GB2397360A - A flywheel for use in an internal combustion engine including a plurality of centrifugal pendulum masses - Google Patents

Abstract

A flywheel 10 for use in an internal combustion engine which comprises a disc formation 12 with a plurality of centrifugal pendulum masses 30. The pendulum masses 30 are disposed symmetrically about the disc formation 12 and adjacent ends 34 of adjacent pendulum masses 30 are pivotally interconnected by links 32 and pivot pins 38, 40, the links 32 being pivotally connected to the disc formation by pivot pins 42. The axes of the pivot pins 42 are positioned radially inwardly of and equidistant from the axis pins 38, 40. The system of symmetrical pendulum masses has a natural frequency which coincides with the torque pulse frequency of the engine and thus provides smooth engine vibration.

Description

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.

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.

This 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 e: :- .: A. ce: À À À . À À À . À c À À c c c À À À- c 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 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, a flywheel for use in an internal combustion engine comprises a disc formation with a plurality of identical centrifugal pendulum masses, the pendulum masses being disposed symmetrically about the disc formation, adjacent ends of adjacent pendulum masses being pivotally interconnected by links, the links being pivotally connected to the disc formation about axes spaced equally from the axis of the pivotal connections between the links and the ends of adjacent pendulum masses, the system of centrifugal pendulum masses having a natural frequency which coincides with the torque pulse frequency of the engine.

À À . - a. .e À . À . À À À À.e es.

The 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 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 pendulums relative to the centre of rotation of the flywheel.

In theory: X = r(1 + Pr2) where Pr = the number of pulses per rev; r = pendulum length; and X = distance of centre of gravity of pendulum to flywheel centre.

Consequently, for a four cylinder 4 stroke engine where Pr = 2, then X/r= 5, that is the centre of gravity of the pendulum must be set at 5 x 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 pendulums and some non-linearity. Preferably the value of X/r for a four cylinder 4 stroke engine will be between 5 and 6.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings in which: À Àe À . À e.

À . . À . e. e À À À À ÀÀ À À. ÀÀe À Figure 1 illustrates in end elevation, a flywheel in accordance with the present invention; 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 with the flywheel illustrated in Figure 1, in a central position; and Figure 4 is a diagrammatic illustration of the centrifugal pendulum mass system of the flywheel illustrated in Figure 1 in a displaced position.

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 engage apertures 44 in the disc formation 12, the pitch circle of the apertures 44 being concentric with the disc formation 12. The axis of the pivot pins 42 are positioned 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 À : - À .: À À À À À À À À À Àe À À. À Of the masses 30 being parallel to the line 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 of the 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.

When the flywheel 10 is accelerated during an expansion stroke of the engine, due to inertia, the masses 30 will lag behind the disc 12, 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 remains balanced, although the centre of gravity of the masses move inwardly. As the flywheel 10 slows down following a torque pulse, the inertia of the masses 30 will cause them to move forwardly relative to the À: :- .: Àe A: : À. : :: À.

:e.e À:- Àe.e 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 movement will reduce the troughs, thereby smoothing out the torque fluctuations.

For the appropriate resonant frequency of the pendulum mass system described above, the ratio X/r is greater than (1 + Pr2) where Pr is the number of torque pulses per rev.

Consequently, while for a four cylinder, four stroke engine which produces two torque pulses per rev, a ratio X/r of 5 to 6, for example 5. 6 is preferred. For a single cylinder, four stroke engine which produces one pulse every two revs, the X/r ratio is preferably from 1.25 to 2; for a two cylinder, four stroke engine which will produce one pulse per rev, 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 rev, 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.

In order to obtain optimum isolation the time interval between torque pulses should be substantially uniform. With some engines, for example a degree V6, which may have unequal firing periods the effect will be reduced since the second order amplitude generated will be reduced.

Some engines are designed in which two cylinders fire simultaneously. In this case the X/r ratio is selected for the appropriate torque pulse : :.: À' Be: * . . a À À À À frequency.

A single rotor rotary Wankel engine produces one torque pulse per revolution of the crank shaft and thus would require a X/r ratio of between 2 and 3.

The number of pendulum masses must be at least three, but more masses may be used, subject to dimensional constraints, for example the size of the flywheel and the X/r ratio.

Claims (14)

À À c'to c cce À C 1 C Ace À c:. c c c Claims.

1. A flywheel for use in an internal combustion engine comprising a disc formation with a plurality of identical centrifugal pendulum masses, the pendulum masses being disposed symmetrically about the disc formation, adjacent ends of adjacent pendulum masses being pivotally interconnected by links, the links being pivotally connected to the disc formation about axes spaced equally from the axis of the pivotal connections between the links and the ends of adjacent pendulum masses, the system of centrifugal pendulum masses having a natural frequency which coincides with the torque pulse frequency of the engine.

2. A flywheel according to claim 1 in which three or more pendulum masses are pivotally mounted on the disc. 1 5

3. A flywheel according to claim 1 or 2 in which the line interconnecting the axis of the pivotal connection of the pendulum mass to the link and the axis of the pivotal connection of said link to the disc, at one end of each pendulum mass is parallel to the line interconnecting the axis of the pivotal connection of the pendulum mass to the link and the axis of the pivotal connection of said link to the disc at the other end of the pendulum mass.

4. A flywheel according to any one of the preceding claims in which the ratio X/r (1 + Pr2), where X is the distance of the centre of gravity of the pendulum masses from the flywheel centre, r is the pendulum length and Pr is the torque pulse frequency if the engine.

5. A flywheel according to claim 4 in which for use with a four cylinder four stroke engine, the ratio X/r being between 5 and

6.

t c c : ee.: :: À e 6. A flywheel according to claim 4 in which for use with a single cylinder four stroke engine, the ratio X/r being between 1.25 and 2.

7. A flywheel according to claim 4 in which for use with a two cylinder four stroke engine, the ratio X/r being between 2 and 3.

8. A flywheel according to claim 4 in which for use with a six cylinder four stroke engine, the ratio X/r being between 10 and 1 1.

9. A flywheel according to claim 4 in which for use with a two cylinder two stroke engine, the ratio X/r being between 2 and 3.

10. A flywheel according to claim 4 in which for use with a single cylinder two stroke engine, the ratio X/r being between 5 and 6.

11. A flywheel according to claim 4 in which for use with a single rotor Wankel engine, the ratio X/r being between 2 and 3.

12. A flywheel according to any one of the preceding claims in which elastomeric buffers are provided to limit movement of the pendulum masses.

13. A flywheel according to any one of the preceding claims in which the pendulum masses are mounted on an annular recess in one face of the flywheel disc.

14. A flywheel for use in an internal combustion engine substantially as described herein, with reference to and as shown in figures 1 to 4 of the accompanying drawings.