GB2497292A

GB2497292A - A balancing device for an internal combustion engine

Info

Publication number: GB2497292A
Application number: GB1120851.9A
Authority: GB
Inventors: Domenico Palmisani; Fiorello Losano
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2011-12-05
Filing date: 2011-12-05
Publication date: 2013-06-12
Anticipated expiration: 2031-12-05
Also published as: GB201120851D0; GB2497292B

Abstract

A balancing device (100) for an internal comÂbustion engine (500) is provided. The balancing device comprises two parallel balance shafts (200, 300) mutually coupled to rotate in opposite directions about a respective rotational axis (X200, X300). Each of the balance shafts (200, 300) comprises an eccentric weight (205, 305) having a center of mass (G205, G305) offset from the rotational axis thereof (X200, X300). The eccentric weights (205, 305) are radially misaligned with each other, and each of the balance shafts (200, 300) comprises a staggered portion (225, 325). Each staggered portion (225, 325) has an axis (Y225, Y325) that is offset from the rotational axis thereof (X200, X300), thereby defining a throw (230, 330) of the balance shaft (200, 300), which is radially aligned with the eccentric weight (305, 205) of the other balance shaft (300, 200) and is arranged to allow the rotation of said eccentric weight (305, 205).

Description

BALANCING DEVICE FOR AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present invention relates to a balancing device for an internal combustion engine, particularly for a reciprocating internal combustion engine.

BACKGROUND

It is known that some reciprocating internal combustion engines may generate vibrations which are inherent in the design of the engine itself.

In particular, inline four-cylinder engines have an asymmetric design such that, during the rotation of the crankshaft, the descending pistons and the ascending pistons of the engine are not always completely opposed in their acceleration, thereby generating a net vertical inertial force twice in each complete revolution of the crankshaft, This net vertical forces cause a second order vibration, whose magnitude increases proportionally with the rotational speed of the crankshaft.

This second order vibration is conventionally eliminated by means of a balancing device, which is located in the oil sump of the internal combustion engine beneath the crank- shaft. The balancing device generally comprises a pair of balance shafts, which are dis-posed side by side in an horizontal plane and which are parallel with the crankshaft. One of these balance shafts is coupled to rotate at twice the angular speed of the crankshaft, whereas the two balance shafts are mutually coupled to rotate at the same angular speed in opposite directions. Each of the balance shafts carries an eccentric weight, namely a weight having its center of mass offset from the rotational axis of the respective balance shaft. The eccentric weights are located on the balance shafts in the same axial position, thereby resulting mutually aligned in a radial direction, i.e. in a direction perpen-dicular to both the rotational axes thereof. The eccentric weights are equally sized and phased so that their counter-rotation generate a vertical vibration having the sarrie mag- -----------iitude of-the undesired-second-order-vibration-generated-by-the-engine1-but-t80°-out-of ----phase, thereby eliminating it.

The magnitude of the counter-vibration generated by the balancing device is proportional to the mass of the eccentric weights and to the square of the distance of their centers of mass from the respective rotational axis. Besides, the mass is proportional to the volume of the eccentric weights and to the density of the material which the eccentric weights are 1.

made of, whereas the distance of the centers of mass is essentially proportional to the radial overall dimension of the eccentric weights.

According to the conventional design described above, the radial overall dimension of the eccentric weights is strictly limited by the distance between the rotational axes of the balance shafts. In fact in order to prevent the eccentric weights to interfere one another during the counter-rotation, the sum of the radial overall dimensions of the eccentric weights must be smaller than the distance between the rotational axes of the balance shafts.

The distance between the rotational axes of the balance shafts is usually determined by the engine layout and/or by the free space available in the oil sump. As a consequence, in order to allow the balancing device to generate a counter-vibration having the due magnitude, it may be necessary to increase the mass of the eccentric weights by in-creasing their axial overall dimensions. However, this doing is generally unwelcomed for several reasons. A first reason is that a greater mass of the eccentric weights leads to an increased power lost by the internal combustion engine to rotate the balance shafts. A second reason is that, being the magnitude of the vibration only linearly proportional to the mass of the eccentric weights, the eccentric weights may become too long compared with the free space available in the oil sump.

In view of the above, it is an object of the present invention to solve the above mentioned drawbacks, providing a solution that allows to keep the distance between the rotational axes of the balancing device as small as possible, without increasing the length of the eccentric weights thereof.

Another object of the invention is to provide a compact balancing device that occupies a lesser space within the oil sump of the internal combustion engine.

Still another object is to meet these goals with a simple, rational and rather inexpensive solution.

SUMMARY

These and/or other objects are attained by the characteristics of the embodiments of the invention as reported in the independent claims. The dependent claims recite preferred and/or especially advantageous features of the embodiments of the invention.

--More particularly, an embodiment of iheJnventionprovides a-balancing device-for-an -in ternal combustion engine, comprising two parallel balance shafts mutually coupled to ro-tate in opposite directions, each one about a respective rotational axis, wherein each of the balance shafts comprises an eccentric weight having a center of mass offset from the rotational axis thereof, wherein the eccentric weights are radially misaligned with each other, and wherein each of the balance shafts comprises a staggered portion having an axis that is offset from the rotational axis thereat, thereby defining a throw of the balance shaft, which is radially aligned with the eccentric weight of the other balance shaft and is arranged to allow the rotation of said eccentric weight.

It should be understood that the eccentric weights are radially misaligned with each other in the sense that their axial positions are mutually misaligned with respect to any direc-tion perpendicular to the rotational axes of the balance shafts, and that the throw of each balance shaft is radially aligned with the eccentric weight of the others balance shaft in the sense that the axial position of the throw is aligned with the axial position of the ec-centric weight in a direction perpendicular to their rotational axes.

Thanks to this solution, being the eccentric weights radially misaligned with each other, they cannot interfere one another during the counter-rotation of the balance shafts. In addition, the balance shafts may be mutually phased so that, during the counter-rotation, the eccentric weight of each balance shaft freely passes through the throw of the other balance shaft, thereby not interfering with the latter either. In this way, the radial overall dimension of the eccentric weights is not as strictly limited by the distance between the rotational axes of the balance shafts as in the conventional balancing device. As a con- sequence. in a balancing device according to this embodiment of the invention, the dis-tance between the rotational axes of the balance shafts may advantageously be smaller than that of a conventional balancing device designed to generate the same counter-vibration. This opportunity implies several other advantages, including that of allowing a reduction of the overall dimensions and/or of the overall weight of the balancing device compared to a conventional balancing device designed to generate the same counter-vibration.

According to an aspect of the invention, each of the eccentric weights of the balancing device may have a radial overall dimension that is greater than the distance between the rotational axes of the balance shaft.

This aspect of the invention has the advantage of strongly increasing the magnitude of the counter-vibration which can be generated by the balancing device for a given dis-tance between the rotational axes of the balance shafts.

According to another aspect of the invention, each of the eccentric weights of the balanc- ing device may have a radial overall dimension that is greater than an axial overall di- _..mensionthereof..

This aspect of the invention has the advantage of reducing the axial length of the eccen-tric weights, thereby providing a balancing device small and compact.

Another aspect of the invention provides that each of the balance shafts may have the staggered portion that is axially disposed just next to the eccentric weight.

This aspect has the advantage of reducing the axial overall dimension of the balancing device, as well as the advantage of keeping the eccentric weights as near as possible one another in the axial direction, so as to minimize the inertial momentum that their counter-rotation generates in the common plane containing the rotational axes of the balance shafts.

Another aspect of the invention provides that each of the balance shafts may have the axis of the staggered portion that is angularly disposed in opposition of phase, i.e. 180° out of phase, from the center of mass of the eccentric weight.

This aspect of the invention advantageously aflows a proper phasing of the balance shafts.

According to an aspect of the invention, each of the eccentric weights of the balancing device is formed in a single body with the respective balance shaft.

This solution has the advantage of simplifying the assemblage of the balancing device.

According to another aspect of the invention, each of the staggered portions of the ba-tancing device is formed En a single body with the respective balance shaft.

This solution has the advantage of further simplifying the assemblage of the balancing device.

According to still another aspect of the invention, the eccentric weights are equally sized and the balance shafts are mutually coupled so that the centers of gravity of the eccen-tric weights are disposed in the common plane of the rotational axis simultaneously and in opposition of phase one another, i.e. 180° out of phase.

This solution advantageously ensures that the counter-rotation of the eccentric weights generates no net inertial force in the common plane containing the rotational axes.

An aspect of the invention provides that the balance shafts of the balancing device are mutually coupled by means of a gearwheel coaxiaJly fitted on a first of the balance shafts, which is in mesh with a gearwheel coaxially fitted on a second of the balance shafts.

This aspect has the advantage of providing a very simple and reliable solution to couple the balance shafts.

Another embodiment of the invention provides an assembly for an internal combustion engine, comprising the balancing device described above and a crankshaft, wherein the crankshaft has a rotational axis parallel to the rotational axes of the balancing device and is coupled to rotate a first of the balance shafts thereof.

This embodiment of the invention has basically the-same advantages mentioned-above; -in particular that of providing an assembly which is globally smaller, lighter and more compact than those comprising a conventional balancing device.

According to an aspect of the invention, the crankshaft is coupled to the flist balance shaft of the balancing device by means of a gearwheel coaxially fitted on the crankshaft, which is in mesh with a gearwheel coaxially fitted on the first balance shaft.

This aspect has the advantage of providing a very simple and reliable solution to couple the crankshaft to the first balance shaft of the balancing device.

According to another aspect of the invention, the eccentric weights of the balancing de-vice are radially aligned with a straight portion of the crankshaft which is axially located between a couple of consecutive crank of the crankshaft.

This solution has the advantage of guaranteeing that the eccentric weights of the balanc- ing device, during their counter-rotation, cannot interfere with the cranks of the crank- shaft, so that their radial overall dimension may be increased in order to obtain a ba!anc-ing vibration of the right magnitude.

According to still another aspect of the invention, the above mentioned straight portion of the crankshaft is axially located at the center of the crankshaft.

This solution has the advantage that the vibration generated by the balancing device is concentrated in the middle of the crankshaft, thereby generating no tilting momentum.

Another embodiment of the invention provides an internal combustion engine comprising the assembly described above.

This embodiment of the invention has basically the same advantages mentioned above, in particular that of providing an internal combustion engine which is globally smaller, lighter and more compact than those comprising a conventional balancing device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings.

Figure I is an exploded prospective view of a balancing device according to an embodk merit of the invention.

Figure 2 is a top view of the baJancing device of figure 1.

Figure 3 is the section Ill-Ill of figure 2.

Figure 4 is a lateral view of an engine assembly according to an embodiment of the in-vention.

Figure 5 is a bottom view of the engine assembly of figure 4.

Figure 6 is a lateral schematic view of an internal combustion engine according to an embodiment of the invention.

DETAILED DESCRIPTION

The balancing device 100 comprises a first balance shaft 200 and a second balance shaft 300, which may be formed in metallic material, such as for example steel or cast iron.

The first balance shaft 200 has a longitudinal axis X200 and comprises an eccentric weight 205, namely a solid body having a center of mass G205 that is offset from the longitudinal axis X200 (see fig.3). The eccentric weight 205 may be entirely formed in a single body with the first balance shaft 200. In the present example, the eccentric weight 205 is a flat body whose smaller size, i.e. the thickness, is parallel with the longitudinal axis X200. In other words, considering a cylindrical coordinate system having the longi-tudinal axis X200 as reference axis, the eccentric weight 205 of the present example has an axial overall dimension L205 (see fig.2), i.e. the maximum length, that is smaller than the radial overall dimension P205 (see fig3), Le. the maximum radius.

With reference to a section plane perpendicular to the longitudinal axis X200 as per fig- ure 3, the eccentric weight 205 has a cross-sectional area that is asymmetrical with re-spect to the longitudinal axis X200. The cross-sectional area may be constant along the entire thickness of the eccentric weight 205. In the present example, the cross-sectional area of the eccentric weight 205 has a "mushroom shape" comprising a smaller internal portion 210, which is located on the longitudinal axis X200, and a bigger external portion 220 jutting radially out from the internal portion 210, which has substantially the shape of a circular segment. The circular edge of the external portion 220 has the center located on the longitudinal axis X200 and determines the radial overall dimension R205 of the eccentric weight 205. The center of mass G205 of the eccentric weight 205 is located almost in the center of the external portion 220, separated from the longitudinal axis X200 by a radial distance D205.

As shown in figure 1, the first balance shaft 200 further comprises a staggered portion 225 having a central axis Y225 that is parallel with, and offset from, the longitudinal axis X200. In this way, the staggered portion 225 defines a throw 230 of the first balance shaft 200. Referring to the above mentioned cylindrical coordinate system, the axial overall dimension L225 of the staggered portion 225 coincides with the axial overall di-mension of the throw 230 and it is a little grater than the axial overall dimension L205 of the eccentric weight 205 (see fig.2). In the present example, the staggered portion 225 is axially disposed immediately next to the eccentric weight 205. More particularly, the staggered portion 225 is axially interposed between the eccentric weight 205 and an en-larged coaxial portion 235 of the first balance shaft 200. The staggered portion 225 may be formed in a single body with the first balance shaft 200, possibly together with the ec- -centricweight 205 and-also-the-enlarged poon235.- With reference to a section plane perpendicular to the longitudinal axis X200 as per fig- ure 3, the staggered portion 225 has an almost elliptical cross-sectional area that is en-tirely offset from the longitudinal axis X200, separated by the latter by a minimum radial distance D225. This cross-sectional area is possibly constant along the entire axial di-mension of the staggered portion 225. The central axis Y225 passes in the center of the cross sectional area of the staggered portion 225 and it is angularly positioned in opposi-tion of phase with respect of the center of mass 0205 of the eccentric weight 205.

The second balance shaft 300 is substantially identical to the first balance shaft 200.

The second balance shaft 300 has a longitudinal axis X300 and comprises an eccentric weight 305, namely a solid body having a center of mass G305 that is offset from the longitudinal axis X300 (see. fig.3). The eccentric weight 305 may be entirely formed in a single body with the second balance shaft 300. In the present example, the eccentric weight 305 is a flat body whose smaller size, i.e. the thickness, is parallel with the longi-tudinal axis X300. In other words, considering a cylindrical coordinate system having the longitudinal axis X300 as reference axis, the eccentric weight 305 of the present example has an axial overall dimension L305 (see fig.2), i.e. the maximum length) that is smaller than the radial overall dimension R305 (see fig.3), i.e. the maximum radius.

With reference to a section plane perpendicular to the longitudinal axis X300 as per fig- ure 3, the eccentric weight 305 has a cross-sectional area that is asymmetrical with re-spect to the longitudinal axis X300. The cross-sectional area may be constant along the entire thickness of the eccentric weight 305. In the present example, the cross-sectional area of the eccentric weight 305 has a "mushroom shape" cornprsing a smaller internal portion 310, which is located on the longitudinal axis X300, and an external portion 320 jutting radially out from the internal portion 310, which has substantially the shape of a circular segment. The circular edge of the external portion 320 has the center located on the longitudinal axis X300 and determines the radial overall dimension R305 of the ec- centric weight 305. The center of mass G305 of the eccentric weight 205 is located al-most in the center of the external portion 320, separated from the longitudinal axis X300 by a radial distance D305.

It should be observed that the eccentric weight 305 of the second balance shaft 300 and the eccentric weight 205 of the first balance shaft 200 are equally sized. In particular, the shape of the eccentric weight 305 is identical to the shape of the eccentric weight 205, and the dimensions L305 and R305 of the eccentric weight 305 are equal respectively to the dimensions L205 and R205 of the eccentric weight 205. Since the eccentric weights 305 and 205 are made of the same material, they have also the same mass and the same position of the center of mass. More precisely, the center of mass 0305 of the ec- centric weight-305,-withrespect-tothe longitudinal-axis X-300,Hsequal-to-the position of-the center of mass 0205 of the eccentric weight 205, with respect to the longitudinal axis X200.

As shown in figure 1, the second balance shaft 300 further comprises a staggered por-tion 325 having a central axis Y325 that is parallel with, and offset from, the longitudinal axis X300. In this way, the staggered portion 325 defines a throw 330 of the second bal-ance shaft 300, Referring to the above mentioned cylindrical coordinate system, the axial overall dimension L325 of the staggered portion 325 coincides with the axial overall di-mension of the throw 330 and it is a little grater than the axial overall dimension L305 of the eccentric weight 305 (see fig.2). In the present example, the staggered portion 325 is S axially disposed immediately next to the eccentric weight 305. More particularly, the staggered portion 325 is axially interposed between the eccentric weight 305 and an en-larged coaxial portion 335 of the second balance shaft 300. The staggered portion 325 may be formed in a single body with the second balance shaft 300, possibly together with the eccentric weight 305 and also the enlarged portion 335.

With reference to a section plane perpendicular to the longitudinal axis X300 as per fig- ure 3, the staggered portion 325 has an almost elliptical cross-sectional area that is en-tirely offset from the longitudinal axis X300, separated by the latter by a minimum radial distance 0325. This cross-sectional area is possibly constant along the entire axial di-Ten5on of the staggered portion 325. The central axis Y325 passes in the center of the cross sectional area of the staggered portion 325, and it is angularly positioned is in op-position of phase with respect of the center of mass G305 of the eccentric weight 305.

It should be observed that the staggered portion 325 of the second balance shaft 300 and the staggered portion 225 of the first balance shaft 200 are equally sized. In particu- lar, the shape of the staggered portion 325 is identical to the shape of the staggered por- tion 225, and the dimensions L325 and D325 of the staggered portion 325 are equal re-spectively to the dimensions L225 and D225 of the staggered portion 225.

As shown in figure 2 and 3, the first balance shaft 200 and the second balance shaft 300 are disposed side by side, so that the longitudinal axes X200 and X300 lie parallel in a common plane A. The first balance shaft 200 and the second balance shaft 300 are axially disposed so that the eccentric weights 205 and 305 are radially misaligned with each other. More precisely, the axial position of the eccentric weight 205 on the first bal-ance shaft 200 and the axial position of the eccentric weight 305 on the second balance shaft 300 are mutually misaligned with respect to any direction perpendicular to the longi-tudinal axes X200 and X300 Besides, the eccentric weight 205 of the first balance shaft 200 is radially aligned with the throw 330 of the second balance shaft 300, whereas the eccentric weight 305 of the second balance shaft 300 is radially aligned with the throw 230 of -the first balance -shaft 200;More precisely;the axit position otthe -eccentric weights 205 on the first balance shaft 200 is aligned with the axial position of the throw 300 on the second balance shaft 300 along a direction perpendicular to the longitudinal axes X200 and X300, whereas the axial position of the eccentric weights 305 on the second balance shaft 300 is aligned with the axial position of the throw 200 on the first balance shaft 200 along another direction but still perpendicular to the longitudinal axes

B

X200 and X300. Moreover, the first balance shaft 200 and the second balance shaft 300 are angularly positioned so that the center of mass 0205 of the eccentric weight 205 and the center of mass 0305 of the eccentric weight 305 are disposed in the common plane A at the same time but in opposition of phase with each other, i.e. 180° out of phase. In other words, looking at the balancing device 100 from an axial point of view as per figure 3, the eccentric weigh 205 of the first balance shaft 200 and the eccentric weight 305 of the second balance shaft 300 are disposed symmetrically with respect to a plane of symmetry B which is perpendicular to the common plane A, and which is disposed paral-lel and equidistant between the longitudinal axes X200 and X300.

The distance DC between the longitudinal axes X200 and X300 of the balance shafts and 300 is smaller than the radial overall dimension R205 and R305 of the eccentric weights 205 and 305. In this way, the eccentric weight 205 of the first balance shaft 200 is inserted in the cavity defined by the throw 330 of the second balance shaft 300, cross-ing the longitudinal axis X300. Likewise, the eccentric weight 305 of the second balance shaft 300 is inserted in the cavity defined by the throw 230 of the first balance shaft 200, crossing the longitudinal axis X200.

The balance shafts 200 and 300 of the balancing device 100 are supported by bearings (not shown) to rotate about the longitudinal axes X200 and X300 respectively. The bal-ance shafts 200 and 300 are also mechanically coupled to each other, in order to rotate always at the same angular speed but in opposite directions. In the present example, the mechanical coupling between the balance shafts 200 and 300 is achieved by means of a first helical gearwheel 240 coaxially fitted on the first balance shaft 200, which is in mesh with a second helical gearwheel 340 coaxially fitted on the second balance shaft 300.

The gearwheels 240 and 340 have the same base diameter, thereby guaranteeing that the balance shafts 200 and 300 rotate in opposite directions at the same angular speed.

It should be observed that the eccentric weights 205 and 305, as well as the staggered portions 225 and 325, are shaped and dimensioned such that, during the counter-rotation of the balance shafts 200 and 300, they never interfere with each other.

As shown in figure 4, the balancing device 100 may be a part of an engine assembly 400, which comprises also an engine crankshaft 405. The crankshaft 405 has a longitu- dinal axis X405 and it is supported by bearings (not shown) to rotate about said longitu- diryal aisX405: Th ernkshaft 405-ma--hav orte or-re--ranks 410-locate-d-in-su----- cession along the longitudinal axis X405. Each of the cranks 410 is offset from the longi-tudinal axis X405 and is coupled with the connecting rod 415 of a reciprocating piston (not shown) of the internal combustion engine. In this way, the reciprocating movements of the pistons may be converted in a rotational movement of the crankshaft 405 about the longitudinal axis X405. The cranks 410 are axially separated from each other by straight portion 420 of the crankshaft 405, which are coaxially aligned along the longitu-dinal axis X405. The cranks 410 and the straight portions 420 may be formed in a single body with the crankshaft 405. In the present example, the crankshaft 405 is designed for an inline four-cylinder internal combustion engine. Accordingly, it has four cranks 410, in-cluding two central cranks angularly disposed in phase with each other, and two external cranks angularly disposed in opposition of phase with respect to the central cranks.

The crankshaft 405 is disposed so that the longitudinal axis X405 is parallel with the lon-gitudinal axes X2tJO and X300 of the balancing device 100. In particular, the longitudinal axis X405 of the crankshaft 405 lies in the already mentioned plane of symmetry B of the balancing device 100 (see figS). The crankshaft 405 is coupled to rotate the first balance shaft 200 and the second balance shaft 300 of the balancing device 100 (in opposite di- rections) at twice the angular speed of the crankshaft 405 itself. In this way, the counter-rotation of the eccentric weights 205 and 305 generate a net inertial force twice in each complete revolution of the crankshaft 405, which is directed perpendicularly with respect to the common plane A of the balancing device 100. The eccentric weights 205 and 305 are sized and phased so that this inertial force generates a second order vibration having the same magnitude of the undesired second order vibration generated by the internal combustion engine, but 180° out of phase, thereby eliminating it. In the present example, the coupling between the balancing device 100 and the crankshaft 405 is achieved by means of a third gearwheel 250 coaxially fitted on the first balance shaft 200, which is in mesh with a fourth gearwheel 425 coaxially fitted on the crankshaft 405. The gearwheel 425 has a base diameter that is twice the base diameter of the gearwheel 250, thereby guaranteeing that the balance shafts 200 and 300 rotate in opposite directions at twice the angular speed of the crankshaft 405.

As shown in figure 4, the crankshaft 405 is axially positioned such that the eccentric weights 205 and 305 of the balancing device 100 are radially aligned with a straight por-tion 420 of the crankshaft 405, axially interposed between two consecutive cranks 410. It should be observed that the axial overall dimension of the two eccentric weights 205 and 305, considered together, is smaller than the axial distance between the two consecutive cranks 410 of the crankshafts 405. In this way, the rotation of the eccentric weights 205 and 305 does not interfere with the rotation of the cranks 410 and the balancing device --100 can -be located-nearer the crankshaft 405 than usual More -precisely,-the eccentric -- weights 205 and 305 are radially aligned with the straight portion 420 located at the cen- ter of the crankshaft 405, between the central cranks 410. In this way, the vibration gen-erated by the counter-rotation of the eccentric weights 205 and 305 does not generate any tilting momentum on the crankshaft 405.

As shown in figure 6, the assembly 400 may be mounted on an internal combustion en-gine 500 having an engine block 505 defining the seats for the bearings of the crankshaft 405. The engine block 505 defines also one or more cylinders (not shown) accommodat- ing the reciprocating pistons that are coupled to rotate the crankshaft 145. In this exam- ple, the engine block 505 have to define four cylinders, The cylinders are closed by a cy-under head 510 fastened at the top of the engine block 505. The balancing device 100 is located beneath the crankshaft 405 and it is accommodated inside an oil sunip 515 fas-tened at the bottom of the engine block 505.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the forgoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and in their legal equivalents.

REFERENCES

balancing device first balance shaft 205 eccentric weight 210 internal portion 220 external portion 225 staggered portion 230 throw 235 enlarged portion 240 first gearwheel 250 third gearwheel 300 second balance shaft 305 eccentric weight 310 internal portion 320 external portion 325 staggered portion 330 throw 335 enlarged portion 340 second gearwheel 400 engine assembly 405 crankshaft 410 crank 415 connecting rod 420 straight portion 425 fourth gearwheel 500 internal combustion engine 505 engine block 510 cylinder head 515 cilsump A common plane ---B--planeofsyrnrnetry DD distance X200 longitudinal axis Y225 central axis G205 center of mass L205 axial overall dimension L225 axial overall dimension R205 radial overall dimension D205 radial distance D225 radial distance X300 longitudinal axis Y325 central axis G305 center of mass L305 axial overall dimension L325 axial overall dimension R305 radial overall dimension D305 radial distance 0325 radial distance X405 longitudinal axis

Claims

<claim-text>CLAIMS1. A balancing device (100) for an internal combustion engine (500), comprising two parallel balance shafts (200, 300) mutually coupled to rotate in opposite directions about a respective rotational axis (X200, X300), wherein each of the balance shafts (200, 300) comprises an eccentric weight (205, 305) having a center of mass (G205, G305) offset from the rotational axis thereof (X200, X300), wherein the eccentric weights (205. 305) are radially misaligned with each other, and wherein each of the balance shafts (200, 300) comprises a staggered portion (225, 325) having an axis (Y225, Y325) that is offset from the rotational axis thereof (X200, X300), thereby defining a throw (230, 330) of the batance shaft (200, 300), which is radially aligned with the eccentric weight (305, 205) of the other balance shaft (300, 200) and is arranged to allow the rotation of said eccentric weight (305, 205).</claim-text> <claim-text>2. A balancing device (100) according to claim 1, wherein each of the eccentric weights (205, 305) has a radial overall dimension (R205, R305) that is greater than a distance (DD) between the rotational axes (X200, X300).</claim-text> <claim-text>3. A balancing device (100) according to any of the preceding claims, wherein each of the eccentric weights (205, 305) has a radial overall dimension (R205, R305) that is greater than an axial overall dimension thereof (L205, L305).</claim-text> <claim-text>4. A balancing device (100) according to any of the preceding claims, wherein each of the balance shafts (200, 300) has the staggered portion (225, 325) that is axially disposed next to the eccentric weight (205. 305).</claim-text> <claim-text>5. A balancing device (100) according to any of the preceding claims, wherein each of the balance shafts (200, 300) has the axis (Y225, Y325) of the staggered portion (225, 325) that is angularly disposed in opposition of phase from the center of mass (0205, G305) of the eccentric weight (205, 305).</claim-text> <claim-text>6. A balancing device (100) according to any of the preceding claims, wherein each of the eccentric weights (205, 305) is formed in a single body with the respective bal-ance shaft (200, 300).</claim-text> <claim-text>-7: Abalancing device (100) according to-anyofThe preceding claims1wherein-each of the staggered portions (225, 325) is formed in a single body with the respective balance shaft (200, 300).</claim-text> <claim-text>8. A balancing device (100) according to any of the preceding claims, wherein the ec-centric weights (205, 305) are equally sized and the balance shafts (200, 300) are mutually coupled so that the centers of mass (G205, 0305) of the eccentric weights (205, 305) are disposed in a common plane (A) containing the rotational axes (X200, X300) simultaneousiy and in opposition of phase with each other.</claim-text> <claim-text>9. A balancing device (100) according to any of the preceding claims, wherein the balance shafts (200, 300) are mutually coupled by means of a gearwheel (240) S coaxially fitted on a first (200) of the balance shafts, which is in mesh with a gearw-heel (340) coaxially fitted on a second (300) of the balance shafts.</claim-text> <claim-text>10. An assembly (400) for an internal combustion engine (500), comprising a balancing device (100) according to any of the preceding claims and a crankshaft (405), wherein the crankshaft (405) has a rotational axis (X405) parallel with the rotational axes (X200, X300) of the balancing device (100) and is coupled to rotate a first (200) of the balance shafts thereof 11. An assembly (400) according to claim 10, wherein the crankshaft (405) is coupled to the first balance shaft (200) of the balancing device (100) by means of a gearw- heel (425) coaxially fitted on the crankshaft (405), which is in mesh with a gearw-heel (250) coaxially fitted on the first balance shaft (200), 12. An assembly (400) according to any claim from 10 to 11, wherein the eccentric weights (205, 305) of the balancing device (100) are radially aligned with a straight portion (420) of the crankshaft (405) which is axially located between a couple of consecutive crank (410) of the crankshaft (405).13. An assembly (400) according to claim 12, wherein said straight portion (420) is axially located at the center of the crankshaft (405).14. Internal combustion engine (5009 comprising an assembly (400) according to any claim from lOto 13.</claim-text>