Patent Publication Number: US-2007102996-A1

Title: Hydraulic full power brake system for trailers

Description:
TECHNICAL FIELD  
      The subject invention relates to a hydraulic brake system for a trailer towed by a passenger car or light to medium duty truck where the hydraulic brake system is electronically controlled.  
     BACKGROUND OF THE INVENTION  
      Light to medium duty vehicles, such as passenger cars, pick-up trucks, sport utility vehicles, etc., are often configured to pull trailers. These trailers are typically utility or work trailers but can include horse trailers and recreational trailers, such as campers, for example. These types of trailers typically include medium duty trailer brakes that are controlled by one of two different methods.  
      One method uses electronic control for actuating magnetic brakes at each trailer wheel. An electrical control signal is used to generate a magnetic brake actuation force. Another method uses hydraulic surge brake control to actuate hydraulic brakes. This is often referred to as a hydraulic over hydraulic system. During a braking event, a trailer tongue connection between the trailer and vehicle has a tendency to dive downwardly. Surge control recognizes this occurrence and utilizes hydraulic control to actuate the hydraulic brakes.  
      Each of these controls provides an effective method for stopping the trailer. However, neither method offers control for emergency stopping situations. In an emergency stopping situation a trailer has increased potential for jack-knifing or roll-over events. Further, neither method offers anti-lock control to prevent wheel lock-up under poor road conditions.  
      Thus, there is a need for a trailer brake system for light to medium duty vehicles that provides improved control for all stopping situations.  
     SUMMARY OF THE INVENTION  
      The subject invention provides a full power hydraulic brake system for a trailer that is controlled by an electronic control unit (ECU). The trailer brake system includes a power unit that maintains a desired level of fluid pressure in the brake system, and a brake control unit that applies trailer wheel brakes in response to a braking request. The trailer brake system optionally includes an anti-lock brake system (ABS) control unit to prevent wheel lock-up.  
      The power unit includes an electric motor that is controlled by the ECU. The electric motor drives a pump to maintain a desired pressure level in an accumulator. The pump supplies hydraulic fluid to the accumulator from a trailer supply reservoir. The pressure in the accumulator is monitored and controlled by the ECU by using a pressure transducer. A pressure limiting valve prevents over-pressure conditions.  
      The brake control unit includes a pressure transducer, an inlet valve that is normally closed, and an outlet valve that is normally open during non-braking. The ECU controls brake pressure in a closed loop circuit with the pressure transducer and the inlet and outlet valves. In response to a braking request, the outlet valve is closed and the inlet valve is pulsed open until an appropriate pressure is provided to a trailer wheel brake component.  
      The ABS control unit includes wheel speed sensors for a least a right side wheel and a left side wheel. The wheel speed sensors communicate speed data to the ECU. The ABS control unit includes inlet and outlet valves for each of the right and left side wheels. The inlet valves are normally open and the outlet valves are normally closed. The ECU generates a control signal based on the speed data to close the inlet valves and open the outlet valves as needed to prevent wheel lock-up.  
      The trailer brake system optionally includes a parking brake that is preferably a spring applied hydraulic release (SAHR) brake. A park brake valve assembly is fluidly connected to the accumulator. The park brake valve assembly applies pressure to the SALR brake to release the parking brake and releases pressure from the SAHR brake to apply the parking brake.  
      These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic view of a vehicle towing a trailer incorporating the subject trailer brake system.  
       FIG. 2  is a schematic diagram of a trailer brake system incorporating the subject invention.  
       FIG. 3  is a schematic diagram showing system inputs and outputs.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       FIG. 1  shows a light to medium duty vehicle  10  that is connected to a trailer  12  with a hitch  14 . Optionally, the trailer  12  could be towed through a fifth wheel connection (not shown). The trailer  12  includes at least one axle having a set of wheels  16  (only one wheel is shown in  FIG. 1 ). The wheel  16  includes a wheel brake member, which is schematically indicated at  18 . The wheel brake member  18  is preferably a disc brake with a caliper that is hydraulically actuated, however, other types of hydraulically actuated wheel brakes could also be used.  
      A trailer brake system  20  generates an electric control signal ES that is used to hydraulically actuate the wheel brake member  18  in response to a braking request. Thus, the trailer brake system  20  provides an electric over hydraulic system for the trailer  12 .  
      The trailer brake system  20  is shown in greater detail in  FIG. 2 . The trailer brake system includes a power unit  22  and a brake control unit  24 . The power unit  22  includes an electric motor  26 , a pump  28 , an accumulator  30 , and a pressure transducer  32 . The trailer brake system  20  includes an electronic control unit (ECU)  34  that actuates the electric motor  26  to drive the pump  28  to maintain a desired fluid pressure within the accumulator  30 . The pump  28  supplies fluid to the accumulator  30  from a trailer supply reservoir  36 . The trailer supply reservoir  36  is preferably solely dedicated to the trailer brake system  20 . The preferred fluid used in the system is DOT3 or DOT4 brake fluid, however, other brake fluids could also be used.  
      Pressure within the accumulator  30  is monitored and controlled by the ECU  34  by utilizing the pressure transducer  32 . When pressure in the accumulator  30  falls below a predetermined minimum pressure or cut-in level, the ECU  34  generates a control signal S 1  to actuate the electric motor  26  to drive the pump  28 , which pumps fluid from the trailer supply reservoir  36  to the accumulator  30 . A pressure limiting valve  38  prevents over-pressure situations, which could result in system damage.  
      The brake control unit  24  includes a pressure transducer  40 , an inlet valve  42 , and an outlet valve  44 . The inlet valve  42  is normally closed and the outlet valve  44  is normally open during non-braking conditions. During a braking event, an electric voltage or current signal proportional to a requested brake pressure is used as an input to the ECU  34 . The ECU  34  then controls brake pressure in a closed loop circuit with the pressure transducer  40  and the inlet  42  and outlet  44  valves. The ECU generates a control signal S 2  such that the outlet valve  44  gets closed and the inlet valve  42  gets pulsed open until an appropriate pressure occurs in a brake circuit  46  at the wheel  16 . To release the pressure, the inlet valve  42  is closed and the outlet valve  44  is opened.  
      In the example shown, the inlet valve  42  supplies fluid pressure to the brake circuit  46  for a left wheel  16   a  and for a right wheel  16   b  positioned laterally opposite the left wheel  16   a.  The trailer  12  could also include additional axles and wheels that may or may not have brake circuits  46 .  
      The trailer brake system  20  could optionally include an anti-lock brake system (ABS) control unit  50 . The ABS control unit  50  includes an inlet valve  52 , an outlet valve  54 , and a wheel speed sensor  56  that is associated with each wheel  16 . Any type of wheel speed sensor  56  could be used such as tone wheel configuration, for example. The wheel speed sensors  56  generate signals  58  that transmit wheel speed data to the ECU  34 .  
      The inlet valve  52  is normally open and the outlet valve  54  is normally closed. During an ABS event, such as slippery or other types of poor road conditions, the wheel  16  has a tendency to lock-up. The ECU  34  generates a control signal S 3  to open and close the inlet  52  and outlet  54  valves as needed to prevent wheel lock-up.  
      If the trailer  12  includes more than two wheels, each additional wheel may or may not be provided with an ABS feature. Preferably, at least one wheel per side (right and left sides) of the trailer  12  is provided with the ABS feature.  
      The trailer brake system  20  could also optionally include a parking brake  60 . The parking brake  60  is preferably a spring applied hydraulic release (SAHR) brake that has a chamber  62  and spring member  64 . A parking valve assembly  66  is fluidly connected to the chamber  62  and to the accumulator  30 . The parking valve assembly  66  is a 3/2 way valve, which has an outlet port  68  in fluid communication with the chamber  62 , a supply port  70  in fluid communication with the accumulator  30 , and a release port  72  in fluid communication with the trailer supply reservoir  36 .  
      The parking valve assembly  66  releases pressure from the chamber  62  via the release port  72  during a park brake request, such that the spring member  64  applies the parking brake  60 . To release the parking brake  60 , pressure is supplied through the supply port  70  to the outlet port  68 , to the chamber  62 .  
      The parking brake  60  could be located at each wheel  16  on the trailer  12 , or could only be located at one wheel  16  depending on application requirements. Further, a short time parking brake function could be supplied without have to incorporate a parking brake  60  into the trailer brake system  20 . To apply a short time park brake request, the brake circuit  46  at each wheel  16  gets applied with a specified amount of pressure like in a normal brake situation.  
      As shown in  FIG. 2 , the pressure transducer  40  of the brake control unit  24  is located downstream of the inlet valve  42  and upstream of the ABS control unit  50 . Further the pressure transducer  40  is also fluidly connected to a return line  80  that returns released fluid to the trailer supply reservoir  36 . A supply line  82  fluidly connects the accumulator  30  to the inlet valve  42 .  
      The ECU  34  is electrically connected to the power unit  22 , the brake control unit  24 , and the ABS control unit  50 . The ECU is connected at  88  to a vehicle battery (not shown) or other power source.  
      Optionally, the trailer brake system  20  could include a roll stability system (RSS) control and/or an electronic stability control (ESC)  90 . For RSS, the trailer brake system  20  would use available data from the system described above to identify potential roll-over events. The ECU  34  would control braking as need to prevent roll-over.  
      For ESC, in addition to using the available data, an accelerometer  92  and a yaw rate sensor  94  are required. The trailer brake system  20  uses information from these sensors  92 ,  94  to identify potential unstable driving conditions, and the ECU  34  would then generate control signals to control braking as needed to improve stability.  
       FIG. 3  shows a schematic diagram of system inputs and outputs. The ECU  34  receives inputs such as a brake request input  100 , a park brake request input  102 , an electric power input  104 , and sensor inputs  106  for the sensors  56 ,  92 ,  94 . In response to a park brake request, the ECU  34  generates a park brake pressure output  108  that is communicated to the parking brake  60 . In response to a braking request, the ECU  34  generates a brake pressure output  110  that is communicated to the wheel brake member  18 .  
      Various system inputs and outputs are also communicated between the ECU  34  and the power unit  22 , brake control unit  24 , and the ABS control unit  50 . The ECU  34  communicates a brake control output  120  to the inlet  42  and outlet  44  valves of the brake control unit  24 . The brake control unit  24  communicates a brake pressure signal  122  from the pressure transducer  40  to the ECU  34 . The ECU  34  communicates a brake control output  124  to the inlet  52  and outlet  54  valves of the ABS control unit  50 .  
      The ECU  34  communicates a pump motor power request  130  to the electric motor  26  of the power unit  22 . The power unit  22  communicates an accumulator pressure output  132  to the ECU  34  via the pressure transducer  32 . The power unit  22  also communicates fluid level output  134  to the ECU  34 .  
      The subject invention provides a hydraulic full power brake system for a trailer towed by a light to medium duty vehicle, which provides several advantages over prior systems. The hydraulic full power brake system is a compact unit that is self-contained and easily installed on a trailer. High braking forces are provided when needed. Further, precise and controlled pressure applications are also provided during emergency stopping conditions. This reduces premature wear and tear on brake components and prevents high mechanical stresses for towing bar and other associated hitch components. Also, by having precise control over braking, the occurrence of undesirable conditions, such as jack-knifing and roll over for example, are significantly reduced.  
      It should be understood that the subject system could be controlled in various different manners. A driver could manually actuate a hand brake, lever, or switch to generate a braking request. Preferably, a pressure transducer (not shown) is used to determine rear axle brake pressure at the towing vehicle. In this situation, the pressure transducer is connected within a brake line to a master cylinder on the vehicle. Optionally, a connection between the trailer and the vehicle can be monitored to determine when a braking request should be generated.  
      Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.