Patent Publication Number: US-8113158-B2

Title: Engine with variable valve actuating mechanism

Description:
This is a national stage application filed under 35 USC 371 based on International Application No. PCT/GB2007/050299 filed May 25, 2007, and claims priority under 35 USC 119 of United Kingdom Patent Application No. 0610633.0 filed May 31, 2006. 
     FIELD OF THE INVENTION 
     The invention relates to an engine with a valve actuating mechanism that uses two cams acting via a summation mechanism to operate the valves. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 6,941,910 shows how a summation lever can be used to combine the motion of two cam profiles in order to produce valve lift, and how the valve lift may be controlled by changing the relative phasing of the two cam profiles. The latter patent also teaches how phasing of the cam lobes relative to each other may be achieved by mounting them on the inner shaft and an outer tube of an assembled camshaft, termed an SCP (single cam phaser) camshaft, which has one set of lobes fixed for rotation with the outer tube and a second set fast in rotation with the inner shaft. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided an internal combustion engine having a valve mechanism that comprises an SCP camshaft operating two sets of valves, the first set of valves being operated via a summation rocker system such that the valve lift characteristic results from the combination of two cam profiles, the second set of valves having a valve lift characteristic that is different from that of the first set, wherein changing the valve lift characteristic of the first set of valves by varying the phase of the inner shaft of the SCP camshaft relative to the outer tube of the SCP camshaft serves additionally to alter the operation of the second set of valves. 
     The present invention is applicable to engines that use a single camshaft to actuate more than one set of valves e.g. intake and exhaust. The application of a cam lobe summation rocker system to one set of valves requires an SCP camshaft to be utilised in order to control the lift characteristic of this first set of valves. The invention takes advantages of the presence of an SCP camshaft to provide the opportunity to utilise any change in phase to bring about a change in the operation of a second set of valves. 
     The second set of valves may be actuated by a conventional rocker system, in which case changing the phasing of the SCP cam will bring about a simple phase change in the valve motion. 
     Alternatively, the second set of valves may be operated via a cam summation system, in which case the lift characteristics of both sets of valves may be changed concurrently. 
     Furthermore, a phaser with two outputs may be used at the front of the SCP camshaft in order to change its timing relative to the crankshaft, as well as the timing of the inner drive shaft relative to the outer camshaft tube. In this case, the two outputs of the phaser may either be independently controllable, or they may be linked such that they are phased in a fixed relationship to one another. 
     The invention has the following advantages when compared to existing designs: —
         The motion characteristic of two sets of valves may be changed in different ways using a single control system.   Control of two sets of valves represents only a small cost increase compared to having only one set of valves with variable opening characteristic.   The system provides a compact design solution.   Having only one control parameter reduces engine calibration complexity.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a side view of valve train system with one cam summation system combined with a conventional rocker system driven by a common SCP camshaft and phaser, 
         FIGS. 1A and 1B  are sections in the planes A-A and B-B of  FIG. 1 , 
         FIGS. 2 and 2A  are isometric views of the valve train of  FIG. 1 , 
         FIG. 2B  is an exploded view of part of the valve train of  FIG. 1 , 
         FIGS. 3 ,  4 ,  5 ,  6  and  8  show different valve timing regimes achievable by valve train system of the invention, 
         FIG. 7  is a side view of an alternative embodiment of the invention, 
         FIGS. 7A ,  7 B,  7 C and  7 D are respectively a section, an isometric view, an end view and an exploded view of a the embodiment shown in  FIG. 7 , and 
         FIGS. 9 and 9A  show isometric views of a still further embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     As both summation lever systems and SCP camshafts are well documented in the prior art, the ensuing description will assume that the reader is conversant with their principles of operation and the details of their construction. 
       FIG. 1  shows an assembled SCP camshaft  10  which, as best shown in the section of  FIG. 1A , is composed of an outer tube  10   a  and an inner shaft  10   b . A phaser  12  mounted on the front end of the SCP camshaft  10  has two outputs, one driving the outer tube  10   a  and the other the inner shaft  10   b  of the SCP camshaft. The phaser may be constructed, for example, as a vane type phaser. 
     The camshaft carries four cam lobes, namely a first cam lobe  14  that operates a first valve  16 , and three cams  18 ,  20   a  and  20   b  which together act on a second valve  22  by way of a summation lever system  24  which will be described in more detail below by reference to  FIG. 2B . As can be seen from  FIGS. 1A and 1B , the cams  14  and  18  are fixed for rotation with the inner shaft  10   b  of the camshaft by pins  30  and  32  that pass with circumferentially elongated slots in the outer tube  10   a  of the camshaft. The cam lobes  20   a  and  20   b , on the other hand are identical with one another and both are fast in rotation with the outer tube  10   a  of the camshaft. 
     The cam lobe  14  acts on the valve  16  through a rocker  34  (see  FIG. 1A ) which contacts the stem of the valve  16  at one end, is supported on a lash adjuster  36  at the other end and has a central cam follower in contact with the cam lobe  14 . 
     The cams  18 ,  20   a  and  20   b  act on the valve  22  through the lever system best shown in  FIG. 2B  which comprises a summation lever  38  and a rocker  40 . A central region of the bell crank summation lever  38  is pivotably connected to the rocker  40 . One end of the summation lever  38  carries a pair or cam follower rollers  42  which are rotatable about a common axis and are held in contact with the two cam lobes  20   a  and  20   b  by means of a spring  44  which acts on an axle of the rollers  42  by way of a cradle  46  carried by a telescopically collapsible guide pin  47  of the spring  44 . The other end of the summation lever  38  carries a second roller follower  43  in contact with the cam lobe  18 . The rocker  40  acts on the stem of the valve  22  at one end and its other end is supported by a lash adjuster  48 . 
     Phasing the inner drive shaft  10   b  relative to the outer tube  10   a  will change the phasing of the valve  16  operated by the conventional rocker  34 , and it will change the lift characteristic of the valve  22  produced by the summation system. 
     A variety of valve motion characteristics may be produced with a system of this kind, two examples being shown in  FIGS. 3 and 4 . In valve timing diagrams shown in all of the accompanying  FIGS. 3 to 6  and  8 , exhaust and intake and exhaust events that correspond with one another have been allocated the same reference numeral in the 100 and 200 series, respectively, and have been illustrated using lines that are matched in style (solid, dotted, chain dotted, etc). 
     In the example shown in  FIG. 3 , the cam summation rocker system is used to operate the exhaust valve in order to generate a controllable second exhaust lift event  102 ,  104  during the intake stroke  202 ,  204 . The intake valve is operated by a conventional rocker system and the intake valve timing is varied relative to the crankshaft as the characteristic of the secondary exhaust lift is changed. 
     In  FIG. 4 , the cams with the summation system act on the intake valves in order to generate a controllable second lift  212 ,  214  in the exhaust stroke  112 , 114 , whilst the exhaust valve has a conventional rocker system and is phased as the intake characteristic is adjusted. 
     It is important to note that in all embodiments of the invention, the range of SCP adjustment used to generate the second lift need only be a proportion of the full adjustment range of the SCP. 
     Furthermore, it would be possible to drive the SCP camshaft via a phasing system having two outputs, examples of which are described in EP 1234954 and EP 1030035. In the first of these patents, the phaser has two independently controllable outputs, and this would allow independent control of both the camshaft tube and the inner drive shaft relative to the engine crankshaft. In the second of these patents, the phaser has two outputs that move in a fixed relationship to one another, allowing the timing of both the camshaft tube and the inner drive shaft to be changed relative to the engine crankshaft in a fixed relationship. The advantage of the latter is that it only requires a single control input to control the timing of both the outer camshaft tube and the inner drive shaft of the SCP camshaft. 
     The use of a phaser with two outputs offers further flexibility to the valve train variations that may be achieved. Examples of these further options based upon the lift curves of  FIG. 3  are shown in  FIGS. 5 and 6 . In  FIG. 5 , the summation rocker system is used to produce a secondary exhaust valve opening, and the phasing of the intake valve is linked to the inner shaft of the SCP camshaft and moves with the closing timing of the secondary exhaust valve lift. 
     In  FIG. 6 , the phasing of the intake valve is linked to the outer tube of the SCP camshaft and hence moves with the exhaust valve opening timing. 
     A further design possibility would be to use a cam summation rocker system on both the intake and the exhaust valve, as shown in  FIG. 7 . This provides further possibilities for varying the motion of the two sets of valves. 
     The summation rocker systems pictured in  FIG. 7  are of a slightly different design from that shown of the embodiment of  FIGS. 1 and 2 . To avoid unnecessary repetition, components serving the same function as previously described have been allocated similar reference numerals but in the 300 series. 
     In this embodiment, the summation levers  338  have only two cam followers  342 ,  343  and a rocker shaft  348  is used to support the valve actuating rockers  340 . This arrangement may be beneficial in some applications as it reduces the number of cam lobes required from six to four, and reduces the overall width of the rocker system for each valve. It may also be convenient to use a torque spring  344  to control the motion of the summation rocker as shown in  FIG. 7D  in place of the compression spring  44  shown in  FIGS. 1 and 2 . 
       FIG. 8  shows the valve motion that could be achieved by using cam summation systems to achieve a controllable secondary exhaust lift and controllable opening duration on the intake valve. The additional exhaust lift only occurs at the two longest intake duration settings, and the exhaust valve has a single fixed event at the standard intake duration and at reduced intake duration settings. In this way, the exhaust valve lift is only varied over part of the SCP phasing range, whilst the intake is varied over the full range. 
     It would of course be possible to use a phaser with two outputs to control the timing of the whole SCP camshaft as well as controlling the relative timing of its two sets of cam lobes. This would allow the timing of the curves shown in  FIG. 8  to be varied with respect to the crankshaft timing as required. 
     Whilst the previous figures have illustrated how this invention may be applied to a single camshaft engine with two valves per cylinder (one intake and one exhaust), it is possible for the system to operate in an engine with more than two valves per cylinder, as shown in  FIG. 9 . 
       FIG. 9  shows how two cam summation rocker systems of the design described in EP 1426569 and U.S. Pat. No. 6,854,434 may be operated by a single SCP camshaft, and bridge pieces  410  may be used to transmit the rocker motion to a pair of valves. 
     It would of course be possible to replace one of the summation rocker systems in  FIG. 9  with a standard rocker system in order to produce the motion characteristics described in  FIGS. 3 to 6 .