Abstract:
A protective cover unit including a main cover for partly covering an aperture for access to brake linings which is accommodated in a disc brake yoke for a disc brake. The main cover includes fastenings to a U-bolt-shaped lining holder which is connected to the brake yoke and runs transversely across the aperture. The main cover abuts against a portion of the brake yoke outer surface which at least partly surrounds the aperture.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a protective cover unit for a disc brake according to the preamble of claim  1  and a disc brake unit including such a protective cover unit.  
       STATE OF THE ART  
       [0002]     Disc brakes for road vehicles, and particularly for heavy utility vehicles, suffer from considerable problems due to fouling of disc brake units by dust, water and waterborne pollutants which contaminate, when the vehicle is in motion, both disc brakes and brake yokes with brake linings. This can have consequences in terms of effects on moving parts. Dirt and corrosion may in particular lead to functional impairment causing uneven or impaired braking effect as between different disc brake units.  
         [0003]     Moreover, differences in braking action and consequently uneven wear of brake linings may occur on the different sides of a disc if the linings are contaminated to different extents. All in all, in the state of the art, these problems reduce the usability of disc brakes and shorten service intervals, thereby increasing costs. This situation has also led to otherwise less efficient drum brakes being regarded as more reliable and as requiring less servicing.  
         [0004]     Various attempts at alleviating the problems of disc brakes have resulted in shaft-mounted protection surrounding the brake disc, but this has entailed problems of impaired cooling, inherent oscillations and extra unsprung weight.  
         [0005]     Brake yokes for disc brakes normally have an aperture for the extraction and insertion of brake linings and for inspection of the interior of the brake yoke. With a view to protecting the brake yoke&#39;s constituent parts and the brake disc against contamination via this aperture, it has been proposed to insert a protective plate which is integral with the lining holder. However, that solution has not entirely solved the problems of contamination via the extraction aperture, and such a protective plate is troublesome to fit and remove and has therefore hindered accessibility. The position of the protective plate within the aperture close to the brake linings is also regarded as hindering air flow and thereby reducing cooling.  
       OBJECTS AND MOST IMPORTANT CHARACTERISTICS OF THE INVENTION  
       [0006]     One object of the present invention is to indicate a protective cover unit for a disc brake of the kind mentioned in the introduction, whereby the problems of the state of the art are reduced. A particular object is to propose a protective cover unit which functions better and is economic to manufacture and fit.  
         [0007]     These objects are achieved in the case of a protective cover unit of the kind mentioned in the introduction by the features in the characterising part of claim  1 .  
         [0008]     The result is a functional solution which is easy to fit to and remove from the lining holder. The fact that it abuts against an outer surface of the brake yoke prevents the formation of dust accumulation pockets which might entail risk of dirt being led into the aperture.  
         [0009]     It should be noted that the space outside the brake yoke is very limited because of proximity to a wheel rim in cases where the brake unit is fitted adjacent to a wheel. However, a main cover according to the invention may, through its connection to the brake yoke, be made so thin and yet stable as not only to perform properly its protective function but also to be clear of a rotating wheel rim.  
         [0010]     The invention results in reduced contamination in the region of the brake yoke and hence a more even braking action and more even lining wear, with the overall effects of greater functional reliability and longer service intervals for the brake disc units here concerned.  
         [0011]     The main cover preferably provides protection for indicating cables from brake linings. In this respect it is of great advantage if the main cover is provided with lateral tabs which press these cables inwards towards the brake yoke, i.e. away from the region of a rotating wheel rim which might otherwise damage these cables.  
         [0012]     In the case of a single-mounted wheel it is advantageous that the main cover be supplemented by an outer cover which reduces dirt ingress via the slits in the main cover.  
         [0013]     Further advantages arise from further aspects of the invention which are indicated by the following detailed description of embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The attached drawings are as follows:  
         [0015]      FIG. 1  depicts schematically a section through a vehicle wheel with a disc brake unit according to the invention,  
         [0016]      FIG. 2  depicts parts of the disc brake unit in  FIG. 1  in a partly dismantled perspective view,  
         [0017]      FIG. 3  depicts a partly dismantled perspective view of an alternative embodiment of a disc brake unit according to the invention,  
         [0018]      FIG. 4  depicts a plan view of a main cover,  
         [0019]      FIG. 5  depicts a side view of the main cover in  FIG. 4  and  
         [0020]      FIG. 6  depicts a plan view of an outer cover. 
     
    
     DESCRIPTION OF EMBODIMENTS  
       [0021]      FIG. 1  thus depicts in section a vehicle wheel with a disc brake unit  1  placed within the circumference of a wheel rim  3  which supports a vehicle tyre  2 . Broken lines at  4  represent a wheelshaft to which the vehicle wheel is fastened.  
         [0022]     The disc brake unit  1  comprises a brake yoke  5 , a brake disc  6  fastened to the wheelshaft  4 , and brake linings  7  which are arranged on brake blocks and are for braking cooperation with the brake disc  6 . The brake yoke  5  comprises brake supports  8  (one depicted) for firm mounting of the brake yoke  5 . Each brake support  8  has its lower region lengthened so as to be designed to constitute a fastening point for a protective shield  9  which comprises a protective plate  10  and a fastening bracket portion  11 .  
         [0023]     A main cover  17  forming part of a protective cover unit according to the invention is fastened to a lining holder  18  in the upper region of the brake yoke S.  
         [0024]      FIG. 2  depicts in perspective the brake yoke  5  with its brake supports  8 ,  8 ′, each of which is provided with a number of fastening holes  15  (shown in the brake support  8 ′) for accommodating fastening bolts for the brake yoke  5 . Ref. B denotes a brake disc  
         [0025]     The outer extremity of the free end of each brake support  8 ,  8 ′ is provided with a fastening eye  13 ,  13 ′ with respective fastening holes  14 ,  14 ′ for fastening screws  12 ,  12 ′ intended to secure a unit comprising the protective plate  10  and fastening brackets  11 ,  11 ′ by cooperation with holes provided in the free end portions of the fastening brackets  11 ,  11 ′. The fastening brackets  11 ,  11 ′ have a flat U-shaped cross-sectional profile and are curved so that they together substantially describe a circular arc which is at a substantially radially even distance from a wheelshaft when the brake shield is in position.  
         [0026]     The contact surface between the protective plate  10  and the fastening brackets  11 ,  11 ′ is substantially planar.  
         [0027]     The radially innermost portion of the protective plate  10  is situated at a distance from the wheelshaft (ref.  4  in  FIG. 1 ) such that a cooling air flow can pass through the resulting gap and proceed radially along the brake disc. The radially outer periphery of the protective plate  10  is drawn somewhat inwards towards the brake disc so as to create a somewhat enclosing structure.  
         [0028]     The brake yoke  5  has in its upper portion an open recess  16  via which brake linings are intended to be extracted when they are being changed. The recess  16  is also used for other service operations relating to the disc brake unit, and for inspection purposes.  
         [0029]     A lining holder  18  in the form of a supporting U-bolt is placed transversely across the recess so as to extend substantially parallel with the wheelshaft. According to the invention, this lining holder  18  is used for fixing a main cover  17  which is intended to provide dirt protection preventing the ingress of pollutants into the recess  16 . To this end, the main cover  17  substantially covers the adjacent outer arcuate section of the brake yoke.  
         [0030]     The main cover comprises a thin sheetmetal structure designed to cover said recess. The fastening of the main cover is by fastening cooperation with the lining holder  18  whereby fastening screws  20  are inserted in countersunk recesses  19  with holes running through the main cover  17  and are screwed firmly into the lining holder  18 .  
         [0031]     The main cover  17  is also provided with tabs  34  intended to cooperate with and protect indicating cables (see  FIG. 5 ) for indicating the state of wear of the brake linings. These cables take the form of wiring routed from the respective brake linings to the vehicle&#39;s control system. This involves a cable from one of the brake linings being routed through a duct in the upper inner region  45  ( FIG. 2 ) of the lining holder and being thus protected from external effects of the main cover  17 .  
         [0032]     A multiplicity of ventilation slits  33  are arranged in the main cover to allow flow of air which has been used for cooling and which emanates from the region of the disc brake during operation of the vehicle. Cooling of the brake unit is thus promoted despite the presence of the main cover.  
         [0033]      FIG. 3  depicts another embodiment of the invention whereby fastening regions  23  distributed along the peripheral region of the protective plate  10  are used for fastening a protective housing  22 . The latter comprises a first portion  24  which runs substantially parallel with the protective plate  10 , and a second portion  25  which runs, in a manner surrounding the brake disc, substantially at right angles to the first portion  24  and the protective plate  10 . A structure enclosing both sides and the circumference of the brake disc is thus formed.  
         [0034]     The fastening regions  23  are matched by corresponding portions of the protective housing  22 , and joining together is done, for example, by spot welding or by upset riveting.  
         [0035]     Adding the protective housing  22  is applicable in the case of a single-mounted wheel, which means that the brake disc is protected from contamination in all directions, which is otherwise protected by the rim of a vehicle wheel.  
         [0036]     In its upper region directed towards the brake yoke  5 , the protective housing  22 , as also the protective plate  10 , is adapted to connecting closely adjacent portions of the brake yoke  5  while leaving a gap for flow of cooling air towards an adjacent wheelshaft (not depicted).  
         [0037]     At its upper portion, the brake disc unit in the case of a single-mounted wheel is supplemented by fitting an additional outer cover  26  outside the main cover  17 . This outer cover  26  is preferably at a substantially even distance from the main cover  17  so as to leave an air gap  27  between the main cover  17  and the outer cover  26 . To this end, the outer cover  26  has a number of spacing portions  35  which help to maintain the continuity of the air gap  27 . The spacing portions  35  also serve as regions for joining together the main cover and the outer cover, e.g. by upset riveting.  
         [0038]     The object of the outer cover  26  is to protect the disc brake unit  1  from ingress of dirt, water etc. via the slits  33  in the main cover  17  (see  FIG. 2 ). The fastening of the outer cover  26  to a main cover is advantageously effected by the same fastening screws as for the main cover  17  as individual parts of the lining holder  18 . Advantageously, both the main cover  17  and the outer cover  26  are manufactured as pressed sheetmetal parts.  
         [0039]      FIG. 4  depicts the main cover  17  in a plan view in which the hatched regions  36  represent the areas where the main cover  17  abuts overlappingly against part of the arcuate, preferably cylindrical, outer surface of the brake yoke, which outer surface partly surrounds the aperture (ref.  16  in  FIG. 2 ). Ref.  38  denotes a turned-down sidewall. Reinforcing grooves  39  and  40  are pressed into the main cover and run circumferentially relative to the disc brake unit.  
         [0040]      FIG. 5  shows the function of the lateral tabs  34 . The routing of an indicating cable  41  from a brake lining is controlled by an inward pressure imparted to it by the lateral tab  34 . The cable is thus prevented from moving radially outwards to the region of a rotating wheel rim (represented by ref.  42 ) which might otherwise damage the cable.  
         [0041]      FIG. 6  depicts the outer cover  26  with holes  44  running through it for fitting fastening screws into the main cover. Spacing and joining portions  35  are designed to cooperate with corresponding pressings  37  in the main cover (see  FIG. 4 ) and to be used for joining these parts together, e.g. by upset riveting. A curved reinforcing groove  43  is pressed in the material.  
         [0042]     The invention may be modified within the scopes of the ensuing claims whereby the constituent parts may be configured otherwise, e.g. so that there is greater or smaller overlapping of surfaces. The pressings may be configured otherwise, as also the provision of holes.  
         [0043]     It is preferable that the protective shield and the protective cover unit be used in combination, but it is not excluded that either may be used without the other.  
         [0044]     Applying the invention to a disc brake results in significant improvements as regards service life and function. It also results in more even brake lining wear and consequently longer service intervals between brake lining changes.