Management & Operations

Un-Wired for Success: The Benefits of Multiplexing in Buses

Posted on August 1, 2003 by By K.R. Levin

Gone are the days of the huge ancient diesel bus rumbling down the highway spewing clouds of choking fumes. Maintaining and repairing those behemoths was not an easy task. Today’s bus is sleeker, lighter, more fuel-efficient and it’s maintained, more often than not, by technicians sporting state-of-the-art laptop computers. The old wiring harness that used to wreak havoc on the psyche of mechanics trying to trace a faulty circuit has been replaced by plug-in modules that can be fixed or reprogrammed in a matter of minutes as compared to hours of trial-and-error fault chasing. Multiplexing simplified Multiplexing is a method of combining several signals for communication on a shared channel or medium. This is much like cable television in the home having the ability to carry many channels through a single wire. Multiplexing began in the telecommunications industry essentially by being able to put more than one call down a single line. And the best method of explaining this complex technology still lies in the communication example. In the old method of wiring, when two people talked to each other they required one wire. When a third person was added, two more wires had to be connected in order for everyone to communicate with each other. As a fourth person joins the conversation, three more wires had to be added to join all the parties. A fifth person increased the wiring complexity geometrically and more people multiplied the problem almost exponentially. This has been the general trend with vehicle wiring as well. As the transportation industry added more and more features to vehicles, the complexity of the electrical system grew to the point where it became unreliable, difficult to understand and often challenging to troubleshoot. This was compounded in bigger vehicles like buses, where large bundles of wires had to be strung from one end of the vehicle to the other. This, of course, made for a convoluted engineering challenge as well as increasing the overall weight of the vehicle. Origins of multiplexing Using the telecommunications example, two people conversing send their signals through a multiplex module, which distributes the signal. Additional people joining the conversation only add one wire per person to the multiplex module. In a vehicle’s electrical system, this in essence means that different components can communicate with each other and the operator more efficiently and effectively. Stated succinctly, multiplexing can:

  • Increase dependability by using fewer electrical components.
  • Decrease the cost of maintenance of the electrical system.
  • Reduce the complexity of harness and connection points. I/O Controls has been producing multiplex modules for 10 years, beginning with the Los Angeles County Metropolitan Transportation Authority (MTA). “We converted one of their buses using I/O Control Multiplex modules to prove the concept. We reduced a lot of wires and, consequently, weight and made the bus more reliable. That particular bus is still running today,” recounts Y-Ping Chu, vice president of sales and marketing for I/O Controls. Bob Neitzel, a bus marketing manager at International Truck and Engine Corp., notes that multiplexing has been an evolutionary process, with the dashboard gauges becoming the first to be multiplexed. Neitzel credits manufacturers with changing the gauges from direct read. “They instead read from a computer and that increased reliability. This consequently reduced wiring complexity,” he says. In a school bus there might be an eight-light system operated by a single switch. As much as 20 to 40 amperes could be running through that switch every time the circuit is on. “That tends to really kill switches,” Neitzel says. “By controlling the circuit with an electronic relay, the power is taken off the switches.” And that’s a large part of what multiplexing does; it takes high amperages off switches, thereby increasing reliability. “The beginning of multiplexing was to improve reliability, reduce current load on switches and reduce wiring. But now with the addition of computer controls we’re moving into an area of virtual control, interlocking safety features, and that’s just the tip of the iceberg.” Vansco Electronics Ltd. has been a leader in manufacturing multiplex modules for a numbers of years. It has developed modules for the transportation industry that satisfy the demanding J1455 environmental standard that includes criteria for temperature, electrical transients, pressure wash and immersion. “These modules control any of the input functions that the chassis manufacturer wants to incorporate. Any switches on the dash — pressure switches, fuel sensors, air pressure sensing, ABS,” explains Ken Landgraff, applications engineer for Vansco. “The outputs can be used for lights, solenoid valves, etc. There are bi-directional outputs that can be used to interface with transmission or engine ECUs. So you can hardwire to the engine and transmission ECU inputs through these modules. Because our system is programmable, it allows for a lot of flexibility and optimization.” Practical applications Multiplexing architecture has been incorporated into automobile design for a couple of decades, but especially now with more complex vehicles being produced every year. In the bus manufacturing sector, multiplexing has found more applications and maintenance benefits than anyone ever expected. From a driver’s standpoint, the new multiplexing buses can run diagnostics of their systems from the moment the bus’ battery system is activated. “On some of our buses, we have a system that’s working with I/O Controls that will actually do a pre-trip inspection for the operator,” says Mike Bottone, director of vehicle technology at the MTA. “The driver pushes a button, and it will cycle all digital parts. It turns on the lights, activates the horn, functions the wheelchair lift, kneels the bus, checks the starter and checks the codes on the engine and the transmission. It basically runs a complete diagnostic of the vehicle,” Bottone says. The bus then tells the operator to proceed or provides a warning light on those areas that may have a problem. Another innovation that is becoming more prevalent with multiplexing is the ability to have external remote sensing devices. Cameras in the bus’ blind spots enhance safety factors when drivers have to change lanes or back up. The school bus industry is always on the cutting edge when it comes to safety precautions. Some multiplexed buses are equipped with external radar transmitters that will detect the presence of a child or person in the danger zone of the vehicle. International’s Neitzel says the multiplex system International’s designed for use on one of its buses disables the transmission from going into gear when the wheelchair lift is in use. “We can send another signal that doesn’t allow the parking brake to go off. It provides another level of electronic architecture which really enables it to do things we have only thought about until now.” Maintenance issues One of the greatest benefits of this technology is the ease of troubleshooting electrical problems in multiplexed buses. What used to take hours now can take only minutes to accomplish. “Electrical gremlins are always challenging to find, and multiplexing makes it easy to find the gremlins,” says Neitzel. When a bus comes into the yard, mechanics can plug laptop computers into the vehicle and get a complete rundown of most every mechanical and electronic system. Says Bottone, “Once mechanics realize they can run down a fault tree or a code list and the system can identify exactly what they’re looking for in fewer hours than ever before, they’re happy. The quicker they diagnose something, the quicker it can be fixed, and the faster that bus is put back on the street.” The tangible benefit is the reduced number of road calls on a bus. Bottone notes that if 100 buses had failures in the course of the day, 60% of them were electrical in nature. “With the multiplexing system and its diagnostics, it basically points you to the exact problem,” he says. Vansco modules are auto-programmed to the point where they can be switched from one vehicle to another even if the two vehicles are of different types. “Let’s say you have three modules on your vehicle,” says Vansco’s Landgraff. “Something happens to one of the modules and you need to remove it. You can replace it with a module from another vehicle or a new one, and it doesn’t even have to be from the same type of vehicle. It will recognize that it’s different from the other two modules on board and program itself with the same program as the other two modules. You don’t need any programming tools.” NYCT cites versatility New York City employs one of the largest bus fleets in the entire country. Steven Lu is the superintendent of technical services for New York City Transit (NYCT). As an electrical engineer, Lu has been closely involved in the design and maintenance of the bus fleet. He enjoys the benefits that multiplexing affords him in being able to experiment and easily change a vehicle’s systems. Says Lu, “We wanted to make the headlights come on in the bus when a fire was detected. To do that in a conventionally wired bus system was very labor-intensive. With a multiplexed system, all you have to do is program it and once the program has been validated, it can be downloaded into the system and it’s done.” Lu goes on to explain how easy it is for him if he wants to do something out of the ordinary; he can test it and then restore or reverse the process at a minimum of cost. As it is with nearly everything, bottom line cost is where management looks when evaluating any new system or program. Multiplexing has undeniably reduced labor costs. Mike Wehr, maintenance director with Milwaukee County Transit System says the multiplex system is approximately 30% less costly to operate in comparison to a standard bus electrical system. “The multiplex introduction reduced road-calls substantially,” he says. “The percentage of the cost per mile attributed to electrical repairs also saw a reduction.” Training and downsides Of course, when any transition is made from one technology to another, the issue of training maintenance personnel becomes paramount. In some cases, the learning curve has been steep. Old school mechanics must learn to embrace the new technology, and most have realized how much easier their job is made with multiplexing. I/O Controls’ Chu believes there is a culture change inherent with converting to a new technology such as multiplexing. “It has to do with training,” he says. “That is the major hurdle in the beginning. Once people are trained, then the system becomes very user-friendly. It’s not because the system is difficult, it’s because they have never been exposed to it.” “The ease of troubleshooting and diagnosing electrical problems using a laptop computer has proven to be a great advantage,” says Wehr. “On the downside, the seasoned mechanic who used a test light to find electrical problems has some difficulty making the transition.” Wehr explains that in the beginning of their transition to multiplexing, there were some concerns about the employees being able to adapt to the multiplex technology, but with training and the continued purchase of basically the same system, the potential mountain became a bump in the road. Investment in new technologies goes hand in hand with investment in training. MTA’s Bottone reinforces this. “We’re actually bringing mechanics up to speed in electronic systems. We have them in class where they’re learning to do diagnostics through laptops, reading fault codes and working with lower voltages versus the 12- and 24-volt systems they’re used to dealing with,” he says. Are there any downsides with multiplexing technology itself? If there are, they are so minimal as to be overwhelmed with the positive aspects. It is a complex system and requires maintenance people to be on their game and pay attention to what they’re doing. Wiring fires are for the most part non-existent because the system monitors itself and cuts off abnormal loads. Battery is key link Bottone feels the only vulnerability is being sure the batteries are in good shape with an adequate charging system. “If the system sees a significant drop in voltage or alternator output, it gives you a hiccup and then you have a little bit of a bigger problem,” he says. “We’ve learned to practice better battery management, alternator system inspections and check-outs to make sure everything is working up to specifications.” Most engineers and bus manufacturers look beyond the downsides and vulnerabilities and envision only limitless possibilities. The future of multiplexing The bus of the future (the very, very near future) will pull into the maintenance yard and automatically download any fault information wirelessly into the supervisor’s office. That information will then be printed out and automatically disseminated to the appropriate departments. In fact, these systems are being offered by Motorola and Orbital, but are still expensive. Vansco is exploring the wireless alternative. Says Landgraff, “We’re looking at not even waiting for the buses to pull into a certain point by having that information beamed in real-time from wherever the buses might be.” NYCT also has a pilot program in place to test the potential of wireless data transfer. “We’re using the multiplex system to broadcast information to another wireless transfer device and collect it on the other side,” says Lu. “Information like how many times the wheelchair device has been cycled, how many times the brakes have been used and so on.” I/O Controls is experimenting with a wireless identification system for drivers. With all the heightened concerns about security, drivers would have to input a special code into the bus before they can start the vehicle. Using wireless technology, the bus can be activated or deactivated at the garage. “The driver keys in a security code, which can then be checked wirelessly against the database in the dispatch office. If all the information is correct then a signal is sent back to the bus that allows it to start,” says Chu. For these transit authorities, multiplexing has made their jobs easier and their vehicles more reliable. The open architecture of multiplexing allows one layer to be built upon another. The crest of the multiplexing mountain has been reached, and now transit authorities can expect far greater reliability resulting in a much smoother ride. K.R. Levin is a freelance writer in North Hollywood, Calif.
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