US2748542A - Means for generating high speed cams - Google Patents

Description

June 5, 1956 H. w. ENGELMAN MEANS FOR GENERATING HIGH SPEED CAMS 2 Sheets-Sheet 1 Filed May 23, 1952 INVENTOR film uflz Wlrgyelman BY '74 MEANS FOR GENERATING HIGH SPEED CAMS Helmuth W. Engelman, Madison, Wis.

Application May 23, 1952, Serial No. 289,706

3 Claims. (Cl. 51-101) (Granted under Title 35, U. S. Code (1952), sec. 266) The present invention relates to a method and means for generating cam profiles and more particularly to a simplified rapid method of producing a master generator from which a master cam may easily be cut, wherein the dimensions of the master generator may be calculated di rectly, said dimensions being such that the master generator may be fabricated readily with relatively simple and inexpensive grinding equipment. This invention is especially suited to the production of high speed cams for internal combustion engines and for other applications where similar cam design problems are encountered.

The desirable characteristics of valve cam profiles are now quite well understood. In order to eliminate valve bounce, spring surging, and vibrations within other members of the valve mechanism, it is necessary that sudden reversals or changes of acceleration be avoided. In other words, the accelerating forces acting on the valve mechanism must vary gradually throughout the valve operation, and the rate of change of accelerating force must not exceed a limitation imposed by the rate of stress propagation of the valve spring. In addition, it can be shown mathematically and geometrically that a cam profile which provides this gradual variation of acceleration must -in corporate a gradual variation of curvature along its pro file.

The present methods of obtaining a satisfactory cam profile with the desirable characteristic described above are based on a calculation of the lift, usually for each degree of cam rotation, but often at closer intervals. Briefly, this procedure consists of assuming values of acceleration and from these, calculating velocities, and from the velocities, calculating the lift. This procedure is laborious, because the solution is not direct. In fact, it is usually necessary to readjust the values of acceleration and recalculate several times in order to obtain a lift curve which satisfies other limitations on the cam profile, such as camshaft sizes, valve timing, and follower dimensions. In order to trans late the calculated lift curve into a master cam, it is neces sary to undertake an extremely painstaking and time consuming machining process followed by additional hand finishing, or to use a very expensive machine which can be set up to cut the desired cam in a relatively short time.

The instant invention provides a simplified method of cam generation which incorporates the desirable features already mentioned including a gradual curvature along the cam profile. This method is based upon an application of the fact noted above, that a cam profile must have a gradual variation of curvature to provide a gradual variation of acceleration, and results in a solid body called a master generator having the desired profile with the essential property of gradual variation of curvature. Ac cording to the instant invention, the first step is the direct calculation of the dimensions of the master generator, determined by solving several simultaneous equations. This solution may be derived in such a way that most design factors may be taken into account. Moreover, errors in these calculations may be checked easily, and in no case interfere with the gradual changes of the acceleration,

nite States Patent 2,748,542 Patented June 5, 1956 Next, the master generator is shaped readily to these dimensions and arranged to be rotatably mounted in a simple duplicating machine where it serves as a guide for forming a master cam.

An object of the present invention is the provision of a simplified method for generating cam profiles.

Another object is to provide a method for generating cam profiles having a complex continuous curvature in a single continuous operation.

A further object of the invention is the provision of a method for cutting a master cam by using a master generator.

Still another object is to provide the means necessary to make possible a simplified method for generating cam profiles.

A final object of the present invention is the provision of easily fabricated master generators which can be readily duplicated to produce master cams of the desired profiles.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawing in which:

Fig. 1 shows a plan view of one embodiment of the master generator,

Fig. 2 is a side elevation of the master generator shown in Fig. 1,

Fig. 3 and Fig. 4 show a plan view and a side elevation respectively of a variation of the embodiment of the master generator shown in Figs. 1 and 2,

Fig. 5 shows a side elevation of another embodiment of the master generator,

Fig. 6 shows a side elevation of a variation of the embodiment of the master generator shown in Fig. 5,

Fig. 7 shows a plan view of a master generator fabricated from a flat sheet,

Fig. 8 is a side elevation of the master generator shown in Fig. 7,

Fig. 9 is a schematic plan view of yet another embodiment in which the master generator takes the form of a mechanism having a variable angular velocity,

Fig. 10 is a schematic plan view of a variation of the mechanism shown in Fig. 9, and

Fig. 10a illustrates a machine in which the master cam generators of Figs. 9 and 10 may be used.

Referring now to the drawing, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Figs. 1 and 2 one type of master generator suitable for use in carrying out the method characterizing the instant invention. This master generator 11 is represented as conical and symmetrically disposed about the shaft hole 12, although it could also be cut from a spheroid. The generating edge 16 is the intersection of the conical surface and a smoothly curved surface 14. This surface 14 may be continuously curved so that it has an hyperbolic or similar cross section, or it may be composed of several planar portions connected by cylindrical portions. Figs. 1 and 2 show a positive form of master generator. The corresponding negative form can be produced by curving surface 14 toward the small end of the conical section. Either form of generator would be contacted by a fiat follower or roller linked to and controlling the movement of a flat grinding surface operative to shape the master cam.

To produce a conventional cam from the positive type of master generator described above, the follower and the grinding surfaces would be parallel and on the same side of the mounting shaft, but with the negative form of generator the follower and the grinding surface would be parallel and on opposite sides of the mounting shaft.

If the surface 14 of the master generator described above is continuously curved, a silencing ramp may be incorporated in it as indicated in Fig. 2. The silencing ramp is used to permit a valve clearance when the valve is closed and provides a means of absorbing lost motion due to the clearance. The methods of adding the ramp to certain embodiments referred to below will be indicated in connection with the description of the respective embodiments.

Figs. 3 and 4 show a variation of the master generator described above, in which the generator is formed by a planar surface 14 intersecting a body of revolution 11 having a curved generatrix and symmetrical about the shaft hole 12. In this variation as in the embodiment described above, the follower would be a fiat plane parallel to the axis of shaft hole 12 or a roller follower similarly disposed.

It is also possible to combine the two variations shown in Figs. 1 and 2 and in Figs. 3 and 4, and substitute a curved surface such as that shown in Fig. 2 for the intersecting plane shown in Fig. 4. It is also possible to use a conic, spherical or cylindrical surface in place of the intersecting plane.

Another embodiment of the master generator is shown in Fig. 5, wherein the master generator 11 is cut from a cylindrical body with a shaft hole 12 located on its central axis. The generating edge is formed by the intersection of the surface of the cylindrical body and a curved surface 14 of the type shown in Fig. 2 and described above. This generator is used with a flat follower or roller follower 18 slanted as shown in Fig. 5 toward the axis of rotation of the generator. Fig. 5 shows a positive form of master generator and the corresponding negative form can be obtained by curving the surface 14- down in the opposite direction.

The showing in Fig. 6 is a variation of that in Fig. 5. In Fig. 6 the master generator 11 is also cut from a cylindrical body with a shaft hole 12 located on its central axis, but the surface 14 is planar. This generator is used with a follower 13 incorporating a curved surface. The follower lSa on the right side of Fig. 6 curved toward the generator taken in combination with the master generator as shown represents a positive form, while the follower 18b on the left side of Fig. 6 taken in combination with the master generator as shown represents the corresponding negative form.

A thin metal plate 11 may also be used for the master generator as shown in Figs. 7 and 8, representing the positive form wherein the plate is first bent and then machined, in the bent position, to a circular outline. Next, the plate is flattened as shown in dotted lines in Fig. 8 to form the cam generating edge 16. To produce the negative form from a plate, the flat plate is first machined to a circular outline and then the desired cam form is obtained by bending the circular disk to a curved surface. It is necessary to avoid any sharp creases or folds in the plate in either form, because such a discontinuity would result in sudden reversals of acceleration. in addition, the upturned edge of the disc in the negative form must not rest flat against the follower at any position of rotation. Both forms of this master generator can be used with a fiat or roller follower parallel to the axis of rotation of the master generator. The curved negative form can also be used with an inclined plate or a curved plate follower.

The embodiment shown in Figs. 7 and 8 may be in verted by providing a lift pin rotated about the axis of rotation for the blank from which a master cam is to be cut. The follower engaging this lift pin is the edge of a fiat plate, which may be formed to the desired contour by cutting an arcuate section of suitable size out of the plate and then bending the plate. More over, the lift pin in this arrangement may be practically any figure of revolution.

In addition, an ellipse, connected by gears to the master cam being cut, may be used as either a positive or negative master generator. However, it is necessary that the ellipse be mounted to rotate about an axis coincident with the center of curvature of that point on the ellipse which is tangent to the base circle. Means for generating a silencing ramp are somewhat more difiicult to incorporate with this type of generator than for other types described above.

All of the master generators described thus far are characterised by selected variations of their effective radius and designed to rotate at a constant angular velocity to obtain the desired accelerating characteristics. It is also possible to generate a master cam by the method described herein with a master generator designed to effect controlled variations of the angular velocity. The embodiment of the master generator described below is of this type.

In Fig. 9, a member 21 with a central shaft hole 12 is fitted with a drive pin 22. Member 21 may be mounted for rotation upon a shaft inserted in hole 12. An arm 23 mounted upon a pivot 24- adjacent to member 21 is provided at one end with a longitudinal slot 25 which engages drive pin 22 and at the other end with a pin or roller 26 operating against a fiat follower 27. With this arrangement the drive pin 22 moving at a substantially constant angular velocity with member 21 produces a variable angular velocity of the arm 23. In use of this embodiment of the master generator, the blank from which the master cam is to be cut is mounted coaxially with member 21.

Several refinements may readily be incorporated in this embodiment of the generator. A ramp may be provided for in the cam profile by modifying the shape of the longitudinal slot 25 in arm 23 at the outer end as shown in Fig. 9. An improved type of ramp and acceleration curve may be incorporated by shaping the end 26 of arm 23 as shown in Fig. 10, or by using the roller 26 as shown in Fig. 9 with a curved follower instead of the flat follower shown. In these variations, the center of the pivot 24 must be on the normal to the curved surface, either on the end 26 or the follower 2'7, at the point of contact at the beginning and the end of the lift. See Fig. 10 for example. It is also possible to produce an improved acceleration curve by further modification of the longitudinal slot 25 in arm 23 as shown in Fig. 9, within the following limitations. At the beginning and end of the lift, the center of curvature of the side of the slot at the point of contact with the drive pin 22 must coincide with the axis of rotation of member 21, and the two sides of the slot must be parallel at the point of maximum travel of the drive pin.

In Fig. 10a there is shown a machine in which the master cam generator of Fig. 10 is used. A shaft 28 is rotatably mounted on a base 29, and is driven by any suitable means. Shaft 28 extends through hole 12 in member 21, which carries a drive pin 22. The arm 23 is mounted on pivot 24 supported by base 29, and has a slot 25 at one end engaging drive pin 22. The other end of arm 23 has a bearing surface or roller 26 which is contacted by a. follower 27, mounted for reciprocating motion. Follower 27 carries or otherwise has connected therewith a grind wheel 30, driven by any suitable means, not shown. The shaft 23 is adapted to support a master cam blank 31, the grinding wheel 38 and master cam blank 31 being in juxtaposition.

The operation of the instant invention according to the procedure described above is as follows. The dimensions of the master generator are calculated directly as indicated above. The master generator is shaped to these dimensions from some suitable material in order to form the desired generating edge. Next, the generator is mounted on a supporting shaft fitted into the shaft hole thereof, said shaft being arranged to support the generator adjacent to a suitable follower 27 in a duplicating grinding machine. Grind means 30 engages a blank 31 from which a master cam is to be cut and is moved in response to the movements of the follower 27 over the generating edge of the master generator.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Having thus described the invention, what is claimed is:

l. A master cam generator having a variable angular velocity comprising a rotatable member fitted with a drive pin projecting from one side thereof parallel to the axis of rotation, a base rotatably supporting said rotatable member, an arm pivotally mounted on said base adjacent to said rotatable member for rotation about an axis parallel to and spaced from the axis of rotation of said rotatable member, said arm having a longitudinally extending opening onto one end thereof, said pin being received in said slot and adapted to impart swinging movement to the arm, said arm having a bearing surface on the end removed from said slot, a follower bearing against said bearing surface, grinding means, and means from each other at the end of the arm to provide a ramp on the master cam profile produced by said generator.

3. A device as described in claim 1, wherein the end of said arm in engagement with said follower is shaped to form a smooth continuous curve extending circumferentially about the pivotal axis of said arm.

References Cited in the file of this patent UNITED STATES PATENTS 966,524 Chace Aug. 9, 1910 1,727,434 Klatt Sept. 10, 1929 1,977,194 Malkovsky Oct. 16, 1934 2,030,907 Alford Feb. 18, 1936 2,146,638 Magid Feb. 7, 1939 2,207,268 Rabe July 9, 1940 2,209,538 Rabe July 30, 1940 2,284,319 Herrmann May 26, 1942 2,351,502 Green June 13, 1944 2,352,608 Archer July 4, 1944 2,457,884 Fulton Jan. 4, 1949 2,653,022 Armstrong Sept. 22, 1953

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