Abstract:
An improvement is disclosed for an engine valve system with variable lift and duration of the type that includes two cams mounted coaxially, a summation rocker coupled to cam followers in contact with both cams and movable in proportion to the instantaneous sum of the lifts of the respective cams, and a valve actuating rocker pivotably coupled to the summation rocker and serving to open an engine valve in dependence upon the movement of the summation rocker. In the invention, at least one of the couplings of the summation rocker with the cam followers and with the valve actuating rocker incorporates an adjustable eccentric which is rotatable to enable the clearance within the valve system to be set.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuing application, under 35 U.S.C. §§120 and 363, of copending international application No. PCT/GB2009/050266, filed Mar. 23, 2009, which designated the United States and was published in English; this application also claims the priority, under 35 U.S.C. §119, of GB patent application No. 0806116.0, filed Apr. 4, 2008; the prior applications are herewith incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to an engine valve system that uses two cams to act on a valve by way of a summation mechanism. 
     BACKGROUND OF THE INVENTION 
       FIG. 1  shows a cam summation engine valve system as disclosed in U.S. Pat. No. 6,941,910. The valve system includes two cams  10  and  12  and a cam summation rocker  14 , herein also termed an “upper rocker,” having cam followers  16  and  18  in contact with both cams. A lower actuating rocker  20  is pivotably connected to the summation rocker  14  and acts, at one end, on a valve  22 , with its other end resting on a hydraulic lash adjuster  24 . An adjustable stop plate  26  is used to limit the expansion of the hydraulic lash adjuster  24  by setting the height of the pivot shaft  30  that connects the lower rocker  20  to the upper rocker  14 . The position of the lower rocker  20  is therefore defined by its contact with the tip of the valve  22 , and the expansion of the hydraulic lash adjuster  24  holding the pivot shaft  30  against the adjustable stop plate  26 . 
     Cam summation valve systems using hydraulic lash adjusters have required an adjustable stop, or a graded shim in order for the system clearance (and hence the valve lift) to be adjusted. The functions of this clearance adjustment are twofold. First, the expansion of the hydraulic lash adjusters is limited so that the correct amount of clearance is maintained in the system while the valves are closed. Second, the valve actuating rocker is held in contact with the tip of the valve by the expansion of the hydraulic lash adjusters and the clearance adjustment system so that any clearance must occur between one of the cam profiles and its respective follower(s). 
     G.B. Patent Application No. 0708967.5 (WO2008/139221), by the instant Applicants, describes a cam summation engine valve system as shown in  FIG. 2 . This figure shows a similar valve system to that shown in  FIG. 1 . In both drawings, like parts have been allocated the same reference numerals to avoid repetition. In  FIG. 2 , the valve actuating lower rocker  20  is mounted on a manually-adjustable pivot  32 . The valve lift is adjustable through a screw mechanism  34  and contact is maintained between the tip of the valve  22  and the lower rocker  20  at all times through a control spring  36 . 
     This configuration replaces the hydraulic-lash-adjusting elements with a mechanical clearance adjustment and maintains the correct amount of clearance in the system while the valves are closed. However, an adjustable pivot  32  is required to allow the amount of clearance in the system to be adjusted. In the absence of such adjustability, there would be no way to compensate for manufacturing tolerances, which may lead to significant variations in valve lift between cylinders, and potentially damaging impact forces between the components of the system. While it provides for clearance adjustment, the system of G.B. Patent Application No. 0708967.5 requires a significant amount of packaging space that may not be available in all engines. 
     Therefore, a need exists to overcome the problems with the prior art as discussed above. 
     SUMMARY OF THE INVENTION 
     The invention provides an engine valve system with variable lift &amp; duration that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that provides a more compact adjustment system, which, nevertheless, retains all of the benefits of manual adjustment. 
     With the foregoing and other objects in view, there is provided, in accordance with the invention, an engine valve system that includes a first cam, a second cam mounted coaxially with the first cam, a summation rocker adjacent to the first cam and the second cam, a first cam follower coupled to the summation rocker, in mechanical communication with the first cam, and movable in proportion to an instantaneous sum of a lift of the first cam, and a second cam follower coupled to the summation rocker, in mechanical communication with the second cam, and movable in proportion to an instantaneous sum of a lift of the second cam. The engine valve system further includes a valve-actuating rocker pivotably coupled to the summation rocker and operable to open an engine valve in dependence upon a movement of the summation rocker and an eccentric coupling the summation rocker to at least one of the first cam follower, the second cam follower, and the valve-actuating rocker, wherein the eccentric is adjustably rotatably operable to adjust a clearance between at least two components within the engine valve system. 
     In accordance with a further feature of the present invention, the eccentric forms at least a portion of the coupling between the summation rocker and the valve-actuating rocker. 
     In accordance with another feature, an embodiment of the present invention includes an adjusting mechanism mechanically coupled to and operable to select an angular position of the eccentric with respect to the valve-actuating rocker. 
     In accordance with an additional feature, an embodiment of the present invention includes an adjusting mechanism mechanically coupled to and operable to select an angular position of the eccentric with respect to the summation rocker. 
     In accordance with a further feature of the present invention, the eccentric forms at least a portion of the coupling between the summation rocker and at least one of the first cam follower and the second cam follower. 
     In accordance with another feature, an embodiment of the present invention also includes an adjustably lockable screw mechanism operable to maintain an angular position of the eccentric. 
     In accordance with a further feature of the present invention, the adjustably lockable screw mechanism is lockable only in predetermined discrete positions. 
     In accordance with yet another feature, an embodiment of the present invention includes a compliant member operable to prevent rotation of the screw mechanism while the engine valve system is in operation. 
     In accordance with a further feature of the present invention, the eccentric has a series of discrete adjustment positions. 
     In accordance with a yet one more feature of the present invention, the eccentric is maintained in a discrete position by the action of a compliant member. 
     In accordance still with an embodiment of the present invention, an engine valve system includes two cams mounted coaxially, a summation rocker coupled to cam followers in contact with both cams and movable in proportion to the instantaneous sum of the lifts of the respective cams, and a valve actuating rocker pivotably coupled to the summation rocker and operative to open an engine valve in dependence upon the movement of the summation rocker, wherein at least one of the couplings of the summation rocker with the cam followers and with the valve actuating rocker incorporates an adjustable eccentric which is rotatable to enable the clearance within the valve system to be set. 
     The present invention advantageously utilizes manual clearance adjustments for a cam summation system to provide clearance in the rocker system at a point in its motion cycle. By comparison, if hydraulic elements are used, their expansion needs to be limited. Many of the advantages that hydraulic elements offer in a conventional valve train are not relevant to cam summation systems, where the expansion of the elements is limited by a manual adjustment or a shim. As a manual adjustment method is already required, it is advantageous to apply the adjustment directly to the valve train system, instead of controlling the position of the valve train components indirectly by limiting the expansion of a hydraulic element. 
     Embodiments of the invention provide a manual adjustment system that is incorporated into the rocker mechanism and may be adjusted while the valve system is assembled into the engine. As with the invention described in G.B. Patent Application No. 0708967.5, the system uses a control spring to maintain contact between the lower rocker and valve tip throughout the operating cycle. 
     An eccentric, i.e. a shaft with two cylindrical surfaces having their axes offset from one another, engaged in the summation lever provides the adjustment of the valve system. This approach offers a lightweight and compact solution for adjusting the system which requires very little additional space compared to the known conventional summation valve systems. 
     Clearance adjustments may be made without the need to disassemble the camshaft and rocker system. The absence of hydraulic elements in the system means that consistent valve lift measurements can easily be taken and this allows the valve lifts of each cylinder to be adjusted and re-measured directly. 
     Additional advantages and other features characteristic of the present invention will be set forth in the detailed description that follows and may be apparent from the detailed description or may be learned by practice of exemplary embodiments of the invention. Still other advantages of the invention may be realized by any of the instrumentalities, methods, or combinations particularly pointed out in the claims. 
     Although the invention is illustrated and described herein as embodied in an engine valve system with variable lift &amp; duration, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Additionally, well-known elements of exemplary embodiments of the invention will not be described in detail or will be omitted so as not to obscure the relevant details of the invention. 
     Other features that are considered as characteristic for the invention are set forth in the appended claims. As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. 
     Before the present invention is disclosed and described, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The terms “a” or “an,” as used herein, are defined as one or more than one. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The terms “including” and/or “having,” as used herein, are defined as comprising (i.e., open language). The term “coupled,” as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. 
     As used herein, the terms “about” or “approximately” apply to all numeric values, whether or not explicitly indicated. These terms generally refer to a range of numbers that one of skill in the art would consider equivalent to the recited values (i.e., having the same function or result). In many instances these terms may include numbers that are rounded to the nearest significant figure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and explain various principles and advantages all in accordance with the present invention. The figures of the drawings are not drawn to scale. 
         FIG. 1  is an elevational side view of the prior-art valve system of U.S. Pat. No. 6,941,910. 
         FIG. 2  is an elevational side view of the valve system described in G.B. Patent Application No. 0708967.5 (WO2008/139221). 
         FIG. 3A  is a perspective view of a valve system of a first embodiment of the invention shown in its assembled state. 
         FIG. 3B  is a partially exploded perspective view of the valve system of  FIG. 3A . 
         FIG. 3C  is an elevational end view of the valve system of  FIGS. 3A and 3B . 
         FIG. 3D  is an elevational view of a section on the line I-I in  FIG. 3C . 
         FIG. 3E  is a partial view of the section of  FIG. 3D  drawn to an enlarged scale. 
         FIG. 4A  is a perspective view of a valve system of a second embodiment of the invention shown in its assembled state. 
         FIG. 4B  is a partially exploded perspective view of the valve system of  FIG. 4A . 
         FIG. 4C  is an elevational end view of the valve system of  FIGS. 4A and 4B . 
         FIG. 4D  is a section taken along the line II-II in  FIG. 4C . 
         FIG. 4E  is a section taken along the line III-III in  FIG. 4D . 
         FIG. 5A  is a perspective view of a valve system of a third embodiment of the invention shown in its assembled state. 
         FIG. 5B  is a partially exploded perspective view of the valve system of  FIG. 5A . 
         FIG. 5C  is an elevational side view of the valve system of  FIGS. 5A and 5B . 
         FIG. 5D  is a section taken along the line IV-IV in  FIG. 5C . 
         FIG. 5E  shows part of the section of  FIG. 5D  drawn to an enlarged scale. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward. It is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. 
     Referring now to  FIGS. 3A through 3E , one embodiment of the present invention is several views.  FIGS. 3A through 3E  show several advantageous features of the present invention, but, as will be described below, the invention can be provided in several shapes, sizes, combinations of features and components, and varying numbers and functions of the components. 
     The first embodiment of the invention, shown in  FIGS. 3A to 3E , has many elements in common with the Applicants&#39; G.B. Patent Application No. 0708967.5 (WO2008/139221), shown in  FIG. 2 . Once again, like reference numerals have been used to designate like components. In particular, an upper rocker  14  with cam followers  16  and  18  is used to operate two valves  22  and is coupled by a shaft  30  to two lower rockers  20  which actuate the respective valves  22 . The lower rockers are, in this case, supported at their ends remote from the valves  22  on fixed pivot posts  132 . A control spring  36  urges the upper rocker  14  downwards so that the lower rockers  20  are kept in contact with the valves  22  at all times. The control spring  36  also biases the upper rocker  14  clockwise as viewed so that the cam follower  16  is maintained in contact with its associated cam lobe at all times and the clearance in the system when the valves are closed and the cam followers are both on the base circles of their cams is developed between the cam follower  18  and its associated cam lobe. 
     The pivot shaft  30  that connects the lower rockers  20  to the summation rocker  14  is formed as an eccentric. The axis of the part of the pivot shaft  30  in contact with summation rocker  14  is offset from the axis of the part engaged in the two lower rockers  20 . This allows the position of the summation rocker  14  to be adjusted with respect to the valve actuating rockers  20  by rotation of the pivot shaft. 
     In order to set the position of the pivot shaft  30 , one of the valve actuating rockers  20  is fitted with an adjusting screw  40  that engages in a recess in the pivot shaft  30  as shown best in the detail view of  FIG. 3E . The pivot shaft  30  is subjected to a unidirectional torque while the valves are being actuated and so it is only necessary for the adjusting screw to react against this torque which will hold the face of the recess in the pivot shaft  30  in contact with the tip of the adjusting screw  40 . The eccentricity of the pivot shaft  30  used to give an acceptable adjustment range will be less than about 1 mm, and hence, the force on the screw need only be very modest to resist the resulting torque. 
     The detail view of  FIG. 3E  provides a detailed view of the adjusting mechanism. The adjusting screw  40  engages in the profiled recess in the pivot shaft  30  and is threaded into the valve-actuating rocker  20 . In order to prevent any rotation of the adjusting screw  40  while the system is in operation, the upper section of the screw is formed with a square section. A retaining spring  42  (see  FIG. 3B ), which is used to clip the valve-actuating rocker  20  onto its fixed pivot post  132 , engages with a flat side of the adjusting screw  40  such that turning the screw deflects the spring. While this allows the screw to be intentionally adjusted, the spring force will prevent the screw from rotating during operation due to vibration. 
     An additional embodiment of the invention, shown in  FIGS. 4A through 4E , uses the same adjustment principle as the previously-described embodiment, but, instead of locating an adjustment screw  40  in the valve actuator, an analogous adjustment screw  40 ′ is incorporated into the summation rocker  14 . This configuration could be advantageous in some applications where the cylinder head configuration prevents easy access to an adjusting screw located in the valve-actuating rocker  20 . 
     As with the previous embodiment, the pivot shaft  30  has a recess which is engaged by the adjustment screw  40 ′, as shown in  FIG. 4D . The adjustment screw  40 ′, once again, has a square section on its upper portion to allow it to be locked in a simple manner and to prevent it from turning when the engine is operating. In this case, the screw  40 ′ is locked by a sliding plunger  50  which mates with the flat faces on the screw  40 ′, and a spring clip  52  that locates around the summation rocker  14  and urges the plunger into its bore so that it remains in contact with the screw  40 ′. 
     The screw  40 ′ may be accessed via the clearance between the camshaft and the central portion of the axle  17  for the two cam followers  16   a  and  16   b  using a small hexagon key. The configuration allows the valve system clearance to be set directly using a feeler gauge to measure the clearance between the single cam follower  18  and its cam lobe. 
     A further embodiment of the invention, which is shown in  FIGS. 5A through 5E , incorporates an eccentric in a shaft coupling the cam follower  18  to the summation rocker  14 . The clearance between the cam follower  18  and its respective cam lobe may be adjusted by directly rotating an axle pin  60  mounted on the summation rocker  14 . The axle pin  60  has aligned cylindrical surfaces which engage aligned mounting holes  62  in the summation rocker  14  and a non-coaxial cylindrical surface that acts as a race for the cam follower  18  which is constructed as a needle bearing. The aligned cylindrical surfaces on opposite sides of the eccentric surface and the two holes  62  are of different size to permit the axle pin  60  to be slid into position. The axle pin  60  would otherwise either not be able to pass through one of the holes  62  or through the centre of the cam follower  18 . 
     The axle pin  60  has an enlarged head  70  which is centrally recessed to receive an implement, such as a hexagon key, to enable it to be turned. Such rotation alters the position of the eccentric cylindrical surface and sets the clearance in the valve system. 
     The head  70  is resiliently urged against the side of the summation rocker  14  by a spring disk  72 . As best seen in  FIG. 5E , the underside of the head  70 , that is to say, the side facing the summation rocker  14 , is formed with radial corrugations or grooves that engage a ball  74  located in a blind bore in the side of the summation rocker  14 . This ball catch mechanism defines predetermined adjustment positions as resistance will be encountered when rotating the head by the need to compress the spring disk  72  as the ball  74  passes from one groove to the next. 
     The spring disc  72  holds the head  70  firmly in contact with the ball  74  at all times in order to prevent any rotation while the valve system is in operation. As with the eccentric pivot shaft, the rotational forces on the adjuster are modest because it only uses a small eccentric distance. 
     It will be appreciated that further alternative embodiments may incorporate a pivot shaft having a series of adjustment steps rather than an adjustment screw. A variety of toothed or ratchet-type arrangements could be configured in order to achieve this objective. 
     The above described embodiments of the invention offer the following advantages as compared to existing configurations:
         No hydraulic elements are required.   No graded components such as shims are required as part of the valve system.   The measures for adjustment can be contained within the existing package space for the summation rocker.   The system can be configured such that no significant disassembly is required to adjust the valve lift.   Simple and repeatable measurement methods may be used to check valve lift.   Adjustments may be made and checked instantly.       

     The foregoing description and accompanying drawings illustrate the principles, exemplary embodiments, and modes of operation of the invention. However, the invention should not be construed as being limited to the particular embodiments discussed above. Additional variations of the embodiments discussed above will be appreciated by those skilled in the art and the above-described embodiments should be regarded as illustrative rather than restrictive. Accordingly, it should be appreciated that variations to those embodiments can be made by those skilled in the art without departing from the scope of the invention as defined by the following claims.