U.S. patent application number 10/796993 was filed with the patent office on 2004-11-04 for engine/pump of a pneumatic type for motor vehicles, a propulsion system including this engine, and a motor vehicle using this system.
This patent application is currently assigned to SISTA EVOLUZIONE S.R.L.. Invention is credited to Morelli, Alberto.
Application Number | 20040219031 10/796993 |
Document ID | / |
Family ID | 32750539 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040219031 |
Kind Code |
A1 |
Morelli, Alberto |
November 4, 2004 |
Engine/pump of a pneumatic type for motor vehicles, a propulsion
system including this engine, and a motor vehicle using this
system
Abstract
Described herein is an engine/pump of a pneumatic type, having a
stator with radial cylinders, within which there can slide
respective pistons, each carrying a roller that engages an annular
cam carried by a rotor. A guide system forces each piston to move,
maintaining its axis rigorously aligned with the axis of the
respective cylinder. The propulsion system that uses said engine
includes high-pressure, medium-pressure and low-pressure tanks, and
an auxiliary engine, which controls one or more compressors. A
motor vehicle which uses the aforesaid system presents innovative
peculiarities as regards construction and location of the tanks of
pressurized air or gas, which are filled with spongy material, and
also as regards construction of the accelerator and brake
controls.
Inventors: |
Morelli, Alberto; (Torino,
IT) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SISTA EVOLUZIONE S.R.L.
|
Family ID: |
32750539 |
Appl. No.: |
10/796993 |
Filed: |
March 11, 2004 |
Current U.S.
Class: |
417/273 ;
417/521 |
Current CPC
Class: |
Y02T 10/6208 20130101;
F02B 53/02 20130101; Y02T 10/12 20130101; Y02T 10/17 20130101; F04B
27/047 20130101; B60K 6/12 20130101; Y02T 10/62 20130101; B60K
2007/0038 20130101; B60Y 2400/15 20130101; F01B 17/02 20130101;
B60K 2007/0092 20130101; B60K 7/0023 20130101; B60K 2006/123
20130101 |
Class at
Publication: |
417/273 ;
417/521 |
International
Class: |
D03D 023/00; F04B
001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2003 |
IT |
TO2003A000184 |
Claims
1. An engine/pump of a pneumatic type for motor vehicles
comprising: a stator defining one or more radial cylinders, in each
of which there is slidably mounted a piston defining in the
cylinder a chamber supplied with a gas or air under pressure; and a
rotor in the form of an annular cam, which surrounds the stator and
co-operates with a camfollower roller carried by each piston for
transforming the reciprocating movement of the pistons caused by
the pressurized fluid into a rotational movement of the annular
cam, in the case of operation as engine, or for performing the
reverse transformation of a rotation of the annular cam into the
reciprocating movement of the pistons, in the case of operation as
pump; in which each piston is connected to the structure of the
stator by a system of guides, which forces the piston to move
maintaining the its axis rigorously aligned with the axis of the
respective cylinder.
2. The pneumatic engine/pump according to claim 1, wherein the
aforesaid guide system associated to each piston comprises at least
one connecting rod having a first end, which is articulated to the
stator about an axis that is parallel to the axis of said
cam-follower roller and passes through the axis of the cylinder,
and a yoke or rocker having an intermediate portion pivoted on the
second end of said connecting rod, one first end articulated to the
piston about the axis of the roller, and the second end engaged by
a guide element that forces it to move at least approximately along
a rectilinear path perpendicular to the axis of the cylinder.
3. The engine/pump according to claim 2, wherein said guide element
is constituted by a carriage guide device, for example of the
pin-slit type.
4. The engine/pump according to claim 2, wherein said guide element
is constituted by an auxiliary connecting rod, which is set
substantially parallel to the axis of the cylinder and has one end
hinged to the stator and the opposite end articulated to the
aforesaid second end of said yoke or rocker.
5. The pneumatic engine/pump according to claim 2, wherein the
distances of the axes of articulation of the two ends of said yoke
or rocker from the axis of the intermediate fulcrum are the same as
one another and are moreover equal to the distance between the axes
of articulation of the ends of said connecting rod.
6. The engine/pump according to claim 1, wherein it comprises a
plurality of cylinders set radially, e.g., according to a star
configuration.
7. The engine/pump according to claim 1, in which the annular cam
of the rotor is shaped so as to render different the duration of
the "active" stroke from that of the "passive" stroke.
8. The engine/pump according to claim 1, in which the annular cam
of the rotor is shaped so as to impart to the reciprocating masses
laws of motion which are harmonic or in any case diversified.
9. The engine/pump according to claim 7, in which the piston is
maintained in the position of TDC for a short interval of angle of
rotation of the engine shaft.
10. The engine/pump according to claim 1, wherein it comprises a
distribution system including: an open/close element, with a
neutral position and two end positions in which the chamber of a
respective cylinder is in communication with the supply of air or
gas under pressure (and, respectively, with the discharge); a fluid
cylinder having the function of booster, which controls the
position of the open/close element; and a pilot solenoid valve,
which controls supply of pressurized fluid to said booster cylinder
to actuate it in one direction or in the other.
11. The engine/pump according to claim 1, wherein it comprises an
electronic control unit, which controls said solenoid valve in a
variable way, according to one or more operating parameters of the
engine.
12. A motor vehicle, wherein it comprises at least one engine
according to one claim 1.
13. The motor vehicle according to claim 11, wherein the engine, or
each engine, is integrated in a respective wheel of the motor
vehicle, the annular cam of the engine being connected to the rim
of the wheel.
14. A propulsion system for motor vehicles, wherein it comprises
one or more engines according to claim 1.
15. A propulsion system according to claim 14, wherein it comprises
one or more tanks of pressurized fluid, for supplying pressurized
fluid to said engine, as well as an auxiliary engine, and one or
more compressors driven by said auxiliary engine in order to
accumulate pressurized fluid within one or more of said tanks.
16. A propulsion system according to claim 15, wherein it
comprises: a low-pressure tank, which receives the exhaust fluid
from the engine/pump; a first stage of a compressor driven by the
auxiliary engine, which takes fluid from the low-pressure tank,
compresses it and feeds it to a medium-pressure tank; and a second
stage of a compressor, which takes fluid from the medium-pressure
tank, compresses it and feeds it to a high-pressure tank.
17. The propulsion system according to claim 16, wherein the
auxiliary engine is located in proximity of at least one of the
medium and high pressure tanks, wherein inside said tanks a foam of
expanded material is arranged performing as a heat exchange means,
and wherein the fluid is sent to said tanks by deviating means
controlled by an electronic control unit.
18. The propulsion system according to claim 16, wherein it
comprises a heat exchanger for cooling the fluid set between the
first compression stage and the second compression stage, and
deviator means for deviating the fluid through said exchanger upon
a command issued by said electronic control unit, according to
pre-set parameters.
19. A motor vehicle according to claim 12, wherein it envisages a
single integrated "accelerator-brake" control with rocking pedal,
which can be rotated in one direction to activate the accelerator
function and in the opposite direction to activate the brake
function, said brake function being obtained by causing the engine
to function as brake, with a further activation up to end-of-travel
of an emergency brake of a conventional type, which acts on the
non-driving wheels.
20. The motor vehicle according to claim 12, wherein it comprises a
system of tanks formed in the beams of a reticular beam structure,
which is integrated in the flat bottom of the boot of the motor
vehicle.
21. The motor vehicle according to claim 20, wherein at least part
of said tanks contains a spongy material.
22. The motor vehicle according to claim 21, wherein the spongy
material is a foam of expanded material with open cells.
23. The motor vehicle according to claim 20, wherein it comprises a
high-pressure tank connected, preferably in a removable way, to the
structure of the motor vehicle.
Description
BACKGROUND FIELD OF THE INVENTION
[0001] It is known that the reciprocating internal-combustion
engine, which is universally adopted for propulsion of motor
vehicles, provides global levels of efficiency that are markedly
variable and particularly modest when this engine is "partialized",
i.e., when, given the same r.p.m., it supplies to the shaft a
torque reduced with respect to the maximum possible value. The
maximum possible value corresponds to the conditions of so-called
"full-throttle" intake. But if the intake duct is "choked", the
pressure is reduced to the minimum operating value, at which the
torque supplied by the gases is the one necessary for compensating
the mechanical losses in conditions of loadless turning of the
engine, i.e., without useful torque exerted on the shaft. In these
conditions, the efficiency is zero, and the consumption is also
minimum but persists with values of the order of one litre of fuel
per hour in the case of automobiles. Between these conditions and
the conditions of maximum intake, the levels of efficiency range
from zero to a maximum, which in the case of currently available
engines can reach 30%-40%. However, not infrequently the efficiency
with which the engine supplies its power in certain running
conditions, e.g., when the vehicle is in town traffic, is just a
few percent, even less than 10% of the maximum efficiency. In these
conditions, there is no great interest in increasing the maximum
efficiency of the engine, even though the potentiality of such an
increase does exist: some reciprocating marine engines reach an
efficiency of 60%.
[0002] A solution designed to improve the energy balance envisages
the accumulation of the energy generated in conditions of high
efficiency and its return for use, also with a high efficiency.
This is the concept underlying operation of electric vehicles.
However, the cycle of charging and discharging of the electrical
accumulators (the so-called batteries) is not free from losses,
especially in the case of rapid charging and discharging. A typical
value can be 70% both as regards charging and as regards
discharging, with the global result of a loss of approximately 50%,
which is a highly penalizing value.
[0003] Much higher values of efficiency are obtained with gas tanks
or gas cylinders under pressure and appropriately insulated
thermally. This is the case of tanks or cylinders that contain
compressed air and are filled with particular foams and that have
open cells, which function as heat sinks by accumulating and
returning the thermal energy of the gas during its variations in
pressure. The levels of efficiency achieved are higher than 90% in
the entire cycle of charging and discharging.
OBJECT OF THE INVENTION
[0004] A purpose of the present invention is to propose a new
engine/pump of a pneumatic type, both for accumulation of energy
and for transformation of this accumulated energy into work of
locomotion.
[0005] A further purpose of the invention is to provide a new
propulsion system that includes the engine according to the
invention, as well as a high-efficiency generator of pneumatic
energy, preferably set on board the vehicle.
[0006] Yet a further purpose of the present invention is to provide
a propulsion system capable of recovering, at a high rate, the
reversible potential energy (gravitational energy and kinetic
energy) of the vehicle as it is travelling.
[0007] Yet a further purpose of the invention is to provide a motor
vehicle which uses the propulsion system according to the
invention, in which the space for the tanks forming part of the
system is exploited in the best possible way.
SUMMARY OF THE INVENTION
[0008] With a view to achieving the above and further purposes, the
subject of the present invention is an engine/pump according to the
annexed claim 1. The subject of the invention is also a motor
vehicle as defined in claim 8, and a propulsion system as defined
in claim 10. Further preferred and advantageous characteristics of
the engine/pump, of the motor vehicle, and of the propulsion system
according to the invention are defined in the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Further characteristics and advantages of the invention will
emerge from the ensuing description with reference to the annexed
drawings, which are provided purely by way of non-limiting example,
and in which:
[0010] FIG. 1 is a diagram of a preferred embodiment of the
invention;
[0011] FIG. 2 is a schematic perspective illustration of a motor
vehicle which uses the propulsion system according to the
invention, in which visible in detail is a reticular structure,
integrated in the flat bottom of the boot, which is exploited to
obtain the tanks forming part of the system;
[0012] FIGS. 3 and 4 are a side view and a plan view, respectively,
of the motor vehicle of FIG. 2;
[0013] FIG. 5 is a cross-sectional view at an enlarged scale of a
detail of the connection of the structure exploited as tank to the
body of the motor vehicle;
[0014] FIG. 6 is a cross-sectional view, in the plane passing
through the axes of the wheel and of one of the cylinders, of a
preferred embodiment of the engine/pump according to the
invention;
[0015] FIG. 6A illustrates a detail at an enlarged scale of a seal
on a piston of the engine/pump;
[0016] FIG. 7 illustrates a cross section of the same engine in the
plane passing through the axes of some contiguous cylinders;
[0017] FIG. 8 illustrates a cylinder as viewed in the direction of
its axis, according to the line X-X of FIG. 7; and
[0018] FIGS. 9, 10 and 11 illustrate diagrams corresponding to the
operation of the engine/pump according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] With reference to the diagram of FIG. 1, illustrated therein
is a propulsion system for a motor vehicle according to the
invention. The references AP, MP and BP designate a high-pressure
tank, a medium-pressure tanks and a low-pressure tank,
respectively. In its application to an average automobile, the
order of magnitude of the internal volumes of the tanks is of tens
of litres for the first two types and of hundreds of litres for the
low-pressure tank, roughly 300 litres. The latter considerable
volume, but preferably also the volumes of the medium-pressure tank
and/or the high-pressure tank, is obtained, in the preferred
embodiment, inside elements which also perform structural
functions, such as the elements 1, 2, 3, 4', 4" (see FIGS. 2-4) of
a reticular structure integrated in the flat bottom of the boot of
the motor vehicle. In particular, FIG. 2 shows clearly in a
perspective view the reticular structure integrated in the flat
bottom of the boot of the automobile, with beam structures 1, 2, 3,
4', 4", having a box-like conformation, i.e., having a closed
section, which are also used as pressure tanks. The tank beams are
also clearly visible in FIGS. 3, 4, which illustrate, respectively,
a longitudinal side view and a plan view of the vehicle. The
elements 1, 2 and 3 are exploited as intercommunicating
low-pressure tanks. The elements 4' and 4" constitute two
medium-pressure tanks. The high-pressure tank is formed by an
element 5 carried by an auxiliary structural element 10, preferably
in a removable way.
[0020] A characteristic common to all the aforesaid tanks is that
of being preferably filled with a foam f having open cells (see
FIG. 5), e.g., of the polyurethane type, with a geometry and a
specific weight such as to fulfil the important function of
rendering practically isothermal the thermodynamic transformations
of the operating gas (preferably nitrogen or air) of the propulsion
system in the various phases of operation, as described in what
follows.
[0021] The tank beams 1-5 are preferably made of a composite
material, such as a polyester or epoxy resin reinforced with glass
or aramidic or carbon fibre ("kevlar") according to the performance
required (carbon is preferred for high pressures, whilst glass is
sufficient for low pressures). This type of construction is
preferably adopted also because there can be easily provided the
connections to the conventional structure of the body of the
vehicle, as indicated, for example, in the detail designated by SO
in FIG. 2.
[0022] To return to FIG. 1, of considerable importance in the
invention is the pneumatic actuator (engine/pump) M/P, which
supplies/receives mechanical energy to/from the wheels to which it
is connected via a particularly innovative crank mechanism. A
preferred configuration of the actuator is provided in FIGS. 6-8.
FIG. 6 is a partial cross-sectional view in the plane passing
through the axes of the wheel and of one of the cylinders. FIG. 7
is a partial cross-sectional view in the plane containing the axes
of the cylinders, (which, in the preferred example illustrated, are
arranged so as to form a star). FIG. 8 is a view, according to the
line X-X of FIG. 7, of a cylinder as viewed in the direction of its
axis.
[0023] The device obtained comprises a stator defining one or more
radial cylinders C, in each of which is slidably mounted in a
fluid-tight way a piston P, which defines, in the cylinder, a
chamber supplied with a gas or air under pressure. A rotor in the
form of an annular cam CM surrounds the stator and co-operates with
a cam-follower roller RO carried by each piston P, for the purpose
of transforming the reciprocating movement of the pistons caused by
the pressurized fluid into a rotational movement of the annular
cam, in the case of operation as an engine, or of performing the
reverse transformation of rotation of the annular cam into the
reciprocating motion of the pistons, in the case of operation as a
pump.
[0024] Particular attention has been paid to the seal device on
each piston, which is preferably of the type illustrated in FIG.
6A, comprising a continuous ring A housed in a seat S of the piston
P and pushed to adhere to the surface of the cylinder C thanks to
the interposition of a ring O of the O-ring type.
[0025] The crank mechanism for transformation of the reciprocating
motion of each piston into a rotational motion of the driven member
(i.e., a transmission shaft or directly a wheel of the motor
vehicle) comprises the roller RO carried by each piston and the cam
CM engaged thereby. The cam is preferably fixed to the driving
wheel itself, designated by R, the rim of which is designated by
U.
[0026] The above configuration enables a differentiation of the
angle of rotation of the engine shaft (i.e., of the wheel, in the
case exemplified) during the "active" travel of each piston, i.e.,
the stroke from the top dead centre (TDC) to the bottom dead centre
(BDC), with respect to the angle of rotation during the "passive"
stroke, i.e., from the BDC to the TDC. In fact, whereas in
traditional centred crank mechanisms the passage from TDC to BDC
corresponds to a rotation through 180.degree., in the case of the
roller-and-cam crank mechanism described above, nothing prevents
positioning of the BDC at a different angle, e.g., at 240.degree.
of rotation of the wheel with respect to the TDC, to obtain an
active stroke corresponding to {fraction (2/3)} of full circle.
Consequently, the passive stroke is reduced to {fraction (1/3)} of
a turn. Both the choice of the ratio between the active stroke and
the passive stroke and the laws of motion of the pistons are widely
variable at the design stage, but preferably said laws will be of a
harmonic type, albeit even having different periods. In general, a
longer active stroke is preferred because a higher specific power
of the engine corresponds to a longer duration.
[0027] Another advantage that can be achieved concerns the
distribution system (i.e., the system for controlling communication
of the chamber of each cylinder with the supply of pressurized
fluid and with the exhaust), in which the phases of intake and
discharge of the gas can have, for instance, durations that are
approximately the same as one another. There is thus an increase in
the duration of the phase that would otherwise be shorter, i.e.,
the intake phase (see the example provided in what follows), and
hence this phase proves to be more difficult to obtain. It is to be
borne in mind, in this regard, that another important
characteristic of the invention lies in the electronic management
(variable valve timing--VVT) of the distribution.
[0028] Since the roller-cam contact generates a lateral thrust Fs
(see FIG. 7) that goes to zero only at the dead centres, i.e., at
the points of end-of-stroke, the invention envisages a device D of
an epicyclical type for balancing said thrust and for ensuring
moreover that the piston will perform a rectilinear translational
motion coaxial with the cylinder. In the example illustrated, the
device D consists of two connecting rods B set at the two sides of
each roller RO, which perform a motion on planes parallel to the
median plane of the roller (said median plane passes preferably
through the axis of the cylinder). Each of the connecting rods B is
hinged, at one end, to the cylinder according to a transverse axis
at (see FIG. 8) passing through the axis of the cylinder itself
and, at the other end, to the medium point of a "yoke" G (in the
example illustrated, a rocker having an H-like conformation, as
visible in FIG. 8) with opposed arms that have the same length, the
end hinges of which are, on one side, connected to the piston P
along the axis of the roller RO and, on the other, to a carriage E
constrained so as to translate in a direction n-n (see the cylinder
in the top position in FIG. 7), perpendicular to the axis of the
cylinder. Thanks to said kinematic mechanism, the motion of the
piston is a rectilinear translational movement along the axis
thereof, provided that the length of the arms of the yoke or rocker
(i.e., the distances of its intermediate fulcrum from the end
articulations) are the same as that of the connecting rod B, which
is, in fact, the case.
[0029] For the purpose of preventing prismatic coupling of the
carriage E, an alternative, non-rigorous, but sufficiently
approximate solution of the carriage envisages connection of the
yoke to a small oscillating connecting rod L on average directed
parallel to the axis of the cylinder (see the cylinders in the
positions top right and bottom left in FIG. 7), simply hinged, at
one end, to the yoke and, at the other end, to the body of the
cylinder (engine base, BA). A characteristic of the yoke G and the
connecting rod L is that they are hinged together with a pin that
is sufficiently long to prevent excessive warpage, albeit elastic,
of the yoke G and of the connecting rod L. For the same reason,
hinging of the connecting rod L to the engine base BA is also
obtained with a long pin N. In this way, any danger of the piston
skirt sliding on the cylinder is obviated. The piston thus proves
to be as if it were "hung" from the centre of the wheel and guided
by the seal gaskets to move co-axially with respect to the
cylinder, forming in this way a piston-cylinder coupling that is
effective both as regards gas tightness and as regards good
mechanical efficiency.
[0030] To return to FIG. 1, starting from AP and following the
arrows appearing along the solid lines, there is followed a work
cycle in which energy is supplied to the wheels. It may be noted
how the gas passes into the medium-pressure tank MP before
supplying the engine/pump actuator M/P to transform the pneumatic
energy into mechanical work of the wheel/wheels R. Said passage of
gas is regulated by the regulator RE which, by bringing about in
part a lamination of the gas itself, causes a loss of energy,
albeit reduced thanks to the presence of the foam in the tanks, as
has already been said. In order to render said losses small, the
medium-pressure tanks PM are set very close both to the
high-pressure tank AP and to the actuators M/P. However, said
passage of gas into an intermediate tank can be omitted, and the
gas can be sent into the actuator directly from the high-pressure
tank AP. This solution is preferred in those cases where it can be
applied, either on account of the possibly non-excessive value
chosen for the high pressure or on account of the sufficient
resistance of the actuator to the consequent thermal and mechanical
stresses. In this way, the solution is simplified and less costly
but, given the same volume of the tank AP, since it is not possible
to adopt very high pressures, the energy accumulated is reduced. On
the other hand, as is known, the energy accumulated must be of an
amount sufficient to make up, as far as possible, for the
instantaneous power needs (the so-called "power peaks") for the
time required by the running cycle of the vehicle. If it is not
always possible to satisfy totally said requirement, the
performance of the vehicle decreases accordingly.
[0031] The distribution of gas to the actuator is activated
preferably by an electro-pneumatic servo-valve EV. To enable a fast
speed of response upon command, this preferably consists of a pilot
micro-solenoid valve .mu.EV (see FIG. 6) associated to a booster BO
and driven by a common encoder (not visible in the drawings), which
reads the angular position of the engine shaft and issues the
opening and closing signals for intake and discharge of gas to/from
the actuator M/P, in both of its functions, namely, as engine M and
as pump P.
[0032] Said functions are obtained by the driver of the vehicle
preferably by pressing on the accelerator pedal A in either of the
two directions indicated in the diagram of FIG. 1: MO (engine)
drive, and PO (pump) braking. If the pedal is pushed further in the
braking direction, conventional brakes FR are activated, which
constitute also the compulsory emergency system. They are
preferably housed in the non-driving wheels (see FIG. 2).
[0033] The distribution system includes: an open/close element OT,
with a neutral position and two end positions, in which the chamber
of a respective cylinder is in communication with the supply of
pressurized air or gas and, respectively, with the exhaust; the
fluid cylinder BO, with a booster function, which controls the
position of the open/close element OT; and a pilot solenoid valve
EV, which controls supply of pressurized fluid to said booster
cylinder (BO), to actuate it in one direction or in the other.
[0034] The work cycle of the gas is represented in FIG. 9. The
ordinate indicates the pressure of the gas; the abscissa indicates
both the angle .theta. of the engine shaft, which is assumed equal
to 0.degree. at the top dead centre (TDC) and equal to 240.degree.
or a value close thereto --this value being preferable to
180.degree. of traditional systems, as already mentioned
previously--at the bottom dead centre (BDC), and the percentage
stroke c/c.sub.0 (which is also equal to the piston displacement V
%), where c.sub.0 is the total stroke.
[0035] By way of example, at point A there starts supply of gas
from the medium-pressure tank MP (said pressure is assumed as being
40 bar), which is interrupted in B, after a rotation
.theta.=90.degree.. Then the gas expands up to C, where it drops to
a pressure of 10 bar, which is assumed as being the maximum
possible pressure existing in the tank BP, and the active stroke
(intake plus expansion) is thus completed. During the return stroke
which starts at BDC with opening of the connection of the cylinder
to the tank BP, the gas is here transferred, at a practically
constant pressure, until TDC is almost reached, at which point the
exhaust valve is closed (point D, corresponding to an angle .theta.
in advance by 15.degree. with respect to TDC), and there is
activated, in the "dead space", which is inevitably non-zero, a
phase of compression of the gas that has remained there up to the
value of intake pressure (40 bar), at which gas is once again
introduced by the tank MP. The dead space is evaluated in the
example as being equal to 1% of the piston displacement V, but it
is possible to make it smaller still by reducing as much as
possible the volume sm determined by the movement of the open/close
element OT (see FIG. 6). A system devised for reducing the dead
space is represented by the protuberance PR made on the top of the
piston P (see FIGS. 6,7).
[0036] However, on account of the small volume of the "dead space",
the value of end-of-compression cannot coincide with the intake
pressure. In this case, the gas intake causes a shock on the crown
of the piston with consequent unpleasant modulation of torque on
the shaft (roughness, noise) if the latter is not exactly in a
position corresponding to TDC. To prevent this effect, the cam is
shaped so as to maintain the piston at TDC for a short time
interval (circular shape of the cam, which is coaxial with the
engine shaft, as illustrated in FIG. 7, which represents
schematically a cam that actuates just one stroke per revolution,
the laws of motion during the active and passive phases of the
stroke itself being shown in FIG. 11).
[0037] In the cycle of the previous example, the pressure of the
tank BP is 10 bar but it could be smaller on account of the gas
intake which the compressor CO is required to make in order to
maintain the maximum pressure both in the tank MP and in the tank
AP. By way of example, let said pressure be 2 bar. The cycle of
utilization of the gas is thus modified into A' B' C' D' of FIG. 9,
with appropriate variation of the angles .theta. of opening and
closing of the solenoid valve. In fact, appropriate gas-pressure
sensors for detecting the pressure in the tanks supply signals to
an electronic control unit ECU (see FIG. 1), which has the job of
automatic management both of the levels of pneumatic energy in the
tanks and of the power of the on-board generator GB, which,
according to the invention, is constituted by a reciprocating
engine regulated to operate according to a "stop & go"
criterion but always in conditions of maximum efficiency given the
same r.p.m. of operation. On the other hand, since the medium power
required by operation of the vehicle varies considerably, the rate
of turning of the internal-combustion engine envisaged will vary
accordingly (see the power/r.p.m diagram associated to the diagram
of FIG. 1).
[0038] As has been said, the gas, after performing its working
cycle, passes into the low-pressure tank BP. From here, it is set
again in circulation by being re-compressed in the high-pressure
tank AP by the compressor CO, which is generally made up of a
number of stages. Indicated in the diagram of FIG. 1 are two
compression stages, designated by Ist and IIst, between which there
is provided a step of cooling of the gas performed by the heat
exchangers SC (indicated in FIG. 2), the activation of which by the
deviator VD is determined by the aforesaid electronic control unit
ECU, according to the inputs of the sensors, which provide
information on the state of charge of the extreme-pressure tanks AP
and BP. The electronic control unit ECU moreover decides the regime
of operation of the generator GB also according to the
position-time product assumed by the stroke-regulation pedal A
(accelerator).
[0039] FIG. 2 shows the auxiliary engine GB located in the front
part of the motor-vehicle. However it is preferably located in the
rear part, close to the high and medium pressure tanks.
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