WO2006003678A1

WO2006003678A1 - A piston assembly for an engine and an engine comprising the same

Info

Publication number: WO2006003678A1
Application number: PCT/IN2005/000226
Authority: WO
Inventors: Prasanta Ray
Original assignee: Prasanta Ray
Priority date: 2004-07-05
Filing date: 2005-07-04
Publication date: 2006-01-12

Abstract

A piston assembly comprising a housing (H) provided with an assembly of rotating pistons, preferably at least a pair of rotating pistons (PP1, PP2) forming air-tight chambers (C1, C2, C3, C4) in the housing (H) and a speed control means mounted on the housing (H) for controlling speed of the rotating pistons in the housing (H) is disclosed. A four-stroke engine comprising the piston assembly is also disclosed.

Description

TITLE

A Piston Assembly for an Engine and an Engine Comprising the same

FIELD OF THE INVENTION

The present invention relates to a piston assembly for an engine and

5 an engine comprising the same. Particularly, it relates to a piston assembly

for a four-stroke engine and the engine comprising the same.

BACKGROUND OF THE INVENTION

The most common form of a four-stroke, internal-combustion, heat

engine is the reciprocating, spark-ignition, otto engine in which a

i o cylindrical piston moves up and down within a cylinder to create the

following four strokes: (a) the induction stroke, when a fresh fuel charge is

sucked in, (b) the compression stroke, when the charge is compressed, (c)

the power stroke, when the charge is ignited by a spark so that it burns and

expands producing motive energy, and (d) the exhaust stroke, when the

15 burnt charge is expelled. Valves open and close inlet and exhaust ports at

appropriate times to let in the fresh fuel charge and let out the burnt charge. These four strokes are repeated cyclically and the reciprocating motion is

converted to a rotary motion by means of a rod hinged to the bottom of the

piston at one end and to the periphery of a wheel at the other.

Another common form of the four-stroke, internal combustion engine

is the reciprocating, compression-ignition, diesel engine where the four

strokes are similar except that air is sucked in by the induction stroke and

compressed by the compression stroke to a high adiabatic temperature when

fuel is injected into the compressed air and ignites automatically from the

high temperature at the start of the power stroke.

i o One drawback of the reciprocating engine is that energy output loss

occurs from the fact that the direction of the thrust created by the expanding

charge is not the same as that of the motion of the output shaft.

Another drawback is the imbalances and vibrations caused by the

presence of a number of oscillating members such as the pistons and valves. An alternate genre of the four-stroke, internal-combustion, heat

engine is the rotary engine where, basically and ideally, (a) the thrust of the

expanding charge is tangential to the rotary motion of the output shaft, and

(b) there are few, if any, oscillating members; most members are rotary.

These features are expected to, and do, overcome, at least to an extent,

the drawbacks of the reciprocating engine mentioned hereinabove.

Many designs of the four-stroke, rotary, internal-combustion engine

have been, and continue to be, tried out. These may be very roughly be

categorized as (a) the off-centre rotating piston engines, (b) the rotating

i o vane engines, and (c) the orbital piston engines. Of many such designs,

some typical ones are described below in brief in their essentials. The ideals

of tangential thrust and absence of imbalances and vibrations are achieved in

these engines in varying measures.

Palleja engine: This engine is a mix of the off-centre rotating piston

_{1 5} and the rotating vane types. A cylindrical rotor mounted off-centrally within a cylindrical housing carries radially arranged vanes that can move out and

draw in. The vanes touch the inside of the cylindrical housing to create

enclosed chambers. The vanes alternately push out and draw in as the

cylindrical member rotates so that the chambers alternately expand and

shrink to create the four strokes.

Wankel engine: A triangular piston (rotor) with convex sides rotates

within a cavity of an oval shape having a slight constriction in the middle

called epitrochoid. The three edges of triangular piston remain in contact

with the walls of the cavity. The centre of rotation of the piston itself

I o circles, or orbits, the centre of the cavity over a small circumference. As it

rotates, the three chambers formed between the sides of the triangular piston

and the wall of the cavity alternately expand and shrink to create the four

strokes. The piston edges open and close the inlet and outlet ports; no vales

are necessary.

15 Epielliptical rotary engine : Somewhat similar to the Wankel engine

described hereinabove. Here, an elliptical rotor rotates within a triangular cavity with rounded edges creating three chambers between the sides of the

rotor and the wall of the cavity. The chambers alternately expand and shrink

to create the four-strokes.

Hybrid engine : This engine is a mix of the reciprocating engine and a

rotary engine. Reciprocating pistons-in-cylinders of the reciprocating engine

type are mounted tangentially around a common output shaft.

Ball-piston engine : This is very roughly like the Palleja engine

described hereinabove with balls replacing the vanes.

Rotating vane engine : This is basically a turbine but with intermittent

i o ignition as in reciprocating engines.

Rotary opposed piston engine : Two pairs of pistons rotate

intermittently around a common axis to create four chambers that alternately

expand, stay expanded for a moment, then shrink and stay shrunk for a

moment to produce the four strokes. BRIEF DESCRIPTION AND OBJECTS OF THE PRESENT INVENTION

The present invention has tangential thrust and, even though having

(angularly) oscillating members, suffers very little from imbalances

because, as shown hereinbelow, the acceleration of an oscillating member

is balanced by an equal deceleration of another identical member. It is a

four-stroke, internal-combustion, heat engine of both the spark-ignition and

the compression-ignition types. The description given hereinbelow

isexpressly for the spark-ignition type, but is also for the compression-

i o ignition type, for which, the spark-plug, see infra, will be considered

replaced by a fuel-injector.

The presently disclosed piston assembly comprises (a) an assembly of

pistons comprising at least one pair of rotating pistons provided in a

cylindrical housing, and (b) a speed-control mechanism for controlling the

_{1 5} speed of the pistons, mounted on the housing.

The assembly of pistons comprises two coaxial pistons, preferably

butterfly-shaped, diametrically-opposed and roughly "V"-shaped pistons,

mounted in "X"-fashion, within a cylindrical housing, with a certain

degree of angular play possible between them, thus forming four roughly

"V"-shaped air-tight chambers.

The speed-control mechanism is mounted on the housing to link the

piston-pairs so that they are capable of turning in the same direction, but

with periodically-fluctuating angular velocities, thereby causing the

aforesaid four chambers to periodically expand and contract while bodily

Q circling in the same direction about the axis of rotation of the piston-pairs.

Such periodic expansion and contraction causes each chamber to go through

the four strokes - viz. induction, compression, power and exhaust - of a

reciprocating four-stroke internal-combustion heat engine.

In accordance with the preferred embodiment of the present invention,

5 the speed-control mechanism, mounted on outside of the housing, causes maximum expansion and maximum contraction of every chamber to occur at

the same (angular) positions in the housing. A spark-plug fitted into the

housing ignites the charge of each chamber at the desired instants - namely,

roughly at the moments of maximum contraction - and inlet and exhaust

ports built into the housing allow induction and evacuation of fuel charges.

The inlet and exhaust ports are apertures only and are opened and closed by

the pistons themselves; valves, as in conventional reciprocating four-stroke

engines, are not needed for the purpose.

Accordingly, the present invention relates to a piston assembly

i o comprising a housing provided with an assembly of rotating pistons,

preferably at least a pair of rotating pistons forming air tight chambers in the

housing and a speed control means mounted on the housing for controlling

speed of the rotating pistons in the housing.

The present invention also relates to a four-stroke engine as and when

₅' ϊ comprising a piston assembly as described herein. In accordance with the present invention, the housing is preferably

cylindrical housing and the pistons are preferably butterfly-shaped pistons.

The pistons have substantially "V"-shaped wings joining at the center and

are provided with undercuts at the center for fitting with each other. The

₅ pistons further comprise the holding means at the center, wherein the

holding means in one of the pistons is on a face provided with the undercut

and in another piston is on the opposite face to the undercut. In accordance

with the preferred embodiment of this invention the holding means are tubes

and tube of one of the pistons is longer than the other.

i o In accordance with the preferred embodiment of this present invention

the pistons, when mounted in the housing, have certain degree of angular

play therebetween. The pistons are mounted in "X"-fashion in the housing

with the holding means of one piston passing through holding means of

another piston. The pistons, when mounted form "V"-shaped air-tight

_{2 5} chambers. The housing further comprises a lid fitted onto projecting holding

means of the pistons and a projection on the inner surface of the bottom to

hold the pistons.

In accordance with one of the preferred embodiments of this invention

₅ the pistons are capable of turning in the same direction, but with

periodically-fluctuating angular velocities and the four chambers formed by

the pistons are capable of periodically expanding and contracting while

bodily circling in the same direction about the axis of rotation of the pistons.

According to another preferred embodiment of this invention the

i o speed control means is mounted on the housing on its outside and comprises

at least a pair of pinions of one size and at least a pair of pinions of another

size, and a flywheel, wherein one of the pairs of the pinions have larger

diameter / circumference than the another pair, preferably exactly twice the

diameter / circumference of the smaller pinions. The pinions having larger

15 diameter are provided with a pin. The pins are provided on the upper surface, preferably near the peripheries of the respective pinions, more

preferably the pins are provided at the same radial distance from the axis of

rotation of smaller pinions. The pin of one of the smaller pinions is longer

than the pin of the another pinion so that, when assembled, the free end of

5 this pin levels with free end of pin of another small pinion. One of the

pinions having smaller diameter is provided with a crescent-shaped window

for engaging pin of another pinion, The pinions having smaller diameter are

provided with a hole for engaging the support S 1.

The flywheel is provided with a groove on one of its face, preferably

i o running from one end to another end of the flywheel. The groove of the

flywheel, when assembled faces towards a pinion of smaller diameter and

engages pins of smaller pinions. The flywheel is provided with an axle on

the face opposite to the face provided with the groove. The flywheel is held

in place by a support S2 fitted on one end to the housing. The axis of

15 rotation of the flywheel lies between the axes of rotation of the smaller pinions and the larger pinions. The axes of rotation of the flywheel, me

smaller pinions and the larger pinions are collinear.

The other objects, advantages and the preferred embodiments of the

\ present invention will become more apparent from the following description

₅ when read in conjunction with the accompanying drawings, which are not

intended for limiting the scope of the present invention, but are incorporated

for illustration of the present invention, particularly the best mode of the

present invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

i o Fig.1 illustrates an exploded view of the assembly of pistons and the

housing of the piston assembly in accordance with the present

invention.

Fig.2 illustrates an isometric view of the pistons assembled in the

housing showing the pistons in place within the housing of the

15 piston assembly in accordance with the present invention. Fig.3 illustrates an exploded view of the speed-control mechanism

of the piston assembly in accordance with the present inven¬

tion.

Fig.4 illustrates an isometric view of the assembled speed-control

₅ mechanism of the piston assembly in accordance with the

present invention.

Fig.5 illustrates the piston assembly in accordance with the present

invention.

Fig.6 illustrates a schematic top view showing the essential compo-

l o nents of the piston assembly and the spark-plug and inlet and

exhaust ports of an engine comprising the piston assembly of

the present invention.

Fig.7 illustrates the mechanism how the pins of the small pinions

draw towards and away from each other as the flywheel

15 rotates. DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the accompanying figures the reference letters are common and

represent the following components and/or features:

H represents the housing of the present piston assembly provided

with a short, cylindrical projection, t, on the inner surface of the bottom of

the housing to engage tube T2.

L represents the lid of the housing of the present piston assembly.

PPl and PP2 represent the piston-pairs of the present piston

assembly.

Tl and T2 represent tubes attached to piston-pairs PPl and PP2

respectively, enabling the piston-pairs to be assembled together coaxially.

Cl, C2, C3 and C4 represent four roughly "V"-shaped air-tight

chambers formed by the piston-pairs of the present piston assembly. Each Chamber circles the axis of rotation of the piston-pairs and carriers an

independent fuel charge.

BPl and BP2 represent two identical pinions of the speed control

means of the present piston assembly fixed rigidly to the ends of the tubes

5 Tl and T2 attached to the piston-pairs. BPl is provided with a hole in the

centre.

SPl and SP2 represent two smaller and identical pinions of the

speed control means of the present piston assembly, each of a circumference

half that of BPl and BP2.

i o In accordance with one of the preferred embodiments of the present

invention SPl engages BPl and SP2 engages BP2 so that, for exactly

every one revolution of BPl (or BP2), SPl (or SP2) revolves exactly

twice.

Pl and P2 represent pins attached rigidly to SPl and SP2

_{1 5} respectively near the circumference at identical radial distances from the axis of rotation of SPl and SP2. In accordance with one of the preferred

embodiments of the present invention, Pl is longer than P2 and sticks out

through a window W provided in SP2.

W represents a window, preferably crescent-shaped window provided

in SP2.

In accordance with one of the preferred embodiments of the present

invention, this enables a certain degree of relative play between the two

small pinions SPl and SP2 by allowing Pl a certain freedom of angular

movement relative to SP2.

FW represents flywheel, supported from one side by support S2,

and having a groove G along a diameter substantially end to end.

In accordance with the preferred embodiment of the present invention,

when parts of the speed-control mechanism are properly assembled, the pins

Pl and P2 engage this groove. In accordance with another preferred embodiment of the present

invention, the axis AFW of rotation of the flywheel lies on the (imaginary)

line joining the axis ASP of rotation of the small pinions and the axis ABP

of rotation of the big pinions; the axis AFW lies between the axis ASP and

₅ the axis ABP in such a manner that the (imaginary circle centred on the axis

ASP, and passing through the locations of Pl and P2, encloses the axis

AFW.

G represents diametric groove running across one face of the flywheel

FW and extending almost from end to end.

i o ASP, AFW & ABP represent axes of rotation of SPl and SP2

(coaxial), of FW and of BPl and BP2 (also coaxial) respectively.

Sl and S2 represents supports for the small pinions and the flywheel

respectively.

SP represents spark-plug, IP represents inlet port and EP represents

5 exhaust port of the engine. Now referring to accompanying figures, Figures 1 and 2 show how

the two piston-pairs PPl and PP2 are assembled coaxially together with

T2 passing through Tl. When so assembled, the piston-pairs form an

assembly, "X"-fashion, with a certain degree of mutual angular movement

₅ or play possible thererbetween. In other words, the "X" shape can narrow

or widen within certain limits. When the piston-pair assembly is placed in

position within the housing H, the short cylindrical inner projection t of the

housing engages the tube T2, and with the lid L of the housing fastened

into place, the whole assembly looks like Figure 2, with portions of the

l o tubes Tl and T2 sticking out of the lid L, as shown, T2 a little more than

Tl.

In accordance with one of the preferred embodiments of the present

invention the piston-pairs form four chambers, preferably roughly "V"-

shaped air-tight chambers Cl, C2, C3 and C4, which can expand and

₅ contract within certain limits. The expansion and contraction occur in pairs

of chambers Cl and C3 constituting one pair and C2 and C4 constituting the other pair. When the pair Cl and C3 expands, the pair C2 and C4

contracts, and vice versa.

In accordance with the present invention, the speed-control mechanism

- Figure 4 and Figure 3, comprises two identical and coaxial small pinions

5 SPl and SP2 provided with pins Pl and P2 respectively, mounted onto

the pinions SPl and SP2, and the flywheel FW provided with a diametrical

groove G across one face, namely, the one that faces SP2. In accordance

with the preferred embodiment of this invention, one of the small pinions

SP2 is provided with a crescent-shaped window.

i o The speed control means further comprises two identical and coaxial

big pinions BPl and BP2 attached to the ends of the tubes Tl and T2 of

the piston pairs pl and P2 respectively. The big pinions BPl and BP2 are

provided with a circular hole at their centre to enable them to be fitted onto

the tubes Tl and T2. Thus, BPl and BP2 also can rotate relatively to

5 each other within the same angular limits as those for the piston-pairs PPl

and PP2 and in correspondence with the latter. According to one of the preferred embodiments of this invention, the

circumference of the smaller pinions SPl and SP2 is exactly half that of the

big pinions BPl and BP2, and the small pinions SPl and SP2 are so

supported by the support Sl [Figure 5] provided on the housing H, that the

₅ small pinions SPl and SP2 engage BPl and BP2 respectively, which

causes, for every one revolution of the big pinions BPl or BP2, two

revolutions of the small pinions SPl or SP2.

In accordance with this invention the pins Pl and P2 are preferably

attached near the peripheries of the small pinions SPl and SP2, and at the

j o same radial distance from the axis ASP of rotation of the small pinions SPl

and SP2. The pin Pl of the small pinion SPl projects out through the

window W of the small pinion SP2 and is longer than P2 so that their free

ends are level with each other.

The flywheel FW is provided with an axle A on one of its faces -

15 being the face away from the pinion SP2 and without a groove G - and is held in place by the support S2 [Figure 4 and Figure 5], which in-turn is

connected to the housing H. The other face - being the face towards the

pinion SP2 - of the flywheel faces the pinion SP2 and, as described

hereinabove, is provided with a diametrical groove G, preferably running

across it form end to end.

The axis of rotation of the flywheel AFW lies between the axes of

rotation of the small pinions and the big pinions ASP and ABP

respectively, and also on the (imaginary) line joining the ASP and ABP,

that is the ASP, AFW and ABP are collinear.

The length of the groove G provided in the flywheel FW is sufficient

to enable the pins Pl and P2 to engage therein G, sliding back and forth in

it, as the small pinions and the flywheel rotate.

The working principle is now explained as follows. Since the flywheel

FW is off-axial to the small pinions SPl and SP2, in a situation where the flywheel revolves with a constant angular velocity, the pins Pl and P2

periodically draw towards, and away from, the axis AFW of rotation of the

flywheel. A small pinion rotates fastest when its pin is farthest from the

AFW, and slowest when its pin is closest to the AFW [Figure 7]. Thus,

while the flywheel rotates with a constant angular velocity, the small pinions

rotate with periodically-fluctuating angular velocities, with each small pinion

going through one complete revolution, and one complete cycle of fastest-to-

slowest-to-fastest rotation, during one complete revolution of the flywheel.

Since the pins are located at the same radial distance from ASP, the fastest

and the slowest angular velocities of SPl and SP2 are the same. Besides,

the pins Pl and P2 are so constrained by the groove that when one is at its

closest to AFW, the other is at its farthest from it; in that situatin, Pl, P2,

ASP₅ AFW and ABP are collinear and the groove G lies parallel to that

(imaginary) line of coUinearity. Thus, the phase difference between the two

small pinions SPl and SP2 is 180 degrees. As the flywheel rotates,

therefore, each small pinion periodically gains on, and falls back from, the other, angularly, so that, while rotating in the same direction, in the

absolute sense, they oscillate relatively to each other. The crescrent-shaped

window W of SP2 accommodates this oscillation by allowing the pin Pl

sufficient angular movement relative to SP2. During every one full

revolution of the flywheel FW, each small pinion attains a state of zero

relative angular motion with the other twice; namely, when their angular

velocities equal. This happens when the groove orients itself at 90 degrees

to the (imaginary) line joining ASP, AFW and ABP, so that Pl and P2

are located at the same radial diatance from AFW but in diametrically

opposite directions from the latter; in that situatin, each small pinion attains,

also, a state of maximum angular gain on, or of maximum angular lag

behind, the other. During every one revolution of FW, therefore, each

small pinion attains a state of maximum gain on the other once, and,

similarly, of maximum lag behind the other also once, with one full cycle of

relative oscillation occurring between the two small pinions in that period.

The big pinions, engaging the small ones, and executing a half-revolution for every full revolution of the small pinions, also go through the same cycle

of fastest-to-slowest-to-fastest rotation during every one revolution of the

flywheel but with the difference that each big pinion executes a half-

revolution only in that period. Over two full revolutions of the flywheel

₅ therefore, each big pinion completes one full revolution and goes through a

double-cycle of fastest-to-slowest-to-fastest-to-slowest-to-fastest rotation; in

that situation, each big pinion attains a state of maximum angular gain on the

other twice, and that of maximum angular lag behind the other, also twice.

Such states of the big pinions coincide with similar states of the small

i o pinions. Whatever is true, in this respect, of the big pinions, is, clearly,

also true of the piston-pairs, for the former are attached rigidly to the latter.

Therefore, each piston-face of a given piston of a given piston-pair attains a

state of closest approach to the opposite piston-face, (belonging to the other

piston-pair), twice, and, likewise, farthest separation from such opposite

j 5 piston-face, also, twice, during every double-revolution of the flywheel

corresponding, as explained hereinabove, to every single revolution of each

piston-pair. In that period, therefore, each chamber - Cl, C2, C3 and C4

- executes a double-cyle of maximum contraction-to-maximum expansion,

thus: maximum contraction-to-maximum expansion-to-maximum

contraction-to-maximum expansion-to-maximum contraction.

5 It is clear that the chambers attain a state of maximum contraction, and

of maximum expansion too, in mutually-opposite pairs, simultaneously:

when chambers Cl and C3 attain maximum contraction — at diametrically-

opposite positions in the housing - the chambers C2 and C4 attain maximum

expansion, again at diametrically-opposite positions in the housing, with the

i o (imaginary) line of symmetry passing (diametrically) through C2 and C4. It

is also clear that such maximum contractions occur at the same pair of

diametrically-opposite positions, for both the pairs of chambers, Cl and C3,

or C2 and C4, and so also for maximum expansion. This is so because such

states of maximum contraction / maximum expansion of the chambers occur,

15 as seen hereinabove, when the flywheel groove orients itself at 90 degrees to

the (imaginary) line joining ASP, AFW and ABP, and, each piston-pair completes an exact half-revolution over every full revolution of the flywheel

which carries the groove. In other words, at the moment of maximum

contraction of any diametrically-opposite pair of chambers, the aforesaid

(imaginary, diametrical) line of symmetry is the same. A single spark-plug,

5 SP, shown in Figure 6, is fitted into the curved wall of the housing and is

positioned on such fine of symmetry passing through a pair of chambers in a

state of maximum contraction. It is made to fire, periodically, at

appropriate, pre-determined instants via the use of an appropriate means;

advance or retardation may be pre-programmed, if and as desired. For the

J o compression-ignition type of engine, SP represents a fuel-injector which

injects fuel periodically at appropriate instants. Inlet and exhaust ports, IP

and EP respectively as shown in Figure 6, are built into the same curved

walls of the housing and are so positioned, and have such angular widths,

that IP starts and stops letting in fresh fuel charges at appropriate,

j 5 predetermined instants, and, likewise, EP starts and stops evacuating burnt

charges at appropriate, pre-determined instants; the opening and closing of

the ports are done by the piston themselves, obviating the need for valves. It

is clear that such starting and stopping times are determined by the angular

width of the piston-pair extremities, the positions and the angular widths of

the ports, and the angular measures of maximum contraction and maximum

5 expansion of the chambers. If and as desired, an overlap too, of the

Induction stroke and the exhaust stroke can be pre-programmed through

appropriate choice of these parameters. The radial distance of the pins Pl

and P2 from ASP, and that of AFW from ASP, plus the angular width of

the piston-pairs, determine the measures of maximum contraction and

i o maximum expansion, which, in turn, determine the compression ratio. It is

evident that, over every two revolutions of the flywheel each chamber

executes the four-stroke cycle of induction, compression, power and

exhaust, once, so that a total of four such complete cycles occur in that

period. The axle A of the flywheel may be considered to be the power

15 OUtput.

The present invention has been described and illustrated with the help

of the accompanying drawings, which are not intended to limit the scope of

the present invention. Various modifications are possible without deviating

from the scope of the disclosed invention.

Claims

I CLAIM:

1. A Piston assembly comprising a housing provided with an assembly of

rotating pistons, preferably at least a pair of rotating pistons,

preferably at least a pair of rotating pistons forming air tight chambers

₅ in said housing and a speed control means mounted on said housing for

controlling speed of said rotating pistons in said housing.

2. A piston assembly as claimed in Claim 1 wherein said housing is pre¬

ferably cylindrical housing.

3. A piston assembly as claimed in Claim 1 wherein said pistons are pre-

i o ferably butterfly-shaped pistons.

4. A piston assembly as claimed in Claim 1 or 3 wherein said pistons have

substantially "V"-shaped wings joining at the center.

5. A piston assembly as claimed in any one of the preceding claims,

wherein said pistons are provided with undercuts at the center for fitting

15 with each other.

6. A piston assembly as claimed in any one of the preceding claims,

wherein said pistons are provided with holding means at the center.

7. A piston assembly as claimed in Claim 6 wherein said holding means

in one of the said pistons is on a face provided with said undercut and

₅ in another piston is on the opposite face to the same undercut.

8. A piston assembly as claimed in Claim 6 wherein said holding means

are tubes and tube of one of the pistons is longer than the other.

9. A piston assembly as claimed in any of the preceding claims, wherein

said pistons, when mounted in said housing, have certain degree of

i o angular play therebetween.

10. A piston assembly as claimed in any one of the preceding claims,

wherein said pistons are mounted in "X"-fashion in said housing

with holding means of one piston passing through holding means of

another piston.

11. A piston assembly as claimed in any one of the preceding claims,

wherein said pistons, when mounted form "V"-shaped air-tight

chambers.

12. A piston assembly as claimed in any one of the preceding claims,

5 wherein said housing is provided with a lid fitted onto projecting

holding means of said pistons.

13. A piston assembly as claimed in any one of the preceding claims,

wherein said housing is provided with a projection to hold the pistons.

14. A piston assembly as claimed in any one of the preceding claims,

l o wherein said pistons are capable of turning in th§ same direction, but

with periodically-fluctuating angular velocities.

15. A piston assembly as claimed in Claim 11 or 14 wherein said four

chambers are capable of periodically expanding and contracting while

bodily circling in the same direction about the axis of rotation of the

5 said pistons.

16. A piston assembly as claimed in Claim 1 wherein said speed control

means is mounted on the said housing on its outside.

17. A piston assembly as claimed in Claim 1 wherein said piston control

means comprises at least a pair of pinions of one size and at least a pair

5 of pinions of another size, and a flywheel.

18. A piston assembly as claimed in Claim 17 wherein said one of the

pairs of said pinions have larger diameter / circumference than the

another pair, preferably exactly twice the diameter / circumference

of the smaller pinions.

I O 19. A piston assembly as claimed in Claim 18 wherein said pinions

having larger diameter are provided with a hole.

20. A piston assembly as claimed in Claim 18 wherein said pinions

having smaller diameter are provided with a pin.

21. A piston assembly as claimed in Claim 20 wherein said pins are

provided on upper surface, preferably near the peripheries of the

respective pinions.

22. A piston assembly as claimed in Claim 21 wherein said pins are

provided at the same radial distance from the axis of rotation of

smaller pinions.

23. A piston assembly as claimed in Claim 20, 21 or 22, wherein pin of

one of the smaller pinions is longer than the pin of the another pinion

so that, when assembled, the free end of this pin levels with free end

of pin of another small pinion.

24. A piston assembly as claimed in Claim 18 wherein one of the said

pinions having smaller diameter is provided with a crescent-shaped

window for engaging pin of another pinion.

25. A piston assembly as claimed in Claim 18 or 24 wherein said pinions

having smaller diameter are provided with a hole for engaging the

support Sl.

26. A piston assembly as claimed in Claim 17 wherein said flywheel is

provided with a groove on one of its face, preferably ranning from one

end to another end of the flywheel.

27. A piston assembly as claimed in Claim 26 wherein said groove of

5 said flywheel, when assembled faces towards a pinion of smaller

diameter and engages pins of smaller pinions.

28. A piston assembly as claimed in Claim 17 wherein said flywheel is

provided with an axle on the face opposite to the face provided with

said groove.

i o

29. A piston assembly as claimed in Claim 28 wherein said flywheel is

held in place by a support S2 fitted on one end to the said housing.

30. A piston assembly as claimed in any one of the preceding claims,

wherein axis of rotation of said flywheel lies between the axes of

rotation of said smaller pinions and said larger pinions.

31. A piston assembly as claimed in any one of the preceding claims,

wherein axes of rotation of said flywheel, said smaller pinions and

said larger pinions are collinear.

32. A piston assembly substantially as herein described with the help of

foregoing description and as illustrated in the accompanying drawings.

33. A four-stroke engine as and when comprising a piston assembly as

claimed in any one of the preceding claims.