Abstract:
A valve assembly having a valve ( 10, 110, 210, 310, 410 ) that is caused to reciprocate between open and closed positions by engagement of a cam follower ( 16, 116, 216, 316,416 ) with a cam ( 14, 114, 214, 314, 414 ) that is carried by a rotatable camshaft ( 12, 112, 212, 312, 412 ). The valve is resiliently urged against the cam by a coil spring ( 18, 118, 218, 318, 418 ), but its return to its closed position is delayed by application of a non-mechanical force against the valve, in opposition to the force imposed by the coil spring, by hydraulic force imposed by hydraulic fluid in a housing ( 22, 122, 322, 422 ) that acts against an enlarged portion ( 10   c   , 110   c,    310   c,    410   c ) of the valve, or by an electromagnetic force imposed by an electromagnetic device ( 228 ) that acts on an enlarged portion ( 210   c ) of the valve ( 210 ). The non-mechanical, hydraulic imposing force in an embodiment of the invention involves the use of a magneto-rheological fluid within a sealed housing ( 322 ), and the viscosity of this magneto-rheological fluid substantially increases when a magnetic coil ( 330 ) in the sealed housing is energized.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the operation of a reciprocable valve of an internal combustion engine. More particularly, this invention relates to a system for selectively varying the rate at which a valve closes from its fully open position. 
     2. Description of the Prior Art 
     As is known in the art, for example, as taught by U.S. Pat. No. 5,002,023 (Butterfield et al.), which is assigned to the assignee of this application and the disclosure of which is incorporated by reference herein, the opening and closing of the reciprocable valves of an internal combustion engine, both the intake valves and the exhaust valves, is customarily actuated by irregularly-shaped cams on a rotating shaft, called a camshaft, whose rotation is effected by a chain or belt drive that connects the camshaft to the engine crankshaft, or to another camshaft in a dual camshaft engine. Typically, each valve is spring-biased against a cam of a camshaft, and its opening and closing cycle is precisely determined by the configuration of the cam against which the valve is spring biased. Occasionally, however, it would be advantageous to engine operation to delay the closing of a valve from a pattern it would otherwise follow if it remained in contact with the cam toward which it is spring biased, and to be able to do so selectively. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided an apparatus and a method for delaying the closing of an internal combustion engine, cam actuated valve from the rate it would otherwise follow based on contact with a cam of a camshaft against which the valve is resiliently biased. The apparatus and method may take the form of one or another of various embodiments, either hydraulic and/or electric, and most such embodiments permit the delayed closing of the valve to occur selectively, that is, only when desired. 
     Accordingly, it is an object of the present invention to provide an apparatus and a method for delaying the closing of an internal combustion engine, cam actuated valve from the rate it would otherwise follow based on contact with the cam against which the valve is resiliently biased. More particularly, it is an object of the present invention to provide an apparatus and a method of the foregoing character in which the delayed closing of the valve occurs selectively, that is, only when desired. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A,  1 B and  1 C are schematic views of an internal combustion engine valve and a cam of a camshaft used to operate such valve, according to a preferred embodiment of the present invention, at various times during the rotation of the camshaft; 
     FIG. 2 is a view like FIG. 1A of an alternative embodiment of the present invention; 
     FIG. 3 is a view like FIGS. 1A and 2 of another alternative embodiment of the present invention; 
     FIG. 4 is a view like FIGS. 1A,  2  and  3  of yet another alternative embodiment of the present invention; and 
     FIG. 5 is a view like FIGS. 1A,  2 ,  3  and  4  of yet another alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1A,  1 B and  1 C illustrate the operation of a valve  10  of an internal combustion engine, and it may be considered to be the exhaust valve of one of the cylinders of the engine. The valve  10  is caused to reciprocate along its longitudinal central axis, vertically as shown in the drawing, by the rotation of a camshaft  12 , which is caused to rotate by a chain or belt drive from an engine crankshaft or another camshaft in a known manner (by elements not shown). The camshaft  12  has an irregularly shaped cam  14  that rotates therewith, and the cam  14  engages a cam follower  16  in the form of an inverted cup that surrounds an enlarged flange  10   a  at the end of the valve  10 , the opposed end of the valve  10  also having an enlarged portion  10   b  that actually functions to open and close an opening in the cylinder that the valve  10  is associated with. 
     The valve  10  is resiliently biased toward its cylinder closing position, that is, its uppermost position as shown in the drawing, by a coil spring  18 , an uppermost end of which engages the inside bottom of the cam follower  16  and the lowermost end of which engages the upper surface of a laterally extending fixed member  20 . Thus, the cam follower  16  would tend to remain in contact with the came  14  at all times during the rotation of the camshaft. However, in the arrangement of FIGS. 1A,  1 B, and  1 C, the return of the cam  10  from its open position in FIG. 1A to its closed position in FIG. 1C is delayed by providing the valve  10  with an enlargement  10   c  and by surrounding the enlargement  10   c  with a housing  22  of sufficient axial extent to permit the travel of the enlargement  10   c  therein throughout the entire range of travel of the valve  10 . The housing  22  has aligned openings  22   a,    22   b  at its top and bottom to permit the reciprocation of the valve  10  with respect to the housing  22 , and the openings at  22   a,    22   b  have sufficient clearance with respect to a stem portion  10   d  of the valve  10  to permit the flow of hydraulic fluid, namely, engine lubricating oil, through the openings  22   a,    22   b  as the valve  10  moves up and down, the entire valve assembly being immersed in engine lubricating oil. Thus, the viscosity of the engine oil with the housing  22 , some of which must be pumped through the opening  22   a  by the enlargement  10   c  as the valve  10  moves from its FIG. 1A position to its FIG. 1B position, will delay the return of the valve  10  to its FIG. 1C position, notwithstanding the biasing force imposed on the cam follower  16  by the coil spring  18 . In that regard, the opening  22   b  should be somewhat larger than the opening  22   a,  to permit the free flow of engine lubricating oil into the housing  22  when the valve  10  moves from its FIG. 1B position to its FIG. 1C position and to permit the free flow of engine lubricating oil from the housing  22  as the valve  10  moves from its FIG. 1A position to its FIG. 1C position. 
     In the embodiment of FIG. 2, each element that corresponds to an element of the embodiment of FIGS. 1A,  1 B and  1 C is identified by a three-digit numeral, the last two digits of which are the same as the two digits of the corresponding element of FIGS. 1A,  1 B and  1 C. In the embodiment of FIG. 2, openings  122   a,    122   b  of a housing  122  are sealed to prevent the flow of engine lubricating oil therethrough as a valve  110  reciprocates under a downwardly directed force imposed by a cam  114  of a rotating camshaft  112  and a resilient upwardly directed force imposed by the coil spring  118  on an enlarged flange  110   a  of the valve  110 . However, the housing  122  does not normally contain engine lubricating oil therein; under these circumstances, therefore, there is no viscous drag on an enlarged portion  110   c  of the valve  110 , and a coil spring  118  will be effective to maintain a cam follower  116  in contact with the cam  114  at all times during the rotation of the camshaft  112  when there is no engine lubricating oil in the housing  122 . However, when it is desired to delay the return of the valve  110 , as it is during certain engine operating conditions, this can be done by the addition of engine lubricating oil to the housing  122  through an inlet/outlet line  124 , and the flow of engine lubricating oil into or out of the housing  122  is selectively permitted or prevented by a servo valve  126 , whose operation is controlled by an engine control unit of the engine with which the valve  110  is associated (elements not shown). In this way, the delayed return of the valve  110  to its closed position can be regulated, and the duration of its open period extended, as required or desired to achieve improved engine operating conditions, and notwithstanding the biasing return force imposed on the cam follower  116  by the coil spring  118 . 
     In the embodiment of FIG. 3, each element that corresponds to an element of the embodiment of FIGS. 1A,  1 B and  1 C, or to an element of the embodiment of FIG. 2, is identified by a three-digit numeral, the last two digits of which are the same as the two digits of the corresponding element of FIGS. 1A,  1 B and  1 C, or to the last two digits of the corresponding element of FIG. 2, as the case may be. In the embodiment of FIG. 3, the return of a valve  210  from its fully open position, as illustrated in FIG. 3, to a closed position corresponding to the position of the valve  10  that is shown in FIG. 1C, is delayed by an electromagnetic valve holding device  228 , which acts on an enlargement  210   c  to magnetically restrain its return against the biasing force of a coil spring  218  against a flange  210   a  of the valve  210  and a cam follower  216 . The operation of the electromagnetic valve holding device  228  is selectively energized or deenergized under control by an engine control unit of the engine with which the valve  210  is associated (elements not shown). In this way, the delayed return of the valve  210  to its closed position can be regulated, and the duration of its open period changed, as required or desired to achieve improved engine operating conditions, and notwithstanding the biasing return force imposed on the cam follower  216  by the coil spring  218 . 
     In the embodiment of FIG. 4, each element that corresponds to an element of the embodiment of FIGS. 1A,  1 B and  1 C, or to an element of the embodiment of FIG. 2, or to an element of the embodiment of FIG. 3, is identified by a 300 series numeral, the last two digits of which are the same as the two digits of the corresponding element of FIGS.  1 A,  1 B and  1 C, or the last two digits of the corresponding element of FIG. 2 or the last two digits of the corresponding element of FIG. 3, as the case may be. In the embodiment of FIG. 4, an enlarged portion  310   c  of a valve  310  is surrounded by an enclosed housing  322  which sealingly accommodates the reciprocation of the valve  310  with respect to the housing  322  at all locations of the travel of the enlarged portion  310   c.  The housing  322  contains a sealed quantity of a magneto-rheological fluid, that is, a fluid whose viscosity materially increases under the influence of an electromagnetic field. The housing  322  contains an electromagnetic coil  330  embedded in its outer wall, and positioned concentrically with a stem  310   d  of the valve  300 , and whenever the electromagnetic coil  330  is energized, the viscosity of the fluid contained in the housing  322  increases markedly, to thereby delay the return of the valve  310  from its fully open position, as illustrated in FIG. 4, to its filly closed position corresponding to the position of the valve  10  in FIG.  1 C. To prevent excessive viscous forces from operating on the enlargement  310   c  of the valve  310 , the enlarged portion  310   c  is provided with apertures  310   e  extending therethrough, to facilitate the flow of fluid from one side of the enlargement  310   c  to the other during periods when the fluid within the housing  322  has a low viscosity. 
     Thus, when the electromagnetic coil  330  is not energized, a coil spring  318  will be effective to maintain the cam follower  316  in contact with the cam  314  at all times during the rotation of the camshaft  312 . However, when it is desired to delay the return of the valve  310 , as it is during certain engine operating conditions, this can be done by the energization of the electromagnetic coil  322 , and in this way the delayed return of the valve  310  to its closed position can be regulated, and the duration of its open period changed, as required or desired to achieve improved engine operating conditions, and notwithstanding the biasing return force imposed on the cam follower  316  by the coil spring  318 . 
     In the embodiment of FIG. 5, each element that corresponds to an element of the embodiment of FIGS. 1A,  1 B and  1 C, or to an element of the embodiment of FIG. 2, or an element of the embodiment of FIG. 3, or an element of the embodiment of FIG. 4, is identified by a 400 series three-digit numeral the last two digits of which are the same as the two digits of the corresponding element of FIGS. 1A,  1 B and  1 C, or the same as the last two digits of the corresponding element of FIGS. 2,  3  or  4 , as the case may be. In the embodiment of FIG. 5, which is otherwise similar to the embodiment of FIG. 2, lubricating engine oil flows into a sealed housing  422  through an inlet line  424 , which is provided with a check valve  432  to allow engine oil to flow freely into a sealed housing  422  during the opening of a valve  410 , but prevents oil from flowing back out of the housing  422  into the inlet line  424  during the closing of the valve  410 . The embodiment of FIG. 5 also is provided with an outlet line  434  to exhaust oil from the housing  422 , and the outlet line  434  is also provided with a check valve  436  to permit oil to be exhausted from the housing  422  during the closing of the valve  410 , while also preventing oil from being drawn back into the housing  422  during the opening of the valve  410 . The outlet line  434  is also provided with a servo valve  426  to selectively open or close the housing  422  to the flow of oil In the embodiment of FIG. 5, it is possible to provide controlled leakage of oil out of the housing  422  by providing a high speed valve (not shown) to open on each valve stroke during the closing of the valve. A slower responding valve (also not shown) could simply limit the flow out of the housing  422 , and therefore the rate at which the valve  410  closes. The use of such a slower responding valve is not as ideal, because it will prevent the valve from remaining fully open, but it will allow several valves to be controlled with one hydraulic valve. 
     The valve  410  of the embodiment of FIG. 5 has an enlarged flange  410   a , an enlarged end  410   b  and an elongate stem  410   d  that extends between the enlarged flange  410   a  and the enlarged end  410   b . The elongate stem  410  is provided with an enlarged portion  410   c  that is surrounded by the housing  422 . 
     Although the best mode contemplated by the inventor for carrying out the present invention as of the filing date hereof has been shown and described herein, it will be apparent to those skilled in the art that suitable modifications, variations and equivalents may be made without departing from the scope of the invention, such scope being limited solely by the terms of the following claims and the legal equivalents thereof.