US3133447A

US3133447A - Reciprocating engine or pump

Info

Publication number: US3133447A
Application number: US715619A
Authority: US
Inventors: Mercier Pierre
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-02-16
Filing date: 1958-02-17
Publication date: 1964-05-19
Anticipated expiration: 1981-05-19

Description

May 19, 1964 P. MERCIER 3,133,447

RECIPROCATING ENGINE 0R PUMP Filed Feb. 17, 1958 4 Sheets-Sheet 1 y lla..

May 19, 1964| P. MERCIER 3,133,447

' RECIPROCATING ENGINE 0R PUMP Filed Feb. 17, 1958 4 Sheets-Sheet 2 l. ...,fhin 54 H.

May 19, 1964 P. MERCIER RECIPROCATING ENGINE OR PUMP 4 Sheets-Sheet 3 Filed Feb. 17. 1958 v wmf mi O O H Il, .f l

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May 19, 1964 P. MERCIER RECIPROCATING ENGINE 0R PUMP 4 Sheets-Sheet 4 Filed Feb. 17, 1958 United States Patent O 3,133,447 RECIIRUCATING ENGINE OR PUMP Pierre Mercier, Piscop, France (l Rte. de Saint Erice, Piscop, Seine et (lise, France) Filed Feb. 17, 1958, Ser. No. 715,619 Claims priority, application France Feb. 16, 1957 4 Claims. (Cl. 74-60) The invention relates to a power transmission mechanism of the wobbler or swash-plate type for internal combustion engines, pumps or compressors having a plurality of cylinders and pistons reciprocable therein. The swash plate is mounted for oscillatory movement without rotating relative to the pistons, and the pistons are connected to the swash plate whereby reciprocatory motion of the pistons is transformed into rotary motion of the crankshaft, or vice-versa.

An object of the invention is to provide a power transmission mechanism of the above-noted type of which the cylinders and pistons, connecting rods, swash-plate and crank-shaft are so designed as to ensure an optimum performance by causing the pistons to move at predetermined accelerations in the vicinity of their dead centers by providing means for adjusting the piston inner dead centers.

In known devices of this type, and in particular in twostroke engines, each connecting rod is subjected. to stresses of different values at the ends of its stroke respectively corresponding to the inner and outer dead centers of the associated piston. This is due to the fact that, in the vicinity of the inner dead center, the inertia of the moving parts and the motive forces, are in opposite directions, while in the vicinity of the outer dead center they have the same direction.

Under these conditions and, in particular, in a high `speed engine, it is desirable to establish a discrepancy betime during which the hot gases will be trapped within the combustion chamber while lengthening the time of scavenging and gas exhausting.

In swash-plate mechanisms hitherto constructed, the sWash-plate is mounted for oscillating movement either concentrically with the crankshaftor concentrically with an inclined crankpin, and the connecting rods of the pis- Itons of the several cylinders are pivotally connected to the said point of articulation is situated at one end or the other of said arc respectively corresponding to the maximum inclined positions of the swash-plate. The arc is intersected `by the axis of the corresponding connecting rod when the piston is at the end of its compression stroke and exhaust stroke so that the sWash-plate will imp-art to the piston strokes of successive acceleration and decelerationtas the .articulation point moves along said arc of circle.

According to the present invention there is provided a sWash-platemechanisrn for engines, pumps or compres- ,sors having a plurality of cylinders and pistons reciprocable therein comprising a sWash-plate mounted concentriice cally with the crankshaft so as to be capable of oscillating about a center and connected to a crank pin of the crankshaft by means of a universal joint of the spherical type, the points of articulation of the connecting rods to the swash-plate all lying in a transverse plane which is spaced from the center of oscillation. The distance between said plane and the center of oscillation is such that when a piston arrives at the end of its compression stroke, the axis of its connecting rod will extend substantially tangential to the arc of circle described by the corresponding articulation point during oscillation of the swash-platc, whereby the motion of the piston will have a substantially greater acceleration towards the end of its compression stroke than towards the end of its expansion stroke,

Thus, the invention provides a novel geometrical coniiguration permitting a differentiation between the acceleration of the piston at the end of its compression stroke and the acceleration of the piston at the end of its expansion stroke. Thus, the axial spacing between the plane containing the points of articulation and the center of oscillation results in a consequent shift of the arc of circle described by each point of articulation during oscillatory movement of the swash-plate. Moreover, the axes of the connecting rods, or at least a portion thereof, are arranged to extend substantially tangential to the corresponding arc of circle when the piston is at the end of its compression stroke.

A more particular object of the invention, with this purpose in view, is to arrange the engine cylinders along generatrix lines of a revolution conical surface.

Other objects and advantages of the invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example.

In these drawings:

FIG. 1 is a diagrammatic partly axial sectional View of a two-stroke engine according to the invention with four cylinders.

.of an engine having opposed pistons and provided with the arrangement shown in FIG. 5, and

FIG. 7 shows a practical construction of a portion of the engine of FIG. 6.

In the embodiment shown in FIG. 1 a twostroke engine according to the invention comprises four cylinders having their axes in the plane of the drawing; it is clear that any number of similar groups of four cylinders may be arranged in a similar manner in other planes containing the longitudinal axis of the crank-shaft. In the example shown, the end-of-stroke acoelerations are given different values for the inner and outer dead centers vrespectively by a suitable inclination of the cylinder axes with respect to the crank-shaft axis and by a shifting of the plane containing the articulation points of the connecting rods on the swash-plate with respect to the geometrical center of oscillation of said plate.

1 is the casing of the engine, and 2 is the crankshaft which is provided with two opposed crank-pins 3 and 4. Four cylinders are shown at 5, o, 7 and 3. The four cylinders are obviously alike, as well as the parts cooperating with them, so that it will be suliicient to describe one cylinder and its associated parts.

The driving cylinder 5 is associated with a scavenging air cylinder 11, coaxial therewith but having Va greater diameter. There is provided a double piston comprising a piston member 12, or head, slidably mounted in the driving cylinder 5 and a piston member 13, or body, slidably mounted in the scavenging cylinder 11. On the piston body 13 is pivoted at 14 the small end of a connecting rod 15, the large end off which is pivoted at 16 on the swashplate 17. The swash-plate 17 is supported in the casing 1 so as to be freely tiltable around an oscillation point 18 on its axis which is also located on the axis of the crankshaft 2. The support of the swash-plate by the casing may be made for example, through a universal joint cornprising an annular member 19 having two right-angled axles, one of which is journalled by diametrically opposite pivot pins 20 in the swash-plate 17 while the other one is journalled in the casing 1 by means of diametrically opposite pivot pins 20a, another point of the axis of the swashplate being secured to the crank-pin 3 of the crank-shaft through a ball-and-socket joint 21. The point 16 of the swash-plate at which the connecting rod 15 is pivoted, as Well as the diametrlcally opposed point 22 at which the connecting rod of the cylinder 8 is pivoted, thus move in the vicinity of the plane containing the axes of both cylinders 5 and 8, as well as the axis of the crank-shaft, as the crank-shaft rotates while the sWash-plate describes its wobbling motion. According to a feature of the invention the plane containing the points 16 and 22 is shifted (to- Wards the left in FIG. l) with respect to the point of oscillation 18 of the swash-plate, which contributes to give to the end-of-stroke accelerations of the piston different values in the respective vicinity of the inner and outer dead centers, Ias explained hereafter.

In the position shown in the drawing, the piston head 12 lies at its inner dead center or compression stroke and the leverage between the points 16 and 18 of the swashplate 17 is substantially right-angled to the direction of the cylinder axis while the connecting rod s substantially aligned with the cylinder axis.

For a position of the crank-shaft angularly spaced by 180 with respect to that shown in the drawing, Le., when the piston will lie at its outer dead center or exhaust stroke, the axis of the swash-plate 17 will make an Iangle 2a with respect to its position shown in the drawing, so that the above-mentioned leverage 18-16 will then also make the same angle 2a with respect to its position shown in the drawing; then the point 16 will be brought to 16' while the connecting rod will be shifted from the position 14-16 to the position 14-16'. It may be seen that the abovementioned leverage, which will then lie at 18-16, will make the cylinder axis an angle having a value dilerent from that of the angle the said leverage makes, as shown in the drawing, when the piston lies at its inner dead center. This angle difference results, on the one hand, from the fact that the cylinder axis is inclined with respect to the crank-shaft axis land, on the other hand, from the fact that the plane of the anchoring points of the connecting rods on the swash-plate 17 is shifted with respect to the point of oscillation of the latter. It is the angular relation of the aforenoted leverage that results in the desired accelerations.

FIG. 2 diagrammatically shows an alternative embodiment in which the axis of the crank-shaft 51 is shown at XX', the crank-pin at 52, the point of oscillation of the swash-plate at 53, the connecting rod anchoring point at 54, the associated piston at 55 and at 56 the cylinder in which said piston is slidably mounted, which has been assumed to be parallel with the axis XX'. The connecting rod interposed between the swash-plate and .the piston is cranked and its two bending points are respectively pivoted at 57 and 58 on an intermediate lever 59 which is, 'im turn, pivoted at 61 on the engine casing.

At the inner dead center, the piston axis lies at 62 while at the outer dead center it lies at 62'; then the intermediate lever lies at 57', 58', 61 and the swash-plate at 53, 54'. The end-of-stroke accelerations of the piston are a function of the inclination of the connecting rod section 54, 57 with respect to the radius 53, 54 of the swash-plate as well as with respect to the radius 61, 57 of the intermediate lever and the inclination of the section rod 58, 62 with respect to the radius 61, 58 of the intermediate lever, as Well as with respect to the axis of the cylinder 56.

By varying the location of the points of articulation of these parts and the length of the various leverages, many combinations of piston acceleration in the vicinity of |its inner dead center and its acceleration in the vicinity of its outer dead center are obtained. It is also possible to so dispose the cylinders that they be steeply inclined to the crank-shaft axis which offers important advantages for the structural design of the engine; finally, the oblique thrust of the piston on the cylinder walls may be reduced, which permits omitting guiding members.

FIG. 3 shows an engine designed according to the diagram of FIG. 2, but wherein, however, the cylinder axes, instead of extending along generatrix lines of a cylindrical surface coaxial with the crank-shaft, are disposed along generatrix lines of two vertically opposite conical surfaces generated by the two straight lines A, A' and B, B symmetrical with respect to the axis XX of the crank-shaft and both intersecting the latter at the same point. In this figure there are shown, as previously, at 56 a cylinder, at 55 the associated piston, at 64 a section of the related connecting rod, at 59 an intermediate lever and its pivot 61, at 65 another section of the connecting rod, at 53 the point of oscillation of the swash-plate 67 and, at 52, the crank-pin of the crank-shaft 51. The engine casing is indicated at 68. On the axis B-B is diagrammatically shown a second cylinder 56 and, on the other side of the general center O of the engine, are located two other cylinders (not shown) respectively symmetrical with the cylinders 56 and 56', with respect to the said center O. Thus, the engine shown in FIG. 3 includes at least four cylinders. It would be possible, furthermore, to dispose other pairs of cylinders on each of the two conical surfaces vertically opposed at O.

In the drawing, there is further shown at 71 the fluid outlet, at 72 a central distributor for the scavenging air, and at 73 a tore chamber communicating with the said sliding valve.

The piston 55 lies at its inner dead center while the piston 55 is located at its outer dead center; the various parts respectively lie in positions similar to those of the parts shown in FIG. 2. lt may be seen that the inclination of the connecting rod is negligible at explosion time when the piston lies at its inner dead center in spite of the very strong inclination of the axis of the cylinders on the crank-shaft axis. This arrangement permits of designing a high compact and, hence, very light engine.

In the embodiment shown in FIG. 4, a set of four

cylinders

101, 102, 103, 104 are arranged with .their axes on four equidistant generatrices of a cylinder on the axis of which is mounted a crank-shaft 105 rotatably mounted in the engine casing only a small portion of which is indicated at 106 in the drawing. In each cylinder are arranged two opposed pistons, such as the piston 107 which is visible in cylinder 101. Alternately, each cylinder could have one end closed and contain one piston only. The connecting rods 111 and 112 of two diametrically opposed pistons are pivoted at the ends of a diameter of a gimbal member 113 which is supported in the casing by two stub shafts 114 located on an axis at right angles to the straight line joining the two points of the gimbal member where the connecting rods 111, 112 are pivoted.

The stub-shafts 114 are mounted on a supporting member which, in this example, consists in two arms 115 pivotally mounted in the casing of the engine about an axis parallel with the common axis of the stub-shafts, in

such a manner that the latter may be shifted along over a short distance in a substantially rectilinear path parallel with the crank-shaft axis, for instance, under the action of a hydraulic jack indicated as at 116.

A awash-plate 117 with a central aperture for accommodating the crank-shaft, is arranged within the gimbal member 113 and is provided with two stub-shafts 118 which enable said sWash-plate 117 to pivot within said gimbal member about an axis at right angles to the axis of the stub-shafts 114 of the gimbal member 113. The other two connecting rods are pivoted to the plate 117 respectively at the ends of a diameter at right angles to the axis of both stub-shafts 118 of the plate.

The sWash-plate 117 is provided with a hub-shaped member 123 the end of which is connected to a crankpin 124 of the crank-shaft 105 through a sleeve 125 the outer surface of which is spherical and tted in a conjugated spherical housing in the hub-shaped member 123, and which has a cylindrical bore which enables it to slide along the rectilinear crank-pin 124 which is parallel with the general axis of the crank-shaft.

The assembly so far described could operate as a cornpressor but it is more particularly designed to be used as an internal combustion engine.

Under the influence of the pressures being successively exerted by the pistons, the outer end of the hub 123 drives the crank-pin in a circular path about the crank-shaft axis. Every axial reaction is absorbed by the casing, through the Cardan-like connection formed together by the plate 117 and the girnbal member 113. The connection between the hub and the crank-pin through the spherical sleeve with a cylindrical bore, is particularly desirable because the bearing surfaces, namely the spherical bearing surface between the hub and the sleeve, as

well as the cylindrical bearing surface between the sleeve and the crank-pin are permanently moving one with respect to the other and, therefore, are subjected to a permanent grinding operation. No local wear of these surfaces, therefore, is 'to be expected, and the joint is able to operate for long periods of time without any material clearance taking place. Furthermore, the lubrication is correct, the unitary pressures are uniform and no excessive heating is to be feared. Finally, the slight possible distortions of the crank-pin, principally flexure distrotions, are absorbed by the spherical joint all the more easily that the surfaces in contact are already moving one with respect `to the other, as already stated hereinabove.

Gperation of the jack 116 makes it possible to move the gimbal member 113 along the crank-shaft axis. During this movement, the spherical'sleeve 125 slides along the crank-pin, so that Vthe only result of this adjustment is a shifting movement as a whole of all the pistons either in one direction or in the other. It is thus possible to increase or to reduce the inner clearance in the cylinders, according to the operating conditions of the engine.

FIG. 5 shows a modication of the embodiment of FIG. 4, which is .different from the latter by the fact that the connecting

rods

126, 127, 123, 129, on one side are pivoted to the plate 131, at the ends of two perpendicular diameters, said plate being supported by two diametrical stub shafts 132 of a cross-like gimbal member 133 the two further

diametrical stub shafts

134, 134A of which are carried on the casing of the engine, through a supporting member which, in this example, consists in pistons 135, 135A'adapted to slide in cylinders 136 extending in directions parallel with the crank-shaft axis. The axis of the stub shafts V132 of the cross member extends along the bisectrix of the angle formed by the diameters which join the points on the plate where the connecting rods are pivoted. The cross member 133 is centrally apertured for accommodating the crank-shaft. The plate 131 also is provided with a hub-shaped member 137 the outer end of which is connected to the crank-pin 124 of the crank-shaft 105 by a spherical sleeve with a cylindrical bore, as in the embodiment described hereinabove.

This device operates in the same manner as that of FIG. 4 with only the slight diierence that, even practically, the center of the Cardan-like joint moves in a direction parallel with the crank-shaft axis instead of describing a short arc of a circle.

FIG. 6 shows a motor-compressor set designed according to the kinematic principle illustrated in FIG. 5. The crankshaft is rotatably mounted in the casing 106 and is provided with two crank-pins 124 on which the two spherical sleeves 125 are slidably mounted. Each piston comprises two portions of different diameters, namely a portion 141 which serves as a power piston and a portion 142 of a larger diameter which serves as a compressor piston; these two pistons operate, respectively, in cylinders 143 and 144 of corresponding diameters. For the sake of clarity, some details have been omitted, namely the timing systems of the motor and of the compressor. Balancing weights rigid with the crank-shaft have been indicated as at 145.

FIG. 7, wherein the same reference numerals are used for corresponding elements of FIG. 5, shows a device for shifting the gimbal member 133 of FIG. 5 axially with respect to the crank-pin 124 to thereby adjust the compression ratio of the engine cylinders (not shown) corresponding to the connecting

rods

126, 127, 128, 129. As shown in FIG. 7, the

stub shafts

134 and 134A are mounted through self-aligning needle bearings 151, the spherical outer race 152 of which is mounted in a bearing 153 rigid with a double piston 154 adapted to have its end portions sliding in a bore 155 of a support cast in one piece together with the casing 166 of the engine. The weak axial component forces possibly exerted upon the

stub shafts

134, 134A of the cross member are absorbed by a -thrust ball bearing 157, through a spherical thrust-piece 15S which cooperates with a cup-member 159 screwed on a lateral extension of the sleeve 152.

Stub shaft 132 provides the same pivotal mounting between gimbal member 133 and plate 131 as shown in FIGURE 5. The axial shifting movement of each piston 154 is insured by a hydraulic system which comprises a stationary piston 161, the piston 154 being itself designed as a cylinder reciprocably mounted on the piston 161. Channels 162, 163 within the rod of the piston 161 ensure a communication between both chambers 164, 165 respectively, of the cylinder, either with a source of pressure fluid, or with a zone of low pressure, so as to cause said cylinder to move, either in one direction or in the other, as it is desired either to increase or to reduce the inner clearance in the cylinders 143 of the engine. The positioning of the inner dead centers of the pistons of the engine may be achieved in a positive manner or, else, with a given resiliency, in order automatically to limit the maximum effort exerted upon the pistons at the moment of the maximum power impulse. For this purpose, in order to drive the pistons 154, use may be made for instance, of an installation which comprises, in combination, a pressure liquid and a pressure gas, the latter being intended to serve as a resilient cushion under a pressure which corresponds to the pressure prevailing in the cylinders of the engine at the moment where the maximum permissible forces are being exerted.

In a general manner, in the above description, there have been disclosed practical and efficient embodiments of the invention, and it should be well understood that changes may be made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as defined in the following claims.

What is claimed is:

l. In a reciprocating device comprising a crank-pin and a crankshaft, said crankshaft including an inclined crank-arm for supporting said crank-pin parallel to the axis of said crankshaft, a plurality of reciprocating pistons, each of said pistons disposed around said crankshaft so that at one end of a stroke, the piston lies at a greater axial distance from said crank-pin than at the other end of the stroke, each of said pistons including a connecting rod pivotally connected thereto, a ball on said crank-pin, a wobble member including a bearing for forming a socket for said ball and a conical skirt portion surrounding said inclined crank-arm, said conical skirt portion including a base remote from said bearing, said ball and said bearing forming a spherical type universal joint between said crank-pin and said wobble member, means for supporting said wobble member for oscillating movement concentrically with said crank-arm about a point of oscillation, and means for pivotally connecting said connecting rods to said base of said conical skirt portion of said wobble member in a common transverse plane axially spaced from said point of oscillation in a direction towards said crank-pin, the distance between said transverse plane and said point of oscillation being such that when a piston arrives at the end of its stroke remote from said crank-pin, the respective connecting rod will extend along an axis substantially tangential to the arc of a circle described by the pivotal connection of the last mentioned connecting rod to said base during oscillation of the wobble Vmember for causing the motion of said piston to have a substantially greater acceleration towards one end of its stroke than towards the other end.

2. In a reciprocating device comprising a crank-pin and a crankshaft in displaced parallel relationship, a crankarm extending from said crank-pin to said crankshaft, said crank-arm being connected to said crankshaft to define a point of oscillation, a plurality of reciprocating pistons disposed around said crankshaft, each of said pistons having a stroke in a plane including the axis of said crankshaft and wherein each of said pistons at one end of a stroke is closer to said crank-pin than the other end of the stroke, each of said pistons including a connecting rod including rst and second ends and means for pivotally connecting said first end of each connecting rod to a respective of said pistons, a ball on said crank-pin, a wobble member including a bearing for forming a socket for said ball and a conical skirt portion surrounding said inclined crank-arm, said conical skirt portion including a base, said ball and said bearing forming a spherical type universal joint between said crank-pin and said wobble member, and means for pivotally connecting said second ends of said connecting rods to said base of said conical skirt portion of said wobble member at locations lying in a common transverse plane axially spaced from said point of oscillation in a direction toward said crank-pin whereby said wobble member oscillates about said point of oscillation in response to the reciprocating movement of said pistons.

3. In a reciprocating device comprising a crank-pin and a crankshaft in displaced parallel relationship, a crankarm including a rst end rigidly connected to said crankpin and a second end connected to said crankshaft and defining a point of oscillation, a plurality of reciprocating pistons, each of said pistons having a reciprocating stroke lying in a plane which includes the axis of said crankshaft and wherein one end of a stroke of the piston lies at a greater axial distance from said crank-pin and closer to said crankshaft than the other end of the stroke, each of said pistons including a connecting rod including a rst end pivotally connected thereto and a second end, a ball on said crank-pin, a wobble member including a bearing for forming a socket for said ball and a conical skirt portion surrounding said inclined crank-arm, said G conical skirt portion including a base, said ball and said bearing forming a spherical type universal joint between said crank-pin and said wobble member, and means for pivotally connecting the second ends of said connecting rods to said base of said conical skirt portion of said wobble vmember, whereby said wobble member oscillates about said point of oscillation in response to the strokes of said reciprocating pistons, said connecting rods being connected to said base at locations lying in a common transverse plane axially spaced from said point of oscillation in a direction towards said crank-pin for causing the motion of said pistons to have a substantially greater acceleration towards one end of its stroke than towards the other end.

4. In a reciprocating device comprising a crank pin and a crankshaft in displaced parallel relationship, a crank-arm including a iirst end rigidly connected to said crank-pin and a second end connected to said crankshaft, to define a point of oscillation, a plurality of reciprocating pistons, each of said pistons having a reciprocating stroke lying in a plane which includes the axis of said crankshaft and wherein one end of a stroke of the piston lies at a greater axial distance from said crank-pin and closer to said crankshaft than the other end of the stroke, each of said pistons includes a connecting rod including a rst end pivotally connected thereto and a second end, a ball on said crank-pin, a wobble member including a bearing for forming a socket for said ball and a conical skirt portion surrounding said inclined crank-arm, said conical skirt portion including a base, said ball and said bearing forming a spherical type universal joint between said crank-pin and said wobble member, and means for pivotally connecting the second ends of said connecting rods to said base of said conical skirt portion of said wobble Vmember whereby said wobble member oscillates about said point of oscillation, said connecting rods being connected to said base at locations lying in a common transverse plane axially spaced from said universal coupling means in a direction towards said crank-pin, the distance between said transverse plane and said point of oscillation being such that when a piston arrives at the end of its stroke remote from said crank-pin, the respective connecting rod will extend substantially tangential to the -arc of a circle described by the pivotal connection of the last mentioned connecting rod to said base during oscillation of the wobble member for causing the motion of said piston to have a substantially greater acceleration towards one end of its stroke than towards the other end.

References Cited in the file of this patent UNITED STATES PATENTS 669,209 Wiesenbach Mar. 5, 1901 1,194,258 Walker Aug. 8, 1916 1,210,649 Holley et al Jan. 2, 1917 1,656,884 Davol Jan. 17, 1928 1,895,851 Jannin Jan. 31, 1933 2,087,567 Blum July 20, 1937 2,105,019 Turner Ian. 11, 1938 2,231,100 Wahlmark Feb. l1, 1941 2,240,912 Porter May 6, 1941 2,257,258 Hulsebos Sept. 30, 1941 2,263,561 Biermann Nov. 25, 1941 2,964,234 Loomis Dec. 13, 1960 FOREIGN PATENTS 1,070,549 France Feb. 24, 1954 36,944 Germany Jan. 27, 1886 121,961 Great Britain Ian. 8, 1920 535,630 Great Britain Apr. 16, 1941

Claims

1. IN A RECIPROCATING DEVICE COMPRISING A CRANK-PIN AND A CRANKSHAFT, SAID CRANKSHAFT INCLUDING AN INCLINED CRANK-ARM FOR SUPPORTING SAID CRANK-PIN PARALLEL TO THE AXIS OF SAID CRANKSHAFT, A PLURALITY OF RECIPROCATING PISTONS, EACH OF SAID PISTONS DISPOSED AROUND SAID CRANKSHAFT SO THAT AT ONE END OF A STROKE, THE PISTON LIES AT A GREATER AXIAL DISTANCE FROM SAID CRANK-PIN THAN AT THE OTHER END OF THE STROKE, EACH OF SAID PISTONS INCLUDING A CONNECTING ROD PIVOTALLY CONNECTED THERETO, A BALL ON SAID CRANK-PIN, A WOBBLE MEMBER INCLUDING A BEARING FOR FORMING A SOCKET FOR SAID BALL AND A CONICAL SKIRT PORTION SURROUNDING SAID INCLINED CRANK-ARM, SAID CONICAL SKIRT PORTION INCLUDING A BASE REMOTE FROM SAID BEARING, SAID BALL AND SAID BEARING FORMING A SPHERICAL TYPE UNIVERSAL JOINT BETWEEN SAID CRANK-PIN AND SAID WOBBLE MEMBER, MEANS FOR SUPPORTING SAID WOBBLE MEMBER FOR OSCILLATING MOVEMENT CONCENTRICALLY WITH SAID CRANK-ARM ABOUT A POINT OF OSCILLATION, AND MEANS FOR PIVOTALLY CONNECTING SAID CONNECTING RODS TO SAID BASE OF SAID CONICAL SKIRT PORTION OF SAID WOBBLE MEMBER IN A COMMON TRANSVERSE PLANE AXIALLY SPACED FROM SAID POINT OF OSCILLATION IN A DIRECTION TOWARDS SAID CRANK-PIN, THE DISTANCE BETWEEN SAID TRANSVERSE PLANE AND SAID POINT OF OSCILLATION BEING SUCH THAT WHEN A PISTON ARRIVES AT THE END OF ITS STROKE REMOTE FROM SAID CRANK-PIN, THE RESPECTIVE CONNECTING ROD WILL EXTEND ALONG AN AXIS SUBSTANTIALLY TANGENTIAL TO THE ARC OF A CIRCLE DESCRIBED BY THE PIVOTAL CONNECTION OF THE LAST MENTIONED CONNECTING ROD TO SAID BASE DURING OSCILLATION OF THE WOBBLE MEMBER FOR CAUSING THE MOTION OF SAID PISTON TO HAVE A SUBSTANTIALLY GREATER ACCELERATION TOWARDS ONE END OF ITS STROKE THAN TOWARDS THE OTHER END.