11/05/2002 – 3-Valve Technology Improves Modular V-8 Efficiency, Performance
|Source: Ford Motor Company|
3-VALVE TECHNOLOGY IMPROVES MODULAR V-8 EFFICIENCY, PERFORMANCE
The new 5.4-liter Triton V-8 engine that will power Ford’s next-generation F-150 is designed with three valves per cylinder, variable-cam timing and a host of other features that provide increased power along with improved refinement and fuel efficiency.
The net result is an engine that delivers 300 horsepower at 5,000 rpm, and 365 ft-lb of torque at 3,750 rpm, both best in class for a full-size pickup. The all-new, aluminum cylinder head — with two intake valves and one exhaust valve per cylinder for 24 valves in total — and a new cast-iron block balance this impressive power with better fuel efficiency and quieter operation.
This new technology builds on Ford’s award-winning modular V-8 engine platform, while taking advantage of the capabilities offered by modern electronic controls. It is important to note that it isn’t a single technology, but rather a suite of enhancements that deliver these consumer benefits.
The new 24-valve engine – will be Ford’s first modular V-8 to use variable-cam timing (VCT). The VCT design allows Ford engineers to optimize intake-and exhaust-valve actuation across the rev range. It represents the industry’s first mass application of dual-equal variable-cam timing, which shifts the intake and exhaust valve timing together.
In combination with precise control of spark timing, fuel injection and use of electrically controlled Charge Motion Control Valves in the intake ports, this technology produces class-leading power and torque, particularly at the lower engine speeds that are so important to applications such as towing and heavy hauling.
Three-valve cylinder head improves power
Why did Ford engineers choose a three-valve-per-cylinder architecture for their next generation of V-8 engines?
The modular V-8 engine family is one of the most important products in Ford’s powertrain lineup. Ford produced more than 1.3 million of these engines in the 2001 calendar year.
While the two-valve modular V-8 line continues to deliver solid, efficient performance, Ford Motor Company’s premium V-8 engines – such as the Mustang Mach I and Cobra, Mercury Marauder or Lincoln Aviator powerplants – have shown the performance potential of multi-valve arrangements.
The use of two intake valves enhances fuel-air mixing prior to combustion. This helps to squeeze all the energy out of each combustion event, improving power delivery and fuel efficiency.
Multiple valves also enhance the engine’s ability to “breathe” – that is, to move large volumes of air in and out of the cylinders – which is a key to generating maximum horsepower. Four-valve engines remain Ford Motor Company’s first choice for luxury and high-performance applications, where horsepower and acceleration are prime concerns.
Yet they require considerable complexity, including two camshafts per cylinder head, which adds both weight and additional moving parts.
Ford engineers discovered they were able to get many of the benefits of a four-valve design – such as a central spark plug and symmetrical combustion chamber – using two intake valves and a single exhaust valve – with reduced weight and complexity compared with four-valve designs. The two intake valves allow peak airflow of approximately 350 cubic feet per minute, compared with about 250 cubic feet per minute in the 5.4-liter Triton V-8, which uses a single intake valve per cylinder. This represents a 40-percent improvement.
As an example of the engine team’s holistic approach, this improvement in peak flow also is due to a completely redesigned intake port, which provides a much straighter path to the cylinder – very similar to the approach taken in racing engines.
With an all-aluminum head, single camshaft, magnesium cam covers and a clean-sheet design approach, Ford’s engineers were able to develop a three-valve head that has virtually no weight penalty over the two-valve V-8 engines. The three-valve head is actually dimensionally smaller and somewhat lighter than the two-valve design for the 5.4-liter engine, while offering more rigidity and strength. It also is easier to manufacture, with simpler drilling angles and straight-machined surfaces.
Variable-Cam Timing (VCT) offers multiple benefits
Ford’s new three-valve cylinder head uses a single overhead camshaft for each bank of cylinders. The cams press down on roller-finger cam followers to open the intake and exhaust valves, which are closed by coil springs as in all Ford’s V-8 engines.
Conventional camshafts are permanently synchronized with the engine’s crankshaft so that they operate the valves at a specific point in each combustion cycle. In Ford’s modular two-valve 5.4-liter V-8 engine, the intake valve opens slightly before the piston reaches the top of the cylinder and closes about 60 degrees after the piston reaches the bottom of the stroke on every cycle, no matter what the engine speed or load is.
Variable-cam timing allows the valves to be operated at different points in the combustion cycle, to provide performance that is precisely tailored to the engine’s specific speed and load at that moment. The timing is set to allow the best overall performance across the engine’s normal operating range.
If conditions require earlier valve opening and closing, for example to achieve more low speed torque, the Powertrain Control Module (PCM) commands solenoids to alter oil flow within the hydraulic cam timing mechanism, which rotates the camshafts slightly. If the valves should open later, to generate more high-speed power, the mechanism retards the cams as needed.
The result is enhanced efficiency under low-load conditions, such as at idle or highway cruising, and increased power for brisk acceleration or times of high demand.
“When you’re driving, you can’t tell that the cams are changing,” said Pete Dowding, Modular Engines Manager. “But you can certainly tell that there’s more power when you ask for it.”
The ability to control valve timing as well as spark timing allowed Ford engineers to design a combustion chamber with a higher compression level than in the two-valve V-8 engines – again, while still using regular gasoline octane levels. Higher compression ratio produces greater efficiency, delivering more power and improved combustion efficiency.
Among the other advantages generated by variable-cam timing and electronic spark control:
Charge Motion Control Valves improve low-speed combustion
The air-fuel mixture entering an engine behaves differently at different engine speeds and loads. At low engine speeds and light loads, relatively little air-fuel mixture is drawn into the cylinders in a given time period, so it moves relatively slowly through the intake runners and into the cylinders. At high engine speeds, the intake mixture speeds up, as a larger volume passes through the intake runners over the same time period.
One of the challenges involved in squeezing the utmost efficiency out of each drop of fuel is to assure that it mixes thoroughly with air, in the right ratio, before it is burned in the cylinders. This is easiest when the air is moving quickly.
At lower speeds and lighter loads, the new three-valve engine uses an electronically controlled metal flap at the end of each intake runner – eight in all. This Charge Motion Control Valve was specially shaped, through CAD modeling and testing, to speed up the intake charge and induce a tumble effect in the combustion cylinder. This causes the fuel to mix more thoroughly, and to burn quickly and efficiently, with reduced emissions, particularly at idle.
The CMCVs are controlled by an electronic motor, and open at a predetermined point as engine speed increases. At higher RPM, they do not affect the intake charge at all. This allows undisturbed maximum flow into the combustion chambers at wide-open throttle. The CMCV motor is sound insulated, so its operation remains transparent to vehicle occupants.
Attention to detail improves refinement
Like the improvements in overall engine performance, improvements in the new three-valve engine’s refinement result from a host of design features, rather than a single breakthrough. For example, the same intake and exhaust manifolds that produce better airflow and improved efficiency also are designed to offer quieter operation.
Ford’s noise, vibration and harshness (NVH) engineers used computer modeling to design vibration-resistant ribbing and reinforcement into the composite intake manifold.
Because the intake area is so important to customers’ perceived sound levels – it is, after all, the closest engine component to the driver’s ears – sound is further managed through use of sound-insulating materials and a three-part tuned mass absorber in the “valley” beneath the intake runners. A new sound-absorbing engine cover wraps around the edges of sound absorbing blankets at the front and rear of the engine.
The intake manifold alone represents a host of refinements to previous models. For the first time, the manifold arrives at the assembly plant with the fuel rail, air cleaner, throttle body and PCV unit in place. This makes assembly much faster and reduces complexity. The main portion of the manifold is friction-welded together for durability. Even the air filter assembly is innovative, with a slide-out drawer offering customers quick access to the cleaner element for service.
The new engine’s pistons also have been shaped with noise reduction in mind. The pistons have longer side skirts than in the past, which helps to control piston movement and minimize piston slap.
The three-valve design itself helped to reduce operating noise, as the engineers were able to balance the forces generated by valve and spring movement against each other, and aim the resultant force vectors toward the engine’s overall center of gravity. This reduces total engine vibration – and vibration equates to noise.
The smaller cylinder heads naturally have a smaller surface area, which helps to reduce radiated noise. Roller-finger camshaft followers used in the cylinder head are both more efficient and quieter than non-roller designs.
Also at the top of the engine, new magnesium cam covers offer the vibration-resistance of aluminum, at reduced weight. They are further isolated from vibration via rubber mounts. Reinforcing ribs cast into the cam covers, as well as a reinforcing plate in the underside of the covers, were both computer designed to minimize audible vibrations.
NVH engineers took a different approach with the engine’s front cover, which must bear the mechanical stresses of the accessory drive belt.
In the new “controlled standoff” design, solid metal is used at the points where the cover bolts to the cast iron engine block, but a rubber gasket damps vibrations between mounting points. This refinement alone is responsible for a one-decibel reduction in overall sound levels.
Behind this cover, the cam chains are now controlled by a new tensioner, which is reshaped to control small side-to-side chain movements, and the sounds associated with them.
The engine block itself is stiffer than in the past, through addition of computer-designed reinforcements cast into the block sidewalls, and thicker metal along the gasket surfaces. This, in combination with a new style oil pan made of a sandwich of metal around a plastic core, helps to minimize sound transmission through the bottom of the engine.
These designs were all validated through extensive measurement in Ford’s Advanced Engineering Center dynamometer cells – acoustic rooms where developmental engines are run while surrounded by sensitive microphones. Ford has eight such dyno cells in its Advanced Engineering Center.
Engineers craft a confident sound quality
While precise control of overall noise is key to delivering a refined powerplant, silence isn’t everything. Ford’s approach to powertrain development includes engineering the right kinds of sounds into each vehicle.
For example, Ford vehicles must provide appropriate audible feedback, as well as brisk acceleration, when the driver steps hard on the gas pedal.
This sound of power – only present during brisk acceleration – is created by tailoring the engine’s NVH package to allow the right amount of fourth-order resonance to reach the passenger compartment. This tonal quality represents the sound of V-8 engine performance, and is tuned through precise shaping of the intake and exhaust systems, as a part of the entire NVH program.
This isn’t a one-size-fits-all approach, however. The Ford F-150 has a distinctive sound under full throttle, different than the unique sound of the Mustang. The Ford Expedition also has its own powertrain character, fitting the engine sound of the Ford Outfitters sport-utility lineup.
Each vehicle development team crafts its entire powertrain package to achieve the brand’s desired characteristics.
On the new three-valve engine, the equal-length intake runners are optimized for both power delivery and sound quality. For example, the variable Charge Motion Control Valves at the end of each intake runner close down to create turbulent airflow at low engine speeds, for efficient burning. At higher engine speeds, they open completely, to allow full airflow and quiet operation.
The exhaust manifolds represent a complete departure from the flat, log-style cast iron manifolds of the past. At first glance, they most closely resemble the high-performance exhaust “headers” from the world of motorsports. Yet in some ways, they outperform their competition counterparts, thanks to computer engineering.
Gretchen West, the Ford engineer who designed these new exhaust manifolds, says she tested both dual-core, pulse-separated exhaust runners and three-foot long fabricated header-style manifolds, and her final design delivers comparable horsepower to both, in a space, weight- and cost-saving design.
The explanation lies in matching the exhaust runner lengths and placement with the engine’s firing order, so that the cylinders help to scavenge each other, increasing both the volume and efficiency of the exhaust gas flow. In dynamometer testing, the asymmetric design proved their merit.
“Past exhaust manifold design practice focused more on mass flow as the primary attribute,” West said. “The more important attribute for performance is the interaction and separation between exhaust pulses. We achieved five more horsepower with this design vs. one that targeted only maximum flow in each individual runner.”
One common misconception is that the hottest point in the exhaust manifold is the area right next to the combustion chamber. West said that combustion continues in the exhaust manifold, which experiences its highest temperatures back by the collector, just ahead of the catalytic converter. This in turn promotes efficient operation of the catalyst, and lower emissions.
The new three-valve cylinder heads were designed with input from the exhaust manifold team. One key result was that the manifold bolt locations were moved. This simple change gave West significantly more flexibility to optimize her design, while still allowing access for the robotic machine that fastens all eight exhaust nuts in a single operation at the engine assembly plant.
The exhaust runners are twice as tall – 60 millimeters vs. 30 millimeters – which helps to improve flow and pulse separation within the manifold core, and are more circular in cross-section, which improves NVH.
The runners also are more widely separated than in past designs. They are braced together with computer-designed webbing, which is curved for NVH efficiency.
Another advantage of the new exhaust manifold design is that it is able to forgo the exhaust gas recirculation port, due to the cylinder head’s unique design. This reduces turbulence, and balances pressures among the exhaust runners.
The new three-valve cylinder head will be manufactured at the Windsor (Ontario) Engine Plant beginning next year with the full engine assembled at the Essex (Ontario) Engine Plant, also in Windsor. The two plants – both past winners of the prestigious Shingo Award for Excellence in Manufacturing – combined to produce 1.1 million V-6, V-8 and V-10 engines in 2001.
Production of the new 5.4-liter, 3-valve Triton V-8 began in August 2002 for the new Ford Falcon, sold in Australia.
“Our new three-valve, 5.4-liter Triton engine, to be launched in the next-generation 2004 F-150 pickup, provides more of the qualities our customers love in a V-8 engine – plenty of power, with instant gratification when you push the accelerator pedal. To this, we’ve added a new level of smoothness, quiet operation and efficiency. It’s the best of all worlds.” — Pete Dowding, Manager, Modular Engine Programs