US3021826A - Rocker arm and multiple valve actuating mechanism - Google Patents

Description

Feb. 20, 1962 A. DE FEZZY ETAL 3,021,826

ROCKER ARM AND MULTIPLE VALVE ACTUATING MECHANISM Filed Nov. 23, 1959 3 Sheets-Sheet I INVENTORS ATTORNEY Feb. 20, 1962 A, DE FEZZY ETAL ROCKER ARM AND MULTIPLE VALVE ACTUATING MECHANISM 5 Sheets-Sheet 2 Filed Nov. 25, 1959 I Y 1 1 1 a? aye Zbmg BY /0K Z2 @TORNEY I a a a yak/7 Feb. 20, 1962 A. DE FEZZY ETAL 3,021,826

ROCKER ARM AND MULTIPLE VALVE ACTUATING MECHANISM Filed Nov. 23, 1959 3 Sheets-Sheet 3 a? I g #19 "WEN goes dlfierffle fezg/ Z4 fiei f'ef wnle W i [M 0/22 6/1277 0/? l A; /l I Pea K I a z! z; BY

2 ATTORNEY 3,021,826 ROCKER ARM AND MULTHLE VALVE ACTUATING NECHANISM Albert De Fezzy, Detroit, George P. Hartley, Northviiie, William S. Kenyon, Huntington Woods, and Joseph A. Peak, Detroit, Mich, assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Nov. 23, 1959, Ser. No. 854,637 19 Claims. (Cl. 123-90) This invention relates generally to a valve actuating mechanism for an internal combustion engine and, more particularly, to a valve actuating mechanism adapted to open and close a plurality of valves simultaneously by actuation of a single rocker arm.

In valve mechanisms of the type described a yoke or bridge member is interposed between one arm of a pivotal- 1y mounted rocker arm and the adjacent ends of the several valve stems which are maintained in thrust engagement therewith by the biasing action of suitable valve return springs. In prior art constructions various means have been provided to restrain or guide the movement of the actuating bridge to equalize the valve actuating movement imparted to the several valves.' The most comon type of such guide means comprises a guide stem formed integrally with or carried by the bridge which is slidably mounted in a crosshead bearing member carried by the valve mounting member, i.e. the cylinder head. The guide hearing may be either stationary or swivel mounted depending upon whether sliding or pivotal thrust engagement is provided between the rocker arm and the common bridge. To insure proper follow between the bridge and rocker arm at all engine speeds, such guided bridge constructions generally require the use of a bridge biasing spring in addition to the normal valve return springs. In other constructions of this type the common bridge is guided by suitable limit stops coacting between the valve stems and/r between the rocker arm and the common bridge. In certain installations the bridge forms an element of and is guided for equalized valve movement by a parallelogram linkage arrangement.

Such prior art constructions are generally either diliicult to adjust for lash or require some form of automatic lash adjusters. Such guided bridge constructions are difiicult to lubricate, particularly under engine starting conditions, and are thus extremely susceptible to lash increasing wear intermediate the actuating bridge, the several valve stems and the load transmitting surfaces of the bridge and rocker arm. Improper lash adjustment and variations in the biasing action of the several valve return springs cause the bridge to skew relative to its guide means under engine operating conditions. Even with otherwise adequate lubrication, such skewing results in scoring and binding of the bridge guiding means and in bending of the valve stems and guides thus locking the bridge and valves in their valve opened position. Subsequent upward movement of the piston in the associated engine cylinder results in destructive impacting of the several valve heads with consequential valve head distortion or breakage, bending of the valve stems and guides and, in certain instances, in permanent distortion in the cylinder head structure. Where valve head breakage occurs, continued engine operation may result in destructive distortion or breakage of the cylinder head, cylinder liner or block, the associated piston and connecting rod and even of the engine crankshaft.

The invention contemplates an improved valve actuating mechanism of the type described which has a minimal number of relatively simple and inexpensive parts, provides a single accessible and relatively simple lash adjustment, minimizes valve stem and pallet wear, and prevents or minimizes damage to the various engine components in case of valve malfunction.

3,Zl,32 Fatentecl Feb. 2, 1%52 The several embodiments of the valve actuating mechanism of the invention, which are herein shown and described for illustrative purposes, each comprise a floating bridge having a pivotal clevis connection with one end of a rocker arm. The rocker arm is pivotally mounted intermediate its ends and pivotally connected at its opposite end for actuation by an adjustable cam operated link or push rod. The bridge is preferably either a sheet metal stamping or a forged casting having two spaced arcuately formed pallet portions thereon which are thrustably engaged by the spring biased ends of adjacent valve stems. The spaced pallet portions are dimensioned to provide for the application of substantially equalized and straight line actuating forces to both the valve stems engaged thereby regardless of any relative weakness which may develop in one or the other of the valve springs within the range of valve opening permitted by suitable abutment stop means.

1 The foregoing and other objects, advantages and features of the invention will be more thoroughly understood from the following description of the several illustrative embodiments thereof, having reference to the accompanying drawings, in which:

FIGURE 1 is a transverse sectional view of a portion of an internal combustion engine and shows the valve closed and equal valve opened positions of a first embodiment of a valve actuating mechanism constructed in accordance with the invention;

FIGURE 2 is a sectional view taken substantially in the plane of the line 2-2 of FIGURE 1;

FIGURE 2a is a sectional view of the rocker arm of FIGURES l and 2 and is taken substantially in the plane of the line 2a+2a in FIGURE 3;

FIGURE 3 is a view similar to FIGURE 1 and shows a. portion of the valve actuating mechanism thereof in an unequal valve opened position, the valve return springs being of unequal strength;

FIGURE 4 is a view similar to a portion of FIGURE 1 and shows a second embodiment of the invention;

FIGURE 5 is a sectional view similar to FIGURE 2 and is taken substantially in the plane of the line 55 of FIGURE 4;

FIGURE 5a is a sectional view similar to FIGURE 2a showing the rocker arm of FIGURES 4 and 5 sectioned substantially in the plane of the line 5a-5a in FIGURE 6;

FIGURE 6 is a view similar to FIGURE 3 and shows the valve mechanism of FIGURE 4 in an unequal valve opened position where one of the valve return springs is of greater strength than the other; and

FIGURE 7 shows the valve actuating mechanism of FIGURE 4 in a valve opened position where the opposite valve spring is of greater strength.

As partially shown in FIGURE 1, the engine indicated generally at 10 comprises a cylinder block 11 having at least one cylinder bore therein reciprocably mounting a piston 12. A cylinder head 13 mounted on and sealed with respect to the cylinder block closes the upper end of the cylinder bore to form an expansible combustion chamber with the reciprocating piston. In casting, the head is cored to provide suitable cooling water passages or jacketing indicated at 15. The cylinder head is also cored to provide a passage 16 opening on the combustion chamber 14 and controllable by two poppet type valves 17 For the purpose of describing the invention, the passage 16 may be either an intake or an exhaust passage depending upon the type of engine. In a two-cycle unillow scavenged Diesel engine, four valves might be used per cylinder to control spaced ports opening to a common intake or exhaust passage, the several ports being arranged equiangularly in radially spaced relation to a centrally located fuel injector. In four-cycle engines, paired intake and/or exhaust valves would of course serve to control ports opening to separate intake and exhaust passages.

I Each of the poppet valve members 17 has a stem portron 18 which is reciprocably mounted in a valve guide bearing 19 having a pressed fit into a mounting bore extending through the cylinder head and intersecting the passage 16. The upper portion of the guide bearings 19 may be of slightly larger diameter to provide annular shoulders abutting'the cylinder head to limit the extent to which the guide bearing is inserted during assembly and to prevent further downward movement of the guide bearing under certain valve operating conditions. The lower portion of the valve stem. projects downwardly into the passage 16 and is flared at its lowerend to provide a valve head 26 which is sealingly engageable with a. valve seating surface defined by a valve seat insert 21 mounted in the adjacent port opening of the passage 16. The upper end of each valve stem is grooved to-receive conically tapered split keys 22 which are held on the stem by the wedging action of a-cooperatively tapered spring retainer 23. Each guide bear-ing19 is embraced by and internally guides a spring 24 which is compressively interposed between the stem carried spring retainer 23 of its associated valve and a-spring seating washer 25 embracing the valve guide bearing and abutting the cylinder head within a counter-bored recess provided therefor at 26. Each of the springs 24 serves as a return spring biasing its associated valve member toward its closed position wherein the head portion thereof sealingly engages the port defining valve seating surface of the insert 21. a

In the embodiment of the invention shown in FIG- URES 1-3, the valves 17 are adapted to beactuated substantially in unison between their closed. and opened positions by the camshaft timed operation of a valve actuating linkage mechanism indicated generally at 36. This mechanism includes a bridge member 32 pivotally connected at 34 to one end of a rocker arm 36. The

bridge 32 defines a pair of arms spaced from and extending transversely of the pivot 34, each arm having an arcuately or spherically formed pallet portion 38 thereon which is engageable with the adjacent upper end-surface 27 of one of the valve stems. It will be noted that the axis of the pivot 34- is normal to a first plane including the axes of the two valve stems and is spaced from and parallel to a second plane normal to the first plane and tangent to both pallet portions of the bridge. As indicated above, the bridge 32 may be a-forged casting or otherwise suitably formed but, as herein shown and described and in accordance with certain of the more specific aspects of the invention, is preferably formed by stamping from suitable steel plate stock with subsequent precision coining of the pallet portions. The formed bridge is then heat treated and hardened to provide suitable strength and wear resistance.

The rocker arm 36 is pivotally journaled intermediate its ends on a shaft 4%) which is supported above the cylinder head in parallel relation to the axis 34 by suitably spaced brackets 42, only one of which is shown. The end of the rocker arm distal from the bridge pivot 34 -is pivotally connected at 44 to a clevis member 46 forming the upper end of a cam operated push rod assembly 48, the axes of the pivot 44 being parallel to the other pivotal axes of the rocker arm. The rocker arm 36 may also be a forged casting or otherwise suitably formed but, as shown in FIGURES 1- 3, is preferably formed from two mating sheet metal stampings 36 and 36". The mating rocker arm halves define lubricant supply passages 37 and 37" therebetween which interconnect several openings 33', 39' and 43' provided to receive bushings 33, 39 and43 therein, respectively. During assembly, the several bushings arepreferably press fitted into their respective mounting bores prior to brazing, spot welding, or otherwise suitably securing the rocker arm halves together. The bushing 39 journals the rocker arm on the shaft 46}, and the bushings 33 and 43 pivotally journal hollow pivot pins 35 and 45, respectively, which extend through aligned openings in the bridge and clevis members 34 and 44 and are secured thereto by sheer riveting of the projecting pivot pin ends.

The bushings 33 and 43 are each provided with at least one radial port 33" and 43", respectively, opening on the adjacent end of the lubricant supply passage 37' or 37'7. The opposite inner ends of the passages 37' and 37 are interconnected by an annular passage 3'1 defined between the rockerarm halves and the bushing 39. The shaft bushing 39 is similarly provided with one or more radial ports 39", at least one of which is mateable during valve actuating movement of the rocker arm with a passage 41' extending radially of the hollow shaft 40. inwardly, the passage 41' intersects the central passage 41 which extends through the shaft and is in continuous communication with the pressurized lubricant supply of the engine through suitable passage means in the shaft mounting bracket members 42 and the cylinder head as indicated generally at 28. It will thus be seen that the quantity and amount of lubricant supplied to the sev- .push rod member 50. The opposite endof the push rod 50 is provided with a spherical pallet 52 which'is thrustably engageable with a spherical seat providedin the lower closed end of a hollow, cup-shaped cam follower guide member 54. The guide member 54 is reciprocably but non-rotatably mounted in-a' guide bore 56 provided in the cylinder head. A cam engaging roller 58 is carried by and suitably journaled with respect to the lower end of the follower guide member. The cam follower 54 and the pushrod 50 are biased downwardly to maintain the roller 58 in engagement with a valve-actuating lobe 60 of a camshaft 62 by a spring 64 which is compressively interposed between a wash r formed spring seat 66 carried by the spherical pallet end of the push rod 50 and a second Washer formed seat 68 which is spring ring retained within the upper end of the follower mounting bore 56. The push rod assembly 48 is adjusted to provide zero lash in the valve actuating linkage 30 under engine operating thermal conditions by means of the threaded adjustment provided between the clevis member-46 and the primary push rod member 50.

As the roller 58 departs from the base circle of the cam lobe 60, the resultant upward actuation of the push rod assembly is transmitted through the rocking movement of the arm 36 and eifects a downward arcuate movementof the pivot 34 thus imparting a downward valve opening movement to the bridge 32. In most engine installations, the springs 24 will normally be selected to have substantially equal compressive biasing rates. Where the valve return springs 24 are of equal rate and initial compressive loading, the downward movement of the bridge 32 will normally carry the valves 17 to corresponding equal valve open positions wherein the spring retainers 23 will be equally and closely spaced from the upper end surfaces of their respective valve guide bearings 19, as shown in broken lines in FIGURE 1. However, in certain engine installations it may be desirable to provide some initial spring unbalance to effect desired intake or exhaust characteristics or impulsing. The biasing rates of the two springs may also become unbalancedunder engine operating conditions. *Under such unbalanced spring fconditions, the downward va-lve'opening movement imparted to the bridge 32 tends to advance or open the valve having the weaker compressive rate ahead of the other valve since the bridge is permitted to cook until the spring reactions applied thereto have been equalized. Such advancing of the weaker-springed valve continues until its spring retainer 23 engages the upper end of its associated guide bearing 19. Such engagement prevents further opening movement of this valve and further downward movement of the pivot 34 rotates the bridge 32 to carry the other valve to an opened position slightly less than that provided the first valve as shown in broken lines in FIGURE 1. Similar valve opening movement occurs between the bridge and valve stems when one of the valve members is restrained or tends to stick relative to its guide member.

With the exception of the rocker arm, which is of different configuration and structure, the several components or elements of the embodiment of the invention illustrated in FIGURES 4-7 are identical with those of the first embodiment and are therefore identified with the same reference numerals. Those portions and elements of the rocker arm structure of this embodiment which are similar in structure and function to those of the previously described rocker arm 36 need not be described in detail but for reference purposes are identified by adding 100 to the corresponding reference numeral of the first embodiment. Such similar rocker arm portions and elements thus have the same last two digits. By way of example, the rocker arm of the second embodiment is indicated generally by the reference numeral 136.

The rocker arm 136 is fabricated from a single sheet metal stamping of suitable stock which is folded as indicated by the dashed line at A intermediate the halves 136 and 136" and is formed to provide lubrication supply passages 137' and 137" and spaced parallel pivot openings 133', 139' and 143' for mounting bushings 133, 139 and 143. In assembly, two sleeves are inserted in the openings 133' and 134' and are then rolled adjacent each end to rivet the folded halves of the stamping together. The several bushings 133, .139 and 143 are then press fitted within their respective mounting bores after which the bearing halves may be further secured together by brazing or spot welding, if desired.

In accordance with certain more specific aspects of this embodiment of the invention, the rocker arm 136 is provided with a limit stop arm 147 extending outwardly beyond the pivot 134 and a limit stop boss 149 formed adjacent the flanges defining the opening 139'. As shown in FIGURES 6 and 7, the limit arm 147 and the boss 149 are alternatively engageable under unbalanced spring conditions with one of the pallet arms of the bridge 136 to limit rotation of the bridge relative to the rocker arm and thereby the degree and timing difierence permitted in the opening of the several valves. Such alternative en agement occurs between the rocker limit 147 or 149 and the pallet arm engaging the valve having the stiffer spring after a predetermined amount of opening of the other weaker-springed valve. After such pallet stop engagement, further opening movement of both valves occurs without regard to spring force differences until the keeper of the weaker spring engages its associated valve guide bearing. Such bearing and keeper engagement, of course, rotates the bridge pallet out of engagement with the rocker arm stop as the other stitfer valve is actuated to its opened position.

It will be apparent that the pivotal movement permitted the bridge 32 in either embodiment results in the application of the valve opening force substantially longitudinally of each valve. The relatively light mass of the bridge and its positive pivotal connection to the rocker arm and otherwise unrestrained pivotal actuating engagement with the valve stems insures proper rocker following movement of the bridge under all engine speed conditions. Hence, the valve return springs are limited in compressive loading and biasing rate to that required to insure proper valve follow of the bridge during valve closing thereby preventing valve seat impacting. This is in marked contrast to the restrained guided bridge valve actuating constructions previously used in such engines wherein either a bridge return spring is necessarily applied or the valve return springs are sufiiciently loaded to provide suflicient between the bridge and rocker arm. Such spring loading of the bridge of course increases the power required to actuate the several valves of the engine and results in lash increasing wear between the load transmitting surfaces of the valve stem, bridge and rocker arm. The unguided clevis bridge of the invention also minimizes lash increasing valve stem wear by permitting rotation of the valves under engine operating conditions as a result of the torsional action of the valve springs, wind-up being imparted thereto by their compression during actuation of the valves to their opened positions. Wear is further minimized by the positive pressurized lubrication supplied to the several rocker pivots and the drainage therefrom which insures proper lubrication of the pallet and valve stem engaged surfaces under engine starting and idle operation and augments the normal spray lubrication thereof which occurs at normal engine speeds.

Use of the clevis bridge of the invention further permits the use of a single relatively simple push rod adjustment for lash. In effecting such lash adjustment, the push rod is first adjusted to carry both pallets of the bridge 32 out of engagement with their respective valve stems thus insuring closing of both valves. The bridge may then be cocked to effect engagement between one of the pallets and its adjacent valve stem. The necessary lash adjustment of the push rod is then half the clearance between the other pallet and stem as determined by feeler gauge.

While the foregoing description has been limited to two embodiments illustrative of the several aspects of the invention, it will be appreciated that various modifications and changes might be made thereinother than those mentioned without departing from the spirit and scope of the invention, as defined in the following claims.

We claim:

1. In an internal combustion engine, a plurality of valves mounted for parallel reciprocation between valve opened and valve closed positions, individual spring means for biasing each of said valves toward its closed position, a rocker arm, a shaft extending transversely of the reciprocable axes of two adjacent valves and mounting said rocker arm for oscillatory movement relative thereto, timing means operable to oscillate said rocker arm in timed relation to the operation of said engine, and a floating bridge pivotally connected to one end of said rocker arm for swinging movement with respect thereto about an axis extending between and spaced from the ends of said two valves and normal to a plane including the axes of said two valves, said floating bridge having spaced arcuately formed pallet portions thereon maintained in slidable and pivotal thrust contact with the adjacent ends of said two valves.

2. In an internal combustion engine, the combination set forth in claim 1 wherein the biasing action and deflection rate of each of the spring means acting on said two valves are substantially equal.

3. In an internal combustion engine, the combination set forth in claim 1 wherein the individual spring means acting on each of said two valves have unequal biasing characteristics.

4. A valve actuating mechanism for an internal combustion engine having a plurality of valves mounted for parallel reciprocation between valve opened and valve closed positions and having individual spring means biasing each of said valves toward its closed position, said valve actuating mechanism including a rocker arm, a shaft pivotally mounting said rocker arm for oscillatory movement relative thereto in a plane including the reciprocable axes oftwo of said Valves, timing means including a rotatably driven cam operably connected to one end of said rocker arm to oscillate said arm in timed relation to the operation of said engine, and a floating bridge pivotally connected to the opposite end of said rocker arm for swinging movement with respect thereto and havingspaced arcuately formed pallet portions thereon maintainable in slidable and pivotal thrust contact with the ends of said two valves,.said pivotal connection being spaced from the ends of said two valves and extending between the reciprocable axes thereof in normal relation to the oscillatory plane of said rocker arm.

5. In a valve actuating mechanism as set forth in claim 4, said floating bridge being a sheet metal stamping having a base portion extending between and including said pallet portions and having two flanges extending upwardly therefrom to define a clevis pivotally connectable to said rocker arm.

6. In a valve actuating mechanism as set forth in claim 4, said rocker arm including two sheet metal stampings suitably secured together and having oppositely disposed parallel bosses defining openings for said shaft and said pivotal connection, said stampings defining alubricant distribution passage therebetween interconnecting said shaft and pivot opening, and passage means in said shaft for supplying pressurized lubricant through said distribution passage to said pivotal connection.

7. In a valve actuating mechanism as set forth in claim 4, said rocker arm being fabricated from a sheet metal stamping, said sheet metal stamping having a plurality of similarly disposed upstanding flanges formed therein defining alignable openings for said shaft and pivotal connection and having symmetrical halves folded about a median line to align said openings, and means suitably securing said folded halves together.

8. In a valve actuating mechanism as set forth in claim 7, said. stamping halves defining a lubricant distribution passage therebetween interconnecting said shaft and pivot opening, and passage means in said shaft for supplying pressurized lubricant through said distribution passage to said' pivotal connection.

9. In a valve actuating mechanism as set forth in claim 4, said floating bridge comprising a sheet metal stamping having a base portion extending between and including said pallet portions and having two flanges extending upwardly therefrom to define a clevis, a. pivot pin extending through and journaled in said rocker arm, said pivot pin pivotally connecting said bridge clevis to said rocker arm, said. rocker arm having a lubricant distribution passage therein interconnecting said shaft and pivot opening, and passage means associated with said shaft for supplying pressurized lubricant through said distribution passage to said pivot pin connection and therefrom to said pallet portions and the valve ends engaged thereby;

10. In an internal combustion engine, a plurality of valves mounted for parallel reciprocation between valve opened and valve closed positions, individual spring means for biasing each of said valves toward its closed position, a rocker arm, a shaft extending transversely of the reciprocable axes of two adjacent valves and mounting said rocker arm for oscillatory movement relative thereto, a lash adjustable cam follower assembly pivotally connected to one end of said rocker arm, timing means including a rotatably driven cam engaged by and operable through said cam followerto oscillate said rocker arm in timed relation to the operation of the engine, a floating bridge pivotally connected to the opposite end of said rocker arm for swinging movement with respect thereto and having arcuately formed palletportions-thereon maintained in slidable and-pivotalthrust contact with the adjacent ends of said valve, said pivotalconnection being about an axis spaced from the pallet engaged ends of said valves and extending between; the reciprocable axes ofsaid valves in normal relation to the oscillatory movement of said rocker arm.

11. In an internal combustion engine, the combination set forth in claim 10 wherein the individual spring means acting on each of said two valves have unequal biasing characteristics whereby valve opening movement of said bridge tends to be imparted to one of said pallet engaged valves prior to valve opening actuation of the other of said pallet engaged valves.

12. In an internal combustion engine, the combination set forth in claim 11 and including stop means associated with and acting between said rocker arm and floating bridge to limit the pivotal movement permitted therebetween thereby limiting the extent to which valve opening movement may be imparted to said one pallet engaged valve prior to valve opening actuation of said other pallet engaged valve.

13. In an internal combustion engine, the combination set forth in claim 11 and including a first stop means associated with and acting between said rocker arm and floating bridge to limit the. pivotal movement permitted therebetween thereby limiting the extent'to which valve opening movement may be. imparted to said one palletengaged valve prior to valve. opening actuation of said.

otherpallet engaged valve, and a secondary stop means associated with said one valve. for-limiting: the opened position thereof whereby after said one. valve has been actuated to-its stop limited opened position further valve opening oscillation of said rocker arm is transmitted through pivotal movement of said floating bridge to carry said other valve to its opened position.

14. In an internal combustion engine, the combination set forth in claim 11 including stop means associated with said one valve for limiting the opened position thereof whereby after said one valve has been-actuated to its stop limited'opeued position further valve opening oscillation of said rocker arm is transmitted through pivotal movement of said floating bridge to carry said-other valve to its opened position.

15. In an internal combustion engine, the combination set forth in claim 10 wherein the individual spring means acting on each of said two valveshave unequal biasing characteristicswhereby valve opening movement of said bridge tends to be imparted to one of said pallet engaged valves prior to valve opening actuation ofthe other of said pallet engaged valves, said floating bridge comprising a sheet metal stamping having a base portion extending between and including said pallet portions and'liaving two flanges extending upwardly therefrom to define a clevis pivotally connectable to said rocker arm, and said rocker arm having a limit boss thereon engageable with the pallet of said floating bridge engaging said other valve to limit the pivotal movement permitted therebetween thereby limiting the extent to which valve opening movement may be imparted to said one valve prior to valve opening actuation of said other valve.

16. in an internal combustion engine, the combination set forth in claim 15 including stop means associated with said one valve for limiting the opened position thereof whereby after said one valve has been actuated to its stop limited opened position further valve opening oscillation of said rocker arm is transmitted through pivotal movement of said floating bridge to carry said other valve to its opened position.

17. In an internal combustion engine, a plurality of valves, a plurality of guide bearings carried by said engine and mounting said valves for parallel reciprocation between seated valve closed positions and normal valve opened positions, a first stop means associated with each of said valves and guide'means for limiting opening movement of each valve substantially beyond its normal valve opened position, individual spring means for biasing each of said valves toward its closed position, and means for actuating saidvalves in pairs between said valve opened and valve'closed positions, said valve actuating means ineluding-a rocker arm, a shaft pivotally mounting said rocirer arm for oscillatory movement relative thereto; an adjustablecam follower pivotally connected to one end of said rocker arm, timing means including a rotatably driven cam operably engaging said cam follower to oscillate said rocxer arm in timed relation to the operation of the engine, a floating bridge pivota-llyconneeted to the-opposite end of said rocker arm for swinging movement with respect thereto and having arcuately formed pallet portions thereon maintained in slidable and pivotal thrust contact with the ends of two adjacent valves, said pivotal connection being about an axis spaced from the ends of said two valves and extending between and in normal relation to a plane including said two valves, and secondary stop means associated with and acting between said rocker arm and floating bridge to limit the pivotal movement permitted therebetween thereby limiting the extent to which valve opening movement may be imparted to one of said pallet engaged valves prior to valve opening actuation of the other of said pallet engaged valves.

18. In an internal combustion engine, a plurality of valves mounted for parallel reciprocation between valve opened and valve closed positions, individual spring means for biasing each of said valves toward its closed position, a rocker arm, a shaft extending transversely of the reciprocable axes of two of said valves and pivotally mounting said rocker arm for oscillatory movement relative thereto, a lash adjustable cam follower assembly pivotally connected to one end of said rocker arm, timing means including a rotatably driven cam engaged by and operable through said cam follower to oscillate said rocker arm in timed relation to the operation of the engine, a floating bridge pivotally connected to the opposite end of said rocker arm for swinging movement with respect thereto and having arcuately formed pallet portions thereon maintained in slidable and pivotal thrust contact with the adjacent ends of said valve, said pivotal connection being about an axis spaced from the pallet engaged ends of said valves and extending between the reciprocable axes of said valves in normal relation to the oscillatory movement of said rocker arm, and stop means associated with and acting between said rocker arm and floating bridge to limit the pivotal movement permitted therebetween thereby limiting the extent to which valve opening movement may be imparted to one of said pallet engaged valves prior to valve opening actuation of the other of said pallet engaged valves.

19. In an internal combustion engine, the combination set forth in claim 18 including stop means associated with each of said valves for limiting movement of each valve substantially beyond its normal valve opened position whereby after said one valve has been actuated to its stop limited opened position further valve opening oscillation of said rocker arm is transmitted through pivotal movement of said floating bridge to carry said other valve substantially to its normal opened position.

References Cited in the file of this patent UNITED STATESPATENTS 1,084,514 Whitlock Jan. 13, 1914 1,198,115 Schenker Sept. 12, 1916 2,522,326 Winter Sept. 12, 1950 2,956,642 Chaplin et a1. Oct. 18, 1960

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