Abstract:
Methods and systems for a vital bus system for communicating data in a control system are provided. The system includes a plurality of data communication buses configured in a multiple redundant orientation and at least one safety supervisor module including a database including a plurality of logic rules. The logic rules are programmed to receive data from the plurality of data communication buses and to determine the validity of the received data from each bus using one or more of the plurality of the logic rules. If the received data is invalid, the logic rules are programmed to restore the validity of the data using one or more of the plurality of the logic rules. If the data can not be restored the logic rules are programmed to transmit an alert to the control system. Otherwise, the logic rules are programmed to transmit the validated data to an intended destination.

Description:
BACKGROUND 
     This invention relates generally to control systems, and more particularly to methods and systems for implementing high integrity control of safety critical control systems. 
     At least some known control systems, including control systems in nuclear power plants, aircraft, and other applications where high reliability is determined to be needed, are qualified for those applications after rigorous testing and certification of all the components of the system. Components that do not meet the rigorous criteria are segregated from the qualified components and are not permitted to perform safety-related functions. Such rigorous testing is expensive and time consuming and may be able to be accommodated in new construction of a new model of equipment or new construction of a power plant. However, retro-fitting components for a safety-related system into an existing system, for example, a standard locomotive can be cost prohibitive. 
     To permit trains to operate autonomously having what is termed a “zero man crew”, operation with de-skilled operators, or operation with a “single man crew” requires a level of safety and reliability of the train control system that heretofore does not exist. Replacing all existing control equipment in all existing locomotives represents a cost that will prohibit implementation of the zero-man-crew concept. A method and system for supervising the operation of low vitality equipment to permit high vitality operation of the vehicle control system is needed. 
     SUMMARY 
     In one embodiment, a high integrity safety critical bus system for communicating data in a control system includes a plurality of data communication buses configured in a multiple redundant orientation and at least one independent safety supervisor module communicatively coupled to and associated with at least two of the plurality of data communication buses, the safety supervisor including a database including a plurality of logic rules. The logic rules are programmed to receive data from the at least two of the plurality of data communication buses and to determine the validity of the received data from each bus using one or more of the plurality of the logic rules. If the received data is determined to be invalid, the logic rules are programmed to restore the validity of the data using one or more of the plurality of the logic rules. If the data can not be restored the logic rules are programmed to transmit an alert to the control system. Otherwise, the logic rules are programmed to transmit the validated data to an intended destination. Therefore, the vitality resides in the independent safety supervisor module rather than the plurality of the legacy or new equipment being required to achieve vitality. By requiring only the independent safety supervisor module portion of the architecture to be the vital element, legacy or new equipment with relatively low integrity may now be supervised by a vital independent safety supervisor module thus achieving system level vitality without the need to make numerous system elements vital as well. 
     In another embodiment, a method of implementing safety critical control of a vehicle includes determining an operational state of a plurality of redundant vehicle control devices using at least one of a plurality of logic rules wherein the vehicle control devices are configured to control a function of the vehicle. The method further includes blocking the operation of ones of the plurality of redundant vehicle control devices that are determined to be in an abnormal state, and transmitting control signals to a selected one of the plurality of redundant vehicle control devices. 
     In yet another embodiment, a vehicle includes a control system and a plurality of low-integrity systems configured to detect operating conditions of the vehicle wherein at least some of the plurality of low-integrity systems are configured to control the operation of the vehicle. The vehicle also includes a safety supervisor module communicatively coupled to and associated with at least one of a control device and an input device associated with each low-integrity system wherein the safety supervisor module is configured to monitor the state of each device using one or more logic rules. The safety supervisor module is also configured to remove control from a device determined to be in an abnormal state wherein supervision of the plurality of low-integrity systems by the safety supervisor module permits operation of the control system as a high-integrity system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cut away view of an exemplary Off-Highway Vehicle (OHV); 
         FIG. 2  is a schematic diagram of an exemplary architecture of a high integrity vehicle communication bus system in accordance with an embodiment of the present invention; and 
         FIG. 3  is an enlarged schematic block diagram further illustrating safety supervisor module, shown in  FIG. 2 , utilizing a safety critical control with miscompare fault detection and accommodation and independent safety supervision. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description illustrates the disclosure by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the disclosure, describes several embodiments, adaptations, variations, alternatives, and uses of the disclosure, including what is presently believed to be the best mode of carrying out the disclosure. The disclosure is described as applied to a preferred embodiment, namely, implementing safety critical control of a vehicle utilizing a safety critical control with miscompare fault detection and accommodation and independent safety supervision. However, it is contemplated that this disclosure has general application to load elevators, jacks, positioners, and other machines that provide an application of force in vertical, horizontal, and a combination of orientations in industrial, commercial, and residential applications. 
       FIG. 1  is a partial cut away view of an exemplary Off-Highway Vehicle (OHV). In the exemplary embodiment, the OHV is a locomotive  10 . Locomotive  10  includes a platform  12  having a first end  14  and a second end  16 . A propulsion system  18 , or truck is coupled to platform  12  for supporting, and propelling platform  12  on a pair of rails  20 . An equipment compartment  22  and an operator cab  24  are coupled to platform  12 . An air and air brake system  26  provides compressed air to locomotive  10 , which uses the compressed air to actuate a plurality of air brakes  28  on locomotive  10  and railcars (not shown) behind it. An auxiliary alternator system  30  supplies power to all auxiliary equipment and is also utilized to recharge one or more on-board power sources. An intra-consist communications system  32  collects, distributes, and displays consist data across all locomotives in a consist. 
     A cab signal system  34  links the wayside (not shown) to a train control system  36 . In particular, system  34  receives coded signals from a pair of rails  20  through track receivers (not shown) located on the front and rear of the locomotive. The information received is used to inform the locomotive operator of the speed limit and operating mode. A distributed power control system  38  enables remote control capability of multiple locomotive consists coupled in the train. System  38  also provides for control of tractive power in motoring and braking, as well as air brake control. 
     An engine cooling system  40  enables engine  42  and other components to reject heat to cooling water. In addition, system  40  facilitates minimizing engine thermal cycling by maintaining an optimal engine temperature throughout the load range, and facilitates preventing overheating in tunnels. An equipment ventilation system  44  provides cooling to locomotive  10  equipment. 
     A traction alternator system  46  converts mechanical power to electrical power which is then provided to propulsion system  18 . Propulsion system  18  enables locomotive  10  to move and includes at least one traction motor  48  and dynamic braking capability. In particular, propulsion system  18  receives power from traction alternator  46 , and through traction motors  48  moves locomotive  10 . Locomotive  10  systems are monitored and/or controlled by an energy management system  50 . 
     Energy management system  50  generally includes at least one computer that is programmed to perform the functions described herein. Computer, as used herein, is not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a processor, a microprocessor, a microcontroller, a programmable logic controller, an application specific integrated circuit, and another programmable circuit, and these terms are used interchangeably herein. 
       FIG. 2  is a schematic diagram of an exemplary architecture of a high integrity vehicle communication bus system  200  in accordance with an embodiment of the present invention. In the exemplary embodiment, communication bus system  200  includes a plurality of data buses, which may be designated by channel numbers, for example, a channel ‘A’ bus  202  and a channel ‘B’ bus  204 . Although described with reference to two redundant communication buses, communication bus system  200  may include any number of redundant channels. 
     A plurality of components are coupled separately to each bus. Separation between buses may comprise electrical separation or may include physical separation in addition to electrical separation. Physical separation generally permits a greater degree of integrity because common mode failures affecting one bus is physically isolated from each other bus facilitating minimizing the possibility of a single incident affecting more than one bus. The components include a locomotive computer  206 , a database  208 , an event log  210 , and a maintenance computer  212 . A channel ‘A’ interface module  214  is coupled to channel ‘A’ bus  202  and a channel ‘B’ interface module  216  is coupled to channel ‘B’ bus  204 . Each interface module  214  and  216  is configured to receive analog and digital signals from vehicle sub-systems and transmit data representing the received analog and digital signals onto respective buses  202  and  204 . The vehicle sub-systems communicating through interface modules  214  and  216  include but are not limited to a speed data sub-system  218 , a power cutoff switch/power interrupt relay (PCS/PIR) sub-system  220  to remove tractive effort, an emergency brake valve sub-system  222 , an automatic brake valve sub-system  224 , and an independent brake valve sub-system  226 . 
     In the exemplary embodiment, buses  202  and  204  are also configured to receive signals from respective data acquisition modules  228  and  230 . Data acquisition modules  228  and  230  are configured to receive signals from vehicle components configured to acquire information relating to the environment proximate the vehicle. The components include, but are not limited to an intra-train distributed power (DP) radio  232 , a global positioning satellite (GPS) system  234 , a wayside data radio  236 , a train display  238 , a user interface  240 , and a video camera  242 . 
     Also in the exemplary embodiment, buses  202  and  204  are configured to transmit signals to respective control function modules  244  and  246 . Control function modules  244  and  246  are further configured to receive digital signals representing commands and transmit analog and digital signals representing the received commands from respective buses  202  and  204  to associated vehicle control sub-systems. Such sub-systems include but are not limited to an emergency brake sub-system  248 , an independent brake sub-system  250 , a train brake sub-system  252 , a positive train control (PTC) sub-system  254 , a distributed power (DP) sub-system  256 , and a trip optimizer (TO) sub-system  258 . 
     Each of emergency brake sub-system  248 , independent brake sub-system  250 , train brake sub-system  252 , PTO sub-system  254 , distributed power (DP) sub-system  256 , and trip optimizer (TO) sub-system  258  of one channel is configured to cross-talk with like sub-systems of any other channel using a cross talk bus  262 . The number of channels depends on the number of communication buses utilized in a particular installation. As used herein, crosstalk defines communication between two or more of the sub-systems so that their results can be checked. 
     System  200  includes an independent safety supervision module  264  communicatively coupled to each communication bus utilized in system  200 . Safety supervision module  264  includes a plurality of logic rules that are applied to data in real-time as the data is transmitted on the communication buses. Safety supervision module  264  processes the rules during transmission of the data to identify and localize faults associated with the communication buses and/or the sub-systems communicatively coupled to the buses. In some cases, the rules may utilize other channel data, historical, or derived data to restore corrupted or missing data. In other cases, when data faults are detected, safety supervisor module  264  blocks the transmission of the data to other components. Utilizing the rules stored in safety supervisor module  264  a commercial off the shelf component or a component having a lower safety integrity level (SIL) than is regulatorily required for the system may be made to comply with the regulatory requirements for the system using safety supervisor module  264 . 
       FIG. 3  is an enlarged schematic block diagram further illustrating safety supervisor module  264  (shown in  FIG. 2 ) utilizing a safety critical control with miscompare fault detection and accommodation and independent safety supervision. In the exemplary embodiment, a safety device  302  such as a locomotive throttle actuator is monitored by respective controlling trip optimizer sub-system  258 . A second safety device  304  such as a redundant throttle actuator is monitored by its respective controlling trip optimizer sub-system  258 . Safety devices  302  and  304  are also monitored by safety supervisor module  264 . Independent monitoring of safety devices  302  and  304  permits additional checking of the respective outputs of safety devices  302  and  304  such that components not initially designed for such operation may be qualified to a higher safety level such as for example, a SIL 4 level. 
     The term “safety” as used herein is not a representation that embodiments of the present invention will make a process safe or that other systems will produce unsafe operation. Rather, safety refers to the probability of an un-acceptable behavior being reduced to an acceptable level as determined by interested parties. Safety, with respect to vehicle operations depends on a wide variety of factors outside of the scope of the present disclosure including design of the control system, installation, and maintenance of the components of the control system, and the cooperation and training of individuals using the control system. Although embodiments of the present invention are intended to be highly reliable, all physical systems are susceptible to failure and provision must be made for such failure. 
     As used herein “high reliability” refers generally to systems that guard against the propagation of erroneous data or signals by detecting error or fault conditions and signaling their occurrence and/or entering into a predetermined fault state. 
     Safety Integrity Level (SIL) is defined as a relative level of risk-reduction provided by a safety function, or to specify a target level of risk reduction. Four SIL levels are defined, with SIL4 being the most dependable and SIL1 being the least. A SIL is determined based on a number of quantitative factors in combination with qualitative factors such as development process and safety life cycle management. The requirements for a given SIL are not consistent among all of the functional safety standards. The international standard IEC 61508 defines SIL using requirements grouped into two broad categories: hardware safety integrity and systematic safety integrity. A device or system must meet the requirements for both categories to achieve a given SIL. 
     The SIL requirements for hardware safety integrity may be based on a probabilistic analysis of the device. To achieve a given SIL, the device must have less than the specified probability of dangerous failure and have greater than the specified safe failure fraction. These failure probabilities are calculated by performing for example, a Failure Modes and Effects Analysis (FMEA). The actual targets required vary depending on the likelihood of a demand, the complexity of the device(s), and types of redundancy used. 
     The SIL requirements for systematic safety integrity define a set of techniques and measures required to prevent systematic failures (bugs) from being designed into the device or system. These requirements can either be met by establishing a rigorous development process, or by establishing that the device has sufficient operating history to argue that it has been proven in use. Electric and electronic devices can be certified for use in functional safety applications according to IEC 61508, providing application developers the evidence required to demonstrate that the application including the device is also compliant. 
     As will be appreciated by one skilled in the art and based on the foregoing specification, the above-described embodiments of the disclosure may be implemented using computer programming or engineering techniques including computer software, firmware, hardware or any combination or subset thereof, wherein the technical effect is implementing safety critical control of a vehicle utilizing a safety critical control with miscompare fault detection and accommodation and independent safety supervision. Any such resulting program, having computer-readable code means, may be embodied or provided within one or more computer-readable media, thereby making a computer program product, i.e., an article of manufacture, according to the discussed embodiments of the disclosure. The computer readable media may be, for example, but is not limited to, a fixed (hard) drive, diskette, optical disk, magnetic tape, semiconductor memory such as read-only memory (ROM), and/or any transmitting/receiving medium such as the Internet or other communication network or link. The article of manufacture containing the computer code may be made and/or used by executing the code directly from one medium, by copying the code from one medium to another medium, or by transmitting the code over a network. 
     Vehicle control systems may include special purpose computers used in controlling the vehicle. Under the direction of a stored control program, the vehicle control system examines a series of inputs reflecting the status of the vehicle and surrounding environment and changes a series of outputs controlling the vehicle. The inputs and outputs may be binary or analog, providing a value within a continuous range. The inputs may be obtained from sensors attached to the controlled equipment and the outputs may be signals to actuators on the controlled equipment. 
     The above-described methods and systems of controlling a vehicle are cost-effective and highly reliable. The methods and systems facilitate utilizing existing, commercial off the shelf, and lower vitality or safety rated equipment in higher safety integrity level systems using independent safety monitoring modules that are configurable to accommodate a varied type of equipment in a cost-effective and reliable manner. 
     While embodiments of the disclosure have been described in terms of various specific embodiments, those skilled in the art will recognize that the embodiments of the disclosure can be practiced with modification within the spirit and scope of the claims.