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(11) | EP 0 454 627 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Engine with double-acting pistons and without connecting rods |
| (57) An internal combustion engine comprises a crank-case (7), a cylinder (21), a piston
(1) reciprocatingly slidable in said cylinder, an output shaft (11) and means for
transforming the reciprocating motion of the piston into a rotating motion of the
output shaft (11). According to the invention, the reciprocating motion of the piston
is transformed into a rotating motion of the shaft by means of a bypocycloid gear
transmission (5, 6) comprising a pair of externally toothed gears (5) connected to
each other by means of a curved shaft (4) and a pair of internally toothed gears (6)
solid to the crank-case (7). During reciprocating motion of the piston in the cylinder,
the externally toothed gears roll along the internally toothed gears and transmit
their motion to the output shaft by means of a flywheel (10). |
[0001] The invention refers to an internal combustion engine comprising a crankcase, a cylinder, a piston reciprocatingly slidable in said cylinder, an output shaft and means for transforming the reciprocating motion of the piston into a rotating motion of the output shaft.
[0002] Known engines of this type are provided with a connecting rod hinged at one end to the piston by means of a pin. The other end of the connecting rod is hinged to a crank which is part of the engine output shaft. These members transform the reciprocating motion of the piston into a rotary motion of the output shaft. The arrangement is such that enormous side thrusts are exerted by the piston in the cylinder. This calls for heavy oversizing of the engine members. On the other hand, this causes an increase of the forces of inertia acting on the moving parts of the engine.
[0003] It is therefore an object of the invention to provide an internal combustion engine with a more efficient kinematic chain for transforming the reciprocating motion of the piston into a rotary motion of the output shaft.
[0004] According to the invention this is obtained providing a hypocycloid gear transmission which connects the piston to the shaft. The hypocycloid gear transmission is known per se, and is described for example by I. Artobolevski "Les mecanismes dans la technique moderne", Moscow 1976, vol.3, page 143. This known kinematic mechanism, however, has never been applied in internal combustion engines having a reciprocating moving piston.
[0005] It is known that the internal combustion engines and especially the diesel engines, would significantly increase their efficiency were they able to operate with double-acting pistons. The reason for their missing application is to be sought in the connecting rod systems currently used for transforming the reciprocating motion of the pistons into a rotary motion of the engine axis.
[0006] According to the invention, such drawback is overcome, as the usual connecting rod mechanism is replaced by a hypocycloid gear transmission, which makes it possible to use a double-acting piston, i.e. a piston provided with two crowns, and sliding in a cylinder which is provided with two heads, said cylinder and said piston forming two opposite chambers. This arrangement enables various advantages be achieved, which will be described later on.
[0007] In a possible embodiment of the invention, either with a single-acting piston or a double-acting piston, the hypocycloid gear transmission comprises a first externally toothed gear meshing with a second internally toothed gear. Said second internally toothed gear has a pitch diameter which is twice the pitch diameter of the first externally toothed gear, and the first toothed gear is solid with a pin supported by said piston, while the second internally toothed gear is solid with the crankcase of the engine.
[0009] As mentioned above, the present invention makes it possible to use double-acting pistons in usual internal combustion engines. Such solution exhibits many advantages with respect to the currently known internal combustion engines, in which the piston reciprocating motion is transformed into rotary motion by known connecting rod assemblies. Among these, the following advantages should be pointed out:
1. Far higher thermal-mechanical efficiency, also because the force necessary to compress the mixture acts directly on the piston, without passing through the crank and the big end of the connecting rod of the engine shaft, as it is the case in the current engines provided with connecting rods.
2. A dynamic balance and thus a stability which is unattainable with the current connecting rod assemblies, also because the piston acts directly and, throughout its stroke, axially to the cylinder with harmonic motion.
3. A significant weight reduction of the kinematic chain of elements involved in the reciprocating motions, as no side thrusts, nor concomitant 2nd-degree forces of inertia are present.
4. According to the above, a substantial reduction in dimensions, weight, complexity of the same kinematic members and in the whole engine block.
5. A consequent significant economy in the costs of production and maintenance.
[0010] An embodiment of the invention is described hereinafter only by way of illustrative but not limiting example, with reference to the attached drawing which shows:
Fig. 1 a longitudinal section taken on line I-I in Figs. 2 and 3;
Fig. 2 a longitudinal section taken on line II-II in Figs. 1 and 3;
Fig. 3 a cross section taken on line III-III in Figs. 1 and 2;
Fig. 4 a cross section similar to Fig. 3 in a different position of the piston;
Fig. 5 a modified embodiment of the engine according to the invention;
Fig. 6 a longitudinal section of a two-cylinder engine; and
Fig. 7 a cross-section according to line VII-VII in Fig. 6.
[0011] The mechanism is essentially made up of a cylinder 21 having two opposite heads 20 for a double-acting operation. For this purpose, sliding within the cylinder 21 is a body 1 constituting a double-acting piston having two crowns 1C and a joining skirt 1A, which delimits a piston-lightening cavity 1D. Said skirt 1A is provided with two opposite apertures 1B. The cylinder is provided with two opposite longitudinal slots 21B which correspond to the apertures 1B in the piston skirt 1A.
[0012] The double-acting piston 1 has a bush 2 supported within the cavity 1D. In the central part of the bush 2 a roller or bushing bearing 3 is mounted, which supports a pin 4. As clearly shown in Fig. 1, the pin 4 is provided with two opposite end portions on which opposite externally toothed gears 5 are solid. The axes of the gears 5 are aligned to each other but out of alignment with respect to the central portion of the pin 4, i.e. the portion supported in bearing 3.
[0013] In the embodiment shown in the enclosed drawing, each externally toothed gear 5 meshes with a relevant internally toothed gear 6. The pitch diameter (and thus the number of teeth) of each internally toothed gear 6 is twice the pitch diameter (and the number of teeth) of the relevant externally toothed gear 5. Each internally toothed gear 6 is solid with the crankcase 7 of the engine. Each externally toothed gear 5 is provided with a pin 8, which is coaxial to the relevant gear 5 and projects outwardly, i.e. opposite the piston 1. Each pin 8 is fitted to a flange or small flywheel 10 which is solid with a shaft 11 of the engine, a bearing 9 being provided to support said pin 8.
[0014] The pin 4 may be formed into two parts mostly mating in correspondence of the bush 2. The pin 4 goes through the apertures 1B and the slots 21B to support the gears 5 outwardly of cylinder 21 and into meshing engagement with the internally toothed gear 6.
[0015] The functioning of the engine is the following: The double-acting piston 1 moves with a reciprocating motion within cylinder 21, while the two chambers formed between the cylinder heads 20 and the relevant piston crowns 1C serves alternatively as compression and expansion chambers for the air-fuel mixture. During the reciprocating movement of the piston 1, the bush 2 is also moved with a reciprocating motion along the cylinder axis. Being the externally toothed gears 5 offset with respect to the axis of bush 2, and meshing with the internally toothed gears 6, the reciprocating motion of the central portion of pin 4 causes the externally toothed gears 5 to roll along the relevant internally toothed gears 6. The axis of each externally toothed gear 5 is thus made to rotate around the axis of the engine shaft 11. The link between gear 5 and shaft 11 obtained by pin 8 and flywheel 10 transmits the rotation of the gear 5 around the axis shaft 11 to the engine shaft 11 itself.
[0016] In the internal combustion engine of the invention, as the reciprocating motion of the piston is transformed into a rotary motion by the hypocycloid mechanism itself without the interposition of connecting rods, the piston moves with harmonic motion, and there are no side thrusts nor concomitant 2nd-degree forces of inertia. Moreover, as the two chambers formed by the cylinder 21, the heads 22 and the piston crowns 1C are in opposite relationship, the pin 4 which drives into rotation the engine shaft 11 is acted upon only by the useful power, while the power required for the compression of the mixture into the opposite compression chamber is transmitted directly by the same piston.
[0017] In a solution embodying a two-stroke-cycle internal combustion engine, the piston may be utilized, on one side, as a motive piston and, on the other, as the piston for the compression of the mixture. In such case, the diameters of the two piston portions may be different from one another.
[0018] This is shown, by way of example, in Fig. 5. In this example, the lower cylinder portion and the relevant lower piston portion have a diameter which is smaller than the upper portions. Moreover, the piston is formed by two crowns 1C′ each provided with a small skirt 1A′. The two crowns 1C and relevant skirts 1A are connected by a central rod 25 which has an X-shaped cross section. The seat for the bush 2 is formed by said central rod 25. The other elements, in particular the gears of the bypocycloid transmission, are the same as described with reference to Figs. 1 to 3 and are designated with the same reference numbers.
[0019] The invention is susceptible of various modifications and changes, for example in relation to the number of cylinders, to the application in two- or four-stroke-cycle engines, in OTTO or Diesel engines, yet all falling within the scope of the inventive idea. While the embodiment shown in the drawing provides for two gears 5 linked to two opposite flanges 10 in such a way that two engine shaft portions 11 can be driven into rotation by the same piston 1, it is possible to provide only one engine output shaft portion, while the opposite gears 5 and 6 are used only for balancing the forces acting on the pin 4.
[0020] In the case two shafts 11 are provided (Figs. 1 to 5), one shaft may be used as output shaft from which power is taken, while the other shaft 11 is used for driving auxiliary members of the engine, such as an alternator or similar engine members. In this case the two shafts may have different cross sections, as shown in Figs. 1 to 4.
[0021] Figs. 6 and 7 show an arrangement with two cylinder-piston units, generically indicated at 30 and 31, which form a multiple-cylinder engine. Each unit 30, 31 is similar to the embodiment of Figs. 1 to 4 and similar or corresponding parts are designated with the same reference numbers increased by 100.
[0022] Each unit 30, 31 comprises a cylinder 121 having two opposite heads (not shown), wherein a corresponding piston 101 having two crowns 101C is slidingly housed. The two crowns of each piston 101 are connected by a central rod 125. The central rod 125 is made in two parts 125A, 125B connected by screws 126. Between said two parts 125A, 125B there is housed a bush 102 and a bushing bearing 103. The latter supports a pin 104 which is provided with two opposite end portions on which opposite externally toothed gears 105 are solid. The axes of the two gears 105 of each unit 30, 31, respectively, are aligned to each other, but out of alignment with respect to the axis of the bushing bearing 103. Each externally toothed gear 105 meshes with corresponding internally toothed gears 106 which, in this particular embodiment, are housed within the corresponding cylinder 121, and are solid therewith.
[0023] Each externally toothed gear 105 is provided with a pin 108 which is coaxial with the relevant gear 105 and is supported by a bearing 109 fitted into a relevant flywheel 110 which is solid with a shaft 111 or 112 respectively. The two shafts 112 project toward each other and are connected to each other and to a gear 135 which meshes with a further gear 136 supported by an output shaft 137 (Fig. 7). The shafts 111 can be used to power auxiliary members of the engine. This arrangement avoids the passage of the useful power through the whole shaft 111, 112, 104. It is however feasable to omit the gears 135, 136, to connect the shafts 112, 112 directly to each other and to take the power from one of the two lateral shafts 111. In this case, if the output shaft is the left-hand shaft 111, the useful power generated by unit 31 must pass through the pin 104 and the shafts 111, 112 of the unit 30.
1. Internal combustion engine comprising a crank-case (7), a cylinder (21; 121), a piston
(1; 101) reciprocatingly slidable in said cylinder, an output shaft (11; 112) and
means (4, 5, 6, 8, 10; 104, 105, 106, 110) for transforming the reciprocating motion
of the piston into a rotating motion of the output shaft (11; 112), characterized
in that said means (5, 6, 8, 10; 105, 106, 108, 110) for transforming the reciprocating
motion into a rotating motion comprise a hypocycloid gear transmission (5, 6; 105,
106).
2. Internal combustion engine according to claim 1, characterized in that said piston
(1; 101) is a double-acting piston provided with two crowns (1C; 101C), and that said
cylinder (21; 121) is provided with two heads (22), said cylinder (21; 121) and said
piston (1; 101) forming two opposite chambers.
3. Internal combustion engine according to claim 1 or 2, characterized in that said hypocycloid
gear transmission comprises a first externally toothed gear (5; 105) meshing with
a second internally toothed gear (6; 106), that said second internally toothed gear
(6; 106) has a pitch diameter which is twice the pitch diameter of the first externally
toothed gear (5; 105), that said first toothed gear (5; 105) is solid with a pin (4;
104) supported by said piston (1; 101), and that the second internally toothed gear
(6; 106) is solid with the crankcase (7) or with the cylinder (121) of the engine.
4. Internal combustion engine according to claim 3, characterized in that housed within
the piston (1; 101) is a bush (2; 102) supporting said pin (4; 104), said pin (4;
104) having two opposed ends, on which ends two externally toothed gears (5; 105)
are solid, the axes of said externally toothed gears (5; 105) being coaxial to each
other and out-of-alignment with respect to the axis of the bush (2; 102).
5. Internal combustion engine according to claim 3 or 4, characterized in that at least
one end of said pin (4; 104) is engaged to the output shaft (11; 112) of the engine.
6. Internal combustion engine according to claim 5, characterized in that said at least
one end of said pin (4; 104) is rotatively engaged in an off-center seat (9; 109)
formed in an enlargement (10; 110) of the output shaft (11; 112).
7. Internal combustion engine according to claim 6, characterized in that said enlargement
(10; 110) forms a flywheel.
8. Internal combustion engine according to one or more of the preceding claims, characterized
in that to said piston (1; 121) two shafts (11, 12; 111, 112) are combined, one of
which forms the output shaft of the engine, and the other drives auxiliary members
of the engine.
9. Internal combustion engine according to one or more of claims 2 to 8, characterized
in that said cylinder (21) has two cylindrical portions having two different diameters,
and that the double-acting piston (1) is formed by two portions having correspondingly
different diameters.
10. Internal combustion engine according to claim 2 and one or more of claims 3 to 9,
characterized in that said double-acting piston (1) has two crowns (1C) connected
by a skirt (1A), said skirt (1A) being provided with two apertures (1B) through which
the pin (4) is made to pass.
11. Internal combustion engine according to claim 2 and one or more of claims 3 to 9,
characterized in that said double-acting piston (1; 101) has two crowns (1C; 101C)
connected by a central rod (25; 125), said central rod supporting said pin (4; 104).
12. Internal combustion engine according to claims 3 and 11, characterized in that said
central rod (125) is formed by two parts (125A, 125B), said two parts forming a seat
for a bearing (103) supporting said pin (104).
13. Internal combustion engine according to one or more of the preceding claims, characterized
in that the hypocycloid gear transmission (105, 106) is housed within the cylinder
(121).
14. Internal combustion engine according to one or more of the preceding claims, characterized
in that it comprises at least two cylinder-piston units (30, 31), and that the power
is taken from a gear (135) connected to the engine shaft (112) and placed between
two adjacent cylinder-piston units (30, 31).
15. Internal combustion engine according to one or more of claims 2 to 11, characterized
in that said engine is a two-stroke-cycle engine, and that the double-acting piston
is used on one side as a motive piston and on the other side as a compressor for the
mixture.