Patent Application
20210180478
The present disclosure relates generally to a valve seat insert in an internal combustion engine, and more particularly to a valve seat insert having a stiffness relief cutout to cushion seating of an engine valve.
Gas exchange valves are used in internal combustion engines to control fluid connections between the cylinder and a supply of intake air or intake air and other gases, such as recirculated exhaust, or between the cylinder and an exhaust manifold for expelling combustion products. Designs are known where a single intake valve and a single exhaust valve are associated with each cylinder in an engine, as well as designs where multiple gas exchange valves of each type are associated with each cylinder. A camshaft, typically rotated at half engine speed, is coupled with valve lifters, bridges, rocker arms, and/or other equipment for opening and closing gas exchange valves at appropriate engine timings.
Such valves are typically moved into contact and out of contact with the engine head or a valve seat insert within the engine head to open and close, and can be moved between opened and closed positions with significant mechanical forces. During operation, engine cylinders and associated hardware, including gas exchange valves and valve seat inserts, can experience temperatures of several hundred degrees Celsius and relatively high fluid pressures. For these and other reasons, gas exchange valve operating conditions can be quite harsh. Gas exchange valves and valve seat inserts can experience undesired wear and/or material deformation over the course of a service life of the engine, or between service intervals.
A gas exchange valve and its valve seat can contact one another in the millions or potentially billions of times between planned service intervals. In some instances, material of the components wears away, is displaced, or the components themselves can otherwise deform. A phenomenon known as valve recession relates to an engine valve receding toward or into the engine head over time. In other instances, material can be transferred from a desired location by way of adhesion between the hot valve head and valve seat insert during service, and alter the pattern of contact between the components in an undesired manner. Engineers have experimented with a variety of different techniques attempting to address the extent and effects of various valve and valve seat wear phenomena. In Japanese Patent Application Publication No. JP8270417A, a convex surface is provided that bulges toward a seat surface of a valve face to address local wear problems.
In one aspect, an engine head assembly includes an engine head having a fireside surface structured to face a cylinder in an engine, and the engine head having formed therein a valve seat bore, and a gas exchange conduit connecting to the valve seat bore. The engine head assembly further includes a valve seat insert having a valve seating surface defining a center axis, a first axial end abutting the engine head within the valve seat bore, and a second axial end. The engine head assembly still further includes a gas exchange valve having a valve head, and being movable between a closed valve position where the valve head contacts the valve seating surface, and an open valve position. The valve seat insert further includes an inner peripheral surface extending circumferentially around the center axis and forming a throat, for communicating gases between the gas exchange conduit and the cylinder, and an outer peripheral surface. The outer peripheral surface includes an upper section adjacent to the first axial end and interference-fitted with the engine head within the valve seat bore, and a lower section extending between the upper section and the second axial end. A stiffness relief channel extends radially between the lower section of the outer peripheral surface and the engine head. The stiffness relief channel is circumferential of the valve seat insert and opens in a direction of the fireside surface.
In another aspect, a valve seat insert for a gas exchange valve controlling gas exchange of a cylinder in an engine includes an annular insert body formed of a metallic material and having an inner peripheral surface, an outer peripheral surface, and a valve seating surface. The valve seating surface defines a center axis extending between a first axial end and a second axial end of the annular insert body. The inner peripheral surface extends circumferentially around the center axis and forms a throat, for communicating gases between a cylinder in the engine and a gas exchange conduit in an engine head in the engine. The outer peripheral surface extends circumferentially around the center axis, and includes an upper section adjacent the first axial end, and a lower section extending between the upper section and the second axial end. The upper section has a full outer diameter dimension, and a cylindrical shape, for interference-fitting the annular insert body in a valve seat bore in the engine head. The lower section has a reduced outer diameter dimension, relative to the upper section, such that the outer peripheral surface is stepped radially inward from the upper section to the lower section, and forms a relief cutout for limiting a stiffness of the valve seat insert.
In still another aspect, a valve seat insert for a gas exchange valve controlling gas exchange of a cylinder in an engine includes an annular insert body formed of a metallic material and including an inner peripheral surface, an outer peripheral surface, and a valve seating surface. The valve seating surface defines a center axis extending between a first axial end and a second axial end of the annular insert body. The inner peripheral surface extends circumferentially around the center axis and forms a throat, for communicating gases between a cylinder in the engine and a gas exchange conduit in an engine head in the engine. The outer peripheral surface extends circumferentially around the center axis, and includes an upper section adjacent the first axial end, and a lower section. The upper section has a full outer diameter dimension, and a cylindrical shape, for interference fitting the annular insert body in a valve seat bore in the engine head. The lower section has a reduced outer diameter dimension, relative to the upper section, and forms a relief cutout that is continuous from the upper section of the outer peripheral surface to the second axial end.
Referring to
Engine head assembly 18 further includes a first gas exchange valve 28 and a second gas exchange valve 29 associated, respectively, with gas exchange conduits 24 and 26. Gas exchange valves 28 and 29 could be substantially identical, or different; however, description herein of gas exchange valve 28 and associated components in the singular should be understood to refer by way of analogy to gas exchange valve 29 and any other gas exchange valves in engine 10. Gas exchange valve 28 is shown more or less vertically oriented and defines a valve reciprocation axis 33. In other embodiments gas exchanged valve 28 could be diagonally oriented relative to a reciprocation direction of piston 16. Engine head 20 includes fireside surface 22 structured to face cylinder 14, and further has formed therein a valve seat bore 40, with gas exchange conduit 24 connecting to valve seat bore 40. Engine head 20 also includes an inner cylindrical bore surface 42 forming valve seat bore 40. Each of gas exchange valves 28 and 29 can be movable between a closed valve position blocking fluid communication between cylinder 14 and the respective gas exchange conduits 24 and 26, and an open valve position at which gas exchange can occur. Gas exchange valves 28 and 29 may be spring-biased towards closed positions, and opened in response to rotation of a camshaft.
Engine head assembly 18 further includes a valve seat insert 38 positioned within valve seat bore 40. Another valve seat insert also shown by way of a reference numeral 38, associated with gas exchange conduit 26. The two valve seat inserts 38 may be substantially identical in at least some embodiments. Referring also now to
Valve seat insert 38 further includes an inner peripheral surface 52 extending circumferentially around center axis 46 and forming a throat 54, for communicating gases between gas exchange conduit 24 and cylinder 14, and an outer peripheral surface 56. Outer peripheral surface 56 includes an upper section 58 adjacent to first axial end 48 and interference-fitted with engine head 20 within valve seat bore 40. A lead-in chamfer 83 is shown at first axial end 48. Upper section 58 is interference-fitted, in particular, with inner cylindrical bore surface 42, and has a cylindrical shape. Outer peripheral surface 56 also includes a lower section 60 extending axially between upper section 58 and second axial end 50.
As discussed above, contact between a gas exchange valve and a valve seat in an engine can subject the components to significant mechanical stress and strain, often at high temperatures. It has been observed that the amplitude and impulse of forces exerted between a valve and valve seat, and other factors, can lead to deformation, damage, undue wear, or other phenomena that result in performance degradation over time. According to the present disclosure, valve seat inserts and/or engine heads can be constructed to enable a reduced stiffness of a valve seat insert that can cushion contact between a valve head and valve seat insert during closing a gas exchange valve.
To this end, a stiffness relief channel 62 extends radially between lower section 60 of outer peripheral surface 56 and engine head 20, with stiffness relief channel 62 being circumferential of valve seat insert 38 and opening at second axial end 50 in a direction of fireside surface 22. It will be recalled that valve seat bore 40 may be formed by inner cylindrical bore surface 42. An axial extent of inner cylindrical bore surface 42 may be such that lower section 60 faces inner cylindrical bore surface 42, and is spaced in a radial direction, relative to center axis 46, from upper section 58 to form a relief cutout 63 in valve seat insert 38. Relief cutout 38 together with inner cylindrical bore surface 42, forms stiffness relief channel 62. Relief cutout 63 may be continuous from upper section 58 to second axial end 50.
In some embodiments, no modification to an existing engine head design is needed to provide stiffness relief channel 62, with a purpose-built valve seat insert being fitted into a cylindrical valve seat bore to form relief channel 62. In other embodiments, relief channel 62 could be formed in whole or in part in an engine head, with an outer peripheral surface of a valve seat insert being uniformly cylindrical. It will be recalled that upper section 58 is interference-fitted with engine head 20. Providing relief channel 62/cutout 63 results in effectively less axial length of valve seat insert 38 that is interference-fitted, and permits valve seat insert 38 to elastically deform in response to closing contact with gas exchange valve 28. Certain additional structural features and refinements to valve seat insert 38 as further discussed herein provide practical implementation strategies.
Referring also now to
Relief cutout 63 may also have a radial width dimension 76, and an axial length dimension 74 that is greater than radial width dimension 76. Radial width dimension 76 extends along the radius of a circle centered on center axis 46. Axial length dimension 74 is parallel to center axis 46. Axial length dimension 74 may also be less than a second axial length dimension 78 of upper section 58 of outer peripheral surface 56, such that a majority of a full axial length of outer peripheral surface 56 is interference-fitted with inner cylindrical bore surface 42. Axial length dimension 74 may further be less than an interference-fitted axial length of upper section 58 with engine head 20. As best shown in
Referring now to
In the case of seat angle 68 in the embodiment of
Referring to the drawings generally, when engine 10 is operated gas exchange valves 28 and 29 may open and close against valve seat inserts 38, with a closing force resulting from a return spring bias and fluid pressures in cylinder 14 and/or the respective gas exchange conduits 24 and 26. In certain earlier strategies valve seat inserts were interference-fitted along an entirety, or substantially an entirety, of an axial length of the seat insert within the engine head. As a result, the relatively tight fit and full interference between components can result in the engine head itself limiting elastic deformation of the valve seat inserts in response to valve contact. According to the present disclosure, valve seat inserts can be expected to elastically deform or flex radially outward when the gas exchange valve contacts and pushes against the respective valve seating surface. Stiffness relief channels 62 and 162 can thus be understood to limit stiffness of valve seat inserts 38, 138, in a manner that is not available in designs having a full length interference fit.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims. As used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.
