Abstract:
A method of determining whether brake wear has exceeded a predetermined maximum in a brake of the kind including at least one first brake part which is moveable into engagement with at least one second brake part which is rotatable with a member to be braked, and an actuator to move the first brake part into engagement with the second brake part an indicator element being movable with the actuator, and the first and second brake parts, the actuator and indicator element being housed in a housing which includes a guide adapted to receive an indicator probe the guide being positioned to correspond to a position beyond which the indicator element will move when brake wear has exceeded a predetermined maximum, the method including moving the indicator probe in the guide towards the indicator element and determining whether the indicator probe engages the indicator element.

Description:
RELATED U.S. APPLICATIONS  
         [0001]    Not applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
         REFERENCE TO MICROFICHE APPENDIX  
         [0003]    Not applicable.  
         FIELD OF THE INVENTION  
         [0004]    This invention relates to a method of determining brake wear and more particularly of determining whether brake wear has exceeded a predetermined maximum in a brake of the kind including at least one first brake part which is moveable into engagement with at least one second brake part which is rotatable with a member to be braked, and an actuator to move the first brake part into engagement with the second brake part.  
         BACKGROUND OF THE INVENTION  
         [0005]    In such brakes, a plurality of first and second brake parts may be provided which are interleaved. The brake parts may be plates which may be immersed in an oil. Such brakes typically are provided for braking an axle shaft within an axle housing.  
           [0006]    Conventionally in order to determine the extent of brake wear, it is necessary to remove the axle from the vehicle or other machine on which the axle is provided, drain the oil and dismantle the axle, to render the brake parts visible. This is obviously a major servicing operation which it is desired to avoid, particularly where brake wear has not exceeded a predetermined maximum.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    According to a first aspect of the invention we provide a method of determining whether brake wear has exceeded a predetermined maximum in a brake of the kind including at least one first brake part which is moveable into engagement with at least one second brake part which is rotatable with a member to be braked, and an actuator to move the first brake part into engagement with the second brake part, an indicator element being movable with the actuator, and the first and second brake parts, the actuator and indicator element being housed in a housing which includes a guide adapted to receive an indicator probe, the guide being positioned to correspond to a position beyond which the indicator element will move when brake wear has exceeded a predetermined maximum, the method including moving the indicator probe in the guide towards the indicator element and determining whether the indicator probe engages the indicator element.  
           [0008]    The method of the invention may be performed without having to dismantle the brake, and where the brake is provided in an axle housing of an axle of a vehicle or machine, without having to remove the axle from the vehicle/machine.  
           [0009]    Accordingly, the invention provides substantially economic advantage over known brake wear determination methods.  
           [0010]    In one embodiment, the indicator element includes a surface with which the indicator probe engages when brake wear has not exceeded a predetermined maximum. Thus by determining that the probe does not engage the indicator element surface when moved in the guide e.g. by moving in the guide beyond a position the probe would move to if the probe had engaged with the indicator element, it can be determined that the amount of brake wear is beyond the predetermined maximum.  
           [0011]    In another embodiment, the indicator element includes a recess in which the indicator probe engages when brake wear has not exceeded a predetermined maximum. In this event, permitted movement of the probe in the guide less than that permitted if the probe engages in the indicator recess would indicate that the amount of brake wear is beyond the predetermined maximum.  
           [0012]    In one example, the method may include moving the indicator probe in the guide towards the indicator element and determining whether the indicator probe engages the indicator element prior to application of the brake. In this case it will be essential for the position of the actuator and hence of the indicator element to be dependent upon the amount of brake wear. Preferably therefore the method includes moving the indicator probe in the guide towards the indicator element and determining whether the indicator probe engages the indicator element whilst the brake is being applied, as in this position, the actuator and hence the indicator element will necessarily be at a position indicative of the amount of brake wear.  
           [0013]    Although the housing may be part of an axle housing, the invention may be applied to other brake configurations where a determination of brake wear beyond a predetermined maximum is desired e.g. without having to dismantle the brake.  
           [0014]    According to a second aspect of the invention we provide a brake including at least one first brake part which is moveable into engagement with at least one second brake part which is rotatable with a rotatable member to be braked, an actuator to apply the brake and an indicator element movable with the actuator, a housing for housing the first and second brake parts, the actuator and indicator element, the housing including a guide adapted to receive an indicator probe, the guide being positioned to correspond to a position beyond which the indicator element will move when brake wear has exceeded a predetermined maximum.  
           [0015]    The invention is particularly but not exclusively applicable where access to the first and second brake parts visually to examine the extent of brake wear is obscured by the housing.  
           [0016]    The guide may be a simple opening in the housing through which the indicator probe is insertable.  
           [0017]    The invention has been particularly developed where the brake has a plurality of first brake parts which are generally parallel and affixed relative to the housing, and wherein the rotatable member to be braked is a shaft which carries a plurality of second brake parts, there being a second brake part interposed between each adjacent pair of first brake parts, and in which the first and second brake parts may be immersed in use, in oil.  
           [0018]    To avoid having to drain oil from the housing before inserting the probe in the opening or other guide, preferably the guide is provided so as to extend downwardly through the housing towards the indicator element. Preferably a scaling device is provided to close the guide when the indicator probe is removed.  
           [0019]    The brake may be of the kind in which the actuator is movable to apply the brake by hydraulic fluid. If desired subsequent to brake application, a residual pressure is applied to maintain the actuator in a position adjacent to the first and second brake parts whilst not applying braking pressure in which case a determination of brake wear may be performed whilst the brake is released, although the determination preferably is made whilst the brake is applied.  
           [0020]    In one embodiment the indicator element includes a surface with which the indicator probe engages when brake wear has not exceeded a predetermined maximum, the indicator probe including a shank which is inserted into and moved within the guide to bring an end of the probe into engagement with the indicator element when brake wear is less than the predetermined maximum, the shank being dimensioned such that a first shank length extends outwardly of the guide when the end of the shank is in engagement with the indicator element, and a second shank length extends outwardly of the guide when the indicator has moved beyond the guide so that the end of the shank does not engage with the indicator element. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0021]    The invention will now be described with reference to the accompanying drawings in which:  
         [0022]    [0022]FIG. 1 is an illustrative side cross sectional view through part of an axle to which the invention is applied, when the brake has not exceeded a predetermined amount.  
         [0023]    [0023]FIG. 2 is a view similar to FIG. 1 but in which the brake wear has exceeded a predetermined amount. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    Referring to the drawings, a brake  10  is provided for braking a rotatable member which in the present case is an axle shaft  12  which extends through an axle housing  14 . The shaft  12  carries a plurality i.e. four brake parts  15   a ,  15   b ,  15   c ,  15   d  which are generally parallel annular plates, the plates  15   a  etc. being keyed to the shaft  12  via a collar  16 . The brake  10  further includes a plurality, i.e., five second brake parts  18   a ,  18   b ,  18   c ,  18   d ,  18   e  which are fixed relative to the axle housing  14  via a collet  19 , and are also in the form of plates. The plates  15   a  etc. which are rotatable with the shaft  12  are interposed between the plates  18   a  etc. which are affixed relative to the housing  14 , one of the rotatable plates  15   a  etc. being interleaved between a pair of the housing-affixed plates  18   a  etc.  
         [0025]    As the shaft  12  rotates, when the brake is not applied, the rotatable plates  15   a  etc. may rotate relative to the fixed plates  18   a  etc.  
         [0026]    The brake  10  further includes an actuator  20  which is an annular piston which is moveable by hydraulic fluid in an annular chamber  21  which can only be seen in FIG. 2, as the hydraulic fluid is introduced into the chamber  21  under pressure. The chamber  21  is formed between the piston  20  and a cylinder part  24  in which the piston  20  slides as it moves.  
         [0027]    When pressure is applied, the piston  20  will move in the direction indicated by arrow A to force the plates  15  etc. which are fixed relative to the shaft  12  and the plates  18   a  etc. which are fixed relative to the housing  14 , together, to cause braking of the shaft  12 .  
         [0028]    In another embodiment, the piston  20  may be actuatable by other fluid means such as pneumatic fluid, or even mechanically. In each case, the piston  20  carries with it an indicator element  25  which in this example is an integral part of the piston  20 , but in another arrangement may be an element secured to the actuator  20  by any suitable means.  
         [0029]    According to the present invention, the brake  10  includes a guide  30  which in this example is a simple opening in the housing  14 . The opening  30  is carefully positioned as described below, so that using an indicator probe as shown at  31 , it can be determined whether the brake  10 , i.e. the plates  15   a  etc. and  18   a  etc. have worn beyond a predetermined and acceptable extent.  
         [0030]    The indicator probe  31  includes an elongate shank  33  and in this example, has a head  35 . The shank  33  is slightly thinner than the guide opening  30  and its length is carefully selected for operational purposes as will appreciated from the following description of use of the indicator probe  31 .  
         [0031]    In FIG. 1 the brake  10  is shown in a condition which it will adopt when the brake is applied, but the plates  15   a  etc. and  18   a , have not worn beyond the predetermined extent. When the shank  33  of the indicator probe  31  is inserted into the guide opening  33 , the probe  31  may be moved in the guide until a nose end  36  of the indicator probe  31  engages with the indicator element  25 . The shank  33  of the indicator probe  31  is selected to be of such length that a first length of the probe  31  will extend from the housing  14 , i.e., in this example, the head  35  will be proud of the housing  14 , to indicate that brake wear has not exceeded a predetermined amount.  
         [0032]    It will be appreciated that as the plates  15   a ,  18   a  etc. Ear, as indicated in FIG. 2, the piston  20  will need to move further in the direction of arrow A in order to apply the brake. Thus in FIG. 2, wherein the plates  15   a ,  18   a  etc. have worn beyond a predetermined amount, the piston  20  will, when the brake  10  is applied, adopt a position further in the direction of arrow A, and in this position, the indicator element  25  will have moved beyond the guide opening  30 .  
         [0033]    Thus if the probe  31  is inserted into the guide opening  30  and moved in the opening  30 , the probe end  35  will fail to engage the indicator element  25  and accordingly the probe  31  can be moved to the position indicated in FIG. 2, behind the indicator element  25  and piston  20 .  
         [0034]    Thus a second length of the shank  33  of the probe  31  will project from the opening  30 , which in the present case, is a very small length indeed, such that the head  35  of the probe  31  can engage or at least lie very close to the housing  14 .  
         [0035]    Usually the plates  15   a ,  18   a  etc, will be immersed in an oil contained within the axle housing  14  to lubricate the brake  10 . Thus preferably the opening  30  is made through the housing from a top  40  of the housing  14  so that oil does not escape from the housing  14  when the opening  30  either is occupied by a probe element  31 , or not. Preferably a sealing device such as a plug (not shown) is provided in the opening  30  when not in use by the probe  31 .  
         [0036]    Of course where the brake  10  is not of the oil immersed type, the opening  30  or other guide may be provided at alternative positions.  
         [0037]    In each case the method may include determining the position for the guide means by measuring from a datum position of the housing  14 , such as for example where the housing  14  is part of an axle housing, an axle centre, or any other datum position which readily can be identified and from which a measurement can be taken.  
         [0038]    Thus the guide opening  30  can be provided at a position corresponding to the position of the indicator element  25  when brake wear has just exceeded an acceptable predetermined amount.  
         [0039]    Various modifications may be made without departing from the scope of the invention.  
         [0040]    For example, the indicator element  25  need not be a surface as indicated in the example described, but may be for example, a recess in the piston  20 , or another part  25  which moves with the piston  20  or other actuator. In that case, when brake wear is less than a predetermined maximum extent, the end  36  of the indicator probe  31  may be received in the recess such that only a short first length of shank  33  extends from the guide  20 , and when brake wear is beyond the predetermined maximum extent, the end  36  of the indicator probe  31  may engage with a surface of the piston  20  or other part which moves with the piston  20 .  
         [0041]    If desired, the indicator probe  31  may permanently be received in the guide opening  30 . Means such as a spring could be provided to urge the probe  31  towards the indicator element  25 , at least where the element  25  is a surface, and to urge the end  36  of the indicator probe  31  past the indicator element  25  in the event of excess brake wear. However the probe  31  would then prevent brake back-off which may be undesirable for the kind of brake described.  
         [0042]    Where the indicator probe  31  is permanently received in the guide opening  30 , if desired, the probe  31  and/or guide opening  30  may include a sensor means to activate a warning light or buzzer in the event that brake wear exceeds a predetermined minimum.  
         [0043]    The invention may be applied to alternative types of brake to that described above. For example, although in the example described a plurality of first brake parts  15   a  etc. and second brake parts  18   a  etc. are provided, the invention is applicable where only single first and second brake parts are provided. Although in the example described with reference to the drawings, the brake parts  15   a ,  18   a  etc. are usually metal and braking is effected by metal-to-metal contact, and the metal wears away with brake use, in another example, one or both of the brake parts may carry friction material which wears with brake use and the invention may thus be used to determine when friction material wear is beyond a predetermined maximum.  
         [0044]    Although the invention has been developed particularly for use with an axle brake in which the brake  10  is provided within an axle housing  14 , the invention has other brake applications, particularly where visual access to the brake parts to determine the extent of brake wear is impaired.  
         [0045]    Whereas the invention has been described with reference to determining brake wear when the brake is applied, the determination may be made with the brake not applied, but in that event, either a residual fluid pressure or mechanical spring means or the like would need to be used to ensure that the actuator  20  and hence indicator element  25  is moved towards the brake parts  15   a ,  18   a  etc. an amount dependant upon brake wear.  
         [0046]    Other variations and modifications may be made as will be apparent to those skilled in the art.