Patent Publication Number: US-6220213-B1

Title: Rocker arm installed in a cylinder head of a valve train of an internal combustion engine

Description:
FIELD OF THE INVENTION 
     The invention concerns a rocker arm installed in a cylinder head of a valve train of an internal combustion engine, said rocker arm comprising on a first end of an undersurface, a support for a cam-actuated push rod, on a second end of the undersurface, a contact surface for at least one gas exchange valve, and between the first and second ends, a cross-bore through which the rocker arm is pivoted on an axle, the rocker arm can be uncoupled in a region of the axle at least partially from a pivoting movement in a region of the contact surface when the rocker arm is subjected to a tilt loading by the push rod. 
     BACKGROUND OF THE INVENTION 
     In a rocker arm of the pre-cited type known form DE-A 33 13 437, the axle is connected to a clearance compensation element. A slide connected to a solenoid acts on the one-way valve of the clearance compensation element in opening direction, i.e. in a direction toward a high pressure chamber. During a positive loading of the one-way valve by the slide when the solenoid is active, the hydraulically maintained rigidity of the high pressure chamber is neutralized. Upon a lifting motion of the cam, the axle of the rocker arm can now be displaced toward the solenoid so that the rocker arm pivots about its contact surface on the gas exchange valve which thus remains closed. 
     A drawback of this prior art rocker arm is that it is supported by hydraulic means so that it possesses a certain degree of undesired elasticity in support direction in the region of its axle. It must be remarked further that the uncoupling unit comprising the solenoid and the slide is a mechanism of a relatively complicated structure and is expensive to manufacture. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to provide a rocker arm of the pre-cited type which eliminates the above-mentioned drawbacks. 
     This and other objects and advantages of the invention will become obvious from the following detailed description. 
     SUMMARY OF THE INVENTION 
     The invention achieves the above objects by the fact that the axle is guided in a slot of a pedestal fixed at least indirectly on the cylinder head, said slot extending in a direction toward the cylinder head, each of the axle and the pedestal comprising at least one reception for a total of at least one locking element, for uncoupling the pivoting movement, said locking element extends entirely in one of the receptions and for coupling the pivoting movement, the locking element can be partly displaced into the other of the receptions which is situated opposite thereto. 
     The measures proposed by the invention create a simple mechanism by which the rocker arm can be uncoupled at its end comprising the contact surface for the gas exchange valve at least partly, but preferably completely, from the lifting movement of the cam which actuates the push rod. The coupling means can be configured as at least one slide, but in a preferred embodiment, the coupling means comprises three slides. 
     The stop proposed by the invention for the axle on the cylinder head-proximate end of the slot creates an exact definition of the position of the receptions for the locking elements (slides) in the base circle phase of the actuating cam. 
     According to a further proposition of the invention, a spring means acts on the axle in valve direction. In the run-off phase of the cam, this spring means effects in a simple manner, a re-displacement of the axle together with the rocker arm out of the uncoupled state. In this way, the rocker arm is maintained together with the push rod in permanent contact with the cam (lost motion effect). 
     Advantageously, the spring means is installed in the slot and is supported at one end on this slot and at the other end, on a top surface of the axle. 
     Although it is conceivable to arrange the receptions for the coupling of the axle to the pedestal at an inclined position relative to the rocker arm, it is preferred to have these receptions extend in the longitudinal direction of the rocker arm. The scope of the invention also extends to a locking element in the form of one single slide but it is preferable to arrange a slide in each reception, in which case, the slide in the axle extends, in the uncoupled state, over the entire length of its reception. 
     In a preferred embodiment of the invention, the entire assembly of slides is displaced in at least one direction of displacement, for instance, in the uncoupling direction, by hydraulic medium pressure. In the other direction (coupling direction), the slide assembly may be displaced by the force of a spring means such as at least one compression spring. Thus, in the absence of hydraulic medium pressure, for instance when the engine has just been started, the rocker arm is in a coupled state and the gas exchange valve concerned can open. 
     According to still another feature of the invention, the servo medium is routed to an end face of one or both of the outer slides through at least one channel for each slide arranged in the pedestal and communicating with a supply in the cylinder head. Another possibility is to route the hydraulic medium to the respective slide through a duct extending along the axle. 
     The compression spring proposed as a displacing means for the slides may be replaced with an electromagnetic, magnetic or other similar means. 
     According to a final proposition of the invention, the two ends of the axle may project out of the rocker arm and each end may be guided in a slot of a separate pedestal. 
     The invention will now be described more closely with reference to the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a valve drive having a rocker arm and an actuating push rod, and 
     FIG. 2 is a cross-sectional view of the rocker arm. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a valve drive  1  in a schematic representation. This valve drive  1  comprises a cam  2  which actuates a push rod  3 . The push rod  3  acts on an end  4  of an undersurface  5  of a rocker arm  6 . Another end  7  of the rocker arm  6  comprises a contact surface  8  for acting on a gas exchange valve  9  (see also FIG.  2 ). 
     Between the two ends  4 ,  7 , preferably in the region of its central transverse plane, the rocker arm  6  comprises a cross- bore  10 . Through this cross-bore  10 , the rocker arm  6  is pivoted on an axle  11 . The axle  11  is guided at both its ends within a slot  12  of a pedestal  13  that is fixed on a cylinder head (not shown). A top surface  14  of the axle  11  is arranged at a distance from a cylinder head-distal end  15  of the slot  12 . A spring means  16  (in the present embodiment, a compression spring) is constrained within the slot  12  between the end  15  of the slot  12  and the top surface  14  of the axle  11 . 
     FIG. 2 further discloses that the axle  11  comprises a reception  17  extending in lever direction. In the present case, the reception  17  is a through-bore. Two further receptions  18 ,  19  arranged in opposing sections of the pedestal  13  are aligned to the reception  17 . A locking element  20 ,  21 ,  22 , configured in the present case as a piston-like slide, extends in each of the receptions  17 ,  18 ,  19 . The length of the locking element  20  is equal to the length of its reception  17 . The locking element  22  arranged in the pedestal  13  is urged toward the locking element  20  by the force of a spring means  23  which, in the present case, is a compression spring. A pressure chamber  25  is arranged in front of an end face  24  of the other locking element  21 . Hydraulic medium can be conducted into this pressure chamber  25  for displacing the entire assembly comprising the slides  20 ,  21 ,  22 . For this purpose, the pressure chamber  25  communicates with a channel  26  extending through the pedestal  13 . Hydraulic medium is fed into the channel  26  from a supply in the cylinder head (not shown). 
     As can also be seen in FIG. 2, the inner end faces  29 ,  30  of the locking elements  21 ,  22  are in permanent contact with the outer end faces  27 ,  28  of the locking element  20 . 
     The rocker arm  6  is shown in FIG. 2 in its coupled state. Due to the coupling of the axle  11  to the pedestal  13  at a cylinder head-proximate end of the slot  12 , the lifting motion imparted to the push rod  3  by the cam  2  is transmitted by the rocker arm  6  in a known manner to the gas exchange valve  9 . If the said lifting motion of the cam  2  is to be uncoupled, the pressure of the hydraulic medium in the channel  26  is raised during the base circle phase of the cam  2  so that the locking elements  20 ,  21 ,  22  are displaced toward the reception  19 . This process is ended when the end faces  27 ,  28 ,  29  extend directly at the slot  12 . At the beginning of cam lift, the rocker arm  6  is displaced, against the force of the spring means  16 , about its pivot point which is now situated in the region of the contact surface  8 . During this time, the axle  11  executes an axially upward movement in the slot  12 . The gas exchange valve  9  thus remains closed. 
     If a renewed transmission of the lifting motion of the cam  2  to the gas exchange valve  9  is desired, the pressure of the hydraulic medium in the channel  26 , and thus also in front of the outer end face  24 , is reduced during a base circle phase of the cam  2  during which the axle is in the position shown in FIG. 2, so that the entire assembly comprising the locking elements  20 ,  21 ,  22  is displaced toward the pressure chamber  25  by the force of the spring means  23 . When the position shown in FIG. 2 is attained, the desired coupling of the axle  11  to the pedestal  13  is accomplished. The rocker arm  6  now follows the lift of the cam  2  in the usual manner and transmits this lift to the gas exchange valve  9 . 
     In the uncoupled state of the axle  11 , the spring means  16  assures a permanent support of the rocker arm  6  and the push rod  3  on the actuating cam  2  particularly in the run-off phase of the cam. At the same time, this assures the alignment of the receptions  17 ,  18 ,  19  required for the coupling function of the locking elements  20 ,  21 ,  22 .