to the cylinder during a single cycle of the cylinder. For example, each injector may deliver a portion of a total fuel injection that is combusted in cylinder14. Further, the distribution and/or relative amount of fuel delivered from each injector may vary with operating conditions, such as engine load, knock, and exhaust temperature, such as described herein below. The port injected fuel may be delivered during an open intake valve event, closed intake valve event (e.g., substantially before the intake stroke), as well as during both open and closed intake valve operation. Similarly, directly injected fuel may be delivered during an intake stroke, as well as partly during a previous exhaust stroke, during the intake stroke, and partly during the compression stroke, for example. As such, even for a single combustion event, injected fuel may be injected at different timings from 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 appropriate combination thereof.

As described above,FIG. 1shows only one cylinder of a multi-cylinder engine.

As such, each cylinder may similarly include its own set of intake/exhaust valves, fuel injector(s), spark plug, etc. It will be appreciated that engine10may include any suitable number of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Further, each of these cylinders can include some or all of the various components described and depicted byFIG. 1with reference to cylinder14.

Fuel injectors166and170may have different characteristics. These include differences in size, for example, one injector may have a larger injection hole than the other. Other differences include, but are not limited to, different spray angles, different operating temperatures, different targeting, different injection timing, different spray characteristics, different locations etc. Moreover, depending on the distribution ratio of injected fuel among injectors170and166, different effects may be achieved.

Fuel tanks in fuel system8may hold fuels of different fuel types, such as fuels with different fuel qualities and different fuel compositions. The differences may include different alcohol content, different water content, different octane, different heats of vaporization, different fuel blends, and/or combinations thereof etc. One example of fuels with different heats of vaporization could include gasoline as a first fuel type with a lower heat of vaporization and ethanol as a second fuel type with a greater 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 is approximately 85% ethanol and 15% gasoline) or M85 (which is approximately 85% methanol and 15% gasoline) as a second fuel type. Other feasible substances include water, methanol, a mixture of alcohol and water, a mixture of water and methanol, a mixture of alcohols, etc.

In still another example, both fuels may be alcohol blends with varying alcohol composition wherein the first fuel type may be a gasoline alcohol blend with a lower concentration of alcohol, such as E10 (which is approximately 10% ethanol), while the second fuel type may be a gasoline alcohol blend with a greater concentration of alcohol, such as E85 (which is approximately 85% ethanol). Additionally, the first and second fuels may also differ in other fuel qualities such as a difference in temperature, viscosity, octane number, etc. Moreover, fuel characteristics of one or both fuel tanks may vary frequently, for example, due to day to day variations in tank refilling.

Controller12is shown inFIG. 1as a microcomputer, including microprocessor unit106, input/output ports108, an electronic storage medium for executable programs and calibration values shown as non-transitory read only memory chip110in this particular example for storing executable instructions, random access memory112, keep alive memory114, and a data bus. Controller12may receive various signals from sensors coupled to engine10, in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor122; engine coolant temperature (ECT) from temperature sensor116coupled to cooling sleeve118; a profile ignition pickup signal (PIP) from Hall effect sensor120(or other type) coupled to crankshaft140; throttle position (TP) from a throttle position sensor; and absolute manifold pressure signal (MAP) from sensor124. Engine speed signal, RPM, may be generated by controller12from signal PIP. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold.

FIG. 2schematically depicts an example fuel system8ofFIG. 1. Fuel system8may be operated to deliver fuel to an engine, such as engine10ofFIG. 1. Fuel system8may be operated by a controller to perform some or all of the operations described with reference to the process flow ofFIG. 9.

Fuel system8can provide fuel to an engine from one or more different fuel sources. As a non-limiting example, a first fuel tank202and a second fuel tank212may be provided. While fuel tanks202and212are described in the context of discrete vessels for storing fuel, it should be appreciated that these fuel tanks may instead be configured as a single fuel tank having separate fuel storage regions that are separated by a wall or other suitable membrane. Further still, in some embodiments, this membrane may be configured to selectively transfer select components of a fuel between the two or more fuel storage regions, thereby enabling a fuel mixture to be at least partially separated by the membrane into a first fuel type at the first fuel storage region and a second fuel type at the second fuel storage region.

In some examples, first fuel tank202may store fuel of a first fuel type while second fuel tank212may store fuel of a second fuel type, wherein the first and second fuel types are of differing composition. As a non-limiting example, the second fuel type contained in second fuel tank212may include a higher concentration of one or more components that provide the second fuel type with a greater relative knock suppressant capability than the first fuel.

By way of example, the first fuel and the second fuel may each include one or more hydrocarbon components, but the second fuel may also include a higher concentration of an alcohol component than the first fuel. Under some conditions, this alcohol component can provide knock suppression to the engine when delivered in a suitable amount relative to the first fuel, and may include any suitable alcohol such as ethanol, methanol, etc. Since alcohol can provide greater knock suppression than some hydrocarbon based fuels, such as gasoline and diesel, due to the increased latent heat of vaporization and charge cooling capacity of the alcohol, a fuel containing a higher concentration of an alcohol component can be selectively used to provide increased resistance to engine knock during select operating conditions.

As another example, the alcohol (e.g. methanol, ethanol) may have water added to it. As such, water reduces the alcohol fuel's flammability giving an increased flexibility in storing the fuel. Additionally, the water content's heat of vaporization enhances the ability of the alcohol fuel to act as a knock suppressant. Further still, the water content can reduce the fuel's overall cost.

As a specific non-limiting example, the first fuel type in the first fuel tank may include gasoline and the second fuel type in the second fuel tank may include ethanol. As another non-limiting example, the first fuel type may include gasoline and the second fuel type may include a mixture of gasoline and ethanol. In still other examples, the first fuel type and the second fuel type may each include gasoline and ethanol, whereby the second fuel type includes a higher concentration of the ethanol component than the first fuel (e.g., E10 as the first fuel type and E85 as the second fuel type). As yet another example, the second fuel type may have a relatively higher octane rating than the first fuel type, thereby making the second fuel a more effective knock suppressant than the first fuel. It should be appreciated that these examples should be considered non-limiting as other suitable fuels may be used that have relatively different knock suppression characteristics. In still other examples, each of the first and second fuel tanks may store the same fuel. While the depicted example illustrates two fuel tanks with two different fuel types, it will be appreciated that in alternate embodiments, only a single fuel tank with a single type of fuel may be present.

Fuel tanks202and212may differ in their fuel storage capacities. In the depicted example, where second fuel tank212stores a fuel with a higher knock suppressant capability, second fuel tank212may have a smaller fuel storage capacity than first fuel tank202. However, it should be appreciated that in alternate embodiments, fuel tanks202and212may have the same fuel storage capacity.

Fuel may be provided to fuel tanks202and212via respective fuel filling passages204and214. In one example, where the fuel tanks store different fuel types, fuel filling passages204and214may include fuel identification markings for identifying the type of fuel that is to be provided to the corresponding fuel tank.

A first low pressure fuel pump (LPP)208in communication with first fuel tank202may be operated to supply the first type of fuel from the first fuel tank202to a first group of port injectors242, via a first fuel passage230. In one example, first fuel pump208may be an electrically-powered lower pressure fuel pump disposed at least partially within first fuel tank202. Fuel lifted by first fuel pump208may be supplied at a lower pressure into a first fuel rail240coupled to one or more fuel injectors of first group of port injectors242(herein also referred to as first injector group). While first fuel rail240is shown dispensing fuel to four fuel injectors of first injector group242, it will be appreciated that first fuel rail240may dispense fuel to any suitable number of fuel injectors. As one example, first fuel rail240may dispense fuel to one fuel injector of first injector group242for each cylinder of the engine. Note that in other examples, first fuel passage230may provide fuel to the fuel injectors of first injector group242via two or more fuel rails. For example, where the engine cylinders are configured in a V-type configuration, two fuel rails may be used to distribute fuel from the first fuel passage to each of the fuel injectors of the first injector group.

Direct injection fuel pump228that is included in second fuel passage232and may be supplied fuel via LPP208or LPP218. In one example, direct injection fuel pump228may be a mechanically-powered positive-displacement pump. Direct injection fuel pump228may be in communication with a group of direct injectors252via a second fuel rail250, and the group of port injectors242via a solenoid valve236. Thus, lower pressure fuel lifted by first fuel pump208may be further pressurized by direct injection fuel pump228so as to supply higher pressure fuel for direct injection to second fuel rail250coupled to one or more direct fuel injectors252(herein also referred to as second injector group). In some examples, a fuel filter (not shown) may be disposed upstream of direct injection fuel pump228to remove particulates from the fuel. Further, in some examples a fuel pressure accumulator (not shown) may be coupled downstream of the fuel filter, between the low pressure pump and the high pressure pump.

A second low pressure fuel pump218in communication with second fuel tank212may be operated to supply the second type of fuel from the second fuel tank202to the direct injectors252, via the second fuel passage232. In this way, second fuel passage232fluidly couples each of the first fuel tank and the second fuel tank to the group of direct injectors. In one example, third fuel pump218may also be an electrically-powered low pressure fuel pump (LPP), disposed at least partially within second fuel tank212. Thus, lower pressure fuel lifted by low pressure fuel pump218may be further pressurized by higher pressure fuel pump228so as to supply higher pressure fuel for direct injection to second fuel rail250coupled to one or more direct fuel injectors. In one example, second low pressure fuel pump218and direct injection fuel pump228can be operated to provide the second fuel type at a higher fuel pressure to second fuel rail250than the fuel pressure of the first fuel type that is provided to first fuel rail240by first low pressure fuel pump208.

Fluid communication between first fuel passage230and second fuel passage232may be achieved through first and second bypass passages224and234. Specifically, first bypass passage224may couple first fuel passage230to second fuel passage232upstream of direct injection fuel pump228, while second bypass passage234may couple first fuel passage230to second fuel passage232downstream of direct injection fuel pump228. One or more pressure relief valves may be included in the fuel passages and/or bypass passages to resist or inhibit fuel flow back into the fuel storage tanks. For example, a first pressure relief valve226may be provided in first bypass passage224to reduce or prevent back flow of fuel from second fuel passage232to first fuel passage230and first fuel tank202. A second pressure relief valve222may be provided in second fuel passage232to reduce or prevent back flow of fuel from the first or second fuel passages into second fuel tank212. In one example, lower pressure pumps208and218may have pressure relief valves integrated into the pumps. The integrated pressure relief valves may limit the pressure in the respective lift pump fuel lines. For example, a pressure relief valve integrated in first fuel pump208may limit the pressure that would otherwise be generated in first fuel rail240if solenoid valve236were (intentionally or unintentionally) open and while direct injection fuel pump228were pumping.

In some examples, the first and/or second bypass passages may also be used to transfer fuel between fuel tanks202and212. Fuel transfer may be facilitated by the inclusion of additional check valves, pressure relief valves, solenoid valves, and/or pumps in the first or second bypass passage, for example, solenoid valve236. In still other examples, one of the fuel storage tanks may be arranged at a higher elevation than the other fuel storage tank, whereby fuel may be transferred from the higher fuel storage tank to the lower fuel storage tank via one or more of the bypass passages. In this way, fuel may be transferred between fuel storage tanks by gravity without necessarily requiring a fuel pump to facilitate the fuel transfer.

The various components of fuel system8communicate with an engine control system, such as controller12. For example, controller12may receive an indication of operating conditions from various sensors associated with fuel system8in addition to the sensors previously described with reference toFIG. 1. The various inputs may include, for example, an indication of an amount of fuel stored in each of fuel storage tanks202and212via fuel level sensors206and216, respectively. Controller12may also receive an indication of fuel composition from one or more fuel composition sensors, in addition to, or as an alternative to, an indication of a fuel composition that is inferred from an exhaust gas sensor (such as sensor126ofFIG. 1). For example, an indication of fuel composition of fuel stored in fuel storage tanks202and212may be provided by fuel composition sensors210and220, respectively. Additionally or alternatively, one or more fuel composition sensors may be provided at any suitable location along the fuel passages between the fuel storage tanks and their respective fuel injector groups. For example, fuel composition sensor238may be provided at first fuel rail240or along first fuel passage230, and/or fuel composition sensor248may be provided at second fuel rail250or along second fuel passage232. As a non-limiting example, the fuel composition sensors can provide controller12with an indication of a concentration of a knock suppressing component contained in the fuel or an indication of an octane rating of the fuel. For example, one or more of the fuel composition sensors may provide an indication of an alcohol content of the fuel.

Note that the relative location of the fuel composition sensors within the fuel delivery system can provide different advantages. For example, sensors238and248, arranged at the fuel rails or along the fuel passages coupling the fuel injectors with one or more fuel storage tanks, can provide an indication of a resulting fuel composition where two or more different fuels are combined before being delivered to the engine. In contrast, sensors210and220may provide an indication of the fuel composition at the fuel storage tanks, which may differ from the composition of the fuel actually delivered to the engine.

Controller12can also control the operation of each of fuel pumps208,218, and228to adjust an amount, pressure, flow rate, etc., of a fuel delivered to the engine. As one example, controller12can vary a pressure setting, a pump stroke amount, a pump duty cycle command and/or fuel flow rate of the fuel pumps to deliver fuel to different locations of the fuel system. A driver (not shown) electronically coupled to controller12may be used to send a control signal to each of the low pressure pumps, as required, to adjust the output (e.g. speed) of the respective low pressure pump. The amount of first or second fuel type that is delivered to the group of direct injectors via the direct injection pump may be adjusted by adjusting and coordinating the output of the first or second LPP and the direct injection pump. For example, the lower pressure fuel pump and the higher pressure fuel pump may be operated to maintain a prescribed fuel rail pressure. A fuel rail pressure sensor coupled to the second fuel rail may be configured to provide an estimate of the fuel pressure available at the group of direct injectors. Then, based on a difference between the estimated rail pressure and a desired rail pressure, the pump outputs may be adjusted. In one example, where the high pressure fuel pump is a volumetric displacement fuel pump, the controller may adjust a flow control valve of the high pressure pump to vary the effective pump volume of each pump stroke.

As such, while the direct injection fuel pump is operating, flow of fuel there-though ensures sufficient pump lubrication and cooling. However, during conditions when direct injection fuel pump operation is not requested, such as when no direct injection of fuel is requested, and/or when the fuel level in the second fuel tank212is below a threshold (that is, there is not enough knock-suppressing fuel available), the direct injection fuel pump may not be sufficiently lubricated if fuel flow through the pump is discontinued.

Referring now toFIG. 3, is shows a second example fuel system for supplying fuel to engine10ofFIG. 1. Many devices and/or components in the fuel system ofFIG. 3are the same as devices and/or components shown inFIG. 2. Therefore, for the sake of brevity, devices and components of the fuel system ofFIG. 2, and that are included in the fuel system ofFIG. 3, are labeled the same and the description of these devices and components is omitted in the description ofFIG. 3.

The fuel system ofFIG. 3supplies fuel from a single fuel tank to direct injectors252and port injectors242. However, in other examples, fuel may be supplied only to direct injectors252and port injectors242may be omitted. In this example system, low pressure fuel pump208supplies fuel to direct injection fuel pump228via fuel passage302. Controller12adjusts the output of direct injection fuel pump228via adjusting a flow control valve of direct injection pump228. Direct injection pump may stop providing fuel to fuel rail250during selected conditions such as during vehicle deceleration or while the vehicle is traveling downhill. Further, during vehicle deceleration or while the vehicle is traveling downhill, one or more direct fuel injectors252may be deactivated.

FIG. 4shows first example direct injection fuel pump228show in the systems ofFIGS. 2 and 3. Inlet403of direct injection fuel pump compression chamber408is supplied fuel via a low pressure fuel pump as shown inFIGS. 2 and 3. The fuel may be pressurized upon its passage through direct injection fuel pump228and supplied to a fuel rail through pump outlet404. In the depicted example, direct injection pump228may be a mechanically-driven displacement pump that includes a pump piston406and piston rod420, a pump compression chamber408(herein also referred to as compression chamber), and a step-room418. Piston406includes a top405and a bottom407. The step-room and compression chamber may include cavities positioned on opposing sides of the pump piston. In one example, engine controller12may be configured to drive the piston406in direct injection pump228by driving cam410. Cam410includes four lobes and completes one rotation for every two engine crankshaft rotations.

A solenoid activated inlet check valve412may be coupled to pump inlet403. Controller12may be configured to regulate fuel flow through inlet check valve412by energizing or de-energizing the solenoid valve (based on the solenoid valve configuration) in synchronism with the driving cam. Accordingly, solenoid activated inlet check valve412may be operated in two modes. In a first mode, solenoid activated check valve412is positioned within inlet403to limit (e.g. inhibit) the amount of fuel traveling upstream of the solenoid activated check valve412. In comparison, in the second mode, solenoid activated check valve412is effectively disabled and fuel can travel upstream and downstream of inlet check valve.

As such, solenoid activated check valve412may be configured to regulate the mass of fuel compressed into the direct injection fuel pump. In one example, controller12may adjust a closing timing of the solenoid activated check valve to regulate the mass of fuel compressed. For example, a late inlet check valve closing may reduce the amount of fuel mass ingested into the compression chamber408. The solenoid activated check valve opening and closing timings may be coordinated with respect to stroke timings of the direct injection fuel pump. By continuously throttling the flow into the direct injection fuel pump from the low pressure fuel pump, fuel may be ingested into the direct injection fuel pump without requiring metering of the fuel mass.

Pump inlet499allows fuel to check valve402and pressure relief valve401. Check valve402is positioned upstream of solenoid activated check valve412along passage435. Check valve402is biased to prevent fuel flow out of solenoid activated check valve412and pump inlet499. Check valve402allows flow from the low pressure fuel pump to solenoid activated check valve412. Check valve402is coupled in parallel with pressure relief valve401. Pressure relief valve401allows fuel flow out of solenoid activated check valve412toward the low pressure fuel pump when pressure between pressure relief valve401and solenoid operated check valve412is greater than a predetermined pressure (e.g., 10 bar). When solenoid operated check valve412is deactivated (e.g., not electrically energized), solenoid operated check valve operates in a pass-through mode and pressure relief valve401regulates pressure in compression chamber408to the single pressure relief setting of pressure relief valve401(e.g., 15 bar). Regulating the pressure in compression chamber408allows a pressure differential to form from piston top405to piston bottom407. The pressure in step-room418is at the pressure of the outlet of the low pressure pump (e.g., 5 bar) while the pressure at piston top is at pressure relief valve regulation pressure (e.g., 15 bar). The pressure differential allows fuel to seep from piston top405to piston bottom407through the clearance between piston406and pump cylinder wall450, thereby lubricating direct injection fuel pump228.

Piston406reciprocates up and down. Direct fuel injection pump228is in a compression stroke when piston406is traveling in a direction that reduces the volume of compression chamber408. Direct fuel injection pump228is in a suction stroke when piston406is traveling in a direction that increases the volume of compression chamber408.

A forward flow outlet check valve416may be coupled downstream of an outlet404of the compression chamber408. Outlet check valve416opens to allow fuel to flow from the compression chamber outlet404into a fuel rail only when a pressure at the outlet of direct injection fuel pump228(e.g., a compression chamber outlet pressure) is higher than the fuel rail pressure. Thus, during conditions when direct injection fuel pump operation is not requested, controller12may deactivate solenoid activated inlet check valve412and pressure relief valve401regulates pressure in compression chamber to a single substantially constant (e.g., regulation pressure±0.5 bar) pressure. Controller12simply deactivates solenoid activated check valve412to lubricate direct injection fuel pump228. One result of this regulation method is that the fuel rail is regulated to approximately the pressure relief of402. Thus, if valve402has a pressure relief setting of 10 bar, the fuel rail pressure becomes 15 bar because this 10 bar adds to the 5 bar of lift pump pressure. Specifically, the fuel pressure in compression chamber408is regulated during the compression stroke of direct injection fuel pump228. Thus, during at least the compression stroke of direct injection fuel pump228, lubrication is provided to the pump. When direct fuel injection pump enters a suction stroke, fuel pressure in the compression chamber may be reduced while still some level of lubrication may be provided as long as the pressure differential remains.

Now turning toFIG. 5, another example direct injection fuel pump228is shown. Many devices and/or components in the direct injection fuel pump ofFIG. 5are the same as devices and/or components shown inFIG. 4. Therefore, for the sake of brevity, devices and components of the direct fuel injection pump ofFIG. 4, and that are included in the direct injection fuel pump ofFIG. 5, are labeled the same and the description of these devices and components is omitted in the description ofFIG. 5

Direct injection fuel pump228includes an accumulator502positioned along pump passage435between solenoid activated check valve412and pressure relief valve401. In one example, accumulator502is a 15 bar accumulator. Thus, accumulator502is designed to be active in a pressure range that straddles the pressure relief valve401. Accumulator502stores fuel when piston406is in a compression stroke and releases fuel when piston is in a suction stroke. Consequently, a pressure differential from piston top405to piston bottom407exits during compression and suction strokes of direct fuel injection pump228. Further, when rod is in communication with the position providing least lift from cam410, the pressure differential is the substantially the same as when direct fuel injection pump228is on a compression stroke. Pressure relief valve401and accumulator502store and release fuel from compression chamber408when solenoid activated check valve is deactivated.

Referring now toFIG. 6, an example of prior art direct injection fuel pump operating sequence is shown. The sequence illustrates direct injection fuel pump operation when fuel flow out of the direct injection fuel pump to the direct injection fuel rail is ceased.

The first plot from the top ofFIG. 6shows direct injection fuel pump cam lift versus time. The Y axis represents direct injection fuel pump cam lift. The X axis represents time and time increases from the left side ofFIG. 6to the right side ofFIG. 6. Cam lift is increases during a compression stroke for 100 crankshaft degrees. Cam lift decreases during the suction stroke for 80 crankshaft degrees.

The second plot from the top ofFIG. 6shows direct injection fuel pump compression chamber pressure versus time. The Y axis represents direct injection fuel pump compression chamber pressure. The X axis represents time and time increases from the left side ofFIG. 6to the right side ofFIG. 6. Horizontal line602represents low pressure pump output pressure at the direct injection fuel pump compression chamber when the low pressure pump is operating, the solenoid activated check valve is in a pass-through state, and there is no net fuel flow to the fuel rail.

Vertical markers T1-T4indicate time of interest during the direct injection fuel pump operating sequence. Time T1represents start of first direct injection fuel pump compression stroke. Time T2represents end of first direct injection fuel pump compression stroke and beginning of direct injection fuel pump suction stroke. Time T3represents end of first direct injection fuel pump suction stroke and beginning of a second compression stroke. Time T4represents the end of the second direct injection fuel pump compression stroke.

FIG. 6shows that direct injection fuel pump compression chamber pressure is near low pressure fuel pump output pressure during first and second compression strokes as well as during first and second suction strokes. The solenoid activated check valve is operated in a pass through state so that the direct injection fuel pump does not pump fuel to the fuel rail. Fuel pressure at in the step-chamber is at low pressure fuel pump outlet pressure. Thus, little if any direct injection fuel pump lubrication is provided.

Referring now toFIG. 7, an example direct injection fuel pump operating sequence of the fuel pump shown inFIG. 4is shown. The sequence illustrates direct injection fuel pump operation when fuel flow out of the direct injection fuel pump to the direct injection fuel rail is ceased.

The first plot from the top ofFIG. 7shows direct injection fuel pump cam lift versus time. The Y axis represents direct injection fuel pump cam lift. The X axis represents time and time increases from the left side ofFIG. 7to the right side ofFIG. 7.

The second plot from the top ofFIG. 7shows direct injection fuel pump compression chamber pressure versus time. The Y axis represents direct injection fuel pump compression chamber pressure. The X axis represents time and time increases from the left side ofFIG. 7to the right side ofFIG. 7. Horizontal line702represents low pressure pump output pressure Horizontal line704represents the pressure relief valve401ofFIG. 4is set to regulate.

Vertical markers T10-T13indicate time of interest during the direct injection fuel pump operating sequence. Time T10represents start of first direct injection fuel pump compression stroke. Time T11represents end of first direct injection fuel pump compression stroke and beginning of direct injection fuel pump suction stroke. Time T12represents end of first direct injection fuel pump suction stroke and start of a second compression stroke. Time T13represents end of the second direct injection fuel pump compression stroke.

FIG. 7shows that direct injection fuel pump compression chamber pressure increases during the first and second compression strokes. Pressure in the step-chamber (not shown) is at low pressure fuel pump output pressure during first and second compression strokes as well as during first and second suction strokes. Consequently, a pressure difference develops between the piston top and bottom allowing fuel to squeeze between the piston and the compression chamber walls lubricating the pump. The pressure difference decreases during the first suction stroke. Consequently, a reduced amount of lubrication may be provided during the suction stroke. Further, when cam lift is zero and the cam base circle is in mechanical communication with the piston, pressure in the compression chamber is reduced to pressure output of the low pressure pump supplying fuel to the direct injection fuel pump. The solenoid activated check valve is operated in a pass through state so that the direct injection fuel pump does not pump fuel to the fuel rail. Thus, during the compression stroke and part of the suction stroke, pressure in the direct injection fuel pump compression chamber is greater than low pressure pump outlet pressure. Consequently, direct injection fuel pump lubrication is increased as compared to the prior art.

Referring now toFIG. 8, an example direct injection fuel pump operating sequence of the fuel pump shown inFIG. 5is shown. The sequence illustrates direct injection fuel pump operation when fuel flow out of the direct injection fuel pump to the direct injection fuel rail is ceased.

The first plot from the top ofFIG. 8shows direct injection fuel pump cam lift versus time. The Y axis represents direct injection fuel pump cam lift. The X axis represents time and time increases from the left side ofFIG. 8to the right side ofFIG. 8.

The second plot from the top ofFIG. 8shows direct injection fuel pump compression chamber pressure versus time. The Y axis represents direct injection fuel pump compression chamber pressure. The X axis represents time and time increases from the left side ofFIG. 8to the right side ofFIG. 8. Horizontal line802represents low pressure pump output pressure

Vertical markers T20-T23indicate time of interest during the direct injection fuel pump operating sequence. Time T20represents start of first direct injection fuel pump compression stroke. Time T21represents end of first direct injection fuel pump compression stroke and beginning of direct injection fuel pump suction stroke. Time T22represents end of first direct injection fuel pump suction stroke and start of a second compression stroke. Time T23represents end of the second direct injection fuel pump compression stroke.

FIG. 8shows that direct injection fuel pump compression chamber pressure is elevated during the first and second compression strokes and during the first suction stroke. Thus, the pressure in the direct injection fuel pump compression chamber is substantially constant at a pressure greater than low pressure pump output pressure. The direct injection fuel pump pressure is at the constant elevated pressure after a first compression stroke of the direct injection fuel pump after the solenoid operated check valve is placed in a pass through mode. Consequently, a pressure difference develops between the piston top and bottom allowing fuel to squeeze between the piston and the compression chamber walls lubricating the pump. Accumulator502inFIG. 5allows pressure in the compression chamber to stay substantially constant during the pump's suction stroke.

While this lube strategy cures an issue of lubrication ceasing when the DI system was in disuse, the lubrication that occurs inFIGS. 7 and 8can even give better lubrication than if only a small fraction the pump's full displacement is being pumped out to the fuel rail.

Another feature is that inFIG. 8, since accumulator pressure is being used to “push down” the piston, the system conserves more energy than it would if controlled as is shown inFIG. 7.

Referring now toFIG. 9a method for operating a direct injection fuel pump is shown. The method ofFIG. 9may be stored as executable instructions in non-transitory memory of controller12shown inFIGS. 1-5. The method ofFIG. 9may provide the sequences shown inFIGS. 7 and 8.

At902, method900determines operating conditions. Operating conditions may include but are not limited to engine speed, engine load, vehicle speed, brake pedal position, engine temperature, ambient air temperature, and fuel rail pressure. Method900proceeds to904after operating conditions are determined.

At904, method900judges whether or not the fuel system is a direct injection system only. If method900judges that there are no port injectors and the system is direct injection only, the answer is yes and method900proceeds to906. Otherwise, the answer is no and method900proceeds to908.

At906, method900judges whether or not the piston in the direct injection fuel pump is reciprocating while less than a threshold amount of fuel is flowing into the direct injection fuel rail from the direct injection fuel pump. In one example, the threshold amount of fuel is zero. In another example, the threshold amount of fuel is an amount of fuel less than an amount of fuel to idle the engine. If method900judges that the piston in the direct injection fuel pump is reciprocating and less than a threshold amount of fuel is flowing into the direct injection fuel rail from the direct injection fuel pump, the answer is yes and method900proceeds to918. Otherwise, the answer is no and method900proceeds to exit.

At908, method900determines an amount of fuel to deliver to the engine via the direct injectors and an amount of fuel to deliver to the engine via the port fuel injectors. In one example, the amount of fuel to be delivered via port and direct injectors is empirically determined and stored in two tables or functions, one table for port injection amount and one table for direct injection amount. The two tables are indexed via engine speed and load. The tables output an amount of fuel to inject to engine cylinders each cylinder cycle. Method900proceeds to910after determining the amounts of fuel to directly inject and port inject.

At910, whether or not to deliver fuel to the engine via port and direct injectors or solely via direct injectors. In one example, method900judges whether or not to deliver fuel to the engine via port and direct injectors or solely via direct injectors based on output from tables at908. If method900judges to deliver fuel to the engine via port and direct injectors or solely via direct injectors, the answer is yes and method900proceeds to912. Otherwise, the answer is no and fuel is not injected via direct injectors while the engine is rotating and the direct injection fuel pump piston is reciprocating. Method900proceeds to914when the answer is no.

At912, method900adjusts the duty cycle of a signal supplied to the solenoid activated check valve412inFIGS. 4 and 5to adjust flow through the direct injection fuel pump so as to provide the amount of fuel desired to be directly injected and to provide the desired fuel pressure in the direct injection fuel rail. The solenoid activated check valve duty cycle controls how much of the pump's actual displacement is being engaged to pump fuel. In one example, the duty cycle is increased to increase flow through the direct injection fuel pump and to the direct injection fuel rail. If the fuel system includes a single low pressure fuel pump, the low pressure fuel pump command is adjusted in response to the amount of fuel to be delivered to the engine. For example, low pressure fuel pump output is increased as the amount of fuel injected to the engine is increased. If the fuel system includes two low pressure fuel pumps, the first low pressure fuel pump output is adjusted in response to the amount of fuel injected by the port fuel injectors. The second low pressure fuel pump output is adjusted in response to the amount of fuel injected by the direct fuel injectors. Fuel is then supplied to the engine via the port and direct fuel injectors. Method900proceeds to exit after the direct and low pressure pumps are adjusted.

At914, method900judges whether or not to deliver fuel to the engine via port injectors. In one example, method900judges to deliver fuel to the engine via only port injectors based on the output of the two tables at908. If the direct fuel injection amount is zero or less than a threshold amount of fuel necessary for the engine to operate at idle speed and port injection is requested, method900proceeds to916. Otherwise, port fuel injection and direct fuel injection are not requested and method900proceeds to918. Port fuel injection and direct fuel injection may not be requested during low engine load conditions such as when the vehicle is decelerating or traveling downhill.

At916, method900adjusts low pressure fuel pump output. If the fuel system includes only a single low pressure fuel pump, the low pressure fuel pump output is adjusted in response to the amount of port fuel injected and the desired port injector fuel rail pressure. If the fuel system includes two low pressure fuel pumps, the first low pressure fuel pump output is adjusted in response to the amount of fuel injected by the port fuel injectors and the port injector fuel rail pressure. The second low pressure fuel pump output is adjusted in response to fuel pressure in a passage that provides fluidic communication between the low pressure fuel pump and the direct injection fuel pump. In particular, the low pressure pump command is adjusted in response to fuel pressure between the low pressure fuel pump and the direct injection fuel pump. Fuel is then injected to the engine via the port fuel injectors and not via the direct fuel injectors.

At918, method900judges whether or not to supply direct injection fuel pump full cam stroke (e.g., compression stroke and suction stroke, and in some examples while the piston is in communication with a cam's base circle) fuel pump lubrication. In one example, method900judges whether or not to supply direct injection fuel pump full cam stroke lubrication based on whether or not accumulator502ofFIG. 5is included in the direct injection fuel pump or fuel system. If the accumulator is present and fuel flow from the direct injection fuel pump is less than a threshold fuel flow rate, the answer is yes and method900proceeds to920. Otherwise, the answer is no and method900proceeds to922.

At920, method900regulates fuel pressure in the direct injection fuel pump compression chamber via a pressure relief valve401and accumulator502as shown inFIG. 5, although other regulation schemes are also envisioned. The fuel pressure in the compression chamber is regulated to a single pressure that is greater than pressure output of the low pressure fuel pump that is supplying fuel to the direct injection fuel pump. By regulating pressure in the compression chamber a pressure differential between the direct injection fuel pump piston's top and bottom develops and fuel flow from the piston top to bottom provides lubrication to the direct injection fuel pump. At the same time, fuel flow out of the direct injection fuel pump to the direct injection fuel rail is stopped because pressure in the direct fuel injection fuel rail is greater than direct injection fuel pump output pressure. Consequently, the direct fuel injection pump is lubricated without raising direct injection fuel rail pressure. Additionally, direct injection fuel pump lubrication is provided when fuel flow through the direct fuel injectors is stopped. In this way, the direct injection fuel pump may be lubricated while direct fuel injection fuel pump output to the fuel rail is zero or less than a threshold fuel flow rate. Method900proceeds to exit after full cam stroke lubrication begins.

At922, method900judges whether or not to supply direct injection fuel pump half cam stroke (e.g., compression stroke) fuel pump lubrication. In one example, method900judges whether or not to supply direct injection fuel pump full cam stroke lubrication based on whether or not pressure relief valve401ofFIG. 4is included in the direct injection fuel pump or fuel system. If the pressure relief valve is present and fuel flow from the direct injection fuel pump is less than a threshold fuel flow rate, the answer is yes and method900proceeds to924. Otherwise, the answer is no and method900proceeds to930.

At930, method900opens the solenoid activated check valve412shown inFIGS. 4 and 5to allow the check valve to operate as a pass through device. The direct injection fuel pump does not develop fuel pressure at outlet404when the solenoid activated check valve is operated in a pass through mode. Consequently, the direct injection fuel rail pressure does not increase; however, the direct injection fuel pump may be operated in this state for a limited amount of time to limit direct injection fuel pump degradation. Method900proceeds to exit after the solenoid activated check valve is operated in a pass through mode.

At924, method900regulates fuel pressure in the direct injection fuel pump compression chamber via a pressure relief valve401as shown inFIG. 4, although other regulation schemes are also envisioned. The fuel pressure in the compression chamber is regulated to a single pressure during the pump's compression stroke that is greater than pressure output of the low pressure fuel pump that is supplying fuel to the direct injection fuel pump. By regulating pressure in the compression chamber a pressure differential between the direct injection fuel pump piston's top and bottom develops and fuel flow from the piston top to bottom provides lubrication to the direct injection fuel pump. At the same time, fuel flow out of the direct injection fuel pump to the direct injection fuel rail is stopped because pressure in the direct fuel injection fuel rail is greater than direct injection fuel pump output pressure. Consequently, the direct fuel injection pump is lubricated without raising direct injection fuel rail pressure. Additionally, direct injection fuel pump lubrication is provided when fuel flow through the direct fuel injectors is stopped. In this way, the direct injection fuel pump may be lubricated while direct fuel injection fuel pump output to the fuel rail is zero or less than a threshold fuel flow rate. Method900proceeds to exit after half cam stroke lubrication begins.

Referring now toFIG. 10, is shows a second example fuel system for supplying fuel to engine10ofFIG. 1. Many devices and/or components in the fuel system ofFIG. 10are the same as devices and/or components shown inFIG. 2. Therefore, for the sake of brevity, devices and components of the fuel system ofFIG. 2, and that are included in the fuel system ofFIG. 10, are labeled the same and the description of these devices and components is omitted in the description ofFIG. 10.

The fuel system ofFIG. 10shows fuel passage1002leading from fuel pump228to port fuel injection rail240and fuel injectors242. Fuel passage1002allows fuel to come in contact with both the step room and pump's compression chamber. The fuel then may pick up heat and exit to the PI fuel system as shown. That fuel enters and exits the high pressure pump; however, the fuel enters and exits at lift pump pressure (e.g., the same pressure as output by low pressure fuel pump208).

FIG. 11shows another example direct injection fuel pump228is shown. Many devices and/or components in the direct injection fuel pump ofFIG. 11are the same as devices and/or components shown inFIG. 4. Therefore, for the sake of brevity, devices and components of the direct fuel injection pump ofFIG. 4, and that are included in the direct injection fuel pump ofFIG. 11, are labeled the same and the description of these devices and components is omitted in the description ofFIG. 11.

The fuel pump ofFIG. 11includes fuel passage1002which allows fuel to come into contact with step room418and pump compression chamber408before proceeding to port fuel injectors. By allowing fuel to come into contact with portions of high pressure fuel pump228, it may be possible to cool high pressure fuel pump228and improve fuel atomization.

Thus, either example pump shown inFIG. 4, 5, or11may be selected and fuel rail pressure greater than lift pump pressure may be provided via engaging the solenoid operated check valve.