Patent Publication Number: US-8991353-B2

Title: Valve system

Description:
TECHNICAL FIELD 
     This disclosure relates to valve systems for internal combustion engines and thermal management thereof. 
     BACKGROUND 
     Automobiles and other vehicles utilize internal combustion engines, in which the combustion of a fuel occurs with an oxidizer (usually air) in a cylinder or other combustion chamber. Combustion of the fuel creates heat, some of which is carried away with exhaust products and some of which is absorbed or retained within the engine. 
     SUMMARY 
     A valve for an engine cylinder is provided, and includes a head. The valve is selectively moveable between a closed position in which the head blocks a port and an open position in which the head unblocks the port. A lower stem of the valve is formed as one-piece with the head. A thermal cavity is formed within, or defined by, the lower stem. The thermal cavity is at least partially filled with a heat transfer medium. 
     An upper stem of the valve is attached to the lower stem opposite the head. A thermal barrier is located adjacent a junction of the lower stem and the upper stem. 
     The above features and advantages, and other features and advantages, of the present invention are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the invention, as defined in the appended claims, when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of portions of a valve system and engine cylinder, showing a thermal barrier in a valve stem; 
         FIG. 2  is a schematic cross-sectional view of portions of a valve system having another thermal barrier; 
         FIG. 3  is a schematic cross-sectional view of portions of a valve system having another thermal barrier and a high-conductivity mid stem; 
         FIG. 4  is a schematic cross-sectional view of portions of a valve system having another thermal barrier; and 
         FIG. 5  is a schematic chart illustrating heat transfer through three illustrative valves. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers correspond to like or similar components wherever possible throughout the several figures, there is shown in  FIG. 1  a valve system  110 , which may be used with various vehicles (not shown) and engines (not shown).  FIG. 1  is a cross-sectional view and illustrates some of the features of the valve system  110  and associated structures and functions. However, those having ordinary skill in the art will recognize additional components that may be used with the valve system  110 . 
     While the present invention may be described with respect to automotive applications, those skilled in the art will recognize the broader applicability of the invention. Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” et cetera, are used descriptively of the figures, and do not represent limitations on the scope of the invention, as defined by the appended claims. Any numerical designations, such as “first,” “second,” or “third,” are illustrative only and are not intended to limit the scope of the invention in any way. 
     The valve system  110  is adjacent to a cylinder  112 , in which combustion occurs. A housing  114  holds and defines portions of the cylinder  112  and the valve system  110 . The housing  114  may be formed from multiple components or may be formed as a single, integral component, such as by casting. 
     An actuator  116  is configured to selectively allow fluid flow through a port  118  to the cylinder  112 . The actuator  116  is shown schematically and may represent many structures, including, without limitation: a rocker, a cam lobe, or a solenoid. The port  118  may be either an intake or an exhaust port. 
     The valve system  110  includes at least one valve  120 . Depending upon the configuration of the engine, there may be a plurality of valves  120  within the valve system  110 . For example, the valve system  110  may include four valves  120 , with two valves  120  used for intake processes and two valves  120  used for exhaust. Alternatively, each individual valve  120  may have its own valve system  110 . For illustrative purposes, only one valve  120  is shown in  FIG. 1 . 
     The valve  120  includes a head  122  which is directly adjacent to the cylinder  112  and the port  118 . During operation of the engine, the actuator  116  moves the valve  120  between a closed position (shown in  FIG. 1 ) in which the head  122  blocks the port  118  and an open position in which the head  122  unblocks the port  118 . The valve  120  generally moves downward (as viewed in  FIG. 1 ) from the illustrated closed position and the open position, in which the valve  120  drops into the cylinder  112  allowing fluid communication through the port  118 . 
     The valve  120  further includes a lower stem  124 , which is formed integrally as one-piece with the head  122 . However, in other configurations, the head  122  and the lower stem  124  may be separately formed and then attached. 
     A thermal cavity  126  is formed within the lower stem  124 , generally along the length of the lower stem  124  and parallel to the direction of movement of the valve  120 . In this configuration, the thermal cavity  126  is at least partially filled with a heat transfer medium  128 . 
     Heat is generated by combustion in the cylinder  112  during operation of the engine, and the head  122  absorbs some of the heat produced by combustion. Portions of the lower stem  124  may also absorb heat produced by combustion, especially when the valve  120  is an exhaust valve. 
     The heat transfer medium  128  takes heat from the head  122  and the lower portion of the lower stem  124  and carries it upward into the rest of the valve  120 . The heat transfer medium  128  may be, for example, sodium or sodium metal. When formed from sodium, the heat transfer medium  128  is inserted into the thermal cavity  126  in solid form, such as pellets. During operation of the engine, the sodium melts and becomes a fluid capable of moving within the thermal cavity  126  and carrying heat from the head  122  and the lower portion of the lower stem  124  to the remainder of the valve  120 . 
     The valve  120  includes an upper stem  130  attached to the lower stem  124  opposite of the head  122 . The upper stem  130  may be attached to the lower stem  124  by, for example and without limitation: mechanical mechanisms, welding, adhesives, or combinations thereof. 
     In the valve system  110 , a valve guide  132  surrounds a portion of at least one of the lower stem  124  and the upper stem  130 . The valve guide  132  may provide an oiled or lubricated interface between the moving valve  120  and the static housing  114 . Alternatively, instead of being formed as a separate component, as shown in  FIG. 1 , the valve guide  132  may be a portion or surface of the housing  114 , such that the valve  120  is in direct contact (along an oiled interface) with the housing  114 . 
     In some configurations, such as that shown in  FIG. 1 , the valve system  110  includes a water jacket  134  that surrounds portions of the valve guide  132 . The water jacket  134  is incorporated into the housing  114  and provides a path for circulation of water or cooling fluids, which are pumped through the water jacket  134 . The cooling fluids draw heat from the valve  120  and dissipate that heat elsewhere, such as through a radiator (not shown). In some situations, the water jacket  134  may alternatively be used to warm the valve system  110 , such as during engine start-up processes. 
     A thermal barrier  136  is adjacent to a junction of the lower stem  124  and the upper stem  130 . The thermal barrier  136  is configured to block or limit transfer of heat between the lower stem  124 —particularly from the heat transfer medium  128 —to the upper stem  130 . By limiting heat transfer into the upper stem  130 , the thermal barrier  136  causes, or allows, heat energy to flow into the housing  114  and the water jacket  134  instead of the upper stem  130 . Reducing heat flow to the upper stem  130  may improve performance or durability of the valve system  110 . 
     The thermal barrier  136  in the valve  120  includes a plug  140 , which is disposed in the lower stem  124  adjacent to the junction of the lower stem  124  and the upper stem  130 . However, the plug  140  may alternatively be disposed in the upper stem  130 . 
     The plug  140  is formed from a ceramic material, such as, without limitation, zirconium oxide or zirconia. The plug  140  has very low thermal conductivity, such that heat carried by the heat transfer medium  128  has difficulty passing the plug  140  and moving further up the valve  120  into the upper stem  130 . Note that all materials and material properties described herein are illustrative only. 
     The remainder of the valve  120  may be formed with different materials from the plug  140 . The lower stem  124  may be formed from a first material, and the upper stem  130  may be formed from a second material, different from the first material. 
     More specifically, and for illustrative purposes only, the first material of the lower stem  124  may be a nickel-chromium alloy or a nickel-chromium-cobalt alloy, such as those sold under the trademarks of NIMONIC or INCONEL. Furthermore, and also for illustrative purposes only, the second material of the upper stem  130  may be a steel alloy, such as AISI M2 steel, or alloys referred to as high speed steel, tool steel, or Molybdenum high speed steel. The nickel-chromium alloy is used for the first material because of its high tensile and creep-rupture properties at temperatures up to 800-1000 Celsius. The nickel-chromium alloy also resists high-temperature corrosion and oxidation. 
     In the exemplary valve  120  shown in  FIG. 1 , the first material of the lower stem  124  has lower thermal conductivity than the second material of the upper stem  130 . Nickel-chromium alloys have thermal conductivity of approximately 8-14 W/m-K, and M2 steel has a thermal conductivity of approximately 18-30 W/m-K. The plug  140  creates the thermal barrier  136  by having lower thermal conductivity than either the lower stem  124  or the upper stem  130 . The illustrative ceramic material forming the plug  140  0.1-1.0 W/m-K, such that the thermal conductivity of the ceramic is likely to be at least one order of magnitude lower than the other materials of the valve  120 . 
     During operation of the valve system  110 —when the temperatures are high—heat produced during combustion in the cylinder  112  is transferred to the head  122  of the valve  120 . That heat is carried from the head  122  up the lower stem  124  by the heat transfer medium  128 . The plug  140  blocks (or at least limits) heat transfer from the lower stem  124  to the upper stem  130 . Therefore, heat from the lower stem  124  is conducted through the valve guide  132  into the housing  114  and the water jacket  134 . 
     In the valve  120  shown in  FIG. 1 , the plug  140  has a cylindrical shape, but the valve  120  may use other shapes, including frustoconical or spherical shapes for the plug  140 . In this configuration, the plug  140  may also be used to close the thermal cavity  126  after the heat transfer medium  128  is added during assembly. Although the plug  140  is shown embedded within the lower stem  124 , the plug  140  may also be a wider cylindrical disc on top of (as viewed in the figure) the lower stem  124 , such that the plug  140  is completely between the lower stem  124  and the upper stem  130 . 
     Referring now to  FIG. 2 , and with continued reference to  FIG. 1 , there is shown a cross-sectional view of a valve system  210 , which may be used with many different engines. The valve system  210  interacts with a cylinder  212  disposed within a housing  214 . An actuator  216  is configured to selectively allow fluid flow through a port  218  to the cylinder  212 . 
     The actuator  216  shown is a rocker, which acts on the top (as viewed in  FIG. 2 ) of a valve  220 . A head  222  of the valve  220  is selectively moveable between a closed position in which the head  222  blocks the port  218  and an open position in which the head  222  unblocks the port  218 . A lower stem  224  is formed as one-piece with the head  222 . 
     A thermal cavity  226  is formed within the lower stem  224 . Again, the thermal cavity  226  is at least partially filled with a heat transfer medium  228 , such as sodium. In the valve  220 , the heat transfer medium  228  is retained within the thermal cavity  226  by a cavity plug  229  inserted through the head  222 . 
     The valve  220  also includes an upper stem  230  attached to the lower stem  224  opposite from the head  222 . A valve guide  232  may surround portions of the upper stem  230  and the lower stem  224 . The housing  214  may include a water jacket  234  or other heat sinks A thermal barrier  236  is adjacent a junction of the lower stem  224  and the upper stem  230 . 
     Unlike the valve  120  shown in  FIG. 1 , the thermal barrier  236  of the valve  220  does not include a ceramic plug. The valve  220  includes a hollow chamber  242  formed in the upper stem  230  adjacent to the junction with the lower stem  224 . The hollow chamber  242  forms the thermal barrier  236  by using air within the hollow chamber  242  as an insulating region. 
     In some configurations of the valve  220 , the hollow chamber  242  includes at least a partial vacuum. With a partial, or full, vacuum in the hollow chamber  242 , the thermal conductivity of the upper stem  230  adjacent to the lower stem  224  is further reduced. The thermal barrier  236  may be further improved in the valve  220  by including a reflective coating substantially covering the hollow chamber  242 . The reflective coating may reduce radiant heat transfer from the lower stem  224  to the upper stem  230  through the hollow chamber  242 . 
     The lower stem  224  and the upper stem  230  of the valve  220  may also be formed from different materials. For example, the lower stem  224  may be formed from a first material, which may be a nickel-chromium alloy, and the upper stem  230  may be formed from a second material, which may be a steel alloy, such as M2 high speed steel. 
     During operation of the valve system  210 —when the temperatures are high—heat produced during combustion in the cylinder  212  is transferred to the head  222  of the valve  220 . Heat is carried from the head  222  up the lower stem  224  by the heat transfer medium  228 , and also by the walls of the lower stem  224 . The hollow chamber  242  blocks (or at least limits) heat transfer from the lower stem  224  to the upper stem  230 . Therefore, heat from the lower stem  224  is conducted through the valve guide  232  into the housing  214  and the water jacket  234  instead of moving further upward. 
     Referring now to  FIG. 3 , and with continued reference to  FIGS. 1-2 , there is shown a cross-sectional view of a valve system  310 , which may be used with many different engines. The valve system  310  works with a cylinder  312  disposed within a housing  314 . An actuator  316  is configured to selectively allow fluid flow through a port  318  to the cylinder  312 . 
     A head  322  of the valve  320  is selectively moveable between a closed position in which the head  322  blocks the port  318  and an open position in which the head  322  unblocks the port  318 . A lower stem  324  is formed as one-piece with, or attached to, the head  322 . 
     A thermal cavity  326  is formed within the lower stem  324 , and is at least partially filled with a heat transfer medium  328 , such as sodium. In the valve  320 , the heat transfer medium  328  is retained within the thermal cavity  326  by a cavity plug  329  inserted through the head  322 . The valve  320  also includes an upper stem  330  opposite the lower stem  324  from the head  322 . 
     A valve guide  332  may surround portions of the upper stem  330  and the lower stem  324 . The housing  314  may include a water jacket  334  or other heat sinks A thermal barrier  336  is formed in a portion of the upper stem  330 . 
     The valve  320  further includes a mid stem  338  or middle stem portion attached to the lower stem  324  between the lower stem  324  and the upper stem  330 . The mid stem  338  forms a portion of the thermal cavity  326 , but is otherwise similar to the upper portions of the lower stem  324 . 
     In the valve  320 , the lower stem  324  is formed from a first material, such as a nickel-chromium alloy. The mid stem  338  is formed from a second material different from the first material. For example, the mid stem  338  may be formed from high speed steel, which has higher thermal conductivity than the nickel-chromium alloy of the lower stem  324 . 
     The valve  320  includes a hollow chamber  342  formed in the upper stem  330  adjacent to the junction with the lower stem  324 . The hollow chamber  342  forms the thermal barrier  336  by using air within the hollow chamber  342  as an insulating region. The upper stem  330  may also be formed from the first material, nickel-chromium alloy, such that the lower stem  324  and the upper stem  330  are formed from similar materials. 
     In some configurations of the valve  320 , the hollow chamber  342  includes at least a partial vacuum. With a partial, or full, vacuum in the hollow chamber  342 , the thermal conductivity of the upper stem  330  adjacent to the mid stem  338  is further reduced. The thermal barrier  336  may be further improved in the valve  320  by including a reflective coating substantially covering the hollow chamber  342 . The reflective coating may reduce radiant heat transfer from the mid stem  338  to the upper stem  330  through the hollow chamber  342 . 
     The valve  320  has a wear cap  346  attached to the upper stem  330  between the upper stem  330  and the actuator  316 . However, the wear cap  346  is not formed from the first material. For example, the wear cap  346  may be formed from the same material as the mid stem  338  (M2 high speed steel) or another material, and may be formed from a material that is more wear resistant than the nickel-chromium alloy. 
     During steady state operation of the valve system  310 —when the temperatures are high—heat produced during combustion in the cylinder  312  is transferred to the head  322  of the valve  320 . Heat is carried from the head  322  up the lower stem  324  by the heat transfer medium  328 , and also by the walls of the lower stem  324 . The hollow chamber  342  blocks (or at least limits) heat transfer from the lower stem  324  to the upper stem  330 . Therefore, heat from the lower stem  324  is conducted through the valve guide  332  into the housing  314  and the water jacket  334  instead of moving further upward. 
     Referring now to  FIG. 4 , and with continued reference to  FIGS. 1-3 , there is shown a cross-sectional view of a valve system  410 , which may be used with many different engines. The valve system  410  works with a cylinder  412  disposed within a housing  414 . An actuator  416  is configured to selectively allow fluid flow through a port  418  to the cylinder  412 . 
     A head  422  of the valve  420  is selectively moveable between a closed position in which the head  422  blocks the port  418  and an open position in which the head  422  unblocks the port  418 . A lower stem  424  is formed as one-piece with, or attached to, the head  422 . 
     A thermal cavity  426  is formed within the lower stem  424 . The thermal cavity  426  may be at least partially filled with a heat transfer medium  428 , such as sodium. The heat transfer medium  428  may be retained within the thermal cavity  426  by a cavity plug  429 . 
     The valve  420  also includes an upper stem  430  attached to the lower stem  424  opposite from the head  422 . A valve guide  432  may surround portions of the upper stem  430  and the lower stem  424 . The housing  414  may include a water jacket  434  or other heat sinks A thermal barrier  436  is adjacent a junction of the lower stem  424  and the upper stem  430 . 
     The thermal barrier  436  of the valve  420  includes a plug  440 , which may be a ceramic plug. Additionally, the thermal barrier  436  includes a hollow chamber  442  formed in the upper stem  430  adjacent to the junction with the lower stem  424  and the plug  440 . The hollow chamber  442  and the plug  440  combine to form the thermal barrier  436  by using air within the hollow chamber  442  as an insulating region and using the very low conductivity of the plug  440  to further insulate. 
     In  FIG. 4 , the plug  440  has a frustoconical shape, but may use other shapes, including cylindrical or spherical shapes for the plug  440 . In some configurations of the valve  420 , the hollow chamber  442  includes at least a partial vacuum. With a partial, or full, vacuum in the hollow chamber  442 , the thermal conductivity of the upper stem  330  adjacent to the lower stem  424  is further reduced. The thermal barrier  436  may be further improved in the valve  420  by including a reflective coating substantially covering the hollow chamber  442 . 
     The lower stem  424  and the upper stem  430  of the valve  420  may also be formed from different materials. For example, the lower stem  424  may be formed from a first material, which may be a nickel-chromium alloy, and the upper stem  430  may be formed from a second material, which may be a steel alloy, such as M2 high speed steel. 
     Heat produced during combustion in the cylinder  412  is carried from the head  422  up the lower stem  424  by the heat transfer medium  428 , and also by the walls of the lower stem  424 . The plug  440  and the hollow chamber  442  block or limit heat transfer from the lower stem  424  to the upper stem  430 . Therefore, heat from the lower stem  424  is conducted through the valve guide  432  into the housing  414  and the water jacket  434  instead of moving further upward the upper stem  330 . 
     Referring now to  FIG. 5 , and with continued reference to  FIGS. 1-4 , there is shown a schematic chart  510 , which graphs simulated operating temperatures of three illustrative valves. The chart  510  shows distance (in millimeters) from a tip of the illustrative valve along an x-axis  512 , and shows temperature differential (in degrees Celsius) along a y-axis  514 . 
     The distance shown along the x-axis  512  is measured from the upper-most tip of the valves, at the interface with the actuator. As the values along the x-axis  512  move toward zero, it is less desirable for large temperature differentials to exist between. 
     A response line for a first valve  520  illustrates heat transfer through a valve having a ceramic plug. The first valve  520  may be substantially similar to the valve  120  shown in  FIG. 1 . A response line for a second valve  522  illustrates heat transfer through a valve having a hollow chamber. The second valve  522  may be substantially similar to the valve  220  shown in  FIG. 2 . 
     A response line for a third valve  524  illustrates heat transfer through a valve having neither a plug nor a hollow chamber. The third valve  524  has a lower stem formed from nickel-chromium alloy and is substantially similar to the lower stem  224  shown in  FIG. 2 . An upper stem of the third valve  524  is formed from M2 high speed steel and is substantially similar to the upper stem  130  shown in  FIG. 1 . The other components of the simulated valves shown in the chart  510  are identical. 
     In each of the illustrated valves, the upper portion of the sodium-filled thermal cavity was at approximately 45 millimeters from the tip of the valves. The values shown in the chart  510  illustrate the different simulated responses of the respective valves during steady state operation, but are not limiting of the invention. 
     As shown in the chart  510 , the temperature of the second valve  522  is reduced along most of its length relative to the third valve  524 , indicating that valves with a hollow chamber reduce temperature relative to valves without a hollow chamber. Similarly, the temperature of the first valve  520  is reduced along most of its length relative to the third valve  524 , indicating that valves with a ceramic plug reduce temperatures relative to valves without. The first valve  520  shows the lowest temperature profile of the three, indicating that the first valve  520  performed better than the second valve  522  or the third valve  524  in this simulation of heat transfer. 
     The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims.