GB2413613A

GB2413613A - A flywheel with pivoted pendulum masses having profiled surfaces for engagement with adjacent masses

Info

Publication number: GB2413613A
Application number: GB0409823A
Authority: GB
Inventors: Robert Harris; Laurence 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: GB0409823D0

Abstract

A flywheel for an internal combustion engine comprises a disc assembly 2 supporting a number of pins 7 on each of which is mounted a pendulum mass 8. On acceleration or deceleration, each pendulum mass is caused to lag or lead the disc respectively such that the centre of mass 9 of each pendulum mass moves towards the centre of the disc assembly as the mass pivots around the associated pins 7, this acting to reduce the amplitude or troughs associated with successive torque pulses. The masses are tuned such that the system is optimised for a particular frequency band of an engine. The side of each mass 8 defines cam surfaces 10, 11, which cooperate with corresponding surfaces 11, 10 of adjacent masses 8 such that the masses can only rotate in synchronisation thereby ensuring the flywheel remains in balance. In an alternative arrangement, two, or more layers of masses may be employed with each layer of masses tuned to a specific frequency band.

Description

Flvwheels 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 O 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 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 - 2 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 ilequency ofthe 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 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.

In accordance with the present invention, there is provided a flywheel for use with an internal combustion engine, the flywheel comprising a disc formation having an axis of rotation mutually perpendicular to the plane of the disc formation and passing through the centre of the disc, the disc formation supporting, in a fixed positional relationship relative to the disc formation, a plurality of pivot points arranged in an annular configuration about the axis of rotation, the flywheel having a plurality of centrifugal pendulum masses each 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 of the masses are arranged such that a plurality of adjacent masses can rotate in phase about their respective pivot points, the profiled surfaces preventing rotation of the masses except when the masses rotate about their respective pivot points together in phase.

The natural frequency of the centrifugal pendulum mass system of the present invention will be a function of the speed of rotation and may consequently wholly eliminate - 3 the response to that engine order vibration. 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 Me present invention tracks the torque pulse frequency of the engine, it is important that: (Ord*k)2 =(R+p)*p 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 The present invention will be described, by way of example only, with reference to the accompanying drawings, with like numerals being used throughout to indicate like components, and in which: Figure 1 is a plan view of a flywheel in accordance with a first embodiment of the present invention; Figure 2 is a perspective view of the pendulum mass system of Figure 1; Figures 3 and 4 correspond to Figures 1 and 2 but with the masses orientated as they would be on experiencing a torque pulse; Figures 5 and 6 illustrate a flywheel similar to that illustrated in Figures 1 and 2 but with alternatively shaped masses; - 4 Figure 7 is a plan view of the mass system for a flywheel for suppressing two frequency bands; and Figure 8 is a perspective view of the mass system of Figure 7.

Referring to Figures 1 and 2, there is illustrated generally as 1 a flywheel for use with an internal combustion engine. The flywheel 1 comprises a disc assembly 2 having an outer peripheral wall 3 forming a recess 4. The disc assembly 2 has a central aperture 5 for locating the disc assembly on the end of the engine crankshaft. The axis of rotation 6 of flywheel 1 is mutually perpendicular to the disc assembly 2.

Equally spaced on the disc assembly 2 about the axis of rotation 6 there are nine pins 7, on each of which there is mounted a respective pendulum mass 8 pivotally connected to its associated pin. Each pendulum mass 8 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 6 with the sector of each of the two circles forming a respective cam surface 10 and 11 which cooperate with corresponding surfaces 11 and 10 of adjacent pendulum masses 8.

Figures 1 and 2 illustrate the position each pendulum mass 8 would adopt if the flywheel 1 was rotated at a constant angular velocity. In this position, the centre of mass 9 of each pendulum mass is aligned radially outward of its respective pin 7 and is maintained in this position by the centrifugal force acting on the mass as the flywheel 1 rotates. - s -

Referring now to Figures 3 and 4, there is illustrated the position the pendulum masses of Figures 1 and 2 adopt when the flywheel 1 is subjected to angular acceleration in the direction of arrow 12. The inertia of the masses causes their centres of gravity 9 to lag behind the disc assembly 2, thus the masses rotate about their respective pins 7 in the direction of arrow 13. 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 8 move in the opposite direction and this relative movement again acts to reduce the troughs thereby smoothing out the torque fluctuations.

The cam surfaces 10 and 1 1 of each pendulum mass engage with corresponding surfaces 11 and 10 of adjacent masses. The kidney shaped geometry ensures that the masses interact with each other and can only rotate about their respective pins 7 if they rotate together. This ensures that the masses remain synchronised 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 3, the pendulum masses 8 are limited in their movement by coming into contact with the inner surface of the peripheral wall 3 defining the recess 4.

This limitation on the rotation of the masses ensures that they do not progress pass the point where cooperating cams could become disengaged. 6

Referring to Figures 5 and 6, there is shown a flywheel system employing pendulum masses of a slightly different configuration to those shown in the previous figures, but which function in the same manner. In the Figure 5 and 6 embodiments, each pendulum mass 8 comprises two components 8a and 8b in the form of planar circular discs rigidly joined together. Alternatively, these may be machined from a single piece of steel. As in the previously described embodiments, each pendulum mass 8 pivots around a respective pin 7 and each mass has associated with it two cam surfaces 10 and 1 1 for interacting with corresponding cam surfaces 11 and 10 of adjacent pendulum masses 8. In this embodiment there is a first set of cam surfaces in an upper plane and a second set of cam surfaces in a separate lower plane. However, in plan view, as seen in Figure 5, the geometry is the same as that in the previous embodiments, for example see Figure 3, and the masses function in exactly the same manner. In this embodiment it is important to have an even number of pendulum masses to ensure correct engagement The dimensions of the flywheel and value of the masses are selected in accordance with the following equation: T-l.(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 - 7 The flywheel will normally have dimensions such as to minimize torque pulses of a particular engine order at engine idle speed, thus the masses are tuned so that the flywheel is optimised for smoothing torque pulses at the idle frequency ofthe engine, and the mass system is optimised for a particular frequency band. In some applications, it may be desirable to broaden the frequency band over which the flywheel is effective, or to reduce torque pulses occurnug at higher order frequencies.

Referring to Figures 7 and 8, there is illustrated an alternative embodiment comprising a lower layer of pendulum masses 8 corresponding to those illustrated in Figures 3 and 4, and an upper layer of masses 14 similar to the pendulum masses 8 but sharing common pivot pins 7 with the lower masses 8 and common dimensions. However, the centre of gravity of the pendulum masses is different such that the upper layer of masses 14 act as a separate system tuned to a different frequency band, enabling the flywheel to damp torque pulses at two discrete or overlapping frequency bands.

Several embodiments of the invention have been described by way of example only and it will be realised that further modifications within the scope of the appended claims will be apparent to those skilled in this art. - 8

Claims

Claims 1. A flywheel for use with an internal combustion engine, the

flywheel comprising a disc formation having an axis of rotation mutually perpendicular to the plane of the disc coronation and passing through the centre of the disc, the disc formation supporting, in a fixed positional relationship relative to the disc formation, a plurality of pivot points arranged in an annular configuration about the axis of rotation, the flywheel having a plurality of centrifugal pendulum masses each 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 ofthe pivot points and dimensions ofthe masses are arranged such that a plurality of adjacent masses can rotate in phase about their respective pivot points, the profiled surfaces preventing rotation of the masses except when the masses rotate about their respective pivot points together in phase.
2. A flywheel as claimed in Claim I, comprising a plurality of pivot points and associated masses arranged in a complete circle centred on the axis of rotation, the position of the masses being locked in phase by cooperating pairs of adjacent profiled surfaces of adjacent masses.
3. A flywheel as claimed in Claim I or 2, wherein the centre of gravity of each mass is located radially outward of the pivot points.
4. A flywheel as claimed in any preceding claim, wherein each profiled surface is a cam surface defining a section of a circle in the plane of the disc formation.
5. A flywheel as claimed in Claim 4, wherein each pendulum mass has two cam surfaces each prescribing a section of a circle in the plane of the disc, each of the two cam surfaces being arranged to cooperate with a corresponding surface of a respective adjacent pendulum mass.
6. A flywheel as claimed in Claim 5, wherein each pendulum mass is planar and substantially kidney shaped, with the cam surfaces located on opposite sides of the pendulum mass, each mass being pivotally connected to a respective pivot point at a location equidistant from the two cam surfaces and radially inward of the centre of mass of the pendulum mass, relative to the axis of rotation.
7. A flywheel as claimed in Claim 5 or Claim 6, wherein each pendulum mass has the form of two circular discs stacked one upon the other, offset and overlapping, with the two IS cam surfaces formed on opposite sides in different planes, whereby adjacent pendulum masses have the upper and lower portions offset in opposite sense such that cooperating pairs of cam surfaces lie in substantially the same plane.
8. A flywheel as claimed in any preceding claim, wherein the centre of mass of each pendulum is offset from the pivot point.
9. A flywheel as claimed in any preceding claim, comprising two sets of pendulum masses sharing common pivot points but arranged in two separate planes, each set of masses being tuned to a separate frequency band. -
10. A flywheel as claimed in any preceding claim, in which the pendulum masses are mounted on an annular recess in one face of the flywheel.
11. A flywheel as claimed in any preceding claim wherein a plurality of pendulum masses define a pendulum mass system having a natural frequency which tracks and substantially coincides with the order of vibration of the engine which is to be suppressed.
12. A flywheel as claimed in any preceding claim further comprising means for restricting the travel of the pendulum masses.
13. 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.