When an internal combustion engine of traditional in- line or vee cylinder configuration is running, its crankshaft is subjected to varying magnitudes of reciprocating and rotary forces during each cycle as a result of combustion events. These variations cause small corresponding oscillatory variations in crankshaft speed which are normally smoothed out by the presence of a relatively heavy flywheel or torque converter assembly at one end of the crankshaft. The flywheel does not, however, dampen crankshaft torsional vibrations and these must be attended to by other means.

It is known to dampen torsional vibrations at an end (hereinafter known as the"front end") of a crankshaft opposite to the flywheel end by a mass which is either elastically or viscously coupled to the crankshaft and rotates therewith. A known configuration of vibration damper device for fitting to the front end of a crankshaft has a hub of relatively low inertial mass with a concentric'inertial ring'of high inertial mass elastically attached to it by an elastomeric material, the parts being either bonded or press-fitted together as an assembly. An alternative configuration comprises a viscous damper device wherein an inertial ring is carried

within a case and is in contact with a fluid of predetermined viscosity. This configuration is generally more expensive and damage-prone than the elastically mounted inertial ring type of vibration damper device.

Both of the aboveknown constructions of vibration damper device may be attached to a hub at the front end of the crankshaft and the hub may also carry a (belt) pulley.

Where it is required to mount both a vibration damper hub and a belt pulley to a crankshaft front end the resulting increase in engine length may compromise the fitting of the engine into the machine/vehicle into which the engine is to be fitted. To minimise the increase in engine length and to reduce costs, it is known for the inertial ring of a metal/elastomer/metal damper device to be configured to have vee grooves formed in an outer circumferencial surface thereof.

The adaptation of the outer surface of the inertial ring of a vibration damper device as a belt pulley may be satisfactory with engines of moderate power rating but, with higher power rated engines, the severe speed variations which the inertial ring will experience can cause the belt (s) to rapidly tighten/loosen ('belt slap') with the result that the belt (s) can turn over or come off.

Engine power rating to engine size ratio is progressively increasing, as either greater power is demanded without increase in engine envelope size or smaller engines are required without loss of power output.

Therefore it is becoming of greater importance to

disassociate the belt driving means from the vibration damper device inertial ring.

The problem can be summarised as the need for a compact and economic to manufacture means of mounting a metal/rubber/metal vibration damper device in association with a belt pulley on the front end of an engine crankshaft without compromising the performance of the damper device or the pulley. The solution should preferably include the capability to assemble the components of a metal/elastomer/metal damper by press- fitting rather than bonding for ease of manufacture, although this is not essential to achieving the objectives of the invention.

The solution must not have a deleterious effect on the integrity of any supplementary power-take-off (PTO) means such as a longitudinal drive from the front end of the crankshaft. PTO drives of this type may transfer a high proportion of the maximum engine power; therefore it is desirable that the drive is taken via a rigid connection directly coupled to the crankshaft.

It is an object of the present invention to provide an apparatus consisting of a (belt) pulley and a crankshaft torsional vibration damper device which is compact both axially and radially.

It is a further object to provide a compact combined pulley/damper apparatus in which the (belt) driving means is substantially disassociated from the inertial ring of the damper device.

It is a yet further object to provide a compact

pulley/damper apparatus via which an axial power-take-off (PTO) drive can be taken from a rigid connection directly coupled to a crankshaft.

It is a yet further object to provide a compact pulley/damper apparatus having a pulley that may be manufactured from sheet metal without suffering fatigue related failures at an intersection of a belt contact part with a mounting part.

It is a yet further object to provide a compact pulley/damper apparatus where a belt contact part of the pulley is in close axial proximity to an associated engine.

It is a yet further object to provide an economic to manufacture pulley/damper apparatus which will be effective on high power rated engines without compromising auxiliary drive belt integrity.

According to a first aspect of the present invention, there is provided a vibration damper apparatus for damping rotating masses comprising: a primary part capable of being mounted on a shaft of an engine; a secondary part connected to said primary part via an elastic damping means; and a pulley secured to said primary part, said pulley being secured to said primary part by a mounting part thereof located to a side of both said primary and secondary parts which, in use, faces said engine.

Preferably, the pulley is secured to a side of the primary part which, in use, is nearest to said engine.

Preferably also, the primary part comprises a hub and the secondary part an inertial ring.

The secondary part may be disposed in a radial direction relative to the primary part. Preferably, the secondary part is disposed in a radial direction to extend beyond the inner bounds of the pulley to provide extra inertia. The secondary part is able to make full use of the diametrical space within the pulley arrangement by extending fully within the void created by the pulley arrangement, providing a particularly compact pulley/ damper apparatus.

The damping means may comprise an insert of elastomeric material.

The damping means insert may be secured to the primary part by bonding or by a vulcanisation process.

The damping means insert may also be secured to the secondary part by bonding or by a vulcanisation process.

Alternatively, the primary part, damping means insert and secondary part may be assembled by press fitting.

The damping means insert may be of generally cylindrical form including a radially inwardly depending generally V-shaped portion.

The mounting part of the pulley may extend generally radially outwardly and may include means to enable it to be bolted to the side of the primary part.

The pulley may have a belt contact part which extends axially relative to the mounting part.

The belt contact part of the pulley may, in use, extend axially away from the engine.

Preferably, the pulley is formed from sheet metal by pressing or spinning.

Preferably also, the pulley is formed to have a generally S-shaped portion joining the belt contact part to the mounting part.

Preferably further, the primary and secondary parts are generally located within a cup-shape formed by the belt contact and mounting parts of the pulley.

Preferably yet further, the cup-shape of the pulley formed by the belt contact and mounting parts has a shallow axial depth.

An additional power take-off (PTO) means may be connected directly to an outward facing side of the primary part. The primary part is then preferably fixedly securable via a rigid connection directly coupled to an engine drive means, typically a crankshaft. The power take-off means conveniently takes the form of a longitudinal drive from the front end of the crankshaft The primary part may have axially extending recesses formed in its outward facing side to reduce the inertial mass of said primary part.

According to a second aspect of the present invention, there is provided an internal combustion engine including a vibration damper device according to any of the eighteen preceding paragraphs.

The foregoing and further features of the present invention will be more readily understood from the following description of a preferred embodiment, by way of example thereof, with reference to the accompanying drawings of which: Figure 1 is an isometric view of a typical

pulley/damper apparatus wherein a metal/elastomer/metal torsional vibration damper device is constructed with integral belt driving means; Figure 2 is a cross-sectional view through the apparatus of Figure 1; Figure 3 is an isometric view of the apparatus of the present invention comprising a torsional vibration damper device assembled as a compact assembly with a belt driving pulley but wherein said belt driving pulley is substantially disassociated from the inertial ring of the damper device; and Figure 4 is a cross-sectional view through the apparatus of Figure 3.

In the context of the present invention, the term "engine"includes any apparatus having a rotatable shaft subjected to variations in oscillatory motion caused by the motion of the reciprocating and rotating masses comprising parts of the apparatus.

Referring to the drawings, Figures 1 and 2 show a known apparatus 10 in which a vibration damper device 12 comprising a metal hub 14, a metal inertial ring 16 and an elastomer insert 18 have been press-fitted together as an unitary assembly prior to fitting to a crankshaft 20. The hub 14 is located tightly against a gear 22 which in turn is held against a shoulder 24 on the crankshaft. The hub 14 and the gear 22 are further secured against radial movement relative to the crankshaft by Woodruff keys 25.

In the example shown in Figures 1 and 2, the vibration damper device 12 is securely clamped to the crankshaft 20

by a two-part taper ring 26 axially located between a spacer 28 and a thrust block 30. The thrust block 30 is pulled towards the crankshaft by screws 32, causing the taper ring 26 to expand in diameter and thus provide the required radial and axial clamping forces. An'O'ring 34 is fitted to the thrust block 30 to prevent oil leaks.

Tappings 36 may be provided in a front face 38 of the hub 14 for attaching a power-take-off (PTO) means (not shown). This PTO face 38 will normally be an SAE (Society of Automotive Engineers) configuration to facilitate the fitment of an SAE standard adaptor (not shown). In operation, a PTO means may be required to transmit up to the full power output of an engine, therefore a substantial power transmitting means between the crankshaft and the PTO face is essential. This is provided in the known apparatus by the strong hub 14 and its rigid connection to the crankshaft 20.

It can be seen that, in this known apparatus, a belt- driving means 40 is provided as an integral part of an outer circumferencial surface of the inertial ring 16.

This arrangement helps minimise the space required to contain a pulley/damper/PTO apparatus but, on an engine of high power rating, can lead to auxiliary driving belt (s) (not shown) turning over or coming off the driving means 40 because the severe speed variations experienced by the inertial ring 16 cause the belt (s) to rapidly tighten and loosen on alternate sides of the belt run. This phenomenon is sometimes referred to as'belt-slap'.

Figures 3 and 4 show the apparatus 100 of the present

invention. In order to provide a strong and rigid PTO transmission means, a hub 114 of similar configuration to the hub 14 of the known apparatus 10 may be secured to the crankshaft 120 in an identical manner to that of the known apparatus. Similar parts of the apparatus of the invention to the parts of the apparatus depicted by figures 1 and 2 will be denoted by like numerals prefixed by"1". The hub 114, an inertial ring 116 and an elastomeric insert 118 may again be pressed together as an integral assembly before fitment to the crankshaft 120.

However, the hub 114 of the apparatus of the present invention is provided with recesses 142 in an axially outward facing surface 138 of said hub 114 to reduce the inertial mass of the hub 114. The hub 114 thereby requires less torsional vibration damping.

In the present invention, the inertial ring 116 does not carry an integral belt driving means but, instead, is shaped to fit at least partially inside the cup shape of a (preferably) spun or pressed belt pulley 144. It will be seen that the pulley 144 is substantially disassociated from the inertial ring 116 of the vibration damper device 112 and will not therefore transmit to the belt (s) (not shown) the severe speed variations seen by the inertial ring 116.

A pulley spun from sheet metal gives the benefits of low inertial mass and compactness when compared with a bar-turned or cast pulley. In the given example, the thinness of a mounting part 146 of the spun pulley 144 enables it to be fitted by screws 148 to a rear face 150

of the hub 114 with minimal addition in engine axial length and, in this position, it will not compromise the attachment of a PTO means to the front face 138 of the hub 114.

A further benefit of fitting a spun pulley may be realised by forming the cup shape of said pulley with a fairly shallow depth relative to the crankshaft 120 so that a portion 116'of the inertial ring 116 may extend outwardly and radially to give the required inertial mass as predetermined by calculation. In Figures 3 and 4, the major diameter of the inertial ring 116 is shown as being approximately equal to the major diameter of the pulley 144 but this is in no way limitative on the invention.

For example, it may be desirable to reduce the extension of the inertial ring 116 in an axially outward direction and to compensate for this by increasing its diameter.

Preferably, axial outward extension of the inertial ring 116 will be matched by a corresponding extension of the hub 114 and the insert 118. Maximising this outward extension will assist in the dissipation of the significant amount of thermal energy which arises from the flexing, in use, of the elastomer insert 118.

It will be seen that the elastomeric insert 118 has a gentle vee shaped portion 152 in cross-section, the purpose being to positively position and retain the inertial ring 116 on the hub 114, in use. It will be seen from Figures 1 and 2 that the'point'of the vee of the insert 18 is facing towards the inertial ring 16, this being the normal configuration. In the present invention,

advantage has been taken of an alternative configuration in which the'point'of the vee faces the hub 114 to provide an increase in the inertial mass of the inertial ring 116.

It is known that a thin-walled pulley 144 may suffer from failure due to fatigue caused by alternating belt loading as the pulley rotates in use. Fatigue is exacerbated by the overhang of a belt contacting part 154 of the pulley 144 and is usually experienced at the intersection 156 between the belt contacting part 154 and the mounting part 146.

In the present invention, the propensity for fatigue has been reduced or eliminated by forming the intersection 156 as an S-shape in order to provide, in use, a resistance to the leverage applied by the belts (not shown). Further, by minimising the overhang of the belt contacting part 154, the leverage force will be less than would be experienced with a large overhang.

The combination of a small overhang and an S-shaped intersection 156 in a thin-walled pulley 144 in the present invention is of special benefit as it provides maximised space both for the inertial ring 116 and for the pulley fastening screws 148 by eliminating the need for further strengthening of the pulley at the intersection.

A PTO driving means (not shown) can be fitted directly to the outward face 138 of the vibration damper hub 114 of the apparatus 100 of the present invention in the same manner as for the known apparatus of Figures 1 and 2.

This can be a very important advantage over other known apparatus (not shown) where PTO power conveying levels are limited by transmission via indirect or unsubstantial means.