WO2001002752A1

WO2001002752A1 - 'isometric combustion' crank mechanisms

Info

Publication number: WO2001002752A1
Application number: PCT/IT2000/000268
Authority: WO
Inventors: Cosimo Sarno
Original assignee: Cosimo Sarno
Priority date: 1999-07-02
Filing date: 2000-06-30
Publication date: 2001-01-11
Also published as: EP1129309A1; ITPZ990003A1; ITPZ990003A0; AU5845700A

Abstract

The main objective of this patent is to propose novel crank mechanisms capable of improving the thermodynamic efficiency of the engine by a) achieving combustion at constant volume or isometric combustion, made possible by allowing the piston to stop at the Top Dead Centre (TDC), b) reducing thermic exchanges and c) reducing and in some cases annulling the lateral forces between piston and cylinder wall. The improvement of the thermodynamic efficiency of the engine improves the performance of the engine, reduces the fuel consumption and improves the quality and reduces the amount of polluting masses. Experimental tests have been carried out on two engine prototypes to support the above.

Description

"ISOMETRIC COMBUSTION" CRANK MECHANISMS TECNICAL FIELD

This invention regards crank mechanisms which when used in internal combustion engines give the possibility to improve thermodynamic efficiency . BACKGROUND ART

Many are the known mechanisms aimed at the transformation of the rotary movement of a crankshaft supported in a crankcase into a reciprocating movement of a piston in a cylinder.

There is one crank mechanism, in the literature, having the same objectives of the proposed ones which, above all, it is different from the proposed one by the number of the hinges constituting the system; this sistem concerned was patented by myself ("FOUR DEAD CENTER CRANK MECHANISM") (PCT/IT89/00075).

DISCLOSURE OF INVENTION

The main objective of this patent is the achievement of combustion at constant volume ("isometric combustion") by means of kinematic mechanisms which allow the "stopping" of the piston around the Top Dead Centre (TDC) ("Stopping" of the piston means that the piston motion is less than 1% of the stroke) for a crank angle which can be more than 60°.

A crank mechanism able to achieve the above objective is constituted by six rods joined between each other by means of a total of eight hinges. Three of the hinges are hinged to the crankcase and one of the hinges is connected to the piston.

Specifically, one of the rods has three hinges.

In this patent the rods have been numbered and at each number it is associated the name of the rod, e,g., in all crank mechanisms, rod No 1 is the crankshaft, or it is referred to the crankshafts when referring to the twin crank variants.

Fig. 1 (Table 1) shows the crank mechanism as follows : there is a traditional crank mechanism (rods 1 and 2) having two connecting rod small end (C and C). A rod is hinged to one of the connecting rod small end (beam-engine 3) which has the other extremity (D) hinged to the crankcase; at the other connecting rod small end (C) it is hinged rod 4 which shares the other extremity (E) with two further rods (5 and 6). These rods have their other extremities hinged to the piston (F) and to the crankcase (G) respectively.

Please refer to Fig. 3 (Table 2) for the description of the motion of the piston. In this figure, the motion of point C, during the rotation of the crank pin (B), has an alternate rotating motion around hinge D and describes a circumference arc which goes from Cs to Ci (rods 1, 2 and 3, respectively AB, BC and CD, delineate a four-bar chain . The point C has a motion which is composed by the motion of point C and by rotations of point C around point C. These rotations are due to changes of the angle γ composed by the segments BC and CD. By means of rod 4, the motion is transmitted to hinge E which, as it is hinged to rod 6, has an alternate rotating motion around the hinge G. The motion is therefore transmitted to the piston which is connected to hinge E by means of rod 5 and hinge F.

The piston will stop (or nearly stop) at the TDC provided that, around the TDC (angle θs, Fig. 3), the point C describes a trajectory belonging to the circumference (or to its around) having centre Es and radius equal to the length of rod 4. Therefore, by choosing the appropriate value of the angle $s, the combustion can be considered to be happening at constant volume.

Figure 3 shows two positions of the top dead centre ABICIC'I and AB2C2C2; to both top dead centre positions it corresponds the same position of the piston, therefore the motion of the piston, if it is not zero, it certainly is extremely close to zero when rod 1 performs angle θs.

Figure 3 also shows that both the forward strokes (compression and exhaust strokes) and the return stroke (expansion and suction strokes) are much faster compared to the traditional crank mechanisms. Therefore, the average speeds of the piston are higher because the above strokes happen at times which are proportional to the angles θi and Su (both angles are less than 180°). CRANK MECHANISM VARIANTS :

The variant to Fig. differs from the main proposed crank mechanism because it does not have two connecting rod small end. It has instead, the beam-engine with an extremity having two hinges (rod 3). In other words, the system is composed by a traditional crank mechanism (rods 1 and 2) having the connecting rod small end (C) connected, near an extremity of rod 3 (beam-engine), to three hinges having an extremity hinged to the crankcase (D) and the other extremity (C) connected to rod 4. This latter rod has the other extremity (E) hinged to the extremities of further two rods (rods 6 and 5), rod 5 connects the system to the piston by means of hinge F whilst rod 6 connects the system to the crankcase by means of hinge G.

The systems described up to now are characterised by having a three hinges rod which, in the first example corresponds to the connecting-rod (rod 2, Fig. 1), whilst in the second example corresponds to the beam-engine (rod 3, Fig. 2); in both systems it is possible to consider that another rod, either rod 4, 5 or 6, could have three hinges by splitting hinge E in hinges E and E', as shown in Figures 6, 7 and 8. In other words, the above crank mechanisms are composed by rods 1, 2 and 3 of one of the two systems of Figures 1 and 2, completed by rods 4, 5 and 6 of one of the systems of Figures 6, 7 and 8.

Another group of crank mechanisms, resulting from the above crank mechanisms and having twin camshafts, can be obtained by making the above crank mechanisms symmetric to the cylinder axle or to an axle which is perpendicular to the plane containing the axles of the camshafts (some examples are illustrated in Figures 4, 5, 11 and 12).

In order to maintain symmetry also during the motion, it is necessary to connect the camshafts between themselves by means of appropriate systems constituted by gearing, toothed chains or belts. Other systems having similar characteristics can be obtained by using a four-bar chain (Fig. 9) to which rod 4, belonging to one of the systems shown in Figures 6, 7 or 8, maybe applied; also in this case it is possible to obtain the twin camshaft variants by making the whole system symmetric to the cylinder axle or to an axle perpendicular to the plane containing the axles of the camshafts; one example is shown in Fig. 10.

We have seen that the twin camshaft variants are symmetric to an axle perpendicular to the plane containing the axles of the camshafts and that, if this symmetry is also maintained during the motion, there will not be any relative rotations between the rod 5 and the piston; therefore rod 5 and piston can become one single element by getting rid of hinge F. In this case the piston will look unusual in its shape, similar to a mushroom with a head and a stem (Figure 12). The descriptions of the systems which are the objects of this patent, including the claims, have been done in a schematic fashion, therefore some of the rods have to be considered entirely or partially split in order to avoid bending and/or twisting moments on the same rods (for example, the split rods in Fig. 12 are rods 1, 2 and 4 and their corresponding symmetric rods). In addition, in cases when symmetry is required, this should be referred to the schematic representation. MULTI-CYLINDER SYSTEMS

As per the traditional crank mechanisms, also for the proposed crank mechanisms, in order to increase the number of cylinders, it is possible to have a development in line increasing the number of the cranks or the number of the crankshafts. Another option would be to have two, possibly similar, systems facing each other or to put them side by side (preferably the same type of systems), and sharing or not sharing some of the elements (Fig. 17).

EQUΠJBRATION

The equilibration of crank mechanisms is achieved by adding masses on the prolongation of the rods having an extremity hinged to the crank case (rods 1, 3 and 6) and opposite to their free extremity.

In order to obtain a satisfactory equilibration, sometimes it is necessary that the mass which is added to the rod, has the centre of gravity slightly shifted from the axle of the above rods. The resultant of the inertia forces of the twin crankshaft systems lies on the symmetry axle; therefore, to obtain a complete balancing of the system it is enough to add another crank mechanism opposite to the first one and synchronized with it, in such a way that the forces of inertia of the second crank mechanism are equal and opposite to the forces of inertia of the first crank mechanism; the propeller obtained in this way is a two-cylinder or any system with an even number of cylinders.

In all cases, the equilibration of a single-cylinder or of a multi-cylinders in line can be obtained, as per the single-crankshafts, by adding masses on the prolongations of the rods hinged to the crankcase and opposite to their free extremities. Finally, a thrust equilibration can be obtained, as per the traditional engines, by adding rotating shafts having eccentric masses. THE PISTON :

In the twin crankshaft systems, due to the simmetry of the system, rod 5 and the piston may become a single piece by getting rid of hinge F. The lack of side thrusts and of slapping allows firstly that the skirts of these pistons is very short as they only function as a guide; secondly, the lack of piston slaps between the piston and the cylinder allows the use of fragile materials with excellent thermic and mechanic characteristics such as ceramic materials. Figure 12 shows an example of piston which has been sectionalized to point out the possibility of utilizing alternative materials.

For example, the whole head of the piston could be made of ceramic material and the stem of aluminium, or the head of aluminium, the piston skirt of bronze and the stem of steel. As pointed out above, due to the lack of side thrusts, the piston skirt of twin crankshaft systems only act as a guide; this function can also be transferred to the stem of the piston or to a prolongation of the piston which will therefore be bound to run in a guide, thus avoiding the need for the head of the piston to have a skirt. Another possibility is to have a rod in agreement with the crankcase, sliding in the stem of the piston (Figures 13 and 14). This rod could be utilised to transport the oil which cools down the relevant parts. This rod, due to its motion in relation to the piston, could also act as an oil pump. THERMODYNAMIC ANALYSIS : In order to obtain the maximum efficacy of an engine, it is important that the "Otto limite cycle" is met. Some of the assumptions of this cycle are:

1) Combustion at constant volume

2) Lack of thermic exchanges between the operating fluid and the walls around it.

It is obvious that the above is an ideal condition which is virtually impossible to achieve. However it is also obvious that closer we get to satisfy the above objectives (1 and 2), better will be the thermodynamic efficiency which will be achieved.

The proposed crank mechanisms, due to the possibility of stopping the piston at the

TDC, for a given crank angle, are capable of meeting objective 1, that is to say that they realise the combustion at constant volume. As to the thermic exchanges, the proposed systems allow improvements because the surface of the cylinder which is exposed to the thermic exchange with the operating fluid is constantly lower or at the most equal (in correspondence to the dead centres) to the traditional systems.

To better explain the problems related to the thermic exchange, we hypothesise to compare the surfaces of the cylinder which are over the piston in two crank mechanisms, a traditional one and one of the proposed ones : at the same angular speed (please refer to Figure 3) and starting from the Bottom Dead Centre (BDC), in the proposed crank mechanism we have that the compression stroke is faster because is subtended by the angle θi<180°, namely the piston is always earlier compared to the traditional crank mechanisms, therefore in this phase and in any other moment the exchange surface is smaller; viceversa, during the expansion stroke, the piston starts its descending motion in an more advanced angular position of the crank (B2), therefore it is constantly late compared to the traditional crank mechanism, up to the BDC. Therefore, also in this phase we have a reduction of the thermic exchange.

The thermic exchange can be further reduced by taking in account the actual possibility of using ceramic materials, as shown in some crank mechanisms described above.

Also in Diesel engines, the use of the above systems allows combustion at constant volume with the following advantages : the first of them is the increase of the engine thermodynamic efficiency because the "Otto" cycle has, with equal compression ratio, a thermodynamic efficiency superior to the Diesel engines; another advantage is that the fuel injection starts and ends with the piston in a position corresponding to the TDC, therefore the start of the injection happens at higher temperatures and pressures, as compared to a traditional system where the injection starts earlier than the TDC; therefore there is a reduction of the delay of the ignition which is known to cause the rough functioning of these types of engines and to cause overload of the elements of the crank mechanism.

With the proposed crank mechanisms it is therefore possible to achieve both combustion at constant volume and reduction of the thermic exchanges, with improvement of the thermodynamic efficiency, of the specific consumption, and of the amount and quality of the polluting masses and of the performance of the engine.

SUCTION AND EXHAUST STROKES

The above strokes are different from the traditional crank mechanism because the valves cross each other with the piston stopped; this means that when the piston starts its suction stroke, the inlet-valve is nearly completely open, therefore causing reduction of the losses of head with consequent beneficial effect on the filling. During the exhaust stroke it is possible to prolong the exhaust of the exhaust gasses, by utilising a portion of the "stopping" angle, also after the piston has reached the TDC, having in this way a spontaneous exhaust not forced by the motion of the piston; the whole leading to an improved exhaust.

The stopping of the piston at the TDC allows the crossing times of the valves to play a less relevant role compared to the traditional systems. The crossing times could also be zero without relevant impact on the performance of the engine. It is therefore possible that, in order to obtain a variable phase of the valves we have to ensure that, during the motion, the inlet cams maybe dephased with the exhaust cams; this will produce a modification of the distribution diagram, that is to say that it is possible to obtain both the desired delay of the inlet-valve closing and the desired early opening of the exhaust valve, also if this implies a change of the intersection angle.

In the proposed types of engines, the achievement of the variable distribution becomes extremely easy if we have a twin camshaft, as it is sufficient to be able to dephase them both between each other and between them and the crank; the above dephasings are obtainable by applying variable turnbuckles on the branches of the belts or of the distribution chains, and also by using wheelworks with an helicoidal shape, the sliding of which on the rotation axle produces the desired dephasing. ORGANIC ANALYSIS

All the proposed crank mechanisms are composed by a number of rods which is higher compared to the traditional one, therefore expecting an increased loss of power by friction.

It is also to be taken in account that the friction normally arising between piston and cylinder wall is, in the traditional engine, equivalent to the power that the whole crank mechanism loses by friction including the losses by pumping, therefore having a high amount of friction. In the proposed single-crankshafts, the lateral forces between cylinder and piston walls are minimal due to the small slopes that rod 5 has, during the motion, in relation to the cylinder axle; the above forces become null in the twin crankshafts; all the above confirms that the frictions between the piston and the cylinder are extremely low or even negligible. We have here demonstrated that the increase in the number of elements causes an increase of the frictions but, on the other hand, the reduction or annulment of the lateral forces causes a reduction of the frictions; therefore, even if the power lost by friction is higher than the traditional engine, it is assumed that this will not be of significant extent.

APPLICATIONS TO THE TWO-STROKE AND FOUR-STROKE ENGINES Referring to the two-stroke engines, the advantage of using the twin crankshaft is due to the fact that the compression chamber of the fuel can be obtained below the piston, excluding the crankcase or part of it.

Figure 12 shows that the compression chamber is delimited by the lower part of the piston, the cylinder and a surface which closes itself on the stem of the piston. It is possible to see the inlet and exhaust lights of the compression chamber provided with automatic valves which however, are not always necessary; it is to be pointed out that the drawing is to be looked at in a schematic way and that it is not shown how the compressed fuel in the compression chamber can communicate with the combustion chamber, as this is a well known issue. The above solution can be usefully applied as a an over-feed to the four-stroke engines, allowing communication through possibly refrigerated pipes, between the exit of the compression chamber and the inlet-valve (positioned on the cylinder head and not shown in Figure 12).

The over-feed is obtainable due to the fact that in the four-stroke engines the induction stroke happens after every two crank turns, whilst in the compression chamber there is a pumping at each turn; therefore after the first turn the pipe is put under pressure (the pressure in the pipe is maintained by possibly automatic and unidirectional valves) and during the second turn, this pressure and the second pumping are used by the induction stroke. ADJUSTMENT SYSTEMS We have seen that in the proposed crank mechanisms it is possible to give the piston a given motion law which will be dependent on the choices made in the planning phase; the choices to be made regard the length of the rods and the coordinates of the hinges connected to the crankcase. A change in the co-ordinates of the hinges connected to the crankcase (for example point D, and for the twin crankshaft crank mechanisms also its symmetric point) will be reflected in a change of the motion law of the piston.

In order to allow a higher flexibility of the engine it could be ideal to have adjustable hinges either "una tantum" (in the assemblage phase or when the engine is stopped) and/or continuously (during the motion).

One system comprises cylindrical elements which are capable to turn around their own axle and are hinged to the crankcase, and which have an eccentric hole where there is hinge D. If the adjustment of the system has to happen when the engine is stopped or during the assembling phase, the cylindrical bearings with eccentric hole can be fixed to the crankcase in a given position (for example, Figures 15 and 16 show a system with four possible adjustments for as many holes for the fixing); if instead the adjustment of the system has to be continuous then the above bearings have to be able to turn around their own axle by using gearings, chains, belts, levers or other. Another system is in such a way that the hinge(s), which are subject to adjustment, are not hinged to the crankcase but to the extremity of a rod (Figure 14) which has the other extremity hinged to the crankcase. The adjustment happens by allowing movements of the above rod around the extremity hinged to the crankcase until the desired position is reached; this position can be fixed or variable (Figure 13 shows an example of the application of the above to a twin crankshaft system; this figure also shows one of the possible leading systems constituted by two rods sharing one extremity and having the other two extremities hinged to the bearings; the desired position is reached by allowing sliding of the extremity shared by the rods into a guide).

Another system could be to fix the first system described above (cylinder with eccentric hole) to an extremity of the second system, also described above. When applying the above systems to the twin crankshaft it is sufficient to make sure that the whole system is symmetric to an axle perpendicular to the plane containing the crankshaft axles.

Claims

1) Mechanism to transform a rotatory motion of a crank in a crankcase to an alternate motion of a piston into a cylinder; this mechanism comprises six rods and eight hinges: a crank rod (rod 1) with extremity A hinged to the crankcase and extremity B hinged to a connecting-rod (rod 2) which has two connecting rod small end (C and C); to one of them (C) it is connected the beam-engine (rod 3) which has the other extremity (D) hinged to the crankcase; to the other connecting rod small end (C) it is connected rod 4 which has the other extremity (E) hinged to rods 5 and 6; rods 5 connects the system to the piston, by means of hinge F, whilst rodό has the other extremity (G) hinged to the crankcase.

2) Mechanism to transform a rotatory motion of a crank in a crankcase to an alternate motion of a piston into a cylinder; this mechanism comprises six rods and eight hinges : a crank rod (rod 1) with extremity A hinged to the crankcase and extremity B hinged to a connecting rod (rod 2) which has the connecting rod small end (C) hinged to a beam-engine (rod 3) which has three hinges (C, C and D); the two hinges C and D are connected to the crankcase and rod 4 respectively; this latter rod has the other extremity (E) hinged to rods 5 and 6; rod 5 connects the system to the piston, by means of hinge F, whilst rod 6 has the other extremity (G) hinged to the crankcase. 3) Crank mechanisms as the ones described in claims 1 and 2 but where also any of the rods, amongst rods 4, 5, or 6, has three hinges, therefore necessitating the splitting of hinge E into E and E'; if the three-hinge rod is rod 4, to the three hinges C, E and E' are respectively connected the rods 2 or 3 (depending on whether claim 1 or 2 are used) and the rods 5 and 6; if the three-hinge rod is rod 5, to the three hinges F, E and E' are respectively connected the piston and the rods 4 and 6; if the three-hinge rod is rod 6, to the three hinges G, E and E' are respectively connected the crankcase and the rods 4 and 5.

4) Crank mechanisms as the ones described in claim 3 where neither the beam-engine (rod 3) nor the connecting-rod (rod 2) have three hinges; that is to say that there is not any more the splitting of hinge C in C.

5) Twin crankshaft crank mechanisms obtained by making the crank mechanisms described in claims 1, 2, 3 and 4 symmetric to the cylinder axle or to an axle perpendicular to the plane containing the axles of the crankshafts; the systems are completed by adding gearings, chains or other elements with the objective to ensure the symmetry and/or the synchronism between the two crank rods. 6) To the crank mechanisms described in claim 5, it is possible to eliminate hinge F which connects rod 5 to the piston; in other words the piston and rod 5 can become one single element.

7) To the crank mechanisms described in claims 5 and 6 it is possible to make rod 5 or the stem of the piston or their extension to slide into a guide; this allows the elimination of the piston skirt as the piston will not have any direct contact with the cylinder.

8) In the crank mechanisms described in claims 5 and 6, it is possible to slide into the rod constituting the piston (rod 5) a rod hinged to the crankcase having a function of guide for the piston and/or pump and/or adduction of the oil for the cooling and lubrification.

9) In the crank mechanisms described in claims 5, 6 and 7, it is possible to utilise the part below the piston as a compression chamber by closing the surface of the cylinder on the rod 5 or on the stem of the piston; this latter will be able to slide in an airtight guide; in the two-stroke engines the chamber will have the usual lights of intake/outtake port, whilst in the four-stroke engines the compression chamber will have at least two openings in which the valves (possibly uni-directional and automatic valves) are placed; one or more valves ensure the entry of the fluid in the compression chamber, the other valve(s) will ensure the exit of the liquid in a pipe, possibly refrigerated, which leads to the inlet valve and which allows communication between the pipe and the combustion chamber.

10) In reference to claim 6, the head and possibly a portion of the piston stem can be made of alternative materials compared to the remaining parts of the piston. 11) The pistons, as per claims 6 and 10 can use ring-like inserts, made of anti-friction materials and/or with particular thermic and mechanic characteristics, as their skirt.

12) To the crank mechanisms described in all the above claims, it is possible to apply to the fixed hinges, an adjustment system composed of cylindrical elements which are capable of rotating in a given place jointed to the crankcase, with an eccentric hole in which the pins are placed; these elements can be fixed to the crankcase in the desired position or can be free to rotate in their lodging controlled by adequate mechanisms.

13) To the crank mechanisms described in all the above claims, it is possible to apply to the fixed hinges an adjustment system composed of rods having an extremity hinged to the crankcase and the other extremity shared by the hinges which are the object of adjustment; these rods can be fixed to the crankcase in the desired position or can be free to rotate around the hinge which is hinged to the crankcase and controlled by adequate mechanisms.

14) To the crank mechanisms described in all the above claims it is possible to apply a variable distribution which implies the possibility to dephase the camshaft in relation to the crank rod, and if it is a twin camhaft also in relation to themselves; these dephasings are obtained by applying variable tumbuckles on the branches of the belts or of the distribution chains, or by using wheelworks with an helical shape, the sliding of which on the rotation axle produces the desired dephasing.

15) The crank mechanisms described above can be made multi-cylinder mechanisms by in-line development and/or by means of appropriate combinations such as the opposition or alignment of two systems, possibly equal between each other, with or without sharing some elements.