Abstract:
a generally conventional lash adjuster is modified by incorporating a coaxially oriented hydraulic control piston assembly within the guide body. The control piston normally fixes latch means, such a plurality of hard spheres, in multiple detents loaded in compression with the other components, to provide a rigid stop, but when the control piston is hydraulically pressurized, the detents are overcome and the piston assembly provides a resilient or soft stop that accommodates extended displacement (retraction) of the lash adjuster within the guide. The hydraulic actuation is preferably implemented with a three-way solenoid valve or the like, for controlling high-pressure oil to a gallery and associated inlet ports for the control piston assembly. In the typical implementation of the invention, the piston need have only two operational positions-denergized to establish the detent or hard stop condition, or fully energized to establish the valve deactivation position. With all of preferably four detents in quadrant symmetry and associated components in compression, side loading is avoided. Moreover, with the present invention, backlash is also avoided.

Description:
BACKGROUND  
         [0001]    The present invention relates to hydraulic lash adjusters for internal combustion engines.  
           [0002]    Automobile engines use only a small fraction of their rated power during most of the running time. It is known that increased fuel economy can be achieved by reducing the air pumping losses to the engine cylinder during steady state running, if in particular, some of the engine cylinders are deactivated while the other cylinders are kept active.  
           [0003]    There are several ways to achieve this cylinder deactivation. One way is a collapsible hydraulic lash adjuster, whereby engine valves are selectively deactivated. A typical hydraulic lash adjuster is a very simple device, consisting basically of a hydraulic cylinder and piston assembly, mounted either in series or in parallel with the valve train. The working chamber of this lash adjuster is connected to the engine lube oil circuit via a one-way check valve. During the time while the engine valve stays open, the valve closing forces are supported exclusively by the column of lube oil trapped in the chamber. Because of the increased pressure level, some of the initial lube oil charge leaks out, shortening the valve train length and insuring proper seating of the valve. Once the valve is seated and the valve closing force is supported by the valve seat, the pressure in the chamber drops. The gap created by the leakage is then quickly refilled via the one-way (no return) valve from the lube oil circuit. By elimination of the gap there is no significant acoustic noise generated and any seat wear is compensated.  
           [0004]    During the engine valve active cycle (valve open), collapsing of the lash adjuster piston assembly is prevented by a lateral latching pin, locked in a corresponding bore of the outer sleeve. During the de-activation cycle, lube oil from a secondary circuit pushes the latching pin out of engagement (against a reset spring) and the lash adjuster carrier, from that point on, will not be able to support the valve train forces and the valve will remain closed (and by that de-activated). The motion of the valve train generated by the cam is instead absorbed by the spring(s) mounted below the lash adjuster carrier.  
           [0005]    The disadvantages of this design are, first, difficulties associated with the latching pin to find its target bore during the very short time available for re-activation (especially critical at higher speed) and, secondly, the high bending (shearing) forces the pin and its retaining bore are exposed to.  
         SUMMARY OF THE INVENTION  
         [0006]    According to the present invention, the hydraulic lash adjuster is modified so that, upon receipt of a valve deactivation signal, the lash adjuster stop limit more reliably and consistently changes from a hard stop to a soft stop. As a result, the excess force stored in the valve closure spring, displaces the lash adjuster through the soft stop such that the tappet pivot point on the lash adjuster is also displaced to a position where the overhead cam acts with reduced force on the roller finger. Thus, the valve does not open during any portion of the cam shaft rotation. Upon denergization of the lash adjuster, the pivot point for the finger arm returns to the normal position, the lash adjuster encounters a hard stop, and the cam can overcome the valve closure spring to open the valve according to the cam timing.  
           [0007]    In essence, a generally conventional lash adjuster is modified by incorporating a coaxially oriented hydraulic control piston assembly within the guide body. The control piston normally fixes latch means, such a plurality of hard spheres, in multiple detents loaded in compression with the other components, to provide a rigid stop, but when the control piston is hydraulically pressurized, the detents are overcome and the piston assembly provides a resilient or soft stop that accommodates extended displacement (retraction) of the lash adjuster within the guide. The hydraulic actuation is preferably implemented with a three-way solenoid valve or the like, for controlling high-pressure oil to a gallery and associated inlet ports for the control piston assembly. In the typical implementation of the invention, the piston need have only two operational positions-denergized to establish the detent or hard stop condition, or fully energized to establish the valve deactivation position.  
           [0008]    With all of preferably four detents in quadrant symmetry and associated components in compression, side loading is avoided. Moreover, with the present invention, backlash is also avoided.  
           [0009]    More particularly, during high power operation (engine valve active) a substantially cylindrical lash adjusting tappet insert is supported by a ring of balls located in one or more cross holes in the lower portion of the tappet body, engaging with a corresponding annular groove in the guide body bore. The hydraulic control piston is located on the centerline of the tappet body and, energized by its own return spring, keeps the balls spread apart so long as there is no pressurized oil present in the control gallery or chamber. All components supporting the valve actuation reaction forces are loaded in compression in a similar way to a ball bearing, which is very advantageous as far as wear and life expectancy are concerned.  
           [0010]    Once the pressurized lube oil is switched on, hydraulic force will overpower the control piston return spring force and move the control piston in the downward direction, allowing the balls to slide down the ramp of the annular groove and by that move towards the center and release the tappet. In this position, the only force trying to push the tappet up is the force of the tappet return spring (deactivation spring) located in the lower portion of the tappet, which is much smaller than the force necessary for valve actuation and by that preventing opening of the associated engine valve.  
           [0011]    In order to reduce the contact stress (Hertzian stress) at the most critical point, the upper portion of this hydraulic control piston is preferably shaped somewhat like a compound pyramid, defining four symmetric pairs of upper and lower ramps. Upon activation of the control piston, the balls move from support at the lower ramps to support at the upper ramps. At the same loads the contact stress between a ball and a flat is much smaller than the contact stress between a ball and a cylinder. Also the included angle of both ramps (lower and upper) can be designed in such a way as to minimize resulting reaction force at the ball/ramp interface. In a similar way the locking surfaces (lower ramp) of the control piston can have a small included (self-locking) angle to eliminate backlash during the valve active (balls engaged) period. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The preferred embodiments of the invention will be described below with reference to the accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 is a partially sectioned view of a portion of an internal combustion engine, showing an exhaust valve opened against its valve spring by the force transmitted from a lobe on the cam shaft, through a pivotable finger arm to the sliding surface at the top of the valve stem, with the lash adjuster according to the invention configured in the normal, deactivated condition to provide a fixed pivot point at the other end of the finger arm;  
         [0014]    [0014]FIG. 2 is a view similar to FIG. 1, showing the cam shaft rotated to retract the lobe acting on the finger arm, whereby the free end pivots clockwise relative to the position shown in FIG. 1 about the normal fixed pivot point of the lash adjuster, such that the valve spring raises the valve stem and the valve member closes against the valve seat;  
         [0015]    [0015]FIG. 3 is a view similar to FIG. 2, showing the result of activating the engine valve deactivation device (lash adjuster) according to the present invention, thereby lowering the finger arm pivot point such that even when the lobe portion of the cam engages the arm, the arm does not pivot sufficiently against the valve stem to open the valve;  
         [0016]    [0016]FIGS. 4A, B, and C show the lash adjuster modified according to the preferred embodiment of the invention with a compund-pyramid-like control piston, in the normal, “hard stop” configuration corresponding to FIGS. 1 and 2;  
         [0017]    [0017]FIGS. 5A and B, show the lash adjuster of FIG. 4, in the activated, or “soft stop” configuration;  
         [0018]    [0018]FIG. 6 shows an alternative form of the control piston;  
         [0019]    [0019]FIG. 7 shows a lash adjuster incorporating the control piston of FIG. 6 (with the ramp angles exaggerated); and  
         [0020]    FIGS.  8 A-F illustrate the phasing of the tappet deactivation for the embodiment of FIG. 7. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    [0021]FIG. 1 is a partially sectioned view of a portion of an internal combustion engine  10 , showing an exhaust valve  12  opened against the valve spring  14  by the force transmitted from a high lobe  16  on the cam shaft  18 , through a pivotable finger arm  20  to the sliding surface at the top  22  of the valve stem  24 , with the lash adjuster  26  according to the invention configured in the normal, deactivated condition to provide a fixed pivot point  28  at the other end of the finger arm  20 .  
         [0022]    [0022]FIG. 2 is a view similar to FIG. 1, showing the cam shaft  18  rotated to retract the high lobe  16  so that the low portion  16 ′ acts on the finger arm  20 , whereby the free end  30  pivots clockwise relative to the position shown in FIG. 1 about the normal fixed pivot  28  point of the lash adjuster, such that the valve spring raises the valve stem and the valve member  32  closes against the valve seat  34 .  
         [0023]    [0023]FIG. 3 is a view similar to FIG. 2, showing the result of activating the lash adjuster according to the present invention, thereby retracting the finger arm pivot point  28 ′ such that even when the high lobe portion  16  of the cam engages the arm  20 , the arm does not pivot sufficiently against the valve stem  24  to open the valve  32 .  
         [0024]    [0024]FIGS. 4A, B, and C show the lash adjuster  26  modified according to the preferred embodiment of the invention with a pyramid-like control piston assembly  36 , in the normal, “hard stop” configuration corresponding to FIGS. 1 and 2. The lash adjuster  26  comprises a conventional main or primary piston assembly  38  and a secondary or control piston assembly  36  that are both situated within a guide body  44 . In the illustrated embodiment, a unitary cylinder unit  42  functions as a tappet and defines both the primary cylinder  42 A and the secondary cylinder  42 B.  
         [0025]    The main or primary piston assembly  38  comprises a first piston  40  situated within the primary cylinder  42 A and operates in the conventional manner described in the Background. A primary hydraulic circuit provides hydraulic fluid from primary inlet gallery  62  and the associated port through the guide body  44 , to port  60  in the first cylinder  42 A for the purpose of adjusting the axial position of the primary piston  40  relative to the first cylinder  42 A. As is conventional, the first piston  40  has a passage  50  normally closed by check valve  52  with associated ball spring and seat  54 . The seat is urged against the base of the first piston  40  by another spring  54 A supported by end wall  56 . In the illustrated form the first piston has a hollow center  46  leading to a vent  48  in the head. Below the head, a narrower neck is captured within an aperture in sleeve  64 , which is in turn fixed to the upper end of the first cylinder  42 A.  
         [0026]    In this manner, the projection of the first piston  40  from the top of the guide  44 , indicated at  100 , can be adjusted by adjusting the projection  102  of the first piston  40  relative to the first cylinder  42 A.  
         [0027]    According to the invention, the second piston assembly  36  is selectively actuated, by a second hydraulic circuit, for permitting a “soft” retracting the first piston assembly  38  within guide body  44 , thereby decreasing the projection  104  of the cylinder  42 A from the guide body  44 . In the illustrated embodiment, where the first cylinder  42 A and second cylinder  42 B are integral with cylinder unit or tappet  42 , displacement of the second piston assembly  36  also displaces the primary piston assembly and with it, the first piston  40 . To the extent the second piston assembly  36  is displaced (retracted), or reaches a resilient end position, the first piston assembly likewise achieves a resilient retracted position within the guide  44 .  
         [0028]    When the cylinder unit  42  is in the retracted (activated) position the pivot point  28 , shown in FIGS. 1 and 2, is displaced downward as shown at  28 ′ in a FIG. 3, thereby altering the leverage as between the lobe  16  and the arm  20  such that the lobe cannot supply sufficient force on the arm to overcome the valve spring  14  and thereby open valve  32 . With the invention, during the activated condition the pivot point with the cam position shown in FIG. 2 is the same as when the lash adjuster is deactivated, but with the cam position shown in FIG. 1 the “soft stop” moves the pivot point downward to the position shown in FIG. 3.  
         [0029]    In the embodiments of FIG. 4, the cylinder unit  42  has a solid central region between piston cylinders  42 A and  42 B, except that two through bores intersect at right angles to form a hydraulic control gallery or chamber  66  immediately surrounding the centerline of the cylinder unit as well as forming four cylindrical slots for receiving a respective four rigid balls  70  having substantially the same diameter as the diameter of the cross bores. At the plane oriented transversely to the centerline and passing through the centers of the cross bores and balls  70  (i.e., as shown in FIG. 4B), the guide body  44  has a respective four arcuate detents  68 , preferably formed by an annular groove along the inside surface of the guide body  44 .  
         [0030]    The balls  70  are supported in the bores at lateral positions such that the lower curvature on each detent forms a rigid stop  92  that maintains a fixed projection of the first cylinder  42 A from the top of the guide body  44 , as indicated at  104 . The balls  70  are urged against the rigid stops  92  by the head  94  of the second, or control piston  74 . In particular, the steep lower slope  96  and ledge  106  on the piston head  94 , in combination with the upward bias of piston spring  82 , keep the balls  70  in the latched position associated with the normal valve operation as explained above with respect to FIGS. 1 and 2.  
         [0031]    The secondary piston assembly  36  has secondary cylinder  42 B with open bottom  78  wherein the outer diameter of the second cylinder is less than that of the first cylinder  42 A below the central region containing the cross bores. The portion  90  of the cylinder unit immediately below the cross bores not only defines a shelf or track at the lower bore wall on which the balls can be supported (as more fully described below), but also defines a shoulder or flange against which the cylinder spring  84  biases the cylinder unit upwardly. Whereas the lower curvature  92  of the detents provides a rigid stop preventing downward movement of the cylinder unit  42  relative to the guide body  44 , in opposition to downward forces applied at the head of the first piston  40 , the upper curvature  92 ′ of the detents provides a rigid stop in opposition to the upward bias on the cylinder unit provided by the cylinder spring  84 , which is seated  86  at the bottom of the cylinder unit  42 .  
         [0032]    When the latching components are released, as will be described more fully below, the cylinder spring  84  bears all the downward forces acting via the first piston  40  through the cylinder unit  42 , and provide the desired provides soft (i.e., resilient) stop, whereby the combustion cylinder valve  32  remains closed throughout the camshaft rotation. The valve is thus “deactivated” when the second cylinder assembly  36  is “activated” in the following manner. Hydraulic fluid is introduced through the secondary inlet port  72  in the guide body  44 , thereby passing through the annulus  68  at the inside wall of the guide body and pressurizing the secondary gallery or control chamber  66 . This pressurization acts on the head  94  of the control piston  74 , urging it downwardly against the bias of the piston spring  82 , which is mounted in seat  80  at the lower end of the secondary cylinder  42 B and which is also seated within the hollow body  108  of the piston. As the control piston moves downwardly within the piston chamber  76 , the lower ramps  96  ride on the lower half of the balls, such that the balls remain substantially stationery. However, upon further movement of the control piston, the balls contact the upper slopes  98  which have a significantly less acute angle, whereby the balls move laterally inward, toward the centerline.  
         [0033]    When the control piston is fully retracted within its cylinder  42 B the balls have moved inwardly away from the detents such that, due to the high pressure in the control chamber  66 , a downward force on the cylinder unit  42  (due to the cam lobe  16  acting via arm  20  on piston  40  per FIG. 1) causes of the balls to roll radially inwardly on the shelf  90  as the balls contact the inner wall of the guide body  44  below the detents  68 . This downward movement of the cylinder unit  42  is now unrestricted by the balls and continues downwardly against the bias of spring  84  until (at the limit if necessary) the second cylinder  42 B bottoms out at the lower end of the guide body  44 . Port  88  vents the fluid in the lower portion of the guide body  44  volume.  
         [0034]    [0034]FIGS. 5A and B, show the lash adjuster at the retraction limit of the activated, or “soft stop” configuration. Whereas the section view in FIG. 4B shows the relationship of the balls  70  to the groove  68  in guide body  44 , the control chamber  66 , and the upper slope  98  of the control piston in the normal, deactivated condition associated with FIG. 4A, FIG. 5B shows the same relationship when the cylinder unit  42  is in the fully retracted limit, condition shown in FIG. 5A.  
         [0035]    It can be appreciated that, as between the conditions shown in FIG. 4A and FIG. 5A, the total projection  100  of the first piston  40  relative to the guide body  44  has been to changed to  100 ′, by the distance  110  that the cylinder unit  42  and associated latching balls, have moved downwardly within the guide body  44 . It should be appreciated further that in FIG. 5A, the control piston  74  may have bottomed out, but this need not be a hard stop, thereby maintaining resiliency in the relationship between the cylinder spring  84  and the force applied to the cylinder unit of the of the flange or the like at  90 .  
         [0036]    When normal operation of the lash adjuster is desired, the hydraulic pressure in the secondary gallery  66  is released. The control piston  74  will rise within the secondary cylinder and the cylinder spring will displace the cylinder unit upwardly, until the balls reach the detents and return to the condition shown in FIG. 4A.  
         [0037]    In some applications it could happen that while the exhaust valve is deactivated the pressure entering the primary piston assembly via  62 ,  60 ,  46  (see FIG. 4A) that provides for normal adjustment of the hard stop could spread the lash adjuster to the point that it would prevent proper reengagement and thus prevent valve reactivation.  
         [0038]    [0038]FIGS. 6, 7 and  8  show another embodiment  112 ,  114  incorporating an anti-pump-up device, which should prevent this. The differential hydraulic forces due to pressure/area relationships, can be designed to always have a positive valve closing force component. FIGS. 7A and B show a lash adjuster incorporating the control piston of FIG. 6 (with the ramp angles exaggerated). The control piston  112  has a rounded top forming a valve seat  116  to be discussed in greater detail below, and upper ramps  118  and lower ramps  120  which form a smaller included angle than the analogous slopes  98  and  96  shown in FIG. 4. In particular, they form an acute angle that is substantially symmetric relative to a plane extending perpendicularly to the device centerline. As with the previous embodiment, the control piston  112  has a substantial cylindrical, hollow body portion  130  extending below the ledge portion  122 . As in the previous embodiment, cylinder unit or unitary tappet  136  is situated in a guide body  44 , with the cylinder unit defining upper or primary cylinder  136 A and lower, or secondary cylinder  136 B, with a substantially solid intermediate region in which cross bores intersect at a central control chamber  138 .  
         [0039]    However, in this embodiment, vent  124  with associated seat  126  is formed in the material web between the first cylinder  136 A and the control chamber  138 . The head of the control piston  112  forms a valve surface or seat  116  for selectively closing or opening the vent  124 . The presence of this vent provides an anti-pump-up feature that prevents the high pressure in the primary cylinder  136 A from spreading the walls of the guide body  44  to the extent that it would prevent exhaust valve reactivation.  
         [0040]    FIGS.  8 A-F illustrate the phasing of the deactivation of the cylinder unit or tappet  136  for the embodiment shown in FIG. 7. FIG. 8A corresponds to the operational condition wherein the exhaust valve is active for sequentially opening and closing the exhaust port of the combustion chamber, and the secondary hydraulic circuit is deactivated with respect to the secondary piston assembly. In this operating mode, the force imposed at the top of the primary piston  40  at the pivot surface is transmitted through the primary piston assembly to the latching balls  70  which are trapped against hard stop surface  142 . The lower slope  120  of the control piston contacts the blocking balls in this hard stop condition. The force component generated by the exhaust valve actuation reaction force will keep the venting valve  116  closed. It should be appreciated that an alternative to the illustrated one-piece control piston with integral valve  116 , could equivalently be implemented using a control piston with captured ball valve member at the top. The lower slopes  120  of the control piston adjacent the apex or hilltop of the acute angle formed by the upper and lower slopes, does not provide a positive downward force against the blocking balls, but rather merely contacts the balls to assure that they maintain their positions laterally outward against the lower curvature  142  of the detents  168  while resting on the shelf  90 .  
         [0041]    When the secondary oil gallery is pressurized, thereby pressurizing the control chamber  138 , the control piston  112  separates from the vent seat  126  and begins moving downwardly against the force of piston spring  132 . While the roller of the arm  20  travels on the cam base circle (see FIG. 2), the dominant force acting on the tappet  136  is the upward force of deactivation cylinder spring  134 . As the valve  116  cracks open, the high pressure in the primary cylinder  136 A collapses, allowing the blocking balls to travel up the lower ramp  120 . With the control piston traveling downward, the apex passes the top of hill position  144  shown in FIG. 8C until the blocking balls roll inwardly onto the upper slopes  118  as shown in FIG. 8D. As in the previously described embodiment, the main hydraulic activation for control chamber  138  is pressurization through port  72  by a secondary hydraulic circuit.  
         [0042]    At the condition shown in FIG. 8C, where the balls are at the maximum laterally outward position, the balls at their 3:00 position contact the apex of the control piston angle, and at the 9:00 position contact the surfaces of the detents that are furthest from the device centerline. The actuating pressure keeps the control piston moving downwardly to the position shown in FIG. 8D whereby the balls remain within the diameter of the tappet  133  and the tappet can resiliently accommodate downward forces via cylinder spring  134  to keep the engine valve deactivated.  
         [0043]    As shown in FIGS. 8E and F, when the pressure in the secondary gallery  138  collapses, the latching piston return spring  132  loads the latching balls against the wall of the guide body. As soon as the tappet  136  reaches the position where the blocking balls register with the detents, the balls will re-engage. The latching piston returned spring is aided by inertia and will thus push the piston through the balls, closing the high pressure chamber venting valve  116 . The high pressure chamber in  136 A expands, eliminating any residual lash.