This invention relates to vehicle drivelines which include torsional vibration dampers and to torsional vibration dampers for use in vehicle drivelines.

Such drivelines effectively comprises a series of lumped inertias connected together by relatively flexible components. This series of inertias is excited by the torsional fluctuations applied to it by an associated combustion engine. At certain engine speeds, the engine may excite various modes of vibration of this driveline system, which occur at particular frequencies. These modes of vibration may cause noise or discomfort for the vehicle's passengers and they may also cause durability failures of driveline components.

It is an object of the present invention to provide a vehicle driveline which at least mitigates the above vibration problem and also to provide a torsional vibration damper which is particularly well suited for use in a vehicle driveline.

Thus according the present invention there is provided a vehicle driveline comprising an engine, a drive transmitting clutch or torque converter, connected with a multi- ratio transmission via an output hub, and one or more transmission output shafts for connecting the transmission with driven wheels of the associated vehicle, the driveline including a harmonic damper connected with the output hub or a rotating part of the driveline located on the wheel side of the output hub.

The harmonic damper may be connected with an input shaft of the transmission.

Alternatively, the transmission may have an input shaft with a first set of gear wheels and a secondary or lay shaft with a second set of gear wheels which engage said first set of gear wheels, the operative ratio of the transmission being selectable by driving the second shaft from the first shaft via different pairs of first and second gear wheels, the harmonic damper being connected with the input shaft of the transmission.

In a further alternative, in a transmission as described in the preceding paragraph the harmonic damper may be connected with the secondary or lay shaft of the transmission.

In a further arrangement, the harmonic damper may be connected with a

transmission output shaft.

For example, in a driveline for a front wheel drive vehicle in which the transmission includes a differential having two output shafts one for each front wheel of the associated vehicle, the harmonic damper being connected with one of the output shafts.

In such a front wheel drive arrangement the output drive shafts may be of different lengths and the harmonic damper is connected with the longer output drive shaft.

By locating the harmonic damper at the locations described above the effectiveness of the damper is significantly improved so that a smaller damper can be used.

The present invention also provides a torsional vibration damper comprising an inner drive member for rotation with a driveline component to be damped and an outer mass connected with the inner drive member via a torsionally flexible attachment means which enables the outer mass to vibrate torsionally relative to the inner drive member to damp a pre-determined range of torsional vibrations of the component, the damper also including a friction damper acting between the outer mass and the inner drive member to broaden the torsional vibration frequency range damped by the damper. By providing the friction damper acting between the outer mass and the inner drive member the range of torsional vibrations which can be damped is significantly increased.

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 shows diagrammatically a typical driveline for a front wheel drive vehicle;

Figure 2 shows an equivalent inertia and spring layout of the driveline of Figure 1 ;

Figure 3 shows a torsional vibration mode analysis of the driveline of Figure 1 ;

Figure 4 shows diagrammatically a driveline in accordance with the present invention for a front wheel drive vehicle which uses a harmonic torsional vibration damper connected with a clutch driven plate hub;

Figure 5 shows diagrammatically a driveline in accordance with the present invention for a front wheel drive vehicle which uses a harmonic torsional vibration damper connected with a transmission input shaft;

Figure 6 shows diagrammatically a driveline in accordance with the present invention for a front wheel drive vehicle which uses a harmonic torsional vibration damper connected with a transmission secondary or layshaft;

Figure 7 shows diagrammatically a driveline in accordance with the present invention for a front wheel drive vehicle which uses a harmonic torsional vibration damper connected with a transmission output shaft connected with an associated driven wheel, and

Figure 8 shows an exploded view of one form of torsional vibration damper suitable for use in the drivelines of Figures 4 to 7. Referring to the drawings, a typical driveline 10 for a front wheel drive vehicle comprises an engine 11 which drive a flywheel 12 against which a clutch 13 acts. Clutch 13 includes a driven plate 14 which is clamped against flywheel 2 by a pressure plate 15 under the action of a diaphragm spring 16 when the clutch is engaged. Output from the clutch is via a driven plate hub 17 which is connected with an input shaft 18 of a multi-ratio transmission 19.

Transmission 19 has a first set of gear wheels 20 on input shaft 18 and a secondary or lay shaft 21 with a second set of gear wheels 22 which engage the first set of gear wheels 20. In a conventional manner the operative ratio of the transmission is selectable by driving the secondary 22 shaft from the input first shaft 19 via different pairs of engaging first and second gear wheels using synchromesh units (not shown) associated with the first set of gear wheels 20. The wheels 23 are driven via drive shafts 24 which exit from opposite sides of a differential 25.

This driveline is effectively a series of lumped inertias connected together by relatively flexible components as shown diagrammatically in Figure 2. This series of inertias is excited by the torsional fluctuations applied to it by the associated combustion engine 11 and at certain engine speeds, the engine excites various modes of vibration of this driveline which occur at particular frequencies as shown, for example, in Figure 3. These modes of vibration cause noise or discomfort for the vehicle's passengers and they may also cause durability failures of driveline components.

In a typical vehicle, the frequencies at which these modes of vibration occurred are:

First mode: 7.58Hz

Second Mode: 80.3Hz

Third Mode: 410.36Hz

Fourth Mode: 1022.2Hz

Fifth Mode: 5099.4Hz In practise, the first mode of vibration (see trace A in Fig. 3) is generally excited when a step change in the torque applied to the vehicle driveline occurs (for example during a change from deceleration to acceleration).

The frequency of the second mode of vibration (see trace B) falls into the range which may commonly be excited by the firing pulses generated by the combustion engine 11 during its operating range. If the frequency of these pulses coincides with the natural frequency of the second mode, then the rotating components within the transmission system are excited into a torsional vibration. This may cause noises (for example gear rattle) to occur, or, in very extreme cases, durability problems such as broken transmission components.

The frequency of the third, fourth and fifth modes (see traces C, D, and E) are usually sufficiently high to be outside the range excited by engine combustion, and therefore do not to cause any concern.

In accordance with the present invention it is proposed to attenuate the second and most troublesome mode of vibration using a harmonic torsional vibration damper connected to either the clutch output hub 17 or some other rotating part of the driveline located on the wheel side of the clutch output hub as shown in Figures 4 to 7.

The harmonic damper essentially comprises an inner drive member for rotation with a driveline component to be damped and an outer mass connected with the inner drive member via a torsionally flexible attachment means which enables the outer mass to vibrate torsionally relative to the inner drive member to damp a predetermined range of torsional vibrations of the component. It has also been established in accordance with the present invention that if the damper also including a friction damper acting between the outer mass and the inner drive member this broadens the torsional vibration frequency range damped by the damper. The formula for the natural frequency F _n of an inertia I suspended by a spring of stiffness K is:-

F _n = l ^* V (k/l)

2n

Therefore k = I ^* (2n ^* F _n ) ²

Thus in order to provide a harmonic damper to absorb energy from the second mode of vibration in the driveline above (at 80.3Hz), using an inertia of 0.003kg. m ² , this inertia should be attached to the driveline by a stiffness of 0.003 ^* (2n * 80.3) ² = 763.7Nm/rad. (equivalent to 13.32Nm/°)-

A harmonic damper with no hysteresis or damping across its spring system will function very effectively as a vibration absorber at its tuned frequency, where only the damper inertia still vibrates. However the vibration amplitude either side of the resonant frequency is increased.

It has been established in accordance with the present invention that if a friction damper is applied between the outer mass and the inner drive member the torsional vibration frequency range damped by the damper is significantly

broadened.

This friction damping is significantly better than using rubber as the springing medium between the inner drive member and the outer mass as rubber has inherent hysteresis. Also friction damping is significantly better than using a viscous fluid damping system which again has significant hysteresis which whilst allowing the harmonic damper to function over a wide frequency band reduces the effectiveness of the damper at the resonant frequency.

Figure 8 shows one form of harmonic damper 30 in accordance with the present invention which uses friction damping between the inner drive member and the outer mass. The damper 30 has an inner drive member in the form of a hub 31 which is pinned at 32 to a shaft (not shown) which is to be damped. The hub can be otherwise secured to the shaft e.g. by splines on the shaft and hub if required. An outer mass

33 is connected with the hub 31 by screws 34 which engage threaded bores 33b in mass 33 so that the mass rotates with the hub but is capable of limited

circumferential movement relative to the hub via circumferential slots 38 in the hub through which screws 34 extend. The mass 33 is supported from the shaft by support bushes 33c which surrounds the shaft which extends into a bore 33d in the mass.

The movement of mass 33 relative to hub 31 is controlled by circumferentially extending springs 35 which are housed in windows 36 in hub 31without any circumferential play and which extend into windows 33a in a spring support plate 33e which is secured to mass 33 by screws 34. The circumferential extent of windows 33a is greater than that of the windows 36 in hub 31 so that as the mass moves increasingly circumferentially relative to hub 31 the springs 35 are

increasingly compressed by the ends of the mass windows 33a which are now in contact with the springs 35.

A spring retaining plate 40 extends over the axially outer face of hub 31 and has holes 41 through which screws 34 extend and windows 42 which, like windows 33a in spring support plate 33e, are larger in circumferential extent than windows 36 and do not therefore contact the springs 35 in the circumferentially central position of the damper. Thus retaining plate 40 moves relative to hub 31 with mass 33 and its windows 42 react with the springs 35 in the same manner as the windows 33a of spring retaining plate 33e to provide the spring damping.

Sandwiched between the hub 31 and the retaining plate 40 is a friction plate 37 and an associated wave washer 39. Friction plate 37 has ears 37a which engage screws

34 so that plate 37 rotates with mass 33 and plate 37 is biased into contact with hub 31 so that movement of the mass 33 relative to hub 31 is damped by the frictional contact of plate 37 on hub 31. Using the above spring and friction damping of the movement of mass 33 relative to hub 31 it is possible to achieve a better compromise between efficient vibration attenuation at the natural frequency and avoidance of additional vibration at lower and higher frequencies.

The damper needs to be attached to a part of the driveline where the amplitude of the vibration is significant, so that it may have a significant effect on the system.

Thus, when attempting to damp the second mode the damper can be attached in a variety of positions either connected with the output hub of the clutch or a rotating part of the driveline located on the wheel side of the output hub.

For example, Figure 4 shows a damper 50 of the same general design as damper 30 described above attached to the output hub 17 of the clutch driven plate 14.

Figure 5 shows the damper 50 attached to the end of the input shaft 18 of the transmission 19 and Figure 6 shows the damper 50 attached to the end of the secondary or layshaft 21. An additional effect of attaching the harmonic damper to the transmission secondary shaft is that its inertia does not need to be accelerated by the gearbox synchromesh system (associated with the input shaft 18) during ratio changes, therefore the damper will have no effect on gear shift effort or

synchromesh life.

Figure 7 shows the damper 50 attached to the longer and thus more flexible output shaft 24a as close as possible to the to the transmission. This location is used because the inner ends of the output shafts which drive the wheels 23 have the greatest vibration amplitude during the second mode of vibration (see figure 3). Additionally, the inner end of the most flexible shaft (i.e. the longer shaft 24a) has a greater amplitude than the other shaft 24 because when using an open differential the torque is applied equally to both shafts 24,24a regardless of their angular displacement. The positioning of the harmonic damper can be seen to have a great effect on its vibration absorption performance. Optimum harmonic damper positioning in the system allows the inertia, and hence size, weight and cost of the assembly to be minimised.

When the damper is applied in the optimum position the vibration absorbing effect is more effective, and reduces the acceleration amplitude across a wider frequency range despite the small inertia. Once again, the wide amplitude effect of the damper is caused by the use of friction damping