Abstract:
A hydro-mechanical system is disclosed for actuating an outwardly opening valve of an engine, such as a crossover passage valve of a split-cycle engine. A developed embodiment includes a body having a plunger cylinder in hydraulic fluid communication with a valve cylinder. A plunger in the plunger cylinder is reciprocated to displace hydraulic fluid into the valve cylinder, the engine valve being opened by the hydraulic fluid displaced by the plunger into the valve cylinder and acting against the valve piston. A valve spring, preferably an air spring returns the engine valve to engage an outwardly facing valve seat to close a gas passage of the engine. Control valves and an energy reusing accumulator, along with valve seating control and lift brake features may also be included.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/963,742 filed Aug. 7, 2007. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to hydro-mechanical valve actuation systems. More particularly, the invention relates to a split-cycle internal combustion engine having a hydro-mechanical system for actuating outwardly opening crossover valves and the like. 
       BACKGROUND OF THE INVENTION 
       [0003]    For purposes of clarity, the following definition is offered for the term “split-cycle engine” as may be applied to engines disclosed in the prior art and as referred to in the present application. 
         [0004]    A split-cycle engine as referred to herein comprises: 
         [0005]    a crankshaft rotatable about a crankshaft axis; 
         [0006]    a compression piston slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston reciprocates through an intake stroke and a compression stroke during a single rotation of the crankshaft; 
         [0007]    an expansion (power) piston slidably received within an expansion cylinder and operatively connected to the crankshaft such that the expansion piston reciprocates through an expansion stroke and an exhaust stroke during a single rotation of the crankshaft; and 
         [0008]    a crossover passage interconnecting the compression and expansion cylinders, the crossover passage including a crossover compression (XovrC) valve and a crossover expansion (XovrE) valve defining a pressure chamber therebetween. 
         [0009]    U.S. Pat. No. 6,543,225 granted Apr. 8, 2003 to Carmelo J. Scuderi (herein Scuderi) contains an extensive discussion of split-cycle and similar type engines. In addition the patent discloses details of a prior version of an engine of which the present invention comprises a further development. 
         [0010]    Referring to  FIG. 1 , an exemplary embodiment of a prior art split-cycle engine concept of the type described in Scuderi is shown generally by numeral  10 . The split-cycle engine  10  replaces two adjacent cylinders of a conventional four-stroke engine with a combination of one compression cylinder  12  and one expansion cylinder  14 . These two cylinders  12 ,  14  perform their respective functions once per crankshaft  16  revolution. The intake air and fuel charge is drawn into the compression cylinder  12  through typical poppet-style intake valves  18 . The compression cylinder piston  20  pressurizes the charge and drives the charge through the crossover passage  22 , which acts as the intake passage for the expansion cylinder  14 . 
         [0011]    A check type crossover compression (XovrC) valve  24  at the crossover passage inlet is used to prevent reverse flow from the crossover passage  22 . A crossover expansion (XovrE) valve  26  at the outlet of the crossover passage  22  controls flow of the pressurized intake charge such that the charge fully enters the expansion cylinder  14  shortly after the expansion piston  30  reaches its top dead center (TDC) position. Spark plug  28  is fired soon after the intake charge enters the expansion cylinder  14  and the resulting combustion drives the expansion cylinder piston  30  down toward bottom dead center (BDC). Exhaust gases are pumped out of the expansion cylinder through poppet exhaust valves  32 . 
         [0012]    With the split-cycle engine concept, the geometric engine parameters (i.e., bore, stroke, connecting rod length, compression ratio, etc.) of the compression and expansion cylinders are generally independent from one another. For example, the crank throws  34 ,  36  for each cylinder may have different radii and be phased apart from one another with top dead center (TDC) of the expansion cylinder piston  30  occurring prior to TDC of the compression cylinder piston  20 . This independence enables the split-cycle engine to potentially achieve higher efficiency levels and greater torques than typical four-stroke engines. 
         [0013]    However, the crossover expansion valve of a split-cycle engine, unlike conventional four stroke engines, has a very small window of actuation timing (about 30 crank angle degrees) in which to open and deliver a turbulent high pressure air/fuel charge into the engine expansion cylinder for ignition, combustion and expansion in the cylinder. In view of the high pressures and small actuation timing involved, an alternative to mechanical valve actuation was desired for actuation of the engine valves, and the crossover expansion valve in particular. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention provides a hydro-mechanical valve actuation system designed for actuating high pressure outwardly opening engine valves, such as the crossover valves of a split-cycle engine, particularly the crossover expansion valve which must quickly force charges of pressurized air/fuel mixture into the expansion cylinder with turbulence to assure rapid combustion of the charges. 
         [0015]    A system according to the invention may include: 
         [0016]    A hydro-mechanical system for actuating an outwardly opening valve of an engine, the system comprising: 
         [0017]    a body having a plunger cylinder in hydraulic fluid communication with a valve cylinder; 
         [0018]    a plunger in the plunger cylinder and reciprocable through pumping and return strokes to displace hydraulic fluid into the valve cylinder; 
         [0019]    an outwardly opening engine valve reciprocable in the body and connected with a valve piston in the valve cylinder, the engine valve being opened by the hydraulic fluid displaced by the plunger into the valve cylinder and acting against the valve piston; 
         [0020]    an actuator for reciprocating the plunger; and 
         [0021]    a valve spring for returning the engine valve to engage an outwardly facing valve seat, thereby closing a gas passage of the engine controlled by the engine valve. 
         [0022]    In addition, the combination of a hydro-mechanical valve actuating system according to the invention with a split-cycle engine may include: 
         [0023]    The hydro-mechanical system outlined above in combination with a split-cycle engine including: 
         [0024]    a crankshaft rotatable about a crankshaft axis; 
         [0025]    a compression piston slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston reciprocates through an intake stroke and a compression stroke during a single rotation of the crankshaft; 
         [0026]    an expansion (power) piston slidably received within an expansion cylinder and operatively connected to the crankshaft such that the expansion piston reciprocates through an expansion stroke and an exhaust stroke during a single rotation of the crankshaft; and 
         [0027]    a crossover passage (port) interconnecting the compression and expansion cylinders, the crossover passage including an outwardly opening crossover compression (XovrC) valve and an outwardly opening crossover expansion (XovrE) valve defining a pressure chamber therebetween; 
         [0028]    wherein the hydro-mechanical system acutates the XovrE valve. 
         [0029]    Further, the split-cycle engine with the hydro-mechanical valve actuating system may also include: 
         [0030]    a hydraulic accumulator having an air spring acting against the accumulator piston to return stored energy in accumulated hydraulic fluid to the main chamber for restoring the plunger to an initial position; 
         [0031]    a timing solenoid valve to control the period of hydraulic actuation pressure generated by the displacement of the plunger and acting against the valve piston; and 
         [0032]    a locking solenoid valve for locking the valve piston and reducing parasitic hydraulic losses. 
         [0033]    These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]      FIG. 1  is a schematic cross-sectional view of a prior art split-cycle engine related to the engine of the invention; 
           [0035]      FIG. 2  is a schematic cross-sectional view of an exemplary split-cycle engine according to the present invention; 
           [0036]      FIG. 3  is a cross-sectional top view of the split-cycle engine taken through line  3 - 3  of  FIG. 2  with fuel injectors superimposed; 
           [0037]      FIG. 4  is a schematic cross-sectional view of a basic embodiment of a hydro-mechanical valve actuating system with a mechanical valve return spring according to the invention; 
           [0038]      FIG. 5  is a view similar to  FIG. 4  but showing air springs and additional features of a developed embodiment of a hydro-mechanical valve actuating system according to the invention for use with a split-cycle engine; and 
           [0039]      FIGS. 6-21  schematically illustrate the sequential operation of the hydro-mechanical valve actuating system of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Split-Cycle Engine 
       [0040]    Referring now to  FIGS. 2 and 3  of the drawings in detail, numeral  50  generally indicates a diagrammatic representation of a split-cycle engine according to the invention. Engine  50  includes a crankshaft  52  rotatable about a crankshaft axis  54  in a clockwise direction as shown in the drawing. The crankshaft  54  includes adjacent angularly displaced leading and following crank throws  56 ,  58 , connected to connecting rods  60 ,  62 , respectively. 
         [0041]    Engine  50  further includes a cylinder block  64  defining a pair of adjacent cylinders, in particular a compression cylinder  66  and an expansion cylinder  68  closed by a cylinder head  70  at one end of the cylinders opposite the crankshaft  54 . 
         [0042]    A compression piston  72  is received in compression cylinder  66  and is connected to the connecting rod  62  for reciprocation of the piston between top dead center (TDC) and bottom dead center (BDC) positions. An expansion piston  74  is received in expansion cylinder  68  and is connected to the connecting rod  60  for similar TDC/BDC reciprocation. The diameters of the cylinders and pistons and the strokes of the pistons and their displacements need not be the same. 
         [0043]    In an exemplary embodiment, the cylinder head  70  provides the means for gas flow into, out of and between the cylinders  66 ,  68 . In the order of gas flow, the cylinder head includes an intake port  76  through which intake air is drawn into the compression cylinder  66 , a pair of crossover (Xovr) passages  78  (at least one passage required) through which compressed air (gas) is transferred from the compression cylinder  66  to the expansion cylinder  68 , and an exhaust port  80  through which spent gases are discharged from the expansion cylinder. Each crossover passage  78  also defines a pressure chamber  81  in which pressurized gas is stored between closing of the crossover expansion (XovrE) valve ( 86 ) during the expansion stroke of the expansion piston  74  on one cycle (crank rotation) of the engine and opening of the crossover compression (XovrC) valve ( 84 ) during the compression stroke of the compression piston  72  on the following cycle (crank rotation) of the engine. 
         [0044]    In the selected embodiment, gas flow into the compression cylinder  66  is controlled by an inwardly opening intake valve  82 , which may be actuated by any suitable engine drive mechanism, such as by an intake cam, not shown. Gas flow into and out of each crossover passage  78  may be controlled by a pair of outwardly opening valves, namely a crossover compression (XovrC) valve  84  at an inlet end of each Xovr passage and a crossover expansion (XovrE) valve  86  at an outlet end of each crossover passage. 
         [0045]    XovrC valve  84  may be actuated in any suitable manner. However, in accordance with the invention, at least XovrE valve  86 , and preferably both valves  84  and  86  are actuated by a hydro-mechanical valve actuation system  100  subsequently discussed in detail. 
         [0046]    Exhaust gas flow out the exhaust port  80  is controlled by an inwardly opening exhaust valve  88  actuated, such as by an exhaust cam, not shown. The cams may be mechanically engine driven or operated by any other suitable engine drive mechanism, with timing as desired relative to the instantaneous angular position of the crankshaft  52 , or alternative torque output device. 
         [0047]    Each crossover passage  78  has at least one high pressure fuel injector  90  disposed therein. The fuel injectors are operative to inject fuel into charges of compressed air within the pressure chambers  81  of the crossover passages  78 . 
         [0048]    Engine  50  also includes one or more spark plugs  92  or other ignition devices. The spark plugs  92  are located at appropriate locations in the end of the expansion cylinder  68  wherein a mixed fuel and air charge may be ignited and burned during the expansion stroke. Alternatively, engine  50  may also be configured as a compression ignition engine, instead of a spark ignition engine, and still be within the scope of this invention. 
       Hydro-Mechanical Valve Actuating System 
       [0049]    Referring now to  FIGS. 4 and 5 , numerals  99  and  100  indicate differing embodiments of a hydro-mechanical system for actuating outwardly opening engine valves, such as crossover passage valves  84  and  86  of the split-cycle engine  50 .  FIG. 4  illustrates a basic embodiment  99  of the hydro-mechanical system according to the invention.  FIG. 5  illustrates a developed embodiment  100  including additional features and improvements not found in the basic embodiment  99 . Both embodiments  99 ,  100  are here described together, wherein like numerals indicate like features of the two embodiments. 
         [0050]    Each embodiment  100 ,  99  includes a mechanism contained within or supported by a body  102  ( FIG. 5 ),  103  ( FIG. 4 ). The body  102 ,  103  could be made as a single piece, such as an engine cylinder head or a separate block, or it could be made as two or more separate assemblies secured together to form a unitary body  102 ,  103 . 
         [0051]    Each body  102 ,  103  includes a plunger cylinder  104  carrying a plunger  106 . A plunger return spring  108  may be used in the plunger cylinder  104  and biases the plunger  106  upwardly in a plunger returning direction. An engine drive actuator, such as an engine driven cam  110  engages a cam follower  112 . The cam follower  112  includes a tappet  114  engaging the cam  110  and a plunger shaft  116  engaging the plunger  106  for actuating the plunger  106  downward. A follower return spring  118  maintains the follower  112  against the cam  110  at all times. 
         [0052]    Plunger cylinder  104  is in fluid communication with a main chamber  120 , which extends through the body  102 , but only partially through body  103 . The main chamber  120  communicates with a valve cylinder  122  that receives a valve piston  124  for reciprocation therein. The valve piston  124  is fixed on the stem  126  of outwardly opening XovrE valve  86  (and optionally on outwardly opening XovrC valve  84 ). XovrE valve  86  has a valve head  130  that closes against an outwardly facing valve seat  132  within crossover passage  78  (not shown) in cylinder head  70  of the split-cycle engine  50 . 
         [0053]    A seating control device or brake  138  is formed in the body  102 ,  103  in an oil passage  140  to the lower end of the valve piston  124 . A check valve  142  in the passage  140  closes during valve closing and directs flow through a restricted return passage such as seating control bleed orifice  144  that, together with valve piston clearance  146  in the valve cylinder  122 , controls the valve seating rate. 
         [0054]    In the basic embodiment  99  ( FIG. 4 ), the main chamber  120  is supplied with hydraulic oil at controlled pressure through a pressure control valve  149  to an inlet  150  from an external source, not shown, or the oil supply of an associated engine, not shown. In the currently developed embodiment  100  ( FIG. 5 ), a check valve  148  is provided in an inlet  150  to receive makeup oil into the main chamber  120  and prevent reverse flow out the inlet. 
         [0055]    In both embodiments  100 ,  99 , the engine valve  86  is opened by hydraulic oil in a manner to be subsequently described. In the basic embodiment  99  ( FIG. 4 ), a mechanical spring  151  in a spring chamber  153  engages the valve piston  124  or stem  126  with a mechanical closing force. In the developed embodiment  100  ( FIG. 5 ), an air piston  152  carried on the valve stem  126  reciprocates in an air cylinder  154  to close the valve  86  in response to air spring pressure to be subsequently more fully described. 
         [0056]    An additional feature found in the body  102  of embodiment  100  ( FIG. 5 ), but not in embodiment  99 , includes a full lift hydraulic lift brake  156  positioned at the top of the valve air cylinder  154 . The brake  156  includes a hydraulic cylinder  158  carrying a reciprocable brake piston  160  engagable by the engine valve stem  126  near the full lift position of the valve  86 . A full lift check valve  162  allowing make-up oil inlet flow, and a restricted return passage, such as bleed orifice  164  restricting oil outflow, combine to slow the valve motion before full lift. 
         [0057]    The body  102  ( FIG. 5 ) also includes a hydraulic overtravel accumulator  166  positioned between the plunger  106  and the XovrE valve  86  to store and recover hydraulic energy. Additionally, a locking solenoid valve  168 , shown in a closed position in  FIG. 5 , is located between the accumulator  166  and the XovrE valve  86  to lock the valve piston  124  and allow energy recovery, therefore reducing parasitic hydraulic losses. 
         [0058]    A timing solenoid valve  170  is positioned beyond the XovrE valve  86  at an outlet end  172  of the main chamber  120 . The timing solenoid valve  170  controls the period of hydraulic actuation pressure generated by the displacement of the plunger  106  which acts against the valve piston  124 . That is, although the cam  110  can offer a long period of high pressure and therefore of valve  86  lift, opening of the timing solenoid valve  168  can truncate the XovrE valve  86  lift period to a fraction of the period of the nominal cam  110 . In this way, the hydro-mechanical system is “lost motion” in that the continued lift of the cam  110  ceases to produce any hydraulic pressure on the valve piston when the timing solenoid valve  168  is open, and therefore the XovrE valve  86  ceases to move further, excepting for inertia motion. 
         [0059]    The accumulator  166  includes an accumulator cylinder  174  in which an accumulator piston  176  reciprocates. A mechanical accumulator return spring  178  fixed on a spring seat  180  may urge the piston  176  downward toward the cylinder end  182 , which communicates with oil in the main chamber  120  through an opening  184 . Optionally, the accumulator cylinder  174  may communicate with an air pressure source through an opening  186  to form an air spring  188  urging the accumulator piston toward the cylinder end  182 . 
         [0060]    Referring further to  FIG. 5 , air pressure from an external source is fed through an air line  190  and pressure control valves  192 ,  194  into the accumulator cylinder  174  to form the air spring  188  therein and into the valve air cylinder  154  to form an air spring  198  therein. 
         [0061]      FIG. 5  also discloses an exemplary oil supply source  200  from an oil container  202 , such as an engine oil pan or from a separate system making use of a different fluid, such as hydraulic fluid or similar. A hydraulic pump  204  draws oil from the container  202  and pumps it through an oil line  206  to the check valve  148  in the inlet  150  of the main chamber  120  to maintain a full oil charge therein. An oil pressure accumulator  208  connected to line  206  reduces pressure variations in the line. Line  206  then extends to the full lift check valve  162  to supply makeup oil to the hydraulic brake cylinder  158  of the full lift brake  156 . 
       Sequence of Operation of Hydro-mechanical System  100   
       [0062]    The Xovr valves  84 ,  86  open against high air pressures retained in the Xovr passage(s)  78  and the XovrE valve  86  opens quickly for only about 30 crank angle degrees. To actuate these valves successfully within the pressures and time intervals allowed, particularly for the XovrE valve, the above-described hydro-mechanical valve actuation system embodiment  100  has been developed. The embodiment  100  also allows variations in the lift and timing of the crossover valves. 
         [0063]    With reference to  FIGS. 6 through 21 , the following is a description of the operation of the embodiment  100  XovrE valve actuation system. In order to provide for adjustments in valve timing and valve lift, the cam  110  is designed to actuate the plunger  106  over a stroke greater than that needed to open the engine valve; thus a lost motion system is provided. 
         [0064]    In an initial position shown in  FIG. 6 , the plunger  106  is at its top dead center position and the inlet check valve  148  is open. The accumulator  166  is empty, and the locking solenoid  168  and timing solenoid  170  are open. The XovrE valve  86  is closed and the seating control check valve  142  is closed. 
         [0065]    Turning to  FIGS. 7-9 , the cam rotates in a clockwise direction. As the lobe of the rotating cam  110  engages the cam follower  112  ( FIG. 9 ), the plunger  106  begins to descend from its top dead center position, forcing oil out of the plunger cylinder  104 , into the main chamber  120 , and out of the main chamber  120  through chamber outlet end  172 , where the oil is drained into the oil container pan  202  (shown by arrows). The inlet check valve  148  moves from an open position to a closed position. The seating control check valve  142  remains closed, the locking solenoid  168  and timing solenoid  170  remain open, and the accumulator  166  remains empty. The XovrE valve  86  also remains closed. 
         [0066]    Turning to  FIG. 10 , as the cam  110  continues its clockwise rotation, the plunger  106  descends further and the timing solenoid valve  170  closes. Closing of the timing solenoid valve  170  blocks the main chamber outlet  172  and forces oil through the valve piston oil passage  140  by opening seat control check valve  142 . The oil passes from the valve piston oil passage  140  to the valve cylinder  122  at the bottom of the valve piston  124 , cracking opening the XovrE valve  86 . The locking solenoid valve  168  remains open, the inlet check valve  148  remains closed, and the accumulator  166  remains empty. 
         [0067]    In  FIG. 11 , the cam  110  has rotated further in the clockwise direction, and the force of the cam lobe against the cam follower  112  continues the descent of the plunger  106 . The locking solenoid valve  168  is now closed, and closing of the locking solenoid valve blocks oil flow to the piston  124  of the XovrE valve  86 , ending the forced lift. However, inertia of the XovrE valve  86  continues its upward motion, and the valve stem  126  engages the lift brake piston  160  of the full lift brake  156 . Excess oil from the continued travel of the plunger  106  that is blocked by the locking solenoid valve  168  enters accumulator  166  to store energy (as shown by arrows). The inlet check valve  148  and timing solenoid valve  170  remain closed, while the seating control check valve  142  remains open. 
         [0068]    Turning to  FIGS. 12 and 13 , as the valve stem  126  moves the piston  160  of the full lift brake  156 , oil is forced through the bleed orifice  164 , thus slowing upward motion of the XovrE valve  86 . The XovrE valve  86  comes to rest at full lift with the full lift brake  156  engaged, and the seating control check valve  142  closes. The plunger  106  descends even further, continuing the flow of oil into the accumulator  166  (as shown by arrows) to store energy. The timing solenoid valve  170 , locking solenoid valve  168 , and inlet check valve  148  remain closed. 
         [0069]    When the cam  110  has rotated to its highest point (at the peak of the lobe) from its initial position, the plunger  106  reaches its bottom dead center position as shown in  FIG. 14 . The maximum amount of energy has now been stored in the accumulator  166 . Timing solenoid valve  170  opens, allowing draining of oil from the valve cylinder  122  (as shown by an arrow) and permitting pressurized air in the valve air cylinder  154  to begin XovrE valve  86  closing by forcing air piston  152  downward. However, the timing solenoid valve  170  may open independently from the rotational position of the cam  110 . In other words, the timing solenoid valve  170  does not have to open precisely at the time the cam  110  reaches its highest point. Also shown in  FIG. 14 , replacement of oil through brake check valve  162  to valve lift brake cylinder  158  begins. Locking solenoid valve  168 , inlet check valve  148 , and seating control check valve  142  remain closed. 
         [0070]    Turning to  FIGS. 15 and 16 , as the plunger  106  begins returning from its bottom dead center position, the accumulator  166  begins to empty (as shown by arrows). Air pressure urges accumulator piston  176  down, returning oil from the accumulator  166  to plunger cylinder  104  and releasing stored energy to retract plunger  106  and drive cam rotation. The full lift brake  156  finishes replenishing, and the brake check valve  162  closes. The closed seating control check valve  142  causes oil to be diverted to bleed orifice  144 , slowing engagement of XovrE valve  86  with valve seat  132 . In  FIG. 16 , the XovrE valve  86  has closed. The timing solenoid valve  170  remains open, and the locking solenoid valve  168  and inlet check valve  148  remain closed. 
         [0071]    Turning to  FIGS. 17-19 , as the cam  110  continues its clockwise rotation, the plunger  106  continues returning toward its top dead center position. The accumulator  166  continues to empty, returning oil to the plunger cylinder  104  (as shown by arrows). In  FIG. 19 , the accumulator  166  has emptied. The locking solenoid valve  168 , inlet check valve  148 , seating control check valve  142 , and XovrE valve  86  remain closed. The timing solenoid valve  170  remains open. 
         [0072]    As shown in  FIG. 20 , while the cam  110  is rotating to bring the plunger  106  back to its TDC position and the accumulator is emptied, the inlet check valve  148  opens, allowing oil replenishment to main chamber  120 . The locking solenoid valve  168 , seating control check valve  142 , and XovrE valve  86  remain closed, while the timing solenoid valve  170  remains open. The accumulator  166  is empty. 
         [0073]    Turning finally to  FIG. 21 , the cam  110  continues to rotate in a clockwise direction back toward its initial starting position to complete a 360 degree rotation. The locking solenoid valve  168  opens, and the main chamber  120  is filled with oil (as shown by arrows) continuously provided as needed by operation of the hydraulic pump  204  delivering oil from the oil container  202  through the open inlet check valve  148 . The timing solenoid  170  remains open, while the seating control check valve  142  and XovrE valve  86  remain closed. The plunger  106  remains at its top dead center position, and the accumulator  166  remains empty. The cycle may then repeat itself, returning first to the step shown in  FIG. 6 . 
         [0074]    In the alternative embodiment  99 , operation of the plunger  106  and the valve piston  124  with the seating control  138  with check valve  142  could be essentially as described above. However, the accumulator  166 , locking solenoid  168  and timing solenoid  170  are omitted and the valve piston air spring  198  is replaced by the mechanical spring  151 . Thus, XovrE valve timing and lift would be fixed and the mechanical spring  151  would absorb valve lift control forces. However, the missing timing devices and accumulator could be added if desired and the mechanical spring could replace the air spring as a XovrE valve closer and lift control. The accumulator could also be added and use a mechanical return spring if desired. 
         [0075]    Although the invention has been described by reference to specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims.