CClleeaann  AAuuttoommoottiivvee  TTeecchhnnoollooggyy......                                                                                        IInnnnoovvaattiioonn  tthhaatt  WWoorrkkss                                                                                      wwwwww..eeppaa..ggoovv//oottaaqq//tteecchhnnoollooggyy  

  WWoorrlldd’’ss  FFiirrsstt  FFuullll  HHyyddrraauulliicc  HHyybbrriidd  SSUUVV    PPrreesseenntteedd  aatt  22000044  SSAAEE  WWoorrlldd  CCoonnggrreessss    In collaboration with its partners, the U.S. Environmental Protection Agency (EPA) has been 

researching advanced technology for the past ten years. EPA has had research partnerships with several organizations including Ford Motor Company, Eaton Corporation, Army’s National Automotive Center and Parker Hannifin Corporation.  

  Hydraulic hybrid technology is one of the EPA research 

areas, with the vehicle presented at SAE being the first-ever SUV with a fully hydraulic drivetrain. 

  Hydraulic hybrids increase vehicle fuel economy in two 

main ways: they allow the engine to be operated at much more efficient modes and they permit the recovery of energy that is otherwise wasted in vehicle braking. 

  The vehicle displayed was a diesel hydraulic hybrid with a projected 55% improvement in fuel 

economy due to the hydraulic hybrid technology.  The hydraulic hybrid technology is projected to increase the cost of a large SUV by about $600, which would be quickly recouped by the consumer’s lower fuel and maintenance costs.   Another 30-40% improvement is available through the conversion of the gasoline engine to a diesel engine. 

  Improved fuel economy reduces greenhouse gas emissions, lowers dependence on imported oil, as 

well as saves consumers money.   

 Full hydraulic hybrid technology means that the conventional transmission and transfer case have been removed and replaced with a hydraulic drivetrain; EPA has also replaced the large gasoline engine with a small diesel engine. 

  The hydraulic components are easily 

packaged in this vehicle because the conventional transmission and transfer case were deleted. 

  Hydraulics are an exciting alternative to batteries for making a hybrid vehicle–while electric hybrids 

add a battery pack, electric generator/motor, and power electronics, hydraulic hybrids add an accumulator (which stores energy as highly compressed nitrogen gas) and one or more hydraulic pump/motors. 

  EPA and its partners have active programs to demonstrate the commercial potential of hydraulic 

hybrids. 

 CClleeaann  AAuuttoommoottiivvee  TTeecchhnnoollooggyy......                                                                                        IInnnnoovvaattiioonn  tthhaatt  WWoorrkkss                                                                                      wwwwww..eeppaa..ggoovv//oottaaqq//tteecchhnnoollooggyy  

FFuullll  HHyyddrraauulliicc  HHyybbrriidd  SSUUVV    

        PPrroojjeecctteedd  DDeessiiggnn  EExxaammpplleess   

 Large 4WD SUV 

 Medium Engine Package 

 Small Engine Package 

Diesel Engine 3.8-liter (170 kw) 1.9-liter (95 kw) Accumulators 15 gals 22 gals 

Weight Increase 360 lbs (163 kg) 125 lbs (57 kg)   

Fuel Economy – label values  

Fuel Economy – label values City 32 mpg 33 mpg 

Highway 22 mpg 23 mpg Combined 27 mpg 28 mpg 

  Cost/Payback 

 Cost/Payback 

Cost Increase $2,200 $1,000 Consumer Payback 2.5 years 1.1 years 

Net Lifetime Savings $4,800 $6,300   

Performance  

Performance 0-to-60 mph acceleration 

(at test weight)  8.9 seconds 11.4 seconds 

Max sustained speed (at GVWR) 

108 mph 90 mph Max sustained grade 

(at 70 mph at GVWR)  9.1% 3.5% 

GVWR plus towing (at 65 mph at 5% grade) 

12,000 lbs 6,900 lbs 

  Economic assumptions:  Mature high-volume production, vehicle life of 14 years and 188,000 miles,  

$1.50 per gallon fuel price, 7% discount rate, and 26% retail price mark-up  For more information:  See “Progress Report on Clean and Efficient Automotive Technologies Under 

Development at EPA”, Interim Technical Report, January 2004, at www.epa.gov/otaq/technology 

 CClleeaann  AAuuttoommoottiivvee  TTeecchhnnoollooggyy......                                                                                        IInnnnoovvaattiioonn  tthhaatt  WWoorrkkss                                                                                      wwwwww..eeppaa..ggoovv//oottaaqq//tteecchhnnoollooggyy  

FFuullll  HHyyddrraauulliicc  HHyybbrriidd  SSUUVV    

PPrroojjeecctteedd  PPeerrffoorrmmaannccee  EExxaammpplleess               

0 2 4 6 8 10 12 14 16 18 20 22 24

Time (s)

0

10

20

30

40

50

60

70

80

Vehi

cle 

Spee

d (m

ph)

Conventional Expedition (5.4L gas)95 kW, 4-cyl engine, 22 gal accum, 5000 psi max95 kW, 4-cyl engine, 22 gal accum, 7000 psi max170 kW, 6-cyl engine, 15 gal accum, 5000 psi max170 kW, 6-cyl engine, 22 gal accum, 5000 psi max

0-70 MPH AccelerationFull Hydraulic Hybrid SUV 

0 1 2 3 4 5 6 7 8

Time (s)

50

55

60

65

70

75

Vehi

cle 

Spee

d (m

ph)

Conventional Expedition (5.4L gas)95 kW, 4-cyl engine, 22 gal accum, 5000 psi max95 kW, 4-cyl engine, 22 gal accum, 7000 psi max170 kW, 6-cyl engine, 15 gal accum, 5000 psi max170 kW, 6-cyl engine, 22 gal accum, 5000 psi max

55 - 70 MPH Passing AccelerationFull Hydraulic Hybrid SUV

 CClleeaann  AAuuttoommoottiivvee  TTeecchhnnoollooggyy......                                                                                        IInnnnoovvaattiioonn  tthhaatt  WWoorrkkss                                                                                      wwwwww..eeppaa..ggoovv//oottaaqq//tteecchhnnoollooggyy  

Accumulator

Shaft

Reservoir

VehicleBrakingKineticEnergy100

10092

82

Wheel

90

Regenerating ModePropulsion Mode

Efficiency82%

(91%)(98%)

HydraulicMotor

Wheel

Accumulator

Reservoir

100

82

Wheel

90

Regenerating Mode

Efficiency

(92%)

Pump

Wheel

Shaft

  EEPPAA  AAddvvaanncceess  iinn  HHyyddrraauulliicc  CCoommppoonneennttss   

Composite Accumulators Charge/Discharge Cycle Efficiency 95 % to 99% 

Overall Weight 240 pounds (22 gallon system) Weight Reduction 80 to 90% (from steel piston type accumulators) 

Specific Energy ~8 kW-sec/kg Energy Density >50 kW-sec/gallon Power Density 3 kW/kg Specific Costs $10/kg 

Operating Pressure 5000 psi Next Generation - Operating Pressure 7000 psi 

Pump Motors Peak Efficiency 95+% 

90+% Efficiency over 60% of the operating map Power Density 5 kW/kg (w/integrated mode valve) 

Next Generation - Power Density 7 kW/kg (w/integrated mode valve)  

This hydraulic system can store and re-deliver about  80% of braking kinetic energy back to the wheels. 

 EPA420-F-04-019 

                                                                                                                                                  March 2004