Hydraulic hybrid transmission

At the 2007 New York International Auto Show, Folsom Technologies (FTI) displayed its 50/100 hp City Car CVT. This unit is designed to go into front wheel drive passenger vehicles of up to 100 hp but, because of its compact size and weight, it is also suitable for application in small city cars of 50 hp or lower. The CVT was configured as a replacement for the 5-speed manual transmission that was originally fitted to the target vehicle, and is approximately the same size. According to FTI, testing of the City Car equipped with their CVT has demonstrated significant economy and performance benefits over the same vehicle fitted with its 5 speed manual transmission. The control system has still to be fully optimized so more economy improvements are anticipated.

The company is also developing the second-generation of a 350 hp - 1,100 lb.ft output torque full-size rear wheel drive passenger vehicle CVT that has been specifically designed to be integrated into a hydraulic hybrid system. Both this and the City Car transmission have been fitted to demonstration vehicles and are currently undergoing in-vehicle testing by a Tier 1 supplier, who is also developing the ratio control electronics and software for the CVTs. The 350 hp CVT, which was developed under a co-funding agreement with the New York State Energy Research and Development Authority (NYSERDA) is currently fitted to a Chevrolet Silverado and is undergoing testing as a standalone CVT. After the control software has been optimized in this mode, the vehicle is scheduled to be fitted with the necessary equipment, i.e., accumulators and control valves, to function as a full hydraulic hybrid. As the transmission was originally designed to suit the Ford Crown Victoria, it is planned to eventually install it as part of a hydraulic hybrid program in a New York City taxi and to conduct durability trials.

FTI's hydromechanical CVTs offer infinite ratio coverage from full reverse through neutral to full forward; and they have a "true" neutral and hence do not require a start-up clutch. They incorporate a proprietary, high efficiency variable displacement hydraulic pump and motor which are connected via epicyclic gearing to the transmission's input and output shafts. As the CVT already incorporates the required hydraulic pump and motor, it can form the core element of a hydraulic hybrid drivetrain. Instead of using commercial hydraulic units, FTI has designed its own patented hydrostatic pump/motor, focusing not just on efficiency but also on cost, size and weight-the transmissions are designed to be a drop-in alternative for existing transmissions. Automotive industry manufacturing techniques and materials have been considered and adopted wherever appropriate during the design and development of these hydraulic units in order to ensure their cost competitiveness. According to FTI, the technology used is totally scaleable and there is virtually no limit to the torque that can be accommodated by a suitably designed FTI CVT. The architecture enables it to be configured in many different ways to satisfy many different applications and space constraints, be it long and thin or short and fat!

For a hydraulic hybrid application, the CVT needs to be paired with a set of accumulators and flow control valves. For passenger car applications, FTI sees its transmissions enabling mild, parallel hybrid functions: regenerative braking, launch assists, acceleration assist and engine starting (for a start-stop function), in addition to normal CVT operation. Commercial vehicles, however, have far more space available in and around the chassis for the installation of larger accumulators. With this extra storage capacity, more of the energy normally lost during braking can be recuperated and performance and economy benefits will be increased.

"Increasing vehicle fuel efficiency and emissions reduction is a high priority and many technologies are becoming available to facilitate these goals," said Lawrence Folsom, president of FTI. "Hybrid vehicles have proven success in increasing vehicle efficiency and hydraulic hybrids offer significant benefits over electric hybrids as they can recuperate a greater percentage of the energy normally lost during braking. Hydraulic motors also have much superior power density compared to their electric equivalents and hence can be integrated into a more compact package. Hydraulic braking energy recovery, which is an available feature of our CVT, offers significant gains in fuel economy and reductions in emissions, as well as greatly reduced brake wear. For operating duty cycles that have frequent start/stops (such as taxis, school buses, garbage haulers, etc.) the fuel savings can be greater than 50% (according to the EPA - see below). Also, the ability to accelerate the vehicle from rest using the stored hydraulic energy will reduce noise pollution as well. Combining the known benefits of a continuously variable transmission with hydraulic energy recovery has the potential to maximize vehicle efficiency gains. The ability to operate and maintain an engine at its 'sweet spot' will drastically reduce emissions and CO2. Our hydromechanical CVT combines two major vehicle improvement technologies into one compact package, therefore significantly greater fuel economy and cost benefits can be expected to be realized."

Independent analysis of the benefits of hydraulic regeneration indicates that significant gains in fuel economy can be had. The United States Environmental Protection Agency has devoted a great deal of energy and expense to the research of hydraulic regeneration and has reported that fuel economy increases in a hydraulic hybrid vehicle can be expected to exceed 50%. According to the EPA "Hydraulic drivetrains are particularly attractive for vehicle applications that entail a significant amount of stop-and-go driving, such as urban delivery trucks or school buses. A major benefit of a hydraulic hybrid vehicle is the ability to capture and use a large percentage of the energy normally lost in vehicle braking. Hydraulic hybrids can quickly and efficiently store and release great amounts of energy due to a higher power density. This is a critical factor in maximizing braking energy recovered and increasing the fuel economy benefit. While the primary benefit of hydraulics is higher fuel economy, hydraulics also increase vehicle acceleration performance. Hydraulic hybrid technology cost-effectively allows the engine speed or torque to be independent of vehicle speed, resulting in cleaner and more efficient engine operation."

FTI is currently developing a number of different CVT applications, including one for a Class III truck with a maximum input/output torque rating of 600 lb.ft/3,000 lb.ft. Again, this has been specifically designed to be installed in a vehicle as part of a hydraulic hybrid driveline configuration. The integrated hydraulic pump and motor use the same basic FTI architecture as the smaller CVTs but are obviously larger in displacement to accommodate the increased torque. The overall size of the CVT is less than the automatic transmission it replaces. It is shorter and, when installed in the vehicle, has increased ground clearance. These benefits have been obtained without compromising floor pan clearance.

In addition to applying its technology to larger vehicles, FTI has produced prototype designs and hardware for smaller applications and is in the final stages of a program to design and build CVTs for a military 6-wheel drive all-terrain vehicle. It shares some of the major components of the CityCar CVT, but has additional functionality such as a locking differential and modular gearing; the latter is to permit the unit to be simply and quickly re-geared to suit different applications.

The lawn and garden equipment and agricultural industries are also being targeted. "The ability to change ratio seamlessly from full reverse through neutral to full forward without the need for a clutch results in a compact and cost efficient system," said Lawrence Folsom." It offers the excellent creep characteristics of hydrostatics which are very desirable for lawn and garden equipment yet has very high efficiency throughout its ratio range. Unlike existing hydrostatic transmissions where 100% of the power is transmitted hydraulically over its entire operating ratio, our CVTs always transmit a portion of the power mechanically. This portion reaches 100% at final ratio and, as a result, our peak hydraulic flow tends to be about 1/3 that of conventional hydrostatic CVTs which means that the hydraulic components can be smaller and lighter. As mechanical power is transmitted more efficiently that hydraulic power, our CVTs are able to offer a higher overall system efficiency, resulting in less noise and heat generation. More and more emphasis is being placed on increasing equipment efficiency in the outdoor power equipment and agriculture industries to reduce pollution."

Non-transmission applications such as torque vectoring axles, hydromechanical cooling fan drives, constant speed PTO drives and machine tool drives are also being addressed by FTI. The first transmission based on the FTI technology is anticipated to reach production status in about 3 years. The company intends to license the manufacturing rights and remain focused on advancing their technology and applying it to new applications. All CVTs are custom designed to suit the specific application and are configured to be drop-in replacements for the vehicle's original transmission.

FTI is a leading designer/developer of hydromechanical CVTs and related equipment. The company also provides complete engineering services to the automotive and other industries from product concept to design release and validation. Technical expertise lies in driveline, vehicle engineering, process equipment and niche volume manufacturing.

For more information visit www.fti-cvt.com