[0001] The present invention relates to a mechanical pump for the injection of fuel intended
for being applied in particular to internal combustion engines with controlled ignition.
[0002] The advantages are known of the use of the direct injection of fuel into the combustion
chamber of the engines with controlled ignition.
[0003] Such advantages can be generally summarized as a lower tendency to the knocking by
the motor, with the consequent possibility of the adoption of higher compression ratios
with higher operating efficiencies, and as a quicker accomodation of the motor to
a fast load change required by the environment.
[0004] In case of use of the direct injection in a controlled-ignition, two stroke cycle
engine, to the aforementioned advantages, also the fact is added that by directly
injecting the fuel into the combustion chamber with a suitable phasing, the loss of
fuel mixture from the exhaust port during the scavenge stroke is avoided, with consequent
beneficial effects on the consumption of fuel and on the emissions of unburnt hydrocarbons.
[0005] It is known in the specific art that in order to be able to carry out a correct fuel
injection, i.e. atomized enough to guarantee a sufficient mixing during the short
contact time with air, a high injection pressure (about 40 bar) is necessary. To the
purpose of ensuring such an injection pressure, the use of a pump of mechanical type
is necessary. Such a pump, analogous as for the particular components and operation
to the pumps adopted in the diesel cycle engines, consists in a pumping element or
plunger sliding with a notable precision inside a cylinder, with a reciprocating motion
controlled by the outside by means of a cam-follower system, or by an eccentric, in
a desmodromic way, driven by the same engine.
[0006] The governing of the fuel delivery takes place generally by diverting to the outside
the exceeding delivery by putting in communication, through a groove provided on the
outer surface of the plunger, the delivery chamber of the pump with the fuel tank
through a reflux port, according to a commonly used technique.
[0007] However, to the contrary of what happens in the diesel cycle engines wherein, with
operating in an excess of air, the power is function of the amount of injected fuel
only (governing by quality), in the controlled-ignition engines the power is a function
of the weight of fresh mix ture (governing by quantity), in which however the air/
fuel ratio must be kept substantially constant.
[0008] In all practical applications, the governing of the delivery of the pump is obtained
by means of the rotation of the plunger around its axis; the plunger has indeed on
its outer surface a helical groove, which allows the reflux of fuel and hence carries
out the governing thereof by fractions of its total stroke, univocally depending on
the angular position of the plunger inside the cylinder in side which it runs.
[0009] The theoretical delivery per plunger stroke would be constant, if blow-by losses
inversely proportional to the square of the pumping rate and directly proportional
to the delivery pressure, growing with the increasing of the pumping rate, did not
exist. Such losses render the actual performance of the pump very variable as a function
of its rotation rate (number of revolutions of the pump per time unit). Substantially,
in a determined angular position of the plunger, the delivery per plunger stroke increases
with increasing rotation rates according to a curve with decreasing derivative.
[0010] This pump delivery variation law does not fit to the requirement of fuel per engine
revolution with the varying of the rotation rate of this latter (number of engine
revolutions per time unit), intrinsic of the control led ignition engines.
[0011] In fact, the necessary amount of fuel per engine revolution increases with the increasing
of the engine rotation rate in accordance with an equal increase of the intaken air
up to the point of optimum proportioning of the engine, i.e., to the point of maximum
actual average pressure corresponding to the maximum driving torque; from this point
on, the necessary amount of fuel per engine re volution decreases in accordance with
an equal reduction of the intaken air.
[0012] The injection pump as described, on the contrary, would feed the motor with an increasing
amount of fuel per engine revolution also beyond the point of maximum actual average
pressure, so as to enrich too much the mix ture and to cause a malfunctioning of the
engine.
[0013] Apart governor devices have been proposed, which pro vide for the reduction of the
amount of fuel per engine revolution at the proper time, i.e., after the point of
maximum actual average pressure.
[0014] One type of such governor devices envisages a tridimensional cam, axially moved by
a centrifuge device driven by the engine, and angularly moved by the element govern
ing the air intake by the engine, which actuates an element governing the angular
position of the plunger of the pump and hence governing the amount of fuel injected
into the engine.
[0015] Such a governor device guarantees a perfect pump - expensive engine coupling, but
is extremely sophisticated,/ bulky and hence, among others, not much suitable to the
use on small engines, such as e.g. those with the two-stroke cycle, intended for light
motorvehicles and motorscooters.
[0016] A second type of these governor devices, of pneumatic type, envisages the use of
a membrane controlled by the suction pressure at the engine intake, which actuates
the said pump plunger angular position governing device.
[0017] Such governor device is certainly simpler than the preceding one, but is less precise
and is acceptable only for uses in semistationary engines, in that establishing a
perfect correspondence between the suction pressure and the amount of intaken air
is quite problematical.
[0018] Purpose of the present invention is hence to propose a mechanical injection pump
for controlled-ignition engines, allowing an optimum coupling with the engine in terms
of fuel feeding, avoiding the use of supplementary governor devices, and which is
at the same time structural ly simple.
[0019] Such purpose is achieved by means of a mechanical pump for the direct injection of
fuel into the combustion chamber of an internal combustion engine, comprising a plunger,
axially sliding inside a cylinder and rotating around its own axis, which delivers
the fuel coming from a tank into a delivery chamber provided within the same cylinder
towards a duct connected with the combustion chamber of the engine up to a position
in the stroke of the plunger at which the fuel flows back, through ducts provided
in the plunger, towards the tank, characterized in that said ducts comprise at least
two helical grooves provided along the outer wall of the plunger, in communication
with longitudinal grooves always provided along the outer wall of the plunger, and
in communication moreover with at least a longitudinal duct provided in the plunger,
said longitudinal grooves and said longitudinal duct putting the helical grooves in
communication with the delivery chamber, in determined positions along the cylinder
axis said helical grooves provided in the plunger being, with one of their portions,
in correspondence of ports provided in the cylinder connected with the tank, for the
flowing back of the fuel into the tank.
[0020] To the purpose of understanding the characteristics and the advantages of the present
invention hereinunder an exemplifying embodiment thereof is disclosed, as illustrated
in the attached drawing table wherein:
Fig. 1 shows a longitudinal section of a mechanical injection pump according to the
invention;
Fig. 2 shows a detail of the pump of fig. 1;
Figs. 3, 4 and 5 show in a detailed way, the pump of fig. 1 in three different operating
positions;
Figs. 6, 7 show in a detailed way, in cross section according to the path A-A, the
pump of fig. 1 in two dif ferent operating positions.
[0021] The pump shown in fig. 1, generally indicated with 10, comprises a pump body 11 wherein
a cylinder 12 and a valve body 13 are housed in a longitudinal connection relation
ship.
[0022] Inside the cylinder 12 a plunger 14 is sliding.
[0023] Within the valve body 13 a shutter 15 aligned with the plunger 14 is housed.
[0024] Between the plunger 14 and the shutter 15 a delivery chamber 16 is defined, which
communicates through two transversal passageways 18 provided in the cylinder 12, with
an annular chamber 19. The annular chamber 19 communicates on one side, through a
passageway 20, with a supply of pressurized fuel and on the other side, through a
passageway 21, with a tank containing the same fuel.
[0025] On the outer wall of the plunger 14 two opposite to each other helical grooves 22
are provided, as well as two longitudinal grooves 23, they too being opposite to each
other, each one of which intersecates at an end a respective helical groove 22 and
ends at the other end in correspondence of the delivery chamber 16.
[0026] Inside the plunger 14 an axial duct 24 (well visible in fig. 2) is moreover provided,
closed at an end, and terminating at its other end in correspondence of the delivery
chamber 16. The axial duct 24 communicates with the two grooves 22 by means of two
transversal bores 25 always provided in the plunger 14.
[0027] Within the shutter 15 an axial duct 26 is also provided, closed at an end, and terminating
at its other end in correspondence of the delivery chamber 16. Within the shutter
15 two transversal through bores 27 are moreover provided, which put the axial duct
26 in communication with the outer of the shutter. The shutter is elastically pressed
in closure position against a seat of the valve body 13 by a spring 28.
[0028] Within the pump 10 moreover ducts 29 for the inflow of pressured oil into the seat
of the cylinder 12 within which the plunger 14 slides; a duct 30 for the recovery
of the fuel leaking out between the said seat of the cylinder 12 and the same cylinder;
and a stud 31 preventing the cylinder 12 from rotating inside the pump body 11 are
provided.
[0029] The operating way of the disclosed pump 10, as applied to a controlled-ignition engine,
not shown, is as follows.
[0030] In the position of fig. 1, the plunger 14 is in its position of lower dead point,
and the fuel inflows through the passage 20, the annular chamber 19 and the passageways
18 into the delivery chamber 16. At the beginning of its stroke upwards, the plunger
14 causes the fuel to flow back into the annular chamber 19. As soon as the upper
edge of the plunger 14 covers completely the ports of the passageways lb, as shown
in fig. 3, the delivery geometrically starts (provided that, as in fig. 6, the longitudinal
grooves 23 are not in correspondence of the ports of the passageways 18), i.e., the
fuel pressurized inside the delivery chamber 16 causes the lifting and hence the opening
of the shutter 15, counteracted by the spring 28; the bores 27 put the duct 26 in
communication with an inner duct 32 of a delivery joint 33 connected with the engine's
combustion chamber and hence the fuel outflows from the delivery chamber 16, through
the duct 26, the bores 27 and the duct 32 into the said combustion chamber. In fig.
4 an intermediate position of the useful stroke of the piston is shown.
[0031] When the upper edge of the two helical grooves 22 reach the lower edges of the ports
of the passageways 18, as shown in fig. 5, the delivery geometrically ends, in that
the fuel pressurized inside the delivery chamber 16 flows back into the helical grooves
22, through the longitudinal grooves 23 and also through the axial duct 24 and the
bores 25, and hence flows back, through the passage ways 18, into the annular chamber
19. The plunger 14, sub sequently, by having ended its stroke upwards, returns downwards,
and at its lower dead point a new cycle begins.
[0032] The governing of the delivery of the pump 10 is obtained by rotating the plunger
14 relatively to the cylinder 12. In fact, by varying the positioning of the upper
edge of the helical grooves 22 relatively to the ports of the passageways 18, the
useful stroke of the plunger 14 varies, as known, and hence the delivery.
[0033] In the angular position of the plunger 14 in which the longitudinal grooves 23 are
in correspondence of the ports of the passageways 18, as shown in fig. 7, a zero delivery
is obtained, in that the fuel present inside the delivery chamber 16 outflows throughout
the upwards stroke of the plunger 14 exactly through the longitudinal grooves 23 and
the passageways 18 into the annular chamber 19.
[0034] In fig. 1 some arrows are shown, which indicate both the reciprocating and the rotary
motion of the plunger 14, as well as the inlet of the fuel to and the outlet of it
from the pump body 11, and the inlet of the oil as herein above mentioned.
[0035] 1he twin helical grooves 22 with their respective longitudinal grooves 23, the axial
duct 24 and the bores 25 increase the reflux section area of the pump, so as to reduce
the influence of the fuel leakage losses on the delivery law to a considerable extent;
in practice, the curve of the delivery per plunger stroke as a function of the rotation
rate of the pump, mentioned in the intro-
duction, which has a growing outline with negative derivative in the known pumps, changes
in the pump 10 in such a way that the curve is growing up to a certain point and then
decreases, as it has been confirmed by experimental results. It is hence clear that
it is possible to fit the variation law of the delivery of the pump 10 per stroke
of the plunger 14, with the varying of the rotation rate of the pump, to the variation
law of the amount of fuel per revolution of the controlled-ignition engine,with the
varying of the rotation rate of the engine, which as it has been outlinec in the introduction,
envisages a growing curve up to the point of maximum actual average pressure, and
decreasing after this point.
[0036] The increase of the reflux section area of the pump 10 leads also to advantages in
the situation of zero de- livery of the pump as mentioned above.
[0037] This favours indeed the reflux of all the fuel present inside the delivery chamber
to a notable extent and the resistance to the reflux is thus notably reduced, in particular
at the high rotation rates of the pump. In the known pumps, on the contrary, at the
high pump rotation rates, this resistance to the reflux is so'high that a fuel delivery
is anyway obtained, even if of minimum value, with consequent increase in consumptions
and environmental polluting substances.
[0038] The pump 10 is found to be particularly advantageous for applications to two-stroke
engines which operate up to high rotation rates. It can be applied however to any
internal combustion engines, whether of the controlled-ignition type or not, and hence
also to a diesel engine, in those cases in which the increase of the reflux section
area leads to technical advantages.
[0039] We underline that this is obtained with a very simple pump configuration, obtainable
by means of elementary mechanical machining processes, and hence constructively cheap.
[0040] Of course, no supplementary devices are thus necessary to the purpose of correctly
coupling the pump and the motor, in terms of feeding.
[0041] By operating on the geometry of the two grooves 22, whose upper edges may be made
become operative at different heights, the delivery law of the pump 10 may be so adapted,
as to fit to the intrinsic requirement of fuel by any engine types.
[0042] Different shapings of the pump as disclosed may be of course obtained.
[0043] More than two helical grooves with their respective longitudinal grooves, connection
passageways to the reflux chamber (in the disclosed and illustrated example, the annular
chamber 19), and connection bores to the axial duct of the plunger may be e.g. provided.
[0044] Instead of one single axial duct, more longitudinal ducts always provided inside
the plunger may be provided, serving to the same function as of the axial duct, and,
e. g., each one of them may be in communication with a respective helical groove.
1. Mechanical pump for the direct injection of fuel into the combustion chamber of
an internal combustion engine, comprising a plunger axially sliding inside a cylinder
and rotating around its own axis, delivering the fuel incoming from a tank into a
delivery chamber provided within the said cylinder, towards a duct connect ed with
the combustion chamber of the engine up to a po- sition of the plunger's stroke in which the fuel flows back towards the tank through
ducts provided in the plung er, characterized in that said duets comprise at least
two helical grooves provided along the outer wall of the plunger, communicating with
longitudinal grooves always provided along the outer wall of the plunger and communicating
moreover with at least one longitudinal duct pro vided inside the plunger, said longitudinal
grooves and said longitudinal duct putting the helical grooves in communication with
the delivery chamber, in determined positions along the cylinder axis said helical
grooves provided in the plunger being, with one of their portions, in correspondence
of ports provided in the cylinder connected with the tank, for the flowing back of
the fuel into the tank.
2. Pump according to claim 1, wherein said longitudinal grooves provided in the plunger
are so positioned, as to be, in determined angular positions of the plunger, in correspondence
of said ports provided in the cylinder for the overall flow back of all the flowed-in
fuel into the delivery chamber.
3. Pump according to claim 1 or 2, wherein an outer longitudinal groove per each helical
groove is provided, said grooves crossing each other.
4. Pump according to claim 1 or 2, wherein one single longitudinal duct centrally
provided along the axis of the cylinder is envisaged.
5. Pump according to claim 4, wherein said axial duct provided in the plunger communicates
with the helical grooves through bores provided inside the plunger, and terminates
at the end of the plunger in correspondence of the delivery chamber.
6. Pump according to claim 3, wherein per each helical and longitudinal groove one
of said cylinder ports is provided.
7. Pump according to claim 3, wherein two pairs of helical and longitudinal grooves
positioned in opposite positions to each other are provided.