Abstract:
The invention relates to a by-wire brake system. There is a need for a trailer brake control circuit for a by-wire brake system. A brake control circuit for trailer brakes in a by-wire brake system includes a hydraulic pump or a supply of pressurized air, a hydraulic reservoir or an air vent, a pair of solenoid operated proportional valves for controlling communication between the pump, the reservoir and the trailer brakes, and a pair of solenoid operated shutoff valves, each controlling communication between the trailer brakes and a corresponding one of the proportional valves.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a control system or circuit for trailer brakes in a by-wire hydraulic or pneumatic brake system. 
   BACKGROUND OF THE INVENTION 
   In a by-wire brake system at least some of the traditional components such as the pumps, hoses, fluids, belts and brake boosters and master cylinders are replaced with electronic sensors and actuators. 
   There is a need for redundant electro-hydraulic and electro-pneumatic control circuits for trailer brakes in a by-wire brake system. The circuits must be capable of functioning even if one of the internal components fail, while at the same time, still achieving all of the requirements for a hydraulic or pneumatic trailer brake system. 
   SUMMARY OF THE INVENTION 
   Accordingly, an object of this invention is to provide a control circuit for electro-hydraulic and electro-pneumatic by-wire trailer brakes which can function even if one of the internal components fails. 
   This and other objects are achieved by the present invention, wherein electro-hydraulic and electro-pneumatic control circuits for trailer brakes in a by-wire brake system include a pair of solenoid operated proportional valves and a pair of solenoid operated shutoff valves. These valves control communication between a pressure source, a reservoir and the trailer brakes. Each shutoff valve is between a trailer brakes and a corresponding one of the proportional valves. Thus, the circuit includes four electro-hydraulic or electro-pneumatic valves. The circuit includes a pair of valves on each side of the circuit. Each side of the circuit includes a proportional valve to achieve the trailer braking function and a shutoff valve to stop the proportional valve from working unintentionally. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of a control circuit of the present invention for hydraulic brakes; 
       FIG. 2  is a schematic diagram of a control circuit of the present invention for pneumatic trailer brakes and non-spring park brakes; and 
       FIG. 3  is a schematic diagram of a control circuit of the present invention for pneumatic trailer brakes and spring park brakes. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a brake control circuit  10  is installed as part of a by-wire brake system (not shown) on a vehicle (not shown) such as a tractor, and is connected to trailer brakes  12  on a trailer (not shown). Brake control circuit  10  includes four solenoid operated valves  18 ,  20 ,  22  and  24 , and is connected to a pump  14  or source of pressurized hydraulic fluid, and to a fluid reservoir  16 . 
   First solenoid operated proportional valve  18  has a first port  30  connected to the source  14 , a second port  32  connected to the reservoir  16 , and a third port  34 . Valve  18  also includes a first valve member  40  movable to a first position wherein the first port  30  is blocked and the second port  32  is communicated with the third port  34 . Vale member  40  is also movable to a second position wherein the second port  32  is blocked and the first port  30  is communicated with the third port  34 . A spring  42  biases the first valve member  40  to its first position. A solenoid  44  is operable to move the first valve member  40  to its second position; 
   Second solenoid operated proportional valve  20  has a first port  50  connected to the source  14 , a second port  52  connected to the reservoir  16 , and a third port  54 . A second valve member  60  is movable to a first position wherein the first port  50  is blocked and the second port  52  is communicated with the third port  54 . Valve member  60  is also movable to a second position wherein the second port  52  is blocked and the first port  50  is communicated with the third port  54 . A spring  62  biases the second valve member  60  to its first position. A solenoid  64  is operable to move the second valve member  60  to its second position; 
   First solenoid operated shutoff valve  22  has a first port  70  connected to the third port  34  of the first valve  18  and a second port  72  connected to the trailer brake  12 . Valve  22  has a third valve member  74  movable to a first position wherein the first and second ports  70  and  72  are blocked, and movable to a second position wherein the first port  70  is communicated with the second port  72 . A spring  76  biases the third valve member  74  to its first position. A solenoid  78  is operable to move the third valve member  74  to its second position. 
   Second solenoid operated shutoff valve  24  has a first port  80  connected to the third port  54  of the second valve  20  and a second port  82  connected to the trailer brake  12 . Valve  24  includes a fourth valve member  84  movable to a first position wherein the first and second ports  80  and  82  are blocked, and movable to a second position wherein the first port  80  is communicated with the second port  82 . A spring  86  biases the fourth valve member  84  to its first position. A solenoid  88  is operable to move the fourth valve member  84  to its second position. 
   The circuit  10  also includes a first pilot line  90  which communicates the third port  34  of the first valve to an end of the first valve member  40 . A second pilot line  92  communicates the third port  54  of the second valve  20  to an end of the second valve member  60 . A load sense line  94  communicating the second ports  72 ,  82  of the third and fourth valves  22 ,  24  to the reservoir  16  via a restriction  96 . 
   The proportional valves  18  and  20  can be controlled in response to a variety of inputs, such as tractor brake pressure, pedal position, change in speeds, and/or other inputs. 
   The output pressure to the trailer brakes  12  is preferably limited by pressure limiting valve (not shown) to 150 bar maximum. Two pressure sensor  98  and  100  make possible fault checking by an electronic control unit (not shown). The pressure sensors  98 ,  100  in conjunction with the proportional valve that is being activated will provide three values to compare to determine which component is malfunctioning. 
   Referring now to  FIG. 2 , a brake control circuit  110  is installed as part of a by-wire pneumatic brake system (not shown) on a vehicle (not shown) such as a tractor, and is connected to an electronic trailer brake controller  111  and to pneumatic non-spring trailer brakes  112  on a trailer (not shown). Brake control circuit  110  includes four solenoid operated valves  118 ,  120 ,  122  and  124 , and is connected to a tank  114  or source of pressurized air and an air vent  116 . A regulating valve  108  regulates the pressure in tank  114  supplied by air compressor  106 . 
   First solenoid operated proportional valve  118  has a first port  130  connected to the tank  114 , a second port  132  connected to the vent  116 , and a third port  134 . Valve  118  also includes a first valve member  140  movable to a first position wherein the first port  130  is blocked and the second port  132  is communicated with the third port  134 . Valve member  140  is also movable to a second position wherein the second port  132  is blocked and the first port  130  is communicated with the third port  134 . A spring  142  biases the first valve member  140  to its first position. A solenoid  144  is operable to move the first valve member  140  to its second position. 
   Second solenoid operated proportional valve  120  has a first port  150  connected to the source  114 , a second port  152  connected to the reservoir  116 , and a third port  154 . A second valve member  160  is movable to a first position wherein the first port  150  is blocked and the second port  152  is communicated with the third port  154 . Valve member  160  is also movable to a second position wherein the second port  152  is blocked and the first port  150  is communicated with the third port  154 . A spring  162  biases the second valve member  160  to its first position. A solenoid  164  is operable to move the second valve member  160  to its second position; 
   First solenoid operated shutoff valve  122  has a first port  170  connected to the third port  134  of the first valve  118 , a second port  171  connected to the vent  116  and a third port  172  connected to the trailer brake  112  via a shuttle valve  138 . Valve  122  has a third valve member  174  movable to a first position wherein the first port  170  is blocked and second port  171  is communicated to third port  172 , and movable to a second position wherein the second port  171  is blocked and port  170  is communicated with the second port  172 . A spring  176  biases the third valve member  174  to its first position. A solenoid  178  is operable to move the third valve member  174  to its second position. 
   Second solenoid operated shutoff valve  124  has a first port  180  connected to the third port  154  of the second valve  120 , a second port  181  connected to the vent  116  and a third port  182  connected to the trailer brake  112  via shuttle valve  138 . Valve  122  has a third valve member  184  movable to a first position wherein the second port  181  is blocked and first port  180  is communicated to third port  182 , and movable to a second position wherein the first port  180  is blocked and port  181  is communicated with the third port  182 . A spring  186  biases the third valve member  184  to its first position. A solenoid  188  is operable to move the third valve member  184  to its second position. Valve  138  communicates the higher pressure to the trailer brakes  112 . 
   The circuit  110  also includes a first pilot line  190  which communicates the third port  134  of the first valve to an end of the first valve member  140 . A second pilot line  192  communicates the third port  154  of the second valve  120  to an end of the second valve member  160 . 
   Referring now to  FIG. 3 , a brake control circuit  210  is installed as part of a by-wire brake system (not shown) on a vehicle (not shown) such as a tractor, and is connected to an electronic trailer brake controller  211  and to pneumatic trailer service brakes  212  and pneumatic spring trailer park brakes  213  on a trailer (not shown). Brake control circuit  210  includes four solenoid operated valves  218 ,  220 ,  222  and  224 , and is connected to a tank  214  or source of pressurized air and an air vent  216 . A regulating valve  208  regulates the pressure in tank  214  supplied by air compressor  206 . 
   First solenoid operated proportional valve  218  has a first port  230  connected to the tank  214 , a second port  232  connected to the vent  216 , and a third port  234 . Valve  218  also includes a first valve member  240  movable to a first position wherein the first port  230  is blocked and the second port  232  is communicated with the third port  234 . Valve member  240  is also movable to a second position wherein the second port  232  is blocked and the first port  230  is communicated with the third port  234 . A spring  242  biases the first valve member  240  to its first position. A solenoid  244  is operable to move the first valve member  240  to its second position. 
   Second solenoid operated proportional valve  220  has a first port  250  connected to the source  214 , a second port  252  connected to the reservoir  216 , and a third port  254 . A second valve member  260  is movable to a first position wherein the first port  250  is blocked and the second port  252  is communicated with the third port  254 . Valve member  260  is also movable to a second position wherein the second port  252  is blocked and the first port  250  is communicated with the third port  254 . A spring  262  biases the second valve member  260  to its first position. A solenoid  264  is operable to move the second valve member  260  to its second position. 
   First solenoid operated shutoff valve  222  has a first port  270  connected to the third port  234  of the first valve  218 , a second port  271  connected to the vent  216  and a third port  272  connected to the pneumatic trailer service brake  212 . Valve  222  has a third valve member  274  movable to a first position wherein the first port  270  is blocked and second port  271  is communicated to third port  272 , and movable to a second position wherein the second port  271  is blocked and port  270  is communicated with the second port  272 . A spring  276  biases the third valve member  274  to its first position. A solenoid  278  is operable to move the third valve member  274  to its second position. 
   Second solenoid operated shutoff valve  224  has a first port  280  connected to the third port  254  of the second valve  220 , a second port  281  connected to the vent  216  and a third port  282  connected to the trailer spring-applied park brake  213 . Valve  222  has a third valve member  284  movable to a first position wherein the first port  280  is blocked and second port  281  is communicated to third port  282 , and movable to a second position wherein the second port  281  is blocked and port  280  is communicated with the third port  282 . A spring  286  biases the third valve member  284  to its first position. A solenoid  288  is operable to move the third valve member  284  to its second position. 
   The circuit  210  also includes a first pilot line  290  which communicates the third port  234  of the first valve to an end of the first valve member  240 . A second pilot line  292  communicates the third port  254  of the second valve  220  to an end of the second valve member  260 . 
   With these circuits  10 ,  110  and  210  the trailer brakes  12 ,  112 ,  212  and  213  can be operated even if one of the internal components fail, while still achieving all of the requirements for a hydraulic or pneumatic trailer brake system in a by-wire brake system. The circuit includes four valves to provide redundancy to ensure brake function in the event of a single valve failure. The circuits include redundancy on each side, with each side having a proportional valve to achieve the trailer braking function and a shut off valve to stop the proportional valve from working unintentionally. The two proportional valves can be used to achieve the braking function either individually or in conjunction with one another. The shut off valves are used to shut off one of the proportional valves if it is malfunctioning or to prevent back flow when only one valve is used. 
   The proportional valves can be sized one of three ways: a) So that service brake mode uses both valves (valves sized for 55-60% of flow rate required). b) So that one valve is used for service brakes with 100% of the flow, and the second valve is at a reduced flow rate (55-60%). c) So that both valves, individually, can be used for service brakes with each being able to flow 100% of the flow. 
   While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.