Abstract:
Variable valve mechanisms utilize magnetorheological fluid (MRF) in lost motion devices for controlling lift and timing of engine valves and the like. The lost motion devices are designed with either of two operational modes, a direct shear mode and a valve mode. In the shear mode, the MR fluid is retained between relatively movable shear surfaces of a lost motion device and the relative motion is controlled by varying the shear strength of the fluid by a magnetic field applied to the MR fluid between the shear surfaces. In the valve mode, the flow rate of MR fluid through an orifice is controlled by varying the magnetic field to control the flow viscosity of the fluid passing through the orifice. The lost motion device units may be applied directly between an input cam and an output valve or may be applied to a pivot for a finger follower or another type of valve actuation.

Description:
TECHNICAL FIELD 
     This invention relates to valve actuating mechanisms for engines and the like and more particularly to a variable mechanism incorporating a magnetorheological fluid lost motion device. 
     BACKGROUND OF THE INVENTION 
     Variable valve actuation mechanisms have been extensively developed and to some extent utilized to improve engine efficiency by reducing or eliminating throttling losses, improving idle stability and controlling the timing of valve opening and closing to increase engine power and/or to improve engine exhaust emissions. The development of such mechanisms has included both mechanical and hydraulic devices including mechanisms with hydraulic lost motion devices in the valve train. However, these devices have not yet reached wide spread commercial application, possibly due to low temperature viscosity problems which may affect hydraulic system performance as well as the cost of engine modifications to apply suitable hydraulic systems. MRF technology has been applied in various ways to fluid dampers, clutches and brakes, vehicle suspensions and other applications but it is not known to have been developed or applied in engine valve actuating mechanisms. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved variable valve actuating mechanism which utilizes magnetorheological fluid (MRF) in lost motion devices applied to a valve actuating system to provide improved variable actuating mechanisms for controlling engine valves and the like. 
     The present invention is directed primarily to the application of MRF technology to valve actuating mechanisms in which the timing and or lift of valve motion can be controlled by lost motion devices using MR fluids. A number of embodiments of MRF lost motion devices designed for application to engine valve actuating mechanisms are illustrated as examples of how MRF technology may be applied to control valve actuation. 
     According to the invention, the lost motion devices are designed with either of two operational modes, a direct shear mode and a valve mode. In the shear mode, the MR fluid is retained between relatively movable surfaces of a lost motion device and the relative motion is controlled by varying the shear strength of the fluid by a controlled electromagnetic flux passed through the fluid within the device. In the valve mode, the MR fluid is displaced from one portion of a chamber to another through an orifice. The flow rate through the orifice is controlled by varying the magnetic field so that the effective viscosity of the fluid is varied to control the rate of fluid volume change in the chamber. 
     The lost motion device units may be applied directly between an input cam and an output valve or may be applied to a pivot for a finger follower or a rocker arm type of valve actuation. Other variations of the application of lost motion devices according to the invention are of course possible. 
    
    
     These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a schematic cross-sectional view of a first embodiment of valve actuating mechanism according to the invention as applied in an engine; 
     FIG. 2 is a cross-sectional view through the lost motion mechanism of FIG. 1 taken normal to the axis of motion; 
     FIG. 3 is a view similar to FIG. 1 but showing an alternative embodiment of valve mechanism applied to an engine in accordance with the invention; 
     FIG. 4 is a view similar to FIG. 2 but showing the lost motion device of FIG. 3; 
     FIGS. 5 and 6 are cross-sectional views similar to FIG. 3 but showing alternative embodiments of lost motion devices; 
     FIG. 7 is a cross-sectional view similar to FIG. 1 showing an apparatus designed for testing of MRF lost motion devices applied to actuate engine valves; and 
     FIGS. 8 and 9 are views similar to FIG. 3 but showing another alternative embodiment of finger follower lost motion device shown operating in the valve mode in fully expanded and fully collapsed positions, respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIGS. 1 and 2 of the drawings, numeral  10  schematically indicates an engine having a support  12 , such as a cylinder head, carrying a valve actuating mechanism  14  including a cam  16 , a valve  18  having a return spring  20 , and a lost motion device  22  connecting the cam  16  with the valve  18 . 
     Lost motion device  22  is an assembly including a drive piston  24  actuated by the cam  16  and a driven piston  26  reciprocable within the drive piston  24  and connected with the stem of valve  18 . The driven piston  26  is contained within the drive piston  24  by an end clip or ring  28 . 
     Driven piston  26  is formed to sealingly engage the interior of the drive piston  24  at inner and outer ends  30 ,  32 , respectively, of the driven piston  26 . Between these ends an annular recess  34  is formed which is filled with a magnetorheological fluid (MRF)  36  having magnetically variable shear strength as is known for use in other applications. The MR fluid  36  is trapped within the recess  34  which has a shallow depth sufficient to retain a shear film of MR fluid in contact with both the drive and driven pistons and contained within the driven piston recess  34 . A piston return spring  38  is provided which seats upon the support  12  and engages the lower portion of the drive piston  24 . 
     Closely surrounding the drive piston  24  is an electromagnetic coil  40 , shown partially in FIG. 1 but more completely in FIG.  2 . Coil  40  includes an outer ring  42  supporting, for example, six inwardly directed poles  44  having ends  46  which are closely spaced from the cylindrical exterior of the drive piston  24 . Electrical turns  48  wound around the poles  44  are oriented to generate a magnetic flux path in the outer ring  42  and between adjacent poles  44  through the side of the driven piston  26 . This side is made of magnetic material so that a magnetic flux is formed which passes through the MR fluid  36  when the coil  40  is energized. The thin crosssections of the drive piston  24 , and the MR fluid-containing recess  34  help to drive a radial, rather than axial or circumferential, flux flow. The relatively thicker cross section of the side of driven piston  26  encourages the flux to flow circumferentially to complete the magnetic loop. The flux strength is preferably controllable although it could be operated with a single strength if desired. 
     Material selection for components like the drive and the driven pistons  24 ,  26  must meet structural constraints and machinability issues that govern their counterparts in conventional valve trains. In addition, materials with high permeability, i.e. a large B/H ratio, are preferred so that the same flux density B (affecting the MR fluid shear strength) can be achieved with a small H, magnetic field strength, for lower power consumption. Material selection must also consider the issue of residual magnetism that is present after the termination of the magnetic flux. This could result in an unwanted drag force. 
     In operation, rotation of the cam  16  cyclically actuates the drive piston  24  in a reciprocating motion. When the coil  40  is not energized, the MR fluid  36  has low shear strength so that movement of the drive piston  24  does not provide sufficient force through the MR fluid  36  to move the driven piston  26  and open the valve  18 . Thus, the valve remains closed. At the other extreme, the MR fluid  36  is preferably chosen to be made essentially stiff or extremely viscous under the magnetic flux developed when the coil  40  is fully charged. Thus, the reciprocating motion of drive piston  24  is carried entirely, or almost completely, to the driven piston  26 , which opens the valve  18  to its full stroke, essentially equivalent to that of the cam lift and motion of the drive piston  24 . 
     In one operational mode, the valve lift and timing could be controlled completely by timing the energizing of the coil  40  so that it is fully energized at the point when the valve  18  is desired to begin opening and fully de-energized at the point where the valve is desired to be closing completely. However, a preferred mode of operation provides for controlling the current through the coil  40  during valve operation so that the shear strength of the MR fluid  36  varies from a low value, where the valve  18  will not open, through various greater values which partially open the valve  18  in increasing amounts until the full energization of the coil  40  is reached and the valve  18  becomes fully opened during each cam rotation. 
     The amount of lift realized at valve  18  affects the reaction force generated by spring  20 . This spring force and a speed-dependent inertia force have to be equalized at the MR fluid interface with the driven piston  26 . Hence, by controlling the shear strength of the MR fluid  36 , different amounts of lift at valve  18  can be realized. Therefore, both the timing of energization and the level of coil  40  current affect the lift event realized at valve  18 . Thus, the manner of electronic control of the valve lift and timing may be suited to the particular valve or engine embodiment in which the MR fluid lost motion device is applied. 
     In each case when the drive piston  24  is depressed, whether or not the valve is opened, the drive piston  24  is maintained against the cam by the drive piston return spring  38 . Further, when the valve  18  is opened and the cam  16  returns to the valve closing point, the valve return spring  20  is adequate to return the valve  18  to the closed position. 
     When the cam  16  comes to the maximum lift position, the driven piston  26  and the valve  18  that is connected with the driven piston  26  also attain their maximum displacement, provided that proper energization at coil  40  exists. During the subsequent closing motion, coil  40  remains energized such that both the drive and the driven pistons  24  and  26  and the valve  18  are displaced together without relative slippage between them. This return motion is controlled by the closing curve of cam  16 . Coil  40  is de-energized upon seating of the valve  18  so that drive piston return spring  38  can return the drive piston  24  without a significant drag force from MR fluid  36 . De-energizing coil  40  prior to seating of the valve  18  would allow the valve  18  to close under the force of spring  20  in an uncontrolled fashion, with upward moving drive piston  24  not being able to provide any braking force. 
     Referring now to FIGS. 3 and 4, there is shown schematically an engine  50  having an alternative embodiment of valve gear with an associated lost motion device. Engine  50  includes a support  52  such as a cylinder head or other engine component. Support  52  carries a valve actuating mechanism  54  including cam  56  and a valve  58  urged in a closing direction by a valve return spring  60 . A pivot  62  is provided which is carried by the support  52  and in turn pivotably supports a finger follower  64  which directly or indirectly engages the valve  58  and is engaged by the cam  56 . 
     The pivot incorporates a lost motion device  66  that includes a plunger  68 , or first member, that is reciprocably carried in a housing  69  disposed in the engine cylinder head, or support  52 , and is urged toward a fixed upper position by a plunger return spring  70 . A fixed plunger-like inner member  72  includes a cylindrical portion  74  with a closed bottom  76  that is mounted against a stop  78  carried by the support  52 . As in the embodiment of FIGS. 1 and 2, a cylindrical portion  74  of the inner member  72  includes a shallow recess  80  in which an MR fluid  82  is contained by suitable seals not shown at the ends of the inner member  72 . 
     Inside the inner member  72 , a stationary internal coil  84  is located, which may be fixed in position by any suitable method, since the inner member  72  remains stationary during operation of the valve mechanism  54 . Coil  84  includes an inner core  86  as shown in FIG.  4  and outwardly extending poles  88  on which electric conductor turns  90  are applied to form the completed coil  84 . 
     As in the previous embodiment, energizing the coil  84  causes the alternate north and south poles of the coil  84  to form a magnetic flux which extends from one of the poles  88  outward and completes the loop through the adjacent cylindrical portion of plunger  68  to an adjacent pole  88  of the coil  84 . The flux passes through the MR fluid  82  contained in the recess  80  and, through control of the coil current, controllably increases the shear strength of the MR fluid  82  as determined by the operating means or program connected with the valve mechanism. 
     Thus, in operation, rotation of the cam  56  when the coil energy is at a maximum causes the finger follower  64  to pivot about pivot  62 , which is held essentially stationary by the high shear strength of the MR fluid  82 . Accordingly, the follower  64  is effective to move the valve  58  to the full open position while the pivot end of the finger follower  64  remains fixed in position on the pivot  62 . When it is desired to reduce the lift of the valve  58  or change the valve timing, the electric power is controlled as desired to reduce the coil current applied during the time when the valve  58  would normally be opened. The reduced coil current allows the pivot  62  to be forced downward at a rate dependent upon the effective shear strength of the MR fluid  82  under the reduced power. 
     If the coil  84  is completely turned off, the plunger  68  of the lost motion device  66  moves downward freely against the force of the return spring  70  so that the finger follower  64  moves down when the cam  56  applies a load against it and the valve  58  remains closed while the plunger  68  moves down to its furthest lower position. As the cam rotates further, the return spring  70  works against the viscous drag of MR fluid  82  in the current off state and returns the finger follower  64  to its normal upper position, maintaining the finger follower  64  against the surface of the cam  56  during operation at all times. 
     FIG. 5 shows an alternative embodiment of lost motion device  66 A modified from that of FIGS. 3 and 4 and wherein functionally similar components are designated by the reference letter A. Lost motion device  66 A includes a plunger  68 A surrounded by a fixed outer member  72 A carried in a housing  69 A and including a cylindrical portion  74 A, mounting an external coil  84 A. The cylindrical portion  74 A has a shallow recess  80 A surrounding the plunger  68 A in which an MR fluid  82 A is contained. A plunger return spring  70 A is also included. These components of the lost motion device  66 A and the surrounding structure operate in the same manner as the numerically corresponding components of the embodiment of FIGS. 3 and 4 to provide a controllable pivot  62 A for a finger follower valve actuating mechanism similar to mechanism  54  (FIG.  3 ). 
     FIG. 6 represents other possible modifications of the embodiment of FIGS. 3 and 4 wherein a lost motion device  92  is provided with an increased number (such as two or more) of shear annuli in order to increase the effective force of the shear action in slowing or stopping the motion of a movable plunger of a valve pivot. In FIG. 6 the lost motion device  92  includes a movable plunger  94  having a pivot surface  96  along the top and a cylindrical wall  98  extending down to an annular seat  100  against which a plunger return spring  70  is engaged to bias the plunger upward. 
     Surrounding the cylindrical wall, there are provided inner and outer cylindrical bodies  102 ,  104 , each having a shallow recess  106  in which MR fluid  107  is contained. The MR fluid  107  is sealed within the recesses  106  by suitable seals, not shown, at the upper and lower edges of the recesses. Within the inner cylindrical body  104 , an internal coil  108  is provided which may be similar to coil  84  of FIGS. 3 and 4, having an inner ring with poles and conductor turns wound on the poles, not shown. 
     The operation of the embodiment of FIG. 6 is similar to that of FIGS. 3 and 4 except that actuation of the coil  108  develops a magnetic flux which penetrates both recesses  106  and thus provides variable shear strength fluid on both sides of the plunger cylindrical wall  98  so as to more effectively control motion of the plunger  94  without increasing the strength of the coil  108 . 
     FIG. 7 illustrates pertinent portions of a test fixture  110 . Although it is not intended as a practical embodiment for use in an engine, it is included in this disclosure because it represents an arrangement which could be utilized with modifications for practicing two different operational modes of the invention. 
     In general, fixture  110  includes a rotary cam  112  actuating a plunger  114  which slides within a housing  116  containing a surrounding magnetic coil  118 . Within the housing  116  is an outer cylinder  120  which is reciprocably driven by the plunger  114  through an upper seal carrier  122 . Cylinder  120  is in turn mounted to a lower seal carrier  123  which engages a lower member  124  that moves with the cylinder  120  against the bias of a plunger return spring  126 . 
     An inner cylinder  128  is fitted closely within the outer cylinder  120  with a small clearance  129  appropriate for developing a shear film of MR fluid. The inner cylinder  128  is guided by an upper seal retainer  130  extending within the upper seal carrier  122  and a lower seal assembly  132  which extends downward to a connection with an engine valve  134 . 
     Upper and lower seals  136 ,  138  seal the ends of a chamber  140  within the outer cylinder  120  in which the inner cylinder  128  is movable. Clearance  129  between the cylinders  120 ,  128  and portions of the chamber  140  above and below the inner cylinder  128  are filled with MR fluid  142 . A through passage  144  extends the length of the inner cylinder  128  and connects upper and lower portions of the chamber  140  to allow the passage of MR fluid  142  freely between the upper and lower chamber portions. A valve spring  146  biases the engine valve  134  toward its closed position and urges the inner cylinder  128  to its furthest upper position as shown in the figure. 
     In operation, rotation of cam  112  reciprocates plunger  114  which drives the outer cylinder  120  downward against the bias of the plunger return spring  126 . The spring  126  maintains the plunger  114  in contact with the cam  112  and so returns the outer cylinder  120  to its upper position each cycle. 
     When the magnetic coil  118  is de-energized, the viscous drag of the MR fluid  142  is low enough as not to cause movement of the inner cylinder  128  against the spring  146 . Thus, the outer cylinder  120  moves freely along the inner cylinder  128  and the valve  134  remains closed in spite of rotation of the cam  112 . 
     As the coil  118  is energized at an increasing level, the MR fluid  142  shear strength adjacent to the coil  118  is increased so that, when the cam  112  forces down the outer cylinder  120 , the shear strength of the fluid in the clearance  129  between the outer and inner cylinders, creates sufficient force capacity to move the inner cylinder  128  down a variable distance, depending on the strength of the magnetic flux and the fluid shear strength caused thereby. Downward movement of the inner cylinder  128  opens the valve  134  against its spring  146 . The spring  146  returns the valve  134  to its closed position when the cam  112  returns the plunger  114  to its upper position, or earlier at a speed higher than the cam-controlled closing speed, if the fluid shear strength permits the valve spring  146  to overcome the shear force of the MR fluid  142 . 
     When the coil  118  reaches maximum strength, the shear strength of the MR fluid  142  reaches a maximum, causing the inner cylinder  128  to be carried downward along with the outer cylinder  120  so that rotation of the cam  112  forces the valve  134  open to its full stroke. The valve  134  is again seated when the cam  112  returns the plunger  114  to its upper position or when the coil  118  is de-energized so that the shear strength of MR fluid  142  is reduced to a negligible amount, allowing the valve spring  146  to again seat the valve  134 . 
     The foregoing operational description involves operation of the mechanism of FIG. 7 in a shear mode wherein the shear strength of the MR fluid  142  is varied in order to vary the motion of the inner cylinder  128  relative to that of the outer cylinder  120 . However, with minor modifications, the same mechanism  110  can be utilized for examining operation of a direct acting follower in the valve mode. 
     This could be accomplished by blocking the through passage  144  and increasing the clearance  129  between the inner and outer cylinders  128 ,  120  until there is a sufficient annular clearance around the inner cylinder  128  to allow free flow of the MR fluid  142  through the clearance  129  from one end of the chamber  140  to the other. If desired, the increased clearance  129  could be limited to a relatively short length of the inner cylinder  128  and the rest of the cylinder could be further reduced in diameter so as not to have a significant effect upon the operation of the annual clearance  129  which serves as a valve orifice. 
     In this “valve” mode of operation, rotation of the cam  112  drives the outer cylinder  120  downward as before and it decreases the volume of the upper portion of the chamber  140 . This decrease causes flow of the MR fluid  142  through the annular orifice or clearance  129  between the two cylinders. The resistance of the fluid to flow may be varied by energizing the magnetic coil  118  in varying degrees up to its maximum strength. 
     As the strength of the coil  118  is increased, the valve actuation varies from staying fully closed to moving partially open and finally to full opening because the flow viscosity, or resistance to flow, of the fluid increases with the increase in magnetic flux from the coil  118 . Thus, as the flow viscosity is maximized, the resistance to flow through the annular orifice  129  raises the pressure in the upper portion of the chamber and drives the inner cylinder  128  downward so as to open the valve  134  as in the previous mode of operation. Thus, the embodiment of FIG. 7 shows not only the operation of a direct acting plunger in the shear mode but also is illustrative of its operation in the so-called valve mode. 
     Referring now to FIGS. 8 and 9, there is shown a lost motion finger follower pivot  148  illustrated in its upper and lower positions, respectively. Pivot  148  is designed for operation in the valve mode and includes a plunger  150  having an enlarged piston  152  intermediate the plunger ends. The piston  152  is contained to reciprocate within a chamber  154  filled with MR fluid  156 . The chamber  154  is formed within a cylinder  158  carried within a support, such as an engine cylinder head, not shown. The lower end of the plunger  150  engages a return spring  160  which seats against the lower end of the cylinder  158  and urges the plunger  150  toward its upper position, shown in FIG. 8. A magnetic coil  162  is mounted around the chamber  154  portion of the cylinder  158  where the MR fluid  156  is contained. 
     In operation, the plunger  150  is engaged by a finger follower  64  driven by a cam  56  as shown in FIG.  3 . When the associated cam  56  is rotated to open an associated valve  58  (FIG. 3) the plunger  150  is either depressed or resists depression depending upon the viscosity of the MR fluid  156  as controlled by the strength of the magnetic coil  162  and the degree of its energization. When the coil  162  is de-energized, the plunger  150  is freely actuated downward by the cam  56  so that the plunger  150  is moved to its lower position shown in FIG. 9 as the MR fluid  156  flows freely past the piston  152  through the surrounding annular orifice  164 . 
     As the strength of the coil  162  is increased, the viscosity of the MR fluid  156  is likewise increased so that it increasingly resists the flow of MR fluid  156  through the orifice  164 . Thus, the motion of the plunger  150  will be resisted by the fluid  156  so that the valve  58  will be partially or fully open depending on the viscosity of the MR fluid  156  and the resulting amount of resistance to motion of the plunger  150 . Again, when the coil  162  is fully energized, the fluid viscosity will be sufficiently high to prevent substantial motion downward of the plunger  150  so that the connected engine valve  58  will be fully opened by rotation of the cam  56 . 
     Plunger  150  is also supported by the biasing spring  160 , ensuring the fully expanded height of the pivot  148  when the coil current is off and there is no pivot reaction force. Then, spring  160  generates sufficient force to displace the MR fluid  156  through the annular orifice  164  by the upward motion of the plunger piston  152 . The dimensions of the annular orifice  164  and the properties of the spring  160  also ensure that when it is desired to de-activate the valve  58  by deactivating the coil  162  the force applied by the finger follower  64  (shown in FIG. 3) can displace the plunger  150  downward freely. The pressure force generated in the chamber  154  plus the force of the spring  160  does not add up to a large reaction force at pivot  148  when the magnetic coil  162  is deactivated and the MR fluid viscosity is low. 
     If desired, the control of fluid viscosity may be maintained consistent throughout the opening and closing motion of the cam  56 , after which the viscosity control will be removed by deactivation of the coil  162 . Alternatively, the coil  162  may be activated after initial motion of the cam starts and deactivated at any time before it ends in order to reduce the stroke of the valve  58 , as shown in FIG. 3, by the timing of the creation of resistance to motion of the plunger  150 . Lift realized at valve  58  can be controlled by timing of energization of the coil  162  and/or by the degree of energization. 
     While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.