WO1993013309A1

WO1993013309A1 - Method for metering the amount of fuel ejected from a fuel injector

Info

Publication number: WO1993013309A1
Application number: PCT/US1991/009707
Authority: WO
Inventors: J. Roger Weber
Original assignee: Caterpillar Inc.
Priority date: 1991-12-23
Filing date: 1991-12-23
Publication date: 1993-07-08
Also published as: AU9170491A

Abstract

It is desirable that the amount of fuel injected into a combustion cylinder of an engine be controlled or metered based upon engine operating conditions. Typically, in unit fuel pump injectors, fuel is passed into a chamber below an axially displaceable plunger, compressed by a downward stroke of the plunger, and ejected from the chamber and injector under pressure. The amount of fuel ejected is controlled by controlling the downward displacement of the plunger or by the use of a scrolled plunger and a spill port. Such a control is imprecise and limited in usefulness. The present invention is a novel method for metering the amount of fuel ejected from the injector (12). Basically, the plunger (56) begins at a first position adjacent a hard stop (58). The plunger (56) is then raised a predetermined distance corresponding to a volume of fuel to be ejected. The plunger is then forced down until the plunger (56) is again against the hard stop (58) thereby ejecting a precisely metered volume of fuel.

Description

METHOD FOR METERING THE AMOUNT OF FUEL EJECTED FROM A FUEL INJECTOR

Technical Field

Fuel injectors having an axially displaceable plunger which compresses fuel in a fuel chamber to a pressure which ejects the fuel through an injection valve into the piston cylinder of an engine, and more particularly a method for precisely metering the amount of fuel ejected from the fuel injector in response to engine operating conditions.

Background Art

In engine combustion systems, the precise control of the quantity and timing of fuel injection is desirable for a number of reasons. Accurate timing improves engine performance from the standpoints of fuel consumption, combustion noise, reduced gaseous emissions, and staying within the structural capabilities of the engine. Consistent and precise delivery of small quantities of fuel at idle load conditions improves smooth idle characteristics. An additional benefit of being able to deliver small, controllable quantities of fuel can be a rate-shaped or split injection, provided the rest of the injection system is configured to allow split injection. Split injection can reduce NO emissions and decrease combustion noise without the fuel consumption penalty common to another common strategy for controlling NO and noise, namely, retarded start of injection timing.

In prior art fuel injectors, a relatively large volume of fuel is pressurized, usually.below a plunger, regardless of the amount of fuel desired for injection. The amount of fuel injected is attempted to be controlled by various means including scrolled plungers sequenced with fuel fill and spill ports. Such injectors are somewhat difficult to manufacture and it is somewhat difficult to properly design and position the plunger scroll, fill port and spill port. In addition, excess fuel in the plunger chamber decreases responsiveness of the injector due to the excess compressible volume. The increased compressibility" manifests itself in sluggish behavior and thereby makes injecting small quantities of fuel difficult. Also, the time required to compress the excessive fuel volume at the start of injection and expand the volume at the end of injection creates longer than desired duration of the injection event. The present invention is intended to solve the above problems. Specifically, it is an object of the present invention to improve the control of the quantity of fuel injected. It is another object to improve the timing of injection by improving the responsiveness of the injector.

It is a further object of the present invention to minimize the volume of pressurized fuel to more closely match the amount of fuel desired for injection.

It is a further object to start the injector fuel fill process with the fuel chamber volume at its absolute minimum and then increase the volume only to the amount desired for injection.

Disclosure of the Invention

In one aspect of the present invention, a method for metering the amount of fuel ejected from the fuel chamber of a fuel injector into an engine combustion chamber is disclosed. In a preferred embodiment, the injector has a fuel chamber adjacent a first end of a plunger. The second end of the plunger is in selective communication with high pressure fluid. The plunger is axially controllably movable between a first position corresponding to a first fuel volume of the fuel chamber and various other positions corresponding to respective various other fuel volumes of the fuel chamber. The first end of the plunger is biased in a direction away from the first position. The magnitude of increase in volume of the fuel chamber is controlled in response to engine operating conditions. The method includes the steps of: displacing the plunger from the first position to one of the other positions, thereby controllably increasing the volume of the fuel chamber from the first fuel volume to one of the preselected other fuel volumes which is greater than the first fuel volume; filling the fuel chamber with fuel; communicating high pressure fluid to the second end of the plunger; moving the first end of the plunger from the other position to the first position; compressing the fuel in the fuel chamber; ejecting under pressure a metered volume of fuel from the fuel chamber which represents the difference in volume between the first fuel volume and the other fuel volume; releasing the force of the high pressure fluid from the second end of the plunger for a preselected time in response to engine operating conditions; and moving the first end of the plunger away from the first position. In another aspect of the present invention, instead of the plunger being spring biased away from the first position, the plunger is spring biased toward the first position. In this aspect of the invention, the plunger includes an intermediate edge facing in the direction of the first end of the plunger. High pressure fluid is selectively communicated to the intermediate edge to move the plunger away from the first position against the bias force. The method of operation is basically the same as set forth above.

Brief Description of the Drawings

Fig. 1 is a cross-sectional elevational view of an injection system of the present invention; and

Fig. 2 is a cross-sectional elevational view of an alternative embodiment of an injection system of the present invention.

Best Mode for Carrying Out the Invention

A preferred embodiment of an injection system 10 including a unit fuel pump injector 12 and a means for selectively communicating high pressure fluid to actuate the injector 14, is shown in Fig. 1. The injector 12 is shown seated against an internal frusto-conical seat 16 located within a stepped bore of a cylinder head 18. An upper portion 20 of the injector 12 along with the means 14 for actuating the injector are housed in a control valve body 22 which is bolted to a spacer bar (not shown) which is bolted to the cylinder head 18. The injector 12 includes a valve assembly 24, a pump assembly 26 and a fuel path 28.

The valve assembly 24 includes a nozzle 30 having a spray orifice 32 and a valve seat 34, a guide body 36, and an injection valve 38 housed within a cavity 40 in the guide body 36 and resiliently biased by a spring 42 toward the valve seat 34. The first end 44 of a spacer block 46 retains the spring 42 in the guide body cavity 40. The valve 38 includes a cylindrical needle portion 48 having a conical tip 50, a spring seat 52, and a cylindrical stop portion 54. The valve 38 is displaceable between a first position at which the tip 50 is seated on the valve seat 34, thereby blocking fluid communication between the fuel path 28 and the spray orifice 32, and a second position at which the tip 50 is upwardly spaced from the valve seat 34 thereby allowing fluid communication. Adjacent the spacer block 46 is the pump assembly 26. The pump assembly 26 includes an axially displaceable plunger 56 resiliently spring biased away from a hard plunger stop 58, which is the second end 60 of the spacer block 46. The plunger 56 includes a first end 62 displaceable between a first position and various other positions, a second end 64, and an intermediate edge 66 between the first and second ends 62,64 which faces towards the first end 62 of the plunger 56. The pump assembly 26 also includes the fuel chamber 68. The fuel chamber 68 is supplied with fuel from the fuel cavity 70 adjacent the spacer block 46 via the one-way ball check valve 72. The fuel cavity 70 is kept full of fuel from an external source (not shown) that provides the fuel to the fuel cavity 70 under slight pressure.

The plunger includes a cylindrical intensifier piston 74 and a cylindrical slave piston 76. The slave piston 76 is guided in the plunger bore 78 formed in the barrel 80 and the intensifier piston 74 is guided in the bore 82 of an insert 84 in the control valve body 22.

The plunger spring 86 is retained between a landing 88 on the barrel 80 and a collar 90 fixedly secured around the slave piston 76.

A hold down clamp 92 holds the complete injector assembly 12 tight against the seat 16.

Formed in the mid portion of the slave piston 76 is an annulus 94 having a bottom edge 96. A first bore 98 extends laterally through the annulus

94. A second bore 100 extends longitudinally axially from the first end 62 of the plunger 56 to the first bore 98. A relief 102 is formed in the slave piston 76 at the first end 62 of the plunger 56. An internal annulus 102 having a top edge

104 is formed in the plunger bore 78. A vent path 106 extends between the internal annulus 102 and the fuel cavity 70.

When the first end 62 of the plunger 56 is against the plunger stop 58, the bottom edge 96 of the slave piston annulus 94 is spaced slightly away from the top edge 104 of the plunger bore internal annulus 102.

The plunger 56 is biased upwards by the spring 86 and displaced downwards by the force of high pressure fluid against the second end 64 of the plunger 56 which is the top 108 of the intensifier piston 74. A pair of lateral bores 110 in the barrel 80 allow fluid which has leaked from the second end 64 of the plunger 56 past the intensifier piston 74 into the plunger spring space 112 to be drained out of the space 112 onto the head 18.

The fuel chamber 68 includes the space of the keyhole slot 114 and the space beneath the first end 62 of the plunger 56 in the plunger bore 78 when the plunger 56 is displaced upward.

The fuel path 28 runs from the fuel chamber 68, through the spacer block 46, through the guide body 36, around the needle valve 38 to the spray orifice 32 of the nozzle 30.

The means 14 for selectively communicating high pressure fluid to the second end 64 of the plunger 56 includes a high pressure fluid source 116 (shown in phantom as a circular opening into the spool valve bore 126) , a vent path 118 to atmospheric pressure, an axially displaceable spool valve 120, a means 122 for displacing the spool valve, and a fluid path 124. The spool valve 120 resides in a spool valve bore 126 having a first internal annulus 128 having an edge 130 and being in constant communication with the high pressure fluid source 116, a second internal annulus 132 having an edge 134 and being in constant communication with atmospheric pressure via the vent path 118, and a third internal annulus 136 between the first and second internal annuluses 128,132. Axial displacement of the spool valve 120 within the spool valve bore 126 is limited at one end by a spool valve stop 138, away from which the spool valve is spring 140 biased and at the other end by a hard stop 142. The spool valve 120 has an annulus 144 about its circumference having a first edge 146 and a second edge 148. The fluid path 124 extends between the third annulus 136 of the spool valve bore 126 and the insert bore 82 adjacent the second end 64 of the plunger 56.

The means 122 for displacing the spool valve 120 includes a piezoelectric motor 150 which expands axially under electrical excitation, an amplifier piston 152 spring 154 biased against the piezoelectric motor 150, a servant piston 156 spring 158 biased away from the amplifier piston 152, and a fluid space 160 between the amplifier piston 152 and the servant piston 156. A valve 162 in communication with low pressure fluid refills the fluid space 160 in case of leaks or drains the fluid space 160 if the volume of the space 160 decreases due to thermal expansion of the piezoelectric motor or fluid. Alternatively, instead of a high pressure fluid actuation system, the axial displacement of the plunger 56 could be controlled directly by a solenoid or by mechanical means.

An alternative embodiment of the present invention is shown in Fig. 2. In this embodiment, the plunger spring 86 is housed between the second end 64 of the plunge 56 and the control valve body 22 and the intensifier piston 74 and slave piston 76 of the plunger 56 are fixedly connected together. Thus, the plunger 56 is biased down against the plunger stop 58. The fluid path 124 extends now to the space beneath the intensifier piston 74, the bottom of the intensifier piston forming an intermediate edge 66 of the plunger 56 facing in the direction of the first end 62 of the plunger 56.

Industrial Applicability

Description of the functioning of the injection system 10 will begin with the various elements in the position shown in Fig. 1, which is with the piezoelectric motor 150 energized, the spool valve 120 displaced to the left allowing high pressure fluid to flow from the high pressure fluid source 116 through the fluid path 124 to the top 108 of the intensifier piston 74, the first end 62 of the plunger 56 against the hard stop 58 and the tip 50 of the valve 38 against the seat 34.

First, voltage to the piezoelectric motor 150 is ended and the motor 150 retracts axially. The amplifier piston 152 is displaced to the right under the force of the spring bias 154. The force of the spring 140 bias between the spool valve stop 138 and the spool valve 120 displaces the spool valve 120 and servant piston 156 to the right until the spool valve 120 abuts the hard stop 142. During the displacement of the spool valve 120, as the first edge 146 of the spool valve annulus 144 covers the edge 130 of the first annulus 128, flow of fluid from the high pressure source 116 to the fluid path 124 is cut-off and as the spool valve 120 continues displacing to the right the second edge 148 of the spool valve annulus 144 uncovers the edge 134 of the second annulus 132 allowing the fluid path 124 to communicate with the vent path 118. Next, because there is now no force resisting the plunger spring 86 bias, the spring 86 expands, axially moving the plunger 56 upwards. As the first end 62 of the plunger 56 is displaced away from the hard plunger stop 58, fuel which is under slight pressure in the fuel cavity 70 flows past the ball check valve 72 into the fuel chamber 68, the fuel path 28, and the longitudinal and lateral bores 100,98 in the plunger 56. As the plunger 56 continues to rise, the bottom edge 96 of the plunger annulus 94 covers the top edge 104 of the internal annulus 102 of the barrel 80 thereby trapping fuel in the fuel chamber 68 and preventing it from being vented back to the fuel cavity 70 through the vent path 118.

When the volume of the fuel chamber 68 has been increased from its first volume, corresponding to the volume in the fuel chamber 68 when the first end 62 of the plunger 56 is against the plunger stop 58, to one of an infinite number of possible other volumes, the difference between a respective other volume and the first volume being the amount of fuel which is to be injected, voltage is again provided to the piezoelectric motor 150. The piezoelectric motor 150 expands axially forcing the amplifier piston 152 to the left. The luid in the fluid space 160 is compressed forcing the servant piston 156 to the left against the spool valve 120. The force of the servant piston 156 displacement overcomes the spring 140 bias between the spool valve 120 and the spool valve stop 138 thereby displacing the spool valve 120 to the left. As the spool valve is displaced to the left, the second edge 148 of the spool valve annulus 144 covers the edge 134 of the second annulus 132 cutting o f communication between the vent path 118 and the fluid path 124. As the spool valve 120 continues displacing to the left, the first edge 146 of the spool valve annulus 144 uncovers the edge 130 of the first annulus 128 of the spool valve bore 126 opening communication from the high pressure fluid source 116 to the fluid path 124. High pressure fluid then flows from the high pressure fluid source 116 around the spool valve 120, into the fluid path 124 and against the second end of the plunger 56.

The force of the high pressure fluid overcomes the plunger spring 86 bias and forces the plunger 56 downward thereby compressing the fuel in the fuel chamber 68. The fuel continues to be compressed until the force of the fuel beneath the tip 50 of the injection valve 38 overcomes the force of the valve spring 42 bias and raises the valve 38, thereby allowing the fuel to be ejected from the fuel path 28 and fuel chamber 68 through the spray orifice 32.

As the first end 62 of the plunger 56 nears the hard plunger stop 58, the bottom edge 96 of the plunger annulus 94 uncovers the top edge 104 of the internal annulus 102 of the spacer block 46, thereby opening communication between the fuel chamber 68 and the fuel cavity 70, causing a sharp decrease in the pressure of the fuel in the fuel chamber 68. This sharp decrease in pressure allows the needle valve spring 42 bias to overcome the pressure remaining in the fuel thereby practically instantaneously closing the orifice 32 and providing a desirable sharp cut-off of injection. The disadvantage to venting the pressure from the fuel chamber 68 is that there is no longer any compressibility left in the fuel chamber 68 and the first end 62 of the plunger 56 hits the hard plunger stop 58 at high speeds which can lead to deterioration. If the vent path 118 is not provided, the pressure of the fuel in the fuel chamber 68 will slow the plunger 56 as the plunger 56 nears the hard plunger stop 58 to a more acceptable impact velocity, with a resultingly slower injection cutoff.

Sometime after the first end 62 of the plunger 56 has hit the hard plunger stop 58, the cycle is ready to be repeated beginning with de-energizing the piezoelectric motor 150. Depending on timing considerations, it may be desirable to de-energize the piezoelectric motor 150 before the first end 62 of the plunger 56 has hit the hard plunger stop 58 but at a time when the momentum of the plunger 56 will still carry the first end 62 of the plunger 56 to the hard plunger stop 58. Note that in the preferred embodiment, the first volume remains constant from cycle to cycle or in other words, the cycle always begins with the first end 62 of the plunger 56 against the hard stop 58.

It may be advantageous if the high pressure fluid source 116 communicates with the second internal annulus 132 rather than the first internal annulus 128 and the vent path 118 communicates with the first internal annulus 128 rather than the second internal annulus 132 so that the piezoelectric motor 150 would only need to be energized to create an injection. The timing of when voltage is supplied to the piezoelectric motor 150 is controlled through a data processor, such as a microprocessor, which processes information received from sensors which sense certain engine operating conditions. Based upon certain logic maps and governing algorithms, the microprocessor determines the amount of fuel which needs to be delivered to the cylinder during the next injection, and also when the injection should begin. Based upon the results of the data processing, the control de-energizes the piezoelectric motor 150 for a preselected period of time. During this time, because the space above the intensifier piston 74 is now in communication with atmospheric pressure, the plunger spring 86 displaces the plunger 56 upwards, thereby allowing fuel to flow into the fuel chamber 68.

Because the plunger 56 and spring 86 basically form a spring mass system, the upward displacement of the plunger 56 is predictable on a dynamic basis as a function of time, and therefore if the amount of fuel which must be delivered at the next injection is known, a period of time can be determined during which the piezoelectric motor 150 must be de-energized to allow the first end 62 of the plunger 56 to be controllably moved from its first position to another position corresponding to a volume of fuel under the plunger 56 which is needed to be injected. Thus, the magnitude of the increase in the volume of the fuel chamber 68 is controlled in response to the engine operating conditions. It is necessary to coordinate the end of the fuel fill process with the beginning of downward displacement of the plunger 56 because the injection system as configured has no way to hold the plunger 56 in a static position. The alternative embodiment shown in Fig. 2 functions in a similar manner, however in this embodiment, high pressure fluid is used to lift the plunger 56 against the force of the spring bias 86, and when it is necessary to compress the fuel for injection, the high pressure fluid is cut-off and the force of the spring 86 bias forces the plunger 56 down compressing the fuel and causing injection. Necessarily, a high force spring 86 would be required for this embodiment. Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure, and the appended claims.

Claims

Clai s

1. A method for metering the amount of fuel ejected from the fuel chamber (68) of a fuel injector (12) into an engine combustion chamber, said fuel chamber (68) being at least partially adjacent a plunger (56) , said plunger (56) being controllably movable between a first position corresponding to a first fuel volume of said fuel chamber (68) and various other positions corresponding to respective various other fuel volumes of said fuel chamber (18) , comprising the steps of: displacing said plunger (56) from said first position to one of said other positions, thereby controllably increasing the volume of said fuel chamber (68) from said first fuel volume to a preselected other fuel volume greater than said first fuel volume; filling said fuel chamber (68) with fuel; and ejecting under pressure a metered volume of fuel from said fuel chamber (68) which represents the difference in volume between said first fuel volume and said other fuel volume.

2. The method of claim 1, wherein the magnitude of increase in said volume of said fuel chamber (68) is controlled in response to engine operating conditions.

3. The method of claim 2, wherein said plunger (56) is axially displaceable.

4. The method of claim 2, wherein said plunger has first and second ends (62,64), said second end (64) of said plunger (56) being in selective communication with high pressure fluid, said first end (62) of said plunger (56) being biased in a direction away from said first position.

5. The method of claim 4, after said fuel chamber (68) has been filled with fuel, including the steps of communicating said high pressure fluid to said second end (64) of said plunger (56); moving said first end (62) of said plunger

(56) from said other position to said first position; compressing said fuel in said fuel chamber (68) ; and ejecting said metered volume of fuel from said fuel chamber (68) .

6. The method of claim 5, including the step of releasing the force of said high pressure fluid from said second end (64) of said plunger (56) for a preselected time in response to engine operating conditions, and moving said "first end (62) of said plunger (56) away from said first position.

7. The method of claim 2, wherein said plunger (56) has a first end (62) and an intermediate edge (66) facing in the direction of said first end (62) , said intermediate edge (66) being in selective communication with high pressure fluid, said first end (62) being biased toward said first position.

8. The method of claim 7, including the steps of communicating said high pressure fluid to said intermediate edge (66) of said plunger (56) ; moving said first end (62) of said plunger (56) away from said first position; and increasing the volume of said fuel chamber

(68)

9. The method of claim 8, including the steps of filling said fuel chamber (68) with fuel; releasing the force of said high pressure fluid from said intermediate edge (66) of said plunger (56) ; moving said first end (62) of said plunger (56) from said other position towards said first position; compressing said fuel in said fuel chamber (68) ; and ejecting said metered volume of fuel from said fuel chamber (68) .

10. The method of claim 1, including the step of cycling said plunger (56) during engine operation from said first position to one of said various other positions and back to said first position, said first fuel volume being constant from cycle to cycle.

11. The method of claim 10, wherein movement of said plunger (56) between said first position and said various other positions is in at least one direction in response to exertion of hydraulic force.

12. The method of claim 1, including the step of cycling said plunger (56) during engine operation from said first position to one of said various other positions and back to said first position, the distance said plunger is displaced from said various other positions to said first position is variable from cycle to cycle.

13. The method of claim 1, wherein said plunger (56) has first and second ends (62,64), said second end (64) being a fixed distance from said first end (62) .

14. The method of claim 10, wherein said plunger (56) has first and second ends (62,64), said second end (64) being a fixed distance from said first end (62) .