Light Truck Ignition and Emissions

While there has certainly been a more car-like approach to building light trucks and SUVs–creature comforts seem to be taking precedence over payload in many cases–there is little doubt that there are some truck-specific engineering differences under the hood.

General Motors, for example, has engineered a whole new engine line under the Vortec name.

This year, the company introduced its 5300 Generation IV iteration of the V8 (pictured), designated LH6 in GM parlance. This engine finds its way into the Chevrolet Trailblazer EXT, GMC Envoy XL, GMC Envoy XUV, GMC Envoy Denali, GMC Envoy XL, Denali, and Saab 9-7.

Among the advanced features of the engine is the displacement on demand (DOD) system, which helps the engine retain its on-road performance with greater fuel economy.

There are certainly a number of construction advances employed in the engine, but many of the fuel-air management technologies are of interest too.

The Displacement on Demand strategy is just one of those. This technology is said to improve fuel mileage by up to 25% in real-world conditions by deactivating half of the engine’s cylinders during light loads.

Managed by the E40 engine control module (ECM), Displacement on Demand automatically shuts down every second cylinder, according to firing order, during light-load operation. In engineering terms, this allows the working cylinders to achieve better thermal, volumetric and mechanical efficiency by reducing heat loss, combustion loss and friction, and lowering cyclical combustion variation from cylinder to cylinder. As a result, Displacement on Demand delivers better fuel economy and lower operating costs.

Displacement on Demand relies on three primary components: De-ac (for deactivation) or collapsible valve lifters, a lifter oil manifold assembly (LOMA), and the E40 ECM.

One of the most sophisticated engine controllers currently found, the E40 measures load conditions based on inputs from vehicle sensors and interprets that information to manage dozens of engine operations, from fuel injection to spark control to electronic throttle control.

The transition from four- to eight-cylinder operation takes less than 20 milliseconds.

The exhaust system for the Gen IV Vortec 5300 is carefully tuned to maintain optimal noise and vibration control. The system requires special pipe tuning to account for both. On short-wheelbase vehicles, this presents some problems, so the concept is still in development. This is why GM has decided to deactivate the DOD system on the Buick Rainier, Envoy Denali, and Saab 9-7. (Can’t have their owners’ ears offended by four-banger resonance, can we?)

When it comes to the technology embedded in these engines, you would be hard pressed to find an equivalent level of technology in the passenger car market in anything but high-end luxury and sports cars.

On a more basic level, the Gen IV Vortec 5300 benefits from the latest spark-plug technology. Its spark plugs have an iridium electrode tip and an iridium core in the conductor. The iridium plug still has a recommended life of 160,000 km, but it offers a number of advantages over the platinum-tip plug previously used in the Vortec 5300. The iridium spark plug has higher internal resistance, maintaining optimal spark density over its useful life. Its “self-cleaning” properties are improved, decreasing potential for plug fouling and further reducing the likelihood of maintenance over the plug’s 160,000-km life. The electrode design improves combustion efficiency for maximum fuel economy and minimum emissions.

The spark plug also formed a design challenge of sorts for Ford engineers when they embarked on a three-valve redesign of the Ford Triton engine line. In fact, Ford’s advertising people had a bit of fun, telling the consumer in television ads that it had designed the F-150 around the new spark plug.

The truth is a bit different.

“They needed to put an extra valve in, take it from a two-valve to a three-valve engine,” says Jeff Boehler, chief engineer, Autolite, Honeywell Consumer Products Group, which designed the spark plug. “So they saved some money, gained a fair amount of power, but they had a fixed bore spacing so they needed a smaller spark plug.

“The working end of it is only 10mm.” Since most spark plugs in road-going vehicles are 14 mm, it may not sound like much of a change, but Boehler says that it required a significant rethinking of the design and electrode, as well as a reengineering of the heat rating.

To be honest, it is a bit of an odd-looking plug, with a cylindrical nose protruding much farther from the threaded area than other plugs, and a ground strap electrode that completely encloses the centre electrode.

“The ground strap is a heat sync at both ends, it is simpler to manufacture, and it helps with the durability.” And, he says, you don’t have to gap it.

“You do have to be careful installing them, because it is a different socket size, and it has a higher installation torque.”

It is the exception in the parts bin, however. Many if not most of the parts found under the hood of a light truck or SUV are quite similar to those found in a passenger car.

The Vortec engine, for example, uses the latest fast-light oxygen sensors. Oxygen sensors need to reach a specific temperature before they can provide the proper feedback to engine management systems, in so-called closed loop mode.

“The sensor’s ceramic element becomes electrically conductive at temperatures above 625-650 degrees F,” says Chuck Ruth, director of automotive marketing, Robert Bosch.

“The sensor element produces a voltage signal that switches almost instantaneously from low voltage to high voltage as the air/fuel mixture changes from lean (too much oxygen) to rich (too little oxygen) and vice versa.

“For many years, heated O2 sensors have been the predominant O2 sensors installed in new cars and trucks, although some vehicles still used unheated sensors into the late 1990s,” says Ruth. “However, increasingly stringent emissions requirements, such as the introduction of OBD II, and advances in engine management technology have brought about new types of more sensitive and durable oxygen sensors. Two recently developed oxygen sensors, the heated planar sensor and the heated wide-band sensor, offer greater sophistication and control in engine management, and the planar sensor already accounts for more than 20% of O2 sensors installed in new domestic vehicles.”

Heated planar sensors use an integrated heating element to bring the sensor up to operating temperature in 12 seconds, which helps reduce cold-start emissions. Wide-band heated sensors send a continuously variable signal to the vehicle engine management system, enhancing emission and performance management.

“Nearly every region in North America requires some sort of automotive emission inspection, and properly functioning oxygen sensors are critical to passing every one of these emission tests. Their long-term durability and reliability is equally important to the catalytic converter, which can easily be damaged if an oxygen sensor is worn out.”

In general terms, the environment under the hood of a truck can be a vicious one.

Towing and heavy loads that passenger cars don’t see can increase exhaust temperatures which can in turn cause internal components, such as sensors and spark plugs, and external components, such as ignition wires and coils, to degrade prematurely.

An added factor in the mix is fuel. While the quality of fuel is something that most consumers take for granted, Doug Morrison, technical service manager, NGK Spark Plugs of Canada, says that the proliferation of ethanol-blended gasoline is not always a positive move.

He says that the increasing use of ethanol as an emissions reduction strategy is “playing a major part in the wear and tear on the plugs.

“The best way is to take a look back at racing in the carburetor age. If a racer was using a regular race fuel, but then switched to an ethanol blend, he would have to increase the jetting.

“If your car was calibrated with 100% regular gasoline and you’re using a fuel type that has 5% to 10% ethanol, it is going to lean you out.”

While all passenger cars can experience this to some extent, Morrison says that the impact is particularly great in light trucks and SUVs due to the towing and heavy loads they can experience.

Morrison says that the leaner mix may improve emissions, but engine management systems can’t compensate enough and this can translate into poor fuel economy.

“In the summer time, people are going to stations with ethanol blends and noticing pinging, but they fail to realize that it is fuel-related.”

The downside for the aftermarket is that technicians can be equally in the dark, look for problems with other systems, but end up with little more than an unhappy customer. Morrison advising changing the plugs for a different heat rating.

The fuels also exacerbate problems with substituting nickel-tipped plugs for the original precious-metal plugs.

“We’re seeing guys complaining at 20,000 km. Nickel can’t stand up to the ignition systems being used today, and a faster-burning fuel makes it worse,” says Morrison. Add heavy towing use, and the life of the plug can get even shorter.

“When you make the tip of that electrode there is an effect with how rapidly the flame kernel spreads,” explains Honeywell’s Boehler. “There is a limited time window. You have a fixed source of energy that you can work with, but you can deliver it more efficiently. The faster you can grow that flame kernel, the better it can be at getting all of the energy out.

“The problem is that when you make the electrode smaller, it could wear faster unless you use some better material.” Hence the need for precious-metal plugs.

Overall, light trucks have become heavy on technology over the past few years. They have become quieter, more powerful, more fuel efficient, and friendlier to the daily driver and commercial user alike.

And, while consumers in many sectors may treat their pickups and SUVs as grocery getters, those selling parts into the aftermarket would do well to remember that beneath the increasingly genteel exterior beats the heart of a heavy hauler, and some owners are bound to see just how much they can take.

Exhaust Market Potential Growing

The light truck market may be one of the few segments of the exhaust business that is seeing good growth.

“It is definitely growing in performance. We separate [the exhaust business] into light truck, tuner and muscle car. It is the one that is growing the most,” says Jim Fox, national account manager, ArvinMeritor Light Vehicle Aftermarket. “New light truck sales have started to slow a bit, but that is not going to impact us for a few years.” Even on the conventional side, he says that trucks are showing promising, positive signs. Big body mufflers and pipe diameters of 3 inches are still no match for the commercial user.

“For commercial vehicles, or those logging in B.C. and places where they take a good beating, we do see some early replacements from extreme conditions.”

This applies to the catalytic converter business, too.

“Certainly trucks are the earlier applications to need replacement, because commercial users are getting into higher mileage sooner. With OE emissions warranties at eight years or 130,000 km, it has to be a fairly heavily used vehicle to be young and exceed that mileage.

“So you need to be ready and be thinking about that. You need to make sure you have a supplier who is on the forefront of that. You have to keep your eye on who your customer base is and what they are putting the mileage on.”

The import factor is another stocking trend to contend with. According to the Motor Equipment Manufacturers Association, over the past dozen years, the number of import nameplate light trucks and sport utility vehicles in North America has increased threefold.

Richard Alameddine, vice-president of marketing, North American Aftermarket, Tenneco Automotive adds another piece of advice. “There’s no question that each year more and more consumers who own foreign-nameplate vehicles will be looking for exhaust and emissions services. The challenge and opportunity for aftermarket providers is to demonstrate that they have all the right products to restore the OE-style sound and performance these consumers clearly prefer.”

Diesel and the Light Truck

NO discussion of the light truck and SUV would be complete without raising the issue of diesel power.

Today’s diesel engines are not the smoking oil burners of yesteryear. The performance crowd has discovered a way to get great gobs of horsepower and torque out at the flick of a switch. And the number of diesel-powered light trucks manufactured in North America in 1999, 435,000, was double the number built only five years earlier.

Yet they struggle for wider acceptance. Manufacturers hope that the even more advanced technologies, and rising concerns over fuel costs and pollution, will bring converts. Two leading suppliers of core “clean diesel” technologies are Delphi and Robert Bosch.

The leading candidate on the technology side is common-rail diesel injection.

The way in which fuel is injected into the cylinders determines the torque, fuel consumption, emissions and noise of diesels. Two factors are important: the fuel pressure as it enters the cylinder, and the shape and number of the injections.

Unlike older technology, a common-rail injection system separates the two functions–generating pressure and injecting–by first storing the fuel under high pressure in a central accumulator rail, then delivering it to the individual electronically-controlled injectors on demand. This ensures that injection pressures of more than 1,700 bar (25,000 psi) are available at all times, even at low engine speeds.

The technology used in Delphi’s Multec 1400 common-rail system is based on solenoid injectors with balanced valve and feedback control strategies. The solenoid concept has been improved by using a valve and an adapter plate to drive the opening and closing of the injector. This system features precise operation even in high-pressure applications of up to 1,600 bar.

Delphi employs a combustion feedback system called accelerometer pilot control (APC). This closed-loop control system allows the engine management system to analyze the quality of the combustion. Information from the APC allows fuel injection to be adjusted as conditions change, ensuring that the system is correctly calibrated.

For its part, Bosch is developing a new control unit (EDC17), which will go into series production in 2006. It will enable complex feedback effects between pressure waves in the storage rail and the amount of fuel injected, for example, to be detected and precisely compensated for. Using revolution counters, the system can analyze the injection parameters of each cylinder and adjust them if necessary.

In contrast to a control system based on engine characteristics, this type of model-based approach makes it possible to have a simple control system which can easily be transferred to a variety of engines, and which benefits from the direct feedback from the engine.