Title:
Internal combustion engine
United States Patent 2321943


Abstract:
This invention relates to internal-combustion engines of the kind having two crank-shafts and is especially but not exclusively concerned with such engines which are intended for use on aircraft. An object of this invention is to provide such an engine having improved means for transmitting...



Inventors:
Charles, Sampietro Achille
Application Number:
US33829240A
Publication Date:
06/15/1943
Filing Date:
06/01/1940
Assignee:
Charles, Sampietro Achille
Primary Class:
Other Classes:
60/605.1, 123/65BA, 123/197.1, 123/303
International Classes:
F02B73/00; F02B75/04; F02B75/22
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Description:

This invention relates to internal-combustion engines of the kind having two crank-shafts and is especially but not exclusively concerned with such engines which are intended for use on aircraft.

An object of this invention is to provide such an engine having improved means for transmitting the power from the two crank-shafts to a common output shaft, such for instance as an air-screw shaft, whereby vibrations arising in 1 either crank-shaft are prevented or largely prevented from affecting the other crank-shaft or the output shaft.

A further object is to provide such an engine including one or more pairs of cylinders, each having a common combustion chamber, in which the compression ratio can be varied by altering the phase relationship of the crank-shafts while the engine is running, for example to prevent detonation when the charging pressure is temporarily increased for the purpose of boosting the power output above the continuous full-load rating.

Another object is to provide, in such an engine having one or more pairs of cylinders, each having a common combustion chamber, resilient coupling and damping means serving both to reduce or prevent the transmission of vibrations arising in the crank-shafts and to vary automatically the phase relationship of the crank-shafts and thereby the compression ratio with variation in load.

Yet another object is to provide in such an engine having one or more pairs of cylinders, each having a common combustion chamber, a servooperated phase-adjusting coupling means in the gearing that constrains the crank-shafts to rotate at equal speeds.

A further object is to provide an engine operating on the two-stroke cycle and provided with spark ignition means, which is capable of having its power output temporarily boosted.

Further objects and advantages of this invention will be apparent from the following description of embodiments thereof illustratively exemplified in the accompanying drawings, in whichFig. 1 is a diagrammatic side elevation of an aero engine, Fig. 2 is a diagrammatic plan of the same engine, Fig. 3 is a diagrammatic front end elevation of the same engine, Fig. 4 is a cross section to a larger scale through a pair of cylinders, taken for example on the line 4--4 in Fig. 1, Fig. 5 is a section of a part of the engine to a still larger scale, taken on the line -5 in Fig. 4, Fig. 6 is an under side elevation of a part of the engine, developed on the line 6-6 in Fig. 4, Fig. 7 is a sectional plan of the turbo-blower assembly, taken on the line 1-1 in Fig. 1, Fig. 8 is a section to a larger scale of a part of Fig. 7, Fig. 9 is a sectional side elevation of coupling 0 and reduction gearing, ig. 10 is a section on the line 10--10 in Fig. 9, Fig. 11 is a section of a modified part of the gearing, Fig. 12 is an electrical circuit diagram of con5 trol mechanism for the part shown in Fig. 11, and Fig. 13 is a diagram of parts associated with the turbine.

The example shown in Figs. 1-10 is a two-stroke aero engine having two crank-shafts and twelve pairs of working cylinders, the two cylinders of each pair having a common combustion chamber.

Referring to Figs. 1 to 6 a crank-case 20 is split on ,he longitudinal vertical middle plane of the engine and in it are journalled two six-throw crank-shafts 21 and 22. These crank-shafts are coupled by gearing in a gear-case 23 which constrains them to rotate at equal speeds in opposite directions. The crank pins of each shaft* 3o are displaced in the following order at angles of 60 deg. from each other: Nos. 1, 4, 2, 6, 3, 5, the directions of displacement being opposite in the two shafts. To each side of the crank-case 21 are secured six light alloy cylinder blocks 24 each aV. containing two cylinder bores 25 and 26 defined by hardened liners. The axes of these bores are inclined to each other at 15 deg. in such a manner that their head ends are closer together than the ends nearer the crank-shafts. Each cylinder block has a light alloy head 21, which is recessed to form a combustion chamber 28 common to the two cylinders of the block.' A fuel-injection nozzle 29 and two sparking plugs 30 are fitted in each head 21 and open into the combustion chamber.

The bore 25 of each block accommodates a piston 31 controlling exhaust ports 32. The pistons 31 on the starboard side of the engine are connected to the respective crank-pins of the shaft 21 by master connecting rods 33, while the pistons 31 on the port side are connected to the respective rods 33 by slave connecting rods 34.

In a similar way the bore 26 of each block accommodates a piston 35 controlling scavenging ports 65 36. The pistons 35 on.the starboard side of the engine are connected to the respective crankpins of the shaft 22 by master connecting rods 37, while the pistons 35 on the port side are connected to the respective rods 37 by slave connecting rods 38. The normal phase relationship of the two crank-shafts may be such that the crankpins of the shaft 21 that controls the exhaust timing lead by 30 deg. the corresponding crank pins of the shaft 22 that controls the scavenge timing as shown in Fig. 4, where the directions of rotation are indicated by arrows. The depths of all the ports 32 and 30 and their positions relative to the ends of the respective cylinder bores may be uniform and such that the duration of opening of any port represents 145 deg. of crank rotation.

The engine is scavenged and charged with air by a centrifugal blower 40 directly coupled to an exhaust-gas-driven impulse turbine 49 (Figs. 1 and 2). As shown in Fig. 7 the blower has two impellers 42 and 43 arranged back to back and of unitary construction. These impellers draw air from intake ports 44 and 45 in the blower casing and discharge into volute chambers 46 and 47 leading respectively to port and starboard delivery elbows 48 and 49. These connect respectively with air manifolds i00 and ! I provided with branches 102 communicating with the scavenging ports 36.

A tubular shaft 50 is bolted to the hub 51 of the impellers 42 and 43 and to the hub of a turbine rotor 52 having a single row of impulse blading 53. Two ball bearings 54 capable of taking journal and thrust loads have their inner races fast on. a spigot 55 on the rotor 52 and their outer races fast in a bearing housing 56 forming a part of the turbine frame 57 and sealed with respect to the rotor 52 by a labyrinth oil-seal 58. Differential expansion of the fixed and rotary parts is accommodated by the bearing means at the blower end which are. shown in detail in Fig. 8. Two ball bearings 59 have their inner races fast on a sleeve 60 fixed to the hub 51 while their outer races are mounted in a ring 61 which has a close sliding fit in a sleeve 62 fixed in a boss 63 of the blower casing. A labyrinth oil-seal 64 is formed between one end of this sleeve and a ring 65 clamped with the inner bearing races on the rotary sleeve 60 by nuts 66. The other end of the sleeve 61 is provided with an inturned flange 67 against which abut compression springs 68 held in a ring 69 reacting against the inner end of the fixed sleeve 62. Differential expansion is accommodated by sliding of the ring 61 in the sleeve 62, the springs 68 ensuring a constant axial clearance in the labyrinth oil-seal 64.

The turbine is provided with a nozzle-box 103 into which debouch twelve exhaust pipes 104 leading respectively from the individual exhaust ports 32. These pipes are so arranged that the differences between their lengths are slight.

One form of the gearing contained within the gear case 23 is shown in Figs. 9 and 10; the various ball and roller bearings are included, but 'r their housings and the case are omitted. A gearwheel 70 is rigid with a reduction gear pinion 7i, these two elements being journalled in bearings 72, 73 and 74 coaxially with the crank-shaft 22.

An air-screw shaft 75 is journalled in bearings 7 76, 77 and 78 co-axial with the crank-shaft 21 and is splined to a reduction gear-wheel 79 meshing with the pinion 1 . A gear wheel 80 is journalled on bearings 82 and 82' co-axially with the crank-shaft 21 and meshes with the gear 7I wheel 70. The gear wheels 78 and 80 are coupled respectively to the crank-shafts 22 and 21 by damped resilient couplings serving to reduce the transmission of torsional vibration from the crank-shafts to the gearing. As these couplings are similar in design, only that between the crank-shaft 22 and the gear wheel 70 will be described in detail. A hub 81 is splined to the crank-shaft 22 and provided with radial vanes 108 and a flange 83. The interior of the gearwheel 70 is hollow and provided with vanes 84 alternating with the vanes 108. The flange 83 is sealed with respect to the wheel 70 by a ring 85 of synthetic oil-resisting rubber having projections 86 between the vanes 108 and the rim of the wheel 70. Pads 87 of similar rubber are disposed between the vanes 84 and the hub 81 and are provided with flaps 88 which co-operate with oil inlet ducts 89 to form non-return valves. The ducts 89 are supplied with oil from a centrifugal collecting channel 90. Rebound compression springs 9 are disposed between the trailing faces of the vanes 108 and the leading faces of the next following vanes 84, and drive como2 pression springs 92, which are stiffer than the springs 91, are disposed between the trailing faces of the vanes 84 and the leading faces of the next following vanes 108. In operation, the chambers between the vanes become filled with 3o oil entering through the duct 89, the springs providing the resilient driving connection and the resistance imposed by the rubber parts 86 and 87 to the escape of oil providing the necessary damping. The resilient coupling in the wheel 80, in this example, has a lower torsional stiffness than the coupling in the wheel 710 for a purpose which will be hereinafter discussed.

The gearing also includes an auxiliary drive wheel 96 mounted rigidly with the wheel 80 and meshing with a pinion 97 integral with a timing shaft 98 which drives dual ignition contactbreaker and distributor units 93 (Figs. 1 and 3) and a battery of fuel-injection pumps 95. Twelve of these pumps feed the injection nozzles 29 respectively by pipes 94, which are shown broken away. Two additional pumps are provided, delivering to pipes 99, for a purpose which will be mentioned hereinafter. The quantity of fuel delivered at each stroke by the twelve pumps feeding the pipes 94 is controllable in the conventional manner by a control lever 105, and the fuel delivery of the two additional pumps feeding the pipes 99 is independently controllable by a lever 106. The pipes 99 lead respectively to two r: ring pipes 106' (Fig. 13) encircling the turbine casing 57 and connected by branches 107 to fuel injection nozzles 109 inserted in the exhaust pipes 104 near the points where they debouch into the nozzle box 103. Each ring pipe supi plies nozzles on alternate exhaust pipes.

This engine operates as follows. Exhaust gases passing through the pipes 104 to the turbine 41 maintain the turbine rotor in rotation and the turbine drives the blower impellers 42 .i and 43 which draw air from the atmosphere through the inlets 44 and 45 and deliver it under increased pressure to the air manifolds 100 and 101. It will be assumed that the charge In a'pair of cylinders has just been ignited by the sparko ing plugs 30 and that the pistons are moving on their out-stroke from the position shown inFig. 4. The piston 31, being in advance of the piston 35, uncovers the exhaust port 32 while the scavenging port 31 is still closed, and the presS sure in the cylinders falls as the exhaust gases pass through the appropriate pipe 104 to the turbine. When the pressure in the cylinders has fallen sufficiently, the piston 35 uncovers the scavenging port 36, and compressed air from the manifold 100 or 101 sweeps through the cylinders, driving substantially the whole of the exhaust gases through the exhaust port 32. Next the piston 31 closes the exhaust port 32 while the scavenging port 36 is still open, and the cylinders are supercharged to an extent dependent on the air pressure in the air manifold. The piston 35 then closes the scavenging port 36 and the compression stroke occurs. During this stroke the appropriate fuel pump operates to inject a charge of a relatively volatile fuel through the nozzle 29 into the turbulent mass of air compressed in the combustion chamber where it is ignited by the sparking plugs 30.

The power output of the engine is regulated by varying the delivery of the fuel pumps to the nozzles 29 by means of the control lever 105.

When the engine is running under light load, the phase displacement between the crank-shafts is the minimum, the compression ratio is the maximum and consequently the fuel consumed per 2s horse-power-hour is the minimum. As the fuel supply is increased and the engine torque consequently rises, the resilient coupling associated with the crank-shaft 21 that controls the exhaust ports yields more than the stiffer resilient 3a coupling associated with the crank-shaft 22 that controls the scavenge ports, so that the phase displacement between the two crank-shafts increases. Consequently the compression ratio decreases, as is required to prevent detonation, and 31 the exhaust port opens and closes earlier in the working cycle of each pair of cylinders. As the expansion ratio in the working cylinders is reduced, the exhaust gases will contain more residual energy per unit weight and the turbine 4 will therefore run faster so that the blower operates to increase the amount of supercharge.

The two additional fuel pumps feeding the injection nozzles 109 in the exhaust pipes serve temporarily to increase the power output of the engine to substantially more than its normal maximum continuous rated output, for example for the purpose of taking off a heavily loaded aircraft. Since at all times part of the gases leaving the exhaust ports of the working cylinders consists of excess air, this air serves to burn the fuel injected through the nozzles 109 when the control lever 106 is actuated. In this way the available heat drop in the exhaust gases is increased, and consequently the power available for driving the blower so that the charging pressure of the engine and its net power output are increased.

The engine hereinbefore described may be modified by substituting positive means, in place of the resilient means, for varying the phase relationship of the two crankshafts. One form of such positive means is shown in Fig. 11 associated with the connecting gear wheel 70A and the crank-shaft 22A, which correspond to the parts 10 and 22 hereinbefore described. The resilient damped coupling between the other crankshaft 21 and the gear wheel 80 that meshes with the wheel 70A is relatively stiff. The wheel, 17A can be advanced and retarded relatively to the shaft 22A by the servo-mechanism now to be described. A hub 120 having internal helical splines 121 is slidably engaged with co-operating splines 122 on the shaft 22A. A rim 123 is provided with straight external splines 124 slidably engaging with internal splines 125 in the bore of the wheel 10A. The hub 120 and the rim 123 are provided with interlaced cylindrical flanges 126 and 121 and rubber rings are disposed in the annular spaces so formed and bonded to the hub and rim portions, forming a relatively stiff resilient coupling. A ball thrust bearing 129 has its inner race clamped to the hub 120 by a bracket ring 130 secured to this hub by screws 131. The outer race of the bearing 129 is rigid with a ring 132 having an external screw thread 133 cooperating with an internal screw thread 134 in the shaft of the pinion 71 A. A crown wheel 135 fixed by screws 136 to the ring 132 meshes with bevel pinions 137 integral with shafts 138 journalled in brackets 139 on the ring 131. Bevel wheels 140 fixed to the shafts 138 mesh with a bevel pinion 141 journalled by bearings 146 and 141 in brackets 142 on the ring 138.

The pinion 141 is integral with a tubular externally splined shaft 143 on which is slidably engaged an internally splined element 144 of a universal coupling 145. The bearings of the pinion 141 are retained by a washer 148 and a bar 149 clamped together by a hollow bolt 150 the bar 149 passing through a transverse slot 151 in the shaft 143. The joint 145 is coupled by a tubular shaft 152 and a second universal joint S153 to the hollow shaft 154 of a reversible serieswound electric motor 155 which is fixed within the shaft of the pinion 1 A for rotation therewith. Within the motor casing are provided a reversing contactor and a limit switch, the external electrical connections being made through slip rings 156, 157 and 158. The limit switch is actuated by a rod 159 slidably mounted in the hollow motor shaft and in the bore of the bolt 150 and provided with abutments 160 and 161 o co-operating with the ends of this bolt. The electrical control mechanism is shown diagrammatically in Fig. 12. A battery 162 has one terminal earthed and the other terminal connected to a brush 163 co-operating with the slip Sring 156 which in turn is connected to a contact blade 164 of a normally-open contactor.

The contact blade 164 can connect alternatively with conductors 165 and 166 which respectively ,include the two contact breakers of the limit switch 168 and connect with the terminals of the motor field coil, 167. The armature 169 of the motor is connected at one side to earth and at the other side by a conductor 110 to a second - contact blade 171 of the contactor. The blade 171 can connect alternatively with conductors 172 and 173 leading to the terminals of the field coil 167. A control switch blade 174 is connected to the live terminal of the battery and can contact alternatively with conductors leading to brushes 175 and 176 co-operating respectively with the slip rings 157 and 158 which are connected to earth through the energising coils 17l and 178 of the contactor.

This mechanism operates as follows. The parts will be assumed to be in the configuration shown in Figs. 11 and 12, that is to say the relative angular position of the wheel 10A and the shaft 22A is at the limit of the range of adjustment ro in which the exhaust-controlling crank-shaft 21 has the minimum phase advance over the scavenge-controlling crank-shaft 22A. Thus one contact breaker of the limit switch 168 is open.

When the control blade 1174 is moved to the r5 right, current flows through the elements 175, 157 and 177 to earth and rocks the contactor armature clockwise, so that the blade 864 contacts with the conductor 165 and the blade T78 with the conductor 073. Current now flows through the following circuit: NSO, I56, 164, 168 (closed contacts), 185, , 167, Il, , 170 and S16 to earth. The motor thus begins to rotate and through the reduction gearing rotates the ring 132 relatively to the shaft of the pinion 7IA in such a direction that this ring is constrained by its screw-thread to move to the left (as seen in Fig. 11). Since the assembly of hub 208 and rim 123 is coupled to the ring 132 by the thrust bearing 129, this assembly is also slid to the left, the helical splines 12 and 122 co-operating to vary the angular relationship of the wheel 70A and the shaft 22A and thus increase the phase advance of the crank-shaft 21 relatively to the crank-shaft 22A. The rod 859 is also free to move to the left so that the limit switch can assume its mid position in which both contact breakers are closed. If the control blade 174 is now returned to its mid position, the motor 155 stops. If however the control blade is kept to the right, as the parts approach the other'limit of their range of adjustment, the head of 'the bolt 150 strikes the abutment 160 on the rod 159 and opens the limit switch contact breaker in the conductor 165 so that the motor stops. Adjustment in the reverse direction is effected by moving the control blade 114 to the left so that current flows through the elements 176, 158 and 178 to earth and rocks the contactor armature counterclockwise, so that the blades 164 and 171 contact respectively with the conductors 166 and 3 172. Current now flows through the following circuit: 163, 156, 164, 168, 166, 167, 172, 171, 110 and 169 to earth, the direction of flow through the field coil 167 being opposite to that occuring when the control blade 174 was moved to the 4 right. The motor accordingly runs in the reverse direction, causing the slidable elements of the adjusting gear to move back to the right. The adjusting movement can be stopped at any desired point, and resumed in either direction. 4 The control blade 171 is capable of automatic actuation in response to variation in charging pressure, for instance on operation of the boosting fuel nozzles provided in the exhaust pipes leading to the turbine. Such an automatic con- 6 trol is shown in Fig. 12. The control blade 174 is connected by a rod 110 to the movable wall of a spring-loaded anaeroid capsule Ill having thd.other wall fixed. The capsule is contained in an air-tight chamber 112 communicating 6 through a damping restriction 113 with a duct 114 leading to one of the air manifolds, say 100.

The duct may be provided with an isolating valve 15. When the valve 115 is open and the manifold pressure exceeds a predetermined value, 6 the capsule III is contracted and moves the blade 174 to the right to energise the slip ring 157, so that the exhaust-controlling crank-shaft 21 is given the maximum lead in relation to the scavenge-controlling crank-shaft 22A and the 6i compression ratio is correspondingly reduced.

When the manifold pressure thereafter falls to a predetermined value, the capsule 1I expands and moves the control blade 174 to the left so that the slip ring 158 is energised and the phase 7( difference between the crank-shafts is reduced to its minimum value.

I claim: 1. An internal-combustion engine including a plurality of pairs of cylinders, the two cylinders of each pair having a common combustion chamber, pistons in said cylinders, two crank-shafts operatively connected respectively to the two pistons of each pair of cylinders, a supercharger for charging said cylinders, gearing constraining said crank-shafts to rotate at equal speeds, and means for temporarily boosting the power output of said engine and including a control member operation of which serves to increase the delivery pressure of said supercharger and means associated with said gearing for varying while the engine is running the angular relationship of said crank-shafts and thereby reducing the compression ratio of said pairs of cylinders when said delivery pressure is increased.

2. An internal-combustion engine including a plurality of pairs of cylinders, the two cylinders of each pair having a common combustion chamber, pistons in said cylinders, two crank-shafts operatively connected respectively to the two pistons of each pair of cylinders, a supercharger for charging said cylinders, means for controlling the delivery pressure of said supercharger, a power-output shaft drivably connected to said 2. crank-shafts by gearing which constrains said crank-shafts to rotate at equal speeds and which includes a resilient connection capable of yielding under torque in one of said crank-shafts and thereby varying the phase relationship of said crank-shafts automatically in response to variations in power output.

3. An internal-combustion engine including a pair of cylinders having a common combustion chamber, pistons in said cylinders, two crank5 shafts operatively connected with said pistons respectively, and' gearing constraining said crank-shafts to rotate at equal speeds, said gearing including two power-transmitting elements normally rotatable as one and constrained to 0 move helically with respect to each other when relatively displaced in the axial direction, a servomotor having a body constrained to rotate with one of said elements and an output member operatively connected to the other of said elements 5 for relatively displacing said elements axially, and a reversing controller for said servo-motor.

4. A two-stroke internal-combustion engine including a plurality of pairs of cylinders, pistons in said cylinders, the two cylinders of each pair o having a common combustion chamber and respectively piston-controlled exhaust and scavenging ports, two crank-shafts operatively associated respectively with the pistons controlling said exhaust ports and the pistons controlling 5 said scavenging ports, a supercharger, a duct communicating continuously between said supercharger and said scavenging ports, control means operable for temporarily boosting the delivery of said supercharger, gearing constraining said 0 crank-shafts to rotate at equal speeds and including means operating in response to increase in delivery of said supercharger for increasing while the engine is running the phase difference of the pistons associated respectively with said 5 crank-shafts, and thereby reducing the compression ratio and advancing the exhaust timing of said pairs of cylinders.

5. A two-stroke internal-combustion engine including a plurality of pairs of cylinders, each pair having a common combustion chamber, and one cylinder of each pair having an exhaust port while the other has a scavenging port, pistons in said cylinders controlling said ports, two crankshafts actuating respectively said exhaust-controlling pistons and said scavenging-controlling pistons, gearing constraining said crank shafts to operate with a phase relationship such that the exhaust-controlling piston of each pair leads the scavenging-controlling piston, means for introducing through said scavenging ports air in excess of that required for combustion for the purpose of scavenging and thereafter supercharging said cylinders, control means operable for temporarily boosting the supercharger pressure, a fuel-injector in each of said combustion chambers, metering and distributing means for causing said injectors to operate during the respective compression strokes, spark ignition means for' igniting the fuel so injected and means associated with said gearing and capable of increasing the phase displacement of said pistons and thereby reducing the compression ratio of said pairs of cylinders in response to increase in the supercharging pressure.

6. An internal-combustion engine comprising two rows of cylinders, two multi-throw crankshafts disposed parallel to each other, pistons in one of said rows of cylinders operatively connected to one of said crank-shafts, pistons in the other of said rows of cylinders operatively connected to the other of said crank-shafts, an output shaft, coupling and reduction gearing between said three shafts for constraining said crank-shafts to rotate at equal speeds and said output shaft to rotate at a lower speed, said gearing including two gear wheels connected respectively to said crank-shafts by damped resilient couplings.

7. An internal-combustion engine as claimed in claim 6 and comprising auxiliaries required to be actuated in timed relation to said crankshafts, wherein a timing shaft for driving said auxiliaries is drivably connected to said gearing at a point therein on the output-shaft side of said Camped resilient couplings. 8. An internal-combustion engine including a pair of cylinders having a common combustion chamber, pistons in said cylinders, two crankshafts operatively connected with said pistons respectively, and gearing constraining said crank-shafts to rotate at equal speeds, said gearing including two power-transmitting elements, a third element capable of moving axially relatively to said two elements and connected to said two elements respectively by axially and helically disposed meshing portions, a servo-motor having two relatively movable parts one of which is fixed to one of said two elements and the other of which is operatively connected to said third element for axially moving the same, and a reversing controller for said servo-motor.

9. A'T internal-combustion engine including a pair of cylinders having a common combustion chamber, pistons in said cylinders, two crank shafts operatively connected with said pistons respectively, gearing constraining said crankshafts to rotate at equal speeds, said gearing including a hollow third shaft co-axial with the first of said crank-shafts, a gear wheel on said third shaft meshing with a gear wheel conStrained to rotate with the second of said crankshafts, a coupling member slidably splined to said first crank-shaft and to said third shaft by splined connections at least one of which is helically disposed, a servo-motor having a body fixed within said third shaft and an output shaft ro-" tatable relatively to said body, a screw-threaded ring co-operating with a screw thread in said third shaft, a thrust bearing connecting said ring to said coupling member, auxiliary gearing drivably connecting the output shaft of said servomotor to said ring for rotating the latter relatively to said third shaft, and a reversing controller for said servo-motor.

ACHILLE CHARLES SAMPIETRO.