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Patent Abstract
In a gas-supply system for internal-combustion engines, a pressure-reducing
valve is set between the reservoir of the gas and a distribution
manifold or rail that feeds the gas to a series of electromagnetically
controlled injectors associated to the various cylinders of the
engine. The reduced pressure supplied by the pressure-reducing valve
is further reduced via a pressure-regulating solenoid valve, to
an extent that depends upon the supply current of its solenoid.
The electrical supply to the solenoid of said solenoid valve is
controlled by an electronic control unit according to the signal
issued by a sensor of the pressure in the rail and according to
stored maps, which supply the optimal pressure value for each operating
condition of the engine.
Patent Claims
What is claimed is:
1. A system for supplying gas for an internal-combustion engine,
comprising: a plurality of electromagnetically controlled injectors,
associated to the various cylinders of the engine; a distribution
manifold or rail communicating with said injectors; a reservoir
for supply of the rail, where pressurized gas is accumulated; a
pressure-reducing valve set in connection between the reservoir
and the aforesaid rail; said system being characterized in that,
downstream of said pressure-reducing valve, in connection between
this and the aforesaid rail, is set a pressure-regulating solenoid
valve, for bringing the pressure for supply of the gas to the rail
from the reduced value supplied by the aforesaid pressure-reducing
valve to a further reduced value, which depends upon the supply
current of a solenoid of said solenoid valve.
2. The supply system according to claim 1, wherein the supply to
the solenoid of the regulation solenoid valve is controlled by an
electronic control unit according to a comparison of the signal
issued by a pressure sensor indicating the pressure existing in
the distribution manifold or rail, with a signal indicating a desired
pressure within the rail.
3. The supply system according to claim 2, wherein the aforesaid
signal indicating the desired pressure is derived according to the
detection of one or more operating parameters of the engine, such
as for example accelerator position, rate of turning of the engine,
and environmental temperature, as well as according to a series
of stored maps indicating the pressure value desirable as different
operating parameters of the engine vary.
Patent Description
BACKGROUND OF THE OF THE INVENTION
[0001] 1. Field of the invention
[0002] The present invention relates to systems for supplying gas,
in particular compressed natural gas, such as for example methane,
for internal-combustion engines, of the type comprising:
[0003] a plurality of electromagnetically controlled injectors,
associated to the various cylinders;
[0004] a distribution manifold or rail communicating is with said
injectors;
[0005] a reservoir for supply of the rail, where pressurized gas
is accumulated; and
[0006] a pressure-reducing valve set in connection between the-reservoir
and the aforesaid rail.
[0007] 2. Prior Art
[0008] A supply system of the known type referred to above is illustrated
in FIG. 1 of the annexed plate of drawings. In said figure, the
reference number 1 designates the electromagnetically controlled
injectors associated to the various cylinders of the engine, which
are supplied with pressurized gas by a distribution manifold or
rail 2. The reference number 3 designates a gas cylinder, which
functions as a reservoir, in which pressurized gas, for example
methane, is accumulated. The outlet of the gas cylinder 3 is connected
via a pipe 4 to the rail 2. Set in series in the pipe 4 are: a safety
valve 5, constituted by a solenoid shutoff valve designed to block
the outlet of the gas cylinder 3; a pressure sensor 6; and a pressure-reducing
valve 7. The reference number 8 designates a sensor of the pressure
in the rail or distribution manifold 2.
[0009] In the case, for example, of a methane supply system, the
initial pressure of the methane inside the gas cylinder 3, when
the latter is full, is in the region of 200 bar. Said pressure of
course drops as the gas cylinder 3 empties, until a minimum value
in the region of 20 bar is reached.
[0010] At the same time, the electromagnetically controlled injectors
1 are able to operate at sensibly lower gas pressures, normally
lower than 10 bar. The purpose of the valve 7 is precisely to bring
the pressure of the gas to a suitable value for proper operation
of the injectors 1. In the practical case, currently used pressure-reducing
valves bring the pressure of the gas in the pipe 9 downstream of
the pressure-reducing valve 6, which takes the gas to the rail 2,
to a pressure value which oscillates (as the pressure of the gas
coming from the pipe 4 varies) between approximately 6.3 bar and
8.5 bar.
[0011] The present invention relates, in particular, to systems
for supplying gas of the type illustrated above, in which the pressure-reducing
valve comprises:
[0012] a valve body, with an inlet connector connected to the reservoir
and an outlet connector connected to the rail;
[0013] a restricted passage defined inside the valve body for communication
between the aforesaid inlet connector and the aforesaid outlet connector;
[0014] an open/close element for control of the communication through
said restricted passage;
[0015] means for return of the open/close element tending to keep
the open/close element in an open condition; and
[0016] a piston member, movable inside the valve body, for controlling
said open/close element, said piston member being subject to the
pressure of the gas downstream of the aforesaid restricted passage.
[0017] FIG. 2 of the annexed plate of drawings illustrates a pressure-reducing
valve of a known type used in supply systems of the type referred
to above. The example illustrated relates to the case of a valve
that provides two successive stages of pressure reduction set in
cascaded fashion. The body of the valve is designated by the reference
number 10. The number 11 designates the inlet connector, designed
to be connected to the pipe (FIG. 1) through which the gas coming
from the reservoir under pressure 3 flows, whilst the reference
number 12 designates the outlet opening, in which there is designed
to be mounted the connector for connection to the pipe 9 that takes
the gas at reduced pressure to the rail 2 (FIG. 1). The connector
11 defines an inlet passage 13 that communicates with the outlet
12 through a series of passages made inside the body 10, as will
be defined further in what follows. Set in said series of passages
is a restricted passage 14 associated to the first stage of the
valve. The gas that enters the valve through the inlet passage 13
arrives at the restricted passage 14 passing through a filter 15
and an electromagnetically controlled safety shutoff valve. The
solenoid valve 16 comprises a solenoid 17 that is able to recall
an anchor 18 into a retracted position, in which an open/close shutoff
element 19 is disengaged from a respective valve seat, leaving a
passage 20 that converges into the restricted passage 14 free. The
restricted passage 14 gives out onto a spherical surface, functioning
as valve seat, which co-operates at the front with an open/close
element 21 constituted by a seal element mounted at a free end of
a stem 22 of a piston member 23. The latter has a bottom head (as
viewed in FIG. 2) of widened diameter, which is slidably mounted,
with the interposition of a seal gasket 24, within a cylindrical
liner 25 fixed to the body of the valve. A helical spring 26 is
set between the bottom head of the piston member 23 and a fixed
cup 27. The spring 26 tends to keep the piston member 23 in its
end-of-travel position downwards (illustrated in the drawing), in
which the bottom head of the piston element 23 is in contact with
a bottom element 28 for closing the cylinder liner 25 and in which
the open/close element 21 is set at a distance from the outlet of
the restricted passage 14, so that in said condition the gas that
arrives at the restricted passage 14 from the inlet passage 13 can
pass into a chamber 29 that is set downstream of the restricted
passage 14, after undergoing a consequent pressure drop. From the
chamber 29, the gas flows via an intermediate passage 30 to a second
stage of the valve, which is identical to what has been described
above from a functional standpoint, via which the gas finally reaches
the outlet opening 12. In what follows, said second stage of the
valve will not be further illustrated, since it corresponds, as
has been said, to the first stage. To return now to the structure
and to the operation of the first stage of the pressure-reducing
valve, the gas that arrives in the chamber 29, in addition to flowing
towards the outlet through the passage 30, also reaches a chamber
31 facing the opposite end of the piston member 23 via an axial
passage 32 made through the piston member 22 and through radial
holes provided in the wall of the stem of the piston member. The
chamber 33, in which the spring 26 is set, is in communication with
the external atmosphere through holes 25a provided in the wall of
the cylinder liner 25. Consequently, the seal gasket 24 performs
the function of preventing the gas present in the chamber 31 from
being able to leak into the chamber 33 and from there come out into
the external atmosphere. A similar function is performed by a seal
gasket 34 provided in a position corresponding to a central hole
of the fixed cup 27 functioning as guide for the sliding movement
of the stem 22 of the piston member 23. Also said gasket in fact
prevents the gas present in the chamber 14 from possibly passing
into the chamber 33 and from there into the external atmosphere.
The seal gaskets 24 and 34 are designed obviously taking into account
the fact that they are set between surfaces in relative movement,
i.e., they are gaskets of a dynamic type. Static gaskets 35, 36,
constituted by seal rings made of elastomeric material, are instead
set between the closing element 28 and the bottom end of the cylinder
liner 25 and between the fixed cup 27 and the body of the valve.
[0018] In operation, the gas coming from the inlet passage 13 passes
initially straight into the chamber 29 through the restricted passage
14, undergoing a pressure reduction through the solenoid valve 16
in its initial opening phase, and is thus sent at reduced pressure
to the passage 30, from which it passes to a second pressure-reducing
stage, or directly to the outlet of the valve (in the case of the
valve being a single-stage one). As the pressure in the chamber
29 increases, however, said pressure is also communicated to the
chamber 31 located at the opposite end of the piston member 23.
On account of the greater effective area at the surface of the head
of the piston member 23 facing the chamber 31, when the pressure
in the chamber 31 reaches the calibration pressure value, i.e.,
the reduction pressure of the first stage, the pressure of the chamber
31 tends to bring about raising (as viewed in the drawing) of the
piston member 23 against the action of the spring 26 until it brings
about closing of the open/close element 21 against its seat. The
open/close element thus remains closed until the pressure in the
chamber 29, and consequently in the chamber 31, drops back to a
value such that the spring causes opening of the open/close element.
There is thus brought about a continuous oscillation of the open/close
element between the open condition and the closed condition, which
keeps the pressure in the pipe 30 downstream of the first reduction
stage within a required range of values. As has already been said,
the operation described above is repeated a second time at the second
stage of the valve, in the case where the valve is a dual-stage
one, as in the example illustrated in the figure, whilst the gas
that arrives at the pipe 30 is sent directly to the rail in the
case of a single-stage valve.
[0019] Drawbacks of the Prior Art
[0020] In the known valves of the type described above, it is necessary
for the dynamics of variation of the regulated pressure not to exceed
.+-.10%, in order to guarantee proper operation of the injection
system. With reference to FIG. 1 of the annexed plate of drawings,
the pressure sensor 8 sensitive to the pressure in the rail 2 sends
its signal to an electronic control unit C, which receives also
the output signal from the pressure sensor 6 set immediately downstream
of the reservoir 3, and controls the injectors 1 and in particular
their opening time according to the supply pressure.
[0021] In order to limit the sensitivity of the regulated pressure
to the pressure of the reservoir and to the flow rate, it is consequently
necessary to adopt, in the valve 10 illustrated in FIG. 2, a spring
26 of high load, which accordingly has a large size. This entails
the adoption of the geometry illustrated in FIG. 2, with the consequent
need to provide two seal gaskets 24, 34 of a dynamic type. It should
also be noted that the structure of the cylinder liner 25, within
which the piston member 23 is slidably mounted, is at times subject
to deformations following upon tightening of the screws 37, which
fix the closing element 28 and the cylinder liner 25 to the body
of the valve. Possible deformations of the structure increase the
risk of leakage of gas towards the outside. Of course, in the case
of a dual-stage valve, the aforesaid drawbacks are twice as many.
[0022] Basically then, the valve of a known type proves cumbersome,
not altogether reliable with respect to the risk of leakage of gas
into the external atmosphere, and finally also has a relatively
complicated and costly structure. In addition to this, the valve
described above does not enable an optimal response during the transient
regimes. There is finally the risk of a deterioration of the load
of the spring over time, with consequent variation of the regulated
pressure.
PURPOSE OF THE INVENTION
[0023] The purpose underlying the present invention is to provide
a supply system of the known type described above which will enable
the drawbacks referred to above to be overcome, which, more in general,
will have a relatively simple and low-cost structure, which, notwithstanding
this, will guarantee an operation that is efficient and reliable,
and which will moreover be safer as regards the risk of leakage
of gas into the external atmosphere.
[0024] In particular, a purpose of the invention is to provide
a system of the type specified above which will be able to implement
efficient regulation of the pressure in the distribution rail in
order to adapt said pressure as required to the operating conditions
of the engine.
THE INVENTION
[0025] With a view to achieving the above and further purposes,
the subject of the invention is a gas-supply system for an internal-combustion
engine having all the characteristics that are specified in claim
1. Further preferred characteristics of the system according to
the invention form the subject of the dependent claims.
BRIEF DESCRIPTION OF THE FIGURES
[0026] Further characteristics and advantages of the invention
will emerge from the ensuing description with reference to the annexed
plate of drawings, which are provided purely by way of non-limiting
example, and in which:
[0027] FIG. 1 is a diagram, already described, of a supply system
according to the known art;
[0028] FIG. 2 is a partially sectioned view, already described,
of a pressure-reducing valve according to the known art;
[0029] FIG. 3 is a cross-sectional view of an example of embodiment
of a pressure-reducing valve that does not form part of the present
invention and that forms the subject of a co-pending patent application
filed in the name of the present applicant;
[0030] FIG. 4 illustrates a variant of FIG. 3, and does not form
part of the invention either;
[0031] FIG. 5 illustrates a gas-supply system that does not form
part of the present invention and that forms the subject of a further
co-pending patent application filed in the name of the present applicant;
[0032] FIG. 6 is a view at an enlarged scale of a first detail
of FIG. 5;
[0033] FIG. 7 is a view at an enlarged scale of a second detail
of FIG. 5; and
[0034] FIG. 8 is a diagram of a supply system according to the
present invention.
DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS OF THE INVENTION
[0035] According to the invention, a supply system is proposed
of the type illustrated in FIG. 8, in which the pressure-reducing
valve 7 is obtained for example according to what is illustrated
in FIG. 3 or in FIG. 4. In what follows the valves of FIGS. 3 and
4 will first of all described, it remaining, however, understood
that the system according to the invention can be used also with
any other type of pressure-reducing valve, including known valves,
such as the valve of FIG. 2.
[0036] In FIG. 3, the parts that correspond or have a function
similar to those of FIG. 2 are designated by the same reference
numbers.
[0037] Also the valve of FIG. 3 has a valve body 10, within which
a restricted passage 14 is defined, set in communication between
an inlet passage 13 made in an inlet connector 11 and an outlet
passage 12 made in an outlet connector 12a. The connector 11 is
designed to be connected to the pipe 4 (FIG. 1), which carries the
gas coming from the reservoir 3. The connector 12a is designed to
be connected to the pipe 9 that takes the gas at reduced pressure
to the rail 2. The example illustrated in FIG. 3 relates to a single-stage
valve that performs a single pressure jump. However, nothing prevents
a valve being envisaged which has, in series, two arrangements of
the type illustrated in FIG. 3 in order to perform two pressure
jumps in succession.
[0038] In the case of the example illustrated in FIG. 3, the restricted
passage 14 is defined by a ring made of metal or of appropriate
plastic material 14a pressed against the end surface of a seat made
in the body 10 of the valve by the connector 11, which is screwed
inside the body 10. The ring 14a, in addition to defining the restricted
passage 14, also defines a conical surface 14b, which functions
as valve seat for a ball-type open/close element 210, preferably
made of metal material, which is pressed against the valve seat
14b by an auxiliary spring 211 that is set between the ball-type
open/close element 210 and a contrast surface defined by the connector
11.
[0039] The valve body 10 has an internal cylindrical cavity, within
which there is fixed a cylindrical bushing 212 functioning as guide
for the sliding movement of a piston member 220. The piston member
220 has a generally cylindrical conformation and has a front end
facing a chamber 290 that is set downstream of the restricted passage
14 and that communicates with the outlet passage 12. On the front
end, the piston member 220 is provided with a cap 60 to push the
ball-type open/close element 210 towards its opening position, against
the action of the spring 211 with high flexibility and low pre-load
that has the sole function of keeping the ball-type open/close element
210 in position. For this purpose, the body of the piston member
220 has a blind axial hole 61, extending from the top end surface
(as viewed in the drawing) of the piston member 220, within which
a helical spring 62 is mounted. The helical spring 62 has one end
pressed against the end surface of the blind axial hole 61 and the
opposite end pressed by a closing element 63 that is withheld in
position by means of a threaded grub-screw 64, which is screwed
within a threaded hole 65 of a ring nut 66, which is in turn screwed
within the end of the valve body 10 opposite to the one on which
the inlet connector 13 is mounted. The top end of the piston member
220 faces a chamber 67, defined by the ring nut 66, which communicates
with the external atmosphere through holes 68 made in the ring nut.
[0040] In the case of the example illustrated, the body of the
piston member 220 has two grooves within which are mounted two rings
made of a material with a low coefficient of friction, for example
PTFE, designated by the reference number 69, for the purpose of
guiding and facilitating sliding of the piston member 220 within
the guide bushing. 212. Furthermore, the piston member 220 is provided
with an annular seal gasket of a dynamic type 70, which is pressed
between an annular contrast surface defined on the outer surface
of the piston member 220 and a ring 71 fixed in any way (for example
screwed) on the bottomend of the piston member 220. The ring 213
defines the position of arrest of the piston member 220, and the
holes 214 enable in any case communication of the chamber 215, which
is in communication with the inlet passage 13, with the chamber
216, which is in communication with the outlet passage 12.
[0041] Operation of the pressure-reducing valve described above
is illustrated in what follows.
[0042] In the resting condition, the spring 62 pushes the open/close
element 210 into its opening position, against the action of the
spring 211. The gas coming from the reservoir 3 (FIG. 1) reaches
the inlet connector 11, and consequently passes through the restricted
passage 14 and from there into the chamber 290. From the chamber
290 the gas reaches, through the outlet connector 12 and the pipe
9 (FIG. 1), the rail 2, with a pressure value adequate for proper
operation of the injectors 1.
[0043] Under the action of the pressure in the chamber 290, however,
the piston member 220 is displaced, against the action of the spring
62, in the direction of the opposite chamber 67 (which is at atmospheric
pressure) until it enables closing of the open/close element 210
against the valve seat 14b. When the pressure in the chamber 290
drops back to the calibration pressure value, the spring 62 again
manages to displace the piston member 220 into the position in which
it causes opening of the open/close element 210. In this way, the
pressure in the chamber 290 varies cyclically, remaining in any
case within a range of reduced values adequate for proper operation
of the injectors.
[0044] A comparison of the principle of operation of the valve
of FIG. 3 with that of the known valve of FIG. 2 shows clearly that
a chief difference between said valves lies in the fact that, in
the case of the valve according to the invention, the piston member
220 is subject to the pressure of the gas downstream of the restricted
passage 14 only in a position corresponding to one of its ends,
whereas in the case of the known valve of FIG. 2, said pressure
was communicated to both ends of the piston member, and the difference
in useful area of said ends was exploited to cause closing of the
open/close element as said pressure downstream of the restricted
passage increased. Furthermore, in the case of the valve of FIG.
3, the open/close element does not move with the piston member as
in the valve of FIG. 2 and is pushed into the opening position by
the piston member as a result of a force exerted on the latter by
the spring 61. The pressure that is created in the chamber downstream
of the restricted passage 14 tends, instead, to push the piston
member, acting only on one of its ends, towards a position in which
it enables closing of the ball-type open/close element 210.
[0045] As a result of the aforesaid geometry, the valve of FIG.
3 consequently does not call for the use of a strongly loaded spring
having the cumbersome dimensions of the spring 26 of the valve of
FIG. 2, and consequently has a simpler and less voluminous structure
and in particular does not call for the use of two seal gaskets
of a dynamic type as in the case of the valve of FIG. 2. In order
to prevent the risk of leakage of the gas into the external atmosphere,
a single seal gasket 70 of a dynamic type is in fact sufficient,
in a position corresponding to the surface of sliding contact between
the piston member 220 and the corresponding guide bushing 212. It
follows that the valve according to the invention, in addition to
being simpler and less cumbersome, is also safer as regards the
risk of leakages of gas to the outside environment.
[0046] A further drawback of the known valve of FIG. 2 that is
eliminated in the valve of FIG. 3 consists in the possibility of
adopting gaskets that are able to guarantee an efficient operation
also with major thermal swings.
[0047] FIG. 4 illustrates a valve (which does not form part of
the invention either) that is substantially identical to the valve
of FIG. 3, with the only difference of presenting, as seal device,
instead of the annular seal device 70, the tubular bellows-type
boot 700, having one end secured to the fixed body of the valve
and the opposite end secured to one end of the piston member, in
such a way that the boot 700, with its deformations, is able to
follow the movements of the piston member. Said boot separates an
annular chamber 701 that surrounds it, within which gas coming from
the chamber 290 can leak, from the space inside the boot, which
communicates instead with the chamber 67 at atmospheric pressure.
[0048] FIG. 5 illustrates a supply system that does not form the
subject of the present invention, which is described herein in so
far as it includes an example of pressure-regulating solenoid valve
that can be used also in the system according to the present invention.
In said system, the pressure-reducing valve 7 also enables actuation
of regulation of the pressure according to desired and pre-set parameters.
In this case, the structure of the pressure-reducing valve 7 is,
for example, of the type shown at an enlarged scale in FIG. 6. As
may be seen, the structure of the valve 7 visible in FIG. 6 is identical
to that of the valve of FIG. 3, with the sole difference that the
spring 62 is eliminated, and the internal cavity 61 of the piston
member 220 is sensitive to a pressure that is applied through a
connection line 80 and a passage 81 made in a connector 82.
[0049] As may be seen in the diagram of FIG. 5, the line 80 is
set downstream of a further electromagnetically controlled valve
83, which functions as pilot solenoid valve. The detailed structure
of the pilot solenoid valve 83 is visible in FIG. 7. Before describing
the example of embodiment of said valve that is illustrated in FIG.
7, however, it is important to note that the function of the pilot
solenoid valve 83 is to receive, at an inlet connector 84, the pressure
of the gas at output from the reservoir 3, which is communicated
to the connector 84 via a line 85 derived from the line 4 upstream
of the pressure-reducing valve 7. The pilot solenoid valve 83 produces,
at an outlet connector 86, a pressure signal reduced with respect
to the pressure at the inlet 84, which is sent, via the line 80,
to the pressure-reducing valve 7. In practice, whereas in the case
of FIG. 3 the piston member 20 was pushed towards the opening position
of the open/close element 210 by the force of the spring 62, in
the case of the valve of FIG. 6, the piston member 220 is pushed
by the pressure signal that arrives through the line 80. Consequently,
by varying said pressure signal, it is possible to vary the response
of the pressure-reducing valve and hence to vary the pressure jump
obtained thereby or, in other words, vary the pressure of the gas
that is sent to the rail 2. The pilot pressure that is transmitted
through the line 80 to the pressure-reducing valve 7 is varied by
the pilot solenoid valve 83 in so far as it depends upon the intensity
of the current with which the solenoid of said valve is supplied,
as will be illustrated in greater detail with reference to FIG.
7.
[0050] To return to the diagram of FIG. 5, the electronic control
unit C receives the signal 8a from the pressure sensor 8, indicating
the value of the pressure existing in the rail 2 and compares it
with a signal 8b indicating the pressure that is desirable within
the rail 2 for each operating condition of the engine. For this
purpose, to the electronic control unit C there may be associated
storage means in which pre-set maps are stored, which supply the
desired value or desired range of values of the pressure in the
rail 2 as the different operating parameters of the system vary.
According to the comparison between the signal 8a and the signal
8b, the electronic control unit C issues an output signal 8c that
drives the solenoid valve 83 for the purpose of obtaining, via the
pressure-reducing valve 7, the pressure jump each time desired.
[0051] In the case of the system of FIG. 5, a closed-loop control
of the pressure in the distribution rail is consequently implemented
(unlike the open-loop control of the system of FIG. 1).
[0052] With reference to FIG. 7, the pilot solenoid valve 83 has
a restricted passage 90, which is defined by a bushing 91 pushed
within a respective seat made in a body 92 of the valve by a helical
spring 93 having one end in contact with the bushing 91 and the
opposite end in contact with a closing element 94 screwed inside
the body 92. The bushing 91 also defines a valve seat 95 for a ball-type
open/close element 96, which is connected to an anchor 97 of an
electromagnet 98 including a solenoid 99 and a spring 100 that tends
to push the open/close element 96 into the closing condition. The
gas enters the valve through a passage 101 made in the inlet connector
84, reaches the restricted passage 90, and from there, if the open/close
element 96 is open, passes into a chamber communicating with an
outlet passage 102 made in an outlet connector 103. As the intensity
of current applied to the solenoid 99 varies, the resultant force
which acts on the anchor 97 and tends to keep the open/close element
96 in a closed condition varies accordingly. A adjustable pressure
jump is thus obtained, which yields at the outlet 102 a reduced
pressure with respect to the pressure at the inlet 101, of adjustable
value.
[0053] Finally, FIG. 8 illustrates a system according to the present
invention, which corresponds to a system of the type of FIG. 1,
in which, downstream of a pressure-reducing valve 7, for example
of the type of FIG. 3 (but any type of valve may be used, including
known valves), is set a solenoid valve 83 substantially of the type
illustrated in FIG. 7. Hence, in this case, the valve 7 functions
simply as a pressure-reducing valve, whilst the function of regulation
of the pressure is entrusted directly to the solenoid valve 83,
which receives at input the reduced pressure that is supplied at
output from the pressure-reducing valve 7 and supplies at output
the pressure for supply of the gas to the rail 2. In said application,
the pressure-reducing valve 7 reduces the pressure down to values
in the region of 15-25 bar, whilst the valve 83, which functions
as pressure regulator, guarantees the advantage of a rapid adaptation
of the pressure to the desired value. The solenoid of the solenoid
valve 83 is controlled by the electronic control unit C according
to the pressure value indicated by the sensor 8 and according to
the desired value 8b, obtained as a function, on the one hand, of
the detection of the various conditions of operation of the engine
(position of the accelerator pedal, rate of turning of the engine,
environmental temperature, etc.) and, on the other hand, for example
as a function of the detection of stored maps, which supply the
ideal values of supply pressure for each specific operating condition
of the engine. A high speed of actuation and an accurate control
of the flow rate is thus obtained. In particular, the opening times
of the electro-injectors are thus optimized and hence reduced, which
provides the possibility of phasing the injection with the opening
of the induction valve of the engine, with beneficial effects on
performance and emissions.
[0054] Of course, without prejudice to the principle of the invention,
the details of construction and the embodiments may vary widely
with respect to what is described and illustrated herein purely
by way of example, without thereby departing from the scope of the
present invention. |