US2809614A - Engine construction - Google Patents

Description

Oct. 15, 1957 F. L. PRESCOTT arm.

ENGINE CONSTRUCTION Filed Dec. 27, 1955 INVENTORS CARL F. BACHLE FORD LPRESCOTT Unite rates ENGINE coNsrnUcrroN Ford L. Prescott, Detroit, and Carl F. Bachle, Grosse Pointe, lvlich, assignors to Continental Aviation and Engineering Corporation, Detroit, Mich., a corporation of Virginia Application December 27, 1955, Serial No. 555,707

8 Claims. (Cl. 121194) Our invention relates to internal combustion engines and more particularly to an opposed piston type internal combustion engine having rocker arm mechanisms connected to each of the opposed pistons thereof, which operate on a single crankshaft.

The invention further relates to a means for absorbing the operating forces tending to separate the aforesaid rocker arm mechanisms, and more particularly to a rocker arm support and compression hold-down support construction adapted to prevent transmission of the aforesaid operating forces to the engine crankcase and rocker arm housing structure.

in the development of opposed piston engines using the rocker arm mechanism, the general practice heretofore was to bolt the trunnions and shafts, on which the rocker arm mechanisms of each piston pivot, firmly to the crankcase and rocker arm housing structure of the engine. This is usually accomplished by connecting the trunnions to the housing structure in positions adjacent the ends of the engine cylinder, and then connecting the trunnions by means of through-bolts and compression struts or spacers. However, when the engine is operating, the forces of eX plosion on the piston power stroke, and the forces constituting a return of some of this power from the crankshaft to compress the pistons on the piston compression stroke, tend to cause a separation of the rocker arm mechanisms. The through-bolts are intended to oppose and absorb these forces, and are so constructed as to main tain a rigid support of the trunnions and shafts in position on the aforesaid housing structure.

The operating forces aforesaid are made up of gas pressure component forces and other mechanical forces which are due to inertia of the engine moving parts. The gas pressure forces act equally in opposite directions on the intake and exhaust strokes. The inertia forces oppose the gas pressure forces during the half-revolution before and after the pistons reach top dead center, and aid the gas forces during the bottom dead center portion of the cycle. The difference between gas forces and inertia forces near top dead center is the force transmitted to the rocker shafts, and therefore absorbed in the through bolts and the compression struts.

in order to obtain the most efiicient operation of the engine, the exhaust piston is preferably phased ahead of the intake piston by 10 to 20 degrees. This allows the exhaust port to open 25 to 40 degrees before the intake, allowing the pressure in the exhaust to drop to a low value before the intake port opens. The exhaust port also closes before the intake port closes, thus allowing the trapped air in the cylinder to be supercharged up to the intake air pressure. The benefits of the phase angle between exhaust and intake pistons is of more value than exact balance of inertia forces, especially since suitable counterweighting may be utilized to remove all objectionable vibration, and the resulting engine is acceptably smooth in operation.

A portion of the unbalanced inertia force must be absorbed in the engine frame itself. Heretofore, the housing structure had to be of relatively heavy construction in order to absorb the compression forces, and heavy spacers had to be inserted between the two portions of the housing structure to which the trunnions are secured in order to prevent the unequal pressures from cracking or otherwise damaging the structure, and also to permit the throughbolts to be sufficiently tightened on assembly. In addition, the lengths of the spacers had to be machined to high manufacturing tolerances so that they would precisely match the distance between the housing structure portions against which they bore, in order to eliminate all possible play of the spacer and provide for rigid assembly of all the parts.

Therefore, an object of the present invention is to provide an improved opposed piston internal combustion engine construction by constructing an improved supporting means for the rocker arm mechanisms, which will successfully absorb the forces of engine operation tending to separate the mechanisms.

Another object of the present invention is to reduce the possibility of engine crankshaft and rocker arm housing structure failure due to unequal loads imposed on the rocker arm mechanisms by providing an improved rocker arm hold down and compressoin through-bolt construction adapted to absorb the aforesaid loads while still supporting the rocker arm mechanisms within the housing structure in substantially rigid relationship.

A further object of the invention is to provide an improved engine structure by constructing a frame and rocker arm housing assembly by which one of the rocker housings forms a stabilizing seat in the connection from one rocker shaft across to the other. To this end, a suitable seat for the lower rocker shaft is formed in the lower rocker housing and a compression strut or spacer, preferably of steel, goes from the lower rocker housing over to the upper rocker shaft. This strut acting with the tightened through-bolt absorbs the internal stress due to the gas and inertia loads acting on the rocker shafts, thus freeing the rocker housings and crankcase of the aforesaid operating loads.

A more complete understanding of our invention may be had by reference to the accompanying drawings illustrating a preferred embodiment of the invention in which like characters refer to like parts throughout the several views and in which Fig. 1 is a fragmentary vertical cross-sectional view through an opposed piston internal combustion engine utilizing the preferred rocker arm hold down and compression through-bolt construction embodying the principles of the present invention.

Fig. 2 is a section on line 2-2 of Fig. 1.

Fig. 3 is a section on line 33 of Fig. 2.

Fig. 4 is a section on line 44 of Fig. 2, and

Fig. 5 is a section on line 55 of Fig. 2.

Referring to the drawings in detail, an opposed piston type internal combustion engine 19 is illustrated having a crankcase 11, an upper rocker arm housing 12a and a lower rocker arm housing 12b secured to opposite faces of the crankcase 11 by bolts 13 or other suitable securing means. A cylinder structure 14 is preferably secured to the upper rocker arm housing 12a as with bolts 15 and slidably secured to the other rocker arm housing 121) as at 16. Opposed pistons 20 are operable within the cylinder 14 and each is preferably connected by means of a link 21 to one end of a rocker arm 22. A crankshaft 23 is operable in the crankcase 11, and is connected by means of connecting rods 24 to the other end of each rocker arm 22.

It should be noted that since the rocker arm housings 12a and 12b are secured to the crankcase 11, the effect is to provide a single individual crankcase and rocker arm housing structure, on which the forces previously described heretofore tended to act, and this transmittal of forces are what the present invention eliminates.

Upper and lower shafts 30a and 30b respectively are the pivotal supports for the rocker arms 22, and are adapted to rest in the half-rounded seats 31 of upper rocker shaft support or trunnion block 32a and lower rocker shaft support or trunnion block 32b. Holes 33 are bored vertically through each of the shafts 30a and 30b and are aligned with holes 34 bored through each trun- The upper trunnion block 3 2a is slidably mounted in a the upper rocker arm housing 12a. The trunnion block 32a is provided with an extension or collar 38, which is slidable within a bushing 32 carried by the upper rocker arm housing 12a, said bushing 39 being preferably secured within a bore 40 of a thickened portion 41 of said upper rocker arm housing.

A through-bolt 45 extends between the upperand lower shafts 38a and 30b respectively, through thecaforesaid aligned bores ,33, 34, and 36 respectively, through shafts a and 30b, the trunnion'blocks 32a and 32b, and the 7 lower rocker arm housing portion 37. Between the lower rocker arm housing 12b and the upper trunnion block portion 38, and bearing thereon, is a through-bolt spacer 46 enclosing the through-bolt 45. Washers 47 and nuts 48 are secured to the threaded ends 49 of the throughbolt 45. The shafts 30a and 30b are flattened at these sections. to provide surfaces on which the washers 47 heat. Suitably located annular O-rings 49a are utilized as illustrated to prevent leakage of oil from the interior of the rocker arm housings 12a and 12b. 7

When the nuts 48 are tightened, the parts'between them are retained in place against separation forces, and the spacer 46 prevents the upper shaft 30a and the upper trunnion block 32a from moving downward, a relatively small clearance being maintained at 50 between the upper trunnion block 32a and the upper rocker arm housing portion 41. The through-bolt is provided withenlarged portions 45a, 45b, 45c, and 45d, and 452, providing a close fit respectively with the bores in the upper shaft 304:, the upper trunnion 32a, the spacer 46, the lower rocker arm housing portion 37, the lower trunnion block 32b, and the lower shaft 30b, and yet avoiding any complete binding within these parts.

It will be observed that all ofthe aforesaid shafts, trunnion blocks, through-bolt and spacer are, due to the particular assembly that is comprised by our invention, rigidly retained against vertical displacement only at the lower rocker arm housing portion 37. Unequal forces acting on the assembly from the rocker arms 22 mounted on the shafts. 30 and 30b will be absorbed solely either by the through-bolt 45 between the nuts 48 or by the spacer 46 between the upper trunnion block 32a and the lower rocker arm housing portion 37, since neither bears vertically on the upper rocker arm housing portion 41.

'Since the construction illustrated is only a preferred members to the crankcase housing, or some other structural member, rather than to the rocker arm housing. In

' thelparticular opposedpiston engine to which the applicants applied this invention, therocker arm housing structure is utilized, but the invention is not so limited.

The important factor to be considered is that the forces of engine operation acting unevenly on the rocker arm mechanisms are absorbed by the through-bolt and spacer supporting and retaining members rather than by any housing or casing structure of the engine as has heretofore been the case.

The present invention accomplishes the desired objects with efiiciency and a minimum of complexity, and permits higher engine operating loads with lighter engine con struc'tion. Moreover, there is no need for manufacturing the spacer to high manufacturing tolerances as heretofore has been done. 7 7

Although we have described and illustrated a preferred embodiment of the invention, it will be apparent to one skilled in the art to which our invention pertains that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

We claim:

1. An opposed piston internal combustion engine comprising separate crankcase and cylinder structures,crocker arm housings secured respectively to opposite faces of said crankcase and provided with extensions supporting said cylinder structure, opposed pistons reciprocating in said cylinder structure, a crankshaft supported by said crankcase, a rocker arm mechanism connecting each piston with the crankshaft and including a rocker shaft and a rocker arm pivotally supported thereby, means supporting said rocker shafts and securely fixed to one of said housing. structures, and means securing said rocker shafts to said rocker shaft supporting means, said other rocker arm housing provided with a bore axially slidabl guiding said rocker shaft supporting means, whereby to provide for free axial displacement of said rocker shaft supporting means in both directions with respect to said other rocker arm housing. 7 V

2. An opposed piston internal combustion engine comprising separate crankcase and cylinder structures, rocker arm housings secured respectively to opposite faces of said crankcase and provided with extensions supporting said cylinder structure, opposed pistons reciprocating in saidcylinder structure, a crankshaft supported by said crankcase, a rocker arm mechanism connecting each piston with the crankshaft and including a rocker shaft and a rocker arm pivotally supported thereby, nreans supporting said rocker shafts and securely fixed to one of said housing structures, and means securing said'rocker shafts to said rocker shaft supporting means and comprising :a through bolt, said other rocker arm housing provided with a bore axially slidably guiding said rocker shaft supporting means, whereby to provide for free axial displacement of said rocker shaft supporting means and.

through bolt in both directions with respect to said other rocker arm housing. 7 y

3. An opposed piston internal combustion engine comprising a crankcase, separate rocker armhousings secured respectively to opposite faces of said crankcase, an engine cylinder assembly carried 'by said rocker arm housings, opposed'pistons reciprocating in said cylinder assembly,

a crankshaft supported by said crankcase, a rockerarrn mechanism connecting each piston with the crankshaft-and each including a rocker'and a' rocker shaft the rocker and rocker shaft of each mechanism being disposed respectively in each rocker arm housing, connecting means extending between said separate rocker arm housings and connecting said rocker shafts, said connecting means constructed to be rigidly securedto one of said rocker arm housings and arranged to permit axial displacement in both directions relative to said other housing.

4. An opposed piston internal combustion engine comprising a crankcase,separate rocker arm housings secured respectively to opposite faces of said crankcase, an engine cylinder assembly'carried by said'rocker arm 'housings, opposed pistons reciprocating in said cylinder assembly, a crankshaft supported by said crankcase, a a

rocker arm connecting each piston with the crankshaft and including a rocker and a rocker shaft, the rocker and rocker shaft of each mechanism being disposed respectively in each rocker arm housing, connecting means extending between said separate rocker arm housings and connecting said rocker shafts, said connecting means constructed to be rigidly secured to one of said rocker arm housings and arranged to permit axial displacement in both directions relative to said other housing, said connecting means comprising a support member for each rocker shaft and disposed in each rocker arm housing, means rigidly securing one of said support members to one of said rocker arm housings, and means clamping said rocker shafts respectively to said support members and in fixed positions relative to the last mentioned housing.

5. An opposed piston internal combustion engine comprising a crankcase, separate rocker arm housings secured respectively to opposite faces of said crankcase, an engine cylinder assembly carried by said rocker arm housing, opposed pistons reciprocating in said cylinder assembly, a crankshaft supported by said crankcase, a rocker arm mechanism connecting each piston with the crankshaft and including a rocker and a rocker shaft, the rocker and rocker shaft of each mechanism being disposed respectively in each rocker arm housing, connecting means extending between said separate rocker arm housings and connecting said rocker shafts, said connecting means constructed to be rigidly secured to one of said rocker arm housings and arranged to permit axial displacement in both directions relative to said other housing, said connecting means comprising a support member for each rocker shaft and disposed in each rocker arm housing, means rigidly securing one of said support members to one of said rocker arm housings, means supporting the other of said support members against lateral displacement With respect to the other housing and permitting axial displacement with respect thereto, and means clamping said rocker shafts rerespectively to said support members and in a substantially fixed position relative to said first mentioned housing.

6. An opposed piston internal combustion engine comprising a crankcase, separate rocker arm housings secured respectively to opposite faces of said crankcase, an engine cylinder assembly carried by said rocker arm housings, opposed pistons reciprocating in said cylinder assembly, a crankshaft supported by said crankcase, a rocker arm connecting each piston With the crankshaft and including a rocker and a rocker shaft, the rocker and rocker shaft of each mechanism being disposed respectively in each rocker arm housing, connecting means extending between said separate rocker arm housings and connecting said rocker shafts, said connecting means constructed to be rigidly secured to one of said rocker arm housings and arranged to permit axial displacement in both directions relative to said other housing, said connecting means comprising a support member for each rocker shaft and disposed in each rocker arm housing, means rigidly securing one of said support members to one of said rocker arm housings, a spacer member disposed between said other support member and the last mentioned rocker arm housing, and a through-bolt arranged to clamp said shafts, said support members, and said spacer in a substantially fixed position relative to the last mentioned rocker arm housing.

7. An opposed piston internal combustion engine comprising a crankcase, a separate rocker arm housing secured respectively to opposite faces of said crankcase, an engine cylinder assembly carried by said rocker arm housings, opposed pistons reciprocating in said cylinder assembly, a crankhaft supported by said crankshaft and including a rocker and a rocker shaft, the rocker and rocker shaft of each mechanism being disposed respectively in each rocker arm housing, connecting means extending between said separate rocker arm housings, and connecting said rocker shafts, said connecting means constructed to be rigidly secured to one of said rocker arm housings and arranged to permit axial displacement in both directions relative to said other housing, said connecting means comprising a support member for each rocker shaft and disposed in each rocker arm housing, means rigidly securing one of said support members to one of said rocker arm housings, a spacer member disposed between said other support member and the last mentioned rocker arm housing, and a through-bolt arranged to clamp said shafts, said support members, and said spacer in a substantially fixed position relative to the last mentioned rocker arm housing, means supporting said other support member against lateral displacement with respect to the other rocker arm housing and permitting axial displacement with respect thereto.

8. An opposed piston internal combustion engine comprising a crankcase, a separate rocker arm housing secured respectively to opposite faces of said crankcase, an en gine cylinder assembly carried by said rocker arm housings, opposed pistons reciprocating in said cylinder assembly, a crankshaft supported by said crankcase, a rocker arm mechanism connecting each piston with the crankshaft and including a rocker and a rocker shaft, said rocker and rocker shaft of each mechanism being disposed respectively in each rocker arm housing, connecting means extending between said separate rocker arm housings and connecting said rocker shafts, said connecting means constructed to be rigidly secured to one of said rocker arm housings and arranged to permit axial displacement in both directions relative to said other housing, said connecting means comprising a support member for each rocker shaft and disposed in each rocker arm housing, means rigidly securing one of said support members to one of said rocker arm housings, a spacer member disposed between said other support member and the last mentioned rocker arm housing, and a throughbolt arranged to clamp said shafts, said support members, and said spacer in a substantially fixed position relative to the last mentioned rocker arm housing, means supporting said other support member against lateral displacement with respect to the oher rocker arm housing and permitting axial displacement with respect thereto, said rocker shafts, rocker shaft support members, spacers, and the rocker arm housing to which said connecting means is secured having aligned bores, said bolt threaded through said bores aforesaid and locking means at each bolt end and for completing said through-bolt assembly, said rocker shaft supports each comprising a trunnion having a half round cylindrical recess supporting said rocker shaft.

References Cited in the file of this patent UNITED STATES PATENTS 2,099,371 Olds Nov. 16, 1937 2,134,811 Church Nov. 1, 1938 FOREIGN PATENTS 620,288 Great Britain Mar. 22, 1949

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