Abstract:
A hydraulic lash adjuster for an engine valve train has a hydraulic lash adjusting arrangement for automatically compensating for lash in an engine valve train, and a lost motion arrangement for inhibiting motion induced in the valve train in response to a lift profile of a rotating cam from being transferred to an engine valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage application under 35 U.S.C. §371 of International Application No. PCT/EP2013/064263, filed on Jul. 5, 2013, and claims benefit to British Patent Application No. 1211926.9, filed on Jul. 5, 2012. The International Application was published in English on Jan. 9, 2014, as WO 2014/006185 A1 under PCT Article 21(2). 
     
    
     FIELD 
       [0002]    The present invention relates to a hydraulic lash adjuster for use in an engine valve train assembly. 
       BACKGROUND 
       [0003]    A typical hydraulic lash adjuster (HLA) comprises a first oil chamber defined between an outer body and a plunger assembly slidably mounted within the outer body, and a spring biased to enlarge the first oil chamber by pushing the plunger assembly outwardly from the outer body to extend the HLA. Typically, the HLA has a second oil chamber, defined by the plunger assembly and which is in fluid communication with the engine&#39;s oil supply. The first oil chamber and the second oil chamber are separated by a one way valve and oil flows from the second chamber into the first chamber through the one way valve when the HLA extends (and hence the first chamber enlarges) because the oil pressure in the second chamber becomes higher than that in the first chamber. Whereas oil can flow into the first pressure chamber via the one way valve, it can only escape the first pressure chamber very slowly, for example, via closely spaced leak down surfaces. Accordingly, a HLA can extend to accommodate any slack in a valve train assembly, such as between the cam and the roller but after it is extended, the incompressible oil in the first chamber provides sufficient rigid support for the HLA to open the valve when a rocker arm pivots (i.e. the incompressible oil prevents the plunger assembly being pushed back inwardly of the outer body so that the HLA acts as a solid body). 
         [0004]    Compression engine brakes are typically used as auxiliary brakes, in addition to wheel brakes, on relatively large vehicles, for example trucks, powered by heavy or medium duty diesel engines. A compression engine braking system is arranged, when activated, to provide an additional opening of an engine cylinder&#39;s exhaust valve when the piston in that cylinder is close to the top-dead-center position of its compression stroke so that compressed air is released through the exhaust valve. This causes the engine to function as a power consuming air compressor which slows the vehicle. 
         [0005]    In a typical valve train assembly used with a compression engine brake, the exhaust valve is actuated by a rocker arm to provide an additional compression brake exhaust valve lift in addition to the main exhaust valve lift. The rocker arm rocks in response to a cam on a rotating cam shaft and acts on the exhaust valve, either directly, or indirectly (for example, by means of a valve bridge) to open it. Lost motion variable valve actuation systems may be used to inhibit the additional compression brake exhaust valve lift when the engine is in normal engine combustion mode. 
         [0006]    A hydraulic lash adjuster may also be provided in the valve train assembly to remove any lash (i.e. gap) that develops between components in the valve train assembly. 
         [0007]    U.S. Pat. No. 7,156,062 describes a valve actuation system that comprises a lost motion system and a separate, distinct automatic lash adjuster. The system is complicated and has a large number of distinct components. 
         [0008]    U.S. Pat. No. 7,484,483 describes a variable valve actuation system that comprises a manual lash adjuster. Manual lash adjusters have the disadvantage of not providing automatic lash adjustment. Instead, a mechanic must adjust a manual lash adjuster during engine servicing. 
       SUMMARY 
       [0009]    An aspect of the invention provides a hydraulic lash adjuster for an engine valve train, the adjuster comprising: a hydraulic lash adjusting arrangement configured to automatically compensate for lash in an engine valve train; and a lost motion arrangement configured to inhibit motion, induced in the valve train in response to a lift profile of a rotating cam, from being transferred to an engine valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
           [0011]      FIG. 1  is a schematic side view of a valve train assembly; 
           [0012]      FIG. 2  is a schematic cross sectional side view of a HLA; 
           [0013]      FIG. 3   a  is a schematic cross sectional side view of a HLA with its components in a first configuration; 
           [0014]      FIG. 3   b  is a schematic cross sectional side view of the HLA of  FIG. 3   a  with its components in a first configuration; 
           [0015]      FIG. 4  is a schematic side view of a valve train assembly; 
           [0016]      FIG. 5  schematic side view of a valve train assembly; 
           [0017]      FIG. 5  is a perspective view of a clip component; 
           [0018]      FIG. 6   a  is a is a schematic cross sectional side view of a HLA; 
           [0019]      FIG. 6   b  is a schematic cross sectional side view of a HLA; 
           [0020]      FIG. 7  is a schematic side view of a valve train assembly; 
           [0021]      FIG. 8  shows a component of an actuator; 
           [0022]      FIG. 8  shows a plot of valve lift against cam angle; 
           [0023]      FIG. 9   b  shows the actuator and the engine brake capsule in a second configuration; 
           [0024]      FIGS. 9   a ,  9   b  and  9   c  each show schematic cross sectional side views of alternative HLAs. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    An aspect of the invention provides a hydraulic lash adjuster for use in an engine valve train assembly, particularly, a hydraulic lash adjuster that provides a lost motion stroke variable valve actuation (VVA) capability. 
         [0026]    Incorporating a lost motion arrangement into a HLA provides a system that is simpler has fewer components than known systems in which HLAs and lost motion systems are separate and distinct. This simplifies manufacturing and reduces costs. 
         [0027]    An aspect of the invention provides a valve train including such an HLA. 
         [0028]      FIG. 1  schematically illustrates a valve train assembly  1  comprising an exhaust rocker arm  3 , mounted for pivotal movement about a rocker shaft  5 . The exhaust rocker arm  3  comprises, at a first end  7 , a rotatably mounted roller  9  for engaging an exhaust cam  11  which is mounted or formed on a rotatable cam shaft  13 . The exhaust cam  11  comprises a base circle  11   a,  a main exhaust lift profile  11   b  and an additional exhaust lift profile  11   c.    
         [0029]    As shown in  FIG. 1 , the exhaust rocker arm  3  comprises, at a second end  15 , a cavity  17  in which is supported a Hydraulic Lash Adjuster (HLA)  19 . The HLA  19  is for contacting an exhaust valve  20  of an engine cylinder  21 . 
         [0030]    Referring to  FIG. 2  the HLA  19  comprises a hollow outer body  21  supported within the cavity  17  by means of a first retaining clip  23 . The hollow outer body  21  comprises a first closed end  25  which protrudes from the cavity  17  and defines a spigot  27  which is received in a socket  29  defined by an E-foot  31 . The E-foot  31  comprises a flat base end  33  for contacting a stem  35  of the exhaust valve  20 . The spigot  27  is retained within the socket  29  by means of a second retaining clip  37 . 
         [0031]    The HLA  19  comprises a first plunger  39  slidably mounted within the hollow outer body  21  and which extends above a second open end  26  of the hollow outer body  21 . In this example, the first plunger  39  is a hollow two part component comprising a first hollow body  39   a  and a second hollow body  39   b.  The second body  39   b  rests co-axially within the first body  39   a,  for example, on a first annular lip  41  defined by the first hollow body  39   a.  A first biasing means  40 , for example a compression spring, located at the first closed end  25  of the outer body  21  biases the first plunger  39  outwardly away from the outer body  21  such that a first open end  45  of the first plunger  39 , defined by respective ends of the first  39   a  and second  39   b  hollow bodies, presses against an upper inner surface  47  of the cavity  17 . 
         [0032]    The HLA  19  further comprises a second plunger  49  slidably mounted within the first hollow body  39   a  of the first plunger  39 . The second plunger  49  is coaxial with and opposes the second hollow body  39   b.  In the position shown in  FIG. 2 , the second plunger  49  rests upon a second annular lip  50  defined by the first hollow body  39   a.  The second plunger  49  defines a first aperture  51  for connecting a first chamber  52 , defined by the hollow outer body  21 , the first hollow body  39   a  and the second plunger  49 , and a second chamber  54  defined by the first hollow body  39   a  the second plunger  49  and the second hollow body  39   b.    
         [0033]    The second oil chamber  54  contains a second biasing means  53 , for example a compression spring, which biases the second plunger  49  away from the second hollow body  39   b.    
         [0034]    The HLA  19  is further provided with a check ball valve  56  which comprises a ball  58  captured by a cage  60  supported in the first chamber  52  by the second plunger  49  and is biased by a third biasing means  62 , for example a small compression spring, to a position closing the first aperture  51 . 
         [0035]    In use, if a lash (i.e. a gap) develops between any of the components in the valve train assembly  1 , the first biasing means  40  can expand the overall effective length of the HLA  19  by pushing the first plunger  39  away from the hollow outer body  21  so as to take up the slack in the valve train assembly  1 . During the course of this motion, the ball valve  58  allows oil to flow from the second chamber  54  to the first chamber  52  through the first aperture  51  so that the first chamber  52  is maintained full of pressurised oil. The oil is prevented from flowing back from the first chamber  52  to the second chamber  54  by the ball valve  60 . The HLA  19  therefore provides for automatic hydraulic lash adjustment. 
         [0036]    The second hollow body  39   b  and the upper inner surface  47  of the rocker arm  3  define a third chamber  68  located above the second chamber  54 . The second hollow body  39   b  defines a second aperture  64  that connects the third chamber  68  and the second chamber  54 . 
         [0037]    Oil is supplied to the third chamber  68  from the engine&#39;s oil supply via an oil supply conduit  65  formed through the rocker shaft  5  and exhaust rocker arm  3  into the HLA  19 . Oil is supplied from the third chamber  68  into the second chamber  54  when the relief valve  70  is open. In effect, the second chamber  54  and the third chamber  54  act as an oil reservoir for supplying the first chamber  52  when the HLA  19  extends and for replenishing oil that escapes from the first chamber  52  via leak down surfaces (illustrated by vertical dashed lines), for example, when the HLA is under load during a valve lift event. 
         [0038]    In this example, the relief valve  70  is a poppet valve comprising an elongate stem  72  that extends along the longitudinal axis of the third chamber  68  and terminates at a first end in a valve head  74  that forms a seal with the second hollow member  39   b  when the relief valve  70  closes the second aperture  64 . Many other types of valve may instead be used. A second end  78  of the stem  72  extends through an upper wall  80  of the HLA  19  where it is contactable by an actuator  82  which is operable to push the relief valve  70  from a first position in which the second aperture  64  is closed, to a second position in which the second aperture  64  is open. A fourth biasing means  84  is located in the third chamber  68  and is arranged to bias the relief valve  70  to the position in which the second aperture  64  is closed. 
         [0039]    In this example, the actuator  82  comprises a lever  84  having a contact head  86 . When the relief valve  70  is in the first position in which it closes the second aperture  72 , the lever  84  is in a position in which the contact head  86  is above and not in contact with the second end  78  of the valve stem  72 . The lever  84  is moveable from this position into contact with the second end  78  of the valve stem  72  so as to push the relief valve  70  against the bias of the fourth biasing means  84  to open the second aperture  64 . The lever  84  may be moved for example by an electro-magnetic system  87  controlled by an engine control system. Other types of actuators may be used to actuate the relief valve  70 , for example, hydraulic actuators. 
         [0040]    The HLA  19  is configurable by means of the actuator  82  to be in either a ‘combustion mode’ in which the relief valve  70  is open, or a ‘braking mode’ in which the relief valve  70  is closed. The ‘combustion mode’ corresponds to normal engine operation in which the engine cylinders provide power strokes. In contrast, the ‘braking mode’ corresponds to engine operation mode in which combustion is inhibited and de-compression engine braking is implemented. 
         [0041]    In the braking mode, pivoting of the exhaust rocker arm  3  in response to the additional exhaust lift cam profile  11   c  engaging the roller  11  causes an additional valve lift of the exhaust valve  20 , once per engine cycle, to provide a de-compression engine brake event. In contrast, in the combustion mode, the pivoting of the exhaust rocker arm  3  in response to the additional exhaust lift cam profile  11   c  engaging the roller  11  is absorbed by a variable valve actuation ‘lost motion stroke’ of the HLA  19  and so the additional valve lift of the exhaust valve  20  is inhibited. 
         [0042]    Referring now to  FIGS. 1 ,  3   a ,  3   b  and  4 , the combustion mode of operation will be explained. As illustrated in  FIG. 1 , the cam shaft  13  is rotating clockwise in the sense of the page and the actuator  82  has configured the HLA  19  in combustion mode by pushing the relief valve  70  to open the second aperture  72 .  FIG. 1  shows the valve train assembly  1  when the roller  9  is engaged with the base circle  11   a  of the cam  11  and the exhaust valve  21  is closed, momentarily before the roller  9  begins to engage with the additional exhaust lift profile  11   c.    
         [0043]      FIG. 3   a  is an enlarged view of the HLA  19  as it is in  FIG. 1  and shows the second plunger  49  resting upon the annular lip  50  formed around the bottom of the first hollow body  39   a  and that there is a gap between the second plunger  49  and the second hollow body  39   b.    
         [0044]    As the roller  9  starts to engage the leading rising slope of the additional exhaust lift profile  11   c,  the exhaust rocker arm  3  starts to pivot clockwise in the sense of the page. As the exhaust rocker arm  3  pivots, the upper inner surface  66  of the exhaust rocker arm  3  pushes the first plunger  39  inwardly of the hollow outer body  21  in the direction of the bottom of the first chamber  52 . As the relief valve  70  is open, the movement of the first plunger  39  is able to displace oil in the first chamber  52  and the resultant pressure difference between the first chamber  52  and the second oil chamber  54  causes the second plunger  49  to move upwards towards the second hollow body  39   b.    
         [0045]    When the first plunger  39  and the second plunger  49  are moving in this way, the outer body  21  remains substantially stationary and no force sufficient to open the exhaust valve  20  is transmitted to it, despite the clockwise pivoting of the exhaust rocker arm  3 . This could continue until the second plunger  49  hits the second hollow body  39   b,  at which point, the HLA  19  would begin to act as a solid body that would transmit an opening force to the exhaust valve  21 , but in this example, even at the point at which the roller  9  engages the peak of exhaust lift profile  11   c,  as shown in  FIG. 4 , the second plunger  49  remains marginally out of contact with the second hollow body  39   b,  as shown in  FIG. 3B , and so the exhaust valve  20  remains closed. In effect, the movement of the second plunger  49  provides for a so called ‘lost motion stroke’, in which the exhaust rocker arm  3  performs a pivoting stroke but the exhaust valve  20  remains closed. 
         [0046]    When the roller  9  engages the rising slope of the main exhaust lift profile  11   b,  the exhaust rocker arm  3  pivots clockwise to a greater extent than when the roller  9  engages the rising slope of the additional exhaust lift profile  11   c.  This motion is sufficient for the second plunger  49  to hit the second hollow body  39   b  which acts as a stopper, at which point, the HLA  19  acts as a solid body due to the incompressible oil in the first chamber  52  and transmits an opening force to the exhaust valve  20  for the exhaust valve to open for the exhaust stroke of the engine cycle. 
         [0047]    The maximum valve lift of the exhaust valve  20  occurs when the roller  9  engages the peak of the main exhaust lift profile  11   b.  As the roller  9  passes out of engagement with the peak of the main exhaust lift profile  11   b,  the exhaust rocker arm  3  starts to pivot anti-clockwise in the sense of the page and the exhaust valve  21  begins to close under the action of a valve return spring. When the roller  9  again becomes engaged with the base circle  11   a  the exhaust valve  21  is closed. Furthermore, the first plunger  39  returns under the bias of the first biasing means  40  from its position shown in  FIG. 3   b  to its position shown in  FIG. 3   a  and, the second plunger  49  returns under the bias of the second biasing means  53  from its position shown in  FIG. 3   b  to its position shown in  FIG. 3   a.    
         [0048]    Referring to  FIGS. 5 ,  6   a ,  6   b  and  7 , the de-compression braking mode of operation will be explained. In this mode, the actuator  82  remains out of contact with the relief valve  70 , which under the bias of the fourth biasing means  84  keeps the second aperture  72  closed.  FIG. 5  shows the valve train assembly  1  when the roller  9  is engaged with the base circle  11   a  of the cam  11  and the exhaust valve  20  is closed, momentarily before the roller  9  commences to engage with the additional exhaust lift profile  11   c.    
         [0049]      FIG. 6   a  is an enlarged view of the HLA  19  as it is in  FIG. 5  and shows that the second plunger  49  rests upon the annular lip  50  formed around the bottom of the first hollow body  39   a.    
         [0050]    As the roller  9  starts to engage the leading rising slope of the additional exhaust lift profile  11   c,  the exhaust rocker arm  3  starts to pivot clockwise in the sense of the page. In this mode of operation, because the relief valve  70  is closed, as the exhaust rocker arm  3  pivots, the oil pressure exerted by the oil in the second chamber  54  on the second plunger  49  and oil pressure exerted by the oil in the first chamber  52  on the second plunger  49  remain balanced so that the first plunger  39  cannot move inwardly of the hollow outer body  21  and the second plunger  49  cannot move upwards towards the second hollow body  39   b.  Instead, the HLA  19  acts immediately as a solid body, due to the incompressibility of the oil in the first oil chamber  52 , and pushes down on the valve stem to open the exhaust valve  20 . The timing of the opening of the exhaust valve  20  is such that it opens by the end of the compression stroke of the engine cylinder so that compressed air is charged from the cylinder to provide de-compression engine braking. The maximum valve lift X (e.g. 1.9 mm) of this additional valve event occurs when the roller  9  engages the peak of the additional exhaust lift profile  11   c,  see  FIG. 7 .  FIG. 6   b  is an enlarged view of the HLA  19  as it is in  FIG. 7  and line have been drawn across  FIGS. 6   a  and  6   b  to illustrate the valve lift X. 
         [0051]    When the roller  9  engages the rising slope of the main exhaust lift profile  11   b,  the exhaust rocker arm  3  pivots clockwise to a greater extent than when the roller  9  engages the rising slope of the additional exhaust lift profile  11   c,  and the HLA  19  acts on the exhaust valve  20  to fully open it for the exhaust stroke of the engine cycle. The maximum valve lift of the exhaust valve  21  occurs when the roller  9  engages the peak of the main exhaust lift profile  11   b.  As in combustion mode, as the roller  9  passes out of engagement with the peak of the main exhaust lift profile  11   b  the exhaust valve  21  begins to close under the action of a valve return spring and is fully closed when the roller  9  returns into engagement with the base circle  11   a.    
         [0052]      FIG. 8  shows a plot of valve lift against cam rotation angle. The curve  101  is for the exhaust valve  20  and the curve  102  is for a corresponding intake valve for the engine cylinder, which is acted on by a intake rocker arm in response to an intake cam . The lost motion stroke absorbed by the HLA  19  in the combustion mode is illustrated by the double headed arrow  100 . In the combustion mode, the exhaust valve  20  remains shut during the ‘lost motion stroke’ and the exhaust valve opens at the point marked ‘EVO’ and closes at the point marked ‘EVC’. In the brake mode, the exhaust valve  21  begins opening at the point ExBr VO for the additional valve event by the end of the cylinder&#39;s compression stroke, to enable compressed air to be discharged from the cylinder. It closes at the point ExBbVc after the main exhaust lift. It will be appreciated that the exact movement of the valve during the additional valve lift will be dictated by the shape of the additional cam lift profile  11   c.    
         [0053]      FIGS. 9   a  to  9   c  illustrate alternative HLAs  19  that may be used in embodiments of the invention. In these Figures, like reference numerals refer to like features previously described. 
         [0054]    In each of  FIGS. 9   a  to  9   c  the first hollow plunger  39 ′ is a single piece component rather than a two piece component as described above. The plunger  39 ′ has an annular region  200  that defines the second aperture  64  and provides a contact surface for stopping the second plunger  49 . 
         [0055]    In  FIG. 9   b , the relief valve  70 ′ is a two piece component comprising a first part  70   a′  which extends from the HLA  19  and which is contactable by the actuator  82 , and a second part  70   b′  which is acted upon by the first part  70   a′  to open the second aperture  62 . 
         [0056]    In  FIG. 9   c , the relief valve  70 ″ comprises a valve needle  70   a″  which extends from the HLA  19  and which is movable by the actuator  82  , to act upon a check ball valve  201  to open the second aperture  62 . The check ball valve  201  has a similar function and components to the check ball valve  60  that closes the first aperture  51 . 
         [0057]    The above embodiments are to be understood as an illustrative example of the invention only. Further embodiments of the invention are envisaged. For example, although in the above described embodiment the HLA is supported in a rocker arm, this need not be the case, and the HLA may be supported in a different location or in a different component in a valve train. Although in the above embodiment the HLA acts directly on an engine valve this need not be the case. Although in the above embodiment the HLA acts on a single valve it may act on multiple valves, for example, by acting on a valve bridge or other such component that carries multiple valves. Although in the above described embodiment the HLA is used in conjunction with an engine de-compression braking operation, uses in conjunction with other operations, for example, Exhaust Gas Recirculation are envisaged. Although in the above described embodiment the lost motion arrangement of the HLA is used to entirely inhibit the additional exhaust valve lift when in combustion mode (i.e. the additional lift does not occur at all), it may be used to partially inhibit valve events (e.g. a valve does lift but not to the extent that it otherwise would have done). Further equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims. 
         [0058]    While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments. 
         [0059]    The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B, and C” should be interpreted as one or more of a group of elements consisting of A, B, and C, and should not be interpreted as requiring at least one of each of the listed elements A, B, and C, regardless of whether A, B, and C are related as categories or otherwise. Moreover, the recitation of “A, B, and/or C” or “at least one of A, B, or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B, and C.