Abstract:
A parking brake for a rail car vehicle including an electric motor driving a hydraulic pump fluidly connected to and controlling a bidirectional hydraulic actuator coupleable to the rail car&#39;s wheel brakes. An electric controller is connected to the pump and controls activation/deactivation of the pump with the controller including various switches. Also included is a coupler for coupling the actuator to one of a brake beam or an actuator of the parking brake.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates generally to manually controlled parking brakes for rail vehicles and more specifically to a manual parking brake for locomotives and car mounted cylinders for rail cars. 
     Current locomotive parking brake systems require high manual input force to apply an unknown brake shoe force through a complex system of levers, chains and brackets. The high manual force could result in injuries to the operator as well as applying an unknown parking brake force on the wheel. 
     Typically, the hand brake or parking brake consists of a device for manually applying a brake shoe to the wheel of a railroad car by turning a hand wheel or pumping a handle connected by gears and/or linkages to the brake shoe. This linkage is the same linkage which is used to apply or release the brakes throughout the train. Typical examples are shown in U.S. Pat. Nos. 4,746,171 and 5,701,974. The manual apply and release forces are required because the car or locomotive does not include a source of air pressure, which is normally used to control the brakes, in the park or isolated position. An example of the hydraulic brakes with a reservoir pump and pump actuated means is shown specifically in U.S. Pat. No. 5,701,975. 
     Although the brake systems of various types have been applied to rail cars, there is a need for a locomotive manual parking brake which is capable of applying a substantially greater known braking force. If such a brake is available, the brake on less than all of the wheels of the locomotive can be applied in park to maintain the locomotive in a brake condition. 
     The parking brake of the present invention includes an electric motor controlling a hydraulic pump fluidly connected to and controlling a bidirectional hydraulic actuator for the wheel brakes. An electrical controller is connected to the pump and controls activation/deactivation and direction of activation of the pump. The controller may include a bidirectional electric motor coupled to a bidirectional pump and a selection switch which selectively connects the electrical motor to an electrical source in opposite polarities. The selection switch also selectively disconnects the electric motor from the electrical source. Alternatively, a unidirectional electric motor and unidirectional pump are connected to the actuator by a selection valve to the actuator. 
     The controller can also include a pressure switch response to fluid pressure between the pump and the hydraulic motor and the controller deactivates the pump for excessive pressure. A pressure relief valve for the fluid pressure between the pump and the hydraulic motor may also be provided. Preferably, the pump is connected to the hydraulic motor by a pair of passages and the controller includes a pair of pressure switches and relief valves, each responsive to pressure in a respective passage. 
     The controller may also include a limit switch responsive to the position of the actuator and the controller deactivates the motor and the pump when the actuator element reaches a predetermined position. The brake system includes a hydraulic reservoir. The controller includes a level switch responsive to the level of fluid in the reservoir and the controller deactivates the motor and the pump for a low level of hydraulic fluid in the reservoir. 
     The controller may activate the pump in one direction of activation if both the pressure and the limit switches are closed. The pump is also activated in the other direction of activation if the pressure switch is closed, even if the limit switch is open. The actuator element may include a coupler for coupling to either the brake bream of the wheel brakes or the actuator or brake cylinder system of the wheel brakes. 
     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a schematic of a hydraulic parking according to the principles of the present invention. 
     FIG. 1B is a connection of the actuator of FIG. 1A to a brake beam of a truck mounted brake. 
     FIG. 1C shows the connection of the actuator of FIG. 1A to the brake cylinder of a brake system. 
     FIG. 2 is a schematic of a modification of the hydraulic parking brake of FIG.  1 . 
     FIG. 3 is a hydraulic schematic of another embodiment of a hydraulic parking brake according to the principles of the present application. 
     FIG. 4 is an electrical schematic for the embodiment of FIG.  3 . 
     FIG. 5 is an electrical schematic of a modification of the embodiment of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A hydraulic parking brake  10  is illustrated in FIG.  1 A. The brake system include a DC electric motor  12  connected by shaft  14  to a hydraulic pump  16 . The electric motor  12  and hydraulic pump  16  may be in a common housing or integrated pack. The hydraulic pump  16  is connected by lines or passages  18  and  20  to the hydraulic actuator  22 . The electric motor  12 , hydraulic pump  16  and the hydraulic actuator  22  are all bidirectional in FIGS. 1A and 2. A unidirectional electric motor  12  (not shown), selection valve  100  and hydraulic pump  16  are shown in FIG.  3 . The hydraulic motor  22  includes a screw  24  with a clevis  26  at the end thereof. A chain  28  is connected to the clevis  26  by pin  30 , as shown in FIG.  1 A. 
     The chain  28  controls, for example, a brake beam  32  which actuates brake shoe  34  as illustrated in FIG. 1B. A typical example is found in U.S. Pat. No. 4,495,921. Alternatively, the chain  28  may be connected to a brake cylinder  36  which controls brake shoe  34  as illustrated in FIG.  1 C. The chain  28  may either be connected to the cylinder  36  directly or to the linkage which drives the brake shoe  34  that is common to the brake cylinder  36 . The actuation device for the brake beam  32  of FIG. 1B is not shown and is well known. 
     A control system to determine the activation/deactivation as well as the direction of operation of the hydraulic motor  22 , pump  16  and actuator  22  includes a selection switch  40 . Switch  40  includes a toggle  42  shown in its open position. Toggle  42  can be connected to contacts  44  or contacts  46  which determine the connection of the polarity of battery  48  to the electric motor  12 . When the toggle  42  engages to contacts  44 , lead  50  of DC motor  12  is connected to the negative terminal of battery  48  and lead  52 , through the to be described circuit, connects lead  70  of the DC motor to the positive terminal of the battery  48 . When toggle  42  engages contacts  46 , lead  50  of the motor is connected to the positive terminal of battery  48  and lead  70  via at least line  52  is connected to the negative terminal of the battery  48 . 
     Lead  52  of switch  40  is connected to lead  70  of the motor through various switches. Lead  52  is connected in series with a normally closed pressure switch  54  which is responsive to the pressure in passage  20  between the hydraulic pump  16  and the hydraulic actuator  22  and, via line  56 , is in series with normally closed pressure switch  58  which is responsive to the pressure in passage  18  between the hydraulic pump  16  and the hydraulic actuator  22 . The pressure switch  58  is connected via line  60  with level switch  62  which is connected via line  64  and  66  to terminal  70  of the electric motor  12  via diode  68 . The level switch  62  may be a float switch sensing the level of hydraulic fluid in reservoir  84 . 
     A normally closed limit switch  74  is connected in series with pressure sensitive switches  54 ,  58  and level switch  62  via line  72 . Line  76  connects the normally closed limit switch  74  to terminal  70  of the electrical motor  12 . The limit switch  74  is responsive to the position of the actuator element or screw  24 . The purpose of limit switch  74  is to deactivate the hydraulic actuator  22  to prevent runout of the screw  24  from hydraulic actuator  22 . 
     Relief valves  78  interconnect the passages  18  or  20  via return line  82 , a check valve  86  and filter  88 . When the pressure in passage  18  or  20  exceeds the value of the relief valve  78 , the passages  18 ,  20  are connected to the low pressure side. If the pressure in return line  82  becomes greater than the pressure for that passage  18  or  20 , the respective check valve  86  will open which will provide a flow back to the low pressure passage  18  or  20 . This maintains a minimum amount of pressure in passage  18  or  20  even after the relief valve  78  has opened. The check valves  86  prevent the high pressure fluid from blowing into the low pressure side. This allows the pump  16  to have a connection to the inlet low pressure fluid in either direction of rotation of the pump. 
     If this pressure is sufficiently high, it opens the respective pressure switch  54  and  58  and deactivates the electric motor  12  and the pump  16 . 
     The operation of the hydraulic parking brake system  10  may begin with moving the toggle  42  of switch  40  to contacts  44 . This places the negative terminal on lead  50  and the positive terminal on lead  52  of the switch  40 . Since the motor  12  and consequently the pump  16  have been deactivated, there is minimum pressure in passages  18  and  20  and the relief valves  78  are closed and the pressure switches  54  and  58  are closed. Assuming appropriate levels of fluid in reservoir  84 , the float switch  62  is closed. If the actuator element  24  is in the position shown, the limit switch  74  is closed. 
     This polarity on motor  12  will drive the hydraulic pump  16  to operate the hydraulic actuator  22  to retract the actuator element  24 . This operation of the chain  28  would apply the brakes. Once the force on the actuator  24  resulting from the brake shoes engaging the wheel and exerting a given amount of brake force, the pressure in passage  18 , for example, will rise causing pressure switch  58  to open. This disconnects the series connection between contact  44 , line  52  and terminal  70  of the motor. 
     The interruption of the current to the electric motor  12  deactivates the pump  16  and the hydraulic actuator  22 . The actuating element  24  or screw is locked in its retracted position. Thus, the electric motor  12 , the hydraulic pump  16  and the hydraulic actuator  22  are deactivated even though the switch  42  may be on contacts  44  attempting to drive the system to apply additional braking force. 
     Once a DC motor  12  has stopped, the locking pressure in passage  18  or  20  is below that of the pressure relief switch  78  disconnecting the pressure switches  54  and  56  from the passages  18  and  20 . Thus, pressure switches  54  and  58  assume their normally closed position allowing reactivation of the DC motor. If there is an attempt to further apply force by connecting toggle  42  to contacts  44 , any additional pressure would very quickly build up in passages  18  or  20  and activate the appropriate pressure switch  58  to again turn off the system. The resetting of switches  54  and  58  allows the DC motor to be operated in the opposite direction to extend the element  24  and thereby release the brakes. 
     To release the parking brakes, toggle  42  and switch  40  is then connected to contacts  46 . This applies the positive terminal of the battery  48  to terminal  50  of the motor  12  and the negative terminal of the battery  48  to the terminal  70  of the motor. The pressure switches  54  and  58  are in their normally closed position. Also, it assumes that the float switch  62  is in its normally closed position. Since the activated element  24  has been retracted, the limit switch  74  is closed. 
     Once the actuator element  24  has been extended to the limit set by the limit switch  74 , limit switch  74  will open and deactivate the motor  12  and pump  16 . The relief side pressure switch  54  is a safety device which will deactivate the system if the actuator  22  becomes jammed. 
     If the extension of element  24  continues beyond a position determined by limit switch  74  and the motor is not cut off by the opening of pressure switch  54 , the limit switch  74  will open. The opening of limit switch  74  will deactivate electric motor  12 , pump  16  and hydraulic actuator  22 . 
     The series connected normally closed pressure switches  54  and  58  and the normally closed float switch  62  are connected via lead  66  and diode  68  to terminal  70  of the DC motor  12 . Line  64  is also connected through line  72 , limit switch  74  and line  76  to terminal  70  directly. 
     The connection of the series of connected switches  54 ,  58  and  62  to the motor  70  through diode  68  can only occur when lead  52  of switch  40  is connected to the positive terminal of the battery  48 . This forward biases the diode to turn on. This exists when toggle  42  engages contacts  44  to retract the actuation element  24 . This allows actuation of the DC motor  12  even if the limit switch  74  is open, signifying that the actuation element  24  has been extended too far. 
     If terminal  52  of switch  40  is connected to the negative terminal of battery  48  by toggle  42  connected to contacts  46 , the polarity across diode  68  from the normally closed switches  54 ,  58  and  62  bias diode  68  off and places the switches in series with the limit switch  74 . Thus, if the limit switch  74  is opened, the DC motor is not activated and therefore the actuating element  24  will not be further extended. 
     In summary, the DC motor  12 , pump  16  and hydraulic actuator  22  can be activated to extend the actuating element  24  if all of the switches  54 ,  58 ,  62  and  74  are closed and can be activated to retract the actuating element  24  if all of the switches  54 ,  58  and  62  are closed, even if the limit switch  74  is open. 
     A modification of the embodiment of FIG. 1 including a bidirectional motor  12  and a bidirectional pump  16  is illustrated in FIG.  2 . The difference is the electrical control circuit and not the hydraulic circuit. Leads  50  and  70  of the electric motor  12  are connected to the battery  48  by a relay  90  which controls toggle  92  between pairs of contacts  94 ,  96 . The relay  90  is connected to the selection switch  40  by line  98  and connected to the series connected switches  62 ,  58  and  54  via line  64 . It should be noted that diode  68  has been deleted and that line  72  of the limit switch is connected to one of the contacts  44  of switch  40 . The other line  76  of the limit switch  74  is connected to line  52  to place it in series with the other switches  62 ,  58  and  54  in the release position of the selection switch  40 . 
     The position of toggle  42  and selection switch  40  controls the relay  90  to have its toggle  92  to either contacts  96  that drive the electric motor  12  in one direction or contacts  94  to drive it in the opposite direction. When the switch  40  is in the applied position with toggle  42  contacting contacts  46 , the switches  62 ,  58  and  54  are in series with the relay  90 . When the toggle  42  or switch  40  is in the release position, the limit switch  74  is also placed in series with the relay  90  and the switches  62 ,  58  and  54 . Thus, as previously stated, the pressure switches and the float switch must be closed for the apply selection to activate the DC motor and the pump irrespective of the condition of the limit switch  74 . In the release position, the continued activation of the DC motor  12  and the pump  16  requires that the pressure switches, the float switch and the limit switch remain closed. 
     An embodiment illustrated in FIG. 3 uses a unidirectional motor  12  and unidirectional pump  16 . The selection of control of apply and release is produced by a selection valve  100  connected between the pump  16  and the actuator  22 ′. Selector  100  is a two position four-way valve. The position shown applies pressure on line  20  and relieve pressure on line  18 . In the second position (not shown), pressure is applied to line  18  and relieved on line  20 . The relief valve  78  and the check valve  86  are only provided on the applied line  20 . Both the apply line  20  and the released line  18  include pressure switches  54  and  58 . Also illustrated is a hand pump  102  which can supplement or be used instead of the electric motor  12  (not shown) and hydraulic pump  16  if there is a failure of the electrical system or the hydraulic pump  16 . 
     The actuator  22 ′ may be a mechanical actuator having an actuator element  24 ′ connected to clevis  26 . Also, it may be a locking actuator as described in U.S. patent application Ser. No. 09/661,565 filed Sep. 14, 2000. Such an actuator is driven into an applied position and stays locked in that applied position until pressure is provided on the release side to release the locking mechanism. A regular actuator  22 ′ would require a hydraulic or fluid lock. In either case, the actuator element  24  would not ever play out as it would in the screw motor  22  of FIGS. 1 and 2. Therefore, it will be noted that no limit switch  74  is required for actuator  22 ′. 
     The modified electrical schematic for the embodiment of FIG. 3 is illustrated in FIG.  4 . The battery  48  is connected to the, motor  12  via fuse  104  prevents circuit overload. An indicator  106  is parallel to the resistor  104 . Contact  91  is in series with the motor  12  and controlled by the motor relay  90 . A fuse  108  with parallel indicator  110  and a pair of zener diodes  112  further drop the voltage provided to the motor relay  90  and the remainder of the switch in the control circuits. A thermal switch  114  with parallel indicator  116  is connected in series with the motor relay  90 . 
     A modified selection switch  40  is shown as including normally opening start switch  41  in series with a relay  43  which controls latching contacts  45  in parallel to the start switch  41 . A normally closed stop switch  47  is also in series with the relay  43  and the start switch  41 . The float switch  62  and the two pressure switches  58  and  54  are in series with the selection switch  40 . 
     Under normal conditions, switches  62 ,  58  and  54  are closed as is stop switch  47 . Upon pressing start switch  41  closed, the relay  43  closes contacts  49  in series with the motor contact relay  90 . This activates relay  90  which closes contacts  91  turning on the motor  12 . Relay  43  also closes contacts  45  providing a path parallel to and latching start switch  41 . Thus, release of start switch  41  will not break the circuit for the relay  43 . The only thing that will reset the relay  43  and turn off the motor  12  and the pump  16  will be the stop switch  47  opening or one of the float switch  62  or pressure switches  58  and  54  opening. 
     It should be noted that if float switch  62  assumes its second position, it is connected to illuminate indicator  118  indicating that fluid is low while the pump is running. If the pump is not running, then there is no direct electrical connection. The indicator  116  in parallel to the thermal  114  will only light when the thermal contacts  114  open. The fuse  104  fuse  108  and diodes  112  would further drop the voltage available to the remainder of the circuit to about 24 volts. 
     If the actuator is the screw actuator of FIGS. 1 and 2, the electrical schematic of FIG. 4 will be modified as illustrated in FIG.  5 . The limit switch  74  is placed in series with the pressure switches  54  and  58  and the float switch  62 . All of the indicators  106 ,  110 ,  160 , and  118  are not shown in FIG. 5, but may or may not be provided. The remainder of the circuit is the same as that in FIG.  4  and operates in the same way. The limit switch  74  includes a normally closed switch portion  71  and a switch portion  73  responsive to the apply/release selector switch. Switch portion  71  is responsive to the position of the actuator and it opens if the screw element  24  plays out in the release position. When applied, switch  73  is closed such that the opening and closing of position element  71  has no effect on the operation or inactivation of the motor and pump. 
     The DC motor  12 , the hydraulic pump  16  and hydraulic actuator  22  are selected so as to produce high torque with low speeds. The goal to be achieved is 35,000 pounds of braking force. This is to hold a 350,000-450,000 pound locomotive. If this braking force can be produced, less than all of the wheels of the locomotive need to be braked. For example, only four of the twelve wheels need to be braked. This reduces the cost of interconnecting the parking brake actuator  24  to all of the brake actuating systems. The battery  48  may be the 72 volt DC battery available in the locomotive or may be another battery or voltage source. 
     For example, the apply side relief valve  78  may be set in the range of 2,500 to 2,800 psi and may be, for example, 2,750 psi. The release side relief valve  78  may be set in the range of 1,200 to 1,550 psi and may be, for example, 1,500 psi. Similarly, the apply limit switch  54  may be set in the range of 2,250 to 2,550 psi and may be, for example, 2,500 psi. The release limit switch  54  may be set in the range of 1,000 to 1,500 psi and may be, for example, 1,250 psi. The DC motor  12  may be for example 1 horsepower, the pump  16  having a capacity of, for example 0.08 inches 3  per revolution and the hydraulic actuator  27  having a capacity of, for example, 2.5 to 3.0 inches 3  per revolution. 
     The brake system  10  has been described with respect to locomotive brakes. It may also be applied on other rail cars providing its own battery source  48 . 
     Although the present invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.