Hydromechanical CVTs for Hydraulic Hybrid Applications
13 April 2007
|The Folsom 50/100hp CityCar CVT.|
Folsom Technologies has developed a line of hydromechanical continuously variable transmissions (CVT) that are configurable either as a standalone CVT or as the CVT component of a hydraulic hybrid system.
At the New York International Auto Show, the company displayed its 50/100hp CityCar CVT. This unit is designed to go into passenger vehicles of up to 100hp but, because of its compact size and weight, it is also suitable for application in small city cars of 50 hp. It is currently fitted to a 50hp city car and is being used for controls development and technology demonstration.
The company is also developing the second-generation of a 350hp full-size rear wheel drive (RWD) passenger vehicle unit with co-funding from NYSERDA.
Instead of using commercial hydraulic units, Folsom designed its own hydrostatic pump/motor, focusing not just on efficiency but also on size—the transmissions are designed to be a drop-in alternatives for existing transmissions—as well as cost.
For a hydraulic hybrid application, the CVT needs to be paired with a set of accumulators and flow valves. For passenger car applications, Folsom 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.
Although the transmissions could support an “all-hydraulic mode” for several miles, Folsom says, the accumulator size would be too big to make this a practical mode of operation for passenger vehicles.
The control logic for the different applications is currently being developed by a Tier 1 supplier, according to the company.
We predict significant fuel savings due to the combination of the CVT effect coupled with hydraulic braking energy regeneration. The fuel savings are obviously dependant upon vehicle applications. For operating duty cycles that have frequent start/stops (such as NYC taxis, school buses, garbage haulers, etc.) the fuel savings can be greater than 50%. A Chevrolet Silverado has been fitted with one of our transmissions and operated in CVT-only mode. Shortly the necessary accumulators and control valves will be added to this vehicle and testing of the complete hydraulic hybrid system should commence in about 3 months.—Martin Hughes, Folsom Technologies
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