WO2005021948A1 - Internal-combustion engine arrangement having a dynamically balanced mass - Google Patents

Abstract

An internal-combustion engine arrangement having a dynamically balanced mass and having engine cylinders whose axis is perpendicular to the central rotary axis of a common crankshaft; each engine cylinder accommodates a reciprocating piston for rotating the crankshaft; the moving mass of the engine cylinders is distributed evenly along the cylinder axes between the two sides; and the engine cylinders are synchronously controlled; and the resultant of the torques generated by the engine cylinders and related to the central rotary axis of the crankshaft (4, 24) is zero. In case of an embodiment having three engine cylinders (l, 2 3) arranged behind one another, the moving mass and force of the central engine cylinder is twice the moving mass and force of each outside engine cylinder. In case of a four-cylinder embodiment the two outside engine cylinders are situated at one side of the axis, and the two inside engine cylinders are situated on the other side of the axis.

Description

INTERNAL-COMBUSTION ENGINE ARRANGEMENT HAVING A DYNAMICALLY BALANCED MASS

FIELD OF THE INVENTION The invention relates to an internal-combustion engine arrangement having a dynamically balanced mass. The axis of the engine cylinders, each accommodating a reciprocating piston for rotating a common crankshaft, is perpendicular to the central rotary axis of the crankshaft, and the moving mass of the engine cylinders is distributed evenly between the two sides along the perpendicular cylinder axes. Further, the engine cylinders are synchronously controlled.

DESCRIPTION OF THE PRIOR ART It is known that engine run is accompanied by substantial dynamic effects (vibrations). It follows from the operational principle of internal-combustion engines that the combustion occurs during a short portion of a full cycle, and work too, is performed during such period. In the classic four-stroke engines the work phase does not occur simultaneously in each cylinder; this results in a more uniform work performance over time, but no advantage is gained as concerns the dynamic effects. By dynamic effects there are meant the force exerted perpendicularly to the crankshaft and the torque applied to the crankshaft by the moving piston and the accessories coupled therewith. The torque of concern here is a bending torque affecting the crankshaft, as opposed to the torque causing rotation of the crankshaft about its central rotary axis. The dynamic effects manifest themselves primarily in the vibration of the engine arrangement, h case of motor vehicles the mounting of the engine and the available mass at rest together alleviate the problems derived from vibrations, and the vibratory energy is absorbed by appropriate damping elements. In a number of applications, however, weight and/or spatial considerations require internal-combustion engines of minimized design. Typically, all engine- operated portable tools, such as chain saws, sprayers, lawn mowers, edge trimmers, etc. may fall into this category. In such tools the engine is in direct contact with the operator's hand or body, and the vibrations generated during engine run have a harmful effect on the health of the operator after prolonged use. Numerous solutions have been found for reducing engine vibrations. Such solutions are summarized, among others, in the book by Bernhard Krause, entitled "Modellmotoren Technik" ("Engineering of Model Engines"), published by Neckar- Verlag, Villingen-Schwenningen, 1996. Figure 3.66 of that book shows a four-cylinder boxer engine. In such engines the cylinders, having identical design and identical dynamic mass are disposed on opposite sides of ^•the crankshaft in a face-to-face arrangement and are operated in synchronism. The resultant of the forces generated by boxer engines and related to their crankshaft is zero, and therefore, from a dynamic point of view, such engines are more favorable than conventional engine arrangements. Between the axes of facing cylinders, however, a certain distance dictated by the possibilities of mechanical positioning, is necessarily present along the crankshaft. Consequently, the two oppositely oriented forces have a torque arm represented by such a distance and thus load the crankshaft with a dynamically varying torque, resulting in a vibration of the engine arrangement. Further, perfectly face-to-face operating opposed-piston engines are known which are shown, for example, in Figure 3.6 of the above-noted book and also described in the "Mϋszaki Lexikon" ("Technical Encyclopedia"), editor-in-chief: Polinszky, Karoly Akademiai Kiadό, ("Academy Presss") 1970, under the entry "opposed-piston engines". Although at first glance such engines appear to be balanced as concerns both forces and torque, it has to be noted that for converting the oppositely oriented movements of the two pistons to a rotary motion, a mechanism of such complexity and size is required as to render the use of such engines uneconomical. In short, the earlier enumerated applications that require minimized engines simply do not admit the utilization of the above-discussed systems.

SUMMARY OF THE INVENTION It is an object of the invention to further develop the principle of boxer engines in such a manner that apart from the balancing of force effects the balancing of torques is ensured as well, and further, the dimensions of the improved engines do not exceed those of conventional engines having the usual power and number of cylinders. The invention provides an internal-combustion engine arrangement having a dynamically balanced mass. The axis of the engine cylinders, each accommodating a reciprocating piston for rotating a common crankshaft, is perpendicular to the central rotary axis of the crankshaft, and the moving mass of the engine cylinders is distributed evenly between the two sides along the cylinder axes. Further, the engine cylinders are synchronously controlled. According to the invention the resultant of the torques generated by the engine cylinders and related to the central rotary axis of the crankshaft is zero.

In accordance with an advantageous embodiment the arrangement is formed of three engine cylinders; the two outside engine cylinders along the crankshaft on one side thereof are of identical dimension and mass. On the opposite side of the crankshaft, centrally between the two outside engine cylinders, the third engine cylinder is disposed, whose piston delivers twice the force effect, and its moving mass is twice the moving mass of the two outside engine cylinders. The pistons of all three engine cylinders have identical stroke lengths. Accordingly, the diameter of the central engine cylinder and its piston is about 1.41 times the diameter of the outside engine cylinders and their pistons. An alternative arrangement is formed of four identical engine cylinders disposed along the crankshaft. Two outside engine cylinders are disposed on one side of the above- noted perpendicular axes, while the two inside engine cylinders are situated on the opposite side of the perpendicular axes. Expediently, the distances between adjoining engine cylinders as viewed along the crankshaft are identical; such a distance corresponds to the minimum distance that can be obtained by the technology applied. The engine arrangement according to the invention ensures a perfect dynamic balance, and, in case of portable applications noted earlier, despite the small dimensions of the engine arrangement, it significantly reduces the vibrations transmitted to the operator.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic kinetic representation of the engine arrangement according to a first embodiment. Figure 2 is a simplified sectional end view of the first embodiment, showing structural details. Figure 3 is a simplified sectional top plan view of the structure shown in Figure 2. Figure 4 is a schematic kinetic representation of the engine arrangement according to a second embodiment.

Figure 5 is a simplified sectional end view of the second embodiment, showing structural details. Figure 6 is a simplified sectional top plan view of the structure shown in Figure 5.

DESCRIPTION OF THE EMBODIMENTS Turning to Figure 1, the engine arrangement illustrated therein is a three- cylinder engine having cylinders 1, 2 and 3. The piston axes of the cylinders 1, 2 and 3 are parallel. The pistons of the two outside cylinders 1 and 3 move in identical directions, while the piston of the central cylinder 3 moves in the opposite direction. The engine cylinders operate in synchronism; they assume one of the end positions shown in Figure 1 simultaneously. The connecting rods of the pistons are coupled with the intermediary of respective bearings 5, 6 and 7 to a common crankshaft 4 which has a rotary axis oriented perpendicularly to the connecting rods. The distances x measured parallel to the rotary crankshaft axis between adjoining bearings 5, 6 and, respectively, between adjoining bearings 6, 7 are identical and should have a structurally feasible minimum length. The two outside cylinders 1 and 3 are of identical construction and have identical moving masses. During engine run the two cylinders 1 and 3 generate identical forces F along the axis of their piston. The magnitude of the forces F varies during the cyclical operation of the cylinders, but is identical for the cylinders 1 and 3 at each point in time. The forces F illustrated in Figure 1 mean the forces generated at the moment of combustion. The central cylinder 2 has a moving mass which is twice the mass and twice the force

(2F) of each cylinder 1 and 3. This condition is fulfilled by providing that the diameter of the piston of the cylinder 2 is approximately 1.41 times the diameter of the pistons accommodated in the cylinders 1 and 3, and the stroke length of the pistons is identical. Turning to Figures 2 and 3, the cylinders 1, 2 and 3 contain respective pistons 9, 10 and 11 each having a respective connecting rod 13, 14 and 15, whose ends coupled to the crankshaft 4 are, in the position depicted in Figure 3, at identical distances 1 from the rotary axis of the crankshaft 4. During operation of the engine arrangement not only the forces derived from the combustion compensate one another as in conventional boxer engines, but the torques, which affect the crankshaft cancel one another as well. Such a result can be readily seen if one considers that the connecting rod 14 of the piston 10 accommodated in the cylinder 2 is jointed to the crankshaft 4 by the bearing 6. If now the torque Fx derived from the cylinder 1 and applied to that coupling location is examined, then it is seen that the torque derived from the cylinder 3 applied to the same coupling location is -Fx. Thus, the resultant torque M of the two torques Fx and -Fx is zero, hi the conventional boxer engines, however, nothing compensates for the fluctuating torque Fx derived from the fluctuating force F; thus, significant dynamic effects appear during their operation. The arrangement illustrated in Figures 1-3 may be multiplied either along the length of the crankshaft 4 or in a V-configuration. The individual balanced units are each designed in accordance with the shown three-cylinder arrangement. The individual engine cylinders may be two-stroke or four-stroke designs, hi case of a two-stroke design, one combustion occurs in each engine cylinder for each revolution of the crankshaft, while in case of a four-stroke design combustion occurs for every other revolution. Therefore, in the latter case a flywheel of suitable inertia is needed. A second embodiment of the invention shown in Figures 4, 5 and 6 is a four- cylinder arrangement suitable for four-stroke engines. Referring particularly to Figure 4, four engine cylinders 20, 21, 22 and 23 of identical construction and design, that is, of identical mass are arranged in pairs opposite and behind one another. This arrangement differs from the classic boxer design in that the cylinder 22 is disposed opposite the cylinder 20 on the same side as the cylinder 21 and is not in a facing disposition; only the outermost cylinder 23 is in such a facing disposition. It follows from such an arrangement that the torques derived from the cylinders 20 and 21 and applied to the crankshaft 24 are of identical magnitude but are of opposite direction with respect to the torques derived from the cylinders 22 and 23. Thus, the arrangement is balanced as far as force and torque are concerned, hi this embodiment the dimension and mass of all the engine cylinders and their pistons is identical. The arrangement along the crankshaft 24 is, however, by one unit longer than the arrangement of Figures 1-3. Figures 5 and 6 show further structural details of the second embodiment, in a manner similar to Figures 2 and 3.

While both the above-discussed embodiments relate to a single engine having a plurality of synchronously-controlled engine cylinders, it will be understood that the invention also encompasses an engine arrangement which is formed of a plurality, synchronously-controlled, single-cylinder engines, or even of a mixture of single- cylinder and multi-cylinder engines, as long as the engine cylinders of such variants have the positional and mass characteristics explained in the two described embodiments. Due to the dynamic balancing, the engine arrangement according to the invention vibrates to a significantly lesser extent and has a quieter run than conventional engine arrangements. This property renders it eminently adapted for use in all kinds of hand-held tools or devices which are in direct contact with the operator's hand or body. Chain saws, back-mounted spraying machines, edge trimmers, hedge cutters and lawn mowers are noted as examples. The generators for spare current sources too, are characteristically vibration-sensitive, and the primary limit for their use is the high noise level they produce. Beside the special engines a balanced arrangement is also significantly advantageous in conventional vehicle engines. For example, the weight of the components participating in the vibration damping and sound damping represents a non-negligible proportion of the vehicle weight, and one part of the engine energy is converted into an unnecessary vibratory energy, representing a loss. The dynamic balance of the engine arrangement reduces the quantity of the listed components and thus significantly improves the efficiency of the vehicle. The balanced arrangement is particularly significant in piloted or robot helicopters, where, because of the high vibration level, some tasks can be performed only to a limited extent. The balanced arrangement results in a significant reduction in the vibration level.

Claims

CLATMS

1. An internal-combustion engine arrangement having a dynamically balanced mass and having engine cylinders whose axis is perpendicular to the central rotary axis of a common crankshaft; each engine cylinder accommodates a reciprocating piston for rotating the crankshaft; the moving mass of the engine cylinders is distributed evenly along the cylinder axes between the two sides; and the engine cylinders are synchronously controlled; characterized in that the resultant of the torques generated by the engine cylinders (1, 2, 3; 20, 21, 22, 23) and related to the central rotary axis of the crankshaft (4, 24) is zero.

2. The arrangement as defined in claim 1, characterized in that it is formed of three engine cylinders (1, 2, 3); two of the three engine cylinders are outside engine cylinders (1, 3) situated along the crankshaft (4) on one side thereof; the two outside engine cylinders (1, 3) have identical dimensions and masses; one of the three engine cylinders (2) is positioned centrally between the two outside engine cylinders (1, 3) on the other side of the crankshaft (4); the centrally positioned engine cylinder (2) and the piston (10) thereof deliver twice the force of each outside engine cylinder (1, 3) and the moving mass of the centrally positioned engine cylinder (2) is twice the moving mass of each outside engine cylinder (1, 3); the pistons (9, 10, 11) of all three engine cylinders (1, 2, 3) have identical stroke lengths.

3. The arrangement as defined in claim 2, characterized in that the diameter of the centrally positioned engine cylinder (2) and of the piston (10) is about 1.41 times the diameter of the outside engine cylinders (1, 3) and pistons (9, 11).

4. The arrangement as defined in claim 1, characterized in that it is formed of four identical engine cylinders (20 to 23) disposed along the common crankshaft (24); two of the four engine cylinders are outside engine cylinders (20 and 23) situated on one side of the perpendicular axes and other two of the four engine cylinders are inside engine cylinders (21 and 22) situated on the other, opposite side of the perpendicular axes.

5. The arrangement as defined in claim 1, characterized in that the distance (x) between adjoining engine cylinders is identical and corresponds to the minimum distance that is feasible with the technology applied.