This invention is related to an anti-skid device of the kind that includes a pulley or a _^ wheel that can be brought in contact with the side of a vehicle wheel so that on the pulley fastened pieces of chains by the rota- tion of the vehicle wheel successively are thrown in under the vehicle wheel. More precisely the invention is related to an actuating mechanism of an anti-skid device of this kind.

An actuating mechanism, that is a mechanism that transport the pulley between its working position in con- tact with the vehicle wheel and its parking position is subjected to many requirements in order to function satisfactorily.

Primarily the device must be able to cope with very large forces since the forces excerted on pulley and its supporting structure when the chain pieces are thrown in under the vehicle wheel are considerable. Normally the pulley is carried freely rotatable in the outer end of a supporting actuator arm. To enable the suitable location of the parking or rest position of the pulley this arm frequently has to be of considerable length. As a conse¬ quence the arm is subjected to very great bending stress. This bending stress also appear in the parking or rest position due to the weight of the pulley, the length of the arm and the shocklike movement of the vehicle on bumpy roads etc.

Furthermore with modern vehicle technique the space available has decreased essentially, for instance at air sprung vehicles.

The environment that the mechanism is to work in un- protected on the under side of lorries and such is hard wearing and it is subjected to salt, dirt and small sto¬ nes. Often the arm must swing over a large angle in order to locate the actuating mechanism and the parking position

of the pulley at suitable and available spaces. In particular the demand for a sturdy arm bearing has turned out to be difficult to combine with a compact mec¬ hanism. The forces excerted on the arm and its axle namely quickly lead to play, alternatively must the journaling be made so large that it becomes space consuming and expensi- ve. The result has been that the arm bέaring and the move¬ ment means must be separated to prevent the lack of preci¬ sion in the bearing of the arm from influencing the demand for precision on the side of the actuating mechanism. This as well as the need for a movement return means for the device, normally a spring has given overall clumsy devi¬ ces.

The result of these contradicting requirements has been that one has been obliged to give up one or several desirable and important features. Also actuation force versus return force has been a compromise since the return spring force is greatest in the active position of the pulley.

The object of the invention is to overcome the above problems and drawbacks and provide a compact, powerful, wear resistent, service free actuation mechanism with a large possible actuating angle for the arm and that can be actuated by pressurized air without lubricant as is avai¬ lable in vehicles.

This object is surprisingly enough achieved by using a so called rotatable vane servo. Surprising since the large forces that are excerted on the bearing arm of the pulley namely will be so great that they very easily in¬ fluence the function of the rotatable vane servo. Causing this to jam or leak. By providing an actuation mechanism with the features defined in claim 1 this object is solved. Preferable furt¬ her developements and preferable development of the inven¬ tion are defined in the subclaims and further details and

advantages of the invention are apparent from the follo- wing description of an embodiment shown in the drawings. In the drawings fig 1 shows the actuation mechanism in accordance with the invention in a first cross section, fig 2 the mechanism of fig 1 seen in a section (B) at a right angle to fig 1 and fig 3 a detail (A). As is apparent from fig 1 and 2 the shown embodiment of the actuation mechanism according to the invention enc- ludes a top 1 and a bottom 2 between which a cylinder 3 has been clamped by means of bolts 4 in the corners of top and bottom. Top and bottom are essentially identical. Top and bottom are recessed concentrically with the cylinder 3 and entirely in correspondency with the outer diameter so that top, bottom and cylinder 3 have interrelated fixed positions. Since the guiding of the cylinder 3 is on its outside the risk of a disturbing development of chips on mounting is eliminated in the inner working space of the actuator. Since top and bottom support the cylinder on the outside this is prevented from deformation leading to ova- lity when for instance only one chamber in the cylinder is under pressure. The circumferential groove (fig 3) at the outer edge of the recess secure that the sealing surface between cylinder and top and bottom is so little that an interrelated sealing deformation can take place and no ad¬ ditional sealing is required. Concentrically with the cy¬ linder 3 from the outer side of top and bottom recesses 6 is machined, which recesses 6 with a tight fit each take up a ball bearing 7. The upper ball bearing in fig 2 is on its upper side in the recess 6 in the top sealed and re¬ tained by means of a lid 8 that seals the top end in this direction. Between the outer ring of the bearing and the lid is a spring washer 25 arranged, which pretensions the bearing inwards and against the lower bearing so that also a certain bearing wear can occur without resulting in any play.

In the bearings 7 a shaft 9 is journaled. The shaft 9

100 extends through the bottom 2 and is sealed by means of a box sealing 10 outside the ball bearing 7.

In order to fasten the above described unit to sui- table brackets on a vehicle holes are arranged in top and bottom extending sideways all the way through.

105 On the shaft 9 a radial wing, vane or flap is faste¬ ned. This vane is constituted by two parallell relatively thin plates 12 and 13, which in their inner end are faste¬ ned to the shaft 9. Since the plates are thin they can be welded to the shaft without deformation of this. The pla-

110 tes 12 and 13 are interconnected by means of a central ri¬ veting 14 with an intermediate distance element 17. Bet¬ ween the -two plates a sealing disk element is arranged constituted by a core 15 of rubber and a circumferential endless essentially square sealing body 16 of PFTE (poly-

115 fluortetraeten) , teflon. When the disk constituted by teflon and rubber has been located between the plates and these have been riveted against each other the plates com¬ press the disk, at this the rubber hydraulically converts the pressure to a radial and axial pressure on the teflon

120 seal that is pressed outwards. By dimensioning of rubber volume, distance element, and plate thickness the comp¬ ression and the sealing forces of the disk are given. In mounted state the teflon sealing will then conform in ra¬ dial axial directions and the plates will have a spring

125 action so that always a certain pretension is obtained axially as well as radially. In this way it is possible to have very sharp edges in the corners and thereby obtain a good seal. The seal will also so to say float freely to the optimal position at all times. The central riveting

130 also increase the stiffness against bending of the vane.

As is apparent from fig 1 a small space is left bet¬ ween the edges of the plates 12 and 13 and cylinder 3. The corresponding gap is also present towards top 1 and bottom

2. In this way the advantage is obtained that even if the

135 bearing 6 with time will show a certain play the sealing 60 can be permitted to follow precisely the contour of the working space 5 as defined by cylinder, top and bottom. In this way the demands on preciseness for the bearings is lowered and the mechanism can coope with forces that are

140 so great that deformation of the shaft' or even possibly of the housing occurs.

In order to obtain a working chamber on each side of the vane a partition is fastened to the inner side of the cylinder and constituted by two cylindrical and identical

145 profiles 18 and 19, which between them in a radially ex¬ tending space enclose a sealing identical to that in the vane. This sealing seals against top and bottom, cylinder and the shaft 9 so that an absolute seal is obtained bet¬ ween the two chambers without the profiles 18 and 19 ha-

150 ving to have the exact same length as the cylinder 3, which in turn enables a very uniform fastening or comp¬ ressing of the cylinder 3 between top and bottom. The profiles 18 and 19 are fastened to the cylinder 3 by means of very sturdy pipe shaped connection nipples 20. Through

155 the connections 20 pressurized air at use is supplied to the working chamber in question in order to press the vane from the working position of the chain provided pulley to the parking position of the chain provided pulley and vice versa (eliminating the return spring). Between the profi-

160 les no riveting exists since the fastening is stabile enough anyhow.

In order to seal the shaft 9 where this extends out through the bottom and top axial grooves 22 are machined in shoulders 21 on the axle. These grooves are located

165 very close to the outer diameter of the axle (one or a few tenths of a millimeter). In the bottom of the groove 22 an 0-ring 23 is located and on top of this a seal 24 preferably of graphit reinforced teflon is placed. The

teflon ring 24 has a dimension that is slightly too big

170 for the groove 22 so that when the teflon rings are pres¬ sed down into the groove a tight fit is obtained providing a good gas seal. The 0-ring is forceably deformed and pro¬ vide together with a teflon seal ^" and its deformation a very great pretension for the teflon seal. In this way a

175 good fastening for the teflon ring against turning in the groove is obtained, which secure that the sliding between seal and top or bottom always take place in the contact surface against these and that the ring is not moved in the groove. At the same time a very great axial sealing

180 pressure is obtained. The very small edge gap that is lo¬ cated between the outer edge or lip of the groove and top and bottom respectively is sealed either by the teflon sealing of the van being pressed into the gap or by the teflon ring being pressed out, since teflon is plastic.

185 This can be further enhanced by a suitable chamfering of the outer wall of the groove. Alternatively on pushing the teflon ring into the groove a bead is obtained filling out the gap. It is also possible to accept a certain small air leakage.

190 If so is desired to secure an even sturdier fastening of the teflon ring 24 the groove 22 can be made slightly conical, which also faciliates its machining.

Almost all sealing in the above described mechanimsm is obtained between a teflon surface and a metal surface,

195 which provides a good seal and low friction. The only ex¬ ception is the small area below the outer diameter of the groove 22. The contact surface will however be small and the material in the two surfaces is preferably choosen different with the axle seal the harder one.

200 Mounting of axle and vane and sealing takes place before top and bottom are put in place by turning the axle between the partition and the cylinder until the van is located opposite the partition. To this centrated position

the turning resistance is low since the sealing disk can

205 swell out downwards and upwards. Top and bottom are then mounted, which preferbly takes place in a fixture and when top and bottom are drawn towards each other and pressed against the seals in an axial direction the radial pres¬ sure is increased in a corresponding degree so that a good

210 seal is secured even at very high pressures.

The above described actuating mechanism can cope with very great bending torques and axial loads in the shaft due to the so to say floating sealing. This cooping with great forces is very essential since, as has been entio-

215 ned above, the forces at devices of this kind easily be¬ come very large. Since the sealing even in the corners is pretensioned a very wear resistent mechanism is obtained. Furthermore it is possible to obtain a very great angular movement up to 300°, which increase the number of vehicles

220 at which mounting is possible.

Due to the efficiency of the sealings the actuation mechanism can be propelled by pressurized air, which re¬ quire far better seals than would for instance a hydraulic device where the capillary forces help in sealing.

225 The double action of the actuation mechanism makes the return spring unnecessary and the mechanism therefor requires less space and the force of the spring do not add to the force that has to be provided by the actuation mechanism

230