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FIG. 1: The kinematics of the Product 1 Supercharged
two-stroke engine for hybrid applications 1. INTRODUCTION Downsizing
is an increasingly popular method for reducing the fuel
consumption of current IC engines. However, when the cylinder volume is reduced,
the engine really needs a high boost pressure to develop enough power for a good
acceleration behavior of the modern passenger cars. To solve this problem, a
very expensive solution was proposed which consists in the association of a
mechanical coupled compressor and a turbocharger with a four stroke, four
cylinder gasoline engine. To avoid the parasitic losses of the compressor,
this is coupled by a clutch, which makes this solution even more complex.
The number of components of this solution is huge and the cost is proportional.
Also the risk of the failure of one part is major. On
the other hand, a large portion of the world population (around 80%) can not buy
a motorized vehicle because of the big costs of the classic technologies.
Considering this fact, some very large companies begin to study special
solutions designed for the emerging markets. Their objectives are very difficult
to be achieved (in conditions of commercial profit) if the cost of the engine
itself is not considered. Unfortunately the actual four stroke engine can
not be made simpler and cheaper being already highly optimized. However,
the simplest thermal machine ever built was the free-piston
engine. Although considered a novelty today, free-piston engines were a topic of
great interest for approximately forty years. They were used as gas-generators
or to drive compressors in many applications. Today's achievements are mostly
investigated in the purpose of creating a simple thermal-electric linear
generator to replace the actual pollutant small chemical batteries (so difficult
to be recycled) or for other limited hybrid applications. The actual great
interest for such engines consists in their simplicity but also in their
efficiency potential. The maximum efficiency of such a machine seems to be
superior to the efficiency of actual reciprocating IC engines. The
new concept proposed in this paper tries
to conserve a part of the free-piston engine advantages. The new solution
consists in an advanced engine for small vehicles and passenger cars as well as for aerial vehicles or stationary
constructions, having a structure similar with a concept described before
(the free piston engine) but with fixed stroke of the
piston (kinematic coupled with the mechanism which transmits the load). 2.
DESCRIPTION AND OPERATION Referring first to the FIG. 2 a two stroke engine 20 comprises two axially disposed stepped pistons 21, connected between them using two stiff rods 22 and forming a solid piston 23. The solid piston 23 transmits its reciprocating motion by a single ordinary connected rod 24 and by a pin 25 to an ordinary crankshaft 26 situated in the space formed between the two stiff rods 22 and the two stepped pistons 21, respectively in the middle zone of the engine 20.
FIG. 2 The small portion of every stepped piston 21 forms a motor piston 28 and works in the conventional way as the movable wall of a combustion chamber 29, which is included in a motor cylinder 30 (FIG. 1). The stepped, or enlarged diameter, portion named pumping piston 32, operates in an adjacent, axially aligned, bore of the cylinder, named pumping cylinder 33. Each pumping cylinder 33 is mounted in a semi-crankcase 34. Two semi-crankcases 34 form a union, respectively a crankcase 35. The fresh air enters in the pumping cylinder 33 on the “down-stroke” of the stepped piston 21 using some flexible inlet valves 37, working automatically, and is compressed on the “up-stroke” being delivered through some transfer passages 38. The transfer passages 38 makes the connection with the combustion chamber 29 using some transfer ports 40, which are opened by the motor piston 28 during the intake stroke. This engine works using a typically two-stroke cycle. After the combustion and expansion the burn gases leave the combustion chamber 29 through at least one exhaust port 44. The transfer ports 40 and the exhaust port 44 are so arranged to obtain a loop scavenging process. To support the crankshaft 26 in the crankcase 35 it uses two bearing covers 49. The engine 20 operates with double effect: when the expansion takes place in one combustion chamber 29, in the opposite combustion chamber 29 takes place the compression stroke and reverse. The difference, comparing with actual piston engines, consists in that the mostly necessary energy for every compression stroke is transmitted directly between one piston and the other using the stiff rods 22 and the crankshaft 26 is not stressed for that. Also the inertia force (which is aligned with the stepped piston axis) to the end of the compression stroke is mostly balanced by the pressure existent in the combustion chamber 29, the value of this pressure being high because already the spark plugs 42 initiated the combustion. Consequently the motion of the solid piston 23 is damped without an important stress of the crankshaft 26 even the masse of the solid piston 23 is significant. If it considers that every two double axially opposed cylinders form one cylinder group, the engine, conformable with the invention, can be achieved with 1, 2, 3, 4, 5 or 6 cylinder groups. Also the engine can work as spark ignition or compression ignition (diesel) engine. There
are at lest 10 constructive variants of this engine, which can be tacked into
account for manufacturing. Due to the special balancing solution, the mass of the solid piston does not limit the engine speed and consequently it can obtain a high level of power density. It is a very simple and cheaper solution because every two stepped pistons uses only one connecting rod and the crankshaft has only one crankpin. Using a special design shape of the pistons (not described here) the overall dimensions and the weight of the engine are generally diminished with 20%. The solid piston can have only one or two stiff rods to make the connection between the stepped pistons and the distance between the crankshaft bearings are similarly to the traditional engines respectively very low. The stroke to bore ratio can be achieved in the limits 0,7÷2 because the pistons are interconnected in the most convenient zone, respectively using the stepped portion which has a large diameter. The connecting rod and the crankshaft transmit mainly the useful work of the engine and can be sized properly. Having an efficient scavenging process this engine can operate with “lean” mixture and the fuel consumption can be radically dropped. The scavenging pump (supercharger) and the crankshaft mechanism is separated and consequently the lubrication problem disappears. There will be no oil burned in the cylinder, lowering the HC emission and the deposits. Also slide bearings can be used for crankshaft and connecting rod. Using the stepped pistons and the control of the exhaust timing it can obtain the supercharger effect and consequently the power density can grow. The engine becomes much smaller in overall dimensions, weight, engine cylinder displacement and combustion chamber volume. The size of the engine is greatly reduced relative to the size of the vehicle in order to minimize the effect of the engine friction losses and to maximize vehicle fuel economy. This advantage is even more relevant to the compression ignition engine (diesel engine), which can balance the big combustion pressure and the inertia forces without to increase the size and the weight of the component parts. The number of the main parts in motion (only 3 for each double cylinder) are minimized so that to obtain a very great durability and reliability of the engine. It can estimate that the total number of the component parts is reduced with 10% compared to the traditional two stroke engine and with 50% compared to the traditional four stroke engine, even this concept has a supplementary device for supercharging. Another object of the present invention is to retain as many of the basic components of a conventional engine as possible. The crankshaft (very small), connecting rod and pistons are all of the same type as those of today's engines. All the technologies used to produce this engine are well known being similar or simpler than the traditional engine manufacturing process. It can easily estimate that the reduction in manufacturing costs is around 40% in comparison with traditional four stroke engine having similar power and emission level. This concept represents a total vibration free engine in the variant which use 4 cylinders. But also in the variant with 2 cylinders the reciprocating masses, which usually produce vibrations, are balanced and dumped by the opposite compression pressure and the opposite combustion pressure. 4.
INDUSTRIAL APPLICABILITY The
low size of this engine and the disposal of the cylinders offer to the
automotive designers a great flexibility. In the first example (FIG. 3) it uses a two cylinder engine located under the back seats of a low size passenger car that has rear wheel drive or four wheel drive. Although this car is high, the stability and the maneuverability can be very good because of an exceptionally low center of gravity.
FIG.
3 This
engine, which can be mad as gasoline or diesel engine, has the parameters
estimated in the table 1:
In the second example (FIG. 4) it uses a two cylinder engine located in the front of the front axle. Such configuration permits also a low center of gravity coupled with very good protection of the passengers.
FIG.
4 5.CONCLUSION
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