EP3940197B1

EP3940197B1 - Piston moving coaxial spherical cam mechanism

Info

Publication number: EP3940197B1
Application number: EP20020323.0A
Authority: EP
Inventors: Pierfrancesco PONIZ
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-07-15
Filing date: 2020-07-15
Publication date: 2022-07-06
Anticipated expiration: 2040-07-15
Also published as: EP3940197A1

Description

The present invention relates to a mechanisms comprising a piston whose back and forth movement, here called reciprocation, spins a cam around same piston's reciprocation axis. Hence said cam is called coaxial to said piston: similar mechanisms are studied because their inertias are easier to be balanced than inertias of crank, rod and piston assemblies.
Prior art about a piston reciprocating over a coaxial cam - such as in WO 2007/036007A1 , or as in United States patent number US7360521B2 , or in European patents EP1821001B1 or EP2989309B1 - depicts cylindrical cams interacting with rollers (or similar) whose reciprocation run is not negligible compared to the diameter of cylindrical cams. Such configuration cannot achieve a stable line of contact between rollers and cam track along the direction of cam radius, since during rollers climb and descent the speed at roller surface is the same of cam track's speed in only one point at a time, causing sliding friction.
Moreover, in the patents listed as prior art - for instance US7360521B2 - a piston is connected to rollers which act on a cylindrical cam track by using reciprocating arms, which constitute cantilevers as long as cam's radius: reciprocating arms are then exposed to massive shear and bending stresses, so that a thick design should be adopted, with great encumbrance and inertia.
The purpose of the present invention is to provide a mechanism [1] wherein a reciprocating piston [2] spins a spherical coaxial cam [17], solving durability and then feasibility problems inherent in prior art.
In accordance with the present invention, there is provided a mechanism [1] comprising: one piston [2]; two stems [3], each terminating with one of two couples of stem pivots [4]; two couples of connectors [5]; two couples of arm pivots [6], each couple protruding from one of two swinging arms [7]; two double conical bushings [8], each one comprising one of two inner conical bushings [9] and one of two outer conical bushings [10]; one frame [11], holding one still pin [12] and two guides [13]; two roller cages [14], each comprising one of two couples of arcs of rollers [15]; one double thrust bearing [16]; one lower cam track [18] and one upper cam track [19]; one axis [20], laying in one plan [21] and passing across one center [22]; one liner [23]; one separation wall [24]; one syringe system [25].
Advantageously, said mechanism [1] comprises:

said double conical bushings [8], each comprising inner conical bushing [9] and outer conical bushing [10], both with external rolling surfaces having the shape of truncated cones whose vertexes stay always in the center [22] of said spherical cam [17], and said cam tracks [18] [19] develop from straight lines all crossing said center [22]. Assembly comprising said cam [17] having spherical geometry and two cam tracks [18] [19] on which act two double conical bushings [8] symmetrically moving on circumference arcs and driven by swinging arms [7] hinged on a still pin [12] is itself novel, and achieves a stable line of contact between double conical bushings [8] and cam tracks [18][19] along the direction of cam radius, solving cited prior art problem of cam track's durability for sliding friction;
said connectors [5], which transmit the push of said stems pivots [4] to said arm pivots [6] allowing shortest cantilever on said swinging arms [7] between said arm pivots [6] and said double conical bushings [8] acting on said spherical cam [17]: hence said connectors [5] grant on said swinging arms [7] minimum bending and shear stress in said plan [21] where said swinging arms [7] move. Moreover said connectors [5] avoid sliding of said stems [3] pushing and pulling said swinging arms [7], preventing friction wear on the surface of said swinging arms [7]. Hence said connectors [5] are themselves novel, and solve the cited prior art problem of high stresses on arms;
said roller cages [14], which bind said swinging arms [7] inside said guides [13] preventing said swinging arms [7] to be put in rotation with said spherical cam [17], keeping the ends of said arm pivots [6] in constant rolling contact with said guides [13], then avoiding sliding friction on said guides and avoiding vibrations on said swinging arms [7] orthogonally to said plan [21]. Moreover, said roller cages [14] grant minimal distance between said guides [13] and said double conical bushings [8] and then minimum bending and shear stress on said swinging arms [7] orthogonally to said plan [21]. Hence said roller cages [14] and said guides [13] are themselves a novel compact solution for the problem mostly neglected in cited prior art of friction and vibrations orthogonally to the plan where arms move.

Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description, with appropriate reference to the accompanying drawings.
In the drawings:

Figure 1 is a front view of mechanism [1] in accordance with a preferred embodiment of the present invention.
Figure 2 is a front and side section view comprising one of said swinging arms [7] with one of said roller cages [14].

Said mechanism [1] converts pure reciprocation motion of said piston [2] along said still axis [20] into pure rotational motion of said spherical cam [17] around same said still axis [20].
Said frame [11] is still and supports whole said mechanism [1]. Said still pin [12] is perpendicular to said axis [20] and said still pin [12] and said two guides [13] are rigidly fixed to said frame [11]. Said frame [11] binds said spherical cam [17] preventing any axial movement through said double thrust bearing [16] so that said spherical cam [17] can only spin around said axis [20]. Said same axis [20] crosses the center of said piston [2] and said axis [20] is orthogonal to said piston's [2] faces, here called piston's front and piston's back.
Said two stems [3] are mutually parallel and mutually symmetrical in respect to said axis [20], and said two stems [3] are both rigidly attached on one end to said piston's [2] back, so that said two stems [3] move reciprocating together with said piston [2] along said reciprocation axis [20].
The end of each of said two stems [3] which is not fixed to said piston [2] terminates with a couple of stem pivots [4] which are connected, through one of said two couples of connectors [5], to a couple of arm pivots [6] protruding from a certain point of one of said two swinging arms [7]. Each connector [5] is pivoted at one end on one said stem pivot [4] and at the other end on one said arm pivot [6].
Said piston [2] and said stems [3] reciprocate together along said axis [20] and said stems [3] push and pull said swinging arms [7] by means of said couples of connectors [5], so that said arms [7] are not fixed to said stems [3] nor directly slide on said stems [3]. Both said swinging arms [7] are mated at one end to said still pin [12] which lays between said swinging arms [7], and said still pin [12] acts as a hinge so that said two swinging arms [7] swing on said plan [21] symmetrically in respect of said axis [20]. Said plan [21] is orthogonal to said still pin [12] and comprises said axis [20], and each couple of arm pivots [6] moves projecting on said plan [21] an arc of circumference path. The furthest end of each said swinging arm [7] in respect of said still pin [12] terminates with one of said two double conical bushings [8]. Each said double conical bushing [8] projects then on said plan [21] an arc of circumference path which is wider than the arc of circumference path projected on said plan [21] by said arm pivots [6].
Said two guides [13] are symmetrical in respect of said axis [20] and may be carved inside said frame [11] and each said guide [13] consists in a couple of flat arc shaped walls facing each other, and the projections of said guides [13] on said plan [21] comprehend the arc of circumference paths projected on said plan [21] by said arm pivots [6]. Each said guide [13] binds one of said two swinging arms [7] through one of said two roller cages [14] to avoid friction on said guide's [13] arc shaped walls, and said two guides [13] prevent said piston [2] and said stems [3] and said connectors [5] and said swinging arms [7] to move perpendicularly in respect of said plan [21] or to spin around said axis [20].
Each of said two roller cages [14] comprehends two flat arc shaped arcs of rollers [15], and each said arc of rollers [15] stays between the end of one of said arm pivots [6] and one of said two arc shaped walls of said guide [13]. Each said arc of rollers [15] may be as long in its arc shaped development as half the arc of circumference path described by each arm's pivot [6] plus the height of said swinging arm [7], so that for all said piston's [2] reciprocation run, said two arcs of rollers [15] of each one of said two roller cages [14] separate both said arm pivots [6] of each said swinging arm [7] from both said arc shaped walls of each said guide [13] in which said swinging arm [7] moves, and said arcs of rollers [15] always roll without sliding on the arc shaped walls of said guides [13] along said arm pivots [6] paths. Both said double conical bushings [8] may comprise said inner conical bushing [9] which is closer to said still pin [12] and said outer conical bushing [10] which is more distant from said still pin [12]. Rolling surfaces of each conical bushing have a truncated cone shape originating from points called cone vertexes. Both cone vertexes originating inner conical bushings [9] rolling surfaces and cone vertexes originating outer conical bushings [10] rolling surfaces always lay where said axis [20] crosses the center of said still pin [12], which coincides with said center [22] of said spherical cam [17]: these specific conditions allow continuous contact between said double conical bushings [8] and said spherical cam tracks [18] [19] on lines laying along the radial direction of said spherical cam [17], avoiding sliding friction.
Rolling surfaces of said two inner conical bushings [9] roll on said lower cam track [18] pushing said spherical cam [17] when said piston [2] moves towards said spherical cam [17], while rolling surfaces of said outer conical bushings [10] roll on said upper cam track [19] pulling said spherical cam [17] when said piston [2] moves away from said spherical cam [17]. Said spherical cam [17] does not shift nor bend in respect of said axis [20] thank to said double thrust bearing [16], so that said spherical cam [17] purely spins around said still axis [20].
Said upper cam track [19] and said lower cam track [18] ascend and descend twice, or more times but always an even number of times, with the same shape around said axis [20], so that the reciprocation of said piston [2] and of said two stems [3] causes said spherical cam [17] to spin around said axis [20] by means of said two couples of connectors [5] and said two swinging arms [7], which move symmetrically in respect of said axis [20]. During the movement of whole said mechanism [1], both said rolling surfaces of said inner conical bushings [9] are always in contact with said lower cam track [18] and both said rolling surfaces of said outer conical bushings [10] are always in contact with said upper cam track [19], without any rolling surface of said conical bushings [9] [10] ever having to slide on said cam tracks [18] [19], nor radially nor tangentially in respect of said spherical cam [17].
Said connectors [5] seen on plan [21] may oscillate from parallel with said axis [20] to 45° outwards from said axis [20], while said swinging arms [7] may swing from -45° to +45° in respect of the position orthogonal to said axis [20] to avoid any jamming during the movement of said mechanism [1].
Said piston [2] may slide inside said liner [23] which is fixed and still with said frame [11] and said liner [23] may end between said piston [2] and said stem pivots [4] with a separation wall [24], so that said two stems [3] which move purely reciprocating along said axis [20] may cross said separation wall [24] by sliding through sealed couplings to separate the volume at said piston's [2] back from the volume occupied by other more lubricated parts such as said double conical bushings [8].
The volume inside said liner [23] and defined between said piston's [2] back and said separation wall [24] may be exploited, like the volume facing said piston's [2] front, to push or suck or compress or expand a working fluid. Hence the application of said mechanism [1] in internal combustion engines, and particularly in two stroke engines where two pistons with short reciprocation run face each other inside one cylinder, or in double effect pumps or compressors or expanders, prevents working fluid to be contaminated by lubricants.
In some applications of said mechanism [1] a syringe system [25] may inject a lubricant or a cooling fluid to said piston [2] through a hole in one of said stems [3] and partially make said lubricant or cooling fluid flow back through a hole in the other of said two stems [3], in the quantity necessary to lube said liner [23] and to refrigerate said piston [2].
The described embodiments are only provided as an example and do not limit the scope of the invention, which is solely defined by the appended claims.

Claims

Mechanism comprising one piston [2] purely reciprocating along one still axis [20] over one cam [17] purely spinning around same said axis [20], where:
- said cam [17] has spherical geometry and then is a spherical cam but purely spins around said axis [20], without other movements like shifting or bending in respect of said axis [20];

- said spherical cam [17] has a lower cam track [18] and an upper cam track [19], and both said cam tracks ascend and descend equally an even number of times around said axis [20], and both said cam tracks develop from straight lines all crossing said spherical cam's center [22].
Mechanism as in claim 1, where:
- two arms [7] are hinged on one end on one still pin [12] which lays between said arms [7];

- said still pin [12] is perpendicular to said axis [20] so that said arms [7] can swing in the plan [21] normal to said still pin [12] and containing said axis [20], and the center of said still pin crosses said axis [20] at the center [22] of said spherical cam [17];

- two stems [3] are fixed at the back of said piston [2], and each one of said two stems [3] move one of said two arms [7] and said two arms [7] act on said cam [17].
Mechanism as in claim 2 where:
- at the ends which are not mating said still pin [12], said two arms [7] act on said spherical cam [17] with two double conical bushings [8], each said double conical bushing comprehending an inner conical bushing [9] closer to said still pin [12] and an outer conical bushing [10] further from said still pin [12];

- said inner conical bushings [9] act on said lower cam track [18], and said outer conical bushings [10] act on said upper cam track [19];

- rolling surfaces of all said conical bushings [9] [10] have a truncated cone shape originating from cone vertexes which always lay in the center [22] of said spherical cam [17].
Mechanism as in claim 2, where:
- the end of each one of said two stems [3] which is not fixed to said piston [2] is connected to a certain point of one of said two arms [7] through connectors [5], and each said connector [5] is pivoted at one end on a pivot [4] on said stem [3] and pivoted at the other end on a pivot [6] on said arm [7].
Mechanism as in claim 4, where:
- said arms [7] swing from +45° to -45° in respect of the position orthogonal to said axis [20];

- said connectors [5] oscillate from parallel with said axis [20] to 45° outwards from said axis [20].
Mechanism as in claim 4, where:
- there are two guides [13] which are symmetrical in respect of said axis [20], and each said guide [13] consists in a couple of arc shaped walls facing each other, and each of said two guides [13] binds one of said two arms [7];

- each said arm [7] passes through one roller cage [14] to avoid friction on said arc shaped walls, and said roller cage [14] comprises two arcs of rollers [15], each said arc of rollers [15] staying between the end of one of said arm pivots [6] and one of said two arc shaped walls of said guide [13];

- each said arc of rollers [15] is as long in its arc shaped development as half the arc of circumference path described by each arm pivot [6] moving on said plan [21], plus the height of one of said arms [7].
Mechanism as in claim 2, where:
- said two stems [3] are mutually parallel and mutually symmetrical in respect to said axis [20];

- said two stems [3] cross one still separation wall [24] sliding through sealed coupling which separate the volume at said piston's [2] back from the volume occupied by other more lubricated parts.
Mechanism as in claim 7, where:
- a syringe system [25] injects lubricant or cooling liquid to said piston [2] through a hole in one of said stems [3] and partially makes said lubricant or cooling liquid flow back through a hole in the other of said two stems [3].
Machine such as pump, compressor, expander, internal combustion engine and particularly two stroke engine where two pistons face each other inside one cylinder, including a mechanism as in one of the preceding claims.