Remember the First Law of Thermodynamics from high school physics? Energy cannot be created or destroyed; it can only be converted from one form to another. This principle of "conversion" underpins virtually every mechanical process that makes a vehicle go, and stop. Every time you start up a vehicle you're converting potential energy to kinetic energy, and every time you stop you're converting the kinetic energy right back into potential energy. When a heavy truck's engine brakes are engaged, a very dramatic energy conversion takes place...
"The engine brake comes under some pretty stressful conditions," says Bruce Sebring, VP sales, Pacbrake Company. "What we're doing is we're opening the exhaust valve at TDC on the compression stroke, and releasing engine compression, and that sometimes puts pressures inside the engine brake housing in the 3,000 to 4,000 psi range.
"It's not uncommon for an engine brake to lose 25 percent of its efficiency at the quarter million mile mark," Sebring says. "It loses efficiency over time, and you never really notice it. It just gets progressively weaker and less effective, and if you don't do maintenance on it, you can accelerate the wear of the engine brake housing itself. Then once that's worn out, you have to replace the housing. But regular maintenance will prevent that, and will keep the engine brake at the efficient level, and will increase your ROI.
"So there are some critical control components in there that need to be addressed on a fairly regular basis," he says. "Fairly regular to me is about a quarter million miles and up you should go in there and, shall we say, freshen up the engine brake. Whenever you're under the valve cover, running the overhead and injector head gasket, etc., the labor's already done, so it's a simple matter to then add these components to the engine brake and get it back to 100 percent efficiency."
"We try to link maintenance of the engine brake to engine overhauls," says Paul Paré, director of marketing for Jacobs Vehicle Systems, maker of the "Jake Brake."
"When you're taking advantage of labor, you can use a tune-up kit during that overhaul," Paré says. "A lot of companies will have scheduled recommended overhauls on their engines, and during that time when the valve cover's off and the brakes are removed, the labor's already spent. So we say, while you're doing an overhaul, put a tune-up kit in there at the same time. It just makes sense. That way you're using genuine parts, and you're restoring your performance."
The difficulty with engine brake maintenance is that drivers can't always tell when the performance of the brake has slipped. According to Paré, engine brake effectiveness is difficult to measure:
"To fully understand performance degradation, we need to get a sample truck that has 400,000 or 500,000 miles on it, put it on a dyno, and check for performance. What is the degradation? Then we put the new 'tune-up kit' parts in and reinstall it and put the truck back on the dyno to check the performance."
Paré says that his company is working with engine OEMs to harmonize maintenance intervals to make the hour-long engine brake tune-up as inobtrusive as possible. As a part of that effort, Jacobs will begin a major training campaign in the coming year to get fleet customers to regularly tune up their engine brakes when they perform engine overhauls.
Those fleets that plan to hold onto their trucks for an extra year, or buy used trucks, to avoid purchasing trucks with '07 engines will need to keep engine brake maintenance in mind.
"Ninety-nine percent of Class-8 trucks built today have an engine brake of someone's manufacturer on it," says Sebring.
"There are some fleets in the Midwest that have never seen value in an engine brake, but that's a diminishing number now. Flat lands, low speeds, low weights… A 55 mph fleet rolling down the interstate hauling triples on flat ground, they really don't see the ROI that someone running in the mountains does. As those trucks come into the marketplace now as trade-ins, and they do not have retarders on them, they get equipped with retarders before the second or third owner buys them. As they move around the country—a fleet of trucks from Ohio might wind up in Los Angeles—suddenly they're in the mountain west and they absolutely need engine brakes. Sometimes the second or third owner has the engine brake installed before putting the truck back in service."
24 VOLT DILEMMA
It will be a while before any technician performs an engine brake tune-up on an '07 engine, but when that time comes the technician may be in for a small surprise, according to Detroit Diesel.
"What is different about the 2007 engine brake from the '02 and '04 brakes is the fact that now the solenoid valve has two lead wires instead of one," says Al Warner, staff project engineer for Detroit Diesel. "In the past, for the older 'Jake brakes' that had two cylinders per housing, that had just a single lead that we call a high-side driver. It was turned on by supplying electricity to the solenoid, and then it was a block return, or block ground.
"Well, with '07, with the new electronics, it gave us the opportunity—early in the program, when we first started this about three years ago—to eliminate the 24V solenoid models from the brake," Warner explains. "We grabbed for that opportunity. So now there is a high-side power source which comes from the switched ignition. Then the solenoid is driven on the low side by PWM-ing—aiding the current in a duty cycle fashion. That way with one solenoid it could be used on either 12V or 24V models of the brake.
"PWM-ing," Warner explains, "is high speed (350 hz) turning on and off the electrical ground. For example, if you run 50 percent duty cycle, then the ground is on 50 percent of the time. Subsequently, you get 50 percent of the current that you would if the ground was on 100 percent. That is about where we currently run the solenoids even though they are perfectly capable of running 100 percent all of the time.
"Also, the circuit is a little smarter than this," he says. "When the brake first comes on, there is a brief surge of 'pull in current' to get the armature moving from it's off position. Once again, the benefits of the reduction in heating due to the current flow are very minor since the oil temp is the real driver of solenoid temperature and it's wear and tear. The whole approach was to reduce cost by elimination of the 24V brake part."
However, after the two wire solenoid design was finalized, the company decided to abandon the 24V option for the '07 EGR engine.
"It's a straight 12V engine, and therefore, the opportunity that we tried to go for with the two-lead solenoid disappeared," Warner says. "Everything was cast in stone at that time, so we still have a two-lead solenoid. And there are minor advantages, because with the pulsing of the current there is somewhat of a reduced thermal load on the solenoid. But that is not the reason why—that is an 'Oh, by the way' advantage."
TWO WIRES TO REMEMBER
In addition to having to hook up two leads to the solenoid instead of one, the technician working on a Detroit Diesel will have to become familiar with a newly-designed injector harness that carries the electrical leads for the engine brake.
"Its arrangement is very different than what we've had in the past, where we feed the lead wires to a hole in the head in the back of the engine," Warner explains. "You know how tight it can get with the firewall there. So we've developed a new injector harness that comes in through the side of the rocker cover, in what's called the intermediate housing—the lower spacer in the rocker cover. It goes up and over the brake to get to the injectors, and we have very elaborate parts that support the injector harness, because we've had some issues in the past."
Detroit Diesel's goals for the new injector harness design were to increase reliability and reduce the already small amout of warranty returns on the engine brake wiring. Warner reports that early feedback from technicians on the new layout has been all positive.
"It has no effect at all on the maintenance of the engine, outside of the fact that you've got to lash it, you've got to connect the solenoids, etc.," he says. "As a cautionary, the one hot lead—and it's only going to be hot with ignition on—if that lead ever shorts the block, or shorts the solenoid, it does result in an engine shutdown situation. That high-side sourcing is shared by other critical actuators on the engine, and it's actually split—with the front solenoid, it shares power with, I believe, the turbo actuator, and the rear solenoid shares its power with the EGR valve.
"When either one of the turbo or the EGR valve are inoperative, then there are codes thrown," Warner explains. "This is different for '07, because in the past all you'd lose was 'Jake' function. So that high-side wire, and I believe we've color-coded it red—the scenario under which it would be left to flop around under the rocker cover should be very rare. It's more about a mistake: somebody forgot to attach it, or something like that."
The engine brake will also have to function effectively in a higher-temperature environment on a 2007 engine, but Pacbrake's Sebring doesn't anticipate any immediate issues there: "We don't foresee any change in performance," he reports. "I don't know the long-term effect of higher temperatures and ultra-low sulfur diesel fuel (ULSD), or different oil formulations. That may or may not play into the maintenance of the engine brake, but I don't foresee anything in the immediate future."
The 2007 emissions regulations will effect engine brakes in another way. Because the new standards have necessitated the use of extensive exhaust aftertreatment devices, truckers will no longer be able to modify their exhausts. That means that the familiar "bark" of the engine brake could someday be a thing of the past.
"Typically you hear excess noise because people are not using the proper muffler system that comes out of the factory," says Jacobs' Paré. Of course, this is an issue of some sensitivity to Jacobs Vehicle Systems, as they are working with municipalities across the country to take down road signs that say "Use of Jake Brakes Not Allowed," and either eliminate them altogether or replace them with the non-brand-specific "Use of Engine Brakes Not Allowed."
"What's happening with the '07 emissions is that the truck owner cannot touch the muffler system anymore, because of the particulate filters integrated with the exhaust system," Paré says. "They can't touch the muffler anymore, you can't throw on straight pipes, so we're not going to have that issue anymore. Noise related to engine retarders is not really an issue anymore, because the emissions regulations have mandated what the muffler system is going to look like, and there are no changes to that muffler system. So the noise coming out of there is equal to normal positive power."
Aside from learning to navigate around things like extra wires and redesigned injector harnesses, maintaining the typical engine brake couldn't be much simpler.
"Basically, the tune-up kit consists of control valves and springs, washers, wiring, screws," says Paré. "You're going to get some wear, like anything else. You've got a part in there that's got a certain tolerance to it, and over time there's the opportunity for the component to wear."
"I think some of the key fleet people that do their own maintenance have very good programs," says Sebring. "Today's engines, however, are million-mile engines, and the majority of large fleets do not expect to remove the valve cover during the first four or five years of use, or at least until the warranty period is up. So, we're talking 400,000 or 500,000 miles, perhaps, and they don't expect to lift the valve cover. So therein lies the key. There is a little bit of a thought process that needs to be addressed: you need to remind the fleet people that this is something they need to look at.
"The tune-up kit has hardware involved, and it's a simple matter of replacing the components," he goes on. "The critical component is the control valve, or spool valve. It's a one-way jet valve and it has a tendency to accumulate carbon under the bb and seat and it does happen to leak after a certain amount of time. So (the kit consists of) control valve, springs, solenoid seals and master piston return springs, and wiring.
"There's a solenoid control wire under the cover that deteriorates as well," he continues. "It doesn't require the removal of the engine brake; it can all be done with the engine brake intact and in place. (The control valve has a small 'bb' controlled by a spring on a seat, and every time the engine brake is turned on and turned off, the bb comes off the seat and oil pressure comes under it, between the bb and the seat. When the engine brake shuts off, then that oil pressure drops off and the spring returns the bb to the seat. So it's a ball and seat arrangement, and as your engine progresses in wear, and carbon becomes an issue in the oil, every time the engine brake is on and off, the ball and seat is subjected to whatever contaminants are in the oil. So as you get contaminant buildup on the ball and seal, that unit becomes a leaky product rather than a zero-leak product.)"
"The engine brake as we know it is being integrated into the '07 engines, and will be further integrated into the 2010 engines," says Sebring. Will those engines be expected to stay in service beyond a million miles? Even if they can run that long, the engine brake is going to need some care long before that mark. Don't forget.