Abstract:
A load adaptive brake system is provided for an appliance which includes a motor, a drive wheel driven by the motor and a rotatable vessel. A brake surface is fixed relative to a non-movable portion of the appliance and at least one brake shoe carried by the vessel to rotate with the vessel. A biasing mechanism is engageable with the brake shoe to press the brake shoe into engagement with the brake surface. A cam is carried on the vessel, but is rotatable with respect thereto, and engageable with a portion of the brake shoe to overcome a bias of the biasing mechanism when the cam is rotated relative to the vessel in a first direction to disengage the brake shoe from the brake surface. A coupling mechanism is arranged between the drive wheel and the cam to selectively couple the motor to the vessel by rotation of the cam in the first direction when the drive wheel is rotating in one direction relative to the cam and to uncouple the motor from the basket when the drive wheel is rotating in a second, opposite direction relative to the cam.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to washing machines and more particularly to a brake system for a washing machine or other appliance that can adapt to the size of the load held within the machine.  
           [0002]    Vertical axis washing machines include a wash basket that spins about a vertical axis. Horizontal axis washing machines include a wash basket that spins about a horizontal axis. Other washer constructions have a tilted axis between vertical and horizontal. During a spin cycle following a rinse cycle, the wash basket spins at a fairly high rate of speed in order to extract water from the clothing that has been rinsed. Conventional vertical axis washing machines typically spin at a rate of about 600 to 650 revolutions per minute (RPM) or more.  
           [0003]    Underwriters Laboratories (UL) require that, when a washing machine lid is opened during the spin portion of a cycle, the basket must stop spinning within 7 seconds. A brake mechanism is therefore required in order to slow down the rapidly spinning basket within this 7 second time interval. For conventional vertical axis washing machines, the brake mechanism typically applies the same braking pressure to the wash basket at any speed and for any wash basket load. This static or standard brake pressure has been satisfactory for the slower spin rate of these conventional machines.  
           [0004]    However, new generations of washing machines are on the horizon that can spin the wash basket during a rinse cycle at much greater speeds, such as on the order of about 800 or greater RPM. The load required to slow and stop the wash basket within the 7 second interval is much greater at these higher rotational speeds. However, when a high braking load is applied to a wash basket that is spinning at this much higher rate and that contains a very light laundry load it produces undesirable consequences. For example, if a light load is held within the basket spinning at about 500 RPM, when the heavy brake load is applied, the washing machine components begin to vibrate and begin to cause significant noise, vibration and even movement or walking of the machine. At a minimum such conditions are unpleasant and could potentially cause more serious consequences.  
           [0005]    Where a washing machine brake is incapable of meeting this 7 second requirement, a lid lock must be employed to prevent access to the wash drum until it has stopped spinning. Such a lid lock adds expense to the machine and creates a significant inconvenience to users.  
         SUMMARY OF THE INVENTION  
         [0006]    In light of the above noted problems, it is an object of the present invention to provide a washer brake mechanism that applies sufficient brake torque for these relatively high RPM machines, but not the same brake torque under all washer conditions. It is another object of the present invention to provide a brake mechanism that does not produce a constant high brake torque that would be sufficient to brake a fully loaded basket of wet laundry and yet which would overpower a lightly loaded basket. It is a further object of the present invention to provide a washer brake mechanism that produces a variable brake torque sufficient for different laundry loads. It is yet another object of the present invention to provide a washer brake mechanism that applies a brake torque that is variable according to particular laundry basket conditions. It is another object of the present invention to provide a load adaptive washer brake mechanism that automatically adjusts the applied brake torque according to the mass of the load held within the wash basket and the rotational speed of the basket.  
           [0007]    It is another object of the invention to provide a load adaptive brake system for an appliance in which a drive motor and the rotatable vessel are selectively coupled and uncoupled and a braking mechanism is selectively engaged and disengaged as the uncoupling and coupling occurs, respectively. It is a still further object of the invention to use the reactive force of the motor to disengage the braking mechanism if the rotating vessel is being slowed too quickly by the braking mechanism. A preferred embodiment of the invention is in a vertical axis washer, although the invention can also be used in horizontal and tilted axis washers as well as other appliances having a rotatable vessel.  
           [0008]    These and other objects, features and advantages of the present invention are provided by a load adaptive brake system for an appliance according to the present invention. In one embodiment, the load adaptive brake system includes a stationary brake drum supported by the washing machine. The brake system also includes a brake plate and a pair of opposed brake shoes supported by the brake plate and including brake linings facing the brake drum. A spring is interposed between first ends of the brake shoes for forcing the brake pads against the brake drum. A cam is slidably carried on a rotary shaft of the washing machine and has a pair of cam surfaces. A roller is disposed on a second end of each of the brake shoes. Each roller bears against one of the cam surfaces of the cam. The cam surfaces each have a profile so that the cam will rotate to at least partly relieve brake pressure on the brake drum as the motor of the washing machine decelerates and applies residual deceleration torque through the motor armature to the cam if the motor is caused to decelerate faster than the normal uncoupled deceleration rate. That is, the motor has a normal deceleration rate when the motor is not coupled to the wash basket. This normal deceleration rate, in a preferred embodiment, is such that the motor would decelerate from full speed, at which the wash basket is rotating at least 500 rpm, and perhaps at 800 or greater rpm, to a stop condition in about 5½-6½ seconds.  
           [0009]    The brake system was developed to be able to apply sufficient brake torque to stop a fully loaded wash basket from a full speed spin to a stopped condition in less than 7 seconds. When this same brake torque is applied to an empty wash basket, the basket is slowed from full speed to a stopped condition in about 2 seconds. While such a speed is well within the time requirements, such abrupt braking causes the entire washing machine to jerk and move about. If, however, the motor is coupled to the empty wash basket as the wash basket is being slowed down, the motor is caused to slow down faster than its normal deceleration speed, resulting in a reaction torque being developed by the motor and transmitted back to the cam, rotating the cam in a reverse direction to release the braking pressure of the brake pads against the brake drum. This causes a reduction in the net brake torque, thereby lengthening the time for the wash basket to come to a complete halt, would also prevent the machine from jerking and moving about. Since the motor naturally stops in less than 7 seconds, coupling the motor with the basket does not cause the coupled combination to stop in greater than 7 seconds because the reaction torque lessens as the stoppage rate approaches 5½ to 6½ seconds, and the lesser reaction torque becomes insufficient to overcome the strength of the spring through the cam, hence reapplying the brakes.  
           [0010]    Thus, in a preferred embodiment, a mechanism is provided to automatically couple the basket to the motor if the basket is being slowed faster than the normal deceleration rate of the motor and to uncouple the motor from the basket if the basket is being slowed slower than the normal deceleration rate of the motor. The profile of the cam is selected such that the reaction torque enables the brakes to be at least partially released through rotation of the cam.  
           [0011]    In another embodiment of the invention, a vertical axis washing machine includes a wash basket that is rotatable about a generally vertical axis. A rotary shaft is coupled to the wash basket and a motor is coupled to the rotary shaft for rotating the wash basket. A brake drum is stationary and supported by a portion of the washing machine. A brake plate supports a pair of brake shoes wherein the brake plate is carried by a portion of the rotary shaft of the washing machine and rotates relative thereto. A pair of brake shoes are supported by the brake plate wherein each brake shoe has a brake lining that can bear against the brake drum. A spring is interposed between first ends of the brake shoes that forces the brake linings against the brake drum. A cam is slidably carried on a portion of the rotary shaft and has a pair of cam surfaces. A pair of cam rollers are supported by respective second ends of the brake shoes. Each cam roller bears against a respective one of the cam surfaces of the cam. Each cam surface has a profile that is adapted to at least partly reduce the amount of brake pressure applied by the brake linings against the drum upon rapid deceleration of the motor through residual torques applied through the motor armature during rapid deceleration.  
           [0012]    In another embodiment a load adaptive brake system is provided for an appliance which includes a motor, a drive wheel driven by the motor and a rotatable vessel. A brake surface is fixed relative to a non-movable portion of the appliance and at least one brake shoe carried by the vessel to rotate with the vessel. A biasing mechanism is engageable with the brake shoe to press the brake shoe into engagement with the brake surface. A cam is carried on the vessel, but is rotatable with respect thereto, and engageable with a portion of the brake shoe to overcome a bias of the biasing mechanism when the cam is rotated relative to the vessel in a first direction to disengage the brake shoe from the brake surface. A coupling mechanism is arranged between the drive wheel and the cam to selectively couple the motor to the vessel by rotation of the cam in the first direction when the drive wheel is rotating in one direction relative to the cam and to uncouple the motor from the basket when the drive wheel is rotating in a second, opposite direction relative to the cam.  
           [0013]    These and other objects, features, and advantages of the present invention will become apparent upon a reading of the detailed description and a review of the accompanying drawings. Specific embodiments of the present invention are described herein. The present invention is not intended to be limited to only these embodiments. Changes and modifications can be made to the described embodiments and yet fall within the scope of the present invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a side elevational view, partly in section, of a washing machine with a standard motor drive and showing the wash plate in an angled orientation.  
         [0015]    [0015]FIG. 2 is a detailed sectional view of the washing machine of FIG. 1 and including a brake mechanism constructed in accordance with the present invention.  
         [0016]    [0016]FIG. 3 is an enlarged view of the brake mechanism shown in FIG. 2.  
         [0017]    [0017]FIG. 4 is a cross section taken along line IV-IV of FIG. 3 illustrating the brake components.  
         [0018]    [0018]FIG. 5 is a top elevational view of the cam driver and pawl of the washing machine of FIG. 1.  
         [0019]    [0019]FIG. 6 is a side elevational view of the pawl of FIG. 5.  
         [0020]    [0020]FIG. 7 is a top elevational view of the drive pulley of the washing machine of FIG. 1.  
         [0021]    [0021]FIG. 8 is a side sectional view of the drive pulley taken generally along the line VIII-VIII in FIG. 7.  
         [0022]    [0022]FIG. 9 is a top elevational view of the drive pulley and pawl where the drive pulley moves counter-clockwise relative to the output shaft.  
         [0023]    [0023]FIG. 10 is a top elevational view of the drive pulley and pawl where the drive pulley moves clockwise relative to the output shaft.  
         [0024]    [0024]FIG. 11 is a graph representing cam torque plotted against cam rotation.  
         [0025]    [0025]FIG. 12 is a graph representing motor reaction torque back into the cam through the motor armature plotted against the brake time.  
         [0026]    [0026]FIG. 13 is a graph representing various cam profiles wherein applied brake torque is plotted against brake time for various cam profiles.  
         [0027]    [0027]FIG. 14 is a graph representing overall brake sensitivity to brake lining coefficient of friction with and without utilizing the cam effect of the present invention wherein brake torque is plotted against brake pad lining coefficient of friction. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    The present invention is particularly useful for a vertical axis washing machine of the type disclosed in FIGS.  1 - 2  and thus the preferred embodiment will be disclosed in this environment, although the invention is not so limited. In fact, the present invention can be utilized in other types of washers such as horizontal axis or tilted axis, as well as any other appliance which has a motor driven rotatable vessel. This could include dryers, centrifuges and other appliances.  
         [0029]    A particular type of vertical axis washing machine is disclosed in U.S. Pat. No. 5,460,018, the disclosure of which is hereby incorporated by reference. The type of machine disclosed therein includes an agitator or wash plate that can operate vertically and also operate at an angle. The wash plate is driven by a drive system that together can operate at significantly higher rotational speeds such as on the order of 500 RPM or more. The present invention is directed to a brake mechanism and system for stopping rotation of the wash basket (rotating vessel) when a lid is opened during the spin cycle. The brake mechanism of the present invention is load adaptive and applies a varying brake torque, dependent upon the mass of the laundry load within the wash basket.  
         [0030]    In FIGS. 1 and 2, reference numeral  20  indicates generally a washing machine of the automatic type, i.e., a machine having a pre-settable sequential controller  21  for operating the washer through a preselected program of automatic washing, rinsing and drying operations in which the present invention may be embodied. The controller  21  may be an electromechanical timer type device or an electronic microprocessor. The machine  20  includes a frame or cabinet  22  surrounding an imperforate tub  24 . A wash basket  26  with perforations or holes is rotatably supported within the tub and comprises a rotatable vessel into which a clothes load is placed. A fill valve  25  is connected to an external water supply (not shown) and is operated to inlet water into the tub. A hinged lid (not shown) is provided in the usual manner to provide access to the interior of the wash basket  26 .  
         [0031]    The wash basket  26  defines a wash chamber and includes a generally cylindrical side wall  30  having a vertical center axis C-C. The side wall  30  includes a partly spherical wall portion  34  adjacent a substantially flat bottom wall  32 . A motor  40  is operatively connected to the basket  26  through a transmission  42  to rotate the basket  26  relative to the stationary tub  24 . A suspension frame  44  supports the motor and tub assembly within the cabinet  22 . The controller  21  is operatively interconnected with the motor and fill valve  25  such that the controller  21  can operate the washer  20  according to a selected program cycle.  
         [0032]    The particular construction and operation of the agitation or clothes mover mechanism is not critical to the present invention, and could comprise one of many different constructions, such as those shown in FIGS.  1 - 2 . The details of these constructions are known, for example as disclosed in U.S. Pat. No. 5,460,018 and U.S. Pat. No. 6,115,863 the full disclosures of which are incorporated herein by reference. Further details of the construction of those mechanisms is not included here, except to the extent necessary to describe the present invention.  
         [0033]    A brake mechanism  64  embodying the principles of the present invention is shown environmentally in FIG. 3, and in greater detail in FIG. 4.  
         [0034]    [0034]FIG. 3 illustrates a detailed cross section of a portion of the wash basket  26  and drive system including the load adaptive brake system or brake assembly  64  according to the present invention. The motor  40  includes a downwardly depending motor shaft  100  that includes a drive pulley  102  thereon. A belt  104  is coupled to the pulley  102  and is rotated by the pulley and motor shaft. The drive pulley, of course, could be replaced with some other type of drive wheel, such as a gear, driven through a gear connection to the motor shaft  100 . The belt  104  is also wrapped around a larger diameter axial pulley  106  that is disposed adjacent the brake assembly  64 . The axial pulley  106  is affixed to an output shaft  62  and rotates in conjunction therewith. The top end of the output shaft includes a splined end that is coupled to a portion of a drive hub so that an agitator or wash plate  50  also rotates in concert with the output shaft  62  and the axial pulley  106 .  
         [0035]    The brake assembly  64  is disposed adjacent the axial pulley  106  and concentric with the output shaft  62  and a spin tube  60  which is affixed to the wash basket  26 . The brake assembly  64  includes a brake drum  110  defining a depending annular wall  112  that is concentric with the shaft  62  and the spin tube  60 . The brake drum  110  is mounted fixed or stationary within the washing machine. In the present embodiment, the brake drum includes a central opening  114  that is fixed to a central stationary tube  116  that is also concentric with and houses the spin tube  60  and output shaft  62 .  
         [0036]    The brake assembly  64  preferably also includes a pair of brake shoes  120 ,  121  pivotally attached at a common pivot  122  to a stationary brake plate  124  (see also FIG. 4), although a single brake shoe could be utilized, or a number of brake shoes greater than two could also be utilized. The brake plate  124  and brake shoes  120 ,  121  in the present embodiment are arranged generally horizontally relative the vertical axis of the machine. The brake plate  124  and the brake shoes  120 ,  121  are carried by the wash basket  26  through a direct connection to the spin tube  60  which, in turn, is connected to rotate with the wash basket  26 . Hence, the brake plate  124  and brake shoes  120 ,  121  rotate with the wash basket.  
         [0037]    Each brake shoe  120 ,  121  includes an arcuate vertical wall  126  that faces the annular wall  112  of the drum  110  when assembled. Each arcuate wall  126  has an exterior surface  128  with a friction enhancing brake lining  130  attached and sandwiched between the wall  126  and the annular wall  112  of the drum. Respective mid sections  132  of the brake shoes  120  and  121  are each attached at the pivot  122  to the brake plate  124  and can move relative to the pivot and one another. Each shoe  120  and  121  has a first end  134  that are opposed and biased away from one another by a biasing element or mechanism such as a coil spring or compression spring  136 . At rest, the spring  136  biases the first ends  134  away from one another forcing the brake lining  130  of each brake shoe into contact with the annular wall  112  of the brake drum  110 . A second end  138  of each brake shoe includes a low-friction roller  140  attached to each shoe. The roller  140  rides against a cam surface as described below. In one embodiment, each roller  140  is a ball bearing roller or track roller pressed in to a portion of each shoe with a roll pin. Such ball bearing rollers provide very low friction contact surfaces that are highly durable providing a highly consistent or constant coefficient of friction over their useful life.  
         [0038]    Prior washing machine brake assemblies typically used a steel roller with a pin passing through the roller. Each pin was zinc coated to provided a low-friction surface contact between the pin and roller. The zinc coating would wear quickly producing a significant increase in coefficient of friction for the roller over the useful life of the roller. Such increase in the coefficient of friction creates a significant and undesirable change in brake performance.  
         [0039]    The present invention also includes a cam assembly generally includes a cam  152 , a cam driver  154 , and a slip sleeve  156 . The cam  152  is received over the spin tube  60  and is free to rotate relative to the spin tube through an angle of less than 180°. A bushing  158  is received between the cam  152  and spin tube  60  and includes a flange  160  that extends between the cam and the brake plate  124 . The cam  152  bears against the flange  160  and thus against the brake plate  124 .  
         [0040]    The cam  152  includes a pair of opposed cam surfaces  162  that have a particular gradual cam profile. The bearing rollers  140  on the second ends  138  of the brake shoes  120  and  121  bear against and ride along the cam surfaces  162  as described below. The cam  152  also includes a radial projection  164  that acts as a stop to limit travel of the bearing rollers  140  along the cam surfaces and to thus limit or control the amount of maximum brake pressure that is applied by the brake shoes against the drum  110  and to prevent further rotation of the cam  152  relative to the spin tube  60 .  
         [0041]    The cam driver  154  is shown in FIG. 5 and is an annular ring that is also received along the spin tube  60  and can also rotate freely relative to the spin tube. The cam driver  154  includes a recess  166  that has a shape corresponding to that of the cam  152 . The cam driver  154  bears against a lower surface of the cam  152  and the cam seats within the recess  166 . The cam driver  154  therefore moves the cam  152  in conjunction with movement of the cam driver. The cam driver  154  includes a lever  168  that extends radially outward from the driver. A pawl  170  is pivotally attached to the lever  168  by a pin  171  and can move relative to the lever through a predetermined angular range. A pair of stops  172  (FIG. 6) project upward from the pawl and bear against the lever  168  in order to limit the angular travel of the pawl.  
         [0042]    The axial pulley  106  is shown in sectional view in FIG. 8 and includes a recess  174  that faces the cam assembly  150 . The pawl  170  is substantially positioned within the recess  174  of the axial pulley. The recess  174  is defined by an annular outer wall  176  that faces the recess. The axial pulley  106  also includes a hub  178  that also faces the cam assembly  150 . The hub  178  has an upper face that includes a bearing  180  that rides against a bottom surface  182  of the cam driver  154 . The axial pulley  106  and vertical shaft  62  rotate as one, and the bearing  180  provides a low-friction contact surface between the hub  178  and the spin tube  60 .  
         [0043]    As shown in FIG. 8, the slip sleeve  156  is received around the hub  178  and is free to rotate around the hub. The slip sleeve  156  includes a lifter  184  extending radially outward from the sleeve. As illustrated in FIGS. 9 and 10, depending upon the rotation direction of the axial pulley  106  relative to the output shaft  62 , both the slip sleeve  156  and lifter  184  will come in contact with one end or the other of the pawl  170  causing the pawl to rock or pivot around the pin  171  in one direction or the other until one of the stops  172  contacts the lever  168  of the driver  154 .  
         [0044]    During the spin mode, the motor  40  drives the drive pulley  106  which moves counter-clockwise relative to the initially stationary basket  26  and connected spin tube  60 . Thus, the drive pulley  106  moves counter-clockwise relative to the cam driver  154  which is carried on the spin tube  60 . This situation is illustrated in FIG. 10.  
         [0045]    As shown in FIG. 10, when the axial pulley  106  rotates in a relative clockwise direction, as indicated by arrow  187 , as compared to the pawl  170  which is carried by the cam driver, the lifter  184  will engage near a second end  170   b  of the pawl  170 , causing the second end  170   b  to move outwardly and a first end  170   a  to move inwardly. This coupling mechanism causes a driving connection to occur between the motor  40  and the basket  26 , and hence the motor and basket are coupled and the basket is caused to rotate at a speed determined by the speed of the motor.  
         [0046]    When the drive pulley  106  rotates in a relative clockwise direction, as indicated by arrow  187  in FIG. 10, as compared to the pawl  170  which is caused by the cam driver, the lifter  184  will engage near the second end  170   b  of the pawl  170 , causing the second end  170   b  to move outwardly and the first end  170   a  to move inwardly. A key or catch  186  is carried on the annular wall  176  within the recess  174  of the drive pulley  106 . The catch  186  comprises a notch that corresponds in shape to the second end  170   b  of the pawl  170 . The catch  186  catches the pawl  170  as described below which rotationally locks up the axial pulley  106  with the cam assembly  150  also as described below.  
         [0047]    The torque of the motor  40 , acting through the pawl  170  on the cam driver  154  causes the cam driver, and hence the cam  152 , to rotate, causing the rollers  140  to ride on the cam towards a thicker profile, thus acting against the spring  136  and releasing the brake shoes  120 ,  121  from the annular wall  112  of the brake drum  110 . When this occurs, and the rollers reach the end of their travel, the entire brake assembly, except the stationary brake drum  110 , will begin to rotate, and hence the spin tube  60 , to which the brake plate  124  and wash basket  26  are secured, will rotate.  
         [0048]    When power to the motor  40  is terminated, the motor will begin to decelerate at a predetermined rate. This will cause the drive torque to no longer be applied through the drive pulley  106  and pawl  170  to the cam driver  154 , hence allowing the power of the spring  136  to cause the rollers  140  to begin to move toward a thinner portion of the cam profile, and allowing the brake shoes  120 ,  121  to engage the brake drum  110 .  
         [0049]    If the wash basket  26  is heavily loaded, it will slow down more slowly than the motor  40 , and the drive pulley  106 , connected to the motor  40 , will rotate counter-clockwise (as in FIG. 9) with respect to the spin tube which carries the cam driver  154  and pawl  170 . As this happens, the lifter  184  will engage the first end  170   a  of the pawl  170  and will release the second end  170   b  from the catch  186 . The motor  40  and wash basket  26  will then be uncoupled and will stop at their own rates.  
         [0050]    If the wash basket  26  is lightly loaded, it will slow down more quickly than the motor. This will cause the drive pulley  106  to rotate clockwise with respect to the cam driver  154  and pawl  170  (FIG. 10). As this happens, the lifter  184  will engage the second end  170   b  of the pawl  170  and cause it to engage the catch  186 , thereby coupling the motor and the wash basket. Since the brake, in this scenario, is causing the basket to slow more quickly than the motor, the motor will generate a reactive torque, which will be transmitted through the cam driver  154  to rotate the cam  152  and to release the brake, thereby reducing the brake torque and lengthening the time required to bring the wash basket to a complete stop.  
         [0051]    Thus, in a heavily loaded basket condition, the motor and basket will be automatically uncoupled and the brake will be able to apply full braking torque on the basket to slow it down. On the other hand, in a lightly loaded basket condition, the motor and basket will be automatically coupled and the reaction torque of the motor will operate through the rotation of the cam to reduce the braking torque, thereby preventing jerking and movement of a lightly loaded washer. In this manner, the braking system automatically adapts to the mass of the load in the basket and effectively adjusts the braking torque in response to the size or mass of the load.  
         [0052]    When viewed from above, as in FIG. 10, the drive pulley  106  rotates in a clockwise direction when the cam assembly locks up with the drive pulley and in a counter-clockwise direction, as in FIG. 10, when the drive pulley and vertical shaft  62  rotate independently of the spin tube, brake assembly and cam assembly components. When the drive system including the drive pulley  106  is rotated in a clockwise direction, the machine is operating in the spin cycle. The drive belt and pulley are rotated at a high RPM, such as for example, 500-800 RPM. The pawl  170  of the cam driver  154  is lifted by the lifter  184  of the slip sleeve  156 . The second end  170   b  of the pawl  170  is received in the catch  186  to lock up the drive pulley  106  and the cam assembly  150 . Torque provided by the motor is transmitted to the drive pulley  106 . Since the cam assembly  150  is locked up with the drive pulley, the cam rollers  140  ride up or along the cam surfaces  162  which thus compresses the biasing element or spring  136 . The brake shoe linings  130  are moved away from the brake drum  110  releasing the brake and permitting the wash basket to rotate freely at the high rate of speed. The amount of torque applied through the drive pulley determines how far up the cam surfaces that the cam rollers  140  move. The more torque applied by the motor, the further the cam  152  rotates and hence the further the cam rollers  140  move along the cam surfaces  162 . The cam surfaces  162  are of a very low profile and therefore it will take longer than in previous constructions for the roller bearings  140  to ramp down when the motor torque is removed.  
         [0053]    The compression force of the spring  136  and the profile geometry of the cam surfaces  162  determine the variability of the brake mechanism  64  of the present invention. A lightly loaded wash basket requires little motor torque applied in order to spin the basket at a high rate of speed. Much additional torque must be input by the motor to spin a heavily loaded basket. The low cam profile of the invention permits the cam to operate and release the brake at much lower motor input torques, and on the order of about 30% of the motor torque than was previously required to operate or release the brake mechanism.  
         [0054]    [0054]FIG. 11 illustrates a graph wherein cam torque is plotted against cam rotation in degrees. As can be seen, the brake mechanism releases the brake with only about 0.85 newton meters (Nm) of torque. When the brake cam operates at such low torque values, the brake cam can be actuated by the reaction torque of the motor armature when the motor decelerates from maximum spin speed to a stopped condition.  
         [0055]    [0055]FIG. 12 illustrates a graphic representation of motor representation of motor reaction torque input back into the brake cam through the motor armature against measured braking time. Motor reaction torque back into the brake cam dissipates over time. With prior art brake mechanism designs, motor reaction torque had little or no effect on brake pressure because a minimum of 2.5 newton meters of drive torque was required to release the brake. Thus, full brake pressure would be applied virtually from the instant the motor drive energy was stopped. In contrast, with the present invention, motor reaction torque is sufficient to act against the brake cam in order to partly relieve brake pressure. The graph shown in FIG. 12 illustrates the torque required to decelerate the motor armature as a function of the brake time. The longer the brake time, the lower the motor reaction torque. When a wash basket is fully loaded, the brake time will be long and in contrast, when the wash basket is lightly loaded the brake time will be short. For long brake times, the amount of motor reaction torque that is fed back into the brake cam is low enough that the motor reaction torque will not relieve or reduce braking pressure. Thus, full brake pressure is applied by the brake of the present invention. For a lightly loaded wash basket, the brake time is significantly shorter. When the brake time approaches 2.5 seconds or less, the motor reaction torque as can be seen in FIG. 12 becomes large enough to partly or completely balance against the brake spring force to at least partly disengage the brake and thus reduce braking pressure. This will extend the braking time. This phenomena produces an adaptable brake mechanism. When the wash basket is lightly loaded, the brake will therefore not fully apply and will prevent vibration, movement of the machine, and possible damage to the components.  
         [0056]    [0056]FIG. 13 is a graphic representation of various cam profiles wherein brake torque is plotted against brake time. The upper curve shows brake torque that is applied by the braking mechanism versus braking time wherein no cam effect was utilized. The lower curve illustrates a brake cam of the present invention having a very low cam profile. The intermediate curves show cams having higher cam profiles. As can be seen upon a review of FIG. 13, applied brake torque is significantly reduced for short braking periods which represent light wash basket loads. This is the primary desired effect of the invention. The upper curve represents a brake mechanism with no cam effect and illustrates that the brake torque is very high for short braking times. This system with no cam effect would produce undesirable results such as system vibration and movement of the washing machine.  
         [0057]    [0057]FIG. 14 is a graphic representation of overall braking sensitivity plotted against brake lining coefficient of friction. FIG. 14 includes two separate data groups, one representing a brake mechanism including the cam effect of the invention and a brake mechanism without the cam effect. Brake torque is actually plotted against brake lining coefficient of friction. As can be seen upon review of this figure, the effect of differences in brake lining coefficient of friction is reduced when a brake mechanism including the cam effect of the present invention is utilized. The upper graph illustrates a greater range of brake torque applied by the brake mechanism and represents a brake mechanism with no cam effect. A reduced differential brake torque is provided when a brake cam of the present invention is utilized for different brake linings.  
         [0058]    The present invention is for a brake mechanism that includes a cam that releases and applies the brakes of the mechanism depending upon rotation of the cam. The cam is in turn rotated by applied motor torque. When the motor torque is released, residual deceleration torque from the motor armature has an effect on the return rotation of the cam. Residual motor torque is applied at the early stages of motor deceleration greater than at the latter stages. Therefore, when a light load of laundry is carried within the wash basket of the washing machine, the braking time is relatively short. However, because the residual motor torque acts to at least partly reduce the amount of braking pressure, the braking time is increased and the brake pressure is reduced at the beginning of the brake cycle. For heavier loads of laundry, the motor deceleration torque has little no effect on brake pressure.  
         [0059]    The present invention has been described utilizing particular embodiments. As will be evident to those skilled in the art, changes and modifications may be made to the disclosed embodiments and yet fall within the scope of the present invention. The disclosed embodiments are provided only to illustrate aspects of the present invention and not in any way to limit the scope and coverage of the invention. The scope of the invention is therefore only to be limited by the appended claims.