Abstract:
A device for controlling the variation of the opening and closing times and durations of a valve ( 8 ) comprises an elastic means ( 18 ) acting upon an assembly consisting of a lever device ( 1 ) and a valve stem ( 11 ) not in the closing direction but in the opening direction of the valve ( 8 ). The assembly consisting of the lever device ( 1 ) and of the opening cam ( 5 ) and the closing cam ( 6 ) fulfils a dual function, one for opening the valve ( 8 ), the other for moving it back for its closure. The control device, which comprises a device for offsetting the angular position of the cam position relative to the crankshaft, allows to control the opening and closing duration of the valve ( 8 ) over a very wide range extending, for opening, from 210° to 350° of crankshaft rotation approximately, by varying the valve opening and closing times independently of each other. It is applicable to a wide range of engines.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a device for controlling the kinematics of at least one valve, the device comprising at least one opening cam and one closing cam, and at least one lever device cooperating with the valve and subject, together with the latter, to the action of an elastic member. 
   PRIOR ART 
   The variable control of valves, i.e. variable timing, is a complex problem that has often been approached. According to several recent studies, the majority of the systems suggested up to now comprise a limited variability of opening durations or do not offer a progressive variation of the opening durations. Certain electro-hydraulic systems offer a higher flexibility of the opening duration, but they suffer from the disadvantage of being very complex and are subject to technical problems that are difficult to solve, such as delays and the compressibility in the hydraulic circuits as well as the space consumption of their components. 
   SUMMARY OF THE INVENTION 
   Based on this state of the art, it is an object of the present invention to propose a control device as cited above which allows to control the opening and closing duration of the valve over a wide range (comprised, for the opening, between 210° and 350° of camshaft rotation approximately), while varying the opening and closing times of the valve(s) independently of each other. The implementation of this device may be provided for a wide range of engines. This object is attained by a control device wherein the elastic member constitutes a detent means acting upon the assembly composed of the lever device and of the stem of the valve in the opening direction of the valve, and in that the assembly comprising the rocker arm and the cam allows the opening of the valve and furthermore generates the return movement of said valve onto its seat for its closure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be described by way of non-limiting examples hereinafter with reference to the enclosed drawings where: 
       FIG. 1  schematically shows a first embodiment of a device of the invention with the valve in the closed position, 
       FIG. 2  shows the device of  FIG. 1  with the valve in the open position, 
       FIG. 3  shows a second embodiment of a device of the invention with the valve in the closed position, and 
       FIG. 4  shows the device of  FIG. 3  with the valve in the open position, 
       FIG. 5  shows an angular offset control for the cams of  FIGS. 1 to 4 , 
       FIGS. 5   a  and  5   b  are front views of the opening and closing cams in  FIG. 5 , 
       FIG. 6  shows a third embodiment of a device of the invention with the valve in the closed position, 
       FIG. 7  shows the device of  FIG. 6  with the valve in the open position, 
       FIG. 8  schematically shows the operation of the device and the superposed adjustment of the cams for a short opening, and 
       FIG. 9  schematically shows the superposed adjustment of the cams of  FIG. 8  for a long opening. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1 and 2  refer to an engine with a cylinder head comprising two valves and two common camshafts for intake and exhaust. A rocker arm  1  with its two sliders  2 ,  3  pivoting around its shaft  4  is controlled by two cams, namely an opening cam  5  and a closing cam  6 , the two cams rotating in opposite directions, as indicated by arrows  5 F,  6 F. Rocker arm  1  further comprises a fork  7  for controlling valve  8 , shown in the closed position in  FIG. 1  and in the open position in  FIG. 2 . 
   Opening cam  5  includes three distinct geometric portions: a first concentric portion Y-A (corresponding to the retention of valve  8  against its seat  10  and to the takeover of rocker arm  1  during the closed valve phase (large radius R 2  of the cam)), a second eccentric portion A-B (causing the opening movement of the valve), and a third concentric portion B-L (small radius R 1  of the cam). 
   In analogy, closing cam  6  comprises a first concentric portion K-B′ (zone of takeover of rocker arm  1  during the open phase of valve  8  (small radius R 3  of the cam)), a second eccentric portion B′-C (causing the closing movement of the valve), and a third concentric portion C-X, corresponding to the retention of valve  8  against its seat  10  (large radius R 4  of the cam). 
   Valve  8  is provided at its lower end with a tulip  9  adapted to press against a seat  10 , the tulip being followed by a stem  11  that is guided by a valve stem guide  12  and fastened by means of a locking device comprising a valve spring seat  13  cooperating with a circular clip  14  and sliding in a tubular valve retainer  15  whose upper part is fitted with a locking ring  16  allowing the closure of a non-referenced valve retainer chamber. Locking ring  16  is provided with a threaded bore for receiving an adjusting pin  16 G for adjusting the initial tension of a spring  17  adapted to act upon stem  11  of the valve (through elements  13 ,  14 ). 
   This damping spring  17  is accommodated in the space formed between the bottom of valve retainer  15  and valve spring seat  13 . The function of this damping spring is easily understood when comparing  FIGS. 1 and 2  and reading the discussion of the operation of the device (see below, point  10  of the present disclosure). 
   Inversely to valve controls of the prior art, an elastic member acting upon valve  8  and rocker arm  1  is formed of a valve relieving spring  18 . The latter tends to open the valve and allows the rocker arm, which retains the valve through valve retainer  15 , damping spring  17  and locking device  13 ,  14 , to follow the profile of the cams. Spring  18  is maintained by an upper spring seat  19 , on one hand, and on the other hand, by a circular shoulder  20  formed around valve retainer  15 . 
     FIGS. 3 and 4  show a variable timing system for an engine with a four-valve cylinder head with valve  8  in the closed and in the open position, respectively. One rocker arm  21  is common to two valves and pivots around a shaft  22 . The rocker arm comprises an arm  23  carrying a contact member  24  (e.g. a roller bearing or, as in the illustrated embodiment, a slider  24 ) and a fork  25  for actuating valve  8 . Opening cam  5  acts upon slider  24  of the arm of the rocker arm, whereas closing cam  6  acts upon a roller bearing  26  turning on an axle  27  mounted on the arm of the rocker arm provided with fork  25 . 
   In this embodiment for four valves per cylinder, the rocker arm is not actuated by a spring that is positioned in the axis of the valve stem but by a detent spring  28  one shank of which rests on a stop  29  while the other shank rests on a stop  30 . The arrangement of the rocker arm is such that detent spring  28  tends to open the valve, as illustrated in  FIG. 4 . This embodiment (common rocker arm for two valves) may also be conceived with the detent and damping systems described with reference to  FIGS. 1–2  and  6 – 7 . 
   The stem, retainer, guide, and seat of the valve are similar to those of the preceding embodiment, as well as the damping system with damping spring  31 , which is retained between a sleeve or threaded ring  16 B closing a non-referenced chamber of a support  32  and sliding on the valve extension rod  57  with threaded end, on one hand, and a support nut  33  that is blocked by a counternut  34 . Valve stem  11  and extension rod  57  are assembled by means of a coupling sleeve  35  that is retained between two counternuts  36 . 
     FIG. 5  shows a device for offsetting the angular position of the camshafts relative to the crankshaft, the device being known per se. Opening cam  5  and closing cam  6  are shown in cross-section in  FIG. 5  and in front view in  FIGS. 5   a  and  5   b , respectively, the cams being the same as those described above. Cam  5  is fastened on opening camshaft  37  and cam  6  on closing camshaft  38 , the camshafts being guided by respective bearings  39 ,  40 . Sleeves  41 ,  42 , provided with helicoidal internal grooves  43 ,  44  and comprising driving gears  45 ,  46  of the camshafts are fastened by dowel pins  47  of the gears on the shaft. Camshaft  38  is provided with a toothed pinion  48  that is chain driven by the crankshaft, the pinion being connected to driving gears  46  by fastening means  49 . 
   Control pieces  50  and  51  are fitted on a distance over the ends of the camshafts. The ends comprise an internal coupling by straight spline  52 ,  53  and an external coupling by helicoidal grooves  43 ,  44 . 
   In order to effect the mutual angular offset of cams  5 ,  6 , one or the other of the control pieces ( 50 ,  51 ), or both, are slidingly displaced to obtain a shorter or longer valve opening duration. 
   This control device is also applicable in other timing gear systems, e.g. with finger control or with direct actuation. 
     FIGS. 6 and 7  show an embodiment for a cylinder head with two or four valves where cams  5  and  6  are arranged on a single camshaft (see also  FIGS. 8 and 9 ). Valve  8  and its attachment as well as the elastic detent and damping members correspond to those of  FIGS. 1 and 2 . 
   Rocker arm  54 , oscillating around its shaft  55 , is similar to the one illustrated in  FIGS. 3 and 4  and comprises two sliders  56  of which only one is visible in the drawing, but it is understood that the control of the angular offset will have to be adapted correspondingly. 
     FIGS. 8 and 9  schematically show the operation and the adjustment of the superimposed combination of the opening cam and the closing cam, the cams being adjusted to result in a short opening of the valve. The positions of the cams for a desired opening duration of the valve are illustrated, where A is the starting point of the opening, B′, B are the points between which the valve is maximally open, and C is the closure end point. 
   According to the example illustrated in  FIG. 8 , the valve is closed on 240° and open on 120°. The arc X-Y represents minimum crossing of the cams when the latter are adjusted to the position of short opening of the valve. 
   In  FIG. 9 , the opening cam is angularly offset by 30° in its rotating direction and the closing cam is angularly offset by 30° in the opposite direction of its rotation. By these angular offsets, the opening time of the valve is shifted to 180° (respective angles being expressed in degrees of cam rotation). 
   It follows that in a general manner, and conversely to the traditional devices of the prior art, the elastic detent means  18 ,  28  acts upon the pair [lever device ( 1 ;  21 ;  54 )−valve stem ( 11 )] in the opening direction of the valve ( 8 ), whereas the pair [rocker arm device−opening cam  5 /closing cam  6 ] fulfills a double function, namely to allow the opening of the valve and to move it back to its seat  10  for its closure. Based on this original conception as described above, the operating mode may be demonstrated as follows (see particularly  FIGS. 1–2  and  8 – 9 ):
         1. The end of the phase in which valve  8  is closed is ensured by the cam surface corresponding to the profile A-Y of opening cam  5 .   2. The opening phase starts when slider  2  has passed point A of cam  5 .   3. Valve detent spring  18  expands and enables slider  2  to follow the eccentric profile A-B.   4. From the moment when slider  2  passes point A, and over about 8° of rotation of cam  5 , the valve remains closed and damping device  17  expands to its initial position (see point  10  below and  FIG. 1 ).   5. From the instant when this initial position is attained, the movement of cam  5  on rocker arm  1  causes the valve to be lifted from its seat  10 .   6. When slider  2  arrives at point B of cam  5 , slider  3  simultaneously contacts concentric surface K-B′ of closing cam  6  which actuates rocker arm  1  during the closing phase. The valve is now maximally open (see  FIG. 2 ).   7. The closing movement of the valve and the compression of detent spring  18  start when slider  3  arrives at point B′ of cam  6  and continue until the slider arrives at point C.   8. For a short opening of the valve, e.g. during 210° of crankshaft rotation, slider  3  contacts surface K-B′ exactly at point B′, and as points B and B′ coincide, the valve immediately starts to close again.   9. For a longer opening up to 350° of crankshaft rotation, three solutions are possible:
           A) either an angular offset of the closing camshaft contrary to the rotational direction, thereby retarding B′-C and thus the closing movement by increasing the distance between B′ and B by means of the angular offsetting device.   B) or an angular offset of the opening camshaft in the rotational direction, thereby advancing A-B and thus the opening movement by increasing the distance between B and B′ by means of the angular offsetting device of the opening camshaft.   C) or the simultaneous application of the two possibilities.   In all three cases, the valve remains maximally open during the time in which slider  3  moves from B to B′.   
           10. The valve contacts its seat  10  about 8° before slider  3  reaches point C. Damping device  17  is compressed—retainer  15  sliding valve spring seat  13  on stem  11 - and compensates the rest of the lifting movement imparted by cam  6  during the entire duration of the valve closure.   11. The valve closure phase is divided into two stages. In a first stage, the valve is kept closed and detent spring  18  compressed by the action of surface C-X of cam  6  on slider  3 .   12. During this action, slider  3  is in waiting position for the flush passage of point Y of cam  5 , which marks the second stage.   13. From then on, rocker arm  1  is taken over by surface A-Y of cam at least 5° of cam rotation before slider  3  arrives at X (in order to ensure a minimum cam crossing XY in the case of a short valve opening).   14. Thus, the transition from one cam to the other is free of shocks, and the cycle may start again.       

   The fact that the drives of the opening and of the closing camshafts are provided with an angular offsetting device with helicoidal grooves, on one hand, and that the profiles of the cams are in agreement, on the other hand, allows to vary the opening and the closing time of the valve independently of each other. Furthermore, the damping device ensures tightness between the seat and the valve without shocks in the timing gear and compensates for the lengthening of the valve due to thermal dilatation. 
   The cams can be mounted on their shafts in different ways and may be rotationally driven in the same direction. It is also possible to provide a respective shaft for each cam or a common shaft or common shafts. 
   Thanks to the original cam profiles, it is possible to obtain short ( FIG. 8 ) or long opening durations ( FIG. 9 ) or any other opening/closing durations between the extremes. Thus, in practice, the device operates as a “variable cam”, figuratively speaking.