Free Piston Power Pack (FP3)

FP3 design is based on "free pistons" being driven back and forth inside cylinders by controlled internal combustion. Permanent magnets are attached to the pistons. As the magnets move, electric power is generated in coils placed around the magnets. The module represents a fresh approach in free piston engine/generator design. Novel features include passive intake valves, located in the crown of the piston and an integral charge compressor.

These improvements eliminate problems hampering earlier free piston engine designs, such as ported cylinder walls with associated piston ring wear and the need for a bulky, external charge compressor. The result is a significant increase in power density (1kW per kg or 1.93 kW per liters).

Mechanical simplicity (software "replaces" the crankshaft), high pressure direct fuel injection, variable exhaust valve lift and timing as well as variable stroke and compression ratio all contribute to excellent fuel efficiency and low levels of harmful exhaust emissions.

The FP3 is an extremely compact, efficient, clean, low-cost, scaleable electric generator with an output up to 450kW. It can be modified to operate on diesel, ethanol, LPG and hydrogen.

Passive Intake ValvesGo Back to Top

Four passive intake valves are located in the crown of each piston. They are seated poppet valves and form the intake ports through which fresh air enters the combustion chamber. The intake valves operate in a completely passive manner, i.e. there are no external controls. The opening and closing of the intake valves is governed by the pressure differential that exists between the compressor and the combustion chamber. The passive intake valves provide three major benefits:

• Uni-flow gas exchange
• Elimination of intake and exhaust slots in the cylinder wall resulting in reduced piston ring wear
• Axial module length reduction by allowing the generator to overlap the combustion chambers

Charge Compressor

Two compressors, driving the gas exchange process, form an integral part of the FP3. This eliminates the need for a bulky, external charge compressor.

Linear Generator

The linear generator is highly integrated into the design of the FP3. It consists of eight ring-shaped NeFeB permanent magnets located on the mover assembly and an eight coil stator. The coils are connected to IGBT inverters which convert the generator output to direct current.

The inverters are controlled by a digital signal processor system maximising the efficiency of the power conversion process.

The generator acts as a linear motor when starting the FP3; power is applied to the stator coils in sequence causing the piston to move.

Electro-Pneumatic Exhaust Valve

The exhaust valve is driven by a high speed, software controlled actuator. The actuator contains two opposing solenoids that open and close the valve. Each solenoid incorporates a gas spring that stores energy required to generate the high forces necessary for rapid operation. The exhaust valve is capable of opening to a stroke of over 7 mm and closing again in 5 ms. The seat diameter of 36 mm provides a large aperture for rapid removal of exhaust gases.

Graph of a test result

Mover Bearing

The interface between the mover and stator is the only major bearing in the FP3. Because the FP3 is not subjected to dynamic lateral piston forces, the contact pressure in the bearing is less than 0.02 MPa. Since the mover speed is less than 10 m/s there is plenty of scope for the design of a lubrication-free bearing.

Piston Seal

The FP3 uses an advanced seal rather than conventional piston rings. The main pressure seal is fitted into the inside surface of the bottom of the cylinder. It is subject to relatively low temperatures. Above the main seal is a labyrinth seal that provides a significant pressure reduction, allowing the use of a low-pressure type seal. The prevailing conditions allow for the design of a lubrication-free piston seal.

The FP3 can take advantage of current research in materials and cooling to achieve a minimal crevice volume. This may allow the use of a contact-less piston seal.

Frequency of Operation

The power delivered by the engine and generator can be increased by raising the operating frequency. To achieve this, the mover of the FP3 has been designed for minimum mass (5.2 kg).

A simple analysis shows that the operating frequency can also be increased by around 60% by sub-dividing the unit into four quarter-size sub-modules.

Features

• Significant technical innovation (protected by international patents)
• Exceptional power density (compared to current engines and fuel cells)
• Unrivalled high fuel economy
• Ultra-low or zero harmful exhaust emissions
• Mechanical simplicity (software "replaces" conventional crankshaft
• Maintenance-free and lubrication-free
• Long service life
• Electronically variable
• Spark ignition timing
• Exhaust valve timing and lift
• Direct fuel injection timing and quantity
• Compression ratio
• Multi-fuel capability
• Gasoline
• Diesel
• Hydrogen
• Ethanol
• LPG
• Etc.

Specifications

• 100 kW peak electrical output power
• Four free piston engine sub-modules
  • 8 cylinders
  • 2.82 litre displacement
• 30 Hz operation (equivalent to 1800rpm in a two stroke crankshaft engine)
• 280x280x660 mm dimensions

Gas Exchange

Orthodox Internal Combustion Engine Vehicle Technology

FP3 versus Orthodox Internal Combustion Engine Technology

The established internal combustion engine powered vehicle has benefited from over 120 years of continuous research, development, testing and refinement. These efforts have resulted in designs that have excellent reliability, low manufacturing cost and good fuel economy.

However, a rapidly increasing and developing world population, as well as a dwindling supply of oil and the threat of global warming, mandate transportation solutions that are not only vastly more fuel efficient but also environmentally sustainable. Regulatory authorities as well as consumers are calling for more efficient and cleaner motor vehicles. It is difficult to further reduce fuel consumption and harmful emissions of the existing motor car without some mechanism of capturing, storing and re-using the vehicle’s kinetic energy, currently completely wasted, when slowing down and braking.

An FP3 powered Series Hybrid Electric vehicle equipped with all wheel electric drive, capable of regenerating maximum braking torque and a Li-Ion battery pack to store and subsequently re-use this recovered energy, provides just such a mechanism. The result is greatly reduced fuel consumption and harmful emissions as well as a much quieter operation.

Series versus Parallel Hybrid Electric Vehicles

Existing Parallel HEVs, such as the Toyota Prius, are powered by an internal combustion engine and conventional drive train. In parallel is installed an electric motor/generator and battery combination, also connected to the wheels. This rather costly, heavy and cumbersome concept allows only marginal power regeneration when slowing down and braking.

In contrast, in an FP3 powered Series HEV, the electric output from the FP3 generator module is fed directly to a Li-Ion Battery Pack and to four electric wheel motors via a power electronic control system. This enables full regeneration (barring losses) and subsequent re-use of the vehicle’s kinetic energy when slowing down or braking.

An FP3 powered Series HEV power train takes up less space, is lighter and of simpler design in comparison with a parallel HEV. The advantages are a significant reduction in fuel consumption and harmful emissions and reduced manufacturing cost.

• significantly smaller, lighter and simpler design
• improved fuel economy
• lower harmful emissions
• quieter operation
• fewer moving parts
• much lower manufacturing cost

When installed in a typical series hybrid family sedan, the following specifications apply:

• 100 kW FP3 complete with electronic control
• Installed Lithium-Ion Battery Power 164 kW
• Electric Wheel Motors 4x50=200 kW
• 200 kW Wheel Motor Drives
• Wheel Motor Gear Ratio 6.75:1
• Torque on Wheels:
     0-100 km/h (62 mph) 2122 Nm (1563 ft-lb)
     150 km/h (93 mph) 1415 Nm (1042 ft-lb)
• Acceleration 0-100km/h (62 mph) in 5.4 seconds
• Curb Weight 1300 kg (2860 lb)
• 100% Regenerative Power
• Overall efficiency of 45% (compared to a current 25%)

FP3 versus Fuel Cell Technology

Fuel cell powered vehicles are under development by many automotive manufacturers and have been released on the market in limited numbers. However, high manufacturing cost, low power density and a short life-span are major impediments to their widespread deployment. These draw-backs are not expected to be resolved for some years to come.

Furthermore, current methods of producing hydrogen contribute to greenhouse gas emissions. There will be little environmental benefit from the use of fuel cells until hydrogen is manufactured from clean energy sources.

When compared to fuel cells, the FP3 has a higher power density and much lower manufacturing cost. The FP3, when powered by hydrogen, makes for a low-cost, mechanical fuel cell.

Other Applications

• HEV passenger vehicles (up to 100 kW, gasoline or diesel)
• HEV trucks (up to 450 kW, diesel) in combination with Pempek Systems' patented Electric Differential Drive Axle
• Public transportation, e.g. buses
• Leisure craft
• Static and portable power generation
• Auxiliary electric power generation

Proposed Series HEV

INTERNAL COMBUSTION ENGINE & LINEAR GENERATOR MODULE:
Linear Generator	Power	40 kW
	Dimensions	225 mm x 225 mm x 520 mm
	Mass	40 kg
Combustion Engine	Cylinders	8
	Bore	52 mm
	Stroke	80 mm
	Capacity	1.36 l
	Power	40 kW
Cylinder Heads	2 Exhaust Valves 22 mm bore (one actuator)
	1 Fuel Injector
	1 Spark Plug
Pistons	3 Passive Intake Valves 20 mm bore
Generators	Mover OD	80 mm
	Mover Length	140 mm
	Number of Coils	6
	Stator OD	110 mm
	Frequency	36 Hz

 

BATTERY ASSEMBLY:
Batteries:	Power	37.5 kW x 3 = 112 kW
	Dimensions	180 x 590 x 170 mm x 3
	Mass	23 kg x 3 = 69 kg
	56 Li-Ion Cells VL7P
	Voltage	200 V
	Power	37.5 kW
	Energy	1.4 kWh

WHEEL MOTORS:
Traction Motor:	Power	30 kW x 4 = 120 kW
	Dimensions	Ø120 x 200 mm
	Mass	13 kg x 4 = 52 kg
	Gear ratio	6.75 : 1

PROPOSED SERIES HEV CONFIGURATION:
Predicted Performance:
Acceleration for a vehicle mass of 1000 kg from 0 to 100 km/h:	6 seconds
Regenerating Capacity for a vehicle mass of 1000 kg:
Vehicle Speed	Retardation
< 43 km/h	10.0 m/s²
50 km/h	8.6 m/s²
60 km/h	7.2 m/s²
80 km/h	5.4 m/s²
100 km/h	4.3 m/s²
120 km/h	3.6 m/s²
Fuel consumption in city traffic measured in accordance with NEDC: 1.6 l/100 km

PATENTS:

Australia	PQ 8065	2000, June
USA	US 6,651559B2	2003, November
Europe	01931200.8	2004, July
Japan	3607909	2005, January
South Korea	10-2002-7001442	2005, September
India	107/KOL/2006	2006, February
Australia	PCT/AU2007/001193	2006, September
International	PCT/AU2007/001193	2007, October

Australian Provisional Patent 2006904838

PUBLICATIONS:

The Free Piston Power Pack: Sustainable power for Hybrid Electric Vehicles - SAE 2003-01-3277.

Hybrid Electric Truck Concept 26-Oct-05

Series HEV 31-Oct-05

Parallel versus Series HEV Fuel Consumption

Status Quo:

An intrepid mob of mechanical, electrical, electronic and software engineers has been developing the FP3 at Pempek's R&D facility since February 2001. Prototype electronic control and power modules, sub-systems and engine components have been designed and manufactured. An electro-pneumatic exhaust valve featuring variable valve timing and lift has been developed, successfully tested and patented. A prototype FP3 is currently undergoing test. The design of a 50kW wheel motor has been completed and the first units are currently being constructed. Our senior project engineer has presented a paper on the FP3 (SAE2003-01-3277) at the SAE Powertrain & Fluid Systems conference in Pittsburgh, PA in October 2003.

Click on the image for a larger size viewing:

Engine Under Test in our Power Technology Shed:

Engine in it's current state is being tested for field oriented positioning

Engine Controller Setup:

Rack of multi processor electronics is used in controlling the engine operation.

Exhaust and Inlet Valves:

The titanium valves are designed and manufactured for our patented "High speed solenoid valves".

Assembled High-Speed Exhaust Valve:

Comprises the exhaust-valve, solenoid, intake-valve, and gas-springs.

Control Electronics:

Electronics of the Free Piston Engine Power Pack are customised, designed, and manufactured in Pempek Systems.

Siemens' High Pressure Fuel Injector:

FP3 uses Siemens injectors for high pressure direct injection of fuel into the combustion chamber.

Fuel Pressure Setup:

Fuel pressure is being adjusted to 80bar for testing of the fuel injectors.

Fuel Injector Test Setup:

Testing the fuel-injectors and their controllers.  Fuel-injectors are controlled by a DSP for precision operation.

Power Electronics:

High power electronics, which controls the engine and its output, are mounted on a water cooled heat-sink