Supercharger device for reciprocating internal combustion engines, particularly for motor vehicles

Supercharger device for reciprocating internal combustion engines, particularly for motor vehicles, comprising, inserted on the induction manifold of the engine, a rotary positive-displacement supercharger driven constantly by the motor shaft, the capacity and therefore the delivery pressure whereof is variable from a minimum value to a maximum value and vice versa by virtue of the corresponding controlled variation of the geometry of the pumping means constituted by a stator cylinder, a rotor and vanes.

BACKGROUND OF THE INVENTION 
The present invention relates to a supercharger device for internal 
combustion engines, particularly for motor vehicles. 
As is known, the maximum power of engines installed on motor vehicles, in 
particular on automobiles, considerably exceeds the power required during 
the normal use of the vehicle, the reserve power being used occasionally 
to achieve maximum acceleration, or maximum speed on level ground, the 
so-called top speed, or to climb the maximum slope. 
In the normal use of the motor vehicle, the employed power generally does 
not exceed 50% of the maximum power and this reduction, obtained by 
choking the induction, is matched by a decrease of the specific 
performance of the engine with consequent high consumptions, imperfect 
combustion and therefore presence of polluting products in the exhaust 
system. 
With the intention of improving the overall efficiency, the supercharging 
of endothermal reciprocating engines, both of the Otto-cycle type and of 
the Diesel-cycle type, has long been proposed, and consists of the 
compression to a greater-than-atmospheric pressure of all, or part of, the 
feed air before induction into the cylinders. Supercharging entails, as is 
known, an increase in mechanical efficiency, since the increase of the 
mechanical losses is much lower than the power increase, as well as an 
increase in volumetric efficiency and in actual thermal efficiency. This 
is followed by a considerable reduction in specific consumption, which can 
reach up to 45%. 
Two types of supercharging are currently employed: the mechanical type and 
the exhaust-gas turbosupercharger type. The first type, used predominantly 
in small- and medium-cylinder capacity engines, draws the power required 
for supercharging from the driving shaft. Superchargers of the "Roots" 
type are used which are driven by the engine with the interposition of a 
multiplier and of a joint which starts the supercharger only at a preset 
number of rpm of the engine. In the second type of supercharging, reserved 
for engines with greater cylinder capacity, the supercharging power is 
supplied by a turbine which is driven by the exhaust gases of the engine, 
and drives a feed supercharger. 
Both systems increase the maximum power of the engine but are substantially 
inactive at low rpm. 
Their use therefore substantially improves the performance of the engine at 
medium and high rpm, but does not modify the power curve in terms of 
optimizing the power output with respect to the conditions of practical 
use of the motor vehicle. 
SUMMARY OF THE INVENTION 
The aim of the present invention is to provide a system for the controlled 
supercharging of reciprocating engines for motor vehicles, both of the 
"Otto" cycle type and of the "Diesel" cycle type, adapted to allow the 
abovesaid optimizing of power output with the consequent possibility of 
considerably reducing the cylinder capacities installed, achieving the 
peaks in required power by supercharging. 
According to the present invention, in fact, a supercharger device for 
internal combustion reciprocating engines, particularly for motor vehicles 
is provided, comprising a positive displacement rotary supercharger 
inserted on the induction manifold of an engine, characterized in that 
said superchanger is constantly driven by the engine shaft, the capacity 
and therefore the delivery pressure of said supercharger being variable by 
virtue of a controlled variation of the geometry of pumping means of said 
supercharger, said pumping means comprising a stator cylinder, a rotor and 
vanes. 
According to an embodiment of the invention, the geometry variation is 
obtained by varying, by virtue of the action of control elements, the 
eccentricity between the axis of the rotor and that of the stator. 
In the zero-eccentricity configuration, the supercharger acts as a simple 
blower, and performs no supercharging action. 
In the maximum-eccentricity configuration, the supercharger performs its 
maximum supercharging, the degree whereof depends on the maximum 
compression ratio between the induction and the delivery of the 
supercharger and the number of rpm being considered. 
Since the supercharger is constantly driven, the passage from one condition 
to the other is immediate and the response to the demand of power increase 
by supercharging is correspondingly immediate since there are no delays 
due to startup inertia. Moreover, the passage from one condition to the 
other can be performed at any rpm rate of the engine, so that 
supercharging, and the consequent power increase, can also be performed at 
low rpm. 
According to another embodiment of the present invention, the variation of 
the geometry of the pumping means is obtained by means of elements adapted 
to produce, upon the action of external control means, the retention of 
the vanes in the respective seats of the rotor. The passage from aspirated 
operation to supercharged operation of the engine therefore occurs by 
acting on said control elements to produce the retention or respectively 
the release of the vanes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIGS. 1 to 4, the letter M generally indicates an 
internal-combustion reciprocating engine, for example an "Otto" cycle 
engine, of the carburation type provided with an induction manifold 10 
whereon is inserted a choke carburettor 11. 
For a better understanding of the invention, the following characteristic 
engine data are considered: 
cylinder capacity 1000 cc 
power 37 KW at 5500 rpm 
max torque 90 N.m at 3000 rpm 
On the induction manifold 10 of the engine M, between the carburettor 11 
and the filter 12, is inserted a positive-displacement rotary supercharger 
13, of the known type comprising a stator 14 and an eccentric rotor 15 
bearing a plurality of vanes 115, freely slideable in respective seats 116 
of the rotor. In the present description the assembly constituted by the 
stator, by the rotor and by the vanes is briefly defined as pumping means. 
According to the present invention, the geometry of the pumping means is 
variable, and in the illustrated example this is obtained by varying the 
eccentricity between the stator cylinder 14 and the rotor 15, by means of 
control elements 16, from zero to a maximum value which depends on the 
difference between the diameters of the stator and of the rotor. For this 
purpose the stator 14 is oscillably suspended from a pivoting pin 17 about 
which it can rotate to move with respect to the rotor 15, which is fixed, 
to pass from the maximum-eccentricity configuration illustrated in FIG. 1 
to that of zero eccentricity illustrated in FIG. 2. 
The control elements 16 may be of different types, for example they can be 
constituted by a hydraulic piston 18 acting in contrast with a spring 19, 
or they can be mechanical and either direct or power-assisted. 
In the configuration of maximum eccentricity, illustrated in FIG. 1, the 
supercharger produces the maximum volumetric capacity and the maximum 
pressure, providing the maximum supercharging of the engine M at the 
number of rpm being considered. The volumetric capacity of the 
supercharger is in fact related to the number of rpm by the following 
relationship 
##EQU1## 
where D is the inner diameter of the cylinder 14, d is the outer diameter 
of the rotor 15, L is the axial length of the supercharger, n is the 
number of rpm being considered and .eta..sub..nu. is the volumetric 
efficiency. 
This supercharging corresponds to a variation in the power W as illustrated 
in the diagram of FIG. 3 wherein the insertion of the supercharging by 
shifting the cylinder 14 of the supercharger with respect to the rotor 15 
occurs, for example, at 3500 rpm. 
In the diagram, the broken-line curve W relates to the power of the engine 
M operating at atmospheric pressure, the curve W relates to the power of 
the same engine supercharged by the supercharger 13 and the solid 
connecting line between the two curves represents the power variation as a 
consequence of the insertion of the supercharger. The maximum power 
variation is closely related to the volumetric compression ratio of the 
supercharger 13 and for a value of 1/1.5 of said ratio it can be 
estimated, other conditions being equal, between 25% and 35% of the 
maximum power developed by the engine M with aspirated operation. 
As is clearly illustrated in the qualitative diagram of FIG. 3, due to the 
characteristics of the vane supercharger 13, the compression ratio whereof 
is substantially independent from the rpm rate, the influence of 
supercharging is particularly considerable at low rpm, the increase in 
power being of the order of 30% already at 2000 rpm of the engine. 
Moreover, again due to the intrinsic characteristics of the 
positive-displacement rotary compressor 13, the increase in the 
temperature of the air due to supercharging is very modest (20-30% lower 
than the temperature increase caused by Roots superchargers) and this, 
together with the considerable turbulence caused by the supercharging, 
significantly reduces detonation phenomena. 
Accordingly, the engine M with the supercharging system according to the 
invention may be advantageously fitted to motor vehicles requiring engines 
with approximately 20-30% higher power, since, in case of need, the power 
demand is met by inserting the supercharger 13 in the specified manner. 
In the idle configuration with zero eccentricity, illustrated in FIG. 2, 
the supercharger performs a simple ventilating effect, with a considerable 
increase in turbulence; the volumetric flow rate of the airflow supplied 
thereby, substantially at atmospheric pressure, being expressed by the 
following relation: 
##EQU2## 
where the symbols have the previously specified meanings. 
For this zero-eccentricity configuration, which is predominant in the 
ordinary use of the motor vehicle, the load on the supercharger is minimal 
and there is no relative movement of the vanes with respect to the 
recesses of the rotor, this in practice eliminating the need for adequate 
lubrication. For this purpose it is advantageous, and also sufficient, to 
bleed on the induction duct of the supercharger 13, for example by means 
of a duct 20, the oil vapors recycled from the engine M. 
FIG. 4 illustrates an advantageous constructive embodiment of the 
supercharger 13. 
According to this embodiment, a plate 30 has a seat 31 for supporting the 
shaft 32 of the rotor 15. The plate 30 has a perfectly planar surface 33 
facing towards the stator cylinder 14 which is oscillably supported by an 
arm 34 articulated to the pivot 17 rigidly associated with the plate 30. A 
series of elastic washers 35, engaged by a locking nut 36, keeps the 
stator cylinder 14 in sealing contact engagement against the surface of 
the plate 30; the seal being ensured by an "O"-type gasket accommodated in 
a front recess of the cylinder. The shaft 32 of the rotor 15 is supported 
by a first bearing and by a second bearing, respectively 37 and 38. In 
order to avoid axial stresses on the first bearing 37, its two faces are 
subject to the same pressure by virtue of the presence of a front recess 
39 and of axial ducts 40 provided on the plate 30; the seal being ensured, 
downstream with respect to the bearing, by a gasket 41 acting on the 
shaft. A pulley 42 is keyed onto the protruding end of the shaft to 
transmit to the rotor 15 the power drawn from the shaft of the engine M. 
FIG. 5 shows a superchanger, according to a further aspect of the invention 
and which differs from the one previously described in that the stator 
cylinder is flanged directly onto the plate 30 having a through seat 43 
which is circular but eccentric with respect to the cylinder 14 wherein a 
bush 44 is accommodated, freely rotatable, and is eccentrically provided 
with the bearing 37 for supporting the shaft 32. 
The eccentricity of the bush 44, with respect to the cylinder 14, is 
identical to that of the shaft 32 with respect to the bush, so that, by 
rotating through 180.degree. the bush 44 is the seat of the plate 30, the 
two eccentricities compensate one another and the rotor 15 arranges itself 
coaxial to the cylinder 14. A pivot 45 is provided on the bush 44 to allow 
the connection of a tensioning element 46 adapted to produce the rotation 
of said bush in its seat. 
FIGS. 6-11 show a supercharger, according to another aspect of the 
invention, in which the variation of the geometry of the pumping means is 
obtained by subjecting the vanes 115 of the rotor to elements adapted to 
produce, upon the action of an external control K, the retention of said 
vanes in the respective seats 116 of the rotor. 
In the embodiment illustrated in FIGS. 6 and 7, the rotor is provided with 
elements for retention by negative pressure, comprising an axial channel 
214 connectable to a negative pressure source and a plurality of derived 
channels 215, axially spaced (FIG. 8), adapted to subject the vanes 115 to 
said negative pressure to keep then fully inserted in their seats 116. As 
illustrated in FIG. 6, the negative pressure source may be constituted by 
the induction manifold 10 of the engine M which is connected to, or 
disconnected from, the duct 214 by means of the valve K constituting the 
external control. If required, the action of the induction manifold may be 
integrated with an accumulation container R and/or with an auxiliary 
negative pressure source, for example constituted by an ejector associated 
with the exhaust manifold and also by temporarily using the supercharger 
as vacuum pump. 
Each of the derived channels 215 ends with a widened aspiration inlet 216 
which faces the lateral wall of the respective vane seat 115. In this 
manner, when the channel 214 is connected to the negative pressure source, 
each vane, as an effect of the negative pressure, is aspirated and drawn 
in forced contact engagement against said wall of its seat and, by virtue 
of the friction, is retained inside said seat after it has been pushed 
therein by the contact with the stator as an effect of the rotation of the 
rotor. To increase the described sealing action, it may be convenient to 
provide auxiliary derived channels 217 which lead onto the dead bottom of 
the seats 115 and act by direct aspiration on the related vane. The 
channels 217 are in any case indispensable to ensure the correct operation 
of the supercharger at high rpm in view of the need to rapidly evacuate 
the air which is on the bottom of the vane seat. 
According to a further aspect of the invention as shown in FIGS. 9 and 10, 
the vanes 115 are subject to the action of mechanical retention elements 
constituted by cylindrical cams 230 rotatably contained in corresponding 
cylindrical seats 231 communicating with the seats 116 and retained 
therein by retention screws 225. The lower end of each cam 230, the active 
surface 232 whereof is profiled for example as illustrated in FIG. 10, is 
provided with a toothed portion 233 engaging with the corresponding 
toothed portion 234, for example in the shape of a cylindrical rack, or of 
an endless screw, of a control shaft 235 slideable and/or rotatable in an 
axial seat 236 of the rotor 10. The small shaft 235 is subject to a 
control, coherent with the type of the sets of teeth 233-234 which may be 
mechanical or fluidodynamic and the actuation whereof moves the cams 230 
angularly to engage or disengage their active surfaces 232 with or from 
the lateral face of the related vane 115. 
Referring to FIG. 11, the cylindrical cams are replaced by wedge-shaped 
radial blocks 240 slideable in corresponding wedge-shaped radial seats 241 
provided on the rotor 15. As visible in FIG. 11 the wedge-receiving radial 
seats 241 taper in the centrifugal direction of the seat. The blocks 240 
have a wedge-shaped surface 242 intended to make contact with the lateral 
surface 115a of the corresponding vane 115 through a slot 243 which 
connects the seats 116 and 241. Each block 240 is subject to the action of 
the centrifugal force which pushes the wedge-shaped surface 242 against 
the lateral surface of the vane 115 to retain the vane and is provided 
with a threaded hole 245 in which the correspondingly threaded portion 246 
of a return shaft 247 engages. 
The other end of the shaft 247, opposite to the threaded portion 246, has a 
pinion 248 engaging with the toothed portion 234 of the control shaft 235 
described with reference to the previous FIG. 9. It is obvious that the 
rotation of the shaft 235 causes a radial movement of the wedge-shaped 
block 240 which, depending on the direction of rotation imparted to the 
shaft, moves, pushed by the centrifugal force, to engage the vane 115 or, 
against the action of said force, to disengage it; the control being 
extremely gradual, to the advantage of a controlled release of the vanes. 
The supercharger as illustrated in FIGS. 6 to 11 substantially has the 
following advantages: 
the rotor, the eccentricity whereof with respect to the stator is fixed and 
constant, may be supported at both ends and therefore is not subject to 
limitations in axial extension with the consequence that, with equal 
delivered power, the diameter can be reduced and the peripheral speed of 
the vanes during supercharging can be reduced accordingly; 
in idle operation, predominant in use, there is no contact between the 
vanes and the stator cylinder so that the heating of the air and the wear 
of the vanes are avoided; 
the rotor of the supercharger may be used as dynamic balancing shaft of the 
engine or at least as integrating element of said shaft. 
The rotor is keyed, directly or by transmission means such as gears, or 
chains, or toothed belts 260, and, besides having a compact configuration, 
allows to angularly time the rotor and the shaft of the engine to 
synchronize the pressure waves caused by each vane with the filling phase 
of each cylinder, thus increasing the degree of filling of the cylinder, 
especially at low rpm, as an effect of the additional dynamic pressure. 
Furthermore, by adopting a transmission element constituted by a pair of 
cylindrical gears, the rotor 10 is counter-rotating with respect to the 
driving shaft and can therefore be sized and counterweighted so as to also 
perform the function of dynamic balancing shaft. In particular in an 
in-line two-cylinder four-stroke engine, the rotor of the supercharger, if 
counterrotating and at equal rpm with the engine, can balance the inertial 
forces due to the first-order harmonics. 
Naturally, the concept of the invention being invariant, the details of the 
execution and the embodiments may be widely varied, with respect to what 
is described and illustrated by way of non-limitative example, without 
thereby abandoning the scope of the invention.