Abstract:
An electro-hydraulic lost motion system for variable valve activation including a master piston and an accumulation piston in a first bore, defining a hydraulic pressure chamber therebetween, in response to rotation of an engine cam. A slave piston in the engine head and hydraulically connected to the pressure chamber opens and closes an engine valve. A servo-valve behind the accumulation piston controls the mobility of the accumulation piston via a fluid control chamber. When the control chamber is made hydraulically rigid, the system actuates the engine valve. When the control chamber is vented through the servo-valve, the accumulation piston is movable in lost motion, preventing the engine valve from opening. All intermediate degrees of valve opening are possible. Preferably, the servo-valve, control chamber, accumulation piston, and a control piston are comprehended in a modular subassembly which may be positioned adjacent the master piston or the slave piston.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to valve trains for internal combustion engines;  
         [0002]     more particularly, to a valve train having an electro-hydraulic link; and most particularly, to an electro-hydraulic valve train that includes a lost motion (LM) capability for variable valve activation.  
       BACKGROUND OF THE INVENTION  
       [0003]     In prior art valve train mechanisms for internal combustion engines, either spark-ignited (SI) or compression-ignited (CI), mechanically operated poppet valves are typically employed, being actuated by a rotary cam and associated linkage known in the art as a valve train. Many arrangements of cam form, cam drive, and cam-to-valve linkage have been proposed and reduced to practice over the years. Some of the most popular have been codified in the art as Type-1, Type-2, etc. through Type-5.  
         [0004]     One of the constraints common to prior art mechanically-actuated valve trains is that the spatial relationship between the cam and its associated valve or valves must observe well-defined geometric rules governing the kinematic behavior of the mechanism. One such constraint is that the cam follower must follow a path that is square to the cam surface (orthogonal of the cam axis of rotation) so that point loading at the interface is avoided. Similarly, a rocker that is in contact with a valve must describe an arc that falls in the same plane as the motion of the valve itself. If these basic mechanical rules are not observed, excessive noise and wear will result.  
         [0005]     Consequently, in the prior art the locations and motion paths of valves and camshafts are constrained within well-defined limits.  
         [0006]     Several alternative mechanisms have been proposed that provide either cam-based lost-motion valve actuation, or in some cases, a cam-less mechanism. See, for example, U.S. Pat. No. 4,716,863 issued Jan. 5, 1988 to Pruzan; see also U.S. Pat. No. 6,227,154 B1 issued May 8, 2001 to Wakeman; see also U.S. patent application Publication No. US 2003/0221663 A1, published Dec. 4, 2003, by Vanderpoel et al. With a cam-less mechanism certainly, and with specific embodiments of the lost-motion mechanism, spatial constraints of valve location relative to the camshaft no longer apply, thus permitting greater architectural freedom in design.  
         [0007]     Given this freedom, there are several important benefits available to an engine design that is free of the constraints of a purely mechanical valve train:  
         [0008]     1. Both SI and CI engines are known to benefit from provision of greater valve flow area and low port restriction, for both inlet valves and exhaust valves. These factors affect volumetric efficiency which in turn influences specific power and fuel consumption. To obtain these benefits, engine designs historically have evolved from two valves to four valves per cylinder, and in some cases to five valves per cylinder. Adding valves beyond four per cylinder is probably not cost-effective in a light-duty automotive engine, but a known way to obtain the benefits recited above with four valves is to move to radially-disposed valves wherein the valve axes are non-parallel to the cylinder axis and may or may not intersect at a point within the cylinder or engine head. This architecture allows larger valves to be specified for a given bore size, and permits straighter, less restrictive port designs. A very few prior art production engines have employed radial valves, a severe problem being the expensive and complex mechanism necessary to address the linkage issues. If such constraints are overcome, then the benefits of a radial valve layout are open to the engine designer. Thus, what is needed in the art is a simplified means for obviating the restraints of prior art mechanical valve trains.  
         [0009]     2. A current trend in diesel engine combustion systems is a shift from conventional diffusion combustion toward a partially pre-mixed combustion mode in which a portion of the fuel charge is injected early during the compression stroke rather than late in the stroke near top dead center (TDC) as in the older prior art. When early injection is attempted with conventional nozzles optimized for late injection and having an included spray angle of about 150°, there is a high probability of fuel&#39;s impinging undesirably on the cylinder walls, leading to premature engine wear. This, in turn, is driving a further trend toward narrower angle spray patterns in an attempt to obtain a long free-plume length before surface impingement. This objective is enhanced by radially-disposed valves, since the injector in a domed firing chamber may be withdrawn further away from the piston. Thus a better match between combustion system and chamber geometry is possible if an enabling technology were available. Again, what is needed in the art is a non-complex means for obviating the restraints of prior art mechanical valve trains to allow radial valving in a domed firing chamber.  
         [0010]     3. Inlet-generated swirl of air and fuel is an important combustion control parameter for most diesel engines and some SI engines. The normal prior art method to generate such in-cylinder swirl motion is through the use of one or more “directed” ports wherein the flow direction is generally tangent to the cylinder wall, so that momentum built up in the intake tract is sustained and translated into rotational swirl in the cylinder. This technique may require a relatively long intake tract in the cylinder head in which to develop the necessary momentum, and this in turn can drive the need for a skewed valve layout in the cylinder head (“skewed” as used herein should be taken to mean a layout wherein the valve pairs do not lie in a line parallel to or orthogonal to the axis of the cylinder bank). Such a layout is problematic for a conventional mechanical valve train since the distance from the camshaft to each valve stem is different, resulting in complex linkage solutions or compromised port design. Again, swirl is fundamental to efficient diesel combustion, so the ability to optimize the inlet port for swirl rather than for valve train considerations would provide a competitive advantage. What is needed in the art is a means for removing valve train considerations as port design constraints.  
         [0011]     Given these incentives to escape from the constraints of mechanical linkages, several electromechanical and electro-hydraulic concepts have been proposed in publications in the engine arts, but none has been accepted or commercialized to date due to excessive cost, complexity, and durability concerns.  
         [0012]     A separate but related interest in the engine arts is variable valve activation (VVA) of engine valves, especially intake valves, also known interchangeably in the art as variable valve deactivation. To selectively shut off one or more engine valves to improve fuel efficiency in low load conditions, various design approaches to partial or total deactivation are well known. In each such design approach, a valve-deactivation strategy is incorporated wherein the rotary motion of an engine cam continues unabated but the lift motion is lost in the translation between the cam and its associated valve(s) by a mechanical decoupling of the valve train. In the prior art, mechanical accommodation is provided for the lost motion via, for example, a variably-latchable rocker arm assembly or a variably-latchable hydraulic valve lifter assembly.  
         [0013]     Various electro-hydraulic systems also have been proposed in the prior art, wherein a primary piston actuated by hydraulic linkage to a cam drives a valve stem, and a lost-motion chamber for accumulating hydraulic fluid may be selectively accessed via a high-speed solenoid valve. See, for example, U.S. Pat. No. 6,227,154 wherein a solenoid-actuated three-port spool valve selects between a valve-actuating piston and a lost-motion piston. A general shortcoming of such systems is the flow restriction imposed by the solenoid valve itself, limiting the speed of response of the system and creating high pumping losses. Further, such designs are not readily applicable to non-overhead cam engines. Further, such prior art designs use engine oil as the hydraulic medium, which oil becomes dirty and degraded with carbon deposits during prolonged use, resulting in wear, clogging, and variable performance of the LM system.  
         [0014]     An alternative approach is known in the prior art and is exemplarily disclosed in U.S. Pat. No. 4,716,863, wherein a slave piston actuated by hydraulic linkage to a master piston and cam drives an intake valve stem, and a solenoid controls the position of a secondary accumulation piston in a sidearm and “thus expansion of the hydraulic line volume, thereby controlling the opening and closing, timing, and displacement of the intake valve.” Access to the pressure chamber formed in the sidearm does not require passage of hydraulic fluid through a valve. A serious shortcoming of this configuration is that a relatively large, powerful, and expensive solenoid is required to manage precise positioning of the accumulation piston against the entire force brought to bear on the face of the piston; such a solenoid typically lacks the desired high rate of response. The above-recited shortcomings resulting from use of engine oil as the hydraulic medium also pertain.  
         [0015]     A further related interest in the engine arts is variation in the timing of opening and closing, and of the amplitude of opening, for both intake valves and exhaust valves for a variety of engine operational modes. This interest extends to both SI and CI engines. When combined with LM capability, the resulting flexibility in valve operation can have very large effects in a wide variety of vehicle and engine parameters, including at least fuel efficiency, ease of starting, low-end torque and turbocharged transient behavior, pollution abatement, vehicle braking; and engine wear, complexity, cost of manufacture, and ease of repair. Comparable improvements in these categories cannot be readily achieved in any way other than VVA/LM.  
         [0016]     What is needed in the art is means for efficiently and economically combining variable valve actuation and lost-motion capability in an electro-hydraulic valve train.  
         [0017]     It is a principal object of the present invention to provide improvements in fuel efficiency, ease of starting, low-end torque and turbocharged transient behavior, pollution abatement, vehicle braking; and engine wear, complexity, cost of manufacture, and ease of repair in an internal combustion engine.  
         [0018]     It is a further object of the present invention to provide such improvements in a compression-ignited engine, whether operating on the Diesel cycle or alternative cycles such as Homogeneous Charge Compression Ignition (HCCI), whether in two-, four-, six- or eight-stroke combustion cycles as are known in the prior art.  
       SUMMARY OF THE INVENTION  
       [0019]     Briefly described, an electro-hydraulic lost motion system for variable valve activation in accordance with the invention includes a master piston freely slidable in a first bore in an internal combustion engine in response to rotation of an engine cam associated with an engine valve, either intake or exhaust.  
         [0020]     The first bore is remote from the valve to be variably controlled and also contains a slidable accumulation piston defining a movable pressure chamber between the master piston and the accumulation piston. The pressure chamber is supplied with hydraulic fluid as may be needed via a port in the first bore.  
         [0021]     A slave piston operative in a slave piston housing adjacent the engine valve is hydraulically connected to the pressure chamber via a passageway such that, in valve activation mode of the system, rotation of the cam causes the slave piston to open and close the valve.  
         [0022]     The outer end of the first bore is closed by a housing including a second bore open toward the accumulation piston and defining a small hydraulic control chamber. A solenoid-actuated servo-valve connects the control chamber to a hydraulic sump.  
         [0023]     The accumulation piston is provided with a hollow rod extending slidably into the second bore. An opening in the accumulation piston provides hydraulic communication between the pressure chamber and the control chamber through the hollow rod, and the hollow rod defines a control piston for varying the volume of the control chamber in accordance with position of the accumulation piston in the first bore. A check valve in the control piston prevents egress of hydraulic fluid into the pressure chamber during LM displacement of the accumulation piston.  
         [0024]     During valve-activation mode, the servo-valve is kept closed, the volume of the control chamber is thus fixed, and accordingly the accumulation piston cannot retract. Consequently, motion of the master piston causes the slave piston to be actuated, opening the engine valve.  
         [0025]     During valve-deactivation mode, the servo-valve is opened during the master piston stroke, the control piston is thus free to slide further into the second bore decreasing the volume of the control chamber by displacing hydraulic fluid through the servo-valve to the sump, and the accumulation piston is displaced in lost motion instead of the slave piston. At the end of the accumulation piston stroke, the servo-valve is closed as a check valve against aspiration of air into the control chamber from the sump. A return spring behind the accumulation piston urges the accumulation piston, and hence the master piston, in a return stroke as the cam lobe moves into the retraction phase. A suction is drawn in the control chamber, causing the chamber to refill with hydraulic fluid from the pressure chamber in readiness for the next lost-motion stroke.  
         [0026]     A lost motion system in accordance with the invention is readily adaptable to either SI or CI engines but is especially suited to diesel-type engines wherein the hydraulic fluid is preferably diesel fuel supplied by the fuel injection system rail supply pump, and especially V-style engines wherein a single camshaft in the V can actuate all intake and exhaust valves. Additionally, when a cam phaser device is incorporated in the camshaft drive, the timing of valve opening, closing, valve lift, and intake/exhaust crossover, can be highly controlled by the judicious manipulation of the two mechanisms to optimize engine operation over a variety of operating modes.  
         [0027]     A particular benefit of an electro-hydraulic valve train in accordance with the invention is that the location of the camshaft during the base engine architectural design phase may be determined by the convenience of the drive arrangement, rather than, as in the prior art, by the location of the valves. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0029]      FIG. 1  is an elevational cross-sectional view of a portion of a V-style internal combustion engine in accordance with the invention, showing a novel lost-motion system and subassembly in the valve train;  
         [0030]      FIG. 2  is an elevational cross-sectional view of a V-style compression-ignited internal combustion engine incorporating the lost-motion system shown in  FIG. 1 , and showing exemplary single- and paired-valve actuations;  
         [0031]      FIG. 3  is a schematic cross-sectional elevational view of the engine shown in  FIG. 2 , showing the driving relationship between the crankshaft, the camshaft, a camshaft phaser, the fuel pumping system, and a lost-motion valve system;  
         [0032]      FIG. 4  is a graph of fluid viscosity as a function of temperature, comparing the Theological characteristics of diesel fuel and SAE 30 engine oil as a hydraulic fluid;  
         [0033]      FIG. 5  is an enlarged cross-sectional view of a first embodiment of a servo-valve, normally-closed, as may be used in the lost motion system shown in  FIGS. 1 and 2 ;  
         [0034]      FIG. 6  is an enlarged cross-sectional view of a second embodiment of a servo-valve, normally-open, as may be used in the lost motion system shown in  FIGS. 1 and 2 ;  
         [0035]      FIG. 7  is an elevational cross-sectional view of a compression-ignited cylinder having a domed firing chamber, showing first and second alternative embodiments of a lost motion system including the lost motion subassembly shown in  FIGS. 1 and 2  located at the engine valve rather than at the camshaft;  
         [0036]      FIG. 8  is an elevational cross-sectional view of a compression-ignited cylinder having a domed firing chamber, showing another embodiment of a lost motion system in accordance with the invention; and  
         [0037]      FIG. 9  is a schematic plan view of an engine head showing exemplary arrangements of valves in a four-valve cylinder.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]     Referring to  FIGS. 1 and 2 , a novel electro-hydraulic lost-motion valve control system  10  in accordance with the invention is shown for use as a component of an internal combustion engine  12 . Engine  12  as shown has a V-style engine block  14  (for example, a V- 6  engine) having a single camshaft  16  (for example, as shown for a V-6 engine in  FIG. 3 ) disposed centrally in a V-shaped well  18  within engine block  14 , although the invention may be readily adapted to other engine layouts. Roller finger followers  20  are pivotably mounted to mounting flanges  22  extending into well  18  from engine block  14  for following the surfaces  23  of individual cam lobes  17  of camshaft  16 .  
         [0039]     The combustion cycle of engine  12  may be two-stroke, four-stroke, six-stroke, or eight-stroke as is known in the prior art.  
         [0040]     Lost-motion valve control assembly  10  comprises a body  24  mounted on flanges  22 . Preferably, body  24  is modular and contains a plurality of assemblies  10  disposed along the length of engine  12  and camshaft  16 , one per valve train for each intake and exhaust valve. Body  24  includes a main bore  26  orthogonal to the axis  28  of camshaft  16  for slidably receiving a free master piston  30  that rides on a finger follower  20  and is freely displaceable thereby in main bore  26  in response to rotation of camshaft  16 . In a currently-preferred embodiment, the finger followers  20  for the intake valves and the exhaust valves of an individual cylinder may be driven by a single cam lobe, the followers being so arranged that they contact the cam lobe at the appropriate phase relationship and thereby impart the cam motion with the correct valve event timing to the LM master piston  30 .  
         [0041]     A lost-motion servo-controlled module  32  is disposed in a shoulder  34  at the outer end of an LM bore  26 ′ and includes an accumulation piston  36  extending into LM bore  26 ′ and cooperating with master piston  30  to define, in conjunction with a first side  35  of piston  36 , a pressure chamber  38  therebetween, having a lost motion volume  39 . In the example shown in  FIGS. 1 and 2 , LM bore  26 ′ is proximate to and coaxial with main bore  26 ; however, as is shown in  FIG. 7 , within the scope of the invention, LM bore  26 ′ may be remote from main bore  26  and may be formed, for example, in the engine head  88 ′ rather than in body  24 .  
         [0042]     Module  32  includes a valve body  40  for a servo-valve  42  linearly actuated by a solenoid  44 . A shell  46  surrounds valve body  40  and solenoid  44 . Accumulation piston  36  includes a flange  48  for engaging shoulder  34  to limit travel of piston  36  away from solenoid  44 . A well  50  provides for and limits travel of piston  36  in the opposite direction. A return spring  52  urges piston  36  away from valve body  40 . Well  50  is in communication with a hydraulic sump (not shown) via a gutter  54  in assembly body  24  preferably extending the length of assembly body  24 . Preferably, well  50  is also modular and extends the length of module valve body  40  such that a linear plurality of modules  32  are in communication, thereby relieving pressure imbalances among the plurality of wells  50  as the individual accumulation pistons are displaced, as described below.  
         [0043]     Valve body  40  includes an axial bore  56  open toward piston  36 . A hollow control piston  58  is fixedly received in a socket  60  formed in a second side  37  of piston  36  and extends partially into bore  56  to define a control chamber  62 , the volume of which thus changes in direct relation to the position of accumulator piston  36  within LM bore  26 ′. A passage  64  through piston  36  allows hydraulic communication between pressure chamber  38  and control chamber  62  via control piston  58 . A check valve  66  prevents backflow of hydraulic fluid from control chamber  62  into pressure chamber  38 .  
         [0044]     Valve body  40  comprises a first body element  40 a and a second body element  40 b and includes a valve chamber  68  having a conventional seat  70 , a first passage  72  between control chamber  62  and valve chamber  68 , and a second passage  74  between chamber  68  and well  50 , the two separate body elements facilitating machining of the passages. Servo-valve  42  regulates flow through passages  72 , 74 .  
         [0045]     A hydraulic fluid supply gallery  76  runs the length of assembly body  24  and communicates with pressure chamber  38  via a check valve  78 .  
         [0046]     An actuation passage  80  in body  24  extends from pressure chamber  38  to a hydraulic line  82  which leads to a slave cylinder block  84  adjacent an engine valve  86  in engine head  88  to be controlled by electro-hydraulic lost-motion valve control assembly  10 . A slave piston  90  disposed in slave bore  85  in block  84  actuates valve  86  in response to hydraulic pressure from pressure chamber  38 . Of course, the actuated valve may be a pair of valves  86   a , 86   b  connected conventionally by a bridge structure  88 , as is known in the prior art.  FIG. 1  shows actuation passages extending from both sides of chamber  38  and body  24 ; this is intended to show that outlets on both sides of the housing are possible, although normally only one such conduit per chamber should be expected.  
         [0047]     Referring now to  FIG. 3 , in a currently preferred embodiment of an electro-hydraulic lost-motion valve control assembly  10  for use in a CI engine such as a diesel engine  12 - a , the hydraulic fluid is diesel fuel supplied from the engine fuel supply system. In a preferred engine layout, camshaft  16  is driven from the flywheel end  92  of crankshaft  94  as by gears  96   a , 96   b , timing belts (not shown), or timing chains (not shown) as is known in the prior art. This location for the camshaft drive elements, adjacent the flywheel  95  and at substantially a nodal point of crankshaft torsional flexure, provides for improved camshaft rotational uniformity over the uniformity resulting from prior art camshaft drives from the non-flywheel, “free” end  97  of the crankshaft. Thus, a more stable and precise valve timing may be obtained.  
         [0048]     A high-pressure fuel pump  98  for dispensing diesel fuel to the fuel rail or rails of the engine is conveniently disposed on the free end of camshaft  16 . An additional transfer pump  100  disposed on fuel pump  98  supplies diesel fuel to the previously-described gallery  76  in body  24 .  
         [0049]     Driving the fuel pump from the free end of the camshaft also makes possible a significant reduction of undesirable pumping pulses experienced at the engine fuel injectors (as occurs in prior art fuel pump systems wherein the fuel pump is driven from the crankshaft, the camshaft, or by an electric motor and typically includes a flywheel to damp out pulses) by adjusting the angular relationship of the pump to the camshaft such that the negative and positive pump pulses are in cancelling phase with the camshaft rotational pulses resulting from engine valve events, thereby smoothing the pump output.  
         [0050]     Referring again to  FIG. 3 , a conventional camshaft phaser  102  may be interposed between camshaft drive gear  96   b  and camshaft  16  so that the phase relationship between the crankshaft and the camshaft may be altered as may be found beneficial. Cam profiles may then be dimensioned for a near-normal lift duration; otherwise, greatly extended duration profiles are necessary to accommodate a full range of desired valve event timings, and normal durations would have to be provided by invoking the lost-motion facility. It is not known in the prior art to combine lost-motion capability with camshaft phasing capability. In the present invention, the combination is made relatively simple by providing the phaser at the flywheel-driven end of the camshaft and disposing the fuel pumping apparatus on the opposite, free end  97  of the camshaft.  
         [0051]     It will be seen that a potential danger is created in providing camshaft phasing together with a valve lost-motion system  10  in an interference engine such as a diesel engine, because failure of control of the lost-motion system can result in destructive collision of the valves with the pistons. However, such combination can provide a hitherto impossible range of valve timing and valve lift, resulting in greatly improved operation and fuel efficiency over a wide range of engine and vehicle operating conditions.  
         [0052]     Referring to  FIGS. 5 and 6 , it is seen that servo-valve  42  may be configured as normally closed ( 42   a ) ( FIGS. 1 and 2 ) or normally open ( 42   b ). In either case, the shaft  43   a , 43   b  is provided with a reduced-diameter portion  45   a , 45   b  having bevels  47   a , 47   b  of approximately equal areas such that the valve is urged by fluid in passage  72  with equal force in the open and closed directions and is thus force-balanced, requiring a relatively small and agile solenoid  44  for actuation in either direction. When servo-valve  42   a  is used, failure of the solenoid simply disables the lost-motion capability, and a vehicle with such an engine could still be driven to a repair shop (“limp-home” mode). However, if an oversized cam is also being employed, failure of an LM system employing servo-valve  42   a  can result in piston/valve interference, as noted above. For servo-valve  42   b , solenoid failure leaves the engine in LM mode with the respective valves unopenable, and such a vehicle would therefore be undriveable if all such valves were affected (no “limp-home” mode). However, failure of servo-valve  42 b does not jeopardize the engine for piston/valve collision.  
         [0053]     The use of diesel fuel as the hydraulic fluid for a lost-motion system in accordance with the invention is a significant improvement in the engine arts. In prior art LM systems, the hydraulic fluid typically is engine oil provided from the engine crankcase. With use as an engine lubricant, engine oil becomes loaded with carbon from exhaust blow-by which causes wear of mechanical parts and clogging of passages. Diesel fuel is highly filtered before entering an engine fuel distribution system and is not subject to long-term reuse as is engine oil. Thus diesel passages can remain clean and free of build-up during engine use. Referring to  FIG. 4 , it is seen that diesel fuel is substantially less viscous than, for example, SAE 30 engine oil, by at least an order of magnitude. This is a critical difference, as in any electro-hydraulic LM system, some hydraulic fluid must flow through an electrically-controlled mechanical valve. Low viscosity of the fluid is important to a low-hysteresis, rapid-response system. Further, diesel fuel has a thermal viscosity coefficient (slopes of the respective curves in  FIG. 4 ) at least comparable to that of engine oil.  
         [0054]     It should be noted that a potentially negative aspect of an electro-hydraulic lost-motion valve train is that the fluid volume per valve line through which the valve actuating force is transmitted is large, and the stiffness of the system is not as great as prior art fully-mechanical mechanisms. Therefore, efforts should be made to minimize the internal fluid volumes without restricting flow areas, for example, through use of techniques that are common in the prior art of diesel fuel injection such as using volume reducers in spring chambers (not shown). Simple calculations suggest that for an exemplary embodiment in which the engine valve opening load is 900 N, the slave piston diameter is 12 mm, and the system dead volume is 4880 mm 3 , the loss of lift from fuel compressibility alone will be about 0.24 mm, or about 2% of nominal.  
         [0055]     In the present invention, diesel fuel is the preferred lubricant for all the camshaft bearings  15 , slave pistons  90 , master pistons  30 , lost-motion accumulation pistons  36 , and servo-valves  42  for electro-hydraulic lost-motion valve control assemblies  10 . As in the prior art, crankcase oil can be used to lubricate lower crankcase components such as, for example, crankshaft bearings  93 , connecting rod bearings  99 , and wrist pins (not shown).  
         [0056]     In operation, referring to  FIGS. 1 and 2 , electro-hydraulic lost-motion valve control assembly  10  operates as follows.  
         [0057]     At a starting position, cam followers  20  are on a base circle portion of camshaft lobe  17 . Gallery  76  is filled with diesel fuel under pressure, for example, about 7 bar. Pressure chamber  38 , control chamber  62 , and passage  80  and line  82  are filled with hydraulic fluid (diesel fuel). Servo-valve  42  is closed, making control chamber  62  and its associated passages hydraulically rigid. Engine valve  86  is closed.  
         [0058]     When the engine is in normal, conventional operating mode, as cam  16  rotates eccentric  110  past finger follower  20 , master piston  30  is moved toward accumulation piston  36 , which cannot move because servo-valve  42  is closed. Thus, pressure chamber  38  is compressed and hydraulic fluid is forced through line  82 , causing slave piston  90  to open engine valve  86 . When eccentric  110  passes TDC on follower  20 , master piston  30  follows follower  20  as it returns to the base circle portion of camshaft lobe  17  in response to force from the engine valve closing spring  87 .  
         [0059]     When the engine is in LM operating mode, servo-valve  42  is initially open. As cam  16  rotates eccentric  110  past finger follower  20 , master piston  30  is moved toward accumulation piston  36 . Because control chamber  62  is hydraulically open to well  50  through servo-valve  42 , and because engine valve spring  87  is stronger than return spring  52 , accumulation piston  36  moves instead of slave piston  90 , displacing hydraulic fluid from control chamber  62  into well  50  from whence the fluid drains via gutter  54 . Accumulation piston  36  moves in LM bore  26 ′ in tandem with master piston  30  in main bore  26 , thus maintaining substantially constant the volume of pressure chamber  38 . At the top of the stroke of the two pistons, servo-valve  42  is closed. When eccentric  110  passes TDC on follower  20 , master piston  30 , accompanied by pressure chamber  38  and accumulation piston  36  follows follower  20  as it returns to the base circle portion of camshaft lobe  17  in response to force from return spring  52 . As this occurs, a vacuum is created in control chamber  62 , and hydraulic fluid from pressure chamber  38  is drawn in via passage  64  and check valve  66 , and an equivalent amount is replenished to pressure chamber  38  from gallery  76  via check valve  78 . At the end of the return stroke, servo-valve  42  is reopened in preparation for the next lost-motion requirement.  
         [0060]     The above operating description explains the sequence of events where the required engine valve motion is as fully described by the cam profile. However, a well-known advantage of lost-motion systems is that late opening (and by definition centered reduced lift and duration valve events) or early closing or altogether skipped valve events are possible. To achieve this functionality, a mechanism having rapid response is necessary, and the apparatus disclosed herein has unique advantages with respect to the prior art. The following are some possible modified valve events.  
         [0061]     For a skipped valve event (normal LM mode), servo-control valve  42  remains off its seat through the positive lift portion of the event so that the master piston displacement translates into a matching displacement of accumulation piston  36 . In turn, hollow control piston  58  displaces fluid from control chamber  62  through the servo-valve to drain via gutter  54 . The control piston is sized to minimize wasted fluid, and a small piston diameter permits a small control valve with minimal energy requirements, a significant improvement over the prior art. Retraction of control piston  58  allows a return of accumulation piston  36  and a subsequent recharging of control chamber  62 . This capability is essential to achieve cylinder disablement, and also for event disablement as where, for example, additional cam bumps (not shown) are provided for engine compression braking or for 2- or 6-stroke operation, which are known in the art to be enablers for some advanced combustion cycles.  
         [0062]     For an early closing valve event, either intake valve or exhaust valve, the sequence of events is as described above; but at the crank angle when it is desired for the engine valve to close, the servo-control valve opens, allowing the accumulation piston to retract and thus permitting the engine valve to seat. As the master piston continues to retract after the engine valve has seated, the servo-control valve closes, allowing the accumulation piston to return with the master piston, thus minimizing wasted fluid.  
         [0063]     For a delayed valve opening event, either intake valve or exhaust valve, the servo-control valve remains open until the appropriate time, at which point it closes, arresting the LM displacement of the accumulation piston. At that point, continued travel of the master piston causes corresponding displacement of the slave piston. A potential weakness of all LM strategies is that the point at which engine valve motion is required and the control valve is to be closed may coincide with a high acceleration portion of the cam profile. This can lead to a high “jerk” motion to the valvetrain system and hence to high stress and instability. To offset this, multiple pulsing of the servo-control valve may be invoked by an algorithm that relates control valve pulses to the system natural frequency so that the undesirable motions are cancelled out, which strategy is analogous to similar strategies in the diesel prior art with this control valve when used for fuel injection. Again, to minimize fluid loss, the servo-valve reopens for the final portion of the master piston return stroke as described above.  
         [0064]     The capability of rapid, multiple actuations of the servo-valve can be extremely useful during a portion of a valve event, such as engine valve closing. In the prior art, it is known to provide a hydraulic snubber for each valve to soften the closing impact. Such snubbers are well-known in art for being vulnerable to a variety of problems, such as oil viscosity variation, leading to variation in snubbing effectiveness, and valve seat recession and/or valve expansion lengthwise affecting duration of snubbing action. For an engine equipped in accordance with the present invention, snubbers may be omitted, at a considerable cost savings. When full duration valve lift is required, appropriate valve seating velocity is enabled by the cam profile, but when early valve closing is required, the servo-valve may be multiply pulsed during the closing stroke to soften the closing impact of the engine valve.  
         [0065]     A first significant advantage of the layout shown in  FIGS. 1 and 2 , and of the invention, is that a single camshaft can replace the four dual overhead camshafts that would typically be used in such an engine in the prior art.  
         [0066]     A second advantage is that, by appropriate layout of the camshaft  16 , roller finger followers  20 , and engine flanges  22 , both the intake and exhaust valves for each engine cylinder may be actuated by a single camshaft lobe  17  (see  FIG. 3 ), thus simplifying the design and manufacture of a camshaft.  
         [0067]     A third advantage is that the entire upper end of the engine is lubricated by a high-quality, low-viscosity, non-carbonizing hydraulic fluid separate from the engine crankcase oil.  
         [0068]     A fourth advantage is that the preferred system takes advantage of known technology in a number of critical areas. For example, the servo-valve  42  is substantially identical with a fuel injection valve currently in production and having a long history of reliability. See U.S. Pat. No. 5,934,643 issued Aug. 10, 1999 to Cooke. For another example, the close piston-to-bore clearances necessary for acceptable leakage with diesel fuel are a core competency in the art of fuel-injected engines; and relaxed tolerances are possible if the additional complication of elastomeric seals such as O-rings are incorporated.  
         [0069]     A fifth advantage is that the positioning and movement of the accumulator piston is governed by a force-balanced servo-valve which permits displacement of a relatively small amount of hydraulic fluid from or to the control chamber to accommodate lost motion of the accumulator piston, as opposed to various prior art systems wherein either all the displaced hydraulic fluid must pass through the control valve (e.g., U.S. Pat. No. 6,227,154 B1; U.S. patent application Publication 2003/0221663 A1) or the entire force of the pressure chamber on the accumulation piston must be resisted by a solenoid (e.g., U.S. Pat. No. 4,716,863).  
         [0070]     Referring to  FIG. 7 , in second and third alternative engine configurations  12 - b , 12 - c , respectively, in accordance with the invention, lost-motion servo-controlled module  32  may be placed in an LM bore  26 ′ formed in the engine head  88 ′, which bore defines a sidearm in communication with slave piston  90 . Bore  26 ′ may be formed co-linear with piston  90  (configuration  12 - b ) or orthogonal thereto (configuration  12 - c ), or at any other angle thereto as may be desired. The camshaft, roller follower, and master piston arrangement from  FIGS. 1 and 2  remain unchanged, but lost-motion volume changes now occur in the head rather than in the engine V. In some applications, locating module  32  in the engine head adjacent the valve being controlled can be advantageous for speed of valve response. However, line pressure losses between the master piston and the accumulation piston must be taken into account.  
         [0071]     Referring to  FIG. 8 , a fourth configuration  12 - d  is similar to first configuration wherein slave piston  90  is disposed in a slave bore in head  88 , except that the motion of slave piston  90  is transmitted to valve  86  via a rocker arm  91 .  
         [0072]     Referring to  FIGS. 7 and 8 , an important engine design freedom conferred by an electro-hydraulic valve train system in accordance with the invention is that the engine valves  86  and their respective seats  86 a may be readily oriented at any desired angle with respect to the engine cylinder  120  and cylinder axis  122 . Further, the firing chamber  124  in head  88 ,  88 ′ need not be flat as in the prior art. An especially desirable shape for firing chamber  124  is domed, as shown in  FIG. 7 , wherein the valve axes  126  may be oriented non-parallel to cylinder axis  122  and preferably radially of a point  128  on cylinder axis  122 . If desired further, the valves may be positioned at a compound angle (not shown) such that the valve axes do not intersect either each other or the cylinder axis. The dome shape may be spherical or not.  
         [0073]     Radial valves offer larger port areas, better breathing, improved injector cooling, and are synergistic to a “narrow angle” diesel combustion chamber which is known in the recent diesel development literature to be favored for advanced “pre-mixed” fuel injection systems. A domed firing chamber provides a longer length of “free plume” spray  132  from a fuel injector  134 .  
         [0074]     Disposing the valve axes at an angle to the cylinder axis also creates valuable room above the firing chamber, permitting installation of a highly-desirable cylinder pressure sensor  130 . Such a sensor, by providing a real-time signal of when a valve is open and closed, can permit timing of the multiple control pulses during valve closing, as described above, to achieve consistent valve seating under any condition of engine operation or wear.  
         [0075]     Referring now to  FIG. 9 , another important advantage of an electro-hydraulic valve train system in accordance with the invention is that the axes of paired intake and exhaust valves need not be placed in a plane containing the motion of a rocker arm as in the prior art. This permits the valving to be “skewed” to produce tangential entry of intake gases and tangential exit of exhaust gases, resulting in swirl of gases within the cylinder which is known to be highly beneficial for good mixing.  
         [0076]      FIG. 9  is a schematic plan view of an idealized cylinder head  200  having three cylinder firing chambers  202   a , 202   b , 202   c , four valves per cylinder (two intake  204  having axes  205 , and two exhaust  206  having axes  207 ), a fuel injector  208  coaxial with the cylinder axis  210 , six head bolts  212  per cylinder, and a single overhead camshaft  214  having an axis  216 . (It should be understood that the firing chambers are non-identical for purposes of illustration, and the head does not represent an actual engine head configuration.)  
         [0077]     Chamber  202   a  shows a conventional prior art orientation of the valves as operated by a mechanical valve train (not shown). Intake valves  204   a  are equidistant from camshaft axis  216 , as are exhaust valves  206   a  and their respective seats. The valves typically are operated in tandem by a mechanical bridge arrangement similar to bridge  89  in  FIG. 2 , the intake valve train extending over the fuel injector in a very compacted arrangement. The valve axes  205 , 207  are parallel to cylinder axis  210 .  
         [0078]     Referring to chamber  202   b , the mechanical relationships should be understood to be identical with those of chamber  202   a . The purpose of chamber  202   b  is to show the effect of prior art intake and exhaust porting accompanying the valve configuration. Separate and identical intake ports  218   b  service intake valves  204   b , and separate exhaust ports  220   b  service exhaust valves  206   b . Because the cylinder, valves, and porting are symmetrically disposed about a plane of symmetry  222  orthogonal, which is also orthogonal to camshaft axis  216 , gases entering and exiting the cylinder have zero net vector tangential to the cylinder wall; that is, in the prior art valve configuration, there is no swirl produced.  
         [0079]     Referring to chamber  202   c , the valve train for which should be understood to include an electro-hydraulic apparatus in accordance with the invention, because the valves are not bound by mechanical actuation linkage restrictions, intake valves  204   c  and exhaust valves  206   c  and their respective seats  204   c ′ and  206   c ′ need not be equidistant from camshaft axis  216  as in the prior art, i.e., the valves are “skewed” with respect to prior art symmetry plane  222 . Further, the valve axes  205   c , 207   c  need not be parallel to cylinder axis  210  but preferably are non-parallel thereto and preferably are disposed radially thereof, as described hereinabove with respect to  FIGS. 7 and 8 . Preferably, firing chamber  202   c  is domed, similar to chamber  124  ( FIG. 7 ).  
         [0080]     A very important benefit of skewed valves is that intake ports  218   c  may be readily configured such that the cylinder-tangential vectors of gases entering through the two intake valves  204   c  reinforce each other, producing a counterclockwise (in this example) swirl  219  of gases in the cylinder, rather than cancel each other as in prior art intake valves  204   b . Further, by selectively deactivating one of exhaust valves  206   c , swirl  221  may be produced in the exhaust gases as well, which can be very helpful in mixing exhaust gases with intake gases in some engine operation modes.  
         [0081]     While the invention has been described by reference to various 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 will have full scope defined by the language of the following claims.