BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to induction heaters used for removing fasteners
and other automotive repair applications requiring the release of hardware from corrosion/thread
lock compounds, or involving the need for thermal expansion in order to remove mechanical
components, including but not limited to the following applications: bearings races,
brake and transmission lines, zirk fittings, manifold bolts, crank shaft bolts, in-line
connectors, removal of objects bonded to metal, hail dent removal, metal shrinking,
fabrication and decal and body trim removal. More specifically, the invention relates
to an eddy current/hysteretic heater apparatus and its method of use for such applications
in the automotive field.
[0002] U.S. Patent Nos. 6,563,096 and
6,670,590, each of which are incorporated by reference in their entirety into this application,
describe embodiments of eddy current/hysteretic heater apparatus and methods of use.
Using the inventions of these patents, automotive repair personnel may quickly heat
metallic elements such as fasteners, enabling their removal from automotive parts,
for example.
[0003] While the inventions of the '096 and '590 have proven useful and commercially successful,
a new design that would allow induction heaters to function successfully at, for example,
240V, 50 Hz input power supplies would be advantageous. In order to accomplish this,
several design changes were required, including: redesigning the transformer to properly
transfer inductive energy to the output load; changing transistor values (Q1, Q2)
which would not otherwise survive higher voltages present as a result of the higher
operating voltage; redesigning the circuit to ensure that integrated circuit U1 and
transistors Q1 and Q2 are not destroyed by voltage transients whose amplitude increases
with the increased input supply voltage; and redesigning the feedback circuit so that
it will function properly with the new transformer and new operating voltage, under
various applicable load conditions. These changes are described below.
SUMMARY OF THE INVENTION
[0004] According to an aspect of the present invention, there is provided a heater apparatus
as specified in claim 1.
[0005] The invention is also directed to a method by which the described apparatus operates
and including method steps for carrying out every function of the apparatus.
[0006] The objects mentioned above, as well as other objects, are solved by the present
invention, which overcomes disadvantages of prior automotive induction heaters and
methods of using them, while providing new advantages not believed associated with
such heaters and methods.
[0007] In general, those of ordinary skill in the art will appreciate that, with respect
to the heater apparatus described in
U.S. Patent Nos. 6,563,096 and
6,670,590, the transformer "turns-ratio" was redesigned to account for the higher input voltage
while keeping the output voltage the same, and that the C3 value was changed to keep
the LC resonance at the same frequency. (The optimum turns-ratio was found to be 15:1
(e.g., 60 turns on the primary winding and 4 turns on the secondary winding)). Additionally,
diodes D11 A, B and C were added to clamp the Q1, Q2 collector voltage swing to a
safe level. (The voltage rating on the transistors was also changed.) Further, D3
and D4 were moved to provide a new configuration in order to clamp the negative-going
voltage transients of the Q1 and Q2 gates to ground. Diodes D13, D14 were also added
in order to clamp the positive-going transients on the U1 outputs to a voltage power
source Vcc.
[0008] Finally, the "base" operating frequency of the oscillator, comprised of components
U1, R3, R4, R5, C5, R6, & C6, was lowered by changing R3, R4 and C5, C6 values. This
increases the dynamic range of the feedback circuits R13/R15, R14/R16, Q3, Q4, Q6,
Q7 and their surrounding bias control and coupling components. The increased dynamic
range helps to maintain the zero-voltage switching condition of Q1 and Q2 during output
open circuit conditions, keeping Q1 and Q2 heat dissipation to a minimum.
[0009] Various other components and/or their values were also changed from the circuit used
in the embodiments disclosed in the '096 and '590 patents to properly rate the components
and to reduce heat dissipation that may occur at the higher input voltage.
[0010] In a particularly preferred embodiment, a heater apparatus 10 is provided and may
be used for automotive repair. Apparatus 10 may be powered by a 240-volt AC power
source, and may utilize a frequency in a range of 15-50 KHz. Apparatus 10 may include
an eddy current/hysteretic circuit with an induction work coil 19. The circuit may
be engaged to the power source. A plurality of hand-held, manipulable applicators
18 may also be provided, and may be functionally engaged to the circuit for use in
applying heat generated by the circuit to desired areas of automotive vehicles.
[0011] In another embodiment, a controller may be provided for allowing only one of the
applicators 18 to be in use at a time. The applicators 18 may be interchangeable in
the connection of each to the eddy current/hysteretic circuit. The applicators 18
may be simultaneously engaged to the eddy current/hysteretic circuit. At least one
of the applicators 18 may include a flexible pad 18 (e.g., FIGURE 3) for accommodating
substantially all configurations of automotive vehicle body areas. Alternatively,
or in addition, at least one of the applicators 18 (e.g., FIGURE 4) may include a
magnetic ferrite structure 23 having an air gap 21 for delivering a concentrated level
of heat to a mechanical part of an automotive vehicle. Each applicator 18 may also
include indicia 32 for indicating an on-condition of the applicator 18. Heater apparatus
10 may also include a sensor which turns an applicator 18 off when no motion is sensed
over a predetermined period of time. A housing 90 may be used to contain the eddy
current/hysteretic circuit and the plurality of applicators 18 when the heater structures
are not in use.
[0012] Heater apparatus 10 may also include a high-frequency isolation transformer 72 functionally
engaged between the eddy current/hysteretic circuit and the plurality of applicators
18. Transformer 72 may have a turns-ratio, as a preferred example, in the 15:1 range.
The eddy current/hysteretic circuit may include insulated gate bipolar transistors
(IGBTs, Q1, Q2). The IGBTs (Q1, Q2) may be protected from suffering collector overvoltage
failure, and also may be protected from suffering negative-going voltage transient
failure. The circuit may also include an oscillator for driving the IGBTs (Q1, Q2).
The oscillator may have a base operating frequency in the range of 15-20 kHz, and
positive-going transients on an output of the oscillator may be clamped to a voltage
power source.
[0013] The eddy current/hysteretic circuit may include a drive circuit, a feedback circuit
for protecting the drive circuit, and an LC circuit for generating power.
DEFINITION OF CLAIM TERMS
[0014] The terms used in the claims of the patent as filed and are intended to have their
broadest meaning consistent with the requirements of law. Where alternative meanings
are possible, the broadest meaning is intended. All words used in the claims are intended
to be used in the normal, customary usage of grammar and the English language.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The novel features which are characteristic of the invention are set forth in the
appended claims. The invention itself, however, together with further objects and
attendant advantages thereof, can be better understood by reference to the following
description taken in connection with the accompanying drawings, in which:
FIGURE 1 is a perspective view of an embodiment of the eddy current/hysteretic heater
apparatus of the present invention;
FIGURES 2A and 2B are top and cross-sectional views, respectively, of the applicator
shown in FIGURE 1;
FIGURE 3 is an enlarged view of one applicator of the eddy current/hysteretic heater
apparatus, in which the applicator includes a flexible pad;
FIGURE 4 is an enlarged view of an applicator, including a magnetic ferrite structure
having an air gap for delivering a concentrated level of heat, which may be electrically
connected to the heat dissipating terminal shown in FIGURE 1, for example;
FIGURE 5 is a schematic view of a preferred embodiment of the power supply of the
induction heating mechanism of the present invention; and
FIGURE 6 is a schematic view of an inverter useful with the induction heating mechanism
of the present invention.
[0016] The components in the drawings are not necessarily to scale, emphasis instead being
placed upon clearly illustrating the principles of the present invention. In the drawings,
like reference numerals designate corresponding parts throughout the several views.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] Set forth below is a description of what are believed to be the preferred embodiments
and/or best examples of the invention claimed. Future and present alternatives and
modifications to this preferred embodiment are contemplated. Any alternatives or modifications
which make insubstantial changes in function, in purpose, in structure, or in result
are intended to be covered by the claims of this patent.
[0018] Referring now to the drawings in greater detail, and more specifically to FIGURES
1-4, an eddy current/hysteretic heater apparatus is shown, made in accordance with
the teachings of the present invention, and generally identified by the reference
numeral 10. Heater apparatus 10 includes structure 12, such as a plug 12, for engaging
apparatus 10 to a source of electrical power (not shown), preferably ordinary AC line
power. A rectifier 14 may be provided for converting the AC power from the source
into DC power. The DC power may contain a natural ripple frequency at twice the line
frequency rate, or may be filtered to remove some or all of the ripple. A high-frequency
inverter 16 of push-pull, half-bridge, full bridge or single-ended variety, either
resonant or not, may also be provided. An applicator 18 may be functionally engaged
to inverter 16 for applying a high-frequency magnetic field to any metallic automotive/mechanical
structure to be heated for obtaining a desired result, as further described below.
Switch 20 may be provided for use in activating apparatus 10.
[0019] Those of ordinary skill in the art will understand that, for example, bidirectional,
high-speed switching devices and inverters exist which would eliminate the need for
a separate rectifier. Accordingly, the use of same as a modification to the above-described
circuitry should be regarded as falling within the scope of the present invention.
[0020] Referring now to FIGURE 1, in operation of apparatus 10, AC power may be delivered
through plug 12 to rectifier 14, where it is converted to DC power of a similar or
higher voltage. The DC voltage may, but need not, be filtered to remove ripple components.
This DC power may then be delivered to high-frequency inverter 16, where the power
may be converted to a high frequency, such as in the range of 5-500 kHz, and most
preferably for the currently described application in the range of 15-50 KHz, depending
on load. This high frequency may then be run through isolation transformer 72 and
heat dissipating terminals 22 (via wire 24), and then delivered to a selected applicator
18, wherein it may be transformed into a high-frequency magnetic field. Thumb screw
81 may be used to tighten and secure applicator 18 to heat dissipating terminal 22.
[0021] When applicator 18 is brought into close proximity with a non-magnetic metallic object
(not shown), a similar, but opposing, high-frequency current may be developed within
the object through known transformer action and a current may be caused to flow within
and through the metallic object, generating heat within the object through its natural
resistance. If the metallic object is of magnetic or ferrous nature, an additional
action of heating, known as magnetic hysteresis heating, may occur in which rapidly
changing high frequency flux causes magnetic domains within the metal to "rub" against
each other, generating heat in a manner analogous to that caused by friction.
[0022] Applicators 18 may be of several differently shaped or sized handheld, manipulable
or rigid elements. One embodiment may include a cylindrical coil of solid and/or stranded
or a combination of both solid/stranded copper wire (FIGURE 2), with an air gap in
the center of the coil where the magnetic field is concentrated to heat metallic objects
placed within this field.
[0023] A second embodiment of applicator 18 may be planar, flexible or rigid structures
in the form of pad 18 (FIGURE 3), for heating relatively small or large areas of (e.g.)
sheet metal with flat or compound-curved surfaces.
[0024] Referring now to FIGURES 2 and 4, a third embodiment of applicator 18 may include
flux-concentrator work coils 19 (FIGURE 4) employing a ferrite, or other suitable
magnetic material having a magnetic permeability substantially greater than air, and
having an air gap 21 (see FIGURE 4, showing an applicator 18 which be electrically
connected, e.g., plugged into, heat dissipating terminal 22 shown in FIGURE 1) in
the magnetic circuit, with the flux density being greater than if the same coil 19
were similarly energized but without core 23. This latter coil 19 may be used for
intense heating of rusted nuts and bolts and the like (not shown) to facilitate their
disassembly, and to locally heat small areas of sheet metal in certain body-work operations,
such as in hail dent removal.
[0025] A fourth embodiment of applicator 18 may include a stranded litz wire of any predetermined
length to wrap around symmetrical as well as asymmetrical metallic objects of any
size or shape for the purpose of releasing such items from corrosion or for thermally
expanding items, such as bearings, races, O-2 sensors, tie rods/tie rod ends, or other
automotive parts, in order to free/release a desired metallic object.
[0026] In a preferred embodiment of apparatus 10, connectors (heat dissipating terminals)
22 (FIGURE 1) may be inserted in cable 24 between inverter 16 and work coil 19, to
allow for exchanging of one applicator 18 for another. A custom connector/heat dissipating
terminal 22 may be used to prevent the conductive heat created from transferring back
through the apparatus, from damaging other components.
[0027] Referring to FIGURES 3-4, it may be seen that a single loop of wire 30 may be incorporated
into either pad 18 or concentrator tip 18 to deliver a small, high frequency voltage
by known transformer action for the illumination of an electric lamp 32, or other
indicia for indicating an "on" or energized condition for applicator 18. A small lamp
32 may serve only to indicate that the applicator 18 is energized, while a larger
lamp 32 may serve not only to indicate activation, but also to serve as a light source
to illuminate the work area.
[0028] Referring to FIGURE 4, a voltage regulator 33 may be inserted between leads 40 of
the applicator and the lamp loop 30 to maintain light output substantially constant
while drive frequency is varied to change the power level, if such capability is incorporated
into apparatus 10, and/or loading on applicator 18 is varied.
[0029] Referring now to FIGURE 5, a preferred embodiment of a power supply useful with the
induction heating mechanism of the present invention is shown. The isolation step-down
transformer, not shown in FIGURE 5, but indicated by T1-C, and by T1-2 and T1-2 in
FIGURE 6, may be a center-tapped inductor. For the purpose of this description, this
will be referred to as the isolation step-down transformer, which has three terminals:
a center tap, and the two ends.
[0030] In a particularly preferred embodiment, commercially known as the "Miniductor," used
primarily for loosening rusty and stuck bolts, an externally-connected, two-leaded
work coil may be placed over or wrapped around the stuck nut or bolt. The Miniductor
is activated to cause heavy high-frequency current to flow through the work coil which,
in turn, inductively heats the target nut or bolt. Thermal expansion resulting from
the high heat causes the nut/bolt to break free.
[0031] Still referring to FIGURE 5, power rectifier BR1 may provide DC power for the unit.
Inductor L1 may be used to feed rectified power to the center tap of the isolation
transfomer, effectively making the power appear as a current source. D11A-C may provide
transient over voltage protection to inverter power transistors Q1 and Q2. Transistors
Q5, Q8, Q9 and Q11 may function as the inverter turn-on/off circuit. This type of
inverter should be turned on only when the power supply voltage is at a low point
(to prevent failure due to overvoltage transients) and, more specifically, at or near
the zero crossings of the power line, when the lightly filtered rectified power is
also at a low point. The inverter may be turned on by a contact closure between S1-1
and S1-2. Resistors R17, R18 and R24 may be used to feed current to zener diodes D9
and D10 to provide a 14-volt power source Vcc, filtered by capacitor C10. When the
rectified power supply voltage is well above 14 volts, the current through R18 and
R24 turns on Q11, which inhibits a closure of S1-1 and S1-2 from turning on the inveter.
When the voltage is low enough, Q11 turns off, and a closure will turn on silicon-controlled
rectifier Q9 and transistors Q5 and Q8, providing the inverter turn-on voltage of
about 14 volts to terminal THSW. When the power supply voltage rises again above 14
volts, SCR Q9 will turn off and turn off the inverter. Overall, this provides for
the turning on and off of the inverter near the zero crossings of the power supply.
[0032] Referring now to FIGURE 6, a preferred embodiment of the power circuit of the inverter
including parallel resonant circuit C3 and the isolation transformer, and power transistors
Q1 and Q2. In normal operation, transistors Q1 and Q2 may be turned on and off alternately,
supplying power to the isolation transformer. Gate driver U1 may be employed to turn
on Q1 and Q2 alternately. The collector voltages of transistors Q1 and Q2 may be sampled
by R15 and R16 and attenuated by the voltage divider components R13 and R9 (working
in conjunction with R15) and R14 and R10 (working in conjunction with R16). The attenuated
signals may then be applied to transistors Q3 and Q4. Transistors Q3 and Q4 may act
as comparators that, via C8 and C9, provide pulses to Q6 and Q7 when the collectors
of Q1 and Q2 approach zero volts. This, in turn, alternately switches the states of
the two gate drivers when the collectors of Q1 and alternately Q2 are at or close
to zero volts. Therefore the on/off transitions of Q1 and Q2 occur at or near when
their collector voltages are at zero volts, minimizing wasted power dissipation. Feedback
from R15 and R16 along with their associated feedback circuits as described earlier,
operate on the diminishing Q1 and Q2 collector voltages, whose rate is determined
by the LC resonance presented earlier but influenced strongly by the load characteristics
of the external work coil and its target metal piece. This action causes the transitions
of Q1 and Q2, the periods of maximum potential wasted heat dissipation, as they transfer
high power pulses from the input power source to the output of the isolation step-down
transformer, to always tend to occur near or at zero collector voltage, greatly minimizing
the wasted heat losses.
[0033] Additionally, C5, C6, R5, and R6 may create a cross-coupled oscillation circuit for
the two gate drivers when the power stage is not yet operating, such that the inverter
will start up properly. The self-oscillation frequency is preferably deliberately
chosen to be below the natural resonant frequency of the power circuit, so that when
the power circuit begins to operate, it will pre-empt the self-oscillation of the
gate driver circuit.
[0034] The values of R15, R13, and R9, and R16, R14, R10 are preferably chosen such that
the switching of Q1 and Q2 occurs as close as possible to the zero voltage point of
the collectors, to optimize inverter efficiency, while ensuring reliable switching.
[0035] It will be understood by those of ordinary skill in the art that D5, D6, D7, and
D8 switch R15 and R16 out of the circuit below about 14 volts, which then allows the
bias circuitry for Q3 and Q4 to function properly in switching the state of U1 output
drivers at the proper timing to keep Q1 and Q2 heat dissipation low. R1 & R2 have
been selected to optimize transition time and energy losses and the efficiency of
the drive circuit device U1. Insulated gate bipolar transistors Q1 and Q2 minimize
drive power requirements (high input impedance) and low output on resistance, providing
minimal collector losses during operation.
[0036] The unit values shown in the drawings have been selected in order to provide an induction
heater capable of being powered by 240 volts (typical European voltage transmission)
and a 50 Hz input power supply.
[0037] Those of ordinary skill in the art will appreciate from the above disclosure that
user-operated power may control the average power delivered to applicator 18 by varying
the drive frequency for a resonant inverter 16, with power reduction being accomplished
by a progressively increasing (preferred) or decreasing the drive frequency away from
resonance. In the case of a non-resonant inverter 16, frequency may be similarly varied
to control power instead. In either case, power may be controlled by changing the
inverter drive waveform from a symmetrical 50/50% duty cycle (if the inverter 16 topology
chosen uses more than one switching device (not shown)) where maximum power is delivered,
to a progressively assymetrical drive waveform where very little power delivery occurs
(e.g., with one transistor conducting 95% of the time, and the other transistor conducting
5% of the time, with a half-bridge resonant converter delivering only 3-5% of full
power).
[0038] In a typical body shop/garage environment, damp to wet concrete floors and grounded
metallic objects such as automotive vehicles on lifts are commonplace. While applicators
18 and cables 24 are insulated, insulation may fail as is known, potentially creating
an electric shock risk. There are two methods for preventing such an occurrence. One
method involves using a standard ground fault interrupter module between the AC source
and input rectifier 14 of apparatus 10.
[0039] Another method involves using a high frequency isolation transformer located between
inverter 16 and each applicator 18.
[0040] Referring again to FIGURES 5-6, those of ordinary skill in the art will recognize
that in the preferred embodiment of the circuits disclosed there and described above,
the following circuits consist of the following components:
-- the drive circuit consists of U1 (output driver transistor located interally),
R1, R2, D3 and D4
-- The feedback circuit consists of R15, D5, D6, R13, R9, Q3, R11, C8, R7, Q6, on
Q1 side, and R16, D7, D8, R14, R10, Q4, R12, C9, R8, and Q7
-- The LC circuit consists of center-tapped, isolation transformer, L1, and C3.
-- The oscillator circuit consists of U1, R3, C5, R5, and R4, C6, R6, and D13, D14
[0041] The above description is not intended to limit the meaning of the words used in the
following claims that define the invention. Persons of ordinary skill in the art will
understand that a variety of other designs still falling within the scope of the following
claims may be envisioned and used. It is contemplated that future modifications in
structure, function, or result will exist that are not substantial changes and that
all such insubstantial changes in what is claimed are intended to be covered by the
claims.
1. A heater apparatus (10) used for automotive repair, powered by a 240-volt AC power
source, and utilizing frequency in a range of 15-50 KHz, comprising:
an eddy current/hysteretic circuit designed to provide induction heating, the circuit
engaged to the power source; and
a plurality of hand-held, manipulable applicators (18) functionally engaged to the
circuit for use in applying induction heating generated by the circuit to desired
areas of automotive vehicles.
2. The heater apparatus (10) of Claim 1, further comprising a controller for allowing
only one of the applicators (18) to be in use at a time.
3. The heater apparatus (10) of Claim 1 or claim 2, wherein the applicators (18) are
interchangeable in the connection of each to the eddy current/hysteretic circuit.
4. The heater apparatus (10) of Claim 2, wherein the applicators (18) are simultaneously
engaged to the eddy current/hysteretic circuit. The heater apparatus (10) of Claim
1, wherein at least one of the applicators (18) comprises a flexible pad (18) for
accommodating substantially all configurations of automotive vehicle body areas.
5. The heater apparatus (10) as claimed in any of claims 1-4, wherein at least one of
the applicators (18) comprises a structure (23) having an air gap (21) for delivering
a concentrated level of heat to a mechanical part of an automotive vehicle.
6. The heater apparatus (10) as claimed in any of claims 1-5, wherein each applicator
(18) includes indicia (32) for indicating an on-condition of the applicator (18).
7. The heater apparatus (10) as claimed in any of claims 1-6, further comprising a sensor
which turns an applicator (18) off when no motion is sensed over a predetermined period
of time.
8. The heater apparatus (10) as claimed in any of claims 1-7, further comprising a high-frequency
isolation transformer (72) functionally engaged between the eddy current/hysteretic
circuit and the plurality of applicators (18).
9. The heater apparatus (10) of Claim 8, wherein the transformer (72) has a turns-ratio
in the range of 15:1.
10. The heater apparatus (10) as claimed in any of claims 1-9, further comprising a housing
(90) containing the eddy current/hysteretic circuit and the plurality of applicators
(18) when the heater structures are not in use. The heater apparatus (10) of Claim
1, wherein the circuit includes insulated gate bipolar transistors (IGBTs, Q1, Q2)),
and wherein the IGBTs are protected from suffering collector overvoltage failure.
11. The heater apparatus (10) as claimed in any of claims 1-10, wherein the circuit includes
IGBTs (Q1, Q2), and wherein the IGBTs (Q1, Q2) are protected from suffering negative-going
voltage transient failure.
12. The heater apparatus (10) as claimed in any of claims 1-10, wherein the circuit includes
IGBTs (Q1, Q2) and an oscillator for driving the IGBTs (Q1, Q2).
13. The heater apparatus (10) of Claim 12, wherein the oscillator has a base operating
frequency in the range of 15-20 kHz.
14. The heater apparatus (10) of Claim 12, wherein positive-going transients on an output
of the oscillator are clamped to a voltage power source.
15. The heater apparatus (10) of Claim 14, wherein the eddy current/hysteretic circuit
includes a drive circuit and a feedback circuit for protecting the drive circuit and,
optionally, wherein the circuit includes an LC circuit (L1, C3) for generating power