The light truck sector is one of the most competitive sales segments in the U.S. auto industry. Sporting lofty price tags and higher profit margins, pickup trucks are the bread and butter for many manufacturers and their dealers. It’s easy to make money selling pickups...when people are buying them. In that respect, light trucks generally sell like hotcakes when gas is cheap and credit is easy to come by. This is the confluence of events that we are witnessing now, with interest rates and crude oil prices both at multi-year lows.
The VM Motori 3.0 liter EcoDiesel has been available in the 2013+ Jeep Grand Cherokee as well as the 2014+ Ram 1500. Photo: FCA US LLC
The 3.0 liter EcoDiesel is a turbocharged DOHC V-6. Its high-pressure common rail injection system can develop pressures up to 29,000 psi (2000 bar). Photo: FCA US LLC
The Ram 1500 EcoDiesel uses urea SCR to meet 50-state emission standards. The diesel exhaust fluid (DEF) filler is located behind the fuel door on the driver’s side of the truck. Photo: FCA US LLC
Yes, conditions are perfect for increased light truck sales, but the consumer is still faced with a dilemma. What happens if I buy a new truck and fuel prices go back up? Certainly, the fun factor tapers off when you are making hefty payments on your rig and now it’s costing you the remainder of your disposable income to keep the tank filled.
Times have changed mightily. Federal regulations regarding fuel economy have brought the light truck into a new age, one where its gas-guzzling ways are being reformed. This has also led to intense competition between the auto manufacturers to claim the fuel efficiency crown and its associated bragging rights. No stones are being left unturned in this clash of competing technologies: gas versus diesel, aluminum versus steel, etc.
The current fuel economy champion in the light truck sector is the Ram 1500 EcoDiesel. Powered by a 3.0 liter V-6 diesel built in Italy by VM Motori, this truck is putting up impressive fuel economy numbers as well as meeting tough emissions regulations that put it on par with many passenger cars. It is the only diesel-powered light truck currently in the U.S. market, going where other manufacturers have feared tread. Numerous technologies have been utilized to achieve the goals of clean emissions and high fuel economy, and the purpose of this article is to present an overview of how Ram truck engineers made it happen.
Clean emissions
The North American (NAFTA) version of the VM Motori 3.0 liter EcoDiesel was first used in the 2013 Jeep Grand Cherokee. It was MY2014 when it appeared in the Ram 1500 pickup, where it immediately left an impression on the truck-buying public. It is a turbocharged 60-degree V6 with 24 valves and double overhead cams (DOHC). While it produces a modest 240 horsepower, the peak torque output is 420 lb-ft @ 2000 RPM, giving the EcoDiesel V-8 torque with 4-cylinder fuel economy.
Building a clean diesel is one thing, but having it meet light-duty vehicle emissions regulations is another level of difficulty. Heavy-duty pickups with diesel engines have strict emissions regulations, but these are not as tough as those that apply to half-ton pickups and other vehicles under 8500 lbs. Gross Vehicle Weight Rating (GVWR).
The holy grail of diesel emissions is known as Tier 2 Bin 5 (T2B5). T2B5 is the minimum EPA emissions rating required for a passenger vehicle to be sold in all 50 states. A car or light truck with a lesser rating does not qualify for sale in California or any of the 14 states that have adopted California emissions regulations (also known as “Green States” or “CARB States”). This rating is critical to vehicle sales, because the Green States are major car-buying markets and represent a high percentage of new car registrations in the U.S. If you can’t sell in those states, you may as well not bother at all.
Diesel engines struggle with two regulated emission gases: particulate matter (PM) and oxides of nitrogen (NOx). While engine tuning has a direct impact on the production of these gases, whatever is done in the combustion chamber to minimize one will typically result in an increase in the other. For instance, PM levels tend to decrease when combustion temperatures rise, but the hotter flame causes an associated increase in NOx. The reverse is also true; cooling the flame will reduce NOx output, but PM then rises. This is the classic two-edged sword, with one caveat: a hotter flame increases engine power output and overall efficiency.
With these dynamics in mind, VM Motori designed the 3.0 liter EcoDiesel to use a hotter combustion flame and then deal with the increased NOx after the fact. This requires the use of urea Selective Catalytic Reduction (SCR) as an exhaust aftertreatment system to reduce NOx to acceptable levels, but brings with it the following advantages:
1. Increased engine power output and fuel economy
2. PM production is lowered, relieving the load on diesel particulate filters and limiting associated regeneration issues.
3. NO2, a component of NOx, is a powerful oxidizer and helps regenerate diesel particulate filters.
An operational challenge with urea SCR is that the driver is responsible for replenishing the Diesel Exhaust Fluid (DEF), also known as AdBlue in Europe. The Ram 1500 is unique in that it utilizes a DEF gauge on the instrument panel, making it easier for the driver to manage the system’s DEF level. Most diesel pickups equipped with urea SCR do not have a gauge, but instead rely on a system of chimes and driver information center warnings to indicate when the DEF is low. The 8-gallon DEF tank is insulated, and the lines are heated to improve system performance in cold weather. The exhaust system is also designed to maintain optimal NOx conversion temperatures without requiring additional energy from the engine and causing an associated decrease in fuel efficiency.
The Ram 1500 EcoDiesel’s DEF tank holds 8 gallons, and the level is indicated on a gauge on the instrument panel. Photo: FCA US LLC
There are a select few motor oils that meet the specification required for the VM Motori 3.0 liter EcoDiesel. Photo: Tony Martin
The Garrett turbocharger used on the EcoDiesel has a rotary electric actuator (REA) to control the variable nozzle. Photo: Tony Martin
Cooled high-pressure EGR is the first line of defense in the EcoDiesel’s NOx reduction strategy. The basic idea is to inject cooled inert gases into the engine’s fresh air charge, which act as a heat sink to reduce combustion temperatures. When used in moderation, EGR is a very effective method for preventing NOx from being formed during the combustion process. It can also be used to warm up a diesel engine more quickly, thus cutting down on white smoke during a cold start. Numerous ECM-controlled actuators are used to control the EcoDiesel’s EGR system, including a swirl valve, airflow control valve, cooler bypass and the EGR valve itself.
The turbocharger plays a major role in the operation of the EGR system. EcoDiesel’s variable geometry turbocharger (VGT) is water-cooled and incorporates a nozzle controlled by a rotary electric actuator (REA) to precisely control boost and exhaust backpressure. If the nozzle is closed, exhaust backpressure rises and causes an increase in EGR flow. Partial closing of the airflow control valve also enables EGR flow by effectively lowering the intake air pressure. The greater the pressure difference, the higher the flow of EGR gases.
What is the “NAFTA” version of the VM Motori 3.0 liter diesel?
The version of the VM Motori 3.0 liter diesel that is sold in North America is not the same as the one that is available in Europe. The North American engine is known as “NAFTA” in reference to the North American Free Trade Agreement between Canada, the United States, and Mexico. The differences between the NAFTA and the European versions are driven by the contrast in emission control regulations. In Europe, the major emphasis is carbon dioxide emissions, and thus diesel engines have become very popular due to their overall fuel efficiency and reduced carbon footprint. NOx is not as big a concern, so the European version has EGR but no urea SCR. Here in North America, NOx is regulated much more tightly (particularly in California and the Green States) and thus the addition of urea SCR to make it 50-state compliant.
EcoDiesel uses a Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF) that are close-coupled to the engine exhaust manifold. This helps warm these components up quickly and then keep them hot during normal vehicle operation, which is critical to fuel economy performance. A hot DPF will regenerate itself more easily without intervention on the part of the engine controls, thus saving fuel that would have been used to initiate an active regeneration. The performance of the DPF is also monitored by a PM sensor that is mounted downstream on the SCR catalyst. Monitoring of DPF and other major emission control system performance is required under OBD II regulations.
High-pressure common rail (HPCR) has been the dominant diesel injection technology for many years, but it could not have maintained its position had it not evolved during that time. The Ram 1500 EcoDiesel uses the latest generation of Bosch HPCR (FCA calls it MultiJet II), which can generate injection pressures up to 29,000 psi (2000 bar). More importantly, the system is capable of breaking each injection event into eight separate pulses and thus maintain exceptional control of the combustion process. This is all accomplished using a solenoid actuator, instead of the more expensive piezocrystal stack that is often utilized for high-performance HPCR injectors. Enhanced control over the injection process makes it easier to increase performance and fuel economy, while simultaneously reducing emissions.
Fuel economy
A clean burning engine is a great starting point when building a light truck for fuel efficiency. However, it takes a holistic approach to make serious gains on the fuel economy front, including many changes that seem almost insignificant by themselves. Add up enough of these improvements, though, and it can turn into a major accomplishment. The key to success is to not take anything for granted and look at every vehicle system as a work in progress.
According to Ram Truck engineers, a 5,000-lb. reduction in vehicle weight equates to a 2 percent increase in fuel economy. Weight reduction is a no-brainer approach to increasing fuel economy, and it starts with the engine itself. The engine block is made of compacted graphite iron (CGI), which is engineered to disperse graphite more evenly and thus be stronger and more durable than conventional cast iron. These properties enable engineers to use less CGI to build a block of equivalent strength. CGI also helps limit the noise, vibration and harshness (NVH) issues that plague conventional diesels. As a further weight reduction measure, other EcoDiesel engine components are made from aluminum, including the cylinder heads and the oil pan.
Pulse width modulation (PWM) technology was used extensively when designing the Ram 1500 EcoDiesel. In this context, PWM is a real technical term as well as being used to describe a design philosophy. The basic idea is look carefully at the vehicle electrical system and determine where energy is consumed with no benefit being realized. The system is then redesigned to use the minimum amount of energy required to get the job done. Examples of this include the forward cooling fan and the fuel delivery system, which not only use less energy but also live longer. Collectively, PWM improvements on the Ram 1500 EcoDiesel resulted in a 0.4 percent increase in fuel economy.
Taking a page directly from the hybrid-electric vehicle book, the Ram 1500 EcoDiesel uses electric power steering (EPS) to increase vehicle fuel economy. EPS does away with the power steering pump and its belt drive, which waste energy most of the time because they are only put to work at low vehicle speeds. The only time that EPS uses energy is when power steering is actually required, which results in fuel savings of up to 1 percent.
The Torqueflite 8-speed automatic transmission is used in both the Jeep Grand Cherokee and the Ram 1500 versions of the EcoDiesel. Photo: FCA US LLC
Another hybrid-pioneered technology used in the EcoDiesel is the start-stop system, which shuts the engine off when idling under certain conditions and then automatically restarts it when the driver depresses the throttle. By limiting excessive idling, the start-stop system generates another incremental improvement in fuel efficiency.
Aerodynamics make a major contribution to the fuel economy performance of the Ram 1500 EcoDiesel. Pickup trucks have traditionally been designed as rolling bricks, with little consideration given as to how their shape impacted fuel consumption. Numerous tricks have been employed to reduce the drag coefficient of the Ram 1500 EcoDiesel, including ECM-controlled Active Grille Shutters (AGS), which block air from passing through the radiator when it isn’t needed for engine cooling. The shutters improve fuel economy but have a side benefit of helping maintain engine temperature in extreme cold weather.
The High Fuel Efficiency (HFE) model of the Ram 1500 EcoDiesel pushes the aerodynamic envelope one step further, with the addition of underbody panels and an air suspension system. The underbody panels are another hybrid car trick that serves to cut down on wind turbulence, which is further reduced when the air suspension automatically lowers the truck body at highway speeds. The air suspension is a closed system, with a nitrogen reservoir and a pump to adjust the air springs.
Ram Truck engineers also looked carefully at energy losses that take place in the Ram 1500 EcoDiesel’s powertrain. When the truck is first started, the engine coolant warms up rapidly but the other fluids take time to get up to temperature. Cold fluids cause more drag in the powertrain, as well as negative effects on vehicle drivability.
To address this issue, they devised a thermal management system that utilizes a heat exchanger with dedicated pathways for coolant, engine oil and transmission fluid. Engine coolant transfers its heat to the other fluids, which serves to warm them up more rapidly and improves shift quality and overall efficiency. The reverse is also true as excessive heat developed by the EcoDiesel’s 8-speed transmission can be dissipated to the cooling system, improving the transmission’s durability and performance. The thermal management system’s impact on fuel economy is definitely worth the trouble, with a 1.7 percent gain in fuel economy realized.
Wrapping it up
No technological stones are being left unturned in the quest for the light truck fuel efficiency crown. While the low-hanging fruit has already been harvested, incremental fuel economy improvements add up quickly and are transforming the pickup’s traditional image. The diesel engine is also proving its resilience as it steps up to meet emission control challenges. It should be fun to see where the road takes us next!
