US1575239A - Method of counterbalancing engine main shafts - Google Patents

Description

March 2 1926. 1,575,239

6. L. WALKER METHOD OF COUNTERBALANCING ENGINE MAIN SHAFTS Filed Feb. 4 1924 2 Sheets-Sheet 1 //vv/v TOR. CL/N TON L. WA LKER.

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March 2 1926. 1,575,239

6. L. WALKER METHOD OF COUNTERBALANCING ENGINE MAIN SHAFTS Filed Feb. 4, 1924 2 Sheets-Sheet 2 /N\/EN TOR. Cu v To/v L. WALKER JQTJQPNEYS.

opposite side.

1,575,239 PATENT OFFICE.

CLINTON L. WALKER, OF YIEDMON'I, CALIFORNIA.

METHOD OF COUNTERBALANCING ENGINE MAIN SHAFTS.

Application filed February 4, 1924. Serial No. 690,682.

To all whom it may concern:

Be it known that I, CLINTON L. VVALKER, a citizen of the United States, residing at Piedmont, county of Alameda, and State of California, have invented new and useful Improvements in Methods of Counterbalancing Engine Main Shafts, of which the following is a specification.

This invention relates to engine main shafts having a multiplicit of cranks or eccentrics, and moreparticu arly to a method of counterbalancing the same.

Much consideration has been given of late to the unbalanced forces inherent or developed in crank shafts used in high-speed internal combustion engines. The usual method employed when applying and positioning counterweights is to place a weight equal and opposite to each part or member to be counterbalanced.

This method is fairly satisfactory where the cranks at one side of the central transverse axis of the shaft are symmetrically arranged and in the sameangular phase on opposite sides of the central transverse plane. Where the cranks or throws of a shaft are not so arranged, the application of counterweights presents a different problem, and this problem is more complicated where space is not available for a counterweight opposite each crank or throw to be.

balanced.

In and by the present invention I provide a method of counterbalancing an engine main shaftof the type wherein the throws or cranks at one side of the central transverse axis are not symmetrically arranged with respect to the cranks or throws at the The object of the invention is to generally improve and simplifv the counterbalancing of a crank shaft of the type mentioned. A further object is to pro vide a method of counterbalancing crank shafts which will permit the use of a single weight to counterbalance a cranks or throws, or which permits division of a single counterweight into a number of smaller weights placed at convenient points longitudinally of the shaft.

' This system of counter-balancing permits a wider range of design than where both halves of the shaft are symmetrically arranged, and in the same angular phase on opposite sides ofthe central transverse plane. In other words, the shaftmay be designed to give a better balance of the innumber of ertia forces of the reciprocating masses and to more nearly neutralize the bearing pressures caused by the centrifugal forces of the rotating masses.

For the purpose of clearly describing and illustrating the invention, reference will be made to the accompanying drawings, in Which- Fig. 1 is a side elevation of a counterbalanced shaft employing eccentrics.

Fig. 2 is an end view thereof.

Fig. 3 is a side elevation of an ordinary four-throw crank shaft counterbalance by my method.

Fig. 4 is an end view of Fig. 3.

By referring to Figs. 1 and 2, it will be noted that a main shaft is illustrated which employs eccentrics as a substitute for the common or ordinary crank throws; this type of shaft being illustrated by preference as it has heretofore been considered one of the most diflicult types of shaft to counterbalance in view of the fact that equal and opposite counterweights cannot be employed.

The shaft illustrated is provided with three main bearings as illustrated at L, M and N, the bearing indicated at L being the central main bearing, and the bearings indicated at Mand N the end bearings. The eccentrics which are employed as a substitute for the usual crank throws and pins are indicated at A, B, C and D. These eccentrics are in this particular instance positioned 90 apart; that is, the eccentrics A and B are positioned 90 apart, the. eccentrics B and C 180 apart, and the eccentrics C and D 90 apart. The eccentrics A and D are therefore opposed to each other and similarly the eccentrics B and C. This particular arrangement produces a staticbal-- ance and also permits a better piston balance and equal distribution of the inertia forces exerted by the pistons.

In the present instance I employ two countcrweights such as illustrated at H and K. The counterweight K counter-balances the eccentrics C and D, and the counterweight H the eccentrics A and B. These counterweights are semi-circular and disk shape as illustrated in Fig. 2, and they are suitably secured to an annular disk forming an integral part of the main shaft The method of positioning the counterweights and determining the weight thereof consists in computing the centrifugal forces due to each member on the crank shaft that runstout of balance by employing the usual formula that centrifugal force equals .00034 \VRN, where W is the weight, R its radius of gyration, and. N the number of revolutionsp Eliminating the constants and considering one speed only, it is seen that the centrifugal force is directly proportional to the weight times the radius of gyration. Consider now that the crank shaft is being held firmly by one end and the center main bearing, leaving half the shaft projecting as a cantilever. Measure the distance along the shaft from the center of the main center bearing to the center of gravity of the eccentric B or other unbalanced weight or mass. Com ute the centrifugal force due to the weig t of B with its radius of gyration for any given number of revolutions per minute by the use of the above formula. The bending moment around the central point 0 of this unbalanced force is the product of this force times its distance along the shaft to the central point 0. Now measure the distance from the center of the main bearin L or the point 0 to the second eccentric in icated at A, which i the next unbalanced weight or mass encountered, and compute its centrifugal force and bending moment around the central point 0 in the same way as for eccentric B. This bending moment it will be noted acts in a radial plane at 90 to the plane of B. B the construction of a 'parallelogram of orces we can readily determine the resultant of these two moments both as to magnitude and the angle of its radial plane of action. In like manner we would proceed with all of the remaining out of center masses taking each in turn to determine its resultant with the resultant already found until a final resultant is found which represents the resultant bending moment of all of the out of center masses both as to magnitude and the angle of its radial plane of action. The center of gravity of the counterweight H-' will lie on the opposite side of the shaft and in a continuation of the radial plane of the .final resultant bending ,moment of all of the out of center masses.

The weight and position of H must be such that its centrifugal force multiplied by the distance of its center of gravity along the shaft to the central point 0 must be e ual and opposite to the final resultant ben ing moment of all of the out of center masses.

The position and weight of the counterbalance H is thus determined, but if it is desired to divide this weight into several weights for the purpose of conveniently placing the same along the shaft, it may be accomplished by placing the weights in the desired ositions longitudinally along the shaft an in such radial planes and of such shapes and weights that their resultant bending moment shall be equal, opposite and in the same radial plane as the resultant bending moment of all of the out of center masses and hence efiuivalent to the action of the single weight plied to any shaft with the cranks or eccen trics set at any angle, and the same rule is followed for each half of the shaft.

For the pur ose of illustrating the method of attaching t e counterwei ht to an ordinary crank shaft, reference is made to Figs. 3 and 4. This shaft is identical in size and throw to the shaft shown in Figs. 1 and 2, and is similarly provided with three main supportin bearings as indicated at L, M and N our cranks are also rovided as indicated at A, B, G and D and four coi'mterweights are em )loyed as indicated at H, K, h and k, the i ea of illustrating the four counterweights being that of showing the possibility of dividing one weight into two or more. a

To determine the position and the magnitude of the weights indicated at H and h, the same rule is followed; that is, the shaft is considered as supported by the central bearing and one end bearing, and the remainder of the shaft is considered as a cantilever. The distance from the central point 0 to each unbalanced weight is determined. For instance, the weights of the respective crank cheeks and pins are deter mined, as also their radii of gyration. The centrifugal force or pull exerted by each .unbalanced member is thus determined and the bending moment exerted thereby with relation to the central point 0 is similarly determined. By parallelograms of forces the resultant of all these bending moments can be determined by plotting the products of the weight times the radius of gyration, times the distance to the center. The resultant will show in magnitude and in direction the total force to be counterbalanced, and will represent the product of the weight of the counterbalance times its radius of gyration, times its distance longitudinally along the shaft to the center bearing; the.

weight being in this instance divided into two weights as shown at H and h. It can thus be'seen that dynamic balance is readily obtained; that equal and opposite weights are not essential; that one or more counterweights may be employed to balance a number of smaller welghts. Thus the cost of manufacture may be materially reduced and the counterweights may be placed where the clearance in the crank case best permits.

The center of gravity of the counterwei ht H is on the line 11. This line falls wit in the angle produced by the center line 2--2 of the throw A and line 3-3 which bisects the angle formed by throws A. and B. Thus the center of gravity of the weight H which serves to counterbalance throws A and B does not coincide with the bisector line 3--3,

This rule can be apbut inclines towards the line 2-2 which is the center line of the throw'farthest from the point or central transverse plane of the shaft.

While the presentmethod number of counterweights to used and to be placed at any desired oint lon itudinally of the shaft, it is pre erred to ave one of the wei hts on each half of the shaft rmits any positioned mi way between the end-crank and the next adjacent crank, such weight to he so proportioned that it will off-set any. tendency on the )art of the shaftto be dellccted between t e center bearing and the end bearing. If the weights are positioned solely at the ends of the shaft, they will not oppose thistendency of the shaft to deflect between the end bearing and the center hearing, and in a high-speed shaft such deflection would cause serious vibration, increased noise and consumption of power, and in extreme cases might ru ture the shaft.

Having thus descri d my invention, what.

, gal force of each throw'multiplied by the distance from the central transverse plane of the shaft, and counteracting this ading moment by weights of such mass and radius of masscenter and distance from the central transverse plane of the shaft that their bending moment will be ual and opposite to that of the throws to be alanced.

2. A counterbalanced engine main shaft having four throws, with throws 1 and 4 set 180 apart and throws 2 and 3 set 180 apart but at 90 from throws 1 and 4, and

counterbalancin weights for each half of the shaft, sai eights being positioned with res t to the throws to be balanced so that t eir center of gravity falls within the angle produced by extending the center line of the outer throw and a line bisecting the angle of the two throws.

3. A counterbalanced engine main shaft having four throws, with throws 1 and 4 set 180 apart and throws 2 and 3 set 180 apart, but at 90 from throws 1 and 4, and counterbalancin weights for each half of the shaft, whic 1 weights have a resultant moment e ual and opposite to'the resultant moment 0 the off-center masses on'the adj acent half of the shaft calculatedby multiplying the mass by its radius of mass center y its distance from the central transverse plane of the shaft, one of such weights on each half of the shaft being positioned midway between the end throw and the next adjacent throw, whereby to prevent deflection of the shaft between the center and end thereof.

4. An engine main shaft having a plurality of throws at each side of the central transverse plane, which throws are not in mirror symmetry, and counterbalancing weights for each half of the shaft having a resultant moment equal and opposite to the resultant moment of the off-center masses on the adjacent half of the shaft calculated by-multiplying the mass by the radius of mass center by the distance from the central transverse plane of the, shaft, one of said counterbalancing weights on each half of the shaft being ositioned midway between the end of the s iaft andthe centraltransverse plane thereof, and being of such mass as to offset thetendency of the shaft to be deflected at the central int of each half.

5. A counterbalance engine main shaft having .four throws, with throws 1 and 4 set 180 apart, and throws 2 and 3 set 180 apart but at 909 from throws 1 and 4, and a single counterbalancing weight positioned between the two throws on each half of the shaft and having its center of gravity within the angle produced by extending the center line of the outer throw and a line bisecting the angle of the two throws, such weight being effective to assist in counterbalancing the two adjacent throws.

CLINTON L. WALKER.

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