Engine Brake Growth Accelerates

Engine Brake Growth Accelerates

Once virtually exclusive to heavy-duty rigs, auxiliary braking technologies now permeate the light- and medium-duty market.

By Chip Cassano

According to trucking lore - and supported by the historical records of the American Society of Mechanical Engineers - the idea for the engine brake was born more than 70 years ago in the midst of a harrowing nighttime descent through Cajon Pass, down old U.S. 66 into San Bernardino, Calif., by Clessie L. Cummins.

It was 1931, and inventor Cummins and two other men were en route from New York to Los Angeles as part of a publicity stunt, intent on setting a new speed record for a cross-continental run in a truck. Cummins was at the wheel of a heavily loaded Indiana truck powered by one of the diesels that bore his name. By his own account, he'd been warned about "Kayhone Pass," but no one thought to tell him how it was spelled. He barreled past the warning signs while his partners slept; by the time he realized his error, he was already caught in the 35-mile, winding downgrade, running in third gear and unable to downshift, his brakes fading fast. A freight train ground slowly across the highway ahead of him.

Cummins and his crew roared onto the tracks moments after the caboose lumbered past. They went on to set a cross-continental record of 97 hours, 20 minutes for the 3,214-mile trip and helped to prove the viability of Cummins' diesel engine. But the memory of Cajon Pass stayed with Clessie Cummins, and 24 years later, in 1955, he began work on a device that would eventually be produced and marketed by the Jacobs Manufacturing Company - the now-ubiquitous "Jake Brake."

Auxiliary Braking Today
Cummins' invention went to market in 1961 and quickly gained in popularity, beginning in the mountainous West. But penetration into the light- and medium-duty truck markets has been slow. Most saw engine brakes on smaller trucks as overkill; if a vehicle wasn't carrying heavy loads at highway speeds over long distances and hilly terrain, why absorb the extra expense of an engine brake?

To a degree, that question is still valid. But a variety of factors - including evolving technologies, heavier demands on medium-duty vehicles, increased congestion on major thoroughfares and a simple increase in public awareness - are converging to make alternative braking technologies a preferred option, or even standard equipment, on more and more light- and medium-duty trucks. To understand why, one must understand the technologies and what they offer.

Technology 101
The technology behind most auxiliary braking is simple - in theory, if not in execution. In layman's terms, an engine brake - the Jake Brake, for instance - operates by opening a valve at the upper limit of a piston's compression stroke and releasing the stored energy of the pressurized air. This release of air retards the rebound effect that would normally drive the piston down through the power stroke. The escape of air past the valve produces the distinctive rat-a-tat-tat many associate with the devices. An exhaust brake, on the other hand, works by increasing backpressure in the engine by obstructing the outflow of exhaust gases (usually by means of a simple butterfly valve). The results are similar: instead of the engine working to move the vehicle, in effect, the vehicle must work to "move" the engine.

This is a standard feature, to a degree, on gasoline engines: Take your foot of the throttle and a butterfly valve typically closes in the intake system, cutting off air to the engine and creating a vacuum. That makes the engine work harder, absorbing energy and decelerating the vehicle. In a diesel engine, however, the throttle only controls the flow of fuel: Cut the throttle and the vehicle will still freewheel. Given the very real risk of overtaxing wheel brakes, the allure of an auxiliary braking system - especially on vehicles operating in hilly terrain or carrying heavy loads - is clear.

For most engine manufacturers, exhaust brakes are the option of choice for lighter-duty vehicles.

Although they can't offer the same levels of stopping power that engine brakes deliver (for comparison purposes, Greg Saele, engine marketing manager for International Truck and Engine, said that the company's Diamond Logic engine brake delivers 275 bhp on the International DT 466 engine, while the Diamond Logic exhaust brake on the same engine delivers only 150 bhp) exhaust brakes are significantly cheaper, simpler and quieter. For all but the most severe operating conditions, that is an acceptable tradeoff.

Now, several vehicle and engine manufacturers, including General Motors, Cummins, and International, have found other, if related, ways to get the stopping power they need - by leveraging the capabilities of the new and increasingly sophisticated turbochargers that have helped manufacturers meet stricter 2004 emission requirements. International's electronic variable-response turbocharger (EVRT) offers a good example.

"The EVRT has moveable vanes that pivot and adjust the turbo boost to the engine speed and load for optimum performance through the entire RPM range with no turbo lag," said Saele. "The vanes are actuated by an electronic servomotor, while precise electronic controls set the boost to deliver the right doses of power at the right times.

"Electronically integrated with the engine and fuel system to drive optimum, efficient vehicle performance, the EVRT turbocharger has also become a crucial component of the new Diamond Logic Exhaust Brake system . . . [which] works by closing the adjustable vanes of the EVRT system to create exhaust plenum backpressure, providing almost identical braking horsepower as current exhaust brakes. Because this can be programmed via the engine's built-in Diamond Logic software, there are no bolt-on hardware devices necessary."

Coupling that technology with today's "smart" automatic transmissions can further increase the systems' performance.

"Our VGT [variable-geometry turbocharger] doesn't give you as much braking horsepower as the butterfly valve, but it's pretty damn close," said Joe Mastanduno, director of diesel engine brand management for Isuzu Motors America. "Put it together with the Allison automatic, though, which is on most of our engines and has a downshifting capability, and the combination offers greater stopping power than you could get with the butterfly valve alone."

What's in It for Me?
The technology isn't free, of course, and Rajesh Singh, product manager for Cummins Inc., quotes ballpark figures of $1,500 and $5,000, respectively, to outfit an engine with either an exhaust or engine brake. The question, of course, is how much the technology is worth to the bottom line. And the answer is, nothing - if you're hauling goose down on empty roads at low speeds with experienced drivers. Otherwise, it's worth a serious look.

The primary benefit of an auxiliary braking system, of course, is increased control. The risk of a runaway vehicle, and the potential liability associated with it, varies dramatically on a case-by-case basis. Mike Shauck, director of medium-duty sales and business developments for Jacobs Vehicle Systems, points to fleets in mountainous areas, hazmat carriers, school buses, dump trucks, tow and rescue, and others in similarly critical roles as projected early adopters of auxiliary braking technologies in medium-duty trucks. (Mandates already require that fire and other emergency-response vehicles be equipped with auxiliary brakes.)

"Think of a fleet of medium-duty tank trucks delivering oil in the Los Angeles area," said Shauck. "You've got a heavy load, steep grades and heavy traffic. That would be an ideal application." It's ideal on another level, as well. Because the potential for wear and tear on wheel brakes is staggering, the potential for savings is equally dramatic. Engine- and exhaust-brake manufacturers like Jacobs and PacBrake point to the potential for three- to five-fold increases in wheel brake life cycles on vehicles where an auxiliary brake is used properly. In fact, several manufacturers point to increased brake life as the primary motivator prompting buyers to look toward auxiliary braking systems. But there are other benefits, as well.

"One feature that is frequently overlooked on the variable-geometry turbo brake and the exhaust brake both is how they create higher backpressure at idle, causing the engine to work harder and warm up much more quickly," said Carlton Bale, product engineer for Cummins. "And diesel engines are notoriously cold at idle."

Mastanduno, of Isuzu, agreed. "We use the variable turbo for a lot of things," he said. "It offers a quicker cold-weather startup, faster warm-up and quicker cab heating. We're even seeing benefits as we integrate the particulate filters that we need to meet the 2007 emissions standards." Finally, auxiliary brakes offer a safety net for less-skilled drivers - an important consideration given today's challenging hiring environment. Is There a Downside?

Not everyone is ready to jump on the bandwagon when it comes to auxiliary braking systems. Caterpillar, for one, offers no braking option on its lighter-duty engines, although it certainly doesn't oppose them. Plenty of aftermarket options are available to buyers who want them.

"For us, it's a question of how we can add value," said Mike Powers, product development manager for Caterpillar's on-highway engine group. "For the braking needs of most medium-duty customers, the exhaust brake has done an adequate job. And we've said, 'Hey, do you guys want us to do this?' And the answer has been that they believe they can do it more cheaply and efficiently. It offers them a choice. Most of the exhaust brakes that I see installed on medium-duty engines are for specialty markets - on fire trucks, on RVs. A lot of times the medium-duty trucks are small enough that their standard service brakes are adequate for their needs."

Engine brakes, too, are subject to periodic criticism for being too noisy, although most brake manufacturers contend that, on a vehicle with an adequate exhaust and muffler system, noise levels fall well within acceptable limits. International's Diamond Logic engine brake addresses the issue, nonetheless, by releasing pressure from the combustion chamber throughout the piston compression stroke, rather than releasing it suddenly at the point of highest compression. The result is an engine brake, Saele said, that is quieter, decibel-wise, than the interior of a passenger car traveling on the freeway.

The good news is that, on most fronts, the technologies are not experimental. Jacobs has been producing engine brakes since the early 1960s and enjoys a reputation that Shauck describes, justifiably, as "bulletproof." The company's engine brakes boast an anticipated life cycle that compares favorably with the life cycle of a diesel engine. And while U.S. buyers in the light- and medium-duty market may not have flocked to auxiliary braking systems, Mitsubishi Fuso - thanks to its roots in the Japanese market, where engine brakes and even the more expensive magnetic retarders have been standard issue on medium-duty vehicles for years - has been equipping its light- and medium-duty vehicles with exhaust brakes for the past 20 years, according to Robert Aquaro, vice president of product insurance for Mitsubishi Fuso Truck of America.

The bottom line? Maintenance intervals aren't affected; engine life might actually increase; additional costs are offset by potential savings in wheel brake service intervals; and vehicles are better equipped to operate under heavier loads, at higher speeds, on hilly terrain and in heavier traffic. In short, auxiliary braking technologies have reached the light- and medium-duty market, and all the signs say they're here to stay.

Chip Cassano is a freelance writer based in Takoma Park, Md.

Web Source: http://www.ttnews.com/lmt/Aug05/accelerates.asp