Info on the Ford 2-stroke:
FORD'S ADVANCED TWO-STROKE ENGINE STARTS CUSTOMER TRIALS;
FIESTA TEST FLEET TAKES TO THE ROAD
ESSEX, England, June 24 /PRNewswire/ -- A pilot run of 25 two-stroke engined Fiestas has been built at Ford's Dagenham plant in the UK. They will be used by key component suppliers and selected fleet operators. A further run of 35 prototype cars will be produced during 1992.
All 60 test vehicles are being built to gain early service experience of this advanced engine concept as part of the run-up to low- volume production of two-stroke cars, planned by Ford for the second half of the decade. About half the test cars have been built with left- hand drive for operation in Germany while the other half have right-hand drive for use in the UK.
The new Ford two-stroke engine has been developed over the past four years in cooperation with the Orbital Engine Company of Western Australia.
Its use of the two-stroke combustion cycle allows the valvetrain to be eliminated and provides double the number of power strokes. This makes the engine more compact, reduces engine weight, increases simplicity and power density and significantly enhances performance feel.
Advanced combustion system
The advanced combustion system uses stratified charge concepts to bring many of the operating advantages previously associated only with diesel engines to gasoline power units. With a specific power/weight ratio about 40 percent higher than today's gasoline engines and a much reduced engine package volume, the engine offers the potential for future vehicles to be designed with greater operating efficiencies than are possible with today's conventional four-stroke powertrains. It also provides smoother running characteristics.
A further advantage that cuts directly against the current two- stroke image is that the new Ford engine also has very low exhaust emissions. As a result of a technological breakthrough that overcomes the traditional disadvantages of two-stroke units, the new Ford engine has already proved it can meet the latest U.S. Clean Air Act emission standards.
The engine development program has employed simultaneous engineering techniques, involving a team of Ford planning, manufacturing, research and development engineers working very closely with Orbital and specialist outside component suppliers, many of which are also participating in the preliminary fleet trials.
The Ford Two-Stroke in Detail
Ford in Europe has been working closely with the Orbital Engine Company on the development of two-stroke engines since signing a licensing agreement with the Australian-based company in the middle of 1988. The engine design is aimed primarily at improving vehicle efficiency, increasing running refinement and lowering exhaust emissions.
The Ford two-stroke is an in-line three-cylinder engine with a displacement of 1,200 cc. It develops 80PS (60kw) at 5,500 rpm (about 10 percent more than an equivalent four-stroke design) with a peak torque of 125 Nm at 4,000 rpm (about 14 percent more than the torque of a 1.2-liter four-stroke). The fuel economy improvement over an equivalent four-stroke engine is between 10 percent and 12 percent.
Significantly, the engine is about 25 percent lower in height than an overhead cam four-stroke and 25 percent shorter than a four-cylinder in axial length. It also weighs about 30 kg (30 percent) less than a typical small car engine. Power density (output per unit mass) is therefore 40 percent higher.
Construction of the engine is based around a light-alloy water- cooled crankcase and cylinder head. The ported two-stroke cycle eliminates the need for a camshaft and poppet valves. By injecting oil into the intake air before it reaches the crankcase the need for an oil pan and renewable oil filter are also eliminated.
Forged steel crank with split roller bearings
Each of the three cylinders has its own self-contained crankcase chamber, separated by cast walls supporting the main bearings between the crankshaft throws and made gas-tight by special low-friction main- bearing seals. The crankshaft is a one-piece case-hardened steel forging fitted with special split roller bearings for all main and big- end journals.
Induction air is drawn into the crankcase by the vacuum created below the piston as it rises in the cylinder on the compression stroke. A set of reed valves, one per cylinder, prevents any backflow during the subsequent crankcase compression cycle as the piston moves down.
Sophisticated oil supply
Oil is supplied by an electrically operated metering pump and injected immediately upstream of the reed valve assembly. The rate of oil injection is varied by the electronic engine management system according to the load and speed of the engine.
In general the fuel/oil mixture ratio varies between about 90 and 420 to 1, reducing the oil concentration under most operating conditions to less than a tenth of that used in conventional two-stroke engines today. This level of highly sophisticated oil injection control has been developed to provide a safe margin of oil mist lubrication for the roller bearings and at the same time significantly reduce exhaust emissions.
The small quantities of oil that enter the cylinder with the induction air are burnt off in the chamber and their combustion products then oxidized by the catalytic converter, which operates without the risk of oil contamination. This eliminates the characteristic blue smoke normally associated with two-stroke engines. About 30 percent of the injected oil is recovered from the crankcase floor and recirculated, giving a projected range of around 20,000 km before the supply tank needs attention.
Extended Service Intervals
As only the spark plugs and air filter need replacement throughout the life of the vehicle, Ford expects that future two-stroke engines will thus be able to extend routine service intervals, reducing cost of ownership levels further than is possible with today's wet-sump four- stroke powertrains.
After the induction air has been drawn into the crankcase by the upwards movement of the piston and the piston moves down on the power stroke, it uncovers a number of transfer ports arranged around the cylinder walls, each connected to the crankcase volume below. This allows the primary induction air from the crankcase to flow into the upper cylinder with the period and timing controlled by the position, shape and size of each port's opening as the edge of the piston crown uncovers the opening and later seals it off.
The incoming flow of air into the upper cylinder has been developed to provide a loop scavenging characteristic which rapidly purges the previous charge from the cylinder in the shortest possible time.
The gas dynamics of this loop scavenging have been finely optimized by the design of the port profiles and the phasing of their events. In four-stroke engines, this process usually requires multiple valves with their added cost and complexity.
Advanced Air-assisted Direct Injection
The fuel mixture is injected directly into the combustion chamber after being prepared by a unique low-pressure compressed-air assisted system.
A reciprocating air pump, mounted in front of a direct-coupled water pump for the coolant, is belt-driven from the crankshaft. It delivers air at around 5-6 bar to a special solenoid-operated injector assembly mounted in the center of each combustion chamber located directly next to the angled spark plug boss.
Fuel is supplied by a higher pressure version of a conventional fuel injection pump. It delivers fuel to the same housing at a slightly higher pressure than the air supply, metering through a separate, independently controlled solenoid-operated side-mounted injector.
The atomized mixture is then injected into the cylinder with a carefully optimized spray pattern that can be controlled by varying both the pulse width (duration) and timing of a specially developed nozzle valve head.
Stratified charge with lean-burn potential
This dual control of the fuel-air mixture, which is independent from the induction air supply, allows the combustion process to take place using a variable stratified charge for much of the operating range.
Instead of burning a uniform mixture, as in a conventional engine, stratified charge engines use a mixture that varies in strength across the chamber. In the Ford two-stroke the fuel-air preparation system promotes a kernel of ignitable gases around the spark plug so that the overall mixture can be leaner.
Load and speed variations are met by a sophisticated combination of fueling and air flow changes. The system reacts much more quickly to transient driver demands giving the engine a very fast response and an excellent performance feel.
Ford's previous research into the Proco stratified charge engine in the USA and fast, lean-burn combustion technology in Europe is now being applied to the development of the advanced gas dynamics of the two- stroke combustion system.
Exhaust Port Shutters
Spent gases leave the cylinder through a single exhaust port in the cylinder wall. The scavenging process is controlled by a movable exhaust port shutter for each cylinder. The shutters are controlled by the engine management system to provide variable exhaust port timing.
The three-cylinder in-line configuration allows all three shutters to be operated by a single rotary actuator, with the system joining from three outlets into one in the exhaust manifold casting.
Simple Oxidation Catalyst
Because of the large proportion of excess air present during light load and mid-range operation, and the inherently lower combustion temperatures produced by the two-stroke engine, only a simple, cost- effective oxidation catalyst system is necessary in the exhaust. No oxygen sensing nor closed loop control, as with a three-way catalyst system, are required.
A close-coupled light-off catalyst is supported by a larger catalyst further down the exhaust system that has been specially designed and optimized to provide the low back pressure two-stroke engines require.
Smoother Firing Pulses
With twice as many firing pulses as a four-stroke, the Ford three- cylinder two-stroke offers running refinement very close to that of an in-line six.
The balancing strategy used in its crankshaft construction confines vibration to the horizontal rather than the vertical plane. This has allowed special dual-compliance engine mounts to be developed that are vertically stiff to support the engine load and horizontally soft to absorb and dampen residual engine vibration more effectively.
More Two-Strokes on the Way
Ford in Europe and the USA is working with Orbital on a number of other two-stroke projects including six-cylinder engines in both naturally aspirated and supercharged forms. Ford research engineers are also performing a coordinating role in the development of the new Jaguar high-performance two-stroke engine recently announced.
Chief Engineer of Powertrain Systems Engineering for Ford in Europe, Jack Paskus, said, "Now that we have proved the advantages of Orbital concepts in our own research engines, we are moving forward towards the pre-program development phase as quickly as we can. We expect to learn a lot from the customer fleet trials and are optimistic that two-stroke engines will bring considerable operating benefits to Ford customers in the future."
/CONTACT: Peter Simons of Orbital Engine Company USA, 517-423-6623/
(F) CO: Ford Motor Company; Orbital Engine Company ST: Michigan IN: AUT SU: