A resilient mounting with a built-in phase shifter, particularly for motor vehicle engines.

A resilient mounting with a built-in phase shifter, particularly for motor vehicle engines

The present invention relates to a resilient mounting, particularly for motor vehicle engines, of the type including a tubular body which is adapted for connection to the body of the motor vehicle, and a rod which is coaxial with the tubular body and is adapted for connection to the engine, elastomeric vibration damping means being interposed between the tubular body and the rod.

This type of mounting may be used where there is a problem in insulating the body against transmitted vibrations in order to reduce induced noise. In the specific field of use in motor vehicles, it is found that in some cases, usually when the engine is operating in the range of between approximately 3000 and 5000 revolutions/minute, the insulating effect of conventional resilient blocks is not sufficient to attenuate the forces transmitted by the engine to the body in the corresponding frequency band of 100 to 170 Hz which is most critical as regards noise in the passenger compartment.

The object of the present invention is to provide a resilient mounting of the type specified at the beginning of the description, which enables this problem to be resolved by a drastic reduction in the vibrations transmitted to the body in the frequency range mentioned above.

According to the invention, this object is achieved by virtue of the fact that the phase-shifting system comprises a main resilient block and an auxiliary resilient system provided with at least one pair of rigid annular elements which are coaxial with the rod and are connected to each other, to the body and to the rod by means of at least three elastomeric elements, the rigidity of the elastomeric elements being selected so as to introduce to the body dynamic forces which are in counterphase with those introduced by the main resilient block in the predetermined frequency range.

By virtue of these characteristics, the reduction of the vertical forces transmitted to the body can reach values of 75% in the predetermined frequency range, considerably reducing the noise in the passenger compartment and thus increasing the comfort of the users.

Further characteristics and advantages of the mounting according to the invention will become clear from the detailed description which follows with reference to the appended drawings, provided by way of non-limiting example, in which: <ul id="ul0001" list-style="none"><li>Figure 1 is a cross-section of a vibration-damping mounting according to the present invention, and</li><li>Figure 2 is a diagram of the equivalent model.</li></ul>

With reference to the drawings, a vibration-damping mounting, generally indicated 10, is interposed between the body S of a motor vehicle and a support bracket A of the engine of the motor vehicle. The vibration-damping mounting 10 comprises a tubular body 11 with a first end 11a which is formed with a flange for fixing to the body S at 12 and a second end 11b to which a cup-shaped cover 13 with a central hole 13a is fixed, for example, by means of plastic deformation. A metal rod 14 is mounted coaxially with the tubular body 11 and has a first threaded end 14a screwed into a corresponding threaded hole 15a in a nut-like element 15, and a second end 14b which is fixed to the bracket A. A shaped annular block 16 of elastomeric material is fixed (for example, by means of vulcanisation) to the nut-like element 15 and has an outer edge which is joined to the tubular body 11 substantially adjacent its first end 11a.

A metal bush 17 is mounted on the rod 14 adjacent its threaded end 14a and has a first end 17a which abuts an annular shoulder 14c of the rod 14 and a second shaped end 17b which abuts the element 15. A shaped, auxiliary annular block 18 of elastomeric material is fixed to the bush 17 and has an outer peripheral edge 18a which is fixed inside a bent L-shaped edge 13b of the cover 13.

Two metal rings, 19 and 20 respectively, are fixed to the auxiliary annular block 18 coaxially with the rod 14 and are spaced axially from each other and radially from the rod and the tubular body 11. The metal rings 19 and 20, which are quadrangular in section, therefore divide the auxiliary annular block 18 into three regions 18b (interposed between the bush 17 and the first metal ring 19), 18c (interposed between the two metal rings 19 and 20) and 18d (interposed between the second metal ring 20 and the cover 13) respectively.

A tubular spacer element 21 is interposed between the bush 17 and the support bracket A, coaxially with the rod 14, and has an external diameter smaller than the internal diameter of the hole 13a in the cover 13.

The tubular body 11 and the cover 13 have respective through-holes 22 and 23 whose function will be explained in the description below.

In order to assemble the vibration-damping mounting 10, it is sufficient to fix the cover 13 to the tubular body 11, for example, by the plastic deformation of its edge indicated E in Figure 1, in correspondence with the end 11b of the tubular body 11, and then, after the spacer 21 has been mounted, to screw the rod 14 to the element 15 which is fixed centrally to the shaped annular block 16.

When the engine is running, as regards the transmission of vibrations to the body, the vibration-damping mounting 10 behaves according to the equivalent model shown in Figure 2, in which the main elements of the model (springs, masses) have been indicated by the same reference numerals as used in Figure 1. The vibrations of the engine cause the periodic displacement of the support bracket A relative to the body S, thus causing the resilient deformation of the main resilient annular block 16 (of predetermined rigidity) and the transmission of a corresponding force to the body S.

The suitable dimensioning of the masses 19 and 20 (the metal rings) and the rigidities of the springs (the portions 18b, 18c, 18d of the auxiliary resilient annular block 18) gives rise to a new force which is transmitted to the body S with a phase displacement of approximately 180^o relative to the first. In other words, the left-hand portion of the equivalent model shown in Figure 2 acts as a "phase shifter" relative to the right-hand portion which is constituted by the main resilient annular block 16. The total force which causes the body S to vibrate is thus reduced. This effect is limited to a frequency band between the characteristic frequencies of the phase shifter constituted by the auxiliary resilient annular block 18 and the metal rings 19 and 20.

During the tests carried out on vibration-damping mountings according to the invention, the vertical forces transmitted to the body were reduced by approximately 75% compared with those transmitted with conventional vibration-damping mountings for excitation frequencies between 75 and 180 Hz. The tests were carried out on an engine of average cubic capacity (1400 cm³) with the masses (the metal rings) having a total weight of approximately 1 kg and the various portions of the auxiliary resilient annular block 18 having rigidities of between 20 and 60 kg/mm.

Since the performance of the mounting depends, to a great extent, on the masses of the rings 19 and 20, this performance can be optimised by varying the masses, even when the mounting is already assembled, for example, by the removal of a predetermined quantity of metal from the rings 19 and 20 by drilling through the through-holes 22 and 23 provided in correspondence with the tubular element 11 and the cover 13.

The main resilient annular block 16 may have apertures of various shapes in order to optimise the radial transmission of the vibrations in predetermined directions.