Abstract:
Several embodiments of anti-rotation devices for precluding rotation of the valve actuating lifters or tappet bodies caused by the action of the cam lobe on the engaged surface of the lifter. In each embodiment, the anti-rotation function is achieved without adding to the reciprocating masses of the engine.

Description:
BACKGROUND OF INVENTION 
     This invention relates to a valve actuating structure for operating poppet valves and more particularly to the rotation prevention structure of a valve lifter for an internal combustion engine. 
     A wide variety of reciprocating machines such an internal combustion engines employ poppet valves that are operated through camshafts via followers in the form of valve lifters such as thimble tappets. These valve lifters are supported for reciprocation in bores formed in an engine body and are operatively interposed between the cam lobes the valve stems. 
     Conventionally, the valve lifters or tappets are formed as cylindrical bodies having an upper surface engaged by the cam and which has a shape of the arc of a circle when viewed in the direction of the camshaft axis. In a perpendicular plane, the upper surface has a generally linear configuration. Thus, the top surface of the valve lifter engaged by the cam lobe is in the form of a section of a cylinder. However, because of this construction, there is likelihood that the operation of the lifter by the rotation of the cam can also cause rotary motion of the lifter about its reciprocal axis. This can result in undue wear of the lifter and/or receiving body of the engine, which can be detrimental to optimum performance. 
     It is, therefore, a principal object to this invention to provide an improved structure that serves the function of preventing rotation of the valve lifter upon operation of the valve and due to rotation of the actuating cam. 
     It is important when considering the valve timing of an engine to minimize the reciprocating masses. As the reciprocating masses increase, the inertia on the entire system increases resulting in the possibility of valve flow and decrease performance. It is, therefore, a still further object to this invention to provide an improved arrangement for precluding rotation of the valve lifter upon its actuation and which is done in a way so as to avoid any increase in the mass of the valve lifter. 
     SUMMARY OF INVENTION 
     This invention is adapted to be embodied in a valve lifter arrangement for operating a poppet valve from the rotating can of a camshaft. The construction comprises an engine body defining a cylindrical bore. A valve tappet having a generally cylindrical body portion is supported for reciprocation in the cylindrical bore. The valve tappet has a head portion adapted to be operated by the cam. In accordance with the invention interengaging portions carried by the valve tappet and the engine body permit reciprocation of the valve tappet in the engine body but prevent rotation thereof. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of an internal combustion engine showing the valve actuating mechanism therefore in solid lines with the outline of the engine being shown in solid lines, but broken away to show the valve operating mechanism. 
     FIG. 2 is an enlarged cross sectional view taken through the axis of reciprocation of the one of the engine valves and is taken along the line  2 — 2  of FIG.  3 . 
     FIG. 3 is a top plan view, looking in a direction perpendicular to the direction of FIG. 2 but with the camshaft removed so as to more clearly show the tappet bodies and the anti-rotation prevention mechanism therefore. 
     FIG. 4 is an enlarged cross sectional view taken along the line  4 — 4  of FIG. 3, showing the valves in their closed positions. 
     FIG. 5 is a view, in part similar to FIG. 4, but showing the actuated valves in their fully opened positions. 
     FIG. 6 is a perspective view showing one of the valve mechanism and the associated anti-rotation device when the valve is closed, with remaining components of the engine being shown in phantom. 
     FIG. 7 is a cross sectional view, in part similar to FIG. 4, but shows another embodiment of the invention, with the valves in their closed positions. 
     FIG. 8 is a cross sectional view, in part similar to FIG. 5, but showing the valves of this embodiments in their fully opened positions. 
     FIG. 9 is a top plan view, in part similar to FIG. 3, and shows a still further embodiment of the invention. 
     FIG. 10 is a cross sectional view taken along the line  10 — 10  of FIG.  9  and with the valve fully opened. 
    
    
     DETAILED DESCRIPTION 
     Referring now in detail to the drawings and initially primarily to FIG. 1, an internal combustion engine constructed in accordance with an embodiment of the invention is shown in part and is identified generally by the reference numeral  11 . The engine  11  is comprised of a main engine body that includes a cylinder head assembly  12 , a cylinder block assembly  13  and a crankcase forming member  14  that are connected together in any suitable manner. 
     The cylinder block  13  forms a plurality of cylinder bores  15 , which are disposed, in the illustrated embodiment, in an in-line arrangement. Although such an arrangement can be used, the invention can be employed with engines having other cylinder configurations such as V-type or opposed engines, as will become readily apparent to those skilled in the art. 
     Since the invention deals primarily with the valve actuating mechanism for the engine  11 , only those components associated with it are shown in detail in this perspective view. These include pistons  16 , only one of which is shown, which reciprocates in the cylinder bores  15  and are connected to drive a crankshaft  17  by means of connecting rods  18  in any well known manner. 
     In the illustrated embodiment, the engine  11  is of the four valve per cylinder type and each cylinder is provided with a pair of intake valves  19  disposed on one side of a plane containing the cylinder bore axis and a pair of exhaust valves  21  formed on the other side of this plane for each of the cylinder bores  15 . The intake and exhaust valves  19  and  21  are of the poppet valve type and are supported for reciprocation in a manner, which will be described later by reference to the remaining figures. 
     In the illustrated embodiment, the valves  19  and  21  are operated by means of a pair of overhead camshafts consisting of an intake camshaft  22 , having intake cam lobes  23 , and an exhaust camshaft  24  having exhaust cam lobes  25 . The camshafts  22  and  24  are rotatably journalled in a manner, which will be described. Each cam lobe  23  and  25  cooperates with a respective thimble type tappet  26 , which is supported for reciprocation in a manner, which will also be described later by reference to the remaining figures. 
     In the illustrated embodiment, the intake and exhaust camshafts  22  and  24  are driven at one end of the engine  11  by means of a timing drive which, in the illustrated embodiment, comprises a toothed timing belt  27  that cooperates directly with a sprocket  28  that is affixed to the exhaust camshaft  24  and which drives the exhaust camshaft at one-half crankshaft speed from a driving sprocket  29  fixed to this end of the crankshaft  17 . 
     On the other hand, the intake camshaft  22  is driven by a timing sprocket  31 , which drives the intake camshaft  22  through a variable valve timing mechanism  32 . In this regard, it should be noted that the described valve timing drive is only typical of one of many, which can be utilized in conjunction with the invention. For that reason, a detailed description of the camshaft drive mechanism is not believed to be necessary to permit those skilled in the art to practice the invention. Those skilled in the art can readily apply the invention to any known type of valve drive and valve actuating mechanism that includes cam lobes, which cam lobes operate thimble tappets either directly or through an intermediary method which may be likely to cause rotation of the thimble tappets in their supporting engine structure. 
     Referring now in detail primarily to FIGS. 2 through 5, a first embodiment of the invention is shown in detail. In this embodiment, the relationship of one of the thimble tappets  26  to a pair of the exhaust valves  21  is described. It is to be understood that the same type of structure is utilized in conjunction with the intake camshaft  22 . 
     Each of the valves, such as the exhaust valves  21 , is of the poppet type and includes a valve head  33  which valves a valve seat  34  formed in an appropriate manner in the respective side of the cylinder head. A stem  35  of the valve  21  is slidably supported in directly in the cylinder head member  12  or in a valve guide  36  which is cast, pressed or otherwise positioned therein. 
     A keeper retainer assembly  37  is fixed to the upper end of the valve stems  35  and is engaged by one end of a valve return spring such as a coil compression spring  38 . The other end of the valve spring  38  is engaged with the cylinder head member  12  in a well known manner so as to urge the respective valve  21  to its closed position. 
     An adjusting shim  39  is interposed between the tip of the valve stems  35  and an undersurface of the head  41  of the thimble tappet  26 . The tapped head  41  is formed at the upper end of a cylindrical body portion  42  and which is reciprocally supported in a bore  43  formed in the cylinder head member  12 . 
     As is typical in this practice, in a plane looking perpendicular to the cylinder bore axis, the tappet head portion  41  is formed with an arcuate curvature  44  that has a radius R (FIG.  2 ). Viewed in a perpendicular direction (FIG.  4 ), it will be seen that this curved surface  44  appears as a straight line. 
     The structure as thus far described may be considered to be conventional and as such, without more, could be subject to the problem of rotation of the thimble tappets  26  in their supporting cylinder head bores  23  which could cause wear of one or both components. 
     In accordance with the invention, therefore, and in this embodiment, and anti-rotation pin, indicated generally by the reference numeral  45  is provided. This anti-rotation construction pin  45  is, in this embodiment, comprised of a single anti-rotation pin  45  mounted in the cylinder head member  12  between the each of the pairs of tappet bodies associated with both the intake and exhaust valves of each cylinder. 
     This anti-rotation pin  45  is comprised of a larger diameter headed portion  46  that is engaged in a pair of machined semi-cylindrical recesses  47  formed in each of the adjacent portions of the tappet bodies  26 . A smaller diameter portion  48  extends upwardly in the area between the tappet bodies and is engaged at its upper end by a bearing portion  49  of the respective camshaft so as to retain it in the cylinder head  12  in the position shown in FIGS. 4 through 6. 
     The anti-rotation recesses  47  have an axial length such that the large diameter anti-rotation portion  46  of the pin  45  can traverse the length of the recesses  47  when the valves move between their fully closed positions as shown in FIG.  4  and their fully opened positions as shown in FIG.  5 . Thus, this structure, which precludes rotation, is not provided by any added material on the tappet bodies  26  and, in fact, they are provided with a reduced weight of reciprocation because of the formation of the recesses  46  therein. Also, because of the fact that the anti-rotation pins  45  are held in place by the camshaft bearing portion  49  no significant assembly problems are presented. 
     The cylinder head member  12  is formed with a bore  51  that will clear the smaller diameter portions  48  as well as the headed portions  46  of the pins  45  so as to facilitate assembly. 
     FIGS. 7 and 8 show another embodiment of the invention. This embodiment differs from that already described only in the construction and mounting of the anti-rotation locking pin. Therefore only two figures corresponding to FIGS. 4 and 5 of the previously described embodiment are believed to be sufficient to permit those skilled in the art to practice this embodiment. In these figures any components that are the same or substantially the same as the components already described have been identified by the same reference numerals. These components will be discussed further only in so far as is necessary to understand the construction and operation of this embodiment. 
     In this embodiment, rather than relying on the camshaft bearing surface  49  for holding the any-rotation device in position, a screw threaded connection is utilized between the anti-rotation locking pin, indicated generally by the reference numeral  71  in these figures. This locking pin  71  has a socket headed portion  72  which is sized so as to fit within the cylinder head bore  51  and permitted to be screwed into a tapped opening  73  formed in the cylinder head assembly  12 . A threaded portion  74  is formed below the socket head  72  for permitting this connection. 
     The socket head  72  is sized so as to fit into the recesses  46  of the tappet bodies  26 . As may be seen in FIG. 8, the head  72  is mounted in the cylinder head assembly  12  in a position so that it will cooperate with the tappet slots  47  through the full length of movement of the valves  21  between their opened and closed positions shown respectively in FIGS. 8 and 7. 
     In all other regards, this embodiment is the same, as that previously described and further description of it is not believed to be necessary to permit those skilled in the art to practice the invention. 
     In the embodiments as already described, the construction has been employed with four valve per cylinder engines and one anti-rotation pin either  45 ,  71  has been employed between two paired valves serving a single cylinder. Although this has the advantage of simplicity, it provides some lack of freedom in where the anti-rotation device may be located around the body of the tappet  26 . 
     FIGS. 9 and 10 show another construction that utilizes a locking pin that is threaded into the cylinder head, like that of the embodiment of FIGS. 7 and 8. Therefore, the locking pin and its parts in this embodiment are identified by the same reference numerals. In addition, the same references numerals have been utilized to identify the components already described and they will not be described again. 
     As may be seen, this embodiment shows the positioning of the anti-rotation pin  71  at a side of the tappet  26  that does not lie on the axis of rotation of the camshaft. Of course, other circumferential locations can be employed as should be readily apparent to those skilled in the art. 
     Thus, from the foregoing description it should be readily apparent that the described constructions provide a very good and simple arrangement for preventing rotation of the valve actuating tappets or lifters around their reciprocal axis due to the action of the cam lobes against the tappet faces. Of course, the foregoing description is that of preferred embodiments of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.