Skip navigation

Braking with Electronics

When Craig Brewster talks about electronically controlled braking systems referred to as either ECBS or EBS the discussion hinges on one word: ECBS has the potential to revolutionize brake systems on medium- and heavy-duty trucks; the potential to help shorten stopping distances; and the potential to improve brake system maintenance. Yet Brewster, chief engineer for Peterbilt Motors Co., also reminds

When Craig Brewster talks about electronically controlled braking systems — referred to as either ECBS or EBS — the discussion hinges on one word: “potential.”

ECBS has the potential to revolutionize brake systems on medium- and heavy-duty trucks; the potential to help shorten stopping distances; and the potential to improve brake system maintenance. Yet Brewster, chief engineer for Peterbilt Motors Co., also reminds himself that ECBS must clear a host of hurdles before that potential becomes reality.

“ECBS in and of itself doesn't create a ‘better’ braking system,” Brewster says. “What it allows for is a different technology platform to be brought to the vehicle, which can take brake systems to a higher level of functionality. From an engineering perspective, ECBS presents an opportunity to put more capabilities into a vehicle. The trick is to use that technology to add value to our products, not just cost.”

Jim Clarke, chief engineer for foundation brakes at Dana Corp., adds that an ECBS system is estimated to cost $1,000 to $2,000 more than the current pneumatic-controlled brake package.

“What ECBS brings to brakes is computational power,” he explains. “It makes brakes intelligent and that helps improve truck braking characteristics. Yet ECBS in its current form is more expensive than traditional pneumatically controlled air brakes. We have to achieve a positive cost-benefit analysis to get fleet acceptance. It will probably be about 10 years before ECBS becomes commercially viable.”

Even though ECBS may be a decade or so away from reality in the U.S., it's getting a lot of attention right now from brake manufacturers and government agencies. That's because both entities believe ECBS is the next generation of brake technology.

Dick Radlinski, formerly an engineer for the National Highway Traffic Safety Administration (NHTSA) and currently president of Radlinski & Assoc., explains that one of the primary advantages of ECBS is faster brake deployment.

“With ECBS, electronic controls replace pneumatic or air controls,” Radlinski says. “That's critical because pneumatic signals travel at the speed of sound, while electronic signals travel at the speed of light. Obviously, where antilock braking systems (ABS) are concerned, signals traveling at the speed of light allow for faster braking time. With air controls, there's a 2/10ths of a second delay in response.”

The electronic control functions will make self-diagnosis possible, resulting in brake maintenance that is easier and less costly, he says. Electronic controls may also balance the brakes better, allowing for more even wear and reduced temperatures, extending brake life and lengthening maintenance intervals. In addition, ECBS could help drivers get a better “feel” for the brake pedal, eliminating the need to use the brakes differently when pulling loaded and unloaded trailers.

Perhaps the biggest benefit of ECBS comes when it is coupled with air disc brake technology. If ECBS and air disc brakes are used on both the tractor and trailer, major reductions in stopping distances are possible.

Brake maker Meritor WABCO illustrated that difference in a series of stopping-distance tests. A fully loaded tractor-trailer equipped with today's drum brakes and going 60 mph needs 330 ft. to stop completely. With air disc brakes the stopping distance drops to 234 ft.

However, if the truck is equipped with both ECBS and air disc brakes, it could come to a stop in just 189 ft., a shorter distance than the average passenger car, which requires 194 ft. at 60 mph.

What makes the difference is that ECBS enables the air-disc brakes on both the tractor and trailer to be activated simultaneously. With a pneumatic control system, there is a delay between activation of the tractor and trailer brakes.


Those kinds of numbers got the attention of several government agencies very quickly. NHTSA has been conducting extensive laboratory and test-track demonstrations of ECBS since 1997; in addition, field tests using 50 Volvo tractors owned by U.S. Xpress have been under way since 1999 and will be completed in 2003. Last year, the Federal Highway Administration (FHWA) awarded SAE a contract to conduct ECBS test track work as well.

Both agencies view ECBS as an “enabling technology” that can provide improved stopping distances, dynamic brake force distribution, combination brake balance, brake fade, self-diagnosis, and continuous brake monitoring.

At this stage, however, neither is planning to require trucks and trailers to be equipped with ECBS anytime soon. “Don't expect a mandate for ECBS — at least not in the foreseeable future,” says Duane Perrin, chief of heavy vehicle research for NHTSA. “We still have a lot of testing ahead of us.”

Perrin points out that although ECBS is offered on truck trailers in Europe, it isn't available in the U. S. He adds that NHTSA also wants to conduct larger fleet tests with thousands of trucks between 2002 and 2005, but that will be subject to available funding.

“Our interest in ECBS is to improve vehicle braking performance, the compatibility with older and newer equipment, and find out what happens to the brakes if something in the ECBS doesn't work right,” he says.

That effort, however, is complicated by the more complex nature of ECBS technology. “We've dealt with simple failure testing, such as how brakes work if an air line connection breaks. With electronics, however, you can't get inside a chip” he explains. “There are endless possibilities for failure and an equally slim likelihood that any will happen. In essence, we don't know what you get when you multiply infinity by zero. That's why we need data from long-term field tests.”

Another issue underlying these government-sponsored tests is the need for regulatory change. Federal Motor Vehicle Safety Standards (FMVSS) 105 and 121 are the rules governing brakes for medium- and heavy-duty vehicles. Those rules require that single-unit trucks must come to a stop from 60 mph in 335 ft. when unloaded and 310 ft. when loaded. Tractor-trailers must come to a stop from 60 mph in 335 ft., whether loaded or unloaded.

The key issue is that both rules require redundant control systems for their air brakes — in essence, a backup system in case the primary pneumatic air hoses fail. Current rules would mandate that redundancy even with an ECBS brake system, making it much more costly.

“FMVSS 121 was written in the 1970s, so it needs to be modified or clarified to allow for ECBS use,” says Allan Korn, chief engineer for Meritor WABCO. He points out that ECBS would need some sort of backup system in the event of a massive electrical failure on the vehicle, for example. Korn thinks that FMVSS 121 will be modified to allow commercial truckers to use ECBS, but won't mandate it.

Dana's Clarke adds that the government is not expected to make a decision about changing FMVSS 105 and 121 until 2005. He says that the government also wants to develop a regulation by 2007 that will require stopping distances to be reduced by 30%.

The real “stumbling block” faced by ECBS, says Radlinski, is the trucking community. Will fleets show enough interest in ECBS to make it commercially viable?

“In Europe, ECBS and air disc brakes are accepted technology… because the OEMs have a greater ability to dictate what goes on their vehicles,” he explains. “In the U.S., fleets have a whole lot more say in the process.”

Meritor WABCO's Korn says ECBS is something of a double-edged sword from this perspective; while it adds greater functionality to trucks, it also adds cost. That's why a payback formula will be a critical factor in the acceptance of ECBS by the U.S. trucking industry.

“We sense fleets are interested, but they need to be convinced that there clearly is a payback with ECBS,” he explains. “One of the exciting things about ECBS is that it can give fleets a higher degree of diagnostic capability — and that can potentially help them save money on maintenance costs.”

Peterbilt's Brewster adds that there are several possible paybacks from ECBS that fleets have to look at. One is the potential for better “brake management,” with wheel-end sensors helping to extend brake lining wear. Better brake adjustment is another potential benefit, along with the diagnostic and prognostic abilities ECBS could provide to help fleets improve scheduled maintenance and repair times.

If fleets start to look at using air disc brakes on their vehicles, ECBS could then help better integrate the performance of air disc-equipped tractors and drum-braked trailers, says Brewster. Finally, there's the issue of reduced insurance premiums, although that's an outside possibility at the moment, he adds.


Overall, brake experts believe that ECBS is a starting point for revolutionizing truck brakes, i.e., making them more responsive and thus making tractor-trailers easier to handle, says Ron Bailey, technical sales manager for Bendix.

“With ECBS, you have the potential to send electronic signals in both directions,” he says. “Not only do you have the potential benefit of better diagnostic and prognostic abilities, but you have the opportunity for better truck safety with things such as rollover protection and stability control. That's because ECBS can ‘sense’ what is happening to the truck and help compensate with the brakes.”

“One of the big benefits with ECBS is timing,” says John McKinley, vp-product and business planning for Haldex Brake Systems. “Since it's an electrical system, you can reduce brake application and release times, especially for trailers. Timing can be a very important improvement.”

Also, since ECBS brings a computer-based control system to a truck's brakes, more advanced capabilities can be integrated to improve vehicle safety. “There is the capability to provide a range of stability control functions, from better skid and slide control to rollover prevention,” says McKinley. “ECBS also has the ability to balance the braking force of the truck and trailer better, as well as equalize brake lining wear from wheel to wheel on the tractor and trailer. That's all because we have a much more sophisticated control system in place.”

McKinley adds that ECBS takes brakes several steps beyond the safety advantage of ABS, which all trucks and trailers are now required to have.

“All ABS can do is release the brakes to prevent wheel lockup and skids,” he says. “ECBS gives you the ability to apply the brakes, in varying degrees, for all kinds of reasons. It also can record and store a variety of data, which could help fleets make better projections for preventive maintenance strategies on their truck brakes. In a sense, ECBS is like a Swiss Army knife — it can do so many things that it's only limitation so far is our imagination.”

“ECBS and air disc brakes are a platform for developing better brake balance control, smart-cruise control options, better vehicle stability, better rollover protection, and self-diagnostic capabilities,” adds Radlinski. “Is ECBS the brake system of the future? I think it is, but how far in the future remains to be seen. I think it will be 10 years before we see ECBS on trucks in significant numbers.”

See this story and more online at

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.