Making a major transition to higher efficiency vehicles, Ford announced its EcoBoost strategy at the North American International Auto Show in January. Three vehicles with a V-6 version of EcoBoost technology will go into production later this year. At the January show, Ford also displayeda concept vehicle that extends the technology to an even more fuel-efficient 4-cylinder engine.
Using a variety of technologies, Ford's stated goal is an improvement in fuel economy and reduction in greenhouse gas emissions fleet-wide by 30 percent by 2020. EcoBoost is one of the company's key initiatives to deliver significant advancements in fuel economy of up to 20 percent while meeting customers' performance expectations. With gasoline direct injection (GDI) technology from Bosch and a turbocharger from Honeywell, Ford has used the existing technology capabilities of key partners, added its expertise and taken some serious steps toward its goal.
EcoBoost is a combination of two aspects: direct injection plus turbocharging. “What's unique about our strategy with EcoBoost is really that we see it as an enabler for fuel economy,” said Craig Stephens, Manager of Powertrain Controls, Research and Advanced Engineering, Ford Motor Company. “There are other gasoline direct injection engines on the market but they are really marketed and designed for performance vehicles.” Ford's goal for gasoline direct turbo injection is engine downsizing to obtain fuel economy benefits. Figure 1 shows the fully dressed EcoBoost V-6 engine.
Achieving low speed torque in a turbocharged engine is one of the challenges that Ford confronted. According to Stephens, considerable effort was made in the EcoBoost design to avoid traditional engine turbo lag, the delay of getting the turbo up to a speed where it can function effectively. To replace a V-8 with a V-6 without incurring customer complaints, the lag problem had to be solved.
Ford uses a Bosch control module but at this point, all the application software in that module was internally developed within Ford. There are a number of challenges in the optimizations that have to occur. “You obviously now have two devices, the turbo and the throttle, an electronic throttle, that can control the air flow into the engine,” said Stephens.
One trade off is fuel economy versus speed of response. There is some optimization that has to be done to achieve the fuel economy and performance benefits. “We spent some time analyzing what are the right signals to measure on the engine,” said Stephens. “That's obviously important from the cost standpoint. We don't want more sensors on there than we need.” Ford engineers also investigated measurements that they could reliably infer and estimate versus those that had to be measured.
Figure 2 shows the actuators and sensors in the 6-cylinder version of the EcoBoost engine. Acronyms in the figure include VCT (Variable Camshaft Timing) and iVCT (intake variable cam timing), as well as BP (Barometric Pressure), MAP (Manifold Absolute Pressure), TIP (Throttle Inlet Pressure), MCT (Manifold Charging Temperature), TCT (Throttle Charge Temperature), ACT (Air Charge Temperature), CHT (Cylinder Head Temperature), UEGO (Universal Exhaust Gas Oxygen) and HEGO (Heated Exhaust Gas Oxygen) sensors.
“Most people who are doing gasoline turbo direct injection will have a mass airflow sensor and a MAP (manifold absolute pressure) sensor,” said Stephens. Ford's system uses only a manifold air pressure sensor. “Our control system analysis showed that we were able to be just as accurate and obviously saved the company a significant amount of money,” said Stephens.
Another one of the tough issues that EcoBoost engineers tackled was the noise, vibration and harshness aspect of a turbocharger. “As the turbo speeds up and slows down, you can get various noises,” explains Stephens. “A lot of time was spent by people designing the air induction system and the turbo to try and minimize that noise.” He noted that there is also a significant controls aspect regarding the control of the wastegate.
An electronically controlled recirculation valve takes care of air that exists when the throttle is closed. The air continues to circulate until it loses momentum. While this approach is not uncommon, Ford gave a lot of attention to the details to achieve the V-8 replacement with a V-6 with little perceptible difference by the customer. “The wastegate has a traditional pneumatic actuator but we can control that by the ECU (electronic control unit),” said Stephens. Figure 3 shows the Honeywell turbocharger with its pneumatic actuator.
One of the key aspects of the program was timing. “The company really wanted it to be delivered quickly and we had about a year less than we would normally have on a program,” said Stephens..
To avoid sacrificing quality for program timing, Ford was aggressive in implementing modern control system design approaches. “The turbo controls were developed entirely in a model-based fashion,” said Stephens. Ford engineers also leveraged hardware-in-the-loop capability in the design process. “Before we ever ran a dyno, we had the control system running on a test bench, a hardware-in-the-loop bench,” said Stephens. “The first morning that we took that module down to the engine dynamometer we basically plugged it in and the engine started and ran. There was no debugging required or anything.”
The control system technology developed for the V-6 is applicable to other powertrains. Stephens views it as a common solution that can be used across all applications. “There is nothing that requires our engine controls to mate up to any particular transmission,” he said. This provides flexibility and opportunities in the transmission portion of the powertrain. Ford has already shown a 4-cylinder version of EcoBoost with a dry dual-clutch transmission that is more efficient than a traditional automatic transmission. Downsizing a larger displacement V-8 to a smaller V-8 to obtain the same performance with improved fuel economy benefits is another possibility.
BOSCH SECOND-GENERATION GDI TECHNOLOGY
Bosch supplies the hardware portion of Ford's EcoBoost GDI system. For second-generation gasoline direct injection, Bosch can supply an entire system or components depending on customer requirements. Three key components of the overall system are the high-pressure pump, the high-pressure sensor and the injectors. Figure 4 shows the complete system.
“The high-pressure pump has a membrane design. It has a little piston that is actuated by some lobes on the camshaft,” said Hakan Yilmaz, Manager of Advanced Engineering, Bosch Gasoline Systems. There can be either three lobes or four lobes on the camshaft depending on the fuel flow and the fuel pressure requirements. The system controls the membrane with a continuous duty-cycle control. “Depending on the pressure requirements in the rail measured by the pressure sensor, we can decide how much pressure we can build by our high-pressure pump,” said Vimaz.
The Bosch pressure sensor uses a stainless steel sensing element with metal thin-film strain gauges. It provides the pressure data in the high-pressure rail.
The driver that actuates the injectors is optimized for each application depending on the number of injectors and the combustion cycle. “This gives us the flexibility to do multiple injections in one combustion cycle,” said Vimaz.
Compared to a port fuel injection (PFI) system where fuel injection must be completed before the intake valve closes, with the direct injection system, fuel can be injected after the intake valve closes. This has several benefits. “One benefit is, since you have the capability of injecting after you close the valve, from a thermodynamics point of view, this has a charge cooling effect so you can take more air charge and that gives you a fuel efficiency benefit of 3 to 4 percent compared to base PFI injection,” said Vimaz.
“The other benefit is since you have more controls on different injection strategies, you can optimize your system with variable valve timing, injection strategies and turbocharging,” explains Vimaz. This allows system designers to eliminate the turbo-lag and reach a peak torque around 1500 rpm.
DRY DUAL-CLUTCH TRANSMISSION
More efficient transmissions are another key part of powertrain technology at Ford. The dry dual-clutch PowerShift six-speed transmission is the latest innovation in its arsenal. “There are two clutches that are controlling essentially two manual transmissions, which are meshed together to allow us to get the efficiency of a manual transmission but get the functionality of an automatic transmission,” said Piero Aversa, Manager of Dry Clutch PowerShift Transmission at Ford. In contrast to the automated manual concept of previous decades, the shift quality is considerably improved.
“With this dual-clutch transmission, when we are making a shift, we bring off one clutch while we are bringing on the other clutch so that we have a seamless delivery of torque to the wheels through the shift, which is very much like a normal automatic transmission,” said Aversa. “We get sort of the best of both worlds with this new transmission.”
Ford has had a wet (hydraulic) dual-clutch transmission in production for European vehicles. The dry dual-clutch version uses a mechatronics approach to add efficiency and durability. “There are two motors that control the clutches and then there are two motors that control the shift actuation forks,” said Aversa. “The two that are controlling the clutches are mounted on the outside of the clutch housing of the transmission,” added Ed Haran, Transmission Systems Supervisor at Ford. “The two that control the shift forks are integrated with the mechatronics actuator module, which is basically a combination of the TCU (transmission control unit) and these two motors as one module.”
The mechatronics design eliminates the torque converter and the hydraulic pump, two power-sapping aspects of a traditional automatic transmission providing a conservative fuel economy improvement of up to 9%. In addition, the dry dual-clutch technology complements the energy efficiency and performance of the EcoBoost engine.
“It mates very well to the EcoBoost technology,” summarized Haran. “It's adding without conflicting with any of their technology.” Ed Haran. Transmission Systems Supervisor at Ford