Abstract:
25A brake assembly ( 10 ) which provides a controllably varying amount of self-energization by the dynamic adjustment of the position of a wedge member ( 22 ) which is based upon a measured amount of friction which exists between a pad assembly ( 14 ) and a rotor ( 12 ).

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a brake assembly and to a method for braking a vehicle or another selectively movable assembly and more particularly, to a brake assembly which provides a controllably varying amount of self-energization. 
   2. Background of the Invention 
   A self-energizing braking system, such as and without limitation that which is shown and described in European Patent Number EP 0953785A3 which is fully and completely incorporated herein by reference, word for word and paragraph for paragraph, generally includes an actuator (e.g., a motor) which selectively provides an actuation force in response to a sensed movement or depression of a braking member, and a self-energization member having at least one wedge portion having a certain fixed angle of inclination which assists in the braking of the selectively movable assembly (e.g., a vehicle) within which the braking system is operatively deployed. It should be realized, at the outset, that while the terms vehicle and selectively movable assembly may be interchangeably used throughout this description, nothing in this description is meant to limit the present invention to a particular type of selectively movable assembly, such as a vehicle. In fact, the present invention may be selectively used in a wide variety of selectively movable assemblies, including but not limited to vehicles. 
   Particularly, the actuation force is typically applied to a pad member and causes the pad member to then engage a portion of the self-energizing braking system (e.g., a rotor) which is attached to a moving wheel, thereby frictionally braking the selectively movable assembly. Particularly, the at least one wedge portion of the self-energization member assists in braking the vehicle (or other selectively movable assembly) by transferring the frictional force (created by the engagement of the pad to the rotor) from a force parallel to the rotor face into a force perpendicular to the rotor face, effectively magnifying the frictional force, thereby desirably reducing the overall actuation force needed to brake the selectively movable assembly in a desired manner. Importantly, the geometric or physical characteristics (e.g., the angle of inclination) of the at least one wedge portion of the self-energization member allows this increase in frictional force to occur without the use of additional actuation energy, thereby conserving energy by actually reducing the overall amount of actuation energy required from the motor and/or from the operator of the vehicle or the selectively movable assembly in order to brake the selectively movable assembly. 
   The self-energizing braking system can be designed to operate in two different modes. In one, the “compression” mode, the force generated by the motor and/or operator acts on the pad in the same direction as the frictional force. The frictional force pushes the pad into the wedge, increasing the normal force between the pad and the rotor and therefore increasing the friction. In the second, the “tension” mode, the frictional force alone is great enough to engage the brake fully (creating theoretically infinite braking force), and the motor and/or operator pushes in the opposite direction as the friction in an effort to reduce the wedging action and therefore reduce the amount of friction created. 
   While the foregoing conventional self-energizing braking system does desirably reduce the amount of actuating force needed to brake a selectively movable assembly, it has some drawbacks. 
   For example and without limitation, this approach does not allow for the use of a relatively low powered motor since the motor must be capable of operating under conditions in which the amount of friction between the rotor and the pad is relatively high and when the amount of friction between the rotor and the pad is relatively low. 
   For example, in a compression mode of operation, (i.e., in an operational mode in which the direction of rotor travel and the input force to the pad are in the same direction), should the friction be relatively low, the gain obtained from the self-energization is typically undesirably low and the motor must work relatively hard to achieve the desired braking of the vehicle. An undersized motor (e.g., a motor which does not provide enough actuation force to ensure desired operation in high and low friction conditions) may not generate the amount of deceleration required by the operator. 
   Moreover, should the friction be relatively high while the braking assembly is in a compression mode of operation, the electromechanical braking system may undesirably enter into a tension mode of operation (i.e., a mode in which the direction of rotor travel and the input force to the pad are in opposite directions) which may cause an inconsistent braking feel or may even cause an undesirably high amount of braking force to be generated. 
   During a tension mode of operation, which occurs when the frictional force is relatively high, an undersized motor may not be able to pull the pad with enough force to prevent it from being frictionally locked onto the rotor. Also, if the friction is too low, while the braking assembly is in a tension mode of operation, the electromechanical braking system may undesirably enter a compression mode of operation. 
   Hence, a current or conventional self-energization braking configuration provides the desired self-energization by the use of at least one wedge portion having a fixed angle of inclination and being mounted to the pad. As earlier delineated, the fixed inclination angle of the wedge allows the wedge to force the pad against the rotor in order to assist the motor in braking the moving assembly. In the current or conventional self-energization braking configuration, the angle of inclination of the wedge may not be too low since, if it were, a high level of friction could cause the electromechanical braking system to go from a compression mode of operation to a tension mode of operation. This transition from one mode of operation to another can create problems for the controller of the system and may be undesirable. If the wedge angle were too high, the effects of self-energization would be too small, leading to more inefficient use of the motor. 
   Moreover, as the pad wears during continued operation of the selectively movable assembly, the position of the wedge changes, thereby causing the amount of provided self-energization or “self-energization gain” to uncontrollably vary, causing the system to deviate from the optimum operating levels for energy efficiency. 
   The present invention addresses these and other drawbacks in a new and novel fashion and represents a braking assembly having a controllably varying amount of self-energization. 
   SUMMARY OF INVENTION 
   It is a first non-limiting advantage of the present invention to provide a self-energizing brake assembly which overcomes some or all of the previously delineated disadvantages of prior self-energizing brake assemblies. 
   It is a second non-limiting advantage of the present invention to provide a method for braking a selectively movable assembly which overcomes some or all of the previously delineated drawbacks of prior braking methodologies. 
   It is a third non-limiting advantage of the present invention to provide a brake assembly. Particularly, the provided brake assembly includes a selectively movable member which provides a varying amount of self-energization; and a controller assembly, which is coupled to the selectively movable member, which selects a certain amount of self-energization, and which moves the selectively movable member by a certain amount in order to cause the member to provide the certain selected amount of self-energization. 
   It is a fourth non-limiting advantage of the present invention to provide a brake assembly. Particularly, the brake assembly includes a rotor member; a pad member which may selectively engage the rotor member, thereby generating a certain amount of frictional braking force; a wedge member; and a controller which measures the certain amount of frictional force and, in response to the measurement, selectively moves the wedge member by a predetermined amount, thereby forcing the pad member against the rotor member and generating frictional braking force. 
   It is a fifth non-limiting advantage of the present invention to provide a method for braking a vehicle. Particularly, the method includes the steps of sensing a desired amount of braking; providing a certain actuation force; selecting a certain amount of self-energization; providing the certain amount of self-energization; using the provided actuation force and the certain amount of self-energization to brake the vehicle. 
   These and other features, and advantages of the present invention will become apparent from a consideration of the following detailed description of the preferred embodiment of the invention and by reference to the following drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a block diagram of a self-energizing brake assembly which is made in accordance with the teachings of the preferred embodiment of the invention; and 
       FIG. 2  is a block diagram of a self-energizing brake assembly which is made in accordance with the teachings of an alternate embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   Referring now to  FIG. 1 , there is shown a controllably varying self-energizing brake assembly  10  which is made in accordance with the teachings of the preferred embodiment of the invention. 
   Particularly, the brake assembly  10  includes a rotor  12  which moves with and which is coupled to a wheel (not shown) of the selectively movable assembly and at least one pad or pad assembly  14 . At the outset, it should be appreciated that the brake assembly  10  may employ several rotors  12  and/or pad assemblies  14  and/or wedges or a single rotor  20  and pad assembly  14  and wedge and that the present invention is not limited to a particular pad and/or rotor and/or wedge configuration. It should be further appreciated that the brake assembly  10  may be operatively deployed within a vehicle or other selectively movable assembly and that each selectively movable wheel of a vehicle may have and may be operatively coupled to a unique brake assembly  10 . 
   Further, the brake assembly  10  includes a caliper assembly or member  18  which is coupled to the body  19  of the moving assembly by a conventional fastener or fastener assembly  21 , a selectively movable wedge or self-energization member  20  which is received in a pocket  15  of the caliper assembly  18 . Particularly, the pocket  15  generally conforms to the generally round shape of the back portion  13  of the wedge member  20  and, in one embodiment, back portion  13  abuttingly engages the surface  11  of the pocket  15 . The brake assembly  10  further includes, a pin or pin assembly  22  which is coupled to the pad assembly  14  and which is coupled to the front position  9  of the wedge member  20 . In this manner, the wedge portion  20  may rotate about the pin or pin assembly  22 . However, since the back portion  13  is received within the pocket  15  and abuttingly engages the surface  11 , the wedge  20  is usually stationary with respect to the caliper body  18  unless purposefully and controllably moved by an external force. 
   The brake assembly  10  further includes, a first actuating force generator or motor  24 , a controller or controller assembly  26  which is operable under stored program control and which is physically and controllably coupled to the motor  24  by bus  25 , and an accelerometer  28  which is physically and communicatively coupled to the controller assembly  26  by the use of the bus  30 . The controller assembly  26  is further coupled to a source of electrical energy  27  by the use of bus  31 . In one non-limiting embodiment of the invention, the brake assembly  10  may also include a gear assembly  56 . 
   As is further shown, the motor  24  has a selectively movable output shaft  40  which, in one non-limiting embodiment, is coupled to the gear assembly  56  which, upon receipt of torque from the shaft  40 , causes the pad assembly  14  to engage the rotor assembly  12  in a direction which is dependent upon the direction that the output shaft  40  is rotating. It should be understood that the gear assembly  56  shown in  FIG. 1  may comprise an intermediate gear (not shown) and a screw actuator (not shown) which may selectively and cooperatively cause the pad assembly  14  to engage the rotor assembly  12  in a direction which is dependent upon the direction that the output shaft  40  is rotating. It should further be understood that the gear assembly shown in  FIG. 1  is for illustrative purposes only and that nothing in this description is meant to limit the actuation means of brake pad  14  to such a gear assembly. Rather, output shaft  40  may, in one non-limiting embodiment, selectively actuate the brake pad  14  without the usage of gear assembly  56  by the use of any desired and conventional actuation means. For example and without limitation, the gear assembly  56  may be substantially similar to the gear assembly which is described within European patent Number EP 0953785A3 which is fully and completely incorporated herein by reference, word for word and paragraph for paragraph. For example, in this non-limiting embodiment, the gear assembly  56  may include a pinion (not shown) which is coupled to the output shaft  40  and which is in engagement with toothing (not shown) which is formed on the radially inner circumference of the pad assembly  14  (i.e., toothing formed on a backing plate (not shown) which is coupled to the pad assembly  14 ). The pinion and toothing cooperatively and selectively causes the pad assembly  14  to engage the rotor assembly  12  in a direction which is dependent upon the direction that the output shaft  40  is rotating. 
   Further, as shown, the controller assembly  28  is physically and communicatively coupled to a selectively depressible brake member  52  by the use of bus  50  and to a transmission shift assembly  55  by the use of bus  59 . The assembly  10  also includes a second motor  60  which has an output shaft  62  which selectively engages the wedge member  20 . The second motor  60  is physically and controllably coupled to the controller assembly  26  by the use of the bus  64 . It should be appreciated that each selectively movable wheel (not shown) of the selectively movable assembly may have a brake assembly which is substantially identical to brake assembly  10 . 
   In operation, the controller  26  senses the depression of the brake member  52 , by the use of the bus  50 , and the currently desired direction of the moving assembly that the braking assembly  10  is operatively deployed within, by the use of bus  59 . The controller assembly  26  causes the pad  14  to be moved in a direction which is dependent upon this sensed direction. That is, if the moving assembly is moving in the “forward” direction or is in drive state or mode of operation, the controller  26  sources electrical power, from the energy source  27 , to the motor  24 , by the use of buses  31  and  25  and this sourced energy causes the output shaft  40  to rotate by a certain amount and by a certain speed in a clockwise manner, effective to provide a certain actuating force which is effective to cause the pad assembly  14  to engage both the rotor  12  and the “forward” wedge by a certain amount, thereby braking and decelerating the moving assembly. Should the sensed direction be in a “reverse” direction, the output shaft  40  is made to rotate in a counterclockwise direction, thereby causing the pad assembly  14  to engage the rotor  12  and the “reverse” wedge by a certain amount. It should be appreciated that the aforementioned description of operation describes a “dual” wedge braking system and that nothing in this description is meant to limit the braking assembly  10  to the “dual” wedge design or architecture. Rather, braking assembly  10  may, in one non-limiting embodiment of the invention, comprise a “single” wedge design or architecture. That is, in this non-limiting “single wedge” embodiment, motor  24  will selectively move the brake pad assembly  14  in an upward direction to apply a braking force and motor  24  will move the brake pad assembly  14  in a downward direction to reduce braking force. It should also be appreciated that, in this non-limiting embodiment, the motor will operate in a single direction (i.e., always clockwise or always counter-clockwise) to apply braking, regardless of the direction of rotor  12 . However, while this architecture does provide braking, it will provide much less self-energization in one direction (i.e., a backward direction) than in the other (i.e., forward direction). This lower amount of self-energization in the backward direction is due to the friction force acting against the motor force. It should be further appreciated that the direction of rotation of the motor shaft  40  is dependent upon the phase of the electrical power signal which is communicated to the first motor  24  from the energy source  27  and through busses  31 ,  25  and the controller assembly  26 . That is, a first phase arrangement produces shaft movement in a clockwise direction while a second phase arrangement produces shaft movement in a counter clockwise direction. In one non-limiting embodiment of the invention, controller assembly  26  adjusts the signal phase as needed. Further, the amount of actuation force is dependant upon the torque transmitted-through the output shaft  40  and the output torque is dependent upon the electrical power signal being communicated to motor  24 , such a signal being controlled by the controller assembly  26 . It should be understood that the present invention is not limited to a particular type of motor  24 . Rather, substantially any desired type of motor which provides a controllable amount of torque may be utilized in brake assembly  10 . 
   Particularly, the amount of required braking or actuation force is determined by the position of the brake member  52  and the amount of gain provided by the member  20 . That is, the position of the brake member  52  is associated with the total required amount of desired braking. In one embodiment, a lookup table may be created and stored within the controller assembly  26  which associates various positions of the member  52  with a unique amount of requested braking force. A positional value, which is not stored within the look up table, may have a braking value associated with it and, such a braking value is, in one embodiment, equal to the braking value associated with the stored braking position value which is closest to the currently measured positional value. Alternatively, the value may be calculated by a conventional interpolation method. The gain is dynamically controllable in a manner to be discussed and each position of the wedge  20  provides a calibratable amount of gain. Hence, the controller assembly  26 , upon the ascertainment of the position of the wedge member  20  and the ascertainment of the position of the braking member  52 , may modulate or vary the amplitude and phase of the power being supplied to the output shaft  40 . It should be appreciated that in the preferred embodiment of the invention, the system can operate in either a compression or a tension mode and is operable in either a forward or a reverse direction. In one non-limiting embodiment, the controller assembly  26  continually determines or ascertain the position of the wedge member  20 . For example, the position of the wedge member  20  is continually monitored by controller  26 , either by use of a sensor (not shown) or by calculating the position of the member  20  by the use of a known initial position and the amount of force applied (and the time with which that force has been applied) to the member  20 . 
   In operation, the accelerometer  28  continually measures (e.g., at periodic intervals of time) the amount of vehicular deceleration and provides this information to the controller assembly  26 , by the use of bus  30 . The controller assembly  26  uses the amount of received deceleration to dynamically calculate an optimal wedge angle of inclination  69  (provided by the front portion  9 ) (i.e., the angle between the wedge and the rotor face), effective to ensure that a relatively high amount of self-energization is always provided by the brake assembly  10 . That is, the wedge angle  69  is controllably varied with each measured change of vehicular deceleration, thereby always ensuring that a relatively large self-energization gain is present, thereby reducing the power required by the first or actuating motor  24 . 
   Particularly, the wedge  20  is moved by the selective energization of the second motor  60 , thereby allowing the output shaft  62  to rotate by a certain amount in a certain desired direction, thereby allowing the wedge member  20  to move in a certain direction and dynamically adjusting the amount of provided self-energization. The energization of the shaft  62  (motor  60 ) occurs when the controller  26  sources power from the power source  27  to the motor  60  through busses  31 ,  64 . Particularly, the wedge angle  69  or α may be calculated by the following equation: 
               Tan   ⁢           ⁢     (   α   )       =           (     input   ⁢           ⁢   force     )     ⁢     μ   .         (     output   ⁢           ⁢   force     )       +   μ             (     Equation   ⁢           ⁢   1     )             
 
   where: μ=coefficient of friction between the pad assembly  14  and the rotor  12 output force=frictional force acting on the rotor  12 input force=force provided by motor  24  acting on the pad assembly  14 . 
   The output force for a vehicle may be calculated as follows: output force (front)=0.5*F×b×R/ rf  (Equation 2)output force (rear)=0.5*F×(1−b)×R/ rf  (Equation 3) where F is the decelerative force; R is the radius of the tire (not shown) which is coupled to the wheel to which the brake assembly  10  is attached; “rf” is the effective radius of the caliper  18 ; and b is the desired percentage of total braking force generated by the front tires. Hence, it should be realized that the foregoing brake assembly has a dynamically or controllably varying amount of self-energization (e.g., the wedge angle  69  may be dynamically varied), thereby allowing a consistently high level of self-energization to be maintained for all operating conditions. The consistently high level of self-energization allows the controller  26  to optimize the power consumption of the brake system. This arrangement also allows for the use of a relatively small, lightweight, low cost, and low powered motor  24 . 
   In a second non-limiting embodiment of the invention, a braking assembly  100  may be provided in which the pad assembly  14  is coupled to a biasing spring  102  which is mounted to the body  19  of the selectively movable assembly by a fastener assembly  104 . In this embodiment, as represented by brake assembly  100  of  FIG. 2 , the brake assembly  100  is braked only by a change in the angle of the wedge member  20  due to a selective energization of the motor  60 , thereby obviating the need for motor  24 . 
   It is to be understood that the invention is not limited to the exact construction and methodology which is set forth above, but that various changes and modifications may be made without departing from the spirit and the scope of the inventions as is further delineated in the following claims.