Abstract:
A slave operated self-contained hydraulic brake system having an electric motor that is mounted on a gear housing. The electric motor moves a threaded rod in a lateral direction. Movement in a first direction results in contact of the rod with a master cylinder piston assembly within a master cylinder. Movement of the master cylinder piston assembly forces hydraulic fluid out of the master cylinder to actuate brakes of a towed vehicle. A pressure sensor is attached to the master cylinder and measures the hydraulic fluid pressures in master cylinder chamber. Movement of the rod in a second direction is detected by a reverse limit switch. Electrical signals are used to control the slave operated self-contained hydraulic brake system. The brake system communicates electrically with a brake control board. Sensors may be provided to provide information to a microprocessor on the control board to add control features to the brake system.

Description:
RELATED APPLICATION(S) 
     This application relates to provisional application Ser. No. 60/167,454 filed on Nov. 24, 1999. 
    
    
     TECHNICAL FIELD 
     The present invention relates to hydraulic brake systems, specifically to electronically and microprocessor controlled slave operated hydraulic brake systems that can be used as an independent brake system for towed trailers that operate in conjunction with the towing vehicle brake system. 
     BACKGROUND OF THE INVENTION 
     Typical hydraulic brake technology is based upon the use of a hydraulic accumulator boosted by a hydraulic pump. These brakes are powered and operated by the application of pressurized hydraulic fluid, which is supplied by a hydraulic accumulator. The accumulator is necessary for the brake system to provide a sufficient amount or volume of hydraulic fluid at a high enough pressure to actuate the braking system. In turn, a conventional hydraulic piston pump supplies the pressurized hydraulic fluid in the accumulator. For the accumulator to remain charged, the hydraulic pump must run continuously. Electric power is supplied to the hydraulic pump by the electric power system of the towing vehicle. A problem with typical hydraulic brake technology is that law requires that in the event that a trailer should become unattached from the towing vehicle, i.e., “breakaway” mode, the trailer brake systems must be able to apply the trailer brakes immediately and to keep the trailer brakes applied for 15 minutes. To achieve trailer brake application for 15 minutes, conventional hydraulic brake systems must keep the brake accumulator charged. The hydraulic pump must run for the duration of the fifteen minutes to maintain brake application. During the period of detachment from the towing vehicle, the electric power requirements of the hydraulic pump must be met by a separate battery carried by the trailer as part of the trailer brake system. The separate battery provides power for the brake system to lock the brake down after breakaway. A brake system that is capable of meeting the 15 minute brake application requirement but which does not require continuous running of a hydraulic pump is desirable. 
     SUMMARY OF THE INVENTION 
     An electrically operated hydraulic brake system is provided that has an electric motor that is mounted on a gear housing. A motor armature preferably has a 3″ shaft with a pinion gear attached to it. The pinion gear comes in contact with a spur gear. The spur gear, on its internal diameter, has an internal acme thread cut into it as an integral part of the gear body. The acme threaded rod has a matching external acme thread cut into its body that threads into the internal acme threads on the spur gear. The acme threaded rod comes in contact with the master cylinder piston assembly. The acme threaded rod is centered within a torque tube by a torque tube bearing. A master cylinder piston assembly is contained within a master cylinder, which also contains hydraulic fluid and a master cylinder spring. A pressure sensor is attached to the master cylinder and measures the hydraulic fluid pressure in the master cylinder chamber. The full reverse travel position of the acme threaded rod is detected by a reverse limit switch, which signals for the electric motor to stop. 
     A metal enclosure is attached to the gear housing that is attached to a master cylinder adapter to which the master cylinder is attached. Attached to the end of the master cylinder is the pressure sensor. The acme threaded rod extends through the spur gear, and the pinion gear comes in contact with the spur gear. The spur gear and pinion gear operate within the gear housing. 
     Electrical signals are used to control the slave operated self-contained hydraulic brake system. Three wires communicate the towing vehicle and the slave operated brake system, i.e., the brake system, that communicates electrically with a brake control board. One of these wires is a ground wire, another is a power wire to operate the brake system and the third is the brake signal wire that is used to actuate the brakes. The brake control board has three wires connected to a gear tooth counter, two wires to the brake system backup battery and four wires to control the brake system electric motor. Four additional sensors send signals to the brake control board. The four sensors include the pressure sensor with three wires, the master cylinder fluid level sensor with two wires, a load sensor with three wires and an anti-lock brake sensor with five wires. These sensors provide additional information to the microprocessor to add other control features to the brake system, such an anti-lock braking. The fluid level sensor will facilitate notification of low fluid conditions to the vehicle operator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the method and apparatus of the present invention may be obtained by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein: 
     FIG. 1 is an exploded view of the slave operated self-contained hydraulic brake system. 
     FIG. 1A is an exploded view of a second embodiment of the slave operated self-contained hydraulic brake system having a solid state rather than a mechanical reverse limit switch. 
     FIG. 2 is an end view of a slave operated self-contained hydraulic brake system. 
     FIG. 3 is a cutaway sectional view of the slave operated self-contained hydraulic brake system of FIG. 1 taken along section line  3 — 3  of FIG.  2 . 
     FIG. 3A is a cutaway sectional view of the slave operated self-contained hydraulic brake system of FIG. 1A taken along section line  3 — 3  of FIG.  2 . 
     FIG. 4 is an elevational view of the slave operated self-contained hydraulic brake system of FIG.  1 . 
     FIG. 5 is a cutaway sectional view of the slave operated self-contained hydraulic brake system of FIG. 1 taken along section line  5 — 5  of FIG.  4 . 
     FIG. 6 is a cross section view of the slave operated self-contained hydraulic brake system taken along section line  6 — 6  of FIG.  2 . 
     FIG. 7 is an overall block diagram of the control circuitry used for controlling the slave operated self-contained hydraulic brake system of FIG.  1 . 
     FIG. 8 is an illustrative circuit diagram of the control circuitry. 
     FIG. 9 is a graph depicting pressure increase over time of the slave operated self-contained hydraulic brake system of FIG.  1 . 
     FIG. 10 is a graph depicting pressure release over time of the slave operated self-contained hydraulic brake system of FIG.  1   
    
    
     DETAILED DESCRIPTION 
     Referring now to the figures and more particularly to FIGS. 1 through 6, shown is a hydraulic brake system  10 . Hydraulic brake system  10  has a gear housing  12  having a first side  14  and a second side  16 . An electric motor  18  has a motor housing  20  and a motor armature  22  (FIG.  3 ). Electric motor  18  is preferably a  12  volt DC motor. The motor housing  20  has a first end  24  and a second end  26 . The second end  26  of the electric motor housing  20  is affixed to the first side  14  of the gear housing  12 . Motor armature  22  has a first end  28  and a second end  30 . The motor armature  22  is rotatably mounted within the motor housing  20 . The second end  30  of the motor armature  22  is located proximate the gear housing  12 . 
     A spur gear  32  is rotatably mounted on the first side  14  of the gear housing  12 . Spur gear  32  preferably has 75 teeth and has internal threads  34  and external threads  36 . A pinion gear  38  is also rotatably affixed to the first side  14  of the gear housing  12 . The pinion gear  38  preferably has 15 teeth and is affixed to the motor armature  22 . Pinion gear  38  is in communication with the external threads  36  of the spur gear  32 . 
     A torque tube  40  has a first end  42  and a second end  44 . The second end  44  of the torque tube is affixed to the first side  14  of the gear housing  12 . A threaded rod  46  also has a first end  48  and a second end  50 . The threaded rod  46  extends through the gear housing  12  and is threadably coupled to the internal thread  34  of the spur gear  32 . The first end  48  of the threaded rod  46  is rotatably mounted within a bearing  52  within torque tube  40 . The second end  50  of the threaded rod  46  extends from the second side  16  of the gear housing  12 . 
     In the embodiment shown in FIGS.  1  and  2 - 6 , a switch activator  54  is slidably received within first end  42  of the torque tube  40 . A reverse limit switch  56  is mounted on the first end  42  of the torque tube  40  and is located proximate the first end  48  of the threaded rod  46 . A metal housing  58  is affixed to the first side  14  of the gear housing  12 . The metal housing  58  surrounds the electric motor  18  and the torque tube  40 . 
     In an alternate embodiment shown in FIGS. 1A and 3A, first end  48  of threaded rod  46  has a magnet (not shown) mounted on or in rod  46  which triggers a hall effect limit switch  57  mounted on torque tube  40 . Switch  57  indicates both reverse and forward limits. 
     A master cylinder adapter  60  is affixed to the second side  16  of the gear housing  12 . A master cylinder  62  has a first end  64  and a second end  66 . The first end  64  is affixed to gear housing  12 . A master cylinder piston assembly  68  is slidably located within the master cylinder  62 . The master cylinder piston assembly  68  (FIGS. 3 and 6) has a recessed area  70  on a first end  72 . Master cylinder piston assembly  68  also has a second end  74 . The recessed area  70  is provided to receive the second end  50  of the threaded rod  46 . 
     A master cylinder chamber  76  is defined by an inner surface of the master cylinder  62 , the second end  74  of the master cylinder piston assembly  68 , and the second end  66  of the master cylinder  62 . A primary cup or seal  78  is provided on the second end  66  of the master cylinder  62  for sealing hydraulic fluid  80  within the master cylinder chamber  76 . Seal  78  is preferably elastomeric. A spring plate  82  is provided adjacent seal  78 . A spring  84  is located within the master cylinder chamber  76 . The spring  84  biases against spring plate  82  and against second end  66  of master cylinder  62  for biasing threading rod  46  away from second end  66  of master cylinder  62 . 
     A pressure sensor  86  (FIGS. 1,  1 A,  4 ,  6  and  7 ) is provided on a master cylinder outlet  87 , which communicates with hydraulic lines that activate the brakes. Master cylinder outlet  87  is located on a second end  66  of the master cylinder  62 . Pressure sensor  86  communicates with master cylinder chamber  76 . A fluid reservoir  88  is preferably located adjacent the master cylinder chamber  76 . The fluid reservoir  88  communicates with the master cylinder chamber  76  via a first or fluid return port  90  and a second or timing port  92 . First port  90  and second port  92  are provided to allow hydraulic fluid to flow from the fluid reservoir  88  to the master cylinder chamber  76  as needed. A fluid level sensor  94  (FIGS. 1,  1 A,  4 ,  6  and  7 ) communicates with an interior of the fluid reservoir  88 . 
     Referring now to FIG. 7, a brake control system  100  is preferably carried on towed vehicle  101 . Brake control system  100  has a brake control board  102 , which has a micro processor  104 . FIG. 7 is a schematic of the various electrical signal and electrical power wires attached to the brake control board  102 . The brake control board  102  is in operative communication with the electric motor  18 , the pressure sensor  86 , the fluid level sensor  94 , a load sensor  106 , an anti-lock brake sensor  108 , limit switch  56  or  57 , and break-away switch  118 . Load sensor  106  is provided on a towed vehicle  101  to sense the weight of the towed vehicle  101 . A ground wire  110 , a power wire  112  and a brake signal wire  114  each communicate a towing vehicle  116  with the brake control system  100 . Break-away switch  118  is provided to break continuity and signal to control board  102  to stop towed vehicle  101  if it separates from the towing vehicle  116 . Limit switch  56  or  57  indicates the position of rod  46  to control board  102 , so that control board  102  can stop movement of rod  46  when it reaches its preferred limits of travel. 
     Towed vehicle  101  preferably carries a backup battery  120  that is in communication with the brake control board  102  via battery cables  122 . Limit switch wires  123  communicate the limit switch  56  or  57  with control board  102 . Load sensor wires  124  communicate the load sensor  106  to with the brake control board  102 . Anti-lock sensor wires  126  communicate the anti-lock brake sensor  108 , which is located on the towed vehicle  101  with the brake control board  102 . If the control board  102  detects a condition of wheel lock on towed vehicle  110 , control board  102  instructs electric motor  18  to move rod  46  such that pressure of hydraulic fluid  80  is adjusted to alleviate the wheel lock condition. Fluid level sensor wires  128  communicate the fluid level sensor  94  with the brake control board  102 . Pressure sensor wires  130  communicate the pressure sensor  86  with the brake control board  102 . 
     Referring now to FIG. 8, shown is a circuit diagram for controlling the electric motor  18  with the microprocessor  104 . 
     FIG. 8 shows how the microprocessor  104  is wired to the brake DC electric motor  18  as well as the orientation of the four field effect transistors (FETs), Forward High Side Driver  150 , Forward Low Side Driver  152 , Reverse High Side Driver  154 , Reverse Low Side Driver  156 , and the four diodes  158  orientation and wiring. 
     Referring to FIGS. 1-8, the mechanical operation of slave operated self-contained hydraulic brake system is as follows. When direct current electric power is applied to the armature  22  (FIG. 3) of electric motor  18 , the armature  22  rotates within the housing  20  of electric motor  18  and in turn rotates the pinion gear  38  (FIGS. 1,  3 ,  5  and  6 ). The teeth of the pinion gear  38  make contact with and match external threads or teeth  38  of the larger spur gear  32  (FIGS. 1,  3 ,  5  and  6 ) and rotate the spur gear  32 . This rotation results in a high rotational torque advantage upon the spur gear  32 , i.e., many rotations from the pinion gear  38  are required for one rotation of the spur gear  32 . The rotation of the spur gear  32  rotates internal threads  34  of the spur gear  32 , which engage threaded rod  46 . This rotation causes threaded rod  46  to move laterally depending upon the direction of the rotation of spur gear  32 . When advanced laterally in one direction, the threaded rod  46  makes contact with the master cylinder piston assembly  68  (FIGS.  3  and  6 ). 
     As a result of a brake application signal, the electric motor  18 , armature  22 , pinion gear  38  and spur gear  32  will rotate in a direction that causes the threaded rod  46  to move in the direction of the master cylinder piston assembly  68  and into the hydraulic master cylinder  62 . This displacement of the threaded rod  46  will in turn displace the master cylinder piston assembly  68 , compress the master cylinder piston spring  84 , and increase the pressure of the hydraulic fluid  80  within the hydraulic master cylinder  62 . Additionally, the increase in pressure of hydraulic fluid  80  will cause the hydraulic fluid  80  to flow through master cylinder outlet  87  and into a hydraulic line or connection  89  and apply hydraulic pressure to a brake  91  (FIG. 3) of trailer or towed vehicle  101 . The pressure application to the trailer system hydraulic brakes  91  will slow down and stop the towed vehicle or trailer  101 . 
     Release of the brake application signal results in current reversal to the electric motor  18 , resulting in opposite direction rotation of the armature  22 , pinion gear  38 , spur gear  32  and threaded rod  46 . This opposite rotation causes the threaded rod  46  to retract from within the hydraulic master brake cylinder  62 . The master cylinder piston assembly  68  follows this retraction due to force applied by the master cylinder piston spring  84 . This travel results in a pressure decrease of hydraulic fluid  80  and inflow into the master cylinder chamber  76  from the trailer brake system. This decrease in pressure results in retraction of the trailer system hydraulic brakes  91 . The system is capable of rapidly increasing and releasing the hydraulic pressure for precise modulation (FIGS.  9  and  10 ), which is especially beneficial in control for anti-lock braking. 
     Referring more particularly to FIG. 7, the brake control board  102  monitors the voltage of the battery  120  for optimum charged voltage range. At such time that the voltage of battery  120  falls below a predetermined optimum minimum charged voltage range, the brake control board  102  will direct charging of the battery  120  until the battery  120  charge reaches a maximum value of the predetermined voltage range. At that time, the brake control board  102  will stop the charging of the battery  120 . The result is that the battery  120  is always at optimum charge. The control board  102  also monitors and tests the battery  120  for charge capacity. For example, the control board  102  will put a temporary electric load on the battery  120  and test for voltage and voltage recovery time. At such time that the brake control board  102  detects that the battery  120  will no longer hold the predetermined required charge, it will send a message to the brake controller  100 , which is preferably located on the towing vehicle  116 , that the battery  120  needs replacement. 
     The signal from load sensor  106 , as shown in FIG. 7, communicates to the main board  102 , which monitors this signal for trailer weight. The main board microprocessor  104  is preferably programmed for a predetermined optimum brake pressure distribution curve and will adjust this curve based upon trailer weight. Therefore, optimum braking can be achieved automatically without operator intervention or adjustment. The optimum brake pressure distribution curve is preferably brake pressure as a function of linear travel of the acme threaded rod  46 . 
     Still referring FIG. 7, when the brakes in the towing vehicle  101  are applied, a resulting brake signal is generated that is proportional to the deceleration of the towing vehicle  101 . The brake signal is transmitted from towing vehicle  101  to brake control board  102 . The brake control board  102  receives the proportional brake signal and calculates the amount of pressure of hydraulic fluid  80  within master cylinder  62  that is proportional to this signal. The brake control board  102  then initiates electric power application to the DC brake motor  18 . This will result in rotation of the pinion gear  38 , which rotates the spur gear  32  that results in axial movement of the threaded rod  46  with an increase in pressure of hydraulic fluid  80  in the hydraulic master cylinder  62 . While applying power to the DC brake motor  18 , the brake control board  102  monitors the signal from pressure sensor  86  for the pressure of hydraulic fluid  80  within master cylinder  62 . When the monitored pressure from the pressure sensor  86  reads the same value as the calculated proportional pressure, the brake control board  102  will cease applying electrical power to the DC brake electric motor  18 . If the brakes of towing vehicle  116  are applied to a greater degree, the proportional brake signal will increase and the brake control board  102  will increase the pressure of hydraulic fluid  80  as described above. This will result in greater braking for the towed vehicle  101 . When the braking force of the towing vehicle  116  is reduced, the resulting proportional brake signal is reduced also, upon receipt of this proportional brake signal, the brake control board  102  reduces the pressure of hydraulic fluid  80 , which reduces the amount of trailer braking. 
     FIG. 8 is a schematic that shows how the microprocessor  104  on the brake control board  102  controls the brake DC electric motor  18  amount of rotation, direction of rotation and time of rotation. The circuit shown is a common “H” bridge with four diodes  158 . The positive 12 volts is applied to the top of the circuit and is isolated from the brake DC electric motor  18  by the orientation of the diodes  158 . The motor  18  is isolated from the 12 volt positive voltage on the outside lines due to the presence of four field effect transistors (FETs) referred to as the forward high side driver  150 , the forward low side driver  152  and the reverse high side driver  154  and the reverse low side driver  156 . When there is an absence of a signal from microprocessor  104  to these FETs, these FETs are in effect an open circuit. The application of a signal to an FET from the microprocessor  104  will cause these FETs to allow current to flow through them and becoming in effect a closed circuit. Therefore, when conditions are such that a program within the microprocessor  104  is to turn on the brake DC electric motor  18  in the forward direction, it will send a voltage signal to the forward high side driver FET  150  and the forward low side driver FET  152  that will in turn activate these two FETs such that these FETs will allow a voltage of 12 volts to be applied to the brake DC electric motor  18 . This voltage application will cause the brake DC electric motor  18  to turn in the “forward” direction and activate the brake system  100 . When the brake DC electric motor  18  needs to be turned off, the signals to these two FETs will be removed, the voltage will no longer be applied to the brake DC electric motor  18  and the motor will cease rotating. 
     Since this system uses a linear actuator instead of hydraulic accumulator and rotational hydraulic pump, it will be able to maintain brake application in the event of a breakaway. The system of the invention will lock the brake down after breakaway, easily meeting the 15 minute hold period required by law. A bleed button may be provided to relieve pressure within the system to allow the trailer to be moved off the road or moved about by holding down the button. Preferably, the bleed button is positioned such that it can be wedged open if need be. 
     The previous description is of a preferred embodiment for implementing the invention, and the scope of the invention should not necessarily be limited by this description. The scope of the present invention is instead defined by the following claims.