GB2413614A

GB2413614A - A flywheel with pendulum masses tracking an order of vibration across engine speeds

Info

Publication number: GB2413614A
Application number: GB0409824A
Authority: GB
Inventors: Robert Harris; Laurence John Albon; Bryan Parsons
Original assignee: SAFE DEVELOPMENTS Ltd
Current assignee: SAFE DEVELOPMENTS Ltd
Priority date: 2004-05-01
Filing date: 2004-05-01
Publication date: 2005-11-02
Also published as: GB0409824D0

Abstract

A flywheel 70 comprises pendulum masses 82, 84 arranged circumferentially about the axis of the flywheel 70. The pendulum masses are tuned to vibrate at an order of vibration of the engine that requires suppression and to track the order of vibration at different engine speeds, at different ranges of amplitude of vibration. Adjacent pendulum masses may be mechanically linked so that they remain in phase and are pivotally mounted to pivot pins 72. Two or more arrangements of pendulum masses 82, 84 are employed within the single flywheel such that the flywheel is optimised to suppress multiple orders of vibration associated with the engine.

Description

24136 14 Flywheels The present invention relates to flywheels and in

particular to flywheels for internal combustion engines, the flywheel including damping means for cyclic torque fluctuations in the output from the engine.

Internal combustion engines produce power in pulses which occur only on the expansion stroke of the engine, for example a single cylinder, four stroke engine will produce one pulse every two revolutions of the crank. Multi-cylinder engines produce more frequent torque pulses and thus have a smoother torque output. The most commonly used engine for passenger cars is the in line four cylinder engine which produces two pulses per revolution. The diesel engine produces significantly higher levels of torque fluctuation due to the higher compression ratios used and, at idle, the engine is unthrottled which further exacerbates the problem. The torque fluctuations can have undesirable affects on the vehicle drivability but more significantly can result in gearbox noise and rattle which is difficult to suppress. The mechanical design of the piston engine introduces some additional vibrations related to the speed of rotation. These are usually referred to as orders of vibration, so that first order corresponds to a vibration occurring once per revolution, second order corresponding to twice per revolution, fourth order corresponding to four times per revolution etcetera. The important orders of vibration for piston engines are half order, first order, second order and fourth order.

A flywheel is attached to the engine primarily to ensure that there is sufficient 1 1 energy stored to keep the engine running and secondarily to smooth torque delivery. The flywheel effectiveness is a function of speed, the energy stored being related to the square of the angular velocity. Thus, at low engine speed, particularly at idle, it is difficult to obtain smooth engine operation with a flywheel designed for mid-range performance.

Using a heavy flywheel specifically for a low speed torque control, would result in a flywheel of high inertia that would adversely affect the vehicle performance.

The problem has been addressed in the past by use of a twin mass flywheel to isolate torque pulses from the transmission. A twin mass flywheel is of similar size and overall inertia to a conventional flywheel but consists of two inertia flywheel components joined together via energy storage devices, for example torsional springs. The first component is attached to the engine crankshaft and provides sufficient inertia to keep the engine turning at idle, whilst the second component is attached to the vehicle clutch plate.

The torsional spring rate is chosen so that the natural frequency of the second component, and clutch plate is lower (typically about half) than the idle torque pulse frequency of the engine, but higher than that associated with the engine cranking speed. This ensures that the spring mass system will attenuate the engine torque pulses at all normal engine speeds.

One disadvantage of the twin mass flywheel is that engine vibration is poorly controlled by the light part of the flywheel which is directly attached to the crankshaft, so that the amplitude of vibrations on the engine side can be significantly worse than those with a conventional flywheel. This can result in expensive component upgrading to withstand these vibrations, so that an engine with a twin mass flywheel may require a chain - 3 rather than belt for the cam drive. Furthermore, the drive line behaviour can be adversely affected resulting in poor response due to the soft spring in the twin mass flywheel.

Copending applications in the name of the present applicant disclose improved flywheel arrangements which address the problems of twin mass flywheels, and examples of these are illustrated in attached Figures I to 4 and Figures 5 to 8.

As illustrated in Figures 1 to 4, a flywheel 10 comprises an annular disc formation 12, apertures 14 being provided at the inner diameter of the disc formation by which the flywheel 10 may be secured to the crankshaft of an internal combustion engine, by means of bolts.

The annular disc formation 12 has an annular recess 16 formed in one face thereof, the recess 16 being formed between inner and outer circumferential walls 18, 20.

Three identical centrifugal pendulum masses 30 are located in the recess 16 at angularly spaced locations. Adjacent ends of adjacent masses 30 are pivotally interconnected to one another by links 32. The ends 34 of the masses 30 are forked, the links 32 being located between the limbs 36 of the forked ends 34 and being pivotally connected thereto by pins 38, 40. The links 32 are pivotally mounted to the disc formation 12 by pivot pins 42. The pivot pins 42 extend from the disc formation 12, the pitch circle of the pins 42 being concentric with the disc formation 12. The axis of the pivot pins 42 are located radially inwardly of and equidistant from the axis pins 38, 40, the line a-a of Figure 3, connecting the axes of pin 42 and pin 38 at one end of each of the masses 30, being parallel to the line a-a interconnecting the axes of pivot pin 42 and pin 40 at the other end of the mass 30.

The masses 30 are of arcuate configuration, the external radius of the masses 30 being slightly less than the radius of the external wall 20 of recess 16, less the separation between the axes of pin 38, 40 and the axis of pin 42, so that as the links 32 pivot about the pivot pin 42, a small clearance will be maintained between the masses 30 and the outer wall of the recess 16. At higher speed contact between the masses 30 and the external wall 20 may be permitted to provide support for the centrifugal pendulum mass system, to reduce stresses in the system.

Rubber buffers 46 are provided on the inner edges of masses 30, for engagement of the inner wall 18 of recess 16, to limit movement ofthe masses 30.

For a four cylinder four stroke engine which will produce two torque peaks per revolution, the ratio X/r where X is the distance between the centre of gravity Cg of the masses 30 and the axis of rotation of the flywheel and r is the pendulum length or separation between the axes of pins 38, 40 and axis of pin 42, is 5.6. This ratio X/r permits the resonant frequency of the pendulum mass system to track the torque pulse frequency of the engine.

With reference to Figure 3, for an application in a four cylinder four stroke engine

I - 5

the dimension of the relative components of the system could be: X=99.8 mm r = 17.50 mm s= 101.5 mm t= 127.5 mm u=97.0mm The mass of the pendulum does not directly effect the frequency of the system but the greater the mass the greater the torque reaction. For a 2.0 litre engine, the total mass of the pendulum would typically be 1.2 Kg.

When the flywheel 10 is accelerated during an expansion stroke of the engine for example, due to inertia, the masses 30 will lag behind the disc 12, as seen in Figure 4, with the trailing ends of masses 30 pivoting outwardly, while the leading ends pivot inwardly.

As the masses are tied together by links 32, the flywheel 10 remains balanced, although the centre of gravity of each of the masses move inwardly. As they flywheel 10 slows down following a torque pulse, the inertia of the masses 30 will cause them to move forwardly relative to the disc portion 12, the leading edges pivoting outwardly and trailing edges pivoting inwardly. The relative rearward movement of the masses on a torque pulse will act to reduce the peaks of these pulses while the relative forward movements will reduce the troughs, thereby smoothing out the torque fluctuations. When the acceleration is repetitive and the natural frequency of the pendulum masses corresponds to the repetition frequency then the acceleration and deceleration due to the fluctuation in the driving torque 1 1 - 6 are absorbed almost entirely by the pendulums and the flywheel body has almost steady and constant motion.

The frequency of the centrifugal pendulum mass system of Figures 1 to 4 is a function of the speed of rotation and may consequently tack and wholly eliminate the response to that frequency. The construction of the flywheel in accordance with the present invention also ensures that engine vibration is smooth and should not require the use of more robust drives for ancillary equipment.

In order that the resonant frequency of the centrifugal pendulum mass system of the present invention tracks the torque pulse frequency of the engine, it is important that the pendulum length is related to the position of the centre of gravity of the pendulum relative to the centre of rotation of the flywheel.

In theory: X=r.(1 +p2) where P = the number of pulses per revolution; r = the pendulum length; and X = the distance of centre of gravity of the pendulum to the flywheel centre.

The pendulum length is defined as the distance between the centre of gravity of the pendulum and the centre of the arc of motion of the centre of mass. All points on the pendulum move in a circular motion with radius equal to the length of the support links, - 7 due to the parallel motion of the support links. The length of the support links is consequently equal to the length of the pendulum.

Consequently, for a four cylinder four stroke engine requiring suppression of second order vibrations, corresponding to firing frequency, where P = 2, then X/r = 5, that is the centre of gravity of the pendulum must be set at 5 times the pendulum length from the axis of rotation of the flywheel. However, in practice, it has been found that a value greater than the theoretical value appears to be more favourable. This is probably due to the mass of the pivot links for the penduluTns and some non-linearity. Preferably the value of X/r for a four cylinder four stroke engine will be between 5 and 6.

For a four cylinder, four stroke engine which produces two torque pulses per revolution, a ratio X/r of 5.6 is preferred. For a single cylinder, four stroke engine which produces one pulse every two revolutions, the X/r ratio is preferably from 1.25 to 2; for a two cylinder, four stroke engine which will produce one pulse per revolution, the ratio X/r is preferably between 2 and 3; and for a six cylinder, four stroke engine where there would be 3 pulses per revolution, the X/r ratio is preferably between 10 and 1 1.

A two stroke engine will have twice the firing frequency of a four stroke engine, so that a twin cylinder, two stroke engine would require a X/r ratio between 5 and 6; and a single cylinder, two stroke engine would require a X/r ratio between 2 and 3.

An alternative flywheel, operating on the saTne principle, is disclosed in Figures 5 to - 8 8.

Referring to Figures 5 and 6 the flywheel 50 comprises a disc assembly 57 having an outer peripheral wall 54 forming a recess 56. The axis of rotation 58 of flywheel 50 is mutually perpendicular to the disc assembly 52.

Equally spaced on the disc assembly 52 about the axis of rotation 58 there are nine pins 60, on each of which there is mounted a respective pendulum mass 62 pivotally connected to its associated pin. Each pendulum mass 62 is in the form of a flat planar disc which is essentially kidney shaped in plan view, the perimeter defining two overlapping circles. The edges of each circle are parallel to the axis of the rotation 58 with the sector of each of the two circles forming a respective cam surface 64 and 66 which cooperate with corresponding surfaces 66 and 64 of adjacent pendulum masses 62.

Figures 5 and 6 illustrate the position each pendulum mass 62 would adopt if the flywheel 50 was rotated at a constant angular velocity. In this position, the centre of mass 68 of each pendulum mass is aligned radially outward of its respective pin 60 and is maintained in this position by the centrifugal force acting on the mass as the flywheel 50 rotates.

Referring now to Figures 7 and 8, there is illustrated the position the pendulum masses 62 of Figures S and 6 adopt when the flywheel 50 is subjected to angular acceleration in the direction of arrow 70. The inertia of the masses causes their centres of * - 9- gravity 68 to lag behind the disc assembly 52, thus the masses rotate about their respective pins 60 in the direction of arrow 72. This movement absorbs energy from the torque pulse thereby reducing the amplitude of that toque pulse associated with a firing stroke.

Conversely, during the torque "trough" associated with a compression stroke, the pendulum masses 62 move in the opposite direction and this relative movement again acts to reduce the troughs thereby smoothing out the torque fluctuations.

The cam surfaces 64 and 66 of each pendulum mass engage with corresponding surfaces 66 and 64 of adjacent masses. The kidney shaped geometry ensures that the masses interact with each other and can only rotate about their respective pins 60 if they rotate together. This ensures that the masses remain synchronized and therefore ensures the flywheel remains in balance. Without this, if one mass should move differently to the others, for example due to different resistive forces on the pin, this would result in an imbalance in the flywheel.

As shown in Figure 7, the pendulum masses 62 are limited in their movement by coming into contact with the inner surface of the peripheral wall 54 defining the recess 56.

This limitation on the rotation of the masses ensures that they do not progress pass the point where cooperating cams could become disengaged.

In order that the resonant frequency of the centrifugal pendulum mass system of the present invention tracks the torque pulse frequency of the engine, it is important that: (Ord*k) = (R+p)*p - lo- where 0rd = Order of vibration to be suppressed k = radius of gyration of pendulum R = distance of the pivot point from the centre of rotation p = length of the pendulum Consequently, for a four cylinder four stroke engine, where it is desirable to suppress the second order, 0rd = 2, then the radius of the pivot point from the centre of the flywheel is, by rearrangement: R = 4*k2/p-p In some applications, it may be desirable to suppress two or more orders of vibration or to suppress vibrations of different amplitudes.

According to the present invention there is provided a flywheel for use with an internal combustion engine, the flywheel comprising: a disc formation and a plurality of pendulum mass systems supported by the disc formation, each pendulum mass system having a natural frequency which tracks and substantially coincides with an order of vibration of the engine that is to be suppressed.

Each pendulum mass system may have a natural frequency selected to suppress a different order of vibration associated with the engine. This enables a flywheel to be tuned to track and isolate first and second (or higher) order vibrations of the engine, which are - 11 possibly associated with torque pulses. A first pendulum mass system may be tuned to a primary torque pulse frequency with a second pendulum mass system tuned to a higher order frequency. The invention may be particularly applicable to engines which have unequal firing period, for example a 90 V4, whereby one pendulum mass system can be tuned to reduce the first order frequencies and the second pendulum mass system tuned to reduce the second order frequencies. However, the two frequency bands may overlap.

Alternatively, different pendulum mass systems may have a natural frequency selected to suppress the same order of vibration, each natural frequency being selected to suppress that order of vibration at different ranges of amplitude of the vibration where, due to non linearities, a single pendulum mass system may be insufficient to suppress an order of vibration at significantly different amplitudes of vibration. The two ranges of amplitude may overlap.

Preferably the disc formation has an axis of rotation mutually perpendicular to the plane of the disc formation, the disc formation having a plurality of pivot points located symmetrically about the axis of rotation, the plurality of pivot points supporting a plurality of pendulum masses of a first pendulum mass system and a plurality of masses of a second pendulum mass system, the pendulum masses of each pendulum mass system being arranged symmetrically about the disc formation, each pendulum mass being mechanically linked to two adjacent pendulum masses of its pendulum mass system, such that all the pendulum masses of each pendulum mass system are locked together in phase. - 12

The above arrangement enables two pendulum mass systems to be supported by a common set of pivot points, which may be pivot pins, but to operate independently of each other with the pendulum masses of each system being maintained in phase.

Advantageously any angular acceleration or deceleration flywheel about the axis of rotation, in response to a torque pulse, causes the pendulum masses to be displaced relative to the pivot points such that the centre of mass of each pendulum mass is radially displaced towards the axis of rotation.

Advantageously, the pendulum masses of each pendulum mass system are of a similar type and are supported by pivot pints common to both mass systems, wherein the centre of mass of each pendulum mass of one pendulum mass system is at a different location to the centre of mass of the pendulum masses of a second pendulum mass system, relative to the location of the pivot pins. This arrangement minimises the number of different component types required and provides for a symmetrical arrangement of masses in the flywheel maintaining the balance of the flywheel.

Each pendulum mass system may comprise a plurality of similar pendulum masses disposed symmetrically about the disc formation, adjacent ends of adjacent pendulum masses being interconnected by links, the links being pivotally connected to the disc formation about axes spaced equally from the axis of the pivot connections between the links and the ends of adjacent pendulum masses, the system of pendulum masses having a natural frequency which coincides with the torque pulse frequency of the engine. This - 13 arrangement provides for the masses to be supported at respective distal ends of the mass and for the masses to pivot about the links.

In an alternative arrangement, the disc formation may support a plurality of pivot points arranged symmetrically about the axis of rotation, wherein each pendulum mass of pendulum mass system is pivotally connected to a respective pivot point, each pendulum mass having at least one profiled surface for engaging with adjacent pendulum mass, wherein the position of the pivot points and dimensions of the masses are arranged such that adjacent masses of each mass system can rotate in phase about their respective pivot points, the profiled surfaces preventing rotation ofthe masses except when the masses of a pendulum mass system rotate about their respective pivot points together in phase.

With this arrangement, each mass pivots about its associated single pivot point and is maintained in phase by the cam surfaces of the mass mechanically engaging corresponding cam surfaces of the two adjacent masses.

Two embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures and particularly with reference to Figures 9 to 11. In the figures: Figure 1 is an end elevation of a first flywheel arrangement; Figure 2 is a partial perspective view of the flywheel illustrated in Figure 1; Figure 3 is a diagrammatic illustration of the centrifugal pendulum mass system of the flywheel illustrated in Figure 1 in a central position; ( - 14 Figure 4 is a diagrammatic illustration of the centrifugal pendulum mass system of the flywheel illustrated in Figure 1 in a displaced position; Figure S is a plan view of a second arrangement of flywheel; Figure 6 is a perspective view of the pendulum mass system of the flywheel of Figure 5; Figures 7 and 8 correspond to Figures S and 6 but with the masses orientated as they would be on the flywheel when experiencing a torque pulse; Figure 9 is a perspective view of a pendulum mass system of a first flywheel arrangement in accordance with the present invention; Figure 10 is a plan view of a pendulum mass system of a second flywheel arrangement in accordance with the present invention; and Figure 11 is a perspective view of the pendulum mass system of Figure 10.

Referring to Figure 9, there is illustrated a flywheel pendulum mass assembly 68 IS having a disc formation 70 arranged to be substituted for the disc assembly illustrated in Figures 1 to 4 of the accompanying drawings.

Disc assembly 70 of Figure 9 has extending therefrom three pivot pins 72 each supporting a first link 74, associated with a first pendulum mass system 76 and a second link 78 associated with a second pendulum mass system 80. The pendulum mass system 76 comprises three pivot pins 72, three links 74 and three masses 82, the masses 82 being supported at either end by links 74 to which they are respectively connected. 1 1 -

The pendulum mass system 80 also comprises the three pivot pins 72 and in addition three links 78 and three masses 84.

Each of the pendulum mass systems 76 and 80 operates in the same way as the pendulum mass system in accompanying Figures 1 to 4, but the two pendulum mass systems are tuned to different orders of vibration associated with the engine which are to be suppressed.

In an alternative arrangement depicted in Figures 10 and 11, a disc formation 88 supports a number of pivot pins 90, each pivot pin 90 in turn supporting a kidney shaped pendulum mass 92 of a first pendulum mass system and a second kidney shaped pendulum mass 94 of a second pendulum mass system. Each mass 92 and 94 supported by a common pivot pin is mounted to the pivot pin, for example by means of a bearing, such that it can pivot on the pin 90 independently of the other pendulum associated with that pivot pin.

Each layer of pendulum masses therefore forms a separate pendulum mass system independent of the other pendulum mass system. Each pendulum mass 92, 94 has cam faces 96 and 98 which engage with corresponding cam faces 98, 96 of adjacent pendulum masses, such that pendulum masses can only rotate about their respective pivot pins if all pendulum masses rotate together in phase.

Each pendulum mass system functions to suppress torque pulses in the manner described with reference to Figures 5 to 8. The pendulum masses 92 and 94 have the same external dimensions, but each mass 94 of the second pendulum mass system has its centre r r - 16 of gravity at a different position to the centre of gravity of each mass 92 of the first pendulum mass system relative to the associated pivot pin 90. This is achieved by either boring a hole 100 in each pendulum mass 94 or by boring the hole 100 and filling the aperture formed with a material denser than the material of the mass. s

The dimensions of the flywheel and value of the masses are selected in accordance with the following equation: T = m.(R+p).R.N2.amp where T = torque pulse amplitude m = total mass of pendulums R = radius of pivot attachment points from centre of flywheel p = distance between pivot and centre of gravity of pendulum N = speed of rotation amp = amplitude of swing of pendulums.

The invention has been described above with reference to two embodiments disclosed in the drawings. However, a skilled person will appreciate that many alternative arrangements are possible within the scope of the appended claims, in particular the flywheel may comprise more than two pendulum mass systems and each pendulum mass system may comprise a different number of pendulum masses to those shown in the specific embodiments illustrated. t - 17

Claims

1. A flywheel for use with an internal combustion engine, the flywheel comprising: a disc formation and a plurality of pendulum mass systems supported by the disc formation, each pendulum mass system having a natural frequency which tracks and substantially coincides with an order of vibration of the engine that is to be suppressed.

2. A flywheel as claimed in Claim 1, wherein each pendulum mass system has a natural frequency selected to suppress a different order of vibration associated with the 1 0 engine.

3. A flywheel as claimed in Claim 1, wherein each pendulum mass system has a natural frequency selected to suppress the same order of vibration, each natural frequency being selected to suppress that order of vibration at different ranges of amplitude of the 1 5 vibration.

4. A flywheel as claimed in Claim 1, 2 or 3, wherein the disc formation has a plurality of pivot points by which the pendulum mass systems are supported.

5. A flywheel as claimed in Claim 4, wherein the disc formation has an axis of rotation mutually perpendicular to the plane of the disc formation and passing through the centre of the disc formation, the disc formation having a plurality of pivot points located symmetrically about the axis of rotation, the plurality of pivot points supporting a plurality 1 b - 18 of pendulum masses of a first pendulum mass system and a plurality of masses of a second pendulum mass system, the pendulum masses of each pendulum mass system being arranged symmetrically about the disc formation, each pendulum mass being mechanically linked to two adjacent pendulum masses of its pendulum mass system, such that all the pendulum masses of a pendulum mass system are locked together in phase.

6. A system as claimed in Claim 4 or 5, wherein angular acceleration or deceleration of the flywheel about the axis of rotation in response to a torque pulse causes the pendulum masses to be displaced relative to the pivot points such that the centre of mass of each pendulum mass is radially displaced toward the axis of rotation.

7. A system as claimed in Claim 4, 5 or 6, wherein the pendulum masses of each pendulum mass system are of a similar type and are supported by pivot pins common to both mass systems, wherein the centre of mass of each pendulum mass of one pendulum 1 S mass system is at a different location to the centre of mass of the pendulum masses of a second pendulum mass system relative to the location of the pivot pins.

8. A flywheel as claimed in any preceding claim, wherein each pendulum mass system comprises a plurality of similar pendulum masses disposed symmetrically about the disc formation, adjacent ends of adjacent pendulum masses being interconnected by links, the links being pivotally connected to the disc formation about axes spaced equally from the axis of the pivot connections between the links and the ends of adjacent pendulum masses. 19

9. A flywheel as claimed in Claim 8, wherein each link is supported on a pivot pin, each pivot pin supporting one link from a first mass system and one link from a second mass system.

10. A flywheel as claimed in Claim 5, or Claim 6 or 7 when dependent on Claim 5, wherein the disc formation supports a plurality of pivot points arranged symmetrically about the axis of rotation, wherein each pendulum mass of each pendulum mass system is pivotally connected to a respective pivot point, each pendulum mass having at least one profiled surface for engaging with an adjacent pendulum mass, wherein the position of the pivot points and dimensions ofthe masses are arranged such that adjacent masses of each mass system can rotate in phase about their respective pivot points, the profiled surfaces preventing rotation of the masses except when the masses of a pendulum mass system rotate about their respective pivot points together in phase.

11. A flywheel as claimed in Claim 10, comprising a plurality of pivot pins and associated masses arranged in a complete circle on the disc formation, the position of the masses being locked in phase by cooperating pairs of adjacent profiled surfaces of adjacent masses.

12. A flywheel as claimed in any preceding claim, wherein the centre of gravity of each mass is located radially outward of the pivot points.

13. A flywheel as claimed in any preceding claim, in which the pendulum masses are - 20 mounted in an annular recess in one face of the flywheel.

14. A flywheel for use with an internal combustion engine, substantially as hereinbefore described with reference to, and/or as illustrated in, one or more of the accompanying drawings.