GB2330178A - A fuel injection system with variable fuel pressure supply to a unit injector - Google Patents

Abstract

A fuel injection system 10 comprises a hydraulically actuated electronically controlled fuel injector 14 - which (see figure 2) has a barrel with a bore, a plunger reciprocating within the bore defining a variable volume pump chamber and a spill port between the pump chamber and a drain - and a pump 18e for supplying fuel of variable pressure to the pump chamber in response to a pressure signal s 11 and means for determining the desired fuel quantity 40 to be injected in order to generate the signal s 11 to control the pump 18e. This allows the injector to infinitely vary the rate of fuel injection during the initial or pilot portion of an injection cycle independent of engine speed or load. Information is also given as to how the time interval between the initial injection and main injection can be varied by controlling the pressure of actuating fluid.

Description

1 TI 0 Descriiption 2330178 METHOD AND APPARATUS FOR FUEL INJECTION RATE

SHAPING FOR A HYDRAULICALLY- ACTUATED UNIT FUEL INJECTION SYSTEM

Technical Field

The present invention relates generally to hydraulically-actuated fuel injection systems and, particularly, to methods and devices for shaping the fuel injection delivery characteristics of such systems.

Background Art

Fuel injection rate shaping is a process of tailoring the amount and rate of fuel delivered during the ig nition delay portion and the main injection portion of an injection cycle. This process modifies the heat release characteristics of the fuel combustion process and is beneficial in achieving, inter alia, favorable emission and noise levels.

Rate shaping devices for conventional mechanically-driven fuel systems may be classified as one of three types: restrictive, retractive, or spill control. Restrictive devices cause a pressure drop of the injection fuel, resulting in lower injection pressure. Retractive devices temporarily store fuel during the initial portion of injection, while spill control devices spill or bleed a portion of the fuel flow from the high pressure fuel injection circuit.

U.S. Patent 5,492,098, issued to Hafner and Liu on February 20, 1996 and assigned to the assignee of the present invention, illustrates a hydraulically actuated, electronically controlled unit fuel r 1 A injection system which variably provides for split or continuous fuel injection independent of the utilizing engine's speed or load. The rate shaping device described in and claimed by that patent is often referred to herein and by the assignee of that patent as PRIME. While PRIME has performed admirably since its commercial introduction, the fuel spill path preferably employed by PRIME constitutes a passage associated with the plunger and a passage associated with the barrel. Such passages permit fuel spillage only when they are open one to the other which occurs only momentarily during the plunger's pumping stroke and always begins at a fixed plunger location. That plunger location is at a fixed distance from the is plunger's retracted position. That spill path diverts fuel from being injected during the plunger's pumping stroke, causes the initial portion of the injection cycle to end, and, thus, substantially fixes the fuel quanti ty injected during that initial portion. Such substantially fixed fuel quantity limits the injection rate shaping available in the initial portion of the injection cycle and, thus, does not achieve all the advantages that full range injection rate shaping provides.

Disclosure of the Invention

In one aspect of the present invention there is disclosed a hydraulicallyactuated electronically-controlled unit injector fuel system adapted for an engine. The system includes means for providing injection rate shaping involving fuel quantity adjustments during an initial portion of the injection cycle using a fuel injector which displaces a fixed volume of space.

6 1 W In another aspect of the present invention there is disclosed a method of operating a hydraulically-actuated electronically controlled unit injector fuel system including controlling the pressure of fuel supplied to a pump chamber of a hydraulically-actuated electronically controlled unit injector, injecting fuel from the pump chamber through fuel orifices in the hydraulically-actuated electronically controlled unit injector during an ---initialportion of the injection cycle, spilling fuel from the pump chamber to a low pressure source after the initial portion, and, after such spilling, injecting fuel from the pump chamber through the fuel orifices during a main portion of the injection cycle.

Brief Description-of the Drawings

Fig. 1 is a diagrammatic, general schematic view of a hydraulicallyactuated electronicallycontrolled unit injector fuel system which includes the present invention.

Fig. 2 is a diagrammatic, enlarged crosssectional view of one embodiment of PRIME applied to one hydraulically-actuated unit fuel injector shown in Fig. 1.

Fig. 3 is a diagrammatic, enlarged partial sectional view of the plunger and barrel assembly of Fig. 2 taken within the encircling line 3.

Fig. 4 is a diagrammatic, sectional view taken along line 4-4 of Fig. 3.

Fig. 5 is a diagrammatic graph showing fuel delivery reduction for an initial portion of an injection cycle as a function of fuel rail pressure for a family of air entrainment percentages for an A 1 4 exemplary unit fuel injector capable of injecting up to about 150 MM3 per plunger stroke.

Fig. 6 is a diagrammatic graph which shows comparative results of laboratory tests measuring fuel injection flow (F) versus time (t) for a hydraulically-actuated unit fuel injector lacking and having the present invention, curve F, and curve F 2r respectively. The tests from which the curves resulted were run at a constant rated engine speed..The total fuel delivery per injection cycle and the actuating fluid pressure were held about the same for the tests.

Best Mode for Carrying-Out the Invention

Referring to Fig. 1, wherein similar reference numerals designate similar elements or features throughout Figs. 2-4, there is shown an embodiment of a hydraulically-actuated electronicallycontrolled injector fuel system 10 (hereinafter referred to as a HEUI fuel system).

The exemplary HEUI fuel system 10 is shown in Fig. 1 as adapted for a direct-injection dieselcycle internal combustion engine 12. While the embodiment of Fig. 1 schematically illustrates an inline six cylinder engine, it should be understood that the present invention is also applicable to other types of engines, such as vee-type engines and also rotary engines, and that the engine may contain fewer or more than six cylinders or combustion chambers.

Referring again to Fig. 1, the HEUI fuel system 10 includes one or more hydraulically-actuated elect ronical ly- controlled injectors 14, such as unit pump-injectors, each associated with a respective combustion chamber of the utilizing engine 12. The 1 HEUI fuel system 10 further includes apparatus or means 16 for supplying hydraulic actuating fluid to each injector 14, apparatus or means 18 for supplying fuel to each injector 14, and apparatus or means 20 for electronically controlling at least the fuel injection quantity, injection timing, and/or actuating fluid pressure, and/or fuel pressure provided by apparatus 18. Further details of the exemplary HEUI fuel system 10, not discussed here, are disclosed in U. S. Patent No. 5, 191, 867 issued to Glassey et al. on March 9, 1993.

The hydraulic actuating fluid supplying means 16 preferably includes an actuating fluid sump 22, a relatively low pressure actuating fluid transfer is pump 24, an actuating fluid cooler 26, one or more actuating fluid filters 28, a source of high pressure actuating fluid or means 30 for pressuring actuating fluid such as a high pressure actuating fluid pump 32, at least one relatively high pressure actuating fluid manifold 34 arranged in fluid communication between the pressurizing means 30 and each of the injectors 14, and apparatus or means 36 for variably controlling the magnitude of the pressure of actuating fluid in the manifold 34.

Preferably, the pump 32 is a gear-driven fixed-displacement axial piston pump and means 36 is an electronically-controlled proportional pressure control valve 38 or rail pressure control valve (hereinafter called the RPM which selectively bypasses a variable amount of actuating fluid from the discharge side of the relatively high pressure pump 32 back to the relatively low pressure sump 22. Alternatively, the pump 32 may be a variable- 1 1 displacement pump such as an axial piston pump and, in that case, the RPCV 38 may be eliminated.

Preferably, the fluid chosen for the actuating fluid is not fuel but is a relatively incompressible liquid having a relatively higher viscosity than fuel under the same conditions. Preferably, the actuating fluid is engine lubricating oil and the actuating fluid sump 22 is an engine lubrication oil sump. In the embodiment of Fig. 1, ---thepump 32 increases the actuating fluid pressure level from a typical engine operating oil pressure level to the actuation pressure level required by the injectors 14. The RPCV 38 is electronically controlled by means 20 to control the actuating fluid is pressure effectively provided by the pump 32 to the manifold 34. The RPCV 38 selectively causes a variable portion of the actuating fluid pressurized by pump 32 to bypass the manifold 34 and return directly to the sump 22.

Apparatus or means 18 for supplying fuel preferably includes a fuel tank or sump 18a, a variable pressure fuel supply means 18b, at least one fuel filter 18c, and at least one fuel rail 18d arranged in fluid communication between the supply means 18b and each of the injectors 14.

Preferably, the variable pressure fuel supply means 18b includes a geardriven fixeddisplacement axial piston pump 18e and means 18f or fuel pressure control valve (FPM for controlling the fuel pressure at the discharge side of the pump 18e by selectively bypassing a variable amount of fuel discharged from the pump 18e back to the fuel tank 18a through a fuel drain line 18g to maintain the desired pressure in the fuel rail 18d. The FPCV 18f provides A q - 7 1 is a function for fuel which is analogous to that provided by the RPCV for actuating fluid. Alternatively, the pump 18e may be a variabledisplacement pump capable of providing higher fuel flowrate or a fixed displacement pump driven by a variable speed driver such as an electric motor. The variable displacement pump may comprise an axial piston pump. However, for any variable displacement pump, the FPC.V 18f may be eliminated.

The FPCV 18f (or, alternatively, variable displacement pump 18e) is electronically controlled by means 20 to control the fuel pressure effectively provided by the pump 18e to the fuel rail 18d.

Means 20 for electronically controlling the fuel injection quantity, injection timing, actuating fluid pressure, and/or fuel pressure provided by means 18 of the HEUI fuel system 10 is preferably a digital microprocessor or electronic control module 40 hereinafter referred to as the ECM.

The ECM 40 contains software decision logic and information defining optimum fuel system operational parameters and controls key fuel system components. One or more sensor signals (S 0 - S 8), indicative of various engine parameters are delivered to the ECM 40 to identify the engine's current operating condition. The ECM 40 uses these input signals to control the operation of the fuel system 10 in terms of fuel injection quantity, injection timing, actuating fluid pressure, fuel pressure, and injection rate shaping.

An exemplary software decision logic will now be discussed for determining the magnitude of the fuel pressure supplied to the injector(s) 14. This logic preferably uses at least three inputs: actual 1 1 1 8 - engine speed, desired fuel quantity, and actual fuel pressure.

Preferably, at least an actual engine speed signal and a desired fuel quantity signal are the inputs for a fuel pressure map and/or equation(s) resident in the ECM 40. Alternatively, an air inlet pressure signal may be added as an input. Based on these input signals, a desired fuel pressure signal (S,,) selected as an output. This desired fuel -pressure signal then is compared with an actual fuel pressure signal to produce a fuel pressure error signal. This fuel pressure error signal and the desired fuel pressure signal become the inputs for a set of mathematical equations and/or maps called the is FPCV control algorithm whose output is a desired electrical current signal, S11.

This desired electrical current signal S is applied to a solenoid operated valve or, alternatively, some other type of electrically- actuated valve in the FPCV 18f or variable pressure pump 18e. By changing the electrical current signal S11. the fuel pressure supplied to the injector(s) 14 can be increased or decreased. For example, increasing the current to the FPCV 18f causes the FPCV 18f to bypass fuel directly to the fuel tank 18a through drain line 18g at a higher pressure thereby increasing the fuel pressure in the fuel rail 18d. Decreasing that current signal to the FPCV 18f causes the FPCV 18f to bypass more fuel to the fuel tank 18a at a lower pressure thereby decreasing the fuel pressure in the fuel rail 18d. This FPCV control algorithm calculates the electrical current signal to the FPCV 18f that would be needed to raise or lower the fuel pressure to result in a zero fuel pressure 1 9 error signal. The resulting fuel pressure in the fuel rail 18d is used to control the fuel quantity injected during an initial portion of the injection cycle.

Preferably, the raw fuel pressure signal, S, sensed on the discharge side of the pump 18e downstream from the FPCV 18f if same is present such as in the fuel rail 18d, is conditioned by conventional means to minimize/eliminate noise and convert the signal into a form usable by the ECM 40.

Referring to Fig. 2,, the injector 14 is is preferably a hydraulically-actuated unit injector.

The injector 14 generally includes an electrical actuator and control valve assembly 42, a body 44, a plunger and barrel assembly 46, and an injection nozzle assembly 48 having a movable needle check 50 and one or more fuel spray orifices 52.

Alternatively, instead of a unit injector, one or more of the assemblies 42, 46, and/or 48 may be a separate, remotely spaced component arranged in fluid communication as needed.

The actuator and valve assembly 42 serves as a means or device for selectively communicating relatively high pressure actuating fluid from the manifold 34 to the respective injector 14 in response to receiving an electrical control signal from the ECM 40. The assembly 42 includes an electrical actuator 54 and a single actuating fluid control valve 56. For example, the actuator 54 may be an on/off-type solenoid and the valve 56 may be a poppet valve or spool valve connected to a movable armature of the solenoid.

The plunger and barrel assembly 46 includes a barrel 58 which has a bore 59, a fuel pump plunger reciprocatably arranged in the bore 59, and spill 1 i 1 1 1 1 1 9 control means 62 for temporarily or intermittently, during the pumping stroke of the plunger 60, spilling fuel which would otherwise be transmitted toward the fuel spray orifices 52. The spill control means 62 spills a portion of fuel contained in a high pressure fuel circuit of the injector 14 which extends between the plunger 60 and the fuel spray orifices 52. Fig. 2 shows an actuating fluid piston or intensifier 64 integrally connected to the plunger 60.

Alternatively, the piston 64 may be a separate, movable component positioned adjacent the plunger 60 as shown, for example, in U.S. Patent No. 5,121,730 issued to Ausman et al. on June 16, 1992. Preferably, the actuating fluid piston 64 has a larger effective is diameter than the fuel pump plunger 60 in order to effect pressure intensification of the fuel contained in a high pressure fuel pump chamber 66 and the rest of the high pressure fuel circuit. Alternatively, the effective diameters of the piston 64 and the plunger 60 may be the same. The fuel pump chamber 66 is defined by the barrel 58 and a leading edge 67 of the plunger 60 which can occupy any location between a fully retracted, fill position (as shown in Figs. 2 and 3) and a fully extended, bottomed position (not shown). Accordingly, the volume of the pump chamber 66 is variable depending upon the position of the plunger 60. Its maximum volume occurs when the plunger occupies its retracted position and is minimized when the plunger occupies its bottomed position.

Preferably, the spill control means 62 temporarily or intermittently spills a portion of the fuel from the high pressure pump chamber 66 during each downward or pumping stroke of the plunger 60.

1 The preferable embodiment of the spill control means 62 is shown in Figs. 3-4 and is applicable to both a freely rotatable fuel pump plunger 60 as well as a non-rotatable fuel pump plunger.

Referring to Figs. 3-4, the preferred embodiment of spill control means 62 is shown. The spill control means 62 includes at least one spill port 68 in the barrel 58 and spill passage means 70 having a single internal axial passage 72 centrally -defined in the plunger 60 for continuously fluidly communicating the pump chamber 66 with one or more radially extending passages 76 in the plunger 60, and an outer circumferential groove or slot 74 formed in the plunger 60 between a leading and a trailing land 78 and. 80, spaced from the leading edge 67 thereof, and being in continuous fluid communication with the passages 76. As best shown in Fig. 4, the radial passages 76 intersect with the passage 72 and are preferably evenly spaced circumferentially from one another. The groove 74 is also arranged to be in intermittent fluid communication with the spill port 68 of the barrel 58 for at least a portion of the plunger's travel relative to the barrel 58 (i.e. while the groove 74 and port 68 open one to another) during each pumping stroke of the plunger 60.

Accordingly, the spill control means 62 associated with the barrel 58, the hydraulicallyactuated fuel pump plunger 60, the electronic control means 20, and the fuel supply pressure means 18b collectively serve as a flexible means 84 (Fig. 1) for variably controlling the fuel injection rate (i.e. fuel injection flowrate versus time profile) of a fuel injection cycle. The spill control means 62, however, can affect the rate at which fuel is injected during 12 lz is the initial portion of the injection cycle, but cannot affect the quantity of fuel injected during that initial injection. By variably controlling the pressure of fuel supplied to the pump chamber 66, however, that fuel quantity can be adjusted to enable the user to achieve the maximum flexibility in fuel injection rate shaping.

Industrial Apiplicabilit Referring to Fig. 1, the actuating fluid supply apparatus 16 consists of a low pressure section and a high pressure section. The low pressure section may, for example, operate at a pressure of about 0.3 to.4 MPa (44 psi to 60 psi) to provide filtered actuating fluid, preferably in the form of lubricating oil, to the high pressure actuating fluid pump 32 as well as the lubricating oil system of the utilizing engine 12. The transfer pump 24 draws oil from the engine oil sump 22 and supplies it through the oil cooler 26 and filter 28 to both the engine 12 and the high pressure actuating fluid pump 32.

The high pressure actuating fluid circuit provides actuating fluid to each injector 14 and operates in a pressure range, for example, from about 4 to 23 MPa (about 580 to 3300 psi). The high pressure actuating fluid flows through lines into the manifold 34 located near the injectors 14. The manifold 34 stores the actuating fluid at a variable actuation pressure ready for injector operation.

Preferably, actuating fluid is discharged from the injector 14 under the engine valve cover (not shown) so that no separate return lines to the sump 22 are required.

1 1 Referring to Fig. 1, the fuel supply means 18 may, for example, operate at a pressure of about 0.07 to.7 MPa (10 psi to 100 psi).to provide filtered fuel to the fuel rail 18d and, subsequently, to the pump chamber 66 through a check valve resident in the injector 14 as is well known to those skilled in the art.

The ECM 40 variably controls the pressure in the high pressure actuating fluid supply apparatus 16 the pressure in the fuel rail 18d to variably control the pressure of fuel injected by the injectors 14 and the quantity of fuel injected during the initial portion of the injection cycle independent of engine speed. Operational maps and/or mathematical equations stored in the ECM programmable memory identify and control selected system components to provide the optimum actuating fluid pressure in the manifold 34 and the optimum fuel pressure in the fuel rail 18d for optimum engine performance.

One of the unique capabilities of the HEUI fuel system 10 is its ability to be tuned by varying the design of system components. Applicants' present invention provides flexible fuel injection rate shaping across the entire load and speed range of the utilizing enginels. The means 84 may be implemented and tuned for an engine combustion system in order to achieve desirable engine performance characteristics.

Preferably, the spill control means 62 is a precision ported spill control device located in the plunger and barrel assembly that adds no additional components to the basic hydraulically-actuated injector 14. Since fuel injection timing of the injector 14 is controlled by the ECM 40 and assembly 42 completely independent of the initial position of 1 the plunger 60, only one controlling edge needs to be manufactured with precision.

In combination with the independent fuel injection pressure control of the HEUI fuel system 10, engine performance can be optimized by varying the idle and light load rate characteristics, independent of rated and high load conditions. The resulting benefits to performance, noise, and emissions generally will depend upon the particular engine and the objectives of the engine manufacturer.

Fig. 6 is a diagrammatic graph which shows comparative results of actual laboratory tests measuring fuel injection flowrate in liters per minute (F) versus time after injection cycle initiation in is milliseconds (t) for a hydraul ically- actuated unit fuel injector equipped with PRIME and having a nominal injection capability of one hundred fifty (150) cubic millimeters per complete stroke of the plunger. The curves F 1 and F2 respectively represent that injector's flowrate for fuel pressures supplied to the injector of one hundred (100) and ten (10) psi. The total fuel flow per injection cycle was held about the same for 3 the curves of Fig. 6 and was about 10 mm This fuel flow was controlled by the amount of,on time" that the injector solenoid 54 was electrically energized.

The "on times" for the curves in Fig. 6 are slightly different to provide about the same total fuel flow through the fuel orifices 52 per injection cycle. The actuating fluid pressure was also held about the same for the curves in Fig. 6 and was about 4 mega pascals (Mpa).

Fig. 5 is a diagrammatic graph of first shot fuel delivery reduction in cubic millimeters versus fuel rail pressure in psi for the illustrated air is - is entrainment percentages in the fuel. First shot delivery reduction is the fuel which was not delivered during the initial portion of the injection cycle (i.e. prior to PRIME allowing fuel to be "spilled'') due to the presence of entrained air in the fuel. The actuating fluid pressure for the curves of Fig. 5 was about 4 MPa. It is to be noted that as fuel rail pressure increases, the first shot delivery loss decreases and the injection losses for various air -entrainment percentages of the fuel approach one another.

Operation of the present invention fuel system 10 will be described by reference to the spill control means 62 shown in Figures 2-4. When the plunger 60 is fully retracted (as shown in those Figs.), the first or leading land 78 of the plunger 60 covers the spill port 68 of the barrel 58. When the ECM 40 (in Fig. 1) energizes the solenoid 54 of a respective injector 14, the control valve 56 is pulled off its high pressure seat to admit high pressure actuating fluid into the injector 14. The actuating fluid hydraulically actuates or drives the piston 64 and consequently the plunger 60 downwardly (from the perspective of Figs. 2 and 3) to begin a pumping stroke. Fuel in the fuel pump chamber 66 is compressed by the plunger 60 so that fuel pressure increases in the pump chamber 66. When the increasing pressure of this fuel reaches the valve opening pressure of the injection nozzle assembly 48, the check 50 unseats to begin the initial injection of fuel through the spray orifices 52. Referring to the exemplary curves F, and F2 (or -first shot,') portion of the injection cycle begins where the curves rise above the---0 1 1 f uel f lowrate (at about 1. 3 ms).

t - 16 Although beginning at about the same time, the fuel flowrates exemplified by the curves F, and F, become dramatically different respectively reaching a maximum of about.25 liters/minute and.5 liters/minute and reflecting injection of substantially different fuel quantities.

As the plunger 60 (illustrated in Figs. 2-4) continues moving (downwardly) on its pumping stroke, the circumferential groove 74 of the plunger 60 temporarily (i.e. intermittently) communicates with the spill port 68 of the barrel 58 so that a portion of the high pressure fuel in the pump chamber 66 is spilled into the port 68 via the spill passage means 70 of the plunger 60. The pressure in the fuel pump chamber 66 is thereby temporarily or intermittently reduced. For a relatively low actuating fluid pressure (as shown in Fig. 6), the spill control means 62 produces a split injection so that there is a time duration between the initial injection portion and the main injection portion described below. For a relatively high actuating fluid pressure (not illustrated), the spill control means 62 reduces the initial rate of fuel injection (or fuel flow rate) but does not cause it to go to -011 before the main injection portion is initiated and, thus, does not produce the split injection described above.

As the plunger 60 continues moving (downwardly) on its pumping stroke, the second or trailing land 80 of the plunger 60 blocks the spill port 68 and the circumferential groove 74 no longer communicates with the spill port 68. The fuel pressure in the fuel pump chamber 66 again rises and the main injection portion of the injection cycle occurs. Referring again to Fig. 6, the main injection 0 - 17 is portion of the injection cycle is represented by the second hump (extending from about 2.0 to about 2.7 ms) of both curves F1 and F2 The curves FI and F2 for the main injection portion of the injection cycle are substantially coincident reflecting the phenomenon that for the balance of the injection cycle the fuel flowrate remains the same regardless of how much air was initially entrained in the fuel. Of course, in actual usage of the HEUI fuel system 10, the 'on time' ---forthe injector's solenoid would be longer for curve F2 than for FI to account for the greater fuel delivery reduction by F2 as compared with F, in the initial portion of the injection cycle due to the greater amount of entrained air in the fuel of F2- As is apparent to one skilled in the art, the time interval between the initial injection portion and the main injection portion of an injection cycle can be controlled by varying the magnitude of the actuating fluid pressure used to hydraulically actuate the injector(s) 14. Varying the magnitude of the actuating fluid pressure in turn varies the speed of the fuel injection pump plunger 60. Varying the magnitude of the fuel pressure entering the pump chamber 66 varies the quantity of fuel injected during the initial portion of the injection cycle. The ECM 40 operates the RPCV 38 and FPCV 18f in a closed loop control strategy respectively using an actuating fluid rail pressure sensor and a fuel rail pressure sensor.

Preferably for accuracy, the actuating fluid rail pressure sensor and fuel pressure sensor are respectively located in the actuating fluid manifold 34 and fuel rail 18d and are calibrated at the utilizing engine's nominal operating temperature. Alternatively, the actuating fluid pressure sensor and 1 18 - fuel pressure sensor may be respectively located elsewhere in the high pressure actuating fluid circuit between the high pressure actuating fluid pump 32 and the hydraul ically- actuated injectors 14 and elsewhere between the fuel pump 18e and the injectors 14.

The present invention HEUI fuel system extends injection rate shaping capability across the entire operating range of the utilizing engine by infinitely adjusting the actuating fluid pressure and fuel pressure supplied to the injector. Other aspects, objects, and advantages of this invention can be obtained

from a study of the drawings, the disclosure, and the appended claims.

is 1 19 -

Claims (14)

Claims

1. A hydraulically-actuated electronically- controlled injector fuel system adapted for an engine comprising:

a fuel injector having a barrel and a hydraulically-actuated fuel pump plunger positioned in a bore of the barrel, said plunger being adapted to be hydraulically actuated by pressurized actuating fluid ---andhaving a leading end which, with said barrel, defines a fuel pump chamber; a spill port defined in said barrel and an outer circumferential groove defined in the plunger and spaced a predetermined distance from said leading end wherein said groove and port are arranged to be in intermittent fluid communication during the pumping stroke of said plunger; a pump for supplying fuel of variable pressure to said fuel pump chamber, said pump providing a pressure which is responsive to a pressure signal; and means for determining the desired fuel quantity to be injected during each pumping stroke prior to said groove and port being in fluid communication and for signaling said pump with a pressure signal corresponding to the desired fuel quantity.

is

2. The fuel system of claim 1 wherein said pump is driven by an electric motor whose speed is variable.

3. The fuel system of claim 1 wherein said pump has an output volume per unit of time which is 1 t - 20 fixed for any pump speed and wherein said fuel system further comprises a valve for controlling the pressure of the fuel discharged by said pump.

4. The fuel system of claim 1 further comprising: means for determining the fuel quantity injected by said injector during the pumping stroke prior to said port and groove being in fluid means for increasing the pressure of the fuel supplied to the fuel pump chamber if the desired fuel quantity injected is greater than the actual fuel quantity injected and for decreasing the pressure of the fuel supplied to the fuel pump chamber if the desired fuel quantity injected is less than the actual fuel quantity injected.

5. A hydraulically-actuated electronically-controlled injector fuel system adapted for an engine comprising:

an injector having a barrel and a hydraulically-actuated fuel pump plunger positioned in a bore of the barrel, said plunger and barrel defining a fuel pump chamber, said plunger adapted to be hydraulically actuated by the actuating fluid; means for infinitely varying the time interval between an initial injection portion and a main injection portion of a fuel injection cycle independent of engine speed and loading; means for determining the desired fuel quantity to be injected during the initial injection portion; and 4 21 - means for variably controlling the pressure of fuel supplied to said fuel pump chamber.

6. The fuel system of claim 5 further comprising:

means for determining the actual fuel quantity injected by said injector during said initial injection portion; means for increasing the pressure of the 10..fuel supplied to the fuel pump chamber if the desired fuel quantity injected is greater than the actual fuel quantity injected and for decreasing the pressure of the fuel supplied to the fuel pump chamber if the desired fuel quantity injected is less than the actual fuel quantity injected.

7. A hydraulically-actuated electronically-controlled injector fuel system adapted for an engine comprising: an injector having a barrel and a hydraulically-actuated fuel pump plunger positioned in bore of the barrel, said plunger and barrel defining fuel pump chamber, said plunger adapted to be hydraulically actuated by the actuating fluid; means for infinitely varying the rate of fuel injection during an initial portion of an injection cycle independent of engine speed and loading; means for determining the desired fuel quantity to be injected during the initial injection portion; and means for variably controlling the pressure of fuel supplied to said fuel pump chamber.

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8. A hydraulically-actuated electronically- controlled injector fuel system adapted for an engine comprising: a source of pressurized hydraulic actuating f luid; an injector having a barrel and a hydraulically-actuated fuel pump plunger positioned in a bore of the barrel, said plunger and barrel defining a fuel pump chamber, said plunger adapted to be hydraulically actuated by the actuating fluid; means for supplying fuel of variable pressure to the fuel pump chamber; means for intermittently spilling fuel from the fuel pump chamber during the pumping stroke of plunger; and means for variably controlling the magnitude of the pressure of the actuating fluid supplied to actuate the plunger.

9. The fuel system of claim 8 further comprising: means for determining the desired quantity of fuel to be injected prior to spilling fuel from the pump chamber; means for determining the actual quantity of fuel to be injected prior to spilling fuel from the pump chamber; and means for increasing and decreasing the pressure of fuel supplied to the pump chamber in response to the desired fuel quantity being greater than the actual fuel quantity and to the desired fuel quantity being less than the actual fuel quantity.

a 1 1 1 v - 23

10. A method of injecting fuel comprising: supplying fuel of a desired pressure to a pump chamber of a fuel injector;. injecting fuel from the pump chamber through orifices in the injector during an initial portion of the fuel injection cycle; spilling fuel from the pump chamber through a spill path after the initial portion; and inj.ecting fuel from the pump chamber through ---orificesafter spilling fuel.

The method of claim 10 further comprising: selecting the desired fuel pressure corresponding to the quantity of fuel to be injected during the initial portion.

12. The method of claim 10 further comprising: measuring the fuel pressure; and adjusting the fuel pressure until the actual fuel pressure is within a predetermined value of the desired fuel pressure.

13. A method of injecting fuel comprising: providing an injector having a barrel with a bore therein and a reciprocatable plunger in the bore to form, with the barrel, a pump chamber; supplying fuel having a pressure corresponding to the quantity of fuel desired to be injected in an initial portion of an injection cycle to the pump chamber; injecting fuel through orifices in the injector during the initial portion; I 4 spilling fuel from the pump chamber to a drain after the initial portion; and injecting fuel through the orifices after spilling fuel.

14. The method of claim 13, said supplying fuel comprising:

measuring the fuel pressure; and adjusting the fuel pressure until its magnitude is within a predetermined value of the desired fuel pressure magnitude.