Mechanical brakes, e. g. friction brakes tend to vibrate, resulting in a noise nuisance from the shock impact of mechanical elements, among other reasons.

Apart from this, such shock impact and vibrations may also cause damage to the mechanical elements. In conclusion, such noise is a nuisance to anybody in the vicinity.

Brakes as used in theater applications and on elevator systems need to be very quiet in operation despite being actuated very frequently. This necessitates, in addition to special electromagnetic circuitry, not detailled in the context of the present description, special silencing means of a mechanical nature and influencing the magnetic flux.

In electromagnetic brakes and clutches a distinction is made between two types of undesirable noise: the first kind is termed"pull-in noise"and occurs when the armature plate is pulled into contact with the backplate, resulting in steel impacting steel. The pull of the armature plate is activated, for example, by the solenoid (brake armature coil) being energized. The second kind is termed "drop-out noise"and occurs when the armature plate is urged against the friction plate, for example, by means of spring force. This thus occurs as soon as the solenoid is taken out of circuit, i. e. deenergized.

Known means of silencing such noise include the insertion of 0-rings or to make use of disc spring coatings which, however, often tend to settle and thus lose their effectiveness with time. Silencing assemblies are also known which, however, as a rule fail to permit simple readjustment or have no means for adapting silencing to any actual circumstances. There is thus a need for a system permitting simple readjustment for silencing means.

Known from an article entitled Ktihles Stoppen mit Federkraftbremsen"in the June 1991 issue of the German design magazine Der Konstrukteur"is a means of DC supply for an electromagnetic released brake via a rectifier.

It is known from the German utility model specification DE-GM 18 89 257 to provide such brakes with a circular arrangement of buffer-type bodies.

From Patent Abstracts of Japan, M-1343, Dec. 1992, Vol 16/No. 569 it is known for silencing mechanical impact noise to employ 0-rings in annular grooves in the housing of the solenoid concentric thereto and to the longitudinal centerline of the brakes and which slightly protrude from the surface of the housing to contact an opposing armature plate and which are compressed on pull of the armature plate. This assembly of two concentric 0-rings fails to be sufficient when higher forces occur and normally fail to have any effect on silencing drop- out noise.

Known from WO 98/21 496 of the present applicant is a further means for silencing mechanical brakes making use of elastic rings, more particularly 0- rings, in the recesses of a mechanical element opposing another mechanical element for damping impact and vibration. In this arrangement, the 0-rings are located eccentric to the longitudinal centerline of the brake and the interior of the 0-rings is filled out by a tough flexible plate for guiding the 0-rings.

However, this known solution also fails to silence drop-out noise in addition to the pull-in noise in all situations.

Accordingly, the objective forming the basis of the present invention is to improve known means of silencing as described above so that, in addition to silencing pull-in noise, the drop-out noise can now be reduced by particularly simple means; preferably the silencing means should also pose no problem in being readjustable for"tuning"to changing situations.

In accordance with the invention this objective is achieved by the characterizing features of the independent claims 1 and 10. In the first case, as it reads from claim 1, the first plurality of damping members is assigned a second plurality of damping members having a significantly lower spring rate and thus higher expansion capacity such that the second plurality of damping members now damps the armature plate even in the drop-out condition, i. e. during braking of the friction plate. In the second case, as it reads from claim 10, the face of the central damping member is configured with two diverse portions, one of which protrudes more axially but is relatively pliant whilst the other portion protrudes less axially and is relatively non-pliant.

Both types of damping members may be axially adjusted with the aid of, for instance, grub screws or the like to permit setting the position of the face of the damping member in the parting plane between the armature plate and backplate.

In all, the mechanical elements provided for silencing pull-in noise and drop- out noise can be mutually adapted, they being selected differing in spring rate for optimum silencing of both pull-in noise and drop-out noise in each being tuned to the other. This adjustment can be made from without to permit setting the brake when installed and for testing.

Further aspects of the invention read from the claims 2 to 9 and from claim 11.

The present invention will now be detailed by way of three different embodiments as shown in the attached drawings in which: Fig. 1 is a section view of the brake in accordance with the invention including the novel silencing system in the backplate; the upper half is marked A and the lower half is marked B; Fig. 2 is a similar section view of a brake including the silencing system in accordance with the invention in the armature plate; again, the upper half is marked A and the lower half is marked B; Fig. 3 is a further section view of a brake including a further aspect of the silencing principle in accordance with the invention showing, in the upper half marked A, the brake with the armature plate pulled-in electromagnetically, and in the lower half marked B, the brake with the armature plate forced away by compression springs, i. e. in the drop-out condition or braking condition ; in the upper half A the solenoid is supplied with current and thus energized and in the lower half B the solenoid is switched off.

Fig. 4 is a detail on a magnified scale taken from the lower half shown in Fig. 3.

Referring now to Fig. 1 there is illustrated a central hub (not identified by reference numeral) axially serrated to mate with a corresponding serration of the friction plate 4 provided with friction linings 6 on both sides. In the concrete case of this application the hub is seated on a shaft (not shown) of a machine or apparatus needing to be braked.

As viewed axially inwards from the friction plate 4 an armature plate 2 is located axially shiftable but non-rotatably within the brake housing. The armature plate 2 is seated concentric to the longitudinal centerline of the brake and clasps the hub of the parts for guiding the friction plate 4 arranged on the hub. At the other side of the armature plate 2 axially opposite the friction plate 4 there is provided the backplate 1 in which a concentric solenoid 3 together with a series of helical springs 5 distributed equispaced circumferentially.

The conventional zero-current-actuated electromagnetic brake as described thus far includes in addition two diverse silencing systems in the backplate 1 which differ from each other mainly by their significantly different spring rates. The silencing system identified by the reference numerals 7, 8,9 in Fig. 1 consists of two pin parts 7 located in a hole drilled parallel to the longitudinal centerline and adjusted by means of a grub screw. The pin 7 is made of brass or non- magnetic steel whilst the pin 7a is made of steel or the like, whereas the plastic interlayer 8 separating the two pin parts is made of plastics. The pin part 7 made of antimagnetic material and facing the armature plate 2 is positioned in the corresponding hole drilled axially-parallel by the effect or setting of the grub screw such that its face facing the armature plate 2 slightly protrudes beyond the face of the backplate 1 facing the armature plate 2. This results in the armature plate 2 being damped on activation of the solenoid 3 to favorably effect, i. e. to silence, the so-called pull-in noise. This silencing system comprising the elements 7,8 and 9 is achieved similar to that as included in WO 98/21 496 of the present applicant as discussed in the introductory part of the description. This silencing system identified by the reference numerals 7, 8 and 9 has a relatively high spring rate, i. e. steep characteristic, at least as compared to the silencing system identified by the reference numerals 9-12 which needs to have a significantly lower spring rate and thus shallow characteristic because it is required to follow the movement of the armature plate 2 on pull-in noise/drop-out of the electromagnet to damp the armature plate 2 also during braking. Due to the damper 8 the pin 7 is able to follow the armature plate down to a nominal air gap. In addition to its silencing action, the damper 8 also serves to prevent premature settling of the elements 11/12 as later detailed.

The two diverse silencing systems are provided multiply distributed circumferentially in the backplate, e. g. symmetrically distributed alternatingly staggered around the circumference.

The second silencing system identified by the reference numerals 9-12 firstly comprises an axially relatively long antimagnetic pin 10 made of brass or non- magnetic steel. Via an O-ring 12 including a plastics plate 11 arranged in interior thereof this antimagnetic pin 10 is impacted by a grub screw 9 more or less strongly, i. e. with adjustable pressure. As evident from the drawing the antimagnetic pin 10 is able to follow movement of the armature plate 2 when the solenoid 3 is taken out of circuit, i. e. in the helical springs 5 becoming effective to urge the armature plate against the friction plate 4 with its friction linings 6 so that even after drop-out of the armature plate 2, i. e. during braking, it acts on the armature plate 2 to damp any vibrations of the armature plate 2 producing noise. Once the armature plate 2 has been displaced regularly by but a few tenths of a millimeter in the direction of the friction plate 4, as shown in Fig. 1 on drop-out, the antimagnetic pin 10 is able to directly follow this drop- out movement because of its inherently high elasticity and its shifting capacity in thus being able to still influence the armature plate 2 in an active braking action of the brake, i. e. when the armature plate 2 is in the position on the left in contact with the friction plate 4 as shown in Fig. 1.

The element 11,12 serves mainly for silencing pull-in noise, but also for silencing drop-out noise, since the armature plate is pulled delayed by contact of the dampers.

The element 8 mainly serves for silencing pull-in noise and to avoid premature fatigue of the elements 11,12 caused by a somewhat harder setting (steeper characteristic by filling out the space available for installation).

Referring now to Fig. 2 there is illustrated an embodiment which differs from the embodiment as described above with reference to Fig. 1 in that the two diverse silencing systems identified by the reference numerals 8, 9, on the one hand, and 9,11, 12, on the other, are not arranged in the backplate 1, but in the armature plate 2 from which they cooperate with the opposite face, i. e. of the backplate 1 in just the same way as described above. This means that the damping member 8 made of a suitable plastics needs to have a very much higher spring rate than that of the damping member 11,12 as shown in Fig. 2 which after activation of the brake continues to remain in contact with the face of the backplate for the purpose of silencing the drop-out noise.

Referring now to Fig. 3 there is illustrated how the same gist is achieved in silencing the armature plate 2 as a function of its final axial setting with differing spring rates. In this case, however, this is achieved by a single central (circulating) central flexible element 13, a magnified detail of which is shown in Fig. 4. This central flexible element 13 which may also be seated in the opposite face of the armature plate 2, similar to that as shown in Fig. 2, comprises, on the one hand, a flat 13a slightly protruding beyond the face of the backplate 1, in the middle of which, however, a bead-type protuberance 13b is provided. Fig. 4 illustrates the effect of this central flexible element with the armature plate 2 deenergized, i. e. showing how the drop-out noise is silenced. When, on the other hand, the armature plate is pulled in by the energized solenoid 3, the armature plate 2 in Fig. 4 is urged more to the right in thereby flattening the middle bead-type part 13b to come into contact with the fully flattened face 13a + 13b of the central flexible element 13 to then act in this position in the sense of silencing pull-in noise, i. e. with a significantly higher spring rate in the above sense.

As aforementioned, the central flexible element 13 as shown in Fig. 3 and Fig. 4 could be accommodated like the damping members of the embodiment as shown in Fig. 2 in the armature plate 2 for then cooperating with the opposite face of the backplate 1. It will likewise be appreciated that the central flexible element 13 could also be rendered axially adjustable e. g. by a screw, even though such a possibility is not detailed in the drawings.

The upper half A of the Fig. 1 or Fig. 2 shows the system mainly for silencing drop-out noise whilst the lower half B shows the system mainly involved in silencing pull-in noise.

Pull-in noise silencing : see Fig. 1 lower half B-the armature plate 2 is urged against the antimagnetic pin 7 including a stiff plastic component 8 as an interlayer. The armature plate 2 does not come into contact fully with the backplate 1. Seetting this stiff element 7,8 from without is possible by means of the grub screw.

Drop-out noise silencing : Drop-out movement of the armature plate 2 likewise moves an antimagnetic pin 10 by the force of the O-ring 12 which is guided in an elastic plastics plate 11. In this case, use is made, in all, of a system which is likewise adjustable from without via grub screws 9.

Tuning : both systems, i. e. for silencing drop-out noise and pull-in noise, must be finely tuned to each other for optimum silencing in both switching conditions.

List of Reference Numerals 1 backplate/solenoid carrier plate 2 armature plate 3 solenoid 4 friction plate 5 helical springs 6 friction linings 7 antimagnetic pin of brass or non-magnetic steel 7a pin of steel or the like 8 plastic interlayer/damper 9 grub screw 10 antimagnetic pin 11 plastics plate 12 0-ring 13 central flexible damping member of suitable plastics 13a flat face portion of 13 13b bead-type face portion of 13