Abstract:
An engine with a lockable valve actuator and method of controlling an engine with such an actuator are disclosed. The actuator may include an actuator cylinder with an actuator piston reciprocatingly disposed therein. The actuator piston may be moved by directing pressurized fluid into the actuator cylinder, and locked into a given position by maintaining the pressurized fluid in the actuator cylinder. The actuator may be used in conjunction with a mechanically driven actuator used to move a valve, with the fluidically driven actuator being used to maintain the valve into a desired position.

Description:
CROSS-REFERENCE  
       [0001]    This application is a continuation of U.S. patent application Ser. No. 10/067,030, which was filed on Feb. 4, 2002. 
     
    
     
       TECHNICAL FIELD  
         [0002]    This disclosure relates generally to internal combustion engines and, more particularly, to engine valve actuators.  
         BACKGROUND  
         [0003]    The operation of an internal combustion engine requires, among other things, the timed opening and closing of a plurality of valves. For example, with a typical four-stroke, diesel engine, one of ordinary skill in the art will readily recognize such an engine operates through four distinct strokes of a piston reciprocating through a cylinder, with intake and exhaust valves operating in conjunction with the piston. In an intake stroke, the piston descends through the cylinder while an intake valve is open. The resulting vacuum draws air into the cylinder. In a subsequent compression stroke, the piston reverses direction while the intake valve and an exhaust valve are closed, thereby compressing the air within the cylinder. This is followed by a combustion or power stroke wherein fuel is injected into the compressed air and thereby ignited, with the resulting force pushing the piston again in the descending direction while both the intake and exhaust valves are closed. Finally, the piston reverses direction with the exhaust valve open, thereby pushing the combustion gases out of the cylinder.  
           [0004]    In certain variations on the typical diesel or Otto cycle, it is desirable to open or close one of the intake and/or exhaust valves at alternative times. For example, in a compression release braking mode, the exhaust valve is opened as the piston approaches a top dead center position during the compression stroke to, in effect, increase engine braking operation. In so doing the engine cylinders draw in air during the intake stroke, compress the air, and then vent the compressed air out of the exhaust valve near top dead center of the piston.  
           [0005]    Another mode of engine operation requiring atypical valve sequencing is known as the Miller cycle. During the Miller cycle, the intake valve is held open during the initial stages of the compression stroke. Such operation reduces the effective compression ratio of the engine and results in a more mechanically efficient power producing engine. Alternatively, the intake valve is closed prior to completion of a normal intake stroke to provide Miller cycle benefits.  
           [0006]    One other situation modifying typical valve operation is internal exhaust gas recirculation. One disadvantage of diesel or Otto cycle engine operation is that all of the fuel brought into the cylinder and compressed may not entirely combust. Among other things, this phenomenon may be undesirable due to an unacceptably high level of pollutants, such as nitrous oxide (NOx) and particulates, being released during the exhaust stroke.  
           [0007]    Exhaust gas recirculation (hereinafter referred to as “EGR”) attempts to curtail such drawbacks of conventional engine operation. With EGR, at least a portion of the exhaust gases is not exhausted to the atmosphere, but rather is introduced back into the engine cylinder to be combusted in subsequent power or combustion strokes of the engine. With typical internal EGR, the exhaust gases are expelled through the exhaust valve and reintroduced to the cylinder through the exhaust valve itself. Such a process requires that the exhaust valve stay open not only through the exhaust stroke, but also on the intake stroke, after the piston reverses direction, thereby creating a vacuum and drawing a portion of the exhaust gases back into the cylinder through the still open exhaust valve.  
           [0008]    One of ordinary skill in the art will readily appreciate that a substantial force is required to open the exhaust valve and maintain the valve in an open position as the piston reciprocates through the cylinder toward the top dead center position. A valve actuator employing highly pressurized oil may be used to apply this force to open the exhaust valve.  
           [0009]    However, holding an exhaust valve in an open position by a valve actuator employing highly pressurized oil requires, for example, pressurized oil on the order of fifteen hundred to five thousand pounds per square inch (10.34 to 34.4 MPa). The engine or machine in which the engine has been mounted therefore has had to provide a high pressure source or high pressure rail and be able to supply the high pressure oil to the actuator when desired. Such a requirement has, among other things, the disadvantage, at least with respect to Miller cycle and EGR operation, of decreasing the engine efficiency in that the engine must continually direct usable work to the high pressure rail to maintain such pressures even though the high pressure oil is only required for a relatively short duration during the engine operation. Not only is the provision of such pressurized fluid taxing on the efficiency of the engine, but with certain machines the provision of such a high pressure rail is simply not available or desirable.  
           [0010]    The present disclosure is directed to overcoming one or more of the problems or disadvantages associated with the prior art.  
         SUMMARY  
         [0011]    In accordance with one aspect of the disclosure, an engine valve assembly includes a valve seat and an engine valve element adapted to move relative to the valve seat between an open position and a closed position. A mechanically driven actuator can be adapted to move the valve element to the open position. A fluidically driven actuator can be adapted to prevent the valve element from moving to the closed position. The fluidically driven actuator can include an actuator piston reciprocatingly disposed in an actuator cylinder. The actuator piston can be adapted to maintain the engine valve element in an intermediate position between the closed position and the open position. The actuator cylinder is in fluid communication with a source of pressurized fluid. The source of pressurized is insufficient to move the valve element toward the open position in an internal combustion engine. A control valve can be adapted to pass the flow of the pressurized fluid to the actuator cylinder during movement of the valve element toward the open position. The valve is operable for maintaining the fluid in the actuator cylinder during movement of the valve element toward the closed position to maintain the valve at the intermediate position.  
           [0012]    In accordance with another aspect of the disclosure, a valve assembly includes an engine cylinder and an engine piston reciprocatingly movable relative to the engine cylinder. An engine valve element is disposed in a port that is connected to the engine cylinder. A source of low pressure fluid is in fluid communication with a fluidically driven valve actuator. A force generated by the source of low pressure fluid is sufficient to move the valve element and take up lash associated with the valve element and the valve actuator. An engine driven mechanical linkage mounted proximate the engine valve element is adapted to move the engine valve element to an open position. A control valve is adapted to control flow of the pressurized fluid from the source of low pressure fluid to the valve actuator.  
           [0013]    In accordance with another aspect of the disclosure, a variable valve actuator includes a valve positioned adjacent an engine cylinder and an engine driven mechanical actuator system adapted to move the valve between first and second positions. A fluidically driven valve actuator in predetermined intermittent fluid communication with a fluid pressurization source is provided. The fluidically driven actuator is adapted to prevent the valve from moving to the second position for a predetermined period of time. A control valve is adapted to shut off fluid communication between the fluid pressurization source and the fluidically driven valve actuator and to prevent fluid from back flowing out of the fluidically driven actuator causing the fluidically driven actuator to become hydraulically locked.  
           [0014]    In accordance with yet another aspect of the disclosure, a method of controlling an engine having at least one valve includes moving the valve from a first position to a second position with a mechanically driven actuator, moving the valve from the second position to an intermediate position between the first and second positions, and holding the valve in the intermediate position with a fluidically driven actuator in a hydraulically locked configuration. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a diagrammatic cross-sectional view of an embodiment of an internal combustion engine showing an engine block, cylinder head and engine valve actuator;  
         [0016]    [0016]FIG. 2 is cross-sectional view of the engine of FIG. 1, taken along line  2 - 2  of FIG. 1;  
         [0017]    [0017]FIG. 3 is a schematic representation of an engine valve actuator shown in a first position;  
         [0018]    [0018]FIG. 4 is a schematic representation of an engine valve actuator shown in a second position;  
         [0019]    [0019]FIG. 5 is a schematic representation of an engine valve actuator shown in a third position;  
         [0020]    [0020]FIG. 6 is a flow chart depicting a sample sequence of steps which may be taken to operate an internal combustion engine valve actuator;  
         [0021]    [0021]FIG. 7 is a graph plotting valve lift vs. engine crank angle during normal operation;  
         [0022]    [0022]FIG. 8 is a graph plotting valve lift vs. engine crank angle during internal exhaust gas recirculation operation;  
         [0023]    [0023]FIG. 9 is a graph plotting valve lift vs. engine crank angle during Miller cycle operation; and  
         [0024]    [0024]FIG. 10 is a schematic representation of an alternative engine valve actuator configuration. 
     
    
     DETAILED DESCRIPTION  
       [0025]    Referring now to the drawings, and with specific reference to FIG. 1, an embodiment of an internal combustion engine is generally referred to by reference numeral  20 . While the engine  20  is depicted and will be described in further detail herein with reference to a four stroke, internal combustion diesel engine, it is to be understood that the teachings of the disclosure can be, employed in conjunction with any other type of engine as well.  
         [0026]    The engine  20  may include a plurality of engine cylinders  22  in each of which is reciprocatingly mounted an engine piston  24 . In the depicted embodiment, six such engine cylinders  22  and six engine pistons  24  are depicted in aligned fashion, but it is to be understood that a greater or lesser number are possible, and that engine cylinder orientations other than in-line, such as, for example, a “V” configuration, are possible as well. A connecting rod  26  may be connected to each engine piston  24 , and in turn be connected to a crank shaft  27  so as to capitalize on the motion of the engine piston  24  to produce useful work in a machine (not shown) with which the engine  20  is associated. Each engine cylinder  24  may be provided within an engine block  28  having a cylinder head  30 , and may further include at least one intake valve  32 , and an exhaust valve  34 .  
         [0027]    Referring now to FIGS. 2-5, the cylinder head  30 , and a pair of exhaust valves  34  are shown in greater detail for one of the engine cylinders  22 . As shown therein, a pair of exhaust ports  38  may be provided in the cylinder head  30  to allow for fluid communication into and out of the engine cylinder  22 . In addition, while FIG. 1 depicts only one intake port  36  per cylinder  22 , it is to be understood that a pair of intake ports  36  are typically provided in each cylinder  22  in a manner similar to the exhaust ports  38  depicted in FIG. 2. In normal engine operation, air may be allowed to enter the engine cylinder  22  through the intake ports  36 , while combustion or exhaust gases may be allowed to exit the engine cylinder  22  through the exhaust ports  38 . An intake valve element  40  may be provided within each intake port  36 , while an exhaust valve element  42  may be provided within each exhaust port  38 .  
         [0028]    Each of the valve elements  40 ,  42  may include a valve head  44  from which a valve stem  46  extends. The valve head  44  includes a sealing surface  48  adapted to seal against a valve seat  50  about a perimeter  52  of the valve ports  36 ,  38 . The valve elements  40 ,  42  further include a bridge  54  adapted to contact the valve stems  46  associated with each engine cylinder  22 . A valve spring  56  imparts force between the top of each valve stem  46  and the cylinder head  30 , thereby biasing the stem  46  away from the cylinder head  30  and thus biasing the valve head  44  into seating engagement with the corresponding valve seats  50  to close the intake and exhaust valves  32 ,  34 .  
         [0029]    As shown best in FIG. 2, movement of the valve elements  40 ,  42  is controlled not only by the springs  56 , but by a cam assembly  58  as well. As one of ordinary skill in the art will readily recognize, rotation of the cam  60  periodically causes a push rod  62  to rise, thereby causing a rocker arm  64 , connected thereto, to pivot about a pivot  66 . In so doing, an end  68  of the rocker arm  64  is caused to move downwardly and thereby open the exhaust valve element  42 . Under normal engine operation, the cam  60  imparts sufficient force to the valve stem  46  to overcome the biasing force of the spring  56  and thereby push the valve head  44  away from the valve seat  50 , to open the exhaust valves  34  (or intake valve  32 ). Further rotation of the cam  60  allows the spring  56  to push the end  68  of the rocker arm  64  upward and the push rod  62  downward until the cam  60  completes another revolution.  
         [0030]    In certain modes of engine operation, such as with the compression release braking, Miller cycle operation, and EGR referenced above, it is desirable for the intake and/or exhaust valves  32 ,  34  to be held open for longer periods, or at a timing sequence other than that dictated by the cam  60 . In such situations, a valve actuator  70  may be used to so hold the intake valve  32  and/or exhaust valve  34  open. As shown in FIGS. 3-5, one example of the valve actuator  70  includes an actuator cylinder  72  in which an actuator piston  74  is reciprocatingly disposed. The actuator cylinder  72  may include an opening  79 , through which an actuator rod  78  may extend in the direction of the rocker arm  64  and the valve stem  46  as well.  
         [0031]    The actuator cylinder  72  may also include a port  80  providing access to an actuation chamber  82 . The port  80  is adapted to place the actuation chamber  82  into fluid communication with a low pressure fluid source  84 . In one embodiment, the pressurized fluid may be lubrication oil of the engine  20  (typically at a pressure level less than one hundred pounds per square inch, for example, on the order of sixty to ninety pounds per square inch (413.7 KPa to 620.5 KPa)). Placement of the fluid source  84  into fluid communication with the actuation chamber  82  may be provided through a fluid passage  85  and be controlled by a control valve  88 . The control valve  88  may include an inlet  92  and an outlet  94 . The control valve  88  may be biased into a first position connecting the port  80  to the low pressure fluid source  84  and be actuated by a solenoid  95  to a second position disconnecting the port  80  from the low pressure fluid source  84 . The solenoid  95  may itself be actuated upon receipt of a control signal or the like from a main control or processor  96  (FIG. 1) of the engine  20 . The fluid source  84  may be in fluid communication with an oil drain, sump, or accumulator  97 , for example, via a check valve.  
         [0032]    The low pressure fluid source  84 , when the control valve  88  is in the first position (FIG. 4), is able to fill the actuator chamber  82  sufficiently to move the actuator piston  74  so as to take up any lash  98  (FIG. 3) existing in the system, such as that between the actuator rod  78  and the valve stem  46  or between the actuator rod  78  and the rocker arm  64 . “Taking up any lash in the system” is defined herein to mean removing any space between movable components. In so doing, when it is desired to hold the exhaust valve  34  in an open position, the control valve  88  can be moved to the second position (FIG. 5) thereby disconnecting the inlet  92  and hydraulically locking the actuator  70 . Pressure within the engine cylinder  22  imparts force on the exhaust valve  34 , and in turn the actuator rod  78 , but the fluid within the actuator cylinder  72 , being incompressible and locked, holds the actuator piston  74 , and thus the exhaust valve  34  (or intake valve  32 ), in the open position.  
       Industrial Applicability  
       [0033]    In operation, the engine  20  can be used in a variety of applications. For example, the engine  20  may be provided on board a prime-mover, vehicle or the like, or any type of machine requiring the provision of mechanical or electrical energy. Such machines may include, but are not limited to, earth moving machines, backhoes, graders, rock crushers, pavers, skid-steer loaders, cranes, trucks, and the like.  
         [0034]    Referring now to FIG. 6, in conjunction with FIGS. 2-5, the engine  20  can be operated so as to open an engine valve and hold an engine valve open in the following manner. By way of background, one of ordinary skill in the art will understand that a typical four-stoke, diesel cycle, internal combustion engine operates through four distinct strokes of the piston  24  through the cylinder  22 .  
         [0035]    In a first or intake stroke, the engine piston  24  descends through the engine cylinder  22  away from the cylinder head  30  while the intake valve  32  is opened by the cam assembly  58 , as indicated in steps  99  and  100 , respectively. FIG. 7 depicts the intake valve  32  and exhaust valve  34  lift of a typical diesel cycle engine wherein engine operation is plotted as seven hundred and twenty degrees of engine crank angle, and with each of the four strokes representing 180° of rotation of the crank shaft  27 . In so doing, air is drawn into the engine cylinder  22 , as indicated in a step  102 .  
         [0036]    In a second or compression stroke, the engine piston  24  reverses its motion, at the direction of the rod  26 , while the intake valve  32  and exhaust valve  34  are closed with springs  56 . Such steps are indicated by reference numerals  104  and  106 , respectively in FIG. 6. As the engine piston  24  ascends through the engine cylinder  22  toward the cylinder head  30 , air is compressed (as indicated by a step  110 ).  
         [0037]    In a third or combustion stroke, fuel is injected directly into the compressed air and thereby is ignited, as indicated by a step  112 . The resulting explosion and expanding gases push the engine piston  24  again in a descending direction (as indicated by a step  113 ) through the engine cylinder  22 , while the intake and exhaust valves  32 ,  34  remain closed.  
         [0038]    In a fourth or exhaust stroke, the engine piston  24  again reverses and ascends through the engine cylinder  22 , but with the exhaust valve  34  open by the cam assembly  58 , thereby pushing the combustion gases out of the engine cylinder  22 . Such steps are indicated in FIG. 6 as steps  114  and  116 , respectively.  
         [0039]    With certain engine operation variations, such as compression release braking, Miller cycle operation, and EGR, it may be desirable to alter the above valve timing and hold one or more valves open against substantial cylinder pressures. The teachings of the present disclosure enable such operation, without resort to highly pressurized oil rails, thereby preserving engine efficiency and simplicity. Taking internal EGR as an example, it is necessary in such operation for the exhaust valve  34  (or intake valve  32 ) to remain open throughout not only the exhaust stroke, but during an interim period between when the exhaust valve  34  is normally closed and when the intake valve  32  opens to conduct the intake stroke. FIG. 8 depicts such altered valve timing in graphical form.  
         [0040]    This can be accomplished by allowing the cam assembly  58  to open the exhaust valve  34  according to a normal exhaust stroke as indicated above (step  116 ), and then using the actuator  70  to maintain the exhaust valve  34  in an open position. More specifically, as the cam assembly  58  moves to open the exhaust valve  34 , the rocker arm  64  pivots downwardly compressing the spring  56 . With the spring pressure overcome by the cam assembly  58 , the pressurized fluid flowing from the low pressure source  84  and filling the actuation chamber  82  is able to move the piston  74 . The piston  74  moves through the lash  98  until the actuator rod  78  engages the rocker arm  64 . This step is indicated by reference numeral  118  in FIG. 6.  
         [0041]    In order to hold the exhaust valve  34  in such a position even after the cam  60  rotates to another position, the control valve  88  is switched from the first position (shown in FIG. 4) to the second position (shown in FIG. 5), as indicated by a step  120 . In so doing, the fluid is locked from escaping the actuation chamber  82  and, due to its incompressibility, prevents the actuator piston  74  from moving and, thus, prevents the exhaust valve  34  from closing. As used herein, a “hydraulically locked” device is defined as a device having substantially no fluid flow and substantially no fluid leakage, and “backflow” is defined as fluid flow from the actuator  70  to the low pressure fluid source  84 .  
         [0042]    In addition to the above example, the actuator  70  may be hydraulically locked using any number of other devices including, but not limited to, check valves. For example, as shown in FIG. 10, a check valve  121  can be provided between the actuator  70  and the low pressure source  84 . The check valve allows the fluid from source  84  to enter the actuator cylinder  72  and move the actuator piston  74 , but not flow back to the source  84 . In conjunction with such structure, a normally closed control valve  122  may be provided also in communication with the low pressure source  84  (or drain  97  or atmosphere). Upon actuation of solenoid  123  of the control valve  122 , the fluid pressure with the actuator cylinder  72  is able to flow to the low pressure source  84  or drain  97 . In so doing, the actuator piston  74  is able to move up, closing the valve  32 ,  34 .  
         [0043]    Continuing with the example of EGR, the exhaust valve  34  is held open as the engine piston  24  ascends to a top dead center position, and remains open after the engine piston  24  reverses and descends while the intake valve  32  is opened, as indicated by steps  124  and  126 , respectively. A portion of the exhaust gases vented from the engine cylinder  22  through the exhaust valve  34  are thereby reintroduced to the engine cylinder  22  by the resulting pressure differential. This step is indicated by reference numeral  128 . After a predetermined stroke length (e.g., ninety degrees of a seven hundred and twenty degree four stroke cycle as shown in FIG. 8), the exhaust valve  34  is closed as indicated by a step  130 , while the intake valve  32  remains open to complete the intake stroke as explained above. The exhaust valve  34  can be closed by switching the control valve  88  back to the first position (shown in FIG. 4) and thereby enabling the spring  56  to push the actuator piston  74  up, and the pressurized fluid out of, the actuator cylinder  72 . Normal engine operation may then resume, beginning with the compression stroke as indicated in FIG. 6.  
         [0044]    The teachings of the present disclosure can also be used to provide Miller cycle benefits. As illustrated in FIG. 9, the intake valve  32  (or exhaust valve  34 ) may be held open during the initial stages of the compression stroke to thereby reduce the compression ratio of the engine and provide the engine efficiencies of the Miller cycle as well known by those of ordinary skill in the art. The intake valve  32  could be so held by employing the actuator  70  after the cam assembly  58  opens the intake valve during the intake stroke. More specifically, as the intake valve  32  is about to be closed by the spring  56  at the conclusion of a normal intake stroke, the control valve  88  could be actuated so as to prevent fluid flow from the actuator  72  back to the low pressure fluid source  84 . In so doing, the actuator piston  74  is locked in position, as is the intake valve  32  as depicted in FIG. 9.  
         [0045]    One of ordinary skill in the art will understand that significant force is required to open the intake and exhaust valves  32 ,  34 , and hold the valves open, during the compression and exhaust strokes, due to the ascending piston and pressurized gases being pushed out of the engine cylinder  22  and thus against the valves  32 ,  34 . The actuator  70 , and its ability to become hydraulically locked, is able to hold the valves  32 ,  34  open under such conditions, without resort to high pressure rails and the drops in engine efficiency incumbent with such conventional systems.  
         [0046]    Other aspects and features of the present disclosure can be obtained from a study of the drawings, the disclosure, and the appended claims.