Abstract:
A brake appliance for gerotor motors has a disc assembly brake comprising interacting discs that are subjected to opposing forces from pressurized fluid in one direction to disengage the discs, and from primary and secondary spring forces in the other direction to engage the discs.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Compact earth excavators are usually tilted at an angle of a few degrees, meaning that they are a little higher in the front end than in the back end, when in operation. This will have the effect that slewing of the excavator occurs whenever the slewing torque of the excavator exceeds the resisting torque of the slewing gear. Slewing or swinging is the rotational movement of the superstructure (such as a crane) relative to the undercarriage. A slewing gear or swinging gear is the system, which provides the movement.  
           [0002]    In order to increase the resisting torque of the slewing gear, gerotor motors have been made with what is called a tight gear set. This means that the internal gear wheel of the gear set of the motor has to be forced around inside the external gear wheel. However, a tight gear set will only apply resistance against rotation in some positions. What is happening, is:  
           [0003]    Torque is applied to the slewing gear from load in the bucket.  
           [0004]    Pressure inside the motor will try to resist the slewing, but internal leaking of fluid means that only the slewing speed is reduced.  
           [0005]    The tight gear set will add additional resistance against slewing when first resistance position is reached, whereby the slewing is stopped.  
           [0006]    Internal leaking of fluid will reduce the pressure, whereby only the tight gear set will apply resistance against slewing.  
           [0007]    If the tight gear set is not able to resist the slewing, it will move on, until the next resistance position is reached.  
           [0008]    A tight gear set can be made with sufficient resistance to resist the slewing. Wear of the gear set will, however, reduce the resistance, and an effective prevention of slewing is only obtained for a short period of the lifetime.  
           [0009]    Therefore, a principal object of this invention is to provide a brake appliance for a gerotor motor that will effectively provide an effective braking torque to resist torque of the slewing gear wheel when associated with a gerotor motor driven vehicle susceptible to developing slewing torque.  
           [0010]    A further object of this invention is to provide a brake appliance for gerotor motors that has a disc assembly brake comprising interacting discs that are subjected to opposing forces from pressurized fluid in one direction to disengage the discs, and from dynamic forces in the opposite direction to engage the discs.  
           [0011]    These and other objects will be apparent to those skilled in the art.  
         SUMMARY OF THE INVENTION  
         [0012]    A brake appliance for gerotor motors to provide resistance to slewing torque imposed upon the output shaft of such a motor includes a disc-type brake involving oppositely disposed interacting braking discs that are subjected to opposing forces from pressurized fluid in one direction to disengage the discs, and from dynamic forces in the opposite direction to engage the discs. The spring forces are provided by a series of spring springs mounted on a slidable piston plate to move the discs into braking engagement with each other. 
       
    
    
     DESCRIPTION OF THE DRAWING  
       [0013]    [0013]FIG. 1 is a longitudinal sectional view of the device of this invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    With reference to FIG. 1, the brake appliance  10  has a housing  12  with a center bore  14 , an outer end  16 , and an inner end  18 . An annular shoulder  19  is formed on the inner end  18  of the housing  12 . An outer bearing chamber  20  is formed in the outer end of housing  12  and supports bearing  22  which is held in place by a conventional snap ring  24  or the like.  
         [0015]    An end cap  26  is positioned against the inner end  18  of housing  12 . End cap  26  has a center bore  28  which is in axial alignment with the center bore  14  of housing  12 .  
         [0016]    An output shaft  30  is rotatably mounted within center bore  14  of housing  12  and is specifically rotatably mounted within the bearing  22 . The shaft  30  has an outer end  32 , and an inner end  34 . A slewing gear wheel  36  is rigidly mounted to the outer end  32  of the shaft  30 . An internal annular cavity  38  is formed in end cap  26 . A brake piston plate  40  is slidably mounted within cavity  38 . A portion of the cavity  38  comprises an annular fluid pressure chamber  42  which is located adjacent the outer face  44  of plate  40 .  
         [0017]    Brake disc wells  46  and  48  are formed in housing  12  adjacent the center bore  14 . The discs  56  extend into mating relationship with the discs  52  by being located within the spaces between the disc  52 . Conventionally, the discs  56  have a width slightly less than the width of the spaces between discs  52  so that the discs  56  are not frictionally engaged with the static discs  52  unless a longitudinal force is exerted upon the discs  56 . The outer geometry of the static brake discs  52  is such that it fits with disc wells  46  and  48  in the housing. Similarly, the inner geometry of the rotating brake discs  56  is such that it fits with splines  54  in the shaft  30 . The discs  52  extending from the stack towards the housing are the static discs, and the discs  56  extending from the stack towards the shaft are the rotating discs.  
         [0018]    A primary spring means  58  is mounted within end cap  26  and bears against brake piston plate  40 . The primary spring means  58  serves to engage the brake by forcing the brake disc  56  into frictional engagement with the brake disc  52 . Similarly, a plurality of secondary springs  60  located in a spaced circular path in wells  62  in brake piston plate  40  also urge the brake disc  56  into frictional engagement with the brake disc  52 .  
         [0019]    Thus, primary springs  58 , placed in wells in the end cap  26 , are acting on the brake piston plate  40 , and secondary springs  60 , placed in wells in the brake piston plate  40 , are acting on the first disc in the brake disc stack, preferably a non-rotating disc. The brake piston plate  40  is free to rotate in the cavity  38 , except for friction in the O-ring sealings, but the brake piston plate  40  is not rotating with the rotating part of the brake disc stack.  
         [0020]    A splined well  64  is formed on the inner end of shaft  30  and is adapted to conventionally receive the splined end  66  of an output shaft of a gerotor motor (not shown).  
         [0021]    The annular fluid pressure chamber  42  is connected to a controllable source of pressurized fluid.  
         [0022]    As previously indicated, the rotating discs  56  are placed on a splined connection on the output shaft  30  upon which the slewing gear wheel  36  is placed. The static discs  52  are placed in spline connection in the housing, and the brake piston plate  40  is able to press the static and rotating discs together, thereby forming a brake torque. The primary springs  58  and secondary spring  60  force the braking action of the engaged discs to take place. However, applying fluid pressure to the chamber  42  on the surface  44  of the plate  40  will disengage the braking action. The transmission shaft  66  will fit into the splined well  64  of shaft  30  when the gerotor motor is mounted on the end cap  26  as previously described.  
         [0023]    Except for the secondary springs  60 , the foregoing structure does not differ from the state of the art. In the present design, the brake piston plate  40  would normally bear against the first static disc  52 , and the last static disc  52  would bear against the housing  12 . With secondary springs  60 , however, the springs  60  will bear against the first static disc  52 , when the fluid pressure chamber  42  is pressurized. Conventional disc brakes are made by MICO, the details of which are basic knowledge to persons skilled in hydraulic motors with multi-disc brakes. The advance in the art is represented by the secondary springs  60  and their functional operation. When fluid pressure is supplied to the chamber  42 , thus normally disengaging the braking action, the secondary springs  60  will add a force to the engaged discs  52  and  56 , creating a torque resistance. Disengaging the brake system by the pressurized fluid will under these circumstances now be impossible. However, shifting between two levels of braking torque is the consequence of applying fluid pressure to the chamber  42 . These two levels constitute primary braking torque and secondary braking torque. The number and dimension of the discs  52  and  56  can be varied, but in any event, serve to provide braking torque that can resist the slewing torque imposed upon slewing gear wheel  36 . The concept of shifting between a static braking torque with the addition of a secondary braking torque is regarded to be novel.  
         [0024]    More specifically, the secondary springs  60  act upon the multi-disc brake and on the brake piston plate  40 , thereby adding a force on the two elements away from each other. With hydraulic pressure applied to the fluid pressure chamber  42 , the brake piston plate  42  will be forced to the right, (FIG. 1) until it reaches the end cap  26 . The secondary springs  60  will, however, still apply a force to the multi-disc brake, and a brake torque is thus still applied to the output shaft  30 . This secondary brake torque comes solely from the secondary springs  60 .  
         [0025]    When hydraulic pressure is released from the fluid pressure chamber  42 , the major spring means  58  force the brake piston plate  40  towards the multi-disc brake, hereby increasing the braking torque to a static braking torque. In a conventional disc brake, the first disc and the last disc in the stack are static discs, meaning that they are rotationally fixed with the housing. Between all static discs, there is a rotating disc, meaning that it is rotationally fixed with the output shaft. When the static discs are forced towards each other, friction between static and rotating discs occurs, and as the rotating discs are rotationally fixed to the output shaft, this friction will apply a braking torque on the output shaft.  
         [0026]    It is therefore seen that this invention will achieve at least its stated objectives.