Abstract:
A method of detecting a leak in a hydraulic trailer brake circuit of a trailer includes providing a controller, a base valve, a first sensor, a second sensor, a control valve having a solenoid, a reduction valve, a hydraulic fluid supply, a first brake output, and a second brake output. The method also includes supplying a first pressure to an inlet of the base valve and outputting a second pressure from an outlet of the base valve to the first brake output. The first pressure is detected by the first sensor and the second pressure is detected by the second sensor, and the detected first and second pressures are communicated to the controller. The difference between the first and second pressures are compared to a threshold, and a leak is detected in the hydraulic trailer brake circuit if the difference satisfies the threshold.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present disclosure relates to a fluid control circuit, and in particular, to a dual line hydraulic trailer brake circuit. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    Tractor trailer combinations generally require a braking system on the trailer that is engaged when a braking system of the tractor is selectively engaged. Often the braking system of the trailer is coupled to the braking system of the tractor to allow the tractor to simultaneously apply the braking system of the tractor and the trailer. Conventional trailer brake circuits include a single line for pressurizing the brakes. 
       SUMMARY 
       [0003]    In one embodiment of the present disclosure, a method of detecting a leak in a hydraulic trailer brake circuit of a trailer includes providing a controller, a base valve, a first sensor, a second sensor, a control valve having a solenoid, a reduction valve, a hydraulic fluid supply, a first brake output, and a second brake output; supplying a first pressure to an inlet of the base valve; outputting a second pressure from an outlet of the base valve to the first brake output; detecting the first pressure with the first sensor and the second pressure with the second sensor; communicating the detected first pressure and the second pressure to the controller; comparing a difference between first pressure and the second pressure to a threshold; and detecting a leak in the air trailer brake circuit if the difference satisfies the threshold. 
         [0004]    In a first example of this embodiment, the method may include de-energizing the solenoid of the control valve via the controller if the difference satisfies the threshold. In a second example, the method may include actuating the control valve to a closed position if the difference satisfies the threshold. In a third example, the method may include supplying an amount of pressurized fluid from the hydraulic fluid supply to the control valve. In a fourth example, the method may include reducing the amount of pressurized fluid supplied to the control valve via the reduction valve. In a fifth example, the method may include providing the base valve with a fixed gain; and determining the difference by multiplying the first pressure by the fixed gain, and then subtracting the second pressure therefrom. 
         [0005]    In a sixth example of this embodiment, the method may include energizing the solenoid if the difference does not satisfy the threshold. In a seventh example, the method may include fluidly coupling the hydraulic fluid supply to the second brake outlet if the solenoid is energized. In an eighth example, the method may include blocking hydraulic fluid from the second brake outlet when the difference satisfies the threshold. In a ninth example, the method may include fluidly coupling a park brake of the trailer to the control valve; and applying the park brake if the difference satisfies the threshold. In another example, the method may include disengaging the park brake of the trailer if the difference does not satisfy the threshold. In a further example, the method may include fluidly coupling the first brake output and the second brake output to the fluid supply in parallel when the difference does not satisfy the threshold. 
         [0006]    In another embodiment of the present disclosure, a hydraulic braking system of a trailer includes a pressurized supply of hydraulic fluid; a base valve including an inlet and an outlet; a control valve including a solenoid, an inlet fluidly coupled to the pressurized supply of hydraulic fluid, and an outlet, the control valve operably controlled between an energized state and a de-energized state; a first brake output fluidly coupled to the outlet of the base valve; a second brake output fluidly coupled to the outlet of the control valve; a first sensor and a second sensor fluidly coupled to the base valve, the first sensor configured to detect a first pressure at the inlet of the base valve, and the second sensor configured to detect a second pressure at the outlet of the base valve; wherein, the control valve is operably controlled to its de-energized state when a difference between the first pressure and second pressure satisfies a threshold. 
         [0007]    In one example of this embodiment, in the de-energized state the pressurized supply is fluidly coupled to the second brake output, and in the energized state the control valve fluidly de-couples the pressurized supply from the second brake output. In a second example, the system may include a controller disposed in electrical communication with the first and second sensors; and the base valve comprises a fixed gain; wherein, the controller compares the first pressure as a function of the fixed gain to the second pressure to determine the difference and whether to operably control the control valve to its energized state or de-energized state. In a further example, the system may include a reduction valve fluidly coupled between the pressurized supply and the control valve, wherein the reduction valve is configured to reduce an amount of fluid pressure supplied by the pressurized supply to the control valve. In yet a further example, the system may include a park brake hydraulically controlled by the second brake output between a disengaged position and an engaged position, wherein in the de-energized state the park brake is in its disengaged position, and in the energized state the park brake is in its engaged position. 
         [0008]    In a further embodiment of the present disclosure, a hydraulic braking system of a trailer towed by a work machine includes a controller; a pressurized supply providing hydraulic fluid; a pilot line providing a pilot pressure; a base valve including a first inlet, a second inlet, and an outlet, where the first inlet is fluidly coupled to the pilot line and the second inlet is fluidly coupled to the pressurized supply; a solenoid control valve disposed in electrical communication with the controller and including an inlet fluidly coupled to the pressurized supply of hydraulic fluid and an outlet, the solenoid control valve operably controlled between an energized state and a de-energized state by the controller; a reduction valve fluidly coupled between the pressurized supply and the solenoid control valve, wherein the reduction valve is configured to reduce an amount of fluid pressure supplied by the pressurized supply to the solenoid control valve; a first control line fluidly coupled to the outlet of the base valve; a second control line fluidly coupled to the outlet of the solenoid control valve; a first sensor and a second sensor fluidly coupled to the base valve, the first sensor configured to detect pilot pressure, and the second sensor configured to detect an output pressure in the first control line; wherein, the solenoid control valve is operably controlled to its energized state when a difference between the pilot pressure and output pressure satisfies a threshold. 
         [0009]    In one example of this embodiment, in the energized state the pressurized supply is fluidly coupled to the second control line, and in the de-energized state the solenoid control valve fluidly de-couples the pressurized supply from the second control line. In another example, the system may include a park brake hydraulically controlled by the solenoid control valve between a disengaged position and an engaged position, wherein in the energized state the park brake is in its disengaged position, and in the de-energized state the park brake is in its engaged position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The above-mentioned aspects of the present disclosure and the manner of obtaining them will become more apparent and the disclosure itself will be better understood by reference to the following description of the embodiments of the disclosure, taken in conjunction with the accompanying drawings, wherein: 
           [0011]      FIG. 1  is a side view of a combined tractor and trailer system; 
           [0012]      FIG. 2  is a control schematic view of a hydraulic system of a combined tractor and trailer brake system; 
           [0013]      FIG. 3  is a control schematic view of a combined hydraulic and pneumatic system of a combined tractor and trailer brake system; 
           [0014]      FIG. 4  is a schematic of a dual line trailer brake circuit; and 
           [0015]      FIG. 5  is a flow diagram of a control process for controlling the dual line trailer brake circuit of  FIG. 4 . 
       
    
    
       [0016]    Corresponding reference numerals are used to indicate corresponding parts throughout the several views. 
       DETAILED DESCRIPTION 
       [0017]    The embodiments of the present disclosure described below are not intended to be exhaustive or to limit the disclosure to the precise forms in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present disclosure. 
         [0018]    Referring to  FIG. 1 , a combined tractor trailer system  100  is shown. In this system, a tractor  102  is shown coupled to and pulling a trailer  104 . The tractor  102  may have a chassis  106  that spans between a front ground engaging mechanisms  108  and a rear ground engaging mechanisms  110 . In the embodiment of  FIG. 1 , each ground-engaging mechanism is in the form of a wheel defined along a respective axle, i.e., a front axle and a rear axle. In other embodiments, however, the ground-engaging mechanism may be a track that propels the tractor  102  along a ground surface. Likewise, the trailer  104  may also include at least one ground-engaging mechanism such as a wheel  126 . 
         [0019]    A cab  112  may be coupled to the chassis  106  and define a location for an operator to be positioned in an operator&#39;s seat  114 . From the cab, the operator may control the tractor  102  and trailer  104  via a plurality of controls. As shown, the cab  112  may include a display  116  or dashboard that visually shows control characteristics of the tractor  102  or trailer  104  such as speed, power, temperature, pressure, direction, and any other type of control characteristic. The display  116  may be a touchscreen display that includes one or more operator controls for selectively controlling the operation of the tractor  102  or trailer  104 . Other controls may include a steering wheel or yoke  118 , a pedal  120  (e.g., a brake pedal, clutch pedal, or throttle pedal), any other type of control such as a joystick, switch, lever, knob, etc. for controlling the tractor trailer system  100 . 
         [0020]    While a tractor  102  is shown and described herein, any type of work machine may utilize the teachings of this disclosure and therefore it is not intended to be limited to applying to only tractors. In other embodiments, a truck configured to tow a trailer may utilize the teachings of this disclosure. Accordingly, the tractor  102  can be any type of work machine used to pull a trailer. 
         [0021]    The tractor  102  may be coupled to the trailer  104  through a hitch member or drawbar  122 . The hitch member or drawbar  122  may be sufficiently strong to transfer motion of the tractor  102  to the trailer  104 . In one embodiment, when the tractor  102  travels in a forward direction, the hitch member  122  pulls the trailer  104  along therewith in approximately the same direction. 
         [0022]    One or more fluid lines  124  may also be provided. For purposes of this disclosure, a fluid may include a gas or liquid. Thus, any pneumatic or hydraulic line may be referred to as a fluid line herein. The one or more fluid lines  124  may selectively fluidly couple a tractor brake system to a trailer brake system. More specifically, the tractor  102  may provide a trailer brake output that is coupled to the trailer brake system. In this configuration, when the user initiates a brake command, both the tractor brake system and the trailer brake system may simultaneously engage to slow the tractor  102  and trailer  104 . 
         [0023]    In some tractor trailer systems, one or more brake pedals may be engaged by an operator to apply a tractor service brake. Brake actuators may be pressurized to apply the brakes, which will be described in greater detail below with reference to  FIG. 2 . Once the operator commands engagement of the tractor braking system, the trailer braking system also must engage to prevent the trailer from contacting or running into a back end of the tractor. In many conventional braking systems, there may be a single hydraulic line that connects between the tractor and trailer braking systems. In addition, a single hydraulic trailer brake valve may have a fixed gain associated with it due to its geometry. Thus, depending upon the fixed gain, an amount of pressure entering the valve if multiplied by the fixed gain to deliver a predetermined outlet pressure. As braking systems change and new federal and international guidelines or standards change, there is a need for both lower and higher outlet pressures depending upon the type of trailer. As a result, an adjustable gain across the hydraulic trailer brake valve is desirable over a fixed gain valve. Other needs and advantages will become apparent from the principles and teachings of the present disclosure. 
         [0024]    In some tractor trailer systems, the trailer braking system includes a hydraulic braking system, a pneumatic braking system, or a combination thereof. An example of a trailer brake system is shown in  FIG. 2 . In this embodiment, a hydraulic braking system  200  of a tractor and a trailer may include a brake controller  202  as shown. The brake controller  202  may be in electrical communication with a vehicle controller (not shown), an engine controller (not shown), a transmission controller (not shown), and any other type of controller for controlling the tractor or trailer. The brake controller  202  may include a plurality of inputs and outputs for receiving and communicating electrical signals or commands to different components within the braking system  200 . In  FIG. 2 , for example, the brake controller  202  may be disposed in electrical communication with a tractor display  250 . This communication may exist over a controller area network (CAN) bus  252  or communication link. The display  250  may allow an operator to selectively communicate instructions to the brake controller  202  for controlling the tractor braking system or the trailer braking system  200 . 
         [0025]    Other operator controls may also be in communication with the brake controller  202 . For example, one or more brake pedals  204  may be selectively engaged by an operator. A brake position sensor  206  may detect a movement of the one or more brake pedals  204  and communicate this movement to the brake controller  202 . Upon application of the one or more brake pedals  204 , a brake valve  212  may be triggered such that fluid from a hydraulic supply line  254  (via a pump or other pressure source) is delivered to brake actuators. In turn, the brake actuators are controllably actuated to deliver hydraulic brake pressure to the tractor braking system to control the speed of the tractor. In  FIG. 2 , the braking system  200  illustrates a right brake actuator  208  and a left brake actuator  210 . In this embodiment therefore the operator may depress a right brake pedal and a left brake pedal to engage the tractor braking system. The right brake pedal and right brake actuator  208  may control brake pressure to a service brake on the right, rear wheel of the tractor, and the left brake pedal and left brake actuator may control brake pressure to a service brake on the left, rear wheel of the tractor. In doing so, the right brake actuator  208  and left brake actuator  210  deliver hydraulic pressure to the tractor service brakes to slow the vehicle. This hydraulic pressure may also be delivered to the trailer braking system as will be described below. 
         [0026]    As is known, an operator may apply the brake pedals to brake the tractor and slow its speed. In addition, an operator may gently apply or tap on the brake pedal, as is often the case with an operator desiring to disable cruise control in a motor vehicle. In the tractor trailer system, it may be desirable to begin braking the trailer as soon as the brake controller  202  detects engagement of the one or more brake pedals  204 . In this example, the brake controller  202  may execute a pre-brake routine or algorithm to begin applying the trailer braking system. In the embodiment of  FIG. 2 , the brake pedal position sensor  206  can send a signal to the brake controller  202  indicating that the operator has begun to depress the pedals  204 . Before any brake pressure or a substantial amount of brake pressure is generated, the brake controller  202  may execute the pre-brake routine and send a signal to the trailer braking system to begin braking the trailer. This signal may be an adjustable or proportional signal from the brake controller  202 . The signal may be received by a trailer brake valve that includes a first solenoid valve and a second 2-way position valve (i.e., an on/off valve). In one example, up to seven bars of pressure may be output from the valve to the trailer brakes to begin a braking operation. 
         [0027]    During this pre-brake routine, the first solenoid valve may receive the signal from the brake controller and deliver the hydraulic pressure to the trailer brakes. The second, 2-way position valve may be disposed in its open position to allow fluid pressure to pass through. However, if there is a failure detected in the system, the second, 2-way position valve can be actuated to its off or closed position to block fluid pressure to the trailer brake system. This “fail-silent” condition may be utilized to protect against possible failures in the system. In any event, hydraulic pressure may still pass through a main hydraulic trailer brake valve  226  ( FIG. 2 ) so that the trailer braking system is engaged during a braking operation. The pre-brake valve set, however, may be disabled or closed so that no output pressure passes through the valve set to the trailer brakes. 
         [0028]    In  FIG. 2 , hydraulic brake pressure from the right brake actuator  208  may be detected by a first pressure transducer  214 , and from the left brake actuator  210  may be detected by a second pressure transducer  216 . The first and second transducers may be in electrical communication with the brake controller  202 . This electrical communication may be either wired or wireless communication, or any other known or to be developed form of communication. As a result, the brake controller  202  can monitor brake pressure from both actuators. 
         [0029]    A shuttle valve  218  may be disposed in fluid communication with the right brake actuator  208  and the left brake actuator  210 . The shuttle valve  218  may be actuated in either direction depending upon which brake pressure is the greatest. As such, the greater of the two brake pressures passes through the shuttle valve  218  and is referred to as brake pilot pressure. In  FIG. 2 , the brake pilot pressure flows downstream from the shuttle valve  218  along a brake pilot line  242 . 
         [0030]    The braking system  200  of  FIG. 2  may also include a hydraulic valve set  220 . This valve set  220  may be similar to the aforementioned pre-brake valve set in that it includes both a proportional solenoid valve and a 2-way shutoff valve. As shown, the brake controller  202  may be in electrical communication with the hydraulic valve set  220  to control its operation. For example, a trailer brake command  248  may be communicated from the brake controller  202  to the valve set  220 . Moreover, the valve set  220  may send signals to the brake controller  202  in response to its operation (i.e., a pressure transducer  224  may communicate a pressure associated with the valve set to the controller  202 ). 
         [0031]    Outlet pressure from the hydraulic valve set  220  may flow through a fluid line  244  as shown in  FIG. 2 . The hydraulic valve set fluid line  244  and the brake pilot line  242  may converge upon a second shuttle valve  222 . Similar to the operation of the first shuttle valve  218 , the greater of the brake pilot pressure and hydraulic valve set pressure may pass through the second shuttle valve  222  and enter hydraulic line  246 . The pressure in hydraulic line  246  may be referred to as the hydraulic pilot pressure. A pressure transducer  228  can detect the hydraulic pilot pressure and communicate this pressure to the brake controller  202 , as shown in  FIG. 2 . This hydraulic pilot pressure may pass through a hydraulic trailer brake control line  230  to the trailer brakes. 
         [0032]    In the system  200  of  FIG. 2 , the trailer may also include a trailer park brake. The trailer park brake may be operably controlled via a hydraulic trailer park control valve  232 . This valve  232  may include a solenoid  234  that is in electrical communication with the brake controller  202 . The hydraulic trailer park control valve  232  may be biased to its vented position to allow pressure to flow through a supplementary hydraulic line  240 . The valve  232  may also be in fluid communication with a tank or reservoir  236  as shown. As such, hydraulic pressure may be delivered from a supply line  238  to the hydraulic trailer park control valve  232 , and in its normally or biased open position, pressure passes therethrough to the hydraulic trailer brake supplementary line  240 . 
         [0033]    Referring to  FIG. 3 , a portion of the braking system  200  of  FIG. 2  is removed and an air or pneumatic trailer braking system  300  is shown. As described above, the trailer braking system may be hydraulic, pneumatic, or a combination thereof. In this disclosure, the pneumatic trailer braking system may use any form of gas for controlling its brakes. However, for sake of simplicity, the type of gas will be referred to as air through the remainder of this disclosure. Thus, the pneumatic trailer braking system  300  will be referred to as the air trailer braking system  300 , but it is to be understood that any type of gas may be used to control the trailer brakes. 
         [0034]    In  FIG. 3 , the air trailer braking system  300  may include an air or pneumatic trail brake valve  302 . The air trailer brake valve  302  may be located downstream from the second shuttle valve  222  of the hydraulic system  200  such that hydraulic pressure is used as an inlet to control the valve  302 . Hydraulic pressure may flow through a pilot pressure line  312  to an inlet of the air trailer brake valve  302 . 
         [0035]    In addition to the air trailer brake valve  302 , the air trailer braking system  300  may also include an air supply line  320 , a shuttle valve  304 , an air trailer park brake control valve (not shown), and a leak detect valve  306 . The shuttle valve  304  is disposed downstream of the air trailer brake valve  302  and the air trailer park brake control valve. Thus, air pressure may be output from the air trailer brake valve  302  via a first pressure line  314  and from the air trailer park brake control valve via a second pressure line  316 . The greater of the two pressures from the first and second line may trigger the shuttle valve  304  open so that air pressure can flow through a first air trailer brake control line  318  to the air trailer brakes. A pressure transducer  310  may be in fluid communication with the control line  318  to detect the pressure and communicate it to the brake controller  202 . 
         [0036]    The leak detect valve  306  may be in the form of a normally open solenoid control valve. The valve  306  may include a solenoid  308  that is disposed in electrical communication with the brake controller  202 . As such, the brake controller  202  can control the leak detect valve  306  between its open and closed positions via a communication link  324  with the solenoid  308 . 
         [0037]    Air pressure may be supplied via the supply line  320  to the leak detect valve  306 . Since the leak detect valve  306  may be biased to its open position, fluid may flow through the valve  306  to the air trailer brake valve  302  and to an air trailer brake supply line  322 . 
         [0038]    The embodiments of  FIGS. 2 and 3  are illustrative of only one example of a braking system for a tractor trailer combination. Other embodiments of a braking system is possible and within the scope of this disclosure. For instance, another embodiment may include one or more electrohydraulic secondary brake valves. 
         [0039]    Referring to  FIG. 4 , a trailer brake control system or circuit  400  is shown. As previously described, a conventional agriculture machine such as a tractor may include a single line hydraulic trailer brake circuit. The single line may provide pressure for applying service brakes on a trailer. Governmental regulations and various safety standards, particularly in Europe, have begun regulating trailer brake circuits and requiring at least two hydraulic lines for trailer braking. To meet governmental regulations and safety standards, a system such as the one illustrated in  FIG. 4  is necessary and provides a primary and secondary hydraulic lines for applying trailer brakes. As will be described, the primary hydraulic line may control service brakes on the trailer, and the second line may control a park brake. 
         [0040]    In  FIG. 4 , the control system  400  may include the hydraulic trailer brake valve  226  as described above and shown in  FIG. 2 . The hydraulic trailer brake valve  226  may be fluidly coupled to a supply  402  of pressurized hydraulic fluid. Moreover, and as described above, the hydraulic trailer brake valve  226  may include an let for receiving pilot pressure from service brakes on the work machine. The pilot pressure may be fluidly coupled to the hydraulic trailer brake valve  226  via line  246 , through which the fluid flows in an inlet direction indicated by arrow  410 . 
         [0041]    The hydraulic trailer brake valve  226  may include a fixed gain that is predefined based on the geometry or design of the valve. In one non-limiting example, the gain may be defined as 3.0, such that outlet pressure may be approximately three times the pilot pressure. In other embodiments, the gain may be defined as any value based on the valve design. Thus, pilot pressure is output via the valve  226  through an outlet at a pressure that is a factor of the gain. Outlet pressure may flow in an outlet direction indicated by arrow  412  through the hydraulic trailer brake control line  230  (i.e., primary line) to the trailer brakes. 
         [0042]    The control system  400  of  FIG. 4  may also include the trailer park brake valve  232  as described above and shown in  FIG. 2 . The trailer park brake valve  232  may be fluidly coupled to the supply  402 , and output pressurized hydraulic fluid via a secondary or supplementary line  240  in an outlet direction as shown by arrow  414  in  FIG. 4 . The trailer park brake valve  232  may be in the form of a solenoid control valve that includes a solenoid  234  electrically coupled to the brake controller  202 . As such, the controller  202  may control the valve  232  between an energized state and a de-energized state. Moreover, the trailer park brake valve  232  and supplementary line  240  are disposed in parallel to the primary hydraulic line  230  shown in  FIG. 4 . The secondary or supplemental line  240  may control fluid pressure for engaging or disengaging a trailer park brake. This will be described in further detail below. Fluid pressure in the supplemental line  240  may be detected or measured by a pressure sensor  408  that is in fluid communication therewith. The pressure sensor  408  is optional, but in those embodiments in which it is present, the sensor  408  may be in electrical communication with the brake controller  202  to provide feedback of the supplemental line pressure to the controller  202 . 
         [0043]    The control system  400  may further include a pressure-reducing valve  406  as shown in  FIG. 4 . The pressure-reducing valve  406  may be located between the supply  402  and the trailer park brake valve  232 . In one non-limiting example, a pump or other fluid supply  402  may provide between 30-200 bar of pressure. The trailer park brake valve  232  may be ill-equipped to handle such high pressures, and thus the pressure-reducing valve  406  is designed to reduce the pressure before it flows to the trailer park brake valve  232 . In one example, the reducing valve  406  may reduce the pressure to less than 50 bar. In another example, the pressure may be reduced to less than 40 bar. In a further example, the pressure may be reduced to between 15-35 bar. In any event, the pressure-reducing valve  406  may be designed to reduce the pressurized fluid from the supply  402  to a pressure that the trailer park brake valve  232  can handle. 
         [0044]    The hydraulic park brake valve  232  may include a spring that biases the valve to block fluid flow therethrough. Pressurized fluid, however, from the supply  402  urges the valve open to counteract against the spring resistance. When pressure is present in the supplemental line  240 , the trailer park brake valve  232  is disposed in its open position to allow fluid to flow therethrough. To open the valve  232 , the controller  202  may energize the solenoid  234 . If it is desired to close the valve and vent the pressure, and thus apply the park brake, the controller  202  may de-energize the solenoid  234 . Thus, when the trailer is in park, the supplemental line pressure may be vented to tank  236 , and when the trailer is not in park the supplemental line pressure may be set by the amount of reduced pressure outlet via the reducing valve  406 . 
         [0045]    Although not shown, the trailer may be equipped with a park brake. The park brake may be a spring-biased such that when there is no pressure in the supplemental line, the spring biases the brake to its engaged position. When there is pressure in the supplemental line, however, the pressure counteracts the spring and disengages the park brake. 
         [0046]    The dual line hydraulic brake circuit  400  of  FIG. 4  is designed for leak detection and also to take the necessary precautions if a leak is detected. A control process  500 , shown in  FIG. 5 , may be provided to detect a leak and control the circuit when a leak is detected. The control process  500  may include a plurality of blocks or steps that may be executed in order to detect the leak and take corrective action. In one embodiment, the control process  500  may be executed by a processor of the brake controller  202 , and an algorithm or software stored in a memory unit of the controller  202  may provide the necessary instructions for executing the process  500 . 
         [0047]    In this process  500 , a first block  502  may be executed by supplying pressurized fluid from the supply  402  to the hydraulic trailer brake valve  226  and the trailer park brake valve  232 . The hydraulic trailer brake valve  226  may also receive pilot pressure via line  246  in block  504 . The pilot pressure may be in response to actuation of service brakes on the work machine or tractor. 
         [0048]    In block  506  of the process  500 , the supply of pressurized fluid may be approximately 30-200 bar. As such, the pressure-reducing valve  406  can reduce the pressure of the pressurized fluid to the trailer park brake valve  232 . As described above, the pressure may be reduced to less than 50 bar. In one non-limiting example, the pressure may be reduced to between 15-35 bar. In a further non-limiting example, the pressure may be reduced to approximately 20 bar. The pressure reduction may depend upon the size and capability of the trailer park brake valve  232 . 
         [0049]    As pressurized fluid is supplied to the trailer park brake valve in blocks  502  and  506 , the brake controller  202  may control the trailer park brake valve  232  between its energized state and de-energized state. In block  508 , the controller  202  may send current to the solenoid  234  to energize the valve  232 . In doing so, the trailer park brake valve  232  may output hydraulic fluid to a supplemental line in block  510 . With fluid pressure in the supplemental line, the park brake is biased or moved to its disengaged position. 
         [0050]    During a normal braking operation, pilot pressure is supplied to an inlet of the hydraulic trailer brake valve  226 , and based on a fixed gain of the valve, hydraulic pressure is output via the valve  226  to a primary line  230  in block  514  which fluidly couples to service brakes on the trailer. During operation, block  516  may be executed as a first pressure sensor  404  detects or monitors pilot pressure, and a second pressure sensor  228  detects or monitors output pressure. Each sensor may be in electrical communication with the brake controller  202 . Thus, the brake controller  202  may continuously monitor the inlet and output pressures of the hydraulic trailer brake valve  226 . 
         [0051]    In addition, the brake controller  202  may be pre-programmed such that it stores the fixed gain of the hydraulic trailer brake valve  226 . In doing so, the controller  202  may execute block  518  by comparing the pilot pressure to the output pressure as a function of the valve gain. Here, the controller  202  can multiply the pilot pressure by the gain, and then subtract the output pressure to determine the difference. In block  520 , the controller  202  may compare the difference to a threshold pressure. The threshold pressure may be a fixed value stored in the memory unit of the controller  202 . If the difference exceeds the threshold, then the controller  202  may determine that there is a leak in the primary line  230 . If the difference does not exceed or satisfy the threshold, then the controller  202  may determine there is no leak. 
         [0052]    If the controller  202  determines there is a leak in block  520 , the controller  202  may then execute block  522  by de-energizing the solenoid  234  of the trailer park brake valve  232 . When the trailer park brake valve  232  is de-energized, its spring biases the valve to a closed position to block hydraulic fluid from flowing therethrough and into the supplemental line  240 . In other words, hydraulic flow is cut off from the supplemental line  240  by the trailer park brake valve  232 . As fluid is cut off from the supplemental line  240 , there is no pressure to hold the park brake in its disengaged position. As such, block  524  may be executed when a leak is detected by applying the park brake. This puts the trailer in a safe state by braking the trailer via the park brake when the leak is detected. The brake controller  202  may also send a warning or instruction to the dashboard or operator screen  116  in the tractor to alert the operator of the detected leak. 
         [0053]    The control process  500  of  FIG. 5  may be executed continuously. However, leak detection is only executed when there is pilot pressure provided to the air trailer brake valve  302 . In other words, only as the operator is applying the service brakes on the work machine is the leak detection process  500  executed. 
         [0054]    While this disclosure has been described with respect to at least one embodiment, the present disclosure can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this disclosure pertains and which fall within the limits of the appended claims.