US2205953A - Mechanism for the interconversion of reciprocation and rotation - Google Patents

Description

June 25,1940. E, s L 2,205,953

MECHANISM FOR THE INTERCONVERSION OF RECIPROCA'I'ION AND ROTATION Filed Jan. 18, 1939 2 Sheets-Sheet 1 M 3:; 3o [l5 32 i 33 35 32 31 a4; '4 I I: 441 F ;Z k\\\\\\ 5 r L V s1 2 ENZI 20 INVENTOR.

June 25, 1940.

E. S. HALL HECHANISI FOR THE INTERCONVERSION OF RECIPROOATION AND ROTATION Filed Jan. 18, 1939 2 Sheets-Sheet 2 P O 1/, mm

INVENTOJZ. w 5? W Patented June 25, 1940 UNITED STATES PATENT OFFiCE MECHANISM FOR THE INTERCONVERSION OF RECIPROCATION AND ROTATION 15 Claims.

This invention relates to mechanism for the interconversion of reciprocation and rotation and its salient object is to provide a practical cylindrical cam mechanism suitable for engines and pumps of the type having the cylinders parallel to the shaft.

Parallel cylinder machines are normally double-ended with similar cylinders at both ends. The invention will be described as applied to-the normal double-ended type of parallel cylinder machine, but it is applicable also to the other types including the single-ended type and the opposed-piston type comprising two single-ended mechanisms with their pistons opposed in the same cylinders.

The principal advantage of parallel cylinder machines is compactness, more capacity in less space and with less bulk and weight. The most compact machine is to be had by making the piston members as short as possible. The piston members are shortest if they are of the straightthru type, i. e., substantially cylindrical and of diameter not greater than the cylinder bore. (An enlarged or crosshead portion extending beyond such cylindrical limits would necessitate corresponding enlargement or omission of the cylinder wall, requiring greater length to provide enough cylinder wall to retain the piston rings.) Objects of this invention are to provide a most compact parallel cylinder mechanism, and to that end, to

' provide a cam mechanism having straight-thru piston members of shortest practical length.

In the cylindrical cam mechanism, it seems apparent at first glance that the nearest approach to true rolling of the roller on the camthe least slippage-should be had if the roller were conical with its apex on the shaft axis, the cam being of corresponding section. However, slippage due to the accelerations and decelerations of the roller required by the changing inclination of the cam is so much greater than any that might be due to incorrect geometry as to make the latter inconsequential, and conical rollers have objectionable end thrust. It has been found that cylindrical rollers, more or less crowned, on a cam whose face, in section, is straight and parallel to the roller axis, are more satisfactory.

With straight-thru piston members, the cylinder surface should be continuous from one cylinder head to the other except where its inner portion must be omitted to clear the cam. With either conical rollers having their axes inclined and meeting on the shaft axis, or cylindrical rollers or conical rollers with parallel axes, more than half of the cylinder surface must be omitted in the region of the cam, and more than half of the piston member must be notched out to clear the cam, leaving only a relatively thin bridge portion of segmental section connecting the two parts of the piston member. This has been the most troublesome weakness of the cylindrical cam mechanism. The torque reaction produces side-thrust on the piston member in the direction tangential to the shaft; cylinder surface in line with that thrust has been omitted to clear the cam, so the piston member must carry the load as a beam between the mouths of the cylinders, but the bridge portion is offset to one side of the load and ill-adapted to carry it. The result is twisting and deflection of the bridge portion, with concentrated bearing loads at the mouths of the cylinders. Moreover, piston inertia puts a one-sided pull on the bridge portion, tending to open up its throat. Early fracture of the bridge portion of the piston member and the wreck of 420 the engine has been the common result.

An object of this invention is to provide a cylindrical cam mechanism free from all these difiiculties, only a small part of the cylinder surface being omitted to clear the cam, the piston {25 members having bridge sections of ample depth and rigidity without departing from the .straightthru type, the loading such that bending of the piston members is avoided, and the resultant side-thrust being such that there is ample cylinder wall area directly in line with it so that beam loading on the piston member is avoided. These results are attained by inclining the rollers so that they reach inward toward a cam of smaller diameter, the axes of the rollers meeting. at a ,35 point farther removed from the shaft. Rollers so inclined induce radial components which hold the bridge portion of the piston member outward against the cylinder surface, and the radial components combine with the tangential torque reaction to form a resultant piston side-thrust directed toward unbroken cylinder area. Moreover, the cam being of smaller diameter, the piston members need not be notched so deeply, not even half-way thru, leaving the bridge section of 4 ample depth and rigidity to carry the inertia loads without undue deflection.

A primary difllculty of cylindrical cam mechanisms, especially when used in engines, has been the failure of the cam. or rollers under the severe 50 loading to which they are subjected. Heavy compression stresses at the contact between the roller and cam induce tension stresses in the roller which tend to split the roller on a radial plane.

If the roller is a shrink fit on its pin, an initial 55 tendency to split is already present. An object of this invention is to provide roller construction much stronger in resisting radial fracture together with improved construction of the piston member. More specifically, an object is to provide an integral roller and pin construction, with a one-piece piston construction permitting the easy assembly of such integral roller and pin units. Carrying the integral idea to its conclusion, another object is to provide spherical rollers or balls as cam followers, with suitable construction of their seats in the piston member tominimize friction therein and to insure fluid film lubrication therein similar to that obtained in the journal bearings of a roller pin. A further object is to provide for mounting the integral roller and pin units or the spherical rollers in the piston member without cutting thru the bridge portion thereof, so that the bridge portion can present an unbroken cylindrical back for operable engagement with the cylinder wall in the direction of the resultant piston side-thrust, and so as to insure still greater rigidity of the bridge portion of the piston member.

The rollers, either spherical or the integral roller and pin type, tho inclined to the piston member, are still centered therein so that no direct operating load tends to rotate the piston member. However, some anti-rotation means should be provided; ordinarily the throat of the piston member may be left in contact with the periphery of the cam. An object of this invention is to provide an improved means for preventing rotation of the piston member comprising a key slidable in a groove in the cylinder wall behind the bridge portion of the piston. Another object is to provide improved construction of the fixed parts of the mechanism to facilitate production and assembly.

These and other objects and features of the invention will be more clear from the following description in connection with the drawings in which Fig. 1 is a longitudinal section thru an embodiment of the invention;

Fig. 2 is an end view of Fig. 1, partly in section, and showing vectors indicating the distribution of lateral loading on a piston member in the transverse plane;

Fig. 3 is a portion of Fig. l with vectors showing the distribution of forces on a piston memher, in the longitudinal plane;

Fig. 4 is a longitudinal section of another embodiment of the invention;

Fig. 5 is an end view of Fig. 4, partly in section; and

Fig. 6 shows an alternate construction of a detail of the embodiment shown in Fig. 4.

Referring to the drawings, in the embodiment of Figs. 13, shaft is operable in bearings 2| in cylinder blocks 22. Cylinders 3|] are bored continuously thru both cylinder blocks 22. Operable in cylinders 30 are piston members 3|. Both cylinders 30 and piston members 3| are notched to clear cam which is fixed on shaft 20.

In each piston member 3| a pair of rollers 32 are mounted, each roller having its roller pin 33 comprising axial extensions integral therewith. Seats for the integral roller and pin units are milled in piston member 3| and include halfjournal bearings for pins 33. The integral roller and pin units are held in position by operable engagement of rollers 32 with cam 25. Rollers 32 and the faces of cam 25 are inclined to the piston member, the axes of rollers 32 meeting at a point farther removed from shaft 20, and the inclination of the rollers permit them to reach inward to cam 25 which is of smaller diameter than would be possible if the roller axes were parallel and normal to the piston axis.

Because of the inclination of rollers 32 and the smaller diameter of cam 25 permitted thereby, the bridge portion 35 of piston member 3| has a section comprising more than half the section of the entire piston member, giving bridge portion 35 ample rigidity and strength to carry inertia loading of the piston without undue deflection of the piston member and presenting to the cylinder bore correspondingly large and unbroken cylindrical bearing area to carry the resultant side loading on the piston member efiiciently.

To prevent rotation of piston member 3|, bearing surfaces 36 on the inner surface of bridge portion 35 may engage the periphery of cam 25.

In operation, the forces on piston member 3| are distributed as indicated by vectors in Figs. 2 and 3. Considering the piston member and the roller together as a free body, pressure P on the piston head is resisted by the reaction of the cam on the roller, whose component C in the longitudinal plane, combines with P to form a resultant pushing the piston member outward against the cylinder wall which reacts with the force Q. During the piston stroke, the reaction of the cam on the roller has also a component tangential to the cylinder circle, the torque reaction, tending to push the piston member sidewise against the cylinder wall which reacts with the force T. The reactions Q and T combine in a resultant R. which is equal and opposite to the resultant side-thrust of the piston member against the cylinder wall. This resultant sidethrust of the piston member, because of the radial component induced by the inclination of the rollers, is directed toward a large unbroken cylinder area so that it can be carried efficiently with low specific loading and without any beam loading on the piston member 3|.

Thus it is clear that inclining the rollers not only permits a smaller cam, less notching of the cylinder and piston member, and a deeper bridge section of greater rigidity, but also changes the loading so that stresses tending to deflect the piston member are largely eliminated, removing the causes of deflection. Making the roller and pin integral, greatly increases the strength of the roller against radial splitting. Milling halfjournals in the piston member permits assembly of the integral roller and pin units in a onepiece piston member, and their assembly on the cam holds them in operable position. Inclining the rollers also facilitates the milling of the halfjournal bearings in the piston member without cutting thru the back of the bridge portion, and the unbroken back surface of the bridge not only adds rigidity to it but also present a better bearing surface to the cylinder wall.

In the embodiment of Figs. 4-6, shaft 4|! is operable in bearings 4| in cylinder blocks 42. Fixed upon shaft 40 between blocks 42 is the cam 45. Separating cylinder blocks 42 is a third casing member 43, large enough internally to clear cam 45. Cylinders 5!) are bored continuously thru both cylinder blocks 42 and casing member 43. Operable in cylinders 50 are piston members 5| notched out to clear the cam 45. Key 56 is fixed in the middle of the back of bridge portion 55 of piston member 5|, and is operable in groove 44 of easing member 43, to prevent rotation of piston member 5|.

' In each piston member 5| a pair of spherical rollers or balls 52, preferably hollow, are mounted in spherical seats 53 and are held in position by operable engagement with cam 45. The line of loading from the cam thru the spherical center to the spherical seat is inclined to the piston, the inclination permitting balls 52 to engage a smaller cam 45 than would be possible if the loading were axial. Moreover, because of the inclined loading, the bridge portion 55 of piston member 5! has a deeper section comprising more than half the section of the entire piston member, giving the bridge portion 55 ample rigidity and strength to carry the inertia loading of the piston without undue deflection and presenting to the cylinder bore correspondingly large and unbroken cylindrical bearing areas to carry the resultant side loading on the piston member efficiently.

The working faces of cam 45 may be slightly concave, of somewhat larger radius of curvature than balls 52, the better to coact therewith. Spherical seats 53 are relatively small in area for more eflicient operation, and the balls 52 are guided by the annular contact 54 in piston member 5|. In Fig. 6, the spherical seat for the ball 52 comprises a slipper 56 of a type especially adapted to insure efficient film lubrication between its working face and ball 52.-

In operation, the loading and results of spherical rollers 52 withtheir offset or inclined seats are similar to those described for Figs. 1-3. Insertion of key 56 in bridge portion 55 of piston member 5| does not weaken the bridge portion as the metal removed is not from the weakest section. Neither key 56 nor groove 44 interferes with the bearing of the piston member in the .cylinder since the resultant piston side-thrust is directed substantially at the center of the area between groove 54 and the internal relief for the cam 45the internal bore thru casing member 43.

In assembling either mechanism shown, it is necessary to assemble each piston member onto the cam before inserting it into its cylinder. With the twopiece cylinder block construction shown in Figs. 1-3, insertion of the piston rings into the cylinders is troublesome. Assembly is much easier with the three-piece construction shown in Figs. 4 and 5. Thepiston members, without the piston rings, may be easily assembled in place on the cam 45 and in casing member 53, the rings added, and then. each cylinder block assembled and bolted to casing member 43. Groove 49 is more easily formed in a separate casing member 43, but the use of groove 54 and key 55 is not necessary. The same anti-rotation system shown in Figs. 1 and 2 may be used with the three-part casing construction if desired.

Having thus described the invention it is clear that all the objects as stated have been attained in a practical and effective manner. While I have shown specific embodiments of the invention, it is understood that changes may be made in the construction and in the arrangement of the various parts without departing from the spirit or scope of the invention as set forth in the following claims:

I claim:

1. A cam mechanism comprising a shaft, a cam rotatable with said shaft, cylinders parallel to said shaft with their axes intersecting a pitch circle whose center is on the axis of said shaft, the outside diameter of said cam being less than said cylinder pitch circle, said cylinders being cut away to clear said cam and extending beyond said cam, a piston member operable in each of said cylinders and substantially cylindrical in exterior form and capable (in the absence of said cam) of being passed straight thru said cylinder, said piston member being cut away to clear said cam, cam followers, and bearing means in said piston member for mounting said followers for rotation in position to coact with said cam along lines of loading inclined to said piston member in a manner inducing side-thrust on said piston member acting to push it away from said shaft and against the outward wall of said cylinder.

2. A cam mechanism comprising a shaft, av

cam rotatable with said shaft, cylinders parallel to said shaft, a piston member operable in each of said cylinders and substantially cylindrical in exterior form and of diameter not greater than the diameter of said cylinders, cam followers, and bearing means in said piston member for mounting said followers for rotation in position to coact with said cam along lines of loading inclined to said piston member and acting to push it away from said shaft and against the outward wall of said cylinder.

3. A cam mechanism comprising a shaft, a cam rotatable with said shaft, cylinders parallel to said shaft, a piston member operable in each of said cylinders and substantially cylindrical in exterior form and of diameter less than the diameter of said cylinders, rollers, and bearing means mounting said rollers for rotation in said piston member with their axes inclined and meeting at a point farther removed from said shaft, said rollers coacting with said cam.

4. A cam mechanism comprising a shaft, a cam rotatable with said shaft, cylinders parallel to said shaft, a piston member operable in each of said cylinders and substantially cylindrical in exterior form and of diameter less than the diameter'of said cylinders, spherical cam followers, and bearing means in said piston member for mounting said followers for rotation in position to coact with said cam along lines of loading inclined to said piston member and acting to push it away from said shaft and against the outward wall of said cylinder.

5. A cam mechanism comprising a shaft, cylinders parallel to said shaft, a piston member operable in each of said cylinders and of such form as to permit being passed straight thru said cylinder, a cam rotatable with said shaft, said cylinders and piston members being cut away inwardly to clear said cam, cam followers operably engaging said cam, and bearing seats for said followers in said piston members, said mechanism so constructed and arranged that the resultant side-thrust on each piston member due to the coaction of said cam followers with said camis always directed toward a considerable unbroken area of cylinder wall so that said piston members are free from beam loading.

6. A cam mechanism comprising a shaft, cylinders parallel to said shaft and spaced about a pitch circle concentric with said shaft, a piscam, and bearings for mounting said followers for rotation in said piston members.

7. A cam mechanism comprising a shaft, cylinders parallel thereto with their axes spaced about a pitch circle concentric therewith, a piston member operable in each of said cylinders and of such form as to permit being passed straight thru said cylinders, a cam on said shaft, a pair of rollers rolling upon opposite faces of said cam, and bearings for said rollers formed in said piston member, said bearings being so formed that said rollers are held in said bearings only by the intervention of said cam between said rollers, said cam having an outside diameter less than that of said cylinder pitch circle, and each of said piston members including a bridge portion passing said cam and having a cross section including the piston axis.

8. A cam mechanism comprising a shaft, cylinders parallel thereto, a piston unit operable in each of said cylinders, a cam on said shaft, a pair of cam followers rolling upon opposite faces of said cam, and bearings for said followers formed in said piston unit, said bearings being so formed that said followers are held in said bearings only by the intervention of said cam between said followers, the axes of rotation of said followers being inclined to and approaching each other at a point farther removed from said shaft.

9. A cam mechanism comprising a shaft, a cam rotatable with said shaft, cylinders parallel to said shaft, a piston member operable in each of said cylinders and substantially cylindrical in exterior form and of diameter not greater than the diameter of said cylinders said piston member including a bride portion passing said cam and of cross section larger than semi-circular, said cam having an outside diameter less than that of the pitch circle of said cylinders, halfjournal bearings formed in said piston member, and integral roller and pin units mounted in said half-journal bearings and operably engaging and held in position in said bearings by said cam.

10. A cam mechanism comprising a shaft, a

- cam rotatable with said shaft, cylinders parallel to said shaft, a piston member operable in each of said cylinders and substantially cylindrical in exterior form and of diameter not greater than the diameter of said cylinders, half-journal bearings formed in said piston member, and integral roller and pin units mounted in said half-journal bearings and operably engaging and held in position in said bearings by said cam, the axes of said units being inclined to said piston member so as to meet at a point farther removed from said shaft.

11. A cam mechanism comprising a shaft, cylinders parallel to said shaft and spaced about a pitch circle concentric with said shaft, a piston member operable in each of said cylinders and of such form as to permit being passed straight thru said cylinder, a cam rotatable with saidv shaft and having an outside diameter substantially equal to that of said pitch circle, said cylinders being cut away to clear said cam, each piston member being cut away to clear said cam so that said piston member comprises essentially two pistons connected by a bridge portion of substantially half the piston section, half-journal bearings formed in said pistons without cutting thru the outward cylindrical surface thereof, said pistons and bridge portion presenting an unbroken outward cylindrical surface to the wall of said cylinder, and integral roller and pin units mounted in said half-journal bearings and operably engaging and held in position by said cam.

12. In mechanism of the class described, a shaft, a cam rotatable with said shaft, cylinders parallel to said shaft, a piston member operable in each of said cylinders and substantially cylindrical in exterior form and of diameter less than the bore of said cylinders, a cam follower operably engaging said cam and comprising a ball, and a seat for said ball in said piston member comprising a bore operably contacting a great circle of said ball and a spherical socket of area substantially less than one-third the area of said ball, the line of loading thru said ball being inclined to the axis of said piston member.

13. In mechanism of the class described, a shaft, a cam rotatable with said shaft, cylinders parallel to said shaft, a piston member operable in each of said cylinders and substantially cylindrical in exterior form and of diameter less than the bore of said cylinders, a cam follower operably engaging said cam and comprising a ball, and a seat for said ball in said piston member comprising a bore operably contacting a great circle of said ball and a slipper pivotally seated in said piston member.

14. In mechanism of the class described, a shaft, a cam rotatable with said shaft, cylinders parallel to said shaft, a piston member operable in each of said cylinders, a cam follower operably engaging said cam and comprising a ball, a slipper operably conforming to said ball and spherically seated in said piston member, the center of curvature of said spherical seat being well within said ball.

15. In mechanism of the class described, a shaft, a cam rotatable with said shaft, cylinders parallel to said shaft, a piston member operable in each of said cylinders, a cam follower operbly engaging said cam and comprising a ball, a slipper operably conforming to said ball and pivotally seated in said piston member, said slipper having the form of a concave-convex lens.

EDWIN S. HALL.

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