(84) |
Designated Contracting States: |
|
DE GB |
(30) |
Priority: |
18.05.1994 US 245589
|
(43) |
Date of publication of application: |
|
22.11.1995 Bulletin 1995/47 |
(73) |
Proprietors: |
|
- CUMMINS ENGINE COMPANY, INC.
Columbus
Indiana 47201 (US)
- TOSHIBA CORPORATION
Tokyo, 105-01 (JP)
|
|
(72) |
Inventors: |
|
- Hickey, Dan K.
Greenwood,
Indiana 46142 (US)
- Perr, J. Victor
Greenwood,
Indiana 46143 (US)
- Rix, David M.
Columbus,
Indiana 47201 (US)
- Bentz, Joseph C.
Columbus,
Indiana 47203 (US)
- Yonushonis, Thomas M.
Columbus,
Indiana 47201 (US)
- Naylor, Malcolm G.
Jonesville,
Indiana 47247 (US)
- Shinosawa, Katsuhiro
Tokyo 105-01 (JP)
- Carroll III, John C.
Columbus,
Indiana (US)
|
(74) |
Representative: Patentanwälte
Gesthuysen, von Rohr, Weidener, Häckel |
|
Postfach 10 13 54 45013 Essen 45013 Essen (DE) |
(56) |
References cited: :
EP-A- 0 450 891 US-A- 4 848 286
|
EP-A- 0 677 656
|
|
|
|
|
- PATENT ABSTRACTS OF JAPAN vol. 9 no. 256 (M-421) ,15 October 1985 & JP-A-60 104765
(YANMAR) 10 June 1985,
- PATENT ABSTRACTS OF JAPAN vol. 10 no. 187 (M-493) ,2 July 1986 & JP-A-61 031659 (YANMAR)
14 February 1986,
|
|
|
|
[0001] The present invention is directed generally toward a fuel pressurizing plunger assembly
for a compression ignition engine (Diesel engine) fuel injector operable with Diesel
fuel that may contain abrading particles and lubricity lowering contaminants, and
particularly to a fuel pressurizing plunger assembly with the features of the precharacterizing
part of claim 1.
[0002] Fuel injector plungers are required to operate under extremely adverse environmental
conditions in a fuel injector assembly. With a mechanical drive train, heavy mechanical
loads are applied to the plunger in both axial and tangential directions. The plunger
must reciprocate within a bore in the injector body that is often distorted so the
original diametral clearance is not maintained, and the plunger is forced against
the bore wall during injector operation, resulting in scuffing. Additionally, low
quality and contaminated fuels contribute to the creation of an adverse plunger operating
environment.
[0003] The plunger material has been modified throughout the years in an effort to make
a plunger that is both scuff-resistant and wear-resistant and capable of functioning
as required under the adverse conditions of the fuel injector environment. However,
third body debris interferes with efficient injector function. Third body debris includes
particles harder than the plunger or injector body bore which are not intended to
be present within the injector. These particles become embedded into the plunger surface
and ultimately cause the plunger and body to be wedged together so that the plunger
cannot reciprocate in the injector body bore and becomes friction welded. The reduction
of fuel lubricity, which could be caused by water contamination of the fuel, and may
be a characteristic of some alternative fuels, is also a factor contributing to the
friction welding of the plunger and injector body together. Injector operation is,
of course, prevented if this occurs.
[0004] The types of fuels increasingly used in Diesel engines, particularly fuels with low
lubricity. alternative fuels and fuels which may be contaminated with water, require
a scuff-resistant fuel injector plunger to maintain efficient engine operation. The
prior art plunger assembly defining the pre-characterizing part of claim 1 (JP - A
- 60 104765) addresses those problems with a plunger assembly with a plunger formed
of a scuff-resistant, wear-resistant ceramic material running in an axial bore of
a body portion that is made of steel. The abrasion resistance of ceramics is said
to be an advantage in the particular surroundings.
[0005] With a mechanical drive train heavy mechanical loads on the plunger in both axial
and tangential directions result in additional requirements for the diametral clearance
of the plunger within the bore in the injector body.
[0006] In view of the above it is the object of the present invention to provide a fuel
pressurizing plunger assembly for a compression ignition engine (Diesel engine) fuel
injector capable of operating efficiently in the presence of high axial and tangential
loads on the plunger in view of fuel used that may contain abrading particles and
lubricity lowering contaminants.
[0007] Above object is achieved by providing a fuel pressurizing plunger assembly with the
features of the pre-characterizing part of claim 1 in combination with the features
of the characterizing part of claim 1. The plunger used is wear- and scuff-resistant
and maintains an optimum diametral clearance so that it does not stick during fuel
injector operation even under adverse engine operating conditions. The injector plunger
is formed from a ceramic material having a thermal expansion coefficient sufficiently
correlated to the thermal expansion coefficient of the fuel injector body to provide
optimum operating clearance between the plunger and injector body during engine operation
while preventing fuel leakage around the plunger. Achieving the optimum fuel leakage
around the plunger during engine operation is critical. Instead of ceramics with low
thermal expansion which allow excessive leakage, high thermal expansion ceramics are
capable of maintaining fuel leakage within acceptable parameters.
[0008] Further improvements of the fuel pressurizing plunger assembly of the invention may
be obtained from the dependent claims. Further objects and advantages will be apparent
from the following description and drawings.
[0009] In the drawings
- Fig. 1
- is a schematic cross-sectional view of a fuel injector assembly in a Diesel engine
incorporating a scuff-resistant anti-stick plunger of the present invention; and
- Fig. 2
- presents graphically the dimensions of the injector body bore and plunger of the present
invention for different materials at different temperatures.
[0010] The plunger in the fuel pressurizing plunger assembly of the invention is a means
for causing a controlled volume of fuel to be injected from the fuel injector. In
this context it is influencing the timing of the fuel injection. Only in a preferred
embodiment it is to be understood as a timing plunger in a more narrowsense, i. e.
a separate intermediate plunger in a multiplunger-arrangement controlling a timing
chamber. Moreover, the fuel injector assembly can well be a unit fuel injector as
well as an in-line fuel injector.
[0011] Fuel injector plunger scuffing and sticking is one cause of high injector RPH (repairs
per hundred). High warranty costs may result from the replacement of failed and inoperable
plungers. The fuel injector body plunger assembly of the present invention provides
a reliable wear-resistant plunger that is free from sticking and scuffing, even when
exposed to extremely abusive engine operating conditions. Consequently, the present
invention effectively lowers both the injector RPH and warranty costs occasioned by
failed and inoperable plungers.
[0012] Referring to the drawings, Fig. 1 illustrates, in cross section, an open nozzle unit
fuel injector 10 with a plunger 12. This type of fuel injector includes a body 14
and an injector nozzle 16. The injector nozzle 16 and the body 14 are axially aligned
and held together by a retainer 18. An axial bore 20 extends throughout the length
of the body 14. A plurality of spaced injection orifices 22 in the nozzle 16 is provided
at the injector cup terminus to optimize fuel injection.
[0013] The injector 10 includes a plunger 12 that reciprocates axially within the injector
along with a link 24 that is engaged by one end of a rocker lever 26. The other end
of the rocker lever 26 is drivingly connected to the camshaft 28 via a pushtube 30.
The rocker lever 26 typically applies both axial and tangential loads to the plunger
12 during engine operation. Arrow (A) represents the axial load applied to the plunger
12 by the rocker lever 26. Arrow (B) represents the tangential or side load applied
to the plunger 12 by the rocker lever 26. The axial load applied by the rocker lever
26 to the plunger 12 as it reciprocates in the injector body 14 can be elevated to
as high as 10,67 kN (2400 pounds). In addition to these axial and tangential loads,
pressures as high as 1690 bar (24,500 psi) are generated by the plunger's downward
stroke as it travels toward the injector nozzle 16. This results in a load of 1690
bar (24,500 psi) acting on the plunger 12 in an upward axial direction, away from
the nozzle 16 and toward the rocker lever 26, as shown by arrow (C).
[0014] The ceramic plunger 12 is sized relative to the injector body bore 20 to provide
a diametral clearance of 1,93 to 3,25 µm (76-128 millionths of an inch). The diametral
clearance can be less than that of known plunger designs due to differences in thermal
expansion between the currently available stainless steel plunger and the ceramic
plunger 12. The aforementioned loads on the plunger 12 and the clamp load on the injector
body 14 often distort the axial bore, which decreases the diametral clearance. The
rocker lever generated side load (arrow B) then forces the plunger 12 against the
wall of the body bore 20. Plunger scuffing and wear occur under such circumstances.
The presence of the third body debris in the injector body bore compounds the plunger
problems under these loads.
[0015] The severity of the plunger operating environment is further increased by low sulfur
and low lubricity fuels and fuels contaminated by water. A ceramic plunger presents
many advantages. The kinds of ceramic materials evaluated for use as plungers are
much harder than the materials currently used for either the plunger or the injector
body. Moreover, the ceramic material has a low reactivity and a low affinity to weld
with petroleum lubricated metal counterfaces. However, the optimum surface finish
must be created for the best sliding wear performance.
[0016] Plungers made from high thermal expansion ceramics, including zirconia, alumina-zirconia
and alumina have been demonstrated to show significantly better scuffing resistance
than plungers made from metal. Although other ceramics, most notably silicon nitride,
also display superior scuff resistance, only high thermal expansion ceramics have
been found to be suitable for use in forming unit fuel injector plungers. The preferred
ceramic materials for use in forming fuel injector plungers are those with a thermal
expansion coefficient greater than 6 x 10
-6/°C and a hardness greater than 800 kg/mm
2. The thermal expansion coefficient of the ceramic selected for the plunger should
match as closely as possible that of the metal forming the injector body.
[0017] Fig. 2 compares the diameters of the injector body bore 20 (Fig. 1) with the diameters
of a plunger currently in use and two ceramic plungers with differing diametral clearances.
Curve A represents the diameter of the injector body bore over the range of temperatures
studied. Curve B shows the changes in plunger diameter when the plunger 12 is formed
from stainless steel. The diametral clearance between the stainless steel plunger
and the injector bore in the assembly tested was 5,0 µm. Curves C and D demonstrate
diametral changes in plunger diameter for two ceramic plungers at different clearances.
The diametral clearance between the plunger and the bore for the assembly represented
by curve C was 2,5 µm, while the clearance at the curve D plunger assembly was 5,0
µm. Fig. 2 clearly demonstrates that a ceramic plunger in accordance with the present
invention can have a smaller diametral clearance in the injector bore than a stainless
steel plunger and still function effectively in the presence of the loads applied
to the plunger during engine operation.
1. A fuel pressurizing plunger assembly for a compression ignition engine (Diesel engine)
fuel injector (10) operable with Diesel fuel that may contain abrading particles and
lubricity lowering contaminants,
wherein the plunger assembly includes
an axial bore (20) located within a body portion (14) of the fuel injector (10), the
axial bore (20) defined by an inner surface of the body portion (14) having a predetermined
bore diameter, said body portion (14) being formed of a metal having a predetermined
thermal expansion coefficient,
a plunger (12) mounted for reciprocating axial movement within said axial bore (20),
this plunger (12) being formed of a scuff resistant, wear-resistant ceramic material,
and
a drive train means for applying a periodic pressurization force to the plunger (12)
for causing a controlled volume of fuel to be injected from the fuel injector (10)
into an engine cylinder at desired intervals during engine operation, this pressurization
force including a substantial side loading force which tends to bias the external
surface of the plunger (12) into contact with the surrounding inner surface of the
axial bore (20),
wherein the plunger (12) has a predetermined plunger diameter slightly less than the
predetermined bore diameter to form a diametral clearance between the axial bore (20)
and the plunger (12),
characterized in that
the diametral clearance between the plunger (12) and the axial bore (20) is 1,93 to
3,25 µm (76 to 128 millionths of an inch),
the ceramic material of the plunger (12) has a low reactivity and a low affinity to
weld with the fuel lubricated inner surface of the axial bore (20) and a thermal expansion
coefficient which is substantially the same as the thermal expansion coefficient of
the metal forming the body portion (14),
the wear-resistant ceramic material of the plunger (12) has a thermal expansion coefficient
greater than 6 · 10-6/°C and a hardness greater that 800 kg/mm2.
2. Plunger assembly according to claim 1, characterized in that the ceramic material
of the plunger (12) is selected from the group consisting of zirconia, alumina-zirconia
and alumina ceramics.
3. Plunger assembly according to claim 1 or 2, characterized in that the plunger (12)
is operably positioned axially within the fuel injector body portion (14) between
a link (24) connected to the drive train and a nozzle end of the unit fuel injector
(10).
4. Plunger assembly according to claim 3, characterized in that the drive train includes
a rocker lever (26), a push tube (30) operatively extending from a camshaft (28) to
one side of the rocker lever (26), the link (24) operatively extending from the other
side of the rocker lever (26) to the plunger (12) to cause the plunger (12) to reciprocate
as the camshaft (28) rotates, whereby a high axial force is imposed on the plunger
(12) by the link (24) as the plunger (12) is advanced toward the injector nozzle and
a side force is simultaneously imposed on the plunger (12) by the link (24) which
biases the plunger (12) toward the inner wall of the axial bore (20).
5. Plunger assembly according to any one of the preceding claims, characterized in that
the plunger (12) is a timing plunger.
1. Kraftstoff unter Druck setzender Plungerkolbenaufbau für einen Kraftstoffinjektor
(10) eines druckgezündeten Motors (Dieselmotors), wobei der Kraftstoffinjektor mit
Dieselkraftstoff betreibbar ist, der abscheuernde Partikel und die Schmierfähigkeit
senkende Verschmutzungen enthalten kann,
wobei der Plungerkolbenaufbau aufweist
eine axiale Bohrung (20), die innerhalb eines Körperabschnitts (14) des Kraftstoffinjektors
(10) angeordnet ist, wobei die axiale Bohrung (20) eine innere Oberfläche des Körperabschnitts
(14) mit einem vorbestimmten Bohrungsdurchmesser definiert, wobei der Körperabschnitt
(14) aus einem Metall mit einem vorbestimmten Wärmeausdehnungskoeffizienten gebildet
ist,
einen Plungerkolben (12), der zur hin- und hergehenden Bewegung innerhalb der axialen
Bohrung (20) eingebaut ist, wobei dieser Plungerkolben (12) aus einem abriebfesten,
verschleißresistenten Keramikmaterial gebildet ist, und
ein Antriebszugmittel zur Ausübung einer periodischen, den Druck erzeugenden Kraft
auf den Plungerkolben (12), wodurch ein gesteuertes Volumen an Kraftstoff aus dem
Kraftstoffinjektor (10) in einen Motorzylinder an bzw. in gewünschten Intervallen
während des Motorbetriebs eingespritzt wird, wobei diese druckerzeugende Kraft eine
wesentliche Seitenbelastungskraft umfaßt, die dazu neigt, die äußere Oberfläche des
Plungerkolbens (12) in Kontakt bzw. Anlage mit der umgebenden inneren Oberfläche der
axialen Bohrung (20) zu drücken,
wobei der Plungerkolben (12) einen vorbestimmten Plungerkolbendurchmesser aufweist,
der etwas geringer als der vorbestimmte Bohrungsdurchmesser ist, um ein Durchmesserspiel
zwischen der axialen Bohrung (20) und dem Plungerkolben (12) zu bilden,
dadurch gekennzeichnet, daß
das Durchmesserspiel zwischen dem Plungerkolben (12) und der axialen Bohrung (20)
1,93 bis 3,25 µm (76-128 Millionstel eines Inch) beträgt,
das Keramikmaterial des Plungerkolbens (12) eine niedrige Reaktivität bzw. Reaktionsbereitschaft
und eine geringe Affinität, mit der Kraftstoff geschmierten inneren Oberfläche der
axialen Bohrung (20) zu verschweißen, und einen Wärmeausdehnungskoeffizienten, der
im wesentlichen dem Wärmeausdehnungskoeffizienten des den Körperabschnitt (14) bildenden
Metalls entspricht, aufweist,
das verschleißresistente Keramikmaterial des Plungerkolbens (12) besitzt einen Wärmeausdehnungskoeffizienten,
der größer als 6 · 10-6/°C ist, und eine Härte größer als 800 kg/mm2 aufweist.
2. Plungerkolbenaufbau nach Anspruch 1, dadurch gekennzeichnet, daß das keramische Material
des Plungerkolbens (12) aus der Gruppe, bestehend aus Zirkon(di)oxid-, Aluminiumoxid-Zirkon(di)oxid-
und Aluminiumoxid-Keramiken, ausgewählt ist.
3. Plungerkolbenaufbau nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß der Plungerkolben
(12) axial betreibbar in dem Kraftstoffinjektorkörperabschnitt (14) zwischen einer
Verbindung (24), die mit dem Antriebszug verbunden ist, und einem Düsenende der Kraftstoffinjektoreinheit
(10) angeordnet ist.
4. Plungerkolbenaufbau nach Anspruch 3, dadurch gekennzeichnet, daß der Antriebszug einen
Kipphebel (26), eine Stoß- bzw. Stößelstange (30) aufweist, die sich betätigungsmäßig
von einer Nockenwelle (28) zu einer Seite des Kipphebels (26) erstreckt, und die Verbindung
(24) aufweist, die sich betätigungsmäßig von dem anderen Ende des Kipphebels (26)
zu dem Plungerkolben (12) erstreckt, um den Plungerkolben (12) hin und her zu bewegen,
wenn die Nockenwelle (28) rotiert, wobei eine hohe axiale Kraft auf den Plungerkolben
(12) durch die Verbindung (24) ausgeübt wird, wenn der Plungerkolben (12) zur Einspritzdüse
vorgeschoben wird, und gleichzeitig eine Seitenkraft auf den Plungerkolben (12) durch
die Verbindung (24) ausgeübt wird, welche den Plungerkolben (12) zu der inneren Wand
der axialen Bohrung (20) drückt.
5. Plungerkolbenaufbau nach einem der voranstehenden Ansprüche, dadurch gekennzeichnet,
daß der Plungerkolben (12) ein Zeitsteuerplungerkolben ist.
1. Arrangement de piston de mise sous pression de combustible pour un injecteur de combustible
(10) de moteur à allumage par compression (moteur Diesel) pouvant fonctionner avec
un combustible Diesel qui peut contenir des particules abrasives et des contaminants
réducteurs du niveau de lubrification,
dans lequel l'arrangement de piston inclut un alésage axial (20) situé dans une partie
de corps (14) de l'injecteur de combustible (10), l'alésage axial (20) défini par
une surface interne de la partie de corps (14) présentant un diamètre d'alésage prédéterminé,
ladite partie de corps (14) étant formée d'un métal présentant un coefficient de dilatation
thermique prédéterminé;
un piston (12) monté pour un mouvement axial de va-et-vient à l'intérieur dudit alésage
axial (20), ce piston (12) étant formé d'un matériau céramique résistant aux éraflures
et résistant à l'usure, et un moyen de transmission pour appliquer une force de mise
sous pression périodique sur le piston (12) pour amener un volume contrôlé de combustible
de l'injecteur de combustible (10) dans un cylindre de moteur à des intervalles souhaités
pendant le fonctionnement du moteur, cette force de mise sous pression incluant une
force de charge latérale significative qui a tendance à incliner la surface externe
du piston (12) en contact avec la surface interne environnante de l'alésage axial
(20),
dans lequel le piston (12) présente un diamètre de piston prédéterminé légèrement
inférieur au diamètre d'alésage prédéterminé pour former un espacement diamétral entre
l'alésage axial (20) et le piston (12),
caractérisé en ce que
l'espacement diamétral entre le piston (12) et l'alésage axial (20) est compris entre
1,93 et 3,25 µm (76 à 128 millionièmes de pouce),
le matériau céramique du piston (12) présente une faible réactivité et une faible
affinité au soudage avec la surface interne lubrifiée par combustible de l'alésage
axial (20) et un coefficient de dilatation thermique qui est pratiquement identique
au coefficient de dilatation thermique du métal formant la partie de corps (14),le
matériau céramique résistant à l'usure du piston (12) présente un coefficient de dilatation
thermique supérieur à 6.10-6/°C et une dureté supérieure à 800 kg/mm2.
2. Arrangement de piston suivant la revendication 1, caractérisé en ce que le matériau
céramique du piston (12) est sélectionné parmi le groupe constitué des céramiques
de zircone, d'alumine-zircone et d'alumine.
3. Arrangement de piston suivant la revendication 1 ou 2, caractérisé en ce que le piston
(12) est, en fonctionnement, positionné de manière axiale à l'intérieur de la partie
de corps d'injecteur de combustible (14) entre une bielle (24) reliée à la transmission
et une extrémité de gicleur de l'injecteur de combustible d'unité (10).
4. Arrangement de piston suivant la revendication 3, caractérisé en ce que la transmission
inclut un levier de culbuteur (26), un tube pousseur (30) s'étendant, en fonctionnement,
d'un arbre à came (28) à un côté du levier culbuteur (26), la bielle (24) s'étendant,
en fonctionnement, de l'autre côté du levier culbuteur (26) au piston (12) pour amener
le piston (12) à aller et venir tandis que l'arbre à cames (28) tourne, par lequel
une force axiale élevée est exercée sur le piston (12) par la bielle (24) tandis que
le piston (12) est avancé en direction du gicleur d'injecteur et une force latérale
est simultanément exercée sur le piston (12) par la bielle (24) qui incline le piston
(12) en direction de la paroi interne de l'alésage axial (20).
5. Arrangement de piston suivant l'une quelconque des revendications précédentes, caractérisé
en ce que le piston (12) est un piston de distribution.