Reciprocating internal combustion engine with a movable head

Abstract

 A reciprocating internal combustion engine is proposed that allows a better exploitation of the energy delivered, produces less polluting emissions and is suitable for utilizing alternative fuels; the engine comprises at least one main piston (5; 53) sliding in a cylinder (4, 52) and operatively connected to a crank-shaft (6) and an elastically yielding head (7; 54) formed by at least one further piston (8; 55) sealingly sliding in the cylinder (4; 52), opposed to the main piston (5; 53), and subjected to the action of opposed first and second elastic means (18, 25; 57, 58) with balanced pre-loads.

Description

[0001] The present invention relates to a reciprocating internal combustion engine with a head structured so as to exploit to best advantage the energy produced by the combustion of an air and fuel mixture.

[0002] As is known, reciprocating internal combustion engines comprise essentially a cylinder block provided with one or more cylinders, a head fastened to the cylinder block, one or more pistons, each sealingly sliding in a corresponding cylinder to execute a given two- or four-stroke working cycle, Otto or Diesel; each piston, together with the head, defines a combustion chamber and is operatively connected to a crank-shaft through a kinematic mechanism with a connecting rod and a crank.

[0003] Generally the head is fastened to the cylinder block by means of bolts, with the interposition of sealing gaskets.

[0004] During the engine's operation, consisting in the repeated execution of working cycle's strokes of induction, compression, combustion, expansion and exhaust, the exploitation of the energy produced by the combustion is entrusted to the piston or pistons, each sliding in a corresponding cylinder, while the head is subjected to considerable thermal and mechanical stresses, thus requiring configuration and size suitable for imparting sufficient resistance thereto.

[0005] Reciprocating engines have also been developed without a fixed head, wherein two opposed cylinders are sliding in opposite directions in just one cylinder to execute a given working cycle; the two pistons define a combustion chamber between them and are operatively connected to a common crank-shaft by means of respective kinematic mechanisms.

[0006] These engines allow a better exploitation of the work produced by the combustion of the mixture, with respect to engines with just one piston per cylinder, but they are penalized by the presence of complex kinematic mechanisms necessary for connecting each piston to the crank-shaft, and by the sudden respective moving away of the pistons, which acts negatively on the cylinder internal pressure drop.

[0007] DE-C-259168 discloses an i.c. engine with a partially movable head formed by complex pistons, with the aim of providing an original timing systems for actuating induction and exhaust parts.

[0008] DE-A-3130767 discloses an i.c. engine with a movable head which permits to change the compression ratio and to smooth the pressure peaks of the cycle.

[0009] EP-A-0488431 discloses an i.c. engine with a head formed by a mobile supplementary piston with the function of varying the volume of the combustion chamber to control the compression and ignition pressure. Said mobile supplementary piston is kept against a fixed stop of a cylinder by the action of a spring. During the engine working cycle, strong impacts of the supplementary piston against said fixed stop of the cylinder occur and cause high noise and breaking of the parts coming into contact.

[0010] The object of the present invention is a reciprocating internal combustion engine that allows to match the following targets:

• better exploitation of the delivered energy;
• possibility of using alternative fuels, also explosive fuels, thanks to a suitable control of the working cycle;
• better ecologic behavior.

[0011] Other objects of the invention are to avoid large stresses on the head and to have a comparatively simple structure, without the complex kinematic mechanisms of the engines with opposed pistons.

[0012] The abovementioned objects are attained with a reciprocating internal combustion engine comprising a cylinder block provided with at least one cylinder, at least one main piston operatively connected to a crank-shaft and sealingly sliding in said cylinder to execute a given working cycle comprising a combustion stage followed by an expansion stage including an expansion stroke of the main piston, and a head associated with said cylinder to define a combustion chamber, said head being fastened to said cylinder block in an elastically yielding manner, said elastically yielding head being formed by at least one further piston sealingly sliding in said cylinder, opposed to said main piston and subjected to the action of first elastic means, characterized in that elastically yielding end-of-stroke means are provided to limit downward strokes of said further piston, said end-of-stroke means being formed by second elastic means allowing said further piston to execute an additional downward stroke at the end of the expansion stroke of said main piston, said second elastic means having a pre-load balancing a pre-load of said first elastic means, so as to subsequently return and keep said further piston in a selected lower end-of-stroke position, thus absorbing and returning part of the energy generated in said combustion stage.

[0013] In the operation of an engine according to the invention, during the combustion stage a pressure peak occurs in the combustion chamber that is in part absorbed by the elastic means in engagement with the elastically yielding head; in this way, the accumulated energy can be returned during the subsequent expansion stage and can possibly be used to accomplish a better exhaust of burnt gases produced by the combustion.

[0014] Thus the energy absorbed by the elastic means during the combustion stage allows a decrease in the value of the maximum pressure in the combustion chamber, with a consequent reduction of stresses on the elements of the engine. The subsequent recovery, during the expansion stage and the additional downward stroke, of the energy accumulated by the elastic means allows the power delivered by the engine to remain at a substantially unchanged level and a better evacuation of the exhaust gases from the cylinder to be accomplished, in favour of a better filling of the same cylinder in the subsequent induction stage and of a more complete combustion, with the consequent reduction of polluting agents in the engine's exhaust gases.

[0015] More precisely, the slight depression caused in the combustion chamber by an additional upward return stroke of the further piston after the additional downward stroke allows the fuel mixture to fill the combustion chamber without being discharged through an exhaust duct, thereby reducing or annulling the fuel losses usually involved with the discharge of the exhaust gas.

[0016] Generally speaking, the engine according to the invention allows the following advantageous results:

• better exploitation of the delivered energy by elastic energy recovery with the piston showing a higher lever arm due to a higher crank angle;
• possibility of using alternative fuels, also explosive fuels, thanks to an optimum control of the working cycle by causing the fuel to explode during the expansion stroke and by reducing the compression stroke to obtain lower pressure values, according to the requirements of different stoicheiometric values of the combustibile mixture;
• better ecologic behavior due to a reduced, or null, use of tossic anti-knocking and anti-explosive products and to the use of cleaner alternative fuels.

[0017] Features and advantages of the invention shall now be illustrated with reference to embodiments of the invention shown as non-limiting examples in the enclosed figures, wherein:

Fig. 1 is a partially sectioned view of a reciprocating internal combustion engine according to the invention;

Fig. 2 is a sectional view taken along the line II-II of Fig. 1;

Fig. 3 is a sectional view taken along the line III-III of Fig. 1;

Fig. 4 shows diagrammatic representations of the engine of Fig. 1 in subsequent stages of a working cycle;

Fig. 5 is an axial sectional view of another embodiment of the engine of Fig. 1;

Fig. 6 shows diagrammatic representations of the engine of Fig. 5 in subsequent stages of a working cycle.

Fig. 7 represents a P-V (pressure-volume) curve of a working cycle of the engine of Fig. 1;

Fig. 8 shows on an enlarged scale the combustion curve in the cycle of Fig. 7.

[0018] There is shown in Fig. 1 an air-cooled, Otto cycle, single-cylinder reciprocating internal combustion engine; the engine is provided with a cylinder block, indicated as a whole with 1, provided with cooling fins 2. There is indicated with 3 a liner forming a cylinder 4 and there is indicated with 5 a main piston provided with gas rings 48, sealingly sliding in the cylinder 4. The piston 5, represented in the position corresponding to its T.D.C. (top dead centre), is connected, as shown diagrammatically in Fig. 4, by means of a pin 45 and a connecting rod 46, to a crank 47 of a crank-shaft 6.

[0019] There is indicated with 7 an elastically yielding head formed by a further piston 8, provided with gas rings 40, that slides sealingly in the same cylinder 4 of the liner 3. The piston 8 is opposed to the piston 5 and in the position corresponding to its lower end of stroke, shown in Fig. 1, it defines with the piston 5 a combustion chamber indicated with 9. The piston 8, also visible in Fig. 3, is provided with a shoulder 10 and with a threaded pin 11 to which a flange 13 is fastened by means of nuts 12. The flange 13 is provided with holes 14 in which there are inserted guide rods 15, that have heads 16 fastened to the base 1 by means of bolts 17. There are indicated with 18 helical springs, coaxial with the rods 15, placed between the head 16 and the flange 13.

[0020] There are indicated with 19 four bolts fastened to the block 1, provided with threaded ends 20; coaxial with the bolts 19 there are respective sleeves 21, each provided with a head 22, and bushes 23, each provided with a plate 26. Bolts 19 and sleeves 21 pass through holes 24 of the flange 13, as also shown in Fig. 2. There are indicated with 25 helical springs, coaxial with the sleeves 21, placed between the flange 13 and the plate 26 of the bushes 23. The springs 18 and 25 are arranged pre-loaded by means of nuts 28, screwed on the threaded extremity 20 of each bolt 19, with the interposition of a washer 31 and of a plate 30. The pre-loads of the springs 18 and 25 are selected so that they balance one another, keeping flange 13 and piston 8 in the selected position of lower end of stroke, as shown in Fig. 1, until the pressure in the combustion chamber 9 does not overcome the pre-load of the springs 25.

[0021] There is indicated with 32 an ignition spark plug screwed into a threaded hole 33 of the further piston 8 and connected, by means of a conductor 34 and a sliding contact 35, to a known ignition current generator, not shown. Conductor 34 and contact 35 are supported by a cap 36, fastened to the plate 30.

[0022] There are not shown in Fig. 1 usual induction and exhaust ports, operated by the piston 5, by means of which a mixture of air and fuel is fed to the cylinder 4 and the burnt gases generated by the combustion of the mixture in the chamber 9 are discharged. These ports are shown in Fig. 4, where they are indicated with 37 and 38, respectively.

[0023] The operation of the engine shown in Figs. 1-3 shall now be illustrated with reference to Fig. 4, through five diagrammmatic representations marked A, B, C, D, E, wherein there are shown the positions assumed by the different elements in the successive stages of a working cycle, that, as previously said, is a two-stroke Otto cycle, represented in Fig. 7.

[0024] There is shown in A the engine during the mixture compression stage, with the piston 5 moving upward toward T.D.C. (top dead center) and the piston 8 in the position of lower end of stroke (step 1-2 of Fig. 7). There is shown in B the engine after ignition, during the mixture's combustion stage, with the piston 5 at the T.D.C. and the piston 8 having moved to the position of upper end of stroke, compressing the springs 25 (step 2-3 of Fig. 7 and dashed-and-dotted line 70, that shows the change in volume due to the displacement of the piston 8). It is possible to show that, due to the upward movement of the piston 8, combustion can be represented by a succession of infinitesimal steps at constant volume, at progressively increasing levels, interspaced by a lot of infinitesimal steps at constant temperature, at progressively increasing levels, as shown in Fig. 8, wherein the dashed lines 71 represent the steps at constant volume (isochors) and the dashed lines 72 represent the steps at constant temperature (isotherms). There is shown in C the engine during the expansion stroke, with the piston 5 moving downward toward B.D.C. (bottom dead centre) and the piston 8 being urged by the springs 25 toward the position of lower end of stroke (steps 3-4 and 4-5 of Fig. 7). It is observed that the restitution of energy takes place at substantially constant pressure (step 3-4 of Fig. 7) and that the steps 2-3-4-5 replace those of a traditional engine, represented by dashed lines. There is shown in D the engine during the exhaust and scavenging stage (step 5-1 of Fig. 7), with the piston 5 at B.D.C., the induction port 37 and exhaust port 38 simultaneously open, and the piston 8 urged by the springs 25, due to the accumulated energy, to execute an additional downward stroke below the position of lower end of stroke, so as to contribute to the exhaust of burnt gases and to the scavenging of the cylinder 4 with fresh mixture. There is shown in E the engine during the mixture's induction and compression stroke, with the piston 5 returning towards T.D.C. and the piston 8, that, under the action of the springs 18, is returned up to the position of lower end of stroke, executing an additional return stroke, that creates a slight depression in the cylinder 4 that is favourable to the entry of the mixture and a larger filling of the cylinder 4. In fact said depression allows the fuel mixture to fill the combustion chamber without being discharged throught the exhaust port 38, thereby reducing or annulling the fuel losses usually connected with the discharge of the exhaust gas residual.

[0025] Thus in the engine according to the invention, the elastically yielding head 7 absorbs energy during the combustion stage, with the advantage of lowering the value of the maximum pressure in the combustion chamber 9 and of reducing the stresses to which the engine's elements are subjected. The energy accumulated by the head 7 is recovered in the subsequent expansion stroke, allowing the energy delivered by the engine to remain substantially unchanged. In addition, executing the additional outward stroke, the head 7 exerts a thrust action on the burnt gases and encourages their evacuation from the cylinder 4, while, during the execution of the additional return stroke, it generates a depression in the cylinder that causes a larger quantity of mixture to flow into it; as a consequence, there are both a better filling and a more complete combustion, together with a reduction of polluting elements in the engine's exhaust gases.

[0026] There is shown in Fig. 5 an Otto cycle, four-stroke single-cylinder reciprocating internal combustion engine; the engine is provided with a cylinder block, of the type cooled with water, indicated as a whole with 50, provided with chambers 51 containing the cooling water; there is indicated with 52 a cylinder, obtained directly in the block 50, in which there sealingly slides a main piston 53, represented in the position corresponding to its T.D.C., operatively connected to a crank-shaft 6, as shown diagrammatically in Fig. 6.

[0027] There is indicated as a whole with 54 an elastically yielding head formed by a further piston 55, sealingly sliding in the same cylinder 52. The piston 55 is opposed to the piston 53 and defines a combustion chamber 56 in the position corresponding to its lower end of stroke, shown in Fig. 5.

[0028] There is indicated with 57 a return-action spring connected to the piston 55 and to a plate 59 provided with a threaded stem 60, by means of which it is screwed onto a cover 61, fastened to the base 50. There is indicated with 58 a spring placed between the piston 55 and the plate 59. The lower end-of-stroke position of the piston 55 is adjusted with the threaded stem 60.

[0029] There are indicated with 62 and 63 an induction port for the mixture and an exhaust port for the burnt gases, respectively, controlled by valves, not shown, and there is indicated with 64 an electrode of a spark plug.

[0030] The operation of the engine of Fig. 5 is illustrated in Fig. 6, through six diagrammatic representations, marked F, G, H, I, L, M, wherein there are illustrated the stages of a working cycle, that, as has been said, is a four-stroke Otto cycle.

[0031] There is shown in F the engine during the mixture induction stroke, with the port 62 open, the piston 53 moving downwards toward B.D.C., and the piston 55 in the position of lower end of stroke. There is shown in G an engine at the end of the compression stroke, at the moment of ignition and when the mixture starts to burn. There is shown in H the engine during the mixture combustion stage, with the piston 53 at T.D.C. and the piston 55 that has moved to the position of upper end of stroke, compressing the spring 58. There is shown in I the engine during the expansion stroke, with the piston 53 that moves downwards toward B.D.C. and the piston 55 that is urged by the spring 58 to the position of lower end of stroke. There is shown in L the engine at the end of the expansion stroke, with the piston 53 near B.D.C. and the piston 55 urged by the spring 58, due to the accumulated energy, to execute an additional downward stroke below the position of lower end of stroke, so as to return part of the elastic energy. There is shown in M the engine during the exhaust stroke, with the exhaust port 63 open, the piston 53 that is moving upward again toward T.D.C. and the piston 55 that, under the action of the spring 57, is returned to the position of lower end of stroke, executing an additional return stroke.

[0032] The invention has been described for the sake of simplicity with reference to single-cylinder engines, but it also applies to multi-cylinder engines.

[0033] The engines described can be fed with usual systems, by means of carburettors, indirect injection systems (with a fuel injector located in an air-intake duct), direct injection systems (with a fuel injector located in the combustion chamber), may be of the induction or supercharged type and may operate on Otto or Diesel cycle.

[0034] The engines according to the invention, with an elastically yielding head, are capable of absorbing part of the energy generated during combustion, and are thus also suitable for utilizing "energetic" fuels, that involve faster and more intense combustions than those with traditional petrol and fuel-oil; for example Diesel-cycle engines with elastically yielding heads can be fed with mixtures of fuel-oil and petrol.

[0035] Moreover these engines can withstand without serious drawbacks even anomalous combustions, such as preignitions or detonations or explosion processes.

[0036] The advantages can be summarised as follows:

• Recovery of the energy absorbed by the elastic system connected to the yielding head. As this fact occurs at more favourable crank angles, other conditions being equal, a better mechanical efficiency is obtained.
• Limitation of the maximum pressures in the cylinder to preset values according to the design's demands.
• Possibility of easily managing each level of generated energy, both in combustions obtained in normal and abnormal processes or as a result of explosions.
• Ease of adjustment of the thermodynamic cycle allowing almost immediate experimental check tests.
• Improved overall management of combustion with advantageous results from the point of view of the reduction of polluting gases.

Claims

1. Reciprocating internal combustion engine comprising a cylinder block (1; 50) provided with at least one cylinder (4; 52), at least one main piston (5; 53) operatively connected to a crank-shaft (6) and sealingly sliding in said cylinder (4; 52) to execute a given working cycle comprising a combustion stage followed by an expansion stage including an expansion stroke of the main piston, and a head (7; 54) associated with said cylinder (4; 52) to define a combustion chamber (9, 56), said head (7; 54) being fastened to said cylinder block (1; 50) in an elastically yielding manner, said elastically yielding head (7; 54) being formed by at least one further piston (8; 55) sealingly sliding in said cylinder (4; 52), opposed to said main piston (5; 53) and subjected to the action of first elastic means (25; 58), characterized in that elastically yielding end-of-stroke means (18; 57) are provided to limit downward strokes of said further piston (8; 55), said end-of-stroke means (18; 57) being formed by second elastic means (18; 57) allowing said further piston (8; 53) to execute an additional downward stroke at the end of the expansion stroke of said main piston (5; 53), said second elastic means (18; 57) having a pre-load balancing a pre-load of said first elastic means (25; 58), so as to subsequently return and keep said further piston (8; 53) in a selected lower end-of-stroke position, thus absorbing and returning part of the energy generated in said combustion stage.

2. Engine according to claim 1, characterized in that said further piston (8) is provided with a flange (13) slidingly engaged by guide means (15, 19, 21) fixed to said cylinder block (1) and forming supports for said first and second elastic means (25, 18).

3. Engine according to claim 1, characterized in that said first and second elastic means (57, 58) are interposed between said further piston (55) and a plate (59) provided with a threaded stem (60), screwed on to a cover (61) fastened to said block (50).

4. Engine according to claim 1, characterized in that said cylinder block (1; 52) is provided with induction ports (37; 62) for combustible mixture and exhaust ports (38; 63) for burnt gases.

5. Engine according to claim 1, characterized in that said cylinder block (1) is provided with induction ports (37) and exhaust ports (38) for a two-stroke working cycle.

6. Engine according to claim 1, characterized in that said block (52) is provided with induction ports (62) and exhaust ports (63) for a four-stroke working cycle.

Drawing