Abstract:
The invention relates to an internal combustion engine, the crankshaft ( 1 ) of which is equipped with a pulley or flywheel ( 4 ) secured to it by fastening means, in which said flywheel ( 4 ) is equipped with at least one pendular element ( 45 ), whose size, mass and position on said flywheel ( 4 ) are determined so as to be tuned to close to the angular frequency of the major harmonic of the cyclic disturbance.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of International Application No. PCT/FR/99/01638 filed Jul. 7, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a reciprocating internal combustion engine including a means of reducing cyclic disturbances for low-speed running. 
     At the current time, all engine manufacturers are looking to reduce the pollution and consumption of vehicle engines in town. 
     A first solution consists in stopping the engine at red lights and then re-starting it. This entails coupling a motor-alternator directly to the crankshaft, and this is expensive. 
     The second solution consists in reducing the rotational speed of the engines at low idle. However, when the low idle speed of an engine is reduced, the cyclic disturbances increase, and this makes its running unstable. The only way to reduce the cyclic disturbances is to increase the moment of inertia of the flywheel. However, this presents numerous drawbacks, namely: it involves a penalizing increase in the mass of the propulsion unit; it necessarily entails improving the performance of the starter motor; and it entails a drop in engine performance, the engine becoming slower to pick up speed. 
     The arrangement according to the present invention makes it possible to simultaneously obtain two antagonist results, namely: a flywheel with a high moment of inertia for dealing with cyclic disturbances, very greatly reducing these, and a lower moment of inertia for the engine because use is made of a flywheel of lower mass. 
     In order to achieve this result, use is made of pendular masses associated either with the flywheel or with a pulley on the other end of the crankshaft. 
     It is known practice for pendular masses to be associated with a crankshaft and one and/or other of its ends in order to damp out the vibrations which arise in the crankshaft itself when subjected to heavy load, which vibrations could cause the crankshaft to break. 
     SUMMARY OF THE INVENTION 
     In the case of the present invention, these pendular systems are being used not to protect the crankshaft against a risk of breakage due to vibration, but to combat the effects due to the moment of inertia of the engine assembly (crankshaft and pistons) when the engine is running at low speed (that is to say when the crankshaft is subjected to very light load) and is therefore subject to cyclic disturbances. 
     Such pendular systems are described in U.S. Pat. No. 5,295,411. 
     Surprisingly, it has been discovered that these same means could advantageously be employed to solve an entirely different problem, namely that of irregularities in the cycle, or “cyclic disturbances” which occur when an engine is running at low speed, the crankshaft then being subject to light load. 
     When wishing to tackle the problem of vibrations at heavy load, as is the case with the means described in U.S. Pat. No. 5,295,411, there is the desire to tune the pendulum (or pendulums) to the harmonics likely to excite the natural torsional mode of the crankshaft throughout the engine speed range. For a four-cylinder four-stroke engine, this angular frequency is of the order of 30,000 to 40,000 rpm. 
     By contrast, in the case of the present invention, the pendulum will be tuned to the number of explosions per revolution and this will be done for speeds close to the low idle speed (700 rpm and below), and thus for light load running. In the case of a four-cylinder four-stroke engine, there are two explosions per revolution which means that the pendulums will be tuned to the harmonic  2 . The pendulums will therefore be tuned to the harmonic of the cyclic disturbance or, at the very least, to near to the angular frequency of its major harmonic. 
     This application of these pendular systems, which are known in themselves, to the very specific problem of cyclic disturbances makes it possible to have a moment of inertia adapted to suit rotational speeds of the order of 500 rpm±200. 
     These systems, the characteristics of which are calculated to be effective against cyclic disturbances at low speed, are inoperative and without effect at high speed. 
     According to the invention, at least one element capable, as the flywheel rotates, of having a pendular movement with respect to said flywheel when rotation occurs with cyclic disturbance is coupled to the crankshaft, for example to the flywheel. If Ω is the mean rotational speed of the engine, then it is known that during running, the instantaneous speed varies between Ω 1  and Ω 2 ; the cyclic irregularity coefficient is          n   =              Ω   1     -     Ω   2            Ω       ;                          
     it may be calculated that, for a reciprocating internal combustion engine,        n   ≈     k     I                   Ω   2                                
     where k is a constant which represents the amplitude of the variation in engine torque and I is the moment of inertia of the engine-receptor assembly. This shows that cyclic disturbances are at their highest when the mean rotational speed is at its lowest. The use of (a) pendular element(s), suitably tuned, makes it possible to compensate for the cyclic disturbances. The size and mass of the pendular elements, and their positions on the flywheel are advantageously chosen so that they are tuned to the major harmonics of the cyclic disturbances. It is found that, in this way, it is possible to run, for example, a 4-cylinder, 4-stroke engine at average speeds of close to 300 rpm without troublesome irregularities and using a flywheel which is lighter by comparison with those used in the state of the art. 
     The subject of the present invention is therefore an internal combustion engine, the crankshaft of which is equipped, for example, with a flywheel, characterized in that said flywheel is equipped with at least one pendular element whose size, mass and position on said flywheel are determined so as to be tuned to close to the angular frequency of the major harmonic or harmonics of the cyclic disturbance. For example, for an in-line 4-cylinder 4-stroke reciprocating engine, the major harmonic of the cyclic disturbance has an angular frequency equal to twice the rotational speed. 
     The present invention may also include the following arrangements taken separately or in combination: 
     a) the flywheel is equipped with at least two housings in which a flyweight can move freely; 
     b) the flywheel is equipped with three housings arranged 120° apart; 
     c) the flywheel is equipped with two groups of three housings arranged 120° apart, the two groups being interspersed symmetrically and each group having different sizes and positions, and different masses; 
     d) the side walls of each housing are planar and separated from one another by a runway track, the flyweight being a roller capable of rolling between the side walls along the runway track; as a preference, the roller is a cylinder of revolution; 
     e) the runway track of the housing, against which the roller rolls, is a surface of revolution about an axis perpendicular to the side walls of the housing; 
     f) the housing may be a cylinder of revolution; 
     g) the cross section of the runway track on a plane parallel to the side walls of the housing is a curve determined by calculation according to the desired reaction on the cyclic disturbance phenomena; 
     h) the side walls of each housing consist of annular cheeks fixed one on each side of the flywheel; the runway track of a housing consists of a ring inserted in an opening made in the flywheel, the interior edge of each annular cheek coming to rest against one end of each ring and constituting a runway track, the means of attaching the flywheel to the crankshaft being arranged in the central region left free by the annular cheeks; 
     i) the flywheel is equipped with three pendular devices arranged 120° apart, each pendular device being double; 
     j) the flywheel is equipped with two groups of three double pendular devices interspersed symmetrically and having different dimension, position and mass characteristics; 
     k) the double pendular system consists of a moving mass connected to the flywheel by two axles, each moving both in a housing formed in the mobile mass and in a housing formed in the flywheel; 
     l) the mobile mass has a T-shaped cross section; 
     m) the mobile mass has a U-shaped cross section; 
     n) the monofilar pendular system consists of an asymmetric flyweight borne in pivoting by an axle; 
     o) the monofilar pendular system consists of a cylindrical flyweight equipped with drillings on just one side, it being possible for these drillings to be separate or combined into a single slot; 
     p) the monofilar pendular system consists of a sealed casing filled with two immiscible liquids of different densities, for example oil and mercury; 
     q) the monofilar pendular system consists of a toothed pinion meshing either with a central pinion or with peripheral teeth; 
     r) the either monofilar or bifilar pendular system is locked in position above a predetermined rotational speed by radial sliders each held by a spring moving under the effect of centrifugal force; 
     s) the pendular system consists of n flyweights arranged n/360° [sic] apart, these flyweights having the shape of a circular sector subtending an angle of n/360° [sic] and mounted so that they can pivot on the flywheel; 
     t) each flyweight in the shape of a circular sector has a bore inside which a mobile mass moves. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     To make the invention easier to understand, one embodiment thereof, depicted in the appended drawing, will be described hereinbelow by way of purely illustrative and nonlimiting example. 
     In this drawing: 
     FIG. 1 depicts a view in axial section on I—I of FIG. 2, of the end of the crankshaft of an engine according to the invention equipped with a flywheel with pendular elements; 
     FIG. 2 depicts a view in elevation, with partial cutaway, of the flywheel of FIG. 1, on II—II of FIG. 1; 
     FIGS. 3 and 4 depict a view in elevation and a view in axial section of an alternative form of FIGS. 1 and 2; 
     FIGS. 5 and 6 depict two views in elevation and in axial section of a second embodiment of the present invention; 
     FIGS. 7 and 8 depict two views in elevation and in axial section of a third embodiment of the present invention; 
     FIGS. 9 and 10 depict two views in elevation and in axial section of an alternative form of the third embodiment of the present invention; 
     FIG. 11 depicts a view in elevation of a second alternative form of the flywheel of FIGS. 1 and 2; 
     FIG. 12 depicts a view in elevation of a third alternative form of the flywheel of FIGS. 1 and 2; 
     FIG. 13 depicts a view in elevation of a fourth alternative form of the flywheel of FIGS. 1 and 2; 
     FIG. 14 depicts a view in elevation of a fifth alternative form of the flywheel of FIGS. 1 and 2; 
     FIG. 15 depicts a view in elevation of a sixth alternative form of FIGS. 1 and 2; 
     FIG. 16 depicts a view in elevation of a seventh alternative form of FIGS. 1 and 2; 
     FIG. 17 depicts a view in elevation of an eighth alternative form of FIGS. 1 and 2; 
     FIG. 18 depicts a view in elevation of an alternative form of the systems described in FIGS. 7 and 9, incorporating locking means similar to those of FIG. 17; 
     FIG. 19 depicts a plan view of a fourth embodiment of the present invention, with an alternative form depicted in dotted lines; 
     FIG. 20 is a perspective view of FIG.  19 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, it can be seen that fitted onto the end  1  of a crankshaft  2  is a sleeve  3  to which a flywheel, denoted by the general reference  4  is coaxially fastened. This fastening is achieved using eight studs  46  distributed uniformly about the axis of the flywheel  4 . 
     The flywheel  4  consists of a solid disk  40  which is thick enough to have a significant moment of inertia suited to the engine with which it is associated. This disk  40  is pierced with three circular openings  41  120° apart, in each of which is inserted a cylindrical ring  42 . The two faces of the disk  40  are covered with annular cheeks  43  which are fastened to the disk  40  by screws  47  cooperating with threaded bores  48  in the disk  40 . These two cheeks  43  cover the ends of the rings  42  and, together with the interior volume of each cylindrical ring  42 , define a closed cylindrical housing  44 . 
     Arranged in each housing  44  is a flyweight consisting of a roller  45 . This roller  45  is a solid cylinder, the length of which is approximately equal to (and in fact slightly shorter than) the thickness of the disk  40 ; this distance is the distance separating the two cheeks  43  and therefore defines the length of the housing  44 . What this means is that the rollers  45  can move freely in their housings  44  and, in particular, can roll along the interior wall of said housings  44 . 
     When the engine is stopped, each of the rollers  45  rests at the bottom of its housing  44 ; as soon as the engine reaches a few revolutions per minute, for example at the speed at which it is driven by the starter motor, the rollers  45 , under the effect of centrifugal force, move to occupy the radial position depicted in FIGS. 1 and 2. 
     When the engine is running at low idle, cyclic disturbances occur and are manifested in successive decelerations and accelerations of the rotational speed of the crankshaft  1 : the rollers  45  then roll along the wall of their cylindrical housings in one direction or the other, thus counterbalancing, or at the very least reducing said cyclic disturbances, said rollers then behaving like pendular elements. 
     In the example depicted, the housings  44  are cylindrical, which means that each roller  45  can be considered as being a pendulum; however, the invention is not restricted to this particular case. 
     Specifically, the interior wall of each housing may be of any cross section: circular (as depicted), elliptical, or other; it may even not be symmetric with respect to the radius of the disk  40  passing through the center of the cross section: this makes it possible to alter the law governing the reaction of the flyweights on the cyclic disturbance phenomena at will. 
     Likewise, in the example depicted, there are three housings  44  and three rollers  45 , but the invention is not restricted to this particular embodiment: there has to be at least one housing and one flyweight, but there could be 2, 3, 4 or even more of these provided that they are arranged at uniform spacings with respect to the center of rotation of the flywheel. 
     FIGS. 3 and 4 depict an alternative form of the embodiment of FIGS. 1 and 2, the same elements bearing the same references. To simplify the figures, only the flywheel  4  has been depicted, the crankshaft  1  and the means of fastening the flywheel  4  to the end of the crankshaft having been omitted because they do not form part of the invention. The same approach will be taken in the other FIGS. 5 to  10 . 
     According to this alternative form, the housing  44  of each roller  45  does not pass through the entire thickness of the flywheel  40  but is hollowed from the latter over just a part of this thickness. Each housing  44  is equipped with a runway ring  42  which projects partially from the housing  44  and is covered by a cover  49 . The roller  45  travels in the cylindrical volume consisting of the bottom  44   a  of the housing  44 , the ring  42  and the cover  49 . 
     The way in which this device works is the same as the way described for the previous FIGS. 1 and 2. 
     FIGS. 5 and 6 depict a second embodiment of the device according to the invention, the elements which are identical to those of FIGS. 1 to  4  bearing the same references. 
     This second embodiment is characterized in that the flywheel  4  has two groups of three housings which are uniformly interspersed. 
     There is, first of all, a group of three housings  44 , arranged 120° apart, each housing containing a flyweight  45 . 
     There is also a second group of three housings  54 , arranged 120° apart. This second group is interspersed with the first, that is to say that the housings  44  and  54  are 60° apart. Each housing  54  is equipped with a runway ring  52 , a flyweight  55  and is closed by a cover  59 . It should be noted that all the dimensional parameters of the housings  54  differ from those of the housings  44 , namely: their distance from the center of the flywheel  40  is shorter, their diameter is smaller and the mass of the flyweight  55  is different. 
     All these parameters can easily be determined by calculation so that the pendular elements  45  and the pendular elements  55  are tuned to close to the angular frequencies of the major harmonics of the cyclic disturbance. 
     FIGS. 7 to  10  illustrate a third embodiment of the invention. 
     Mathematical calculations show that it is preferable in certain cases to have double pendular systems, these being the systems known to specialists by the name of “bifilar” systems. 
     In FIGS. 7 to  10 , there are three groups of pendular devices arranged 120° apart. 
     In FIGS. 7 and 8 it can be seen that the flywheel  4  has a peripheral groove  60 . The portions  61   a  of three T-shaped masses  61  arranged 120° apart sit in this groove  60 . Each portion  61   a  of a mass  61  is equipped with two circular drillings  62 . The flywheel  40  is pierced with three pairs of circular drillings  63  arranged 120° apart. Each pair of drillings  63  corresponds to two drillings  62  in a mass  61 . Axles  64  pass through the drillings  62  and  63 . The axles  64  have a diameter smaller than that of the drillings  62  and  63 . Each mass  61  therefore constitutes the equivalent of a pendulum suspended from two wires. When the rotational speed of the engine drops and then increases, each mass  61  swings in one direction and then in the other. The various parameters of these double pendulums: dimensions, position and mass, are determined by mathematical calculation so that they are tuned to an angular frequency close to the angular frequency of the chosen harmonic, in this case the major harmonic of the cyclic disturbance of the engine under consideration. 
     FIGS. 9 and 10 illustrate an alternative form of the device of FIGS. 7 and 8, the shape of each ass being inverted and U-shaped so as to form a caliper, identical elements bearing the same references. 
     Each mass  71  is a component, the cross section of which is U-shaped so that it sits over the flywheel  40 . For this purpose, each mass  71  is equipped with two side walls  70 , the spacing of which is slightly greater than the thickness of the flywheel  40 . 
     The side walls  70  are equipped with drillings  72  which correspond to the drillings  62  in FIGS. 7 and 8; the flywheel  40  is equipped with the same drillings  63  as it was in FIGS. 7 and 8 and axles  74  (corresponding to the axles  64 ) pass through the drillings  63  and  72 . 
     The operation is identical to that of the device depicted in FIGS. 7 and 8. 
     Note that FIGS. 5 and 6 depict a system having two groups of three flyweights  45  and  55  but the invention is not restricted to this particular arrangement: it is possible to have a number “n” of groups of flyweights, arranged on “q” different radii, the flyweights of each group having different masses “m”. It does, however, prove necessary for the number “n” to be at least equal to 2 and for the flyweights to be offset by angles equal 360/n to for balancing reasons. 
     Similarly, there could be any number “n” of masses such as  61  or  71 , of different masses “m”, placed on “q” different radii, “n” being greater than or equal to 2 and the masses  61  or  71  being offset by angles equal to 360/n for balancing reasons. 
     FIGS. 11 to  18  depict various alternative forms which have been designed to prevent the flyweights or rollers from slipping. 
     In FIG. 11, it can be seen that the rollers  45  moving freely in cylindrical housings  44  have been replaced by asymmetric flyweights constituting the pendular mass  80  which are mounted on an axle  81  arranged at the center O of the housing  44  so that they can pivot in a housing  82 . 
     In FIG. 12, it can be seen that the flyweight  80  consists of a cylinder which can turn freely inside the housing  82  by virtue of a ball bearing  83 . Drillings  83  all made on the same side of the diameter  85  have the effect of introducing asymmetry into the mass of the flyweight  80 , thus constituting the pendular mass. 
     In FIG. 13, it can be seen that the three drillings  83  of FIG. 12 have been combined into a single semicircular slot  83   a.    
     In FIG. 14, it can be seen that arranged in the cylindrical housing  82  of center O is a sealed cylindrical casing  86 , also of center O, this sealed casing  86  being filled with two immiscible liquids of different densities, for example with oil  87  and mercury  88 . Under the effect of centrifugal force, the mercury forms a lenticular shape  88  as depicted and constitutes the pendular mass. 
     In FIG. 15, it can be seen that the housing  82  is provided on its inside with teeth, with which a pinion  89  which constitutes the pendular mass, meshes. 
     In order to avoid the noises caused by the pinions  89  coming into contact with the teeth  82   a,  an axle  81  is preferably provided and stops the pinion  89  from having any play. 
     FIG. 16 depicts an arrangement that is the reverse of that of FIG.  15 . In this case, the pinion  89 , acting as a pendular mass, meshes with the centered axle  81   a  which has teeth. The toothed axle  81   a  may be stationary or mounted so that it can pivot about its axis O. 
     The devices described in FIGS. 11 to  16  operate exactly like the devices described in FIGS. 1 and 2 or  3  and  4 . 
     FIGS. 17 an  18  depict arrangements which make it possible to cancel the effect of the pendular masses above a certain speed, whether this be using a monofilar pendulum (FIG. 17) or a bifilar pendulum (FIG.  18 ). 
     FIG. 17 corresponds to FIG.  2  and the same elements bear the same references. Arranged in the circular openings  41  made in the flywheel  40  are cylindrical rings  42  in each of which a roller  45  can move. A slider  90  can move in a housing  91 , the axis of which is radial. A tension spring  92  keeps the slider  90  in contact with the closed end  91   a  of the housing  91 . When the rotational speed of the flywheel  40  increases, the slider  90  moves radially against the action of the spring  92 . At its opposite end to the closed end  91   a  of the housing  91 , the slider  90  has a curved surface  93  intended to act as a seat for the roller  45 . Quite obviously, the ring  42  has an appropriate opening to allow the slider  90  to pass. When stationary, the parts occupy the positions depicted in dashed line: that is to say the slider  90  rests against the closed end  91   a  of its housing  91  and the roller  45  can move freely. As the speed increases, the roller comes to adopt the position depicted in solid line and therefore acts like the pendulum it is supposed to according to the present invention. Above a certain rotational speed, defined as a function of the mass of the slider  90  and of the strength of the spring  92 , the slider  93  [sic] locks the roller  45  in place and the roller therefore becomes inoperative. 
     FIG. 18 depicts a locking system which fulfills the same role as the one in FIG. 17, but for a bifilar pendular system like the one of FIGS. 7 and 8. In this FIG. 18, the elements which are the same as those in FIGS. 7 and 8 bear the same references and are not described again. Unlike in FIG. 7, the device comprises four bifilar pendular masses  61  arranged 90° apart (instead of three at 120°). 
     The flywheel  40  has four radial housings  91 , 90° apart, the axes of these housings  91  coinciding with the axes of symmetry of said flywheel  40  separating the four bifilar pendular masses  61 . 
     As was the case in FIG. 17, sliding in each housing  91  against the action of a tension spring  92  is a slider  90 , but the end  94  of the slider is in the shape of a 90° wedge instead of being a semi-cylindrical seat  93 . 
     The way in which this device works is similar to the way in which the device of FIG. 17 works. 
     When stationary, each slider  90  rests against the closed end  91   a  of its housing  91  under the effect of its tension spring  92 . It is only above a speed that is determined as a function of the mass of each slider  90  and of the strength of its spring  92  that the sliders  90  will slide under the effect of centrifugal force to lock the masses  61  in place, so that the masses then become inoperative. 
     FIGS. 19 and 20 depict a fourth embodiment of the invention. 
     With reference to these figures, it can be seen that the pendular masses consist of six flyweights  100 , each flyweight  100  being mounted so that it can pivot on the flywheel  40  by means of an axle  101  and a bearing or rolling bearing  102 . The axles  101  are arranged 60° apart and the flyweights  100  have the shape of a circular sector subtending an angle of 60°. 
     As illustrated in FIG. 20, the axles  101  are borne by a circular flange  103 . 
     According to an alternative form, depicted in dotted line in FIG. 19, each flyweight may have a bore  104 , centered on its bisector, arranged beyond the axle  101  with respect to the center of the flywheel  40 , in which a mobile mass  105  can move in a similar way to what is depicted in FIGS. 1 to  6 . 
     Quite obviously, the invention is not restricted to the case in which there are six flyweights, it being possible for there to be any number “n” of flyweights, but preferably more than 3 of these.