RECIPROCATING INTERNAL COMBUSTION ENGINE WITH HYPOCYCLOID CRANK MECHANISM

Abstract: A reciprocating internal combustion engine comprises a crankshaft (4) rotatable relative to the engine block (2) and having at least one crank (4a) with which a piston (6a) is associated for sliding in a cylinder (5a) connected to the block (2). Each piston (6a) is connected to the respective crank (4a) by means of a hypocycloid crank-mechanism device which includes a principal eccentric (10a) rotatable eccentrically relative to the crank (4a) and surrounded by a principal annular member (8a) which is rotatable coaxially relative to the principal eccentric and from which a connecting element (7a) of the respective piston (6a) extends.

Description: RECIPROCATINGINTERNALCOMBUSΗONENGINEWITH HYPOCYCLOIDCRANKMECHANISM The present invention relates to reciprocating internal combustion engines in which the pistons are connected to the drive shaft by means of a so-called "hypocycloid" crank mechanism. "Hypocycloid crank mechanism" is intended to define a particular type of crank mechanism in which, unlike conventional connecting-rod and crank mechanisms in which each piston is articulated to a connecting rod by means of a pin, each piston is fixed, by means of a rod, to an annular member in which an intermediate element is rotatable, the intermediate element in turn being mounted rotatably in an eccentric position relative to a crank pin of the drive shaft. In a hypocycloid crank mechanism, the eccentric intermediate element rotates, as a result of the rotation of the drive shaft, with an angular velocity equal to that of the drive shaft but in the opposite direction, since its centre of rotation always coincides with the axis of the respective crank pin. The particular structure of hypocycloid crank mechanisms enables considerable advantages to be achieved in comparison with conventional crank mechanisms . In hypocycloid crank mechanisms, it is in fact possible to achieve a pure sinusoidal motion of the pistons so that no lateral thrusts of the pistons relative to the cylinders are generated. As a result, the pistons may be partially or wholly without skirts . Moreover, both rotational and counter-rotational inertial forces and torques of orders higher than the 1st order which are generated when the engine is in operation are completely cancelled out and do not therefore require compensation. It is consequently possible to produce four-cylinder and eight- cylinder engines which are intrinsically balanced or to achieve balancing of single-cylinder, two-cylinder, three- cylinder and five-cylinder engines easily, simply by balancing of the 1st-order rotational and/or counter- rotational inertial forces and/or torques by means of counterweights fixed to the cranks of the drive shaft and/or to the intermediate eccentric elements . All things considered, an engine of this type has a simpler structure than conventional engines and also has the advantage of being more compact, enabling visibility from the passenger compartment of a vehicle in which it is mounted to be improved and allowing the designer greater stylistic freedom. The life of the engine is also increased in comparison with engines with conventional crank mechanisms by virtue of the fact that the engine is subject to fewer vibrations since inertial forces and torques of orders higher than the 1st order are absent and the engine is also consequently less noisy. In particular, the invention relates to a reciprocating internal combustion engine comprising a crankshaft mounted so as to be rotatable relative to the engine block and having at least one crank with which a piston is associated for sliding, as a result of the rotation of the crankshaft, in a cylinder connected to the block, each piston being connected to the respective crank by means of a hypocycloid crank-mechanism device including a principal eccentric mounted rotatably in an eccentric position relative to the crank and surrounded by a principal annular member which is rotatable coaxially relative to the principal eccentric and from which a connecting element of the respective piston extends . Although an engine of the type indicated above has various advantages in comparison with conventional engines , it may be affected by a disadvantage which is that, when the engine is operating in lightly loaded conditions, for example, during the starting-up or stopping of the engine, and when a piston is close to the middle of its stroke in the respective cylinder, a condition of instability arises which may lead to stoppage of the engine . In order to overcome this disadvantage, the subject of the invention is an engine of the type defined above, characterized in that an auxiliary eccentric is connected rigidly to each principal eccentric, the auxiliary eccentric being mounted so as to be diametrally offset relative to the respective principal eccentric and being surrounded by an auxiliary annular member rotatable coaxially relative to the auxiliary eccentric and associated with rectilinear guide means connected to the block so as to be slidable along an axis substantially transverse the axis of the cylinder. By virtue of this concept, the engine according to the invention is free of any condition of instability in operation so that any possibility of stoppages occurring in operation is avoided, enabling optimal reversibility to be achieved between the rectilinear motion of the pistons within the respective cylinders and the rotary motion of the drive shaft . According to a secondary characteristic of the invention, each annular member connected to a respective piston has additional guide means for guiding its movement along an axis parallel to the axis of the respective cylinder, the additional guide means including a rod parallel to the axis of the respective cylinder, disposed inside the block, and engaged for sliding by a bush fixed to the respective annular member. By virtue of this characteristic, the operation of the engine according to the invention is particularly reliable and precise even if, after many operating cycles, play in its elements such as to introduce possible unreliability in their relative positioning may arise. Further characteristics and advantages of the invention will become clearer from the following detailed description, provided purely by way of non-limiting example, with reference to the appended drawings, in which: Figure 1 is a sectioned side elevational view of a first embodiment of the engine according to the invention, Figure 2 is a front elevational view of a portion of the engine of Figure 1, sectioned on the line II-II of Figure 1, Figure 3 is a side elevational view of a detail indicated by the arrow III of Figure 1, Figure 4 is a front elevational view of the detail of Figure 3, sectioned on the line IV of Figure 3, Figure 5 is a view similar to Figure 1 of a variant of the engine of Figure 1, Figure 6 is a sectioned side elevational view of another embodiment of the engine according to the invention, Figure 7 is a view similar to Figure 6 of a variant of the engine of Figure 6 , Figure 8 is a sectioned side view of another embodiment of the engine according to the invention, Figure 9 is a front view sectioned on the line IX-IX of Figure 8 , Figures 10 and 11 are views similar to Figures 8 and 9, respectively, showing a variant of the engine of Figures 8 and 9, Figure 12 is a sectioned side view of another embodiment of the engine according to the invention, Figure 13 is a front view sectioned on the line XIII-XIII of Figure 12 , Figure 14 is a sectioned side view of another embodiment of the engine according to the invention, and Figure 15 is a front view sectioned on the line XV-XV of Figure 14. With reference initially to Figures 1 to , an internal combustion engine according to the invention is generally indicated 1. The engine 1 comprises a block 2 which supports for rotation, by means of crankshaft bearings 3, a crankshaft 4 having a plurality of cranks 4a, preferably formed integrally with the shaft 4. In the region of each crank 4a, the block 2 has a cylinder 5a in which a respective piston 6a is mounted for sliding, the piston being formed so as to have substantially only a crown and a small peripheral annular portion which is in contact with the lining of the cylinder 5a and is sufficient to accommodate a pair of piston rings, typically a split ring and an oil-scraper ring. The piston 6a is connected to the crank 4a by means of a so-called hypocycloid crank mechanism which is intended to convert the rectilinear reciprocating motion of the piston 6a in the cylinder 5a into a rotary motion of the crankshaft 4. In particular, the piston 6a is connected rigidly, by means of a rod-like connecting element 7a, to an annular member 8a in which an intermediate element 10a is mounted rotatably, the intermediate element 10a having, in an eccentric position, a hole 11 in which the respective crank 4a of the shaft 4 is mounted rotatably. The piston 6a may be formed as an element separate from the connecting element 7a and may be connected thereto by means of a pair of parallel pins engaging respective holes formed in a corresponding end of the element 7a and a pair of seats formed in a inner surface portion of the piston 6a . Alternatively, the piston 6a may be formed integrally with the connecting element 7a. Connected rigidly to the intermediate element 10a is another, auxiliary intermediate element 10b of substantially identical shape but offset therefrom diametrally relative to the hole 11, the hole 11 being common to the two elements 10a and 10b and having the same crank 4a of the shaft 4 extending through it. The element 10b in turn is surrounded by an auxiliary annular element 8b connected by means of a respective connecting element 7b to another piston 6b mounted for sliding in a cylinder 5b which is also fixed to the block 2. In particular, the cylinder 5b is arranged at an inclination of between 60° and 120° to the cylinder 5a so that the cylinder 5b constitutes a guide for the movement of the piston 6b, the guide being disposed predominantly transversely or having a substantially transverse component relative to the axis of the cylinder 5a, that is, to the axis of movement of the piston 6a. In practice, the auxiliary cylinder 5b constitutes a device for guiding the movement of the auxiliary annular member 8b along an axis predominantly transverse the axis of the cylinder 5a. The engine 1 thus has the structure of an engine with a V- shaped cylinder configuration with an inclination of between 60° and 120°, usable in engines, for example, with four, six or eight cylinders . The axis of the cylinder 5b is preferably inclined at 90° to the axis of the cylinder 5a so that the engine 1 is a 90° V- shaped engine . In any case, both of the pistons 6a and 6b of the pair of adjacent cylinders 5a and 5b are connected to the same crank 4a of the shaft 4 by means of respective hypocycloid crank mechanisms, the respective intermediate eccentric elements 10a, 10b being mutually offset by 180° so that each piston constitutes a rectilinear guide element for guiding the movement of the respective annular member along an axis substantially transverse the axis of the other cylinder. The unit composed of the intermediate members 10a and 10b is advantageously formed in two pieces each of which defines one half of the hole 11 and which can be connected to one another by means of screws 12, facilitating assembly and dismantling of the hypocycloid crank-mechanism device. In Figure 5 , in which the same reference numerals have been used to indicate parts identical or similar to those of the previous variant, an engine according to the invention is generally indicated la. In this engine, the annular member 8a has a bush 15a the axis of which is arranged parallel to the respective connecting element 7a and which is engaged for sliding on a guide rod 17a fixed to the block 2. Similarly, the annular member 8b also has a bush 15b the axis of which is parallel to that of the respective connecting element 7b and which is engaged for sliding on a respective guide rod 17b, also fixed to the block 2. By virtue of the presence of the rods 17a and 17b and of the respective bushes 15a and 15b fixed to the annular members 8a and 8b, the operation of the engine la is completely free of instabilities, even when play arises between its elements after many operating cycles. Figure 6 shows an in-line engine lb, for example, of the type with four cylinders, in which the auxiliary annular member 8b is connected rigidly by means of the connecting element 7b to a respective bush 19 which is engaged for sliding on a guide rod 20 fixed to the block 2 externally and protected from the outside atmosphere by an external fairing 21. In practice, the unit constituted by the rod 20 and by the bush 19 constitutes a kind of "false cylinder" which is in a V-shaped arrangement relative to the cylinder 5a and the function of which is again that of constituting a guide transverse the axis of the cylinder 5a for the movement of the auxiliary annular member 8b. Figure 7 shows a variant of the engine of Figure 6, which is indicated lc, and in which the annular members 8a and 8b have additional guides in a similar manner to the embodiment shown in Figure 5. In particular, the member 8a and the member 8b have respective bushes 15a, 15b, each of which is engaged for sliding on a respective guide rod 17a, 17b fixed to the block along an axis parallel to the axis of the respective connecting element 7a, 7b. Figures 8 and 9 show another embodiment of the engine according to the invention which can be used to produce an engine with 4 cylinders in line. In this embodiment, the auxiliary annular member 8b has a pair of arms 7c which are parallel to one another and to the axis of the connecting element 7a and which extend from the principal annular member 8a; respective coaxial bushes 19a are fixed to the ends of the arms 7c and both bushes 19a engage a common guide rod 20a fixed inside the block 2 along an axis perpendicular to the axis of the cylinder 5a. Figures 10 and 11 show a variant of the embodiment of Figures 8 and 9 in which the respective engine, which is indicated le, comprises additional means for guiding the movement of the annular members 8a and 8b in a similar manner to the variants of Figures 5 and 7. The additional guide means include a bush 15a fixed to the principal annular member 8a and mounted for sliding along a guide rod 17a fixed to the block 2 in a position parallel to the axis of the cylinder 5a. Figures 12 and 13 show a further embodiment of the engine according to the invention which is indicated If and which can be used to produce a two-cylinder in-line engine. In this embodiment, a pair of pistons 6a is associated with the same crank pin 4a on which a pair of respective principal eccentric members 10a is mounted rotatably, each of the principal eccentric members 10a being surrounded, in a rotatable manner, by a respective principal annular member 8a. A common auxiliary eccentric member 10b is fixed to each of the eccentric members 8a in a position diametrally offset by 180° and is disposed in an intermediate position between the principal eccentric members 10a, surrounded by an auxiliary annular member 8b having a pair of bushes 19b arranged in diametrally opposed positions and engaging respective parallel guide rods 20b fixed to the block 2 in positions transverse the axes of the two cylinders 5a. Figures 14 and 15 show a further embodiment of an engine according to the invention, generally indicated lg, which is similar to that shown in Figures 12 and 13 and is intended to be used to produce an engine with 4 cylinders in line . In this case, each of the pistons 6a is associated with a respective crank 4a on which the unit formed by the principal eccentric member 10a and the auxiliary eccentric member 10b is mounted rotatably. The latter member is rotatable inside an auxiliary annular member 8b which has a pair of bushes 19b fixed in diametrally opposed positions, each for engaging a respective guide rod 20b fixed inside the block 2 in a position transverse the axis of the cylinders 5a . Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of protection defined by the appended claims .

Claims: CLAIMS 1. A reciprocating internal combustion engine comprising a crankshaft (4) mounted so as to be rotatable relative to the engine block (2) and having at least one crank (4a) with which a piston (6a) is associated for sliding, as a result of the rotation of the crankshaft (4) , in a cylinder (5a) connected to the block (2) , each piston (6a) being connected to the respective crank (4a) by means of a hypocycloid crank-mechanism device including a principal eccentric (10a) mounted rotatably in an eccentric position relative to the crank (4a) and surrounded by a principal annular member (8a) which is rotatable coaxially relative to the principal eccentric and from which a connecting element (7a) of the respective piston (6a) extends, characterized in that an auxiliary eccentric (10b) is connected rigidly to each principal eccentric (10a) , the auxiliary eccentric (10b) being mounted so as to be diametrally offset relative to the respective principal eccentric (10a) and being surrounded by an auxiliary annular member (8b) rotatable coaxially relative to the auxiliary eccentric and associated with rectilinear guide means (5b, 6b; 19, 20; 19a, 20a; 19b, 20b) connected to the block (2) so as to be slidable along an axis substantially transverse the axis of the cylinder (5a) . 2. An engine according to Claim 1, characterized in that the rectilinear guide means comprise at least one rod (20a; 20b) disposed inside the block (2) and engaged for sliding by at least one bush (19a; 19b) fixed to the auxiliary annular member (8b) . 3. An engine according to Claim 1, characterized in that the rectilinear guide means consist of a pair of parallel rods (20b) disposed inside the block (2) and both engaged for sliding by respective bushes (19b) connected to the auxiliary annular member (8b) in diametrally opposed positions . 4. An engine according to Claim 1, characterized in that the rectilinear guide means comprise a rod (20) disposed outside the block (2) and engaged for sliding by a bush (19) connected to an appendage (7b) which extends radially from the auxiliary annular member (8b) . 5. An engine according to Claim 1 , characterized in that the rectilinear guide means comprise an auxiliary cylinder (6b) which is inclined at between 60° and 120°, preferably about 90°, to each of the cylinders (5a) of the engine, and in which a respective piston (6b) , connected to the auxiliary annular member (8b) by means of a connecting element (7b) , is mounted slidably so that the engine has pairs of adjacent cylinders (5a, 5b) arranged in a V-shaped configuration. 6. An engine according to any one of Claims 2 to 5 , characterized in that each annular member (8a, 8b; 8a) connected to a respective piston (6a, 6b; 6a) has additional guide means for guiding its movement along an axis parallel to the axis of the respective cylinder (5a, 5b; 5a) , the additional guide means including a rod (17a, 17b; 17a) which is parallel to the axis of the respective cylinder (5a, 5b; 5a) , is disposed inside the block (2) , and is engaged for sliding by a bush (15a, 15b; 15a) fixed to the respective annular member (8a, 8b; 8a) .

Inventors: ANSELMO MICHELE, TITOLO ANDREA, ANSELMO, MICHELE, TITOLO, ANDREA
Applicants: ANSELMO MICHELE, FIAT AUTO SPA, TITOLO ANDREA, ANSELMO, MICHELE, FIAT AUTO S.P.A., TITOLO, ANDREA
Application year: 2000
Main classification: F01B9
IPC codes: F01B9, F02B75