(Dearborn, October 2, 2009) In the late spring of 2009 Ford Motor Company began launching its first production vehicles powered by gasoline turbocharged direct injected (GTDI) engines. Ford has chosen to badge its GTDI engines as EcoBoost as indication of its intentions to use them as replacements for similarly powerful but larger displacement engines that use more fuel.
Ford is by no means the first automaker to go down the GTDI path. The Volkswagen Group uses similar engines extensively among its various brands, badged as TFSI. General Motors has also offered a 2.0-liter GTDI four cylinder in several models in recent years while Ford affiliate Mazda has had a 2.3-liter GTDI in the MazdaSpeed3.
In January 2008 at the North American International Auto Show, Ford announced its intention to begin rolling out EcoBoost and making the technology mainstream and affordable. The technology will also aid Ford in taking a holistic approach to weight reduction through downsizing to smaller lighter powertrains that require less structure to support them. Since that time Ford has increased its projected volumes from 750,000 units annually to over 1.3 million. The automaker also plans to offer EcoBoost engines in 90 percent of product line by 2013.
The first EcoBoost engine to enter production was the 3.5-liter V6 that is available as an option in the Ford Flex, Lincoln MKS and MKT. The EcoBoost 3.5 is also the standard engine in the 2010 Taurus SHO. While the 355 hp engine doesn't fit the image most people have of a fuel efficient engine, it makes sense in light of the overall strategy. Ford is using the Ecoboost V6 where competitors would opt for a similarly powerful V8. Compared to a V8 of similar output, the V6 gets about 10-20 percent better fuel efficiency.
Similarly, Ford's new 2.0-liter four cylinder EcoBoost that debuts in 2010 will be used to replace 3.0-liter V6 applications. Since producing more power and torque generally requires consuming more air and fuel, it might seem that a similarly powerful turbocharged engine would not be any more efficient than a larger engine. Dan Kapp, Ford's Director of Powertrain research and development explained why the EcoBoost engines are in fact more efficient.
At the fundamental level, engine researchers and designers use two measures for evaluating an engine, brake mean effective pressure (BMEP) and brake specific fuel consumption (BSFC). These are displacement independent measures of output and efficiency. BMEP is essentially the torque divided by displacement while the BSFC is the consumption at a given BMEP and engine speed.
Internal combustion engines typically have minimal BSFC where BMEP peaks and load is maximized. At partial or light load conditions, the efficiency is reduced as a result of pumping losses. The downsized GTDI strategy attacks this problem from two main directions. Reducing the displacement of the engine means that it will be working harder more of the time it is operating so that it is higher up the load curve. Adding a turbocharger forces more air into the engine overcoming the pumping losses at partial loads.
The result is that the region of peak BMEP is significantly expanded over a larger engine speed and load range. This translates to a larger region of improved BSFC. At the same time the increased BMEP also results in improved engine response and drivability. All of this explains the fundamental rationale for the GTDI approach. However, as with all other combinations of technologies, the key is in the execution.
Ford's powertrain engineering staff has expended a significant amount of energy on the up-front work required to get the engines to market quickly while at the same time getting them to perform as efficiently and smoothly as possible. In the process of developing the 3.5-liter V6 EcoBoost engine Ford has applied for or been granted 125 US patents.
From the time that the V6 EcoBoost engine program was kicked off in mid 2006, only 36 months elapsed until it reached production. While the GDTI variant was based on the existing Duratec 35 it has a number of differences including the obvious direct injection and turbocharging. Those two differences necessitated a number of internal changes.
Direct injection affords a number of advantages over port injection, however the latter does have an advantage when it comes to fuel mixing. Spraying the fuel into the ports promotes mixing, as the air swirls around the intake valves. The swirling helps most of the fuel to vaporize prior to combustion. Ford developed its own in-house computational fluid dynamics tools that were used extensively for this program.
The team developed a spray model that allowed them to experiment with the timing and injector pulse widths as well as the shape of the piston bowls. When the fuel is injected directly into the cylinder some of it inevitably contacts the piston or cylinder walls where it can condense. The CFD models allowed the engineers to evaluate hundreds of different combinations before ever building any parts. The shape of the piston bowl that was devised helps to keep the air-fuel mixture swirling to promote the evaporation of the fuel that impinges on the metal parts. The end result is more complete combustion for reduced consumption and emissions.
Another of the problem the engineers were able to address early in the process through modeling and lab testing was cold start. Over 90 percent of the emissions produced by modern engines occur during cold-start. The catalytic converter is not effective until the internal temperature rises. Getting hot exhaust gases into the catalyst as early as possible to raise its temperature and light it off are critical.
Adding a turbocharger into the exhaust stream increases the thermal mass and reduces the temperature of the exhaust gas before it gets to the catalyst. This is exacerbated by cold metal internal parts inside the engine. When the fuel hits the metal parts it condenses. Thus the shape of the combustion chamber and piston bowl also play a part in getting the fuel vaporized during cold start to minimize emissions. Besides the hardware, the EcoBoost engine also takes advantage of the high pressure direct injection system to provide dual injection pulses. This helps promote atomization of the fuel for more complete burning.
Duratec 3.5 piston on the left, EcoBoost 3.5 piston on the right
Once the basic design was narrowed down, prototype parts were evaluated in single cylinder optical engines. Transparent cylinders and pistons allow the engineers to evaluate combustion process to ensure that there are no hot spots or unburned fuel. The transparent parts allow the use of a laser to illuminate the air-fuel mixture for both still photographic analysis as well as high speed video. Ford has the ability to analyze the fuel burn in slow-motion with a camera that can shoot at 10-20,000 rpm. The optical engine also allows the modeling engineers to validate the CFD models. Once the basic components are tested and validated, complete engines can be built up.
At this point the powertrain controls engineers take over much of the responsibility. Like most other manufacturers Ford is model based development to create the control systems. Ford uses a modeling tool called Matlab to develop and simulate the control models. Matlab control models can be incorporated into both virtual engine models and actual engine electronics for software in the loop and hardware in the loop simulation.
Part of the Matlab tool suite is a package called Simulink that allows the models to be turned into automatically generated computer code for the ECU. Over the past 15 years a lot of progress has been made on automatic code generation from models, however such code still is not as compact or efficient as code produced by hand translation. There are some applications where auto-code is used in production, but according to Dr. Mrdjan Jankovic, technical leader for controls on EcoBoost, the auto-code was not used for this application. Jankovic does expect to see auto-code used in future Ford engine controls.
Developing a control system for an engine is not as simple as just monitoring all of the sensors around the engine and making adjustments to maintain an optimal air-fuel ratio. The operation of an engine is a very dynamic process and drivers expect the powertrain to be responsive to their commands. One of the causes of poor response and drivability is inertia. At its most basic level the output of an engine is controlled by the flow of air and fuel into the combustion chamber. The air flow is generally controlled by the throttle plate (although some newer engines with advanced variable valve timing are able to eliminate the need for a throttle). The air has some distance to flow from the throttle to the cylinder and throwing other components like turbochargers into the path complicates things further.
Jankovic and his team spent a considerable amount of time analyzing the behavior of the engine under a wide variety of conditions. As a result they were able to develop an array of algorithms that use the data from the driver inputs, transmission control, and all of the vehicle sensors to create anticipatory models of what will happen. For example we were shown acceleration curves for a vehicle with the EcoBoost engine compared to the 2007 GTDI inline-six in the BMW 335i. Following each shift of the transmission there was a significant drop-off in acceleration that took time to recover.
The EcoBoost vehicle had much shorter acceleration "holes" and therefore much more consistent acceleration. The control strategy is able to use the leading information about an impending shift and preemptively make adjustments to throttle and fuel control so that as soon as the shift is completed, the engine has already begun responding with improved torque.
Another strategy the team was able to develop as a result of having both variable valve timing and direct injection was the use of scavenging to improve low end torque. In a port fuel injected engine, the overlap period where the intake and exhaust valves are open has to be limited in order to prevent unburned fuel from going straight out the exhaust. Since direct injection allows the fuel to be sprayed in after the exhaust valve closes, the overlap can be increased.
Because the intake air is pressurized by the turbocharger, adding extra overlap can help push the exhaust gases out of the cylinder. Having more "clean" air can help the engine produce more torque, particularly at low engine speeds. This helps improve the driveability and reduces the need to rev the engine higher, again helping fuel economy.
These and many other developments from the EcoBoost team contributed to the 125 new patent filings just for the first V6 engine.
The first public appearance of what was to become the EcoBoost V6 was in January 2007 at the North American International Auto Show in the Lincoln MKR concept. A year later in Detroit, Ford announced its EcoBoost strategy with the V6 debuting in production earlier this year. Over the next year, two more four cylinder EcoBoost engines will debut in Europe and North America. A 1.6-liter will appear in Ford's new C-segment lineup beginning with the C-Max that debuted in Frankfurt last month. A 2.0-liter will supplant some V6 applications although Ford has not yet revealed which vehicles would get the new engine. The Escape crossover and Fusion sedan are likely candidates.