VW's Breakthrough 69 MPG Diesel Hybrid
By Todd Kaho
What if the standard fuel tank in a VW Rabbit carried enough to propel you 1,000 miles between fill-ups? If that Rabbit was motivated by the same clean diesel TDI hybrid powertrain featured in Volkswagen’s latest concept/developmental vehicle, the standard 14.5 gallon capacity could do just that.
VW recently pulled the wraps off a Golf TDI Hybrid concept vehicle that tops all current U.S. fuel economy standards by a substantial margin. According to Volkswagen, the Golf TDI Hybrid consumes just 3.4 liters of diesel per 100 kilometers traveled. That translates to just over 69 miles per U.S. gallon (European fuel economy cycle) in a four door hatchback that’s equivalent to the North American VW Rabbit. The current 2008 Rabbit is offered in the States with a 2.5-liter inline five- cylinder that achieves an EPA fuel economy rating of 22 mpg city and 29 mpg on the highway.
VW, a diesel technology leader for decades, utilized engine downsizing combined with hybrid electric drive assist to achieve the Golf TDI Hybrid’s remarkable fuel economy. Rather than the current four cylinder TDI offerings that are so popular in the European market, Volkswagen teamed this hybrid with a small 1.2-liter three-cylinder clean diesel that’s said to produce approximately 74 horsepower with the help of a turbocharger and direct injection (TDI) technology. Add in the boost of a 27 horsepower electric motor and you get a total of 101 combined horsepower with 235 lbs-ft of torque. That’s enough to give the TDI Hybrid respectable performance. The system features regenerative braking to help keep the 220 volt nickel-metal-hydride (NiMH) battery pack topped off. Impressive, too, is that the Golf TDI Hybrid produces just 89g/km of CO2 in the EU combined test cycle.
Making the most of that power is VW’s 7-speed DSG gearbox rather than the continuously variable transmission (CVT) found in most hybrids. DSG (Direct Shift Gearbox) utilizes a dual-clutch design and provides the convenience of a traditional automatic transmission with the driver control of a manual. With seven gear ratios to work with, the DSG in the TDI Hybrid can make the most of the power at hand for maximum acceleration and fuel economy.
VW says the TDI Hybrid offers the ability to run on either emissions-free electric power, on the clean diesel engine, or a combination of the two as power demands require. It features an automatic stop-start function to switch off the diesel when the Golf is stationary. One of the common obstacles VW had to overcome when pairing diesel with electric drive was restarting the engine quickly and seamlessly in the stop-start mode, which is more challenging with diesel since these engines fire on compression rather than spark ignition.
Will VW bring the TDI Hybrid stateside? It’s too early to tell, but if fuel prices continue to rise, the demand will certainly be there. We hope to bring you a first drive of this breakthrough green car in the not-too-distant future.
Want to know more about VW’s advanced technology programs? Be sure to check out these articles on GreenCar.com:
Volkswagen 1-Liter 235 MPG Extreme Fuel Efficiency Car
VW Conjures Up a Hydrogen Powered Microbus
Volkswagen TSI Engines have Better Fuel Economy and Emissions
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