Patent Abstract:
A vehicle brake monitor assembly for an air disk brake includes a brake actuator having a pushrod projecting from inside a chamber of said brake actuator. The pushrod releasably actuates a lever arm of a caliper thereby moving the disk brake into a braking position when the pushrod is in an extended position and releasing the disk brake from the braking position when the pushrod is in a retracted position. The pushrod includes a pushrod shaft and a contact member biased in a telescoping relationship relative to the pushrod shaft and the lever arm of the caliper abuts the contact member counteracting the bias of the contact member. A sensor is integrated with the assembly proximate the contact member and detects movement of the pushrod relative to the lever arm and to the pushrod shaft.

Full Description:
[0001]    This application claims priority to U.S. Provisional Patent Application No. 61/356,325 file on Jun. 18, 2010. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]    The present invention is related to an electronic stroke monitor for a vehicle brake. More specifically, the present invention is related to an electronic stroke monitor of an air disc brake for use on a heavy duty truck. 
         [0003]    The number of miles traveled by heavy-duty trucks and passenger busses increases significantly every year. Because the size of passenger cars being driven has become smaller due to the increased price of gasoline, it has become increasingly necessary to ensure the proper performance of brake actuators and brake systems of these heavy-duty vehicles to provide the truck operator every opportunity to avoid a loss of control. Therefore, various systems have been developed to monitor the stroke of a brake actuator for use on drum brakes widely used in industrial trucking. 
         [0004]    However, on heavy-duty passenger vehicles, such as, for example, busses, the use of air disc brakes is becoming more popular. To date, a viable brake monitoring system for use on an air disk brake has not been developed. 
         [0005]    Brake monitoring systems used on air drum brakes are directed toward monitoring the length of stroke of a pushrod projecting from inside a chamber of the brake actuator. The monitoring enables the user to determine if the brake actuator is functioning properly, is subject to an over-stroke condition, or is subject to a hanging or dragging brake condition. Monitoring these conditions by monitoring the stroke of the pushrod is possible because the pushrod of the brake actuator is fixedly attached to the actuation device of the drum brake. In the case of a hanging or dragging brake, the actuation device of the drum brake is immobilized in an actuated position preventing the pushrod from returning to an un-actuated position when the brake pedal is released by the vehicle operator. 
         [0006]    However, the pushrod of an air disk brake actuator is not fixedly attached to the lever arm of a caliper that actuates the disk brake. Therefore, should a hanging or dragging brake condition occur, the lever arm becomes separated from the pushrod rendering the type of monitoring system used on a drum brake non-functional for a disk brake. An electronic sensor that monitors the stroke of the pushrod senses that the pushrod has returned to its un-actuated position and incorrectly senses that the brake is operating normally. Therefore, it has become necessary to develop a vehicle brake monitoring assembly that is capable of identifying and distinguishing between an over-stroke condition and a hanging brake condition of an air disk brake. 
       SUMMARY OF THE INVENTION  
       [0007]    A vehicle brake monitor assembly for an air disk brake includes a brake actuator having a pushrod projecting from inside a chamber of the brake actuator. The pushrod releasably actuates a lever arm of the caliper moving the disk brake into braking position when the pushrod is disposed in an extended position and releases the disk brake from the braking position when the pushrod is disposed in a retracted position. The pushrod includes a pushrod shaft and a contact member biased in a telescoping relationship relative to the pushrod shaft. The lever arm of the caliper abuts the contact member and counteracts the bias of the contact member preventing the contact member from telescoping from the pushrod shaft. A sensor is integrated with the assembly proximate the contact member. The sensor detects movement of the pushrod relative to the lever arm and the pushrod shaft. 
         [0008]    The sensor that is positioned proximate the contact member detects differences in transmission along a length of the contact member that enables the determination of the condition of the brake actuator. For example, the sensor detects when the brake is operating in a normal condition, is subject to a dragging brake condition, is subject to an over stroke condition, or subject to an out of adjustment condition. As set forth above, prior attempts to monitor all these conditions on an air disk brake have proven futile. In particular, prior monitoring devices have been unable to identify a hanging brake condition due to separation between the pushrod and a lever arm of the air disk brake. This separation results when the lever arm is immobilized in an actuated position and a vehicle operator releases a brake pedal causing the pushrod to retract into the brake actuator. The telescoping design of the present invention allows the sensor to detect when the lever arm is immobilized in an actuated position. 
         [0009]    A further benefit of the present inventive assembly is its use with a conventional brake caliper without modification to the caliper. Prior attempts to monitor air disk brake systems require modifying the brake caliper in an attempt to determine if the lever arm is immobilized in an actuated position. By providing a sensor pack proximate the pushrod of the actuator, the inventive assembly has eliminated the need to modify the caliper of an air disk brake system, to detect a dragging brake condition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]    Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0011]      FIG. 1  shows a side sectional view of the brake monitoring assembly of the present invention; 
           [0012]      FIG. 2   a  shows a first embodiment of the pushrod of the present invention; 
           [0013]      FIG. 2   b  shows an alternative embodiment of the pushrod of the present invention; 
           [0014]      FIG. 3  shows an expanded view of the pushrod of the present invention; 
           [0015]      FIG. 4  shows the brake actuator in an extended position in a normal operating condition; 
           [0016]      FIG. 5  shows a partial sectional view of the brake actuator in an over stroke condition; and 
           [0017]      FIG. 6  shows the brake actuator of the present invention having a hanging or dragging brake condition. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    A brake actuator is shown generally at  10  in  FIG. 1 . The brake actuator  10  includes a brake monitor assembly  12  for determining if the brake actuator is functioning in a normal condition or a fault condition as will be explained further hereinbelow. The brake actuator  10  includes a pushrod  14  disposed inside a service chamber  16 . It should be understood by those skilled in the art that the service chamber  16  can also be used in cooperation with a secondary chamber or power spring chamber (not shown), and various other brake activator configurations, as might be necessary for a given vehicle braking system. 
         [0019]    The service chamber  16  includes a diaphragm  18  that is secured between an upper housing member  20  and a lower housing member  22 . Therefore, the service chamber  16  is separated by the diaphragm  18  into a pressure side  24  (best seen in  FIG. 4 ) and a return side  26  which houses a return spring  28 . Pressurized air enters the pressure side  24  of the service chamber  16  through air pressure port  30 , the pressure of which is monitored by pressure sensor  32 . Although the pressure sensor  32  is shown proximate the service chamber  16 , it is contemplated by the inventors that the pressure sensor  32  is located at the treadle valve (brake pedal) of the vehicle. It should be understood to those of ordinary skill in the art that each embodiment also includes a separate pressure sensor (not shown) located at the brake pedal to identify pressure being applied by the vehicle operator to the brake pedal. When the operator actuates the brake pedal, pressurized air passes through the air pressure port  30  forcing the diaphragm  18  against the pushrod  14  causing the pushrod  14  to extend outwardly from the service chamber  16  in a known manner. 
         [0020]    When the vehicle operator depresses the brake pedal, as set forth above, air pressure enters the pressure side  24  of the service chamber  16  through the air pressure port  30  forcing the pushrod  14  outwardly from the service chamber. A lever arm  34  disposed inside a caliper  36  is pivoted by the pushrod  14 , when extending outwardly, causing the brakes (not shown) of the vehicle to actuate in a known manner. When the vehicle operator removes pressure from the brake pad, air is vented from the pressure side  24  of the service chamber  16  and the return spring  28  forces the pushrod  14  inwardly of the service chamber  16  allowing the lever arm  34  to return to its unactuated position. It should be understood by those of skill in the art, that the caliper  36  described above functions in a normal manner. 
         [0021]    Referring now to  FIG. 2A , the pushrod  14  includes a contact member  38  that circumscribes a pushrod shaft  40 . The contact member  38  defines a terminal end  41  that abuts the lever arm  34  of the caliper  36 . The pushrod shaft  40  is received in a tubular opening  42  defined by the contact member  38 . An adjustment shim  44  is disposed at a base  46  of the tubular opening  42  and is sandwiched between a shaft stop  48  of the pushrod shaft  40  and the base  46 . The adjustment shim  44  is provided in a plurality of thicknesses from which the length of the pushrod  14  is adjusted to provide dimensional accuracy between terminal end  41  of contact member  38  and lever arm  34  as will become more evident below. 
         [0022]    The pushrod shaft  40  defines an elongated opening  50 , which receives a biasing member  52  shown here in the form of a spring. The biasing member  52  is compressed between a floor  53  and a terminal wall  54  of the elongated opening  50 . Therefore, the biasing member  52  provides a biasing force that telescopes the contact member  38  from the pushrod shaft  40 , affectively lengthening the pushrod  14 . 
         [0023]    The pushrod shaft  40  defines a circumscribing groove  56  into which a retaining member  58  that is fixedly attached to an inner wall  60  of the tubular member  42  is received. The retaining member  58  slides in an axial direction defined by the pushrod shaft  40  within an expanse of the groove  56 . A stop  62  prevents the biasing member  52  from separating the contact member  38  from the pushrod shaft  40  when abutted by the retaining member  58 . The stop  62  takes the form of a spring clip or equivalent received by a notch  63  ( FIG. 3 ) in the pushrod shaft  40 . 
         [0024]    A sensor element  64  is sandwiched between the service chamber  16  and the caliper  36 . A sensor  66  is disposed inside the sensor element  64  and is provided sensing access to the contact member  38 , which is received through an opening  68  in the sensor element  64 . The sensor  66  communicates through communication line  70  with a controller or central processing unit  72 . The sensor  66  is contemplated by the inventors to take the form an optical sensor, a magnetic sensor, a mechanical sensor, or a radio frequency enhanced sensor. For clarity, however, the following description will describe an optical sensor, further contemplated to be an infrared sensor. The exemplary embodiment makes use of an Optek infrared optical OPB733TR sensor capable of both transmitting an infrared signal and receiving a reflected infrared input. However, it should be understood by those of skill in the art, that any of the sensors explained above are operable. As best represented in  FIG. 2   a , the contact member  38  defines a non-reflective surface  74 , a semi-reflective surface  76 , and a fully reflective surface  78 . 
         [0025]    As best seen in  FIG. 1 , a sealing boot  80  seals to the pushrod shaft  40  at an upper end and to the sensor element  64  at an opposite end. Therefore, the contact member  38 , and the non-reflective, semi-reflective, and fully reflective surfaces  74 ,  76 ,  78  are protected from environmental contamination that is known to enter the service chamber  16 . A secondary seal  82  seals the sensor element  64  to the caliper  36 , which is fully enclosed to protect the lever arm  34  from environmental contamination. Therefore, the contact member  38  and the sensor  66  are completely protected from the environment, preventing the optical sensor  66  and the reflective surfaces  74 ,  76 ,  78  from becoming fouled. 
         [0026]    An alternative embodiment is shown in  FIG. 2   b  where common elements have the same numbers as those elements disclosed in  FIG. 2   a . The alternative embodiment makes use of an alternative contact member  84  and a linear sensor  86 . The alternative contact member  84  includes an alternative reflective coating  88  that has a variable reflective surface. A first end  90  of the contact member is more reflective than a second end  92  of the contact member with a gradual transition in between. The sensor detects the variation in the amount of reflectivity to determine the location of the alternative contact member  84 , and therefore the lever arm  34  as will become more evident in the description below. 
         [0027]    The sequence of brake monitoring will now be described. It is contemplated by the inventors that the sensor  66  takes the form of an infrared sensor that transmits an infrared signal toward the contact member  38  which has varying degrees of reflectivity as described above to reflect the infrared signal back toward the sensor  66 , which in turn signals the controller  72  the degree of reflectivity via communication lines  70 . It should be understood to those of skill in the art that other optical sensors may be used, including photoelectric digital lasers, ordinary lasers, and equivalents. 
         [0028]    During normal operation, when the brake is released (shown in  FIG. 1 ), the optical sensor transmits a light signal toward the non-reflective surface  74  of the contact member  38  receiving no reflective signal from the contact member  38 . The brake application pressure, as indicated by the pressure sensor  32 , is less than or equal to about 2 psi. Therefore, no active fault is signaled to the vehicle operator. 
         [0029]    Referring now to  FIG. 4 , pressure is applied to the brake pedal by the operator causing air to fill the pressure side  24  of the service chamber  16  to actuate the lever arm  34 . Because the pushrod  14  is forced outwardly from the service chamber  16  by the diaphragm  18 , the sensor  66  is positioned proximate the semi-reflective surface  76  of the contact member  38 . The pressure sensor  32  signals air pressure of greater than or equal to about 2 psi indicating normal operation of the brake actuator  10  so long as the sensor  66  detects reflectivity from the semi-reflective surface  76 . It is contemplated by the inventors that the semi-reflective surface  76  reflects about thirty percent of the light transmitted from the sensor  66 . It should be noted that the biasing member  52  remains fully compressed because the lever arm  34  counteracts the biasing force of the biasing member  52  during normal, activated condition. 
         [0030]      FIG. 5  shows an overstroke condition causing the controller  72  to signal the operator that a fault condition exists. In the overstroke condition, the pushrod  14  extends outwardly of the service chamber  16  beyond normal extension length so that the sensor  66  transmits light to the fully reflective surface  78  and detects a full reflectivity. The brake pressure, as detected by the pressure sensor  32 , is greater than or equal to about 2 psi. Therefore, the sensor  66  signals the controller  72  full reflectivity with normal application pressure causing the controller to signal an over stroke condition to the operator. 
         [0031]      FIG. 6  represents a dragging brake condition. The dragging brake condition is identified by the controller  72  both when the vehicle is moving at road speed and when the vehicle is not moving at road speed. In the dragging brake condition, air pressure has been released from the pressure side  24  of the service chamber  16  causing the return spring  28  to retract the pushrod  14  into the service chamber  16 . However, because the brake is now subject to a dragging condition, the lever arm  34  is retained in the actuated position causing separation with the contact member  38 . Because the lever arm  34  is no longer counteracting the biasing force of the biasing member, the biasing member  52  causes the contact member  38  to telescope from the pushrod shaft  40 . Therefore, the sensor  66  now transmits light toward the semi-reflective surface  76  of the contact member  38  as opposed to transmitting light toward the non-reflective surface  74  as is typical of a normally functioning brake. Because the pressurized air has been vented from the pressure side  24  of the service chamber  16 , the brake application pressure now reads less than or equal to about 2 psi. The combination of the semi-reflective surface  76  being detected by the sensor  66  and the low air pressure of less than or equal to about 2 psi causes the controller  72  to indicate a dragging or hanging brake condition. 
         [0032]    A further fault condition is indicated when the sensor  66  detects the non-reflective surface  74  when the brake pedal is depressed by the operator causing an air pressure reading of greater than or equal to about 12 psi. In this instance, the controller signals a non-functioning actuator condition to the operator. 
         [0033]    The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. 
         [0034]    Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, a hall effect or equivalent sensor can be used in combination with a magnet affixed to the contact member  38  having varying degrees of magnetism. It is therefore to be understood that within the specification, the reference numerals are merely for convenience, and are not to be in any way limiting, the invention may be practiced otherwise than is specifically described.

Technology Classification (CPC): 1