Background of the Invention
[0001] This invention relates to the art of induction heating and, more particularly, to
a method for inductively heating valve seat inserts for an engine component such as
an engine head or the like.
[0002] The invention is particularly applicable to heating exhaust valve seat inserts in
a cast aluminum engine component and will be described with particular reference thereto;
however, it will be appreciated that the invention has broader applications and may
be used for heating a variety of conically shaped metal surfaces in other environments.
[0003] Internal combustion engines generally employ conically shaped valve seats which coact
with reciprocating poppet valves for controlling the flow of gases to and from the
engine cylinders. The valve seats for the exhaust valves must have extremely high
wear characteristics at high engine operating temperatures. To counteract such wear
and increase desirable physical properties in the valve seats, the conical seat surfaces
are inductively heated during engine manufacture and then quench hardened by conventional
liquid or mass quenching techniques.
[0004] Induction heating of multiple valve seats in an engine component may be adapted to
automatic processing in a single operation where, for example, a plurality of single
turn inductors are positioned immediately adjacent the conically shaped exhaust valve
seat. Such apparatus and methods are to which reference is directed. disclosed in
U. S. Pat. Nos. Re 29,046 and 3,837,934/ There, the inductors are independently movable
on a common frame relative to the engine component and are biased toward the valve
seats. The frame itself is moved into contact with the engine component so that each
inductor contacts the valve seat which it is to heat. The inductors are then locked
in position and the frame retracted slightly for purposes of establishing a desired
magnetic coupling distance between the inductors and valve seats. The foregoing patents
disclose methods which have provided extremely good results when induction heating
ferrous exhaust valve seats in cast iron engine components.
[0005] However, recent efforts to improve gasoline mileage and obtain vehicle weight reductions
have brought about an ever increasing use of aluminum for major engine components.
Although use of aluminum for manufacturing such major components provides substantial
benefits insofar as weight reduction is concerned, attendant difficulties and problems
have been encountered in several areas,.including exhaust valve seats. Aluminum does
not have sufficient strength and hardness properties to itself accommodate or comprise
the valve seat surfaces. As a result of these shortcomings, it is necessary that the
exhaust valve seat surfaces be provided through use of seat ring inserts constructed
of a hardenable material installed in the cast aluminum engine component by suitable
means such as, for example, a force fit or the like. For cost reduction purposes as
well as for purposes of assuring accurate location and concentricity of the valve
seat surfaces, it is highly desirable that machining of the inserts for obtaining
final valve seat conformation take place subsequent to mounting of the inserts into
the engine component.
[0006] While machining of the conical valve seat surfaces does not present any significnt
problems, subsequent surface hardening must be performed in a manner which will not
deleteriously affect the aluminum engine component and/or the pressure fit between
the engine component and the ferrous metal insert. Because it is customarily necessary
to harden exhaust valve seat surfaces at approximately 1700°F and since the melting
point of typical aluminum alloys employed for engine components is generally in the
range of 1200° - 1400°F, heating of and heat transfer through the seat inserts must
be carefully controlled during the hardening process. Without appropriate control,
the inserts may radially expand against the associated receiving bores in the engine
component to destroy.the pressure fit relationship therebetween and/or otherwise damage
the integrity of the engine component metal adjacent thereto. In more severe cases,
the aluminum engine component metal could be unacceptably brought close to its melting
temperature. Both of the foregoing situations are extremely undesirable in that they
can ultimately adversely affect engine operation or expected engine life. The specific
heating methods disclosed in U. S. Pat. Nos. Re 29,046 and 3,837,934 are useful in
inductively heating valve seats and valve seat insert surfaces when conventional gray
cast iron engine components are involved. They are not, however, as effective for
use with aluminum or the like components because of the above noted problems and characteristics
which are generally associated therewith. In view of these factors, the inserts were
often made of expensive steel and hardened in furnaces before assembly into the engine
component. This involves costly materials as well as costly post assembly machining
of the hardened seat inserts.
[0007] It has, therefore, been considered desirable to develop a method for inductively
heating the seat surface of ferrous seat ring inserts installed in aluminum engine
components for purposes of overcoming the foregoing problems. One such method and
apparatus is disclosed in the commonly assigned, U. S. patent application Ser. No.
147,829, filea May 8, 1980, and which involves method conceived subsequent to conception
of the subject invention. The foregoing application generally relates to use of a
conducting ring or shield in operative association with each heating inductor for
shielding the inductive energy of the inductor from the aluminum engine component.
This then prevents or controls heating of the aluminum engine component around and
adjacent to the valve seat insert. The method in this prior application did not solve
the problem of undue seat insert expansion during heating. Although providing a solution
to one of the major problems, the subject new method is deemed to provide another
approach for enhancing the ability to harden ferrous seat rings in the general environment
of aluminum engine components.
Brief Summary of the Invention
[0008] The present invention relates to inductively heating a metal valve seat insert within
an engine component such as an engine head or the like subsequent to installation
and machining of the insert within the component.
[0009] The invention further relates to a method for inductively heating the insert prior
to quench hardening while maintaining a pressure fit between the metal insert and
a non-ferrous engine component. The method utilizes high power induction heating techniques
which facilitate obtaining the necessary insert heating to a satisfactory preselected
depth in a very short time interval.
[0010] According to the present invention, the method comprises the steps of:
(a) locating a generally circular inductor adjacent the insert;
(b) energizing the inductor with a primary power source having a frequency of at least
greater than 200 kilohertz and a selected power greater than approximately 12 kilowatts
and providing a power source density at the seat of at least 25 kilowatts per square
inch;
(c) maintaining the inductor in an energized condition for some predetermined period
of time less than 3 seconds to transform the metal forming the valve seat into an
austenitic structure to some predetermined depth; and,
(d) thereafter quenching the valve seat material.
[0011] According to a more detailed aspect of the invention, the step of energizing is performed
at a frequency generally in the range of approximately 250-500 kilohertz at a selected
power generally in the range of 15-25 kilowatts and with said step of machining being
performed in a time period of less than 1 second. In the preferred arrangement for
practicing the method, the frequency is approximately 400 kilohertz at a selected
power of approximately 20 kilowatts.
[0012] According to a further aspect of the invention, the step of maintaining continues
until the metal forming the valve seat is formed into an austenitic structure to a
depth of generally no greater than 0.035 inches. In the preferred method, this depth
is maintained at approximately 0.024 inches.
[0013] The principal object of the present invention is the provision of a new method which
is extremely reliable and effective for purposes of inductively heating a conical
surface on a ferrous ring insert, such as a cast iron insert, disposed in a non-ferrous
component and, in particular, an internal combustion engine component.
[0014] Another object of the invention is the provision of such a method which will not
cause deleterious heat transfer through the insert and/or to the component metal immediately
surrounding and adjacent to the insert.
[0015] Still another object of the invention is the provision of a new method for inductively
heating a ferrous valve seat insert having a pressure fit in an aluminum engine component
so that such heating will not deleteriously affect the pressure fit and wherein an
inexpensive ferrous material like cast iron may be used for the insert.
[0016] Further objects and advantages for the invention will become readily apparent to
those skilled in the art upon a reading and understanding of the following specification.
Brief Description of the Drawings
[0017] The invention may take physical form in certain parts and arrangements of parts,
a preferred embodiment of which will be described in detail in the following specification
and illustrated in the accompanying drawings which form a part hereof and herein:
FIGURE 1 is a partial cross-sectional view illustrating the preferred manner of practicing
the subject new method; and,
FIGURE 2 is an enlarged cross-sectional view of a portion of FIGURE 1 for better-showing
the relationship between the inductor and valve seat surface to be heated.
Detailed Description of the Preferred Embodiment
[0018] Referring now to the drawings wherein the showings are for purposes of illustrating
the preferred embodiment of the invention only and not for purposes of limiting same,
FIGURE 1 shows an induction heating device A disposed in operative communication with
a cast aluminum engine component B. Specific details of the features and operation
of induction heating device A are disclosed in detail in the commonly assigned United
States Pat. No. Re 29,046. Essential and non-essential subject matter from that patent,
as well as from commonly assigned U. S. Pat. No. 3,837,934, are incorporated hereinto
by reference.
[0019] More particularly, engine component B includes at least one exhaust passageway 10
having an annular valve seat insert 12 formed of cast iron and closely disposed coaxially
within a recessed cylindrical exhaust port 14. A guide opening or port 16 is coaxial
with exhaust port 14 and receives the stem of a conventional poppet valve (not shown)
when the engine is assembled.
[0020] Annular valve seat insert 12 includes a conically shaped valve seat surface 30 which
is installed into the engine component, machined and thereafter hardened in accordance
with the subject invention. Insert 12 comprises a standard component typically constructed
from steel or cast iron; however, cast iron is preferred because of costs. Installation
of insert 12 into the receiving bore at exhaust port 14 may be by any one of a number
of conventional methods including, for example, a pressure or force fit and the like.
When a pressure fit technique is employed, the insert is normally chilled to obtain
some degree of contraction and thereby more readily accommodate installation. Following
installation, the insert is fixedly-retained in port 14 by opposed forces particularly
occurring at interface area 32 between the outer side wall of the.insert and the receiving
bore side wall.
'It will be readily appreciated that a plurality of exhaust ports with associated inserts
A are typically involved with any engine component B in the same manner best described
in U. S. Pat. No. Re 29,046.
[0021] Continuing with reference to FIGURE 1, induction heating device A includes a generally
cylindrical electrically insulated body 40 having a somewhat smaller cylindrical electrically
insulated body insert 42 extending coaxially outward from the inner end thereof. A
locating pin or nose 44 extends coaxially outward from body insert 42 to accommodate
locating the induction heating device coaxially of exhaust port 14 in a known manner.
[0022] Interposed between body 40 and body insert 42 of the induction heating device is
a single turn inductor generally designated 50. This inductor comprises a split circular
ring of copper of generally rectangular cross-section and includes a pair of spaced
legs 52,54 extending therefrom axially through body 40 and outwardly from the body
outer end. Inductor 50 as well as legs 52,54 are hollow and communicate with each
other in such fashion to define a continuous fluid passageway therethrough. This passageway
accommodates passage of a suitable coolant from a source (not shown) disposed adjacent
to or spaced from the overall induction heating device as is known.
[0023] A power source 60 is operatively connected by leads 62,64 to conductor 50 as at,
for example, legs 52,54, 'respectively. In accordance with the present invention,
the power source comprises an oscillator having an output frequency capability generally
in the range of 200-500 kilohertz (kHz) and a power capability of generally between
12-25 kilowatts (kw). In practice, it is preferred to use an oscillator having an
output frequency of approximately 400 kHz to provide a radio frequency which will
create a relatively low reference depth in the heating pattern caused by flux generated
around conductor 50.. Also, the preferred power is approximately 20 kw. Since the
heated area of conical surface 30 is about 0.5 square inches (in
2), the power density is in the general range of 40 kw/in
2. This is drastically higher than any power density previously used for heating the
valve seats of internal combustion engines. A time delay device is advantageously
incorporated between leads 62,64 for turning the power source 60 off after a preselected
heating time or interval. In accordance with the present new method, this heating
time is quite short and is typically less than 1 second.
[0024] In practicing the new method, aluminum engine component B will typically have a plurality
of exhaust ports 14 which all have similar inserts 12 which are to be inductively
heated in a simultaneous manner. Apparatus adapted for this purpose is shown in U.
S. Pat. No. Re 29,046 and includes means for causing induction heating device A to
be positioned in an associated exhaust port 14 with locating pin 44 coaxially aligning
the device relative to the exhaust port. Device A is bottomed out with inductor 50
engaging conical valve seat surface 30 of seat insert 12. Thereafter, the heating
device is backed out slightly so that some preselected gap is present between.the
inductor and conical valve seat surface 30 to effect a desired coupling relationship
therebetween.
[0025] With reference to FIGURE 2, this gap is generally designated by letter a and comprises
a distance of approximately 0.040 inches. While this particular gap has been found.particularly
suitable in most cases where-a ferrous valve seat insert disposed in an aluminum engine
component is to have a conical valve seat surface hardened, it will be appreciated
that it may be varied somewhat as deemed necessary or appropriate for a specific application
of the new method. The side or flat surface 70 of inductor 50 is generally parallel
to seat surface 30 and has a width at least slightly greater than that of the seat
surface.
[0026] As previously noted, it is necessary to prevent deleterious heating of or heat transfer
through the entirety of insert 12 in the preferred environment here under discussion.
It has been discovered that acceptable heating results-could be obtained if seat surface
30 was quickly brought to temperature and then quenched prior to the time that any
deleterious heat transfer could occur. Moreover, it is necessary at the same time
to obtain a suitable depth of heating to assure that the hardened seat surface will
have sufficiently high wear characteristics at high operating temperatures. To that
end, it has also been discovered that a depth of generally no greater than 0.035 inches
will provide wholly satisfactory results without in any way impairing engine operation
or engine life.. In practice, a depth of approximately 0.024 inches has been found
entirely satisfactory and is preferred when using the subject new method.
[0027] Thus, and in accordance with the invention, a high power, low time induction heating
method is employed whereby seat surface 30 of seat insert 12 is sufficiently heated
to an acceptable depth for purposes of transforming the seat material into the austenitic
range for subsequent transformation into the martensitic range. As shown in FIGURE
2, the depth of such transformation is generally designated by the letter d and may
comprise a depth of up to approximately 0.035 inches, although 0.024 inches is generally
preferred. By using the prefrred frequency of approximately 400 kHz, a relatively
shallow reference depth is heated in the seat surface and by using the preferred power
of approximately 20 kw to obtain a power density of about 40 kw/in
2, the valve seat is heated to an acceptable transformation temperature at a very rapid
rate. Indeed, and when using the preferred ranges noted, it has been found that a
time interval of approximately 0.5 seconds will provide entirely satisfactory heating
and hardening results to a depth of approximately 0.024 inches..
[0028] On completion of the induction heating cycle, the seat rings or the entire engine
component are subjected to quenching in a manner known in the art. Because heating
of seat surfaces 30 is so rapid and is substantially limited to or isolated at these
surfaces to a preselected shallow depth, there is no deleterious heating of the whole
insert or heat transfer through seat inserts 12. These factors might otherwise adversely
affect or alter the close fitting relationship between the seat inserts and exhaust
ports. This result represents a substantial improvement over results obtained from
prior known techniques in inductively heating valve seats or valve seat inserts.
Example
[0029] In using the foregoing new method, cast iron valve seat inserts have been successfully
hardened to a case depth of 0.030 inches using a heat cycle of 0.5 seconds with a
radio frequency oscillator (400 kw) and a power density of 40 kw/in
2. The advantages of using a soft cast iron insert in an aluminum cylinder head rather
than a prehardened alloy steel insert resides in the fact that it permits easy machining
of the soft cast insert with subsequent hardening of the valve seat by induction hardening
techniques. This then achieves the requisite seat durability while, at the same time,
yielding considerable improvement by way of increased productivity.
[0030] Valve seat inserts have also been hardened at a 0.2 second heat time with this new
method to approximately the case depth of 0.030 inches by using considerably more
than 40 kw/in
2 power density. Even though it reduces the tendency to induce heat into the insert,
the 0.5 second heating cycle is considered somewhat more tolerable in that it provides
a more uniform and constant case depth.
[0031] By way of comparison, the preferred parameters of the subject method using a primary
power source having a frequency of approximately 400 kHz and a power of approximately
20 kw with a heating cycle of approximately 0.5 seconds provides a case depth of approximately
0.024 inches and a hardness of "58" on the Rockwell C scale in cast iron seat inserts.
Prior techniques which typically employ the same frequency at a power of approximately
7 kw with a heating cycle of approximately 7-8 seconds provides a case depth of between
0.050-0.060 inches and a hardness of "58" on the Rockwell C scale. Such parameters,
while acceptable for gray cast iron engine components having integral cast iron valve
seats simply will not provide suitable results in the environment of cast aluminum
engine components utilizing ferrous seat ring inserts.
[0032] The invention has been described with reference to a preferred embodiment. Obviously,
modifications and alterations will occur to others upon a reading and understanding
of the specification. It is intended to include all such modifications and alterations
insofar as they come within the scope of the appended claims or the equivalents thereof.
1. A method of hardening a conical valve seat on a ferrous valve seat insert coaxially
disposed in a bore of a non-ferrous engine component, said method comprising the steps
of:
(a) locating a generally circular inductor adjacent to and matching said insert;
(b) energizing said inductor with a primary power source having a frequency of at
least greater than 200 kHz and a selected power of at least approximately 12 kw and
producing a power density at the seat of at least about 25 kw/in2;
(c) maintaining said inductor in an energized condition for some predetermined period
of time less than 3 seconds to transform the metal forming said valve seat into an
austenitic structure to some predetermined depth generally corresponding to the reference
depth for the frequency of said power source; and,
(d) therefter quenching said valve seat material.
2. The method as defined in claim 1 wherein said step of-energizing is performed at
a frequency greater than approximately 250 kHz and less than approximately 500 kHz.
3. The method as defined in claim 2 wherein said step of energizing is performed at
a frequency of approximately 400 kHz.
4. The method as defined in claim 1 wherein said step of energizing is performed at
a selected power to create a power density at said seat generally in the range of
25-45 kw/in2.
5. The method as defined in claim 4 wherein said step of energizing is performed at
a power density of approximately 40 kw/in2.
6. The method as defined in claim l'including limiting said step of maintaining to
a time period of less than 1 second.
7. The method as defined in claim 1 wherein said step of energizing is performed generally
at a frequency of approximately 400 kHz and a power of approximately 20 kw and wherein
said step of maintaining is limited to generally less than 1 second.
8. A method of hardening a conical valve seat on a ferrous valve seat insert coaxially
fixed in a bore of an aluminum engine component while preventing deleterious heat
transfer by conduction through said insert or loosening of said insert, said method
comprising the steps of:
(a) locating a generally circular inductor adjacent said insert;
(b) energizing said inductor with a primary power source having a frequency of at
least greater than 200 kHz and a selected power of at least approximately 12 kw and
producing a power density at the seat of at least about 25 kw/in ?
(c) maintaining said'conductor in an energized condition for a preselected period
of time for transforming the metal forming said valve seat into an austenitic structure
to a predetermined depth generally no greater than about 0.035 inches; and,
(d) thereafter quenching said valve seat material.
9. The method as defined in claim 8 wherein said step of energizing is performed at
a frequency generally in the range of approximately 250-500 kHz at a selected power
to create a power density at said seat generally in the range of 25-45 kw/in2 and
said step of maintainihg is performed in a time period of less than 1 second.
10.. The method as defined in claim 8 wherein said step of maintaining is performed
for transforming to-a predetermined depth of approximately 0.024 inches in approximately
0.5 seconds.