The only energies needed to drive a car are used to:

1.   Move the car body through the air.
2.   Roll the tires over the street.

This requires typically less than 1/5 of the consumed energy. The remaining more than 80% are lost as heat or used to drive accessories. The main losses are fuel conversion losses in the engine and those from braking.

Technical data and the Calculation of Fuel Consumption are shown in the Media Library: Technical Report / The 130 mpg Car / pages 14-16.

Reducing the energy consumption to drive the car is reached by:

1. Moving

a.   Low air drag.

The shape of the car body determines the air drag. A practical comparable size for the passenger compartment has been considered here. The air drag of current cars is high, because of unfavorable air flow underneath the car and the needs to cool an inefficient engine. Best air drags of production cars are 0.27 - and of experimental cars below 0.16. An air drag of 0.22 is used in the calculation of fuel consumption.

2. Rolling

b.   Low weight.

Lower weight requires less power to accelerate, move, and brake the car. However, if the power for accelerating the car is mainly recuperated braking energy, the weight is here of lesser importance.

The small and light powertrain and the self-supporting structure of the car platform, reduce the overall weight of the car considerably. Cars of comparable size currently weigh ca. 3,100 lb. Due to a lighter, smaller powertrain and simpler car body, a weight of 2,200 lb has been used in the calculation

c.   Low rolling resistance.

The resistance is determined by the quality of the tire (rolling resistance) and the weight of the car. Best current coefficients of rolling resistance are 0.0055 to 0.007. A coefficient of 0.0060 has been used in the calculation.

Improved energy conversion efficiency:

To increase the overall fuel consumption, the losses within the powertrain and those from braking have to be lowered. Both losses are considerably reduced by separating the operating profile of the engine from that of the car. This is made possible by the accumulator, acting as buffer between both operational requirements. The functioning is here obtained by:

d.   Constant operating conditions for the engine.

Independent from the power needed to drive the car, the engine charges the accumulator under full power and only for a short period of time. Here, the engine operates under its best possible operating conditions of constant pressure and speed to minimize fuel consumption and emissions.

In addition, the free-piston engine has inherently fewer losses (friction, heat) and is significantly lighter, thus reducing the weight of the car. Best current engines have a specific fuel consumption of 0.310 lb/hp·h but operate at an average of about 0.450 lb/hp·h. A consumption of 0.284 lb/hp·h (175 gr/kW·h) has been used in the calculation.

e.    Recuperation of the entire braking energy.

Braking consumes a large part of the energy, about 40% during city driving of the NEDC. This is twice as much as energy used for driving at constant speed. The recuperation of this energy with a high ‘round-trip-efficiency’ reduces the consumption considerably.

The high power peaks during braking require very powerful drive motors to recuperate the high amounts of energy. Motors which are powerful enough to accelerate the light car (e.g. 150 hp) are too small to recuperate the entire braking energy (600 hp).

A comparable electric powertrain, able to recapture the entire braking energy, is significantly heavier. The weight of the currently best electric motors is 20 times higher than that of the new hydraulic motor. The weights of the energy storage devices (battery, accumulator) are about the same. As result, the weight of the car would increase by about 50% - from 2200 lb to 3300 lb - consequently increasing the fuel consumption.

The calculation of fuel consumption is based on the 130 MPG INGOCAR driving the NEDC Cycle. (New European Driving Cycle). This, as other standardized driving cycles, does not reflect a typical driving pattern. The effectiveness of the Hydrostatic Powertrain improves under more realistic conditions.

The fuel consumption for constant speeds is: