Seal for an actuating device for a drum brake
The present invention relates to actuating devices for drum brakes for passenger vehicles and more particularly, for seals employed with such actuating devices. 
     BACKGROUND OF THE INVENTION 
     Usually drum brakes are operated by a Bowden cable which extends via corresponding deflection means into the brake drum and/or the brake bowl. Details can be taken from page 135 of the Brake Handbook, 9th edition (Bartsch publishing house) or from FIGS. 4 and 5 and the pertinent description of EP-OS 309 079. Deflection of the Bowden cable as well as a corresponding seal entail difficulties. Therefore, one has proceeded to provide the actuating device with an actuating lever which projects through a corresponding aperture in the brake carrier into the brake drum. The end of the actuating lever disposed within the brake drum actuates the brake shoes, e.g. by way of an expanding lock (see the above-mentioned literature), while a Bowden cable makes catch at the end of the actuating lever disposed outside of the drum in the direction of trajectory motion. 
     In order to not impair the effect of the drum brake by the ingress of spray water, it has been suggested to seal the through hole where the brake lever passes through by providing a flat seal with a corresponding slot permitting the swing movement of the actuating lever. However, because of the lever&#39;s extension transversely to the direction of slot, the seal&#39;s slot is always somewhat open on both sides of the brake lever so that sufficient sealing of the brake drum vis-a-vis spray water is not safeguarded. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Therefore, the present invention sets out from a seal for an actuating device of a drum brake corresponding to the type described in the preamble of the main claim and has for its object to improve such a seal in respect of its sealing effect and its fastening. 
     This object is achieved by providing a pleated bellows as a seal held within a recess surrounding the through hole through which the lever projects. 
     A simple and reliable fastening of this seal can be obtained by an annular clamping ring held in the recess by teeth engaging the wall of the recess, the ring facing the bottom of the bellows seal against the bottom of the recess to create a seal. It is thereby possible by exploiting the surface unevenness of the preferably cast brake carrier to retain the clamping ring firmly and under bias within the recess hole, while assembly can be effected by simply inserting the clamping ring. 
     In order to augment the surface pressure between the second end of the pleated bellows and the bottom of the recess, it is advisable in further improving this invention to provide a circumferential sealing bead on the bottom surface of the bellows facing the recess bottom. Owing to the thereby increased pressure it is more easily possible to compensate for any unevenness on the bottom of the recess. 
     To avoid tensile stress within the pleated bellows during the actuating movement of the actuating lever and thus possibly a reduced sealing effect, the bellows is compressed beneath the actuating lever by a step on the lever engaging the bellows seal to compress the seal when the lever is in the retracted position. 
     The bellows seal is held against the step by the end of the return spring of the actuating lever extending through the lever. Double use is made of the return spring thereby. 
     In order to keep the pleated bellows as small as possible, the through opening is a slot and the recess and bellows seal are elliptically shaped in this way the sealing surface is arranged as closely as possible around the pivot opening of the lever, and a small sealing surface being obtained as a result. The slotted shape of through the opening further diminishes the possibility of ingress of spray water into the brake&#39;s interior and thus supports the sealing effect. 
     In order to not load the pleated bellows during its actuation, the bellows seal is formed so as to be preloaded when the lever is in the retracted position and largely unloaded when the lever moves to actuate the brake according to the features of claim 5 and/or the employment of the features. Exploiting the axial preload and/or the unsymmetrical design of the pleated bellows in the swivelling direction permit to achieve a substantially symmetrical and tension-free condition of the pleated bellows in the actuating position of the actuating lever. Damage to the pleated bellows by actuation of the lever is thus precluded. 
     Forming the wall of the recess with a groove, and an interfit attachment on the clamping ring, accomplishes in a simple manner a torsion-preventing means for the clamping ring. The same applies to the pleated bellows by forming a protrusion on the perimeter of the second end interfit into the groove according to claim 10. 
     An improvement of this invention provides for a simplified assembly of the pleated bellows to the clamping ring by projections formed on the bellows overlying the clamping ring to these elements are combined with the clamping ring to form a construction unit. 
     One embodiment of the present invention will be explained hereinbelow with reference to the accompanying drawings in which 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1, is a broken and partial cross-sectional view of an actuating lever which is provided at its end with an expanding lock and which extends through a through hole in the brake carrier, as well as of an associated inventive seal; 
     FIG. 2, is, on a reduced scale, a partial side view of a clamping ring pertaining to the seal according to FIG. 1; 
     FIG. 3, is a top view of the clamping ring according to FIG. 2; 
     FIG. 4, is the pleated bellows according to FIG. 1 in a reduced and cross-sectional side view; and 
     FIG. 5, is a top view of the pleated bellows in FIG. 4. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows as an actuating device 2 an expanding lock which is actuated by swivelling an actuating lever 4 in the direction of the double arrow S. The effect of this expanding lock is described in principle on page 135 of the Brake Handbook, 9th edition, of Bartsch publishing house in respect to FIG. 13 and, therefore, shall not be explained herein in more detail. It is essential that the expanding lock is operated by way of the actuating lever 4 which projects through a through hole 6 of a brake carrier 7 illustrated only in a broken fashion. The through hole 6 is slot-shaped and simultaneously may serve as lateral guidance for the actuating lever 4. Making catch at the top end of the actuating lever is the end of a Bowden cable indicated by a circle 3 and moving, in case of need, the actuating lever 4 to assume the actuating position, drawn in broken lines under B, in which the drum brake is operative. 
     The brake carrier 7 is provided with a recess 12 which is confined by a circumferential wall 10 and by a circumferential surface 19 on the bottom. The recess 12 passes over into the slot-shaped through hole 6, the lateral surfaces of which guide the swivelling movement in the direction of the arrow S of the actuating lever 4. The interior of the brake drum lying beneath the illustrated part of the brake carrier 7 is sealed in relation to the outside space lying above the brake carrier 7 by means of a pleated bellows 1. The first end 8 of the pleated bellows lying in the upper part in FIG. 1 embraces with a correspondingly designed opening an upper portion of the actuating lever, while a circumferential sealing bead 23 abuts on the circumferential surface 19 of the second end 9 of the pleated bellows, which is in the lower part of the drawing, and thereby prevents fluid from entering the drum&#39;s inside through the through hole 6. 
     At its second end 9, the pleated bellows 1 comprises a circumferential edge 17 which carries the sealing bead 23 and likewise receives the force for sealing by the sealing bead 23 which force is applied on the surface 16 of a flange portion formed on the second end of the pleated bellows 1. This force is exerted by a clamping ring 14 which, substantially, is ellipse-shaped (see FIG. 3) and, disposed on the bellows surface 16. The clamping ring 14 is formed on its external periphery with transversely outward sharing teeth 15 which press against the wall 10 of the recess 12 after the clamping ring 14 has been pressed into the oval recess 12. 
     Starting from the edge (see FIGS. 1, 4 and 5), each end of the pleated bellows 1 is formed with a projection 28, 29 each of forming which a groove with the edge 17. This groove embraces the annular clamping ring 14 on opposite sides from its inner edge so that a single construction unit composed of clamping ring 14 and pleated bellows 1 is formed. This permits rather easy mounting of the seal. 
     On its side on the right hand in the drawing, the clamping ring 14 is provided with an attachment 18 which projects radially outwardly into a correspondingly shaped groove 27 formed into the wall of the recess 12 this arrangement serves as a torsion-preventing means. In a corresponding fashion, the lower edge 17, of the bellows 1 is formed with an extension 20 which likewise projects into the groove 27 and which serves both for aligning the pleated bellows in relation to the clamping ring and as a torsion-preventing means. 
     The pleated bellows 1 shown in the unmounted condition in FIG. 4 is of asymmetrical configuration, in its unloaded position as shown in FIG. 4, corresponding basically to the actuating position B in FIG. 1. 
     The actuating lever 4 is furnished in its upper area on both of its sides with a step 25 which limits movement of the first end 8 of the pleated bellows 1 downwards. Advantageously, preventing movement of the first end 8 upwardly is performed by the end of the return spring 11 which makes catch at an opening in the upper section of the actuating lever. 
     The teeth 15 can be (yet need not be) distributed over the entire external edge 30 of the clamping ring and are disposed at their ends largely in parallel to the wall 10. Corresponding cutting edges can enhance the clamping effect. 
     Upon actuation of the actuating lever 4 from its inactive position shown in FIG. 1 into the actuating position illustrated in broken lines, it may occur that the bellows is expanded in the actuating direction. From this results that the two sides of the lower second end 9 of the pleated bellows are urged crossly to the actuating direction. This may have as a consequence reduction of the sealing effect of the pleated bellows, while simultaneously the material of the pleated bellows extending into the through hole 6 will still disturb the movement of the actuating lever and, possibly, the material may in addition be damaged by the moved actuating lever. 
     In order to remedy this, the edge of the circumferential surface on each side of the through hole or slot is provided with a cast nose 35, each of protruding which upwardly in the drawing, and which prevent displacement of the corresponding parts of the pleated bellows 1 into the slot or through hole 6 and thus augment the sealing effect. The continuous cast nose 35 shown in FIG. 1 can be replaced by a number of post-type cast noses which are short in their extension in the actuating direction, whereby weight is economized while the effect remains the same.