USOO6286637B1

(12) United States Patent (10) Patent No.: US 6,286,637 B1

(54) CONTACTLESS EDDY CURRENT BRAKE 4,326,236 4/1982 McNair et al. ...................... 361/170
FOR CARS 4,775,145 * 10/1988 Tsuyama ... ... 272/73
5,254,061 10/1993 Leask ..................................... 482/63
(75) Inventors: Kyi Hwan Park; Kap Jin Lee, both of * cited by examiner
KwangJu (KR)
Primary Examiner Robert J. Oberleitner
(73) Assignee: Kwangju Institute of Science & Assistant Examiner Xuan Lan Nguyen
Technology (KR) (74) Attorney, Agent, or Firm Martine & Penilla, LLP
(*) Notice: Subject to any disclaimer, the term of this (57) ABSTRACT
patent is extended or adjusted under 35 A contactleSS eddy current brake for cars is disclosed. In the
U.S.C. 154(b) by 0 days. brake, two cores are arranged around the edge of a brake disc
while being spaced apart from each other at an angle of 90.
(21) Appl. No.: 09/243,713 Each of the cores is wound with a coil, thus forming an
(22) Filed: Feb. 3, 1999 electric magnet. A speed Sensor is positioned around the
axle, thus Sensing revolutions of the wheel. A control unit
(30) Foreign Application Priority Data calculates a DC or AC control current in response to a speed
Mar. 9, 1998 (KR) ................................................... 98-7665
Signal output from the Sensor, thus outputting an appropriate
Dec. 29, 1998 (KR) ................................................. 98-60145 control current value to the coils. A current amplifier Sup
plies the control current value from the control unit or a
(51) Int. Cl." ........................................................ B60L 7700 current value from a brake pedal to the coils of the cores.
(52) U.S. Cl. .................. ... 188/158; 303/152 The control unit allows a DC current to be supplied to the
(58) Field of Search ..................................... 188/158, 159, coils when the car runs at a high Speed or allows an AC
188/161, 162, 156, 157; 303/152 current with different phases to be supplied to the coils when
the car runs at a low Speed or is stopped on a slope. In Such
(56) References Cited a case, the DC current is variable in accordance with a
U.S. PATENT DOCUMENTS
pedaling force, while the AC current is variable in the
frequency in accordance with the pedaling force.
4.203,046 5/1980 Homann et al. ......................, 310/93
4,235,316 * 11/1980 Blomberg......................... 188/181 R 2 Claims, 7 Drawing Sheets

Current Amp. 7 Control Unit

Fig. 3)

Current Amp. 7 Control Unit

Brake Peda
Sensor
U.S. Patent Sep. 11, 2001 Sheet 3 of 7 US 6,286,637 B1

Fig. 5)

7 Control Unit

Fig. 6a

8O

2O
O
Time sec.)
U.S. Patent Sep. 11, 2001 Sheet 4 of 7 US 6,286,637 B1

Fig. 6b

0.2
0.1
O
O 1. 2 3
Time sec.)

Fig. 7a)

100

Time sec.)
U.S. Patent Sep. 11, 2001 Sheet 5 of 7 US 6,286,637 B1

Fig. 7b)

Fig. 7c)

Time sec.)
U.S. Patent Sep. 11, 2001 Sheet 6 of 7 US 6,286,637 B1

Fig. 7d)

NN
N
teNW 3-9
%
525

Prior Art
U.S. Patent Sep. 11, 2001 Sheet 7 of 7 US 6,286,637 B1

71
e Arras 4.
SN

2 2 S S2
e
certa
 US 6,286,637 B1
1 2
CONTACTLESS EDDY CURRENT BRAKE housing 10 causes the outside pad 30 to press against the
FOR CARS disc 40, so that the two brake pads 20 and 30 perform a
braking operation. When the brake pedal is released, the
BACKGROUND OF THE INVENTION piston 50 elastically returns to the original position by the
1. Field of the Invention restoring force of the spring 51, thus allowing the disc 40 to
The present invention relates to a contactleSS eddy current be released from the two pads 20 and 30.
brake for cars. However, Since the above disc brake is necessarily pro
2. Description of the Prior Art Vided with a complex hydraulic System, So that the con
AS well known to those skilled in the art, known contact Struction of the brake is undesirably complicated, this results
brakes for cars are designed to be operated by hydraulic or in an increase in the production cost while manufacturing
pneumatic pressure, thus pressing against the brake disc of the brakes. Another problem experienced in Such brakes
a wheel using frictional brake pads and making a cargo slow resides in that the brakes fail to immediately stop a car, but
or Stop. However, Such known contact brakes are problem allow the car to travel a free running distance for a time until
atic in that the brake pads are frictionally abraded due to the pressurized oil from the master cylinder effectively acts
frictional contact of the brake pads with the brake disc and
15 on the piston in the cylinder actuator. This may undesirably
cause traffic hazards.
there exists a time delay while increasing the frictional
preSSure against the brake disc. Another problem experi FIG. 9 is a sectional view, showing the construction of a
enced in the known brakes resides in that the brakes have a typical eddy current brake used as a retarder. AS shown in the
large volume and fail to effectively brake the wheels while drawing, the eddy current brake comprises a Stator and a
driving a car at a high Speed. rotor. The stator comprises a coiled Solenoid 71 which is
In a detailed description, known contact brakes for cars supported by an annular frame 70. The above Solenoid 71
are devices that frictionally preSS against the brake disc of a surrounds a ring 72 which is coupled to a radial arm 73. On
wheel, thus making a cargo slow or Stop. Such contact the other hand, the rotor comprises a magnetic disc 77,
brakes are designed to convert kinetic energy of rotating 25
which is made of a magnetic material and is connected to a
wheels into thermal energy using a mechanical friction bent arm 76. The above rotor is firmly locked to an axle
means prior to dissipating the thermal energy into the using a bolt 78, so that the rotor is rotatable in cooperation
atmosphere, thereby performing a desired braking operation. with the axle. In order to allow the rotor to be rotatable
The contact brakes, operated by hydraulic pressure, are independently of the stator, both a spline 74 and a bearing 75
typically classified into two types: drum brakes and disc are interposed between the rotor and Stator.
brakes. The known disc brakes individually comprise a When activating the above brake while driving a car, the
plurality of brake pads, which are positioned around both coiled Solenoid 71, positioned around the magnetic disc 77,
sides of a brake disc integrated with a wheel, and frictionally is turned on, thus forming a magnetic flux. The magnetic
preSS against the brake disc when it is necessary to make a flux is perpendicularly introduced Into the magnetic disc 77
cargo slow or Stop. 35 prior to flowing to another Solenoid (not shown) from Said
FIG. 8 is a sectional view, showing the construction of a disc 77. An eddy current is thus induced in the magnetic disc
typical disc brake. AS shown in the drawing, the disc brake 77 due to the Faraday's law. A Lorentz force is generated by
comprises two movable pads or inside and outside pads 20 the relative action between the eddy current and the mag
and 30 which are set in a housing 10 while being parallel to netic flux, thus forming a braking torque. However, Such an
each other with a gap being formed between them. A disc 40, 40 eddy current brake is problematic in that it is not suitable for
which is integrated with and rotatable along with a wheel, is being used as a main brake System for cars Since the braking
positioned in the gap between the two pads 20 and 30 in a torque is too low when a car runs at a low Speed.
way such that the disc 40 is normally spaced apart from both In recent years, a brake, which uses a liquid having a
pads 20 and 30. A cylinder actuator, comprising a piston 50 preSSure capable of being variable in accordance with the
and a cylinder 60, is positioned at one side of the inside pad 45 power of the magnetic field or the electric field and over
20, with the piston 50 being capable of pressing he two pads comes the problems experienced in brakes using the
20 and 30 against both sides of the disc 40 using pressurized Solenoids, has been actively Studied. However, the brakes,
oil from a master cylinder (not shown). The cylinder 60 of using Such a liquid, are problematic in that they necessarily
the actuator is provided with an oil port 61 at its end wall for use expensive devices and have a complex construction. In
Selectively introducing the pressurized oil from the master 50 addition, it is necessary to propose more effective and
cylinder into said cylinder 60. A spring 51 is set in an annular reliable brake Systems in accordance with an increase in the
groove 52, formed on the interior wall of the cylinder 60, so maximum speed of a car.
that the spring 51 normally biases the piston 50 relative to SUMMARY OF THE INVENTION
the cylinder 60 in a direction where the piston 50 returns to
its original position. That is, when a brake pedal (not shown) 55 Accordingly, the present invention has been made keep
is released, the spring 51 elastically forces the piston 50 to ing in mind the above problems occurring in the prior art,
return from an operational position to a released position. and an object of the present invention is to provide a
When operating a brake pedal while driving a car, a back contactleSS eddy current brake for cars, which introduces a
preSSure is formed in the master cylinder, So that the master magnetic field to a copper brake disc, thus inducing an eddy
cylinder out puts pressurized oil. The pressurized oil from 60 current in the disc, and applies a contactleSS braking torque
the master cylinder is, thereafter, introduced into the cylin to the disc due to a relative action between the eddy current
der 60 of the actuator through the oil port 61, thus acting on and the magnetic field formed by an electric magnet, thus
the piston 50. The piston 50 thereby causes the inside pad 20 providing a desired slip ratio.
to instantaneously press against the disc 40. In Such a case, Another object of the present invention is to provide a
the housing 10 also moves to the right in the drawing under 65 contactleSS eddy current brake for cars, which is designed to
the guide of a slide unit (not shown) due to the hydraulic Selectively apply a DC current to coils of a core when a car
pressure acting in the cylinder 60. Such a movement of the runs at a high Speed, or to apply an AC current with different
 US 6,286,637 B1
3 4
phases to the coils when the car runs at a low Speed or is integrated with an axle 5, is positioned between the two ends
Stopped on a slope, thus providing a variable braking torque of the (core 1 while being spaced apart from the two ends.
for the wheels in accordance with conditions of the car, with When a magnetic flux 3 is perpendicularly introduced into
the DC current being variable in accordance with a pedaling the disc 4 or the rotary conductor, an eddy current is induced
force acting on a brake pedal and the AC current being in Said rotary conductor 4. Due to a relative action between
variable in the frequency in accordance with the pedaling the magnetic flux 3 and the eddy current, a repulsive force
force. is generated in the gap between the conductor 4 and the core
A further object of the present invention is to provide a 1. Such a repulsive force, caused by the eddy current, is a
contactleSS eddy current brake for cars, which has a con function of an input current, which is applied to the coil 2 So
troller used for controlling the DC or AC current when a car as to form both a desired rotating Speed and a desired density
Starts to slip, thus providing an appropriate torque to the of magnetic flux of the disc 4. When the input current is a
wheels.
constant current, the braking torque is increased or
In order to accomplish the above objects, the present decreased in proportion to the rotating Speed of the disc 4.
invention provides a contactleSS eddy current brake for cars, 15 In addition, when the currents, applied to the electric
compromising: a brake disc concentrically integrated with magnets, vary in accordance with a Sine function while
an axle of a car and provided inside a wheel of the car; two having different phases (90), a braking torque is generated
cores arranged around the edge of the disc while being in accordance with the same theory as that of conventional
Spaced apart from each other at an angle of 90, each of Said induction motors.
cores being wound with a coil, thus forming an electric
magnet; a Speed Sensor positioned around the axle, thus Due to Such operational characteristics, the eddy current
Sensing revolutions of the wheel; a control unit calculating brake is preferably used as an anti-lock brake System. That
a DC or AC control current in response to a Speed signal is, when the wheels slip on the ground Surface, the brake of
output from the Sensor, thus outputting an appropriate con this invention automatically reduces the braking torque, thus
trol current value to the coil of each of the cores, and a 25
effectively preventing the wheels from being undesirably
current amplifier Supplying the control current value from locked. Therefore, when the brake of this invention is used
the control unit or a current value from a brake pedal to the as an anti-lock brake System, it is possible to allow the brake
coils of the cores. System to perform an optimal torque control and Suddenly
Stop a car. Such an optimal torque control desirably results
BRIEF DESCRIPTION OF THE DRAWINGS in a shortest brake distance. Such a shortest brake distance
The above and other objects, features and other advan is accomplished when there exists a maximum friction factor
tages of the present invention will be more clearly under between the wheels and the ground surface. The friction
stood from the following detailed description taken in con factor varies in accordance with the Slip ratio which is
junction with the accompanying drawings, in which: caused by a difference between the rotating speed of the
FIG. 1 is a perspective view of an eddy current brake of 35 wheels and the running Velocity of a car. Therefore, it is
possible to accomplish an optimal torque control by main
this invention, showing the operational theory of the brake; taining an appropriate slip ratio agreeing with the conditions
FIG. 2 is a perspective view, showing the dimension of the of the ground Surface.
brake of this invention;
FIG.3 is a block diagram, showing the construction of the In order to accomplish the above-mentioned optimal
brake of this invention;
40 torque control, the brake of this invention is provided with
a control unit 7 as shown in FIG. 3. The above control unit
FIG. 4 is a perspective view of an eddy current brake for 7 receives a Speed Signal, representing the revolutions of the
cars in accordance with the preferred embodiment of the wheels, from a Speed Sensor 6 positioned around the axle 5
present invention; of the disc 4. Upon receiving the Signal from the Sensor 6,
FIG. 5 is a circuit diagram of a current amplifier used in 45 the control unit 7 outputs a control Signal representing an
the brake of this invention; input current for the coil 2 of the core 1, thus accomplishing
FIGS. 6a and 6b are graphs, showing the simulation an appropriate slip ratio.
results of an anti-lock brake System (ABS) having a typical The braking torque is a nonlinear function represented by
hydraulic brake; both the input current for the coil 2 and the rotating Speed of
50
FIGS. 7a to 7d are graphs, showing the simulation results the disc 4. In addition, there exists an uncertainty in a
of an ABS having an eddy current brake (ECB) of this dynamic model of a brake System. It is thus possible to
invention; design a brake System, which effectively endures the uncer
FIG. 8 is a sectional view, showing the construction of a tainty of both the load torque of the brake and the friction
typical disc brake, and 55 factor between the wheels and the ground Surface, using a
FIG. 9 is a sectional view, showing the construction of a Sliding mode controller or a kind of consistent controller.
typical eddy current brake used as a retarder. FIG. 2 is a perspective view, showing the dimension of the
DESCRIPTION OF THE PREFERRED eddy current brake of this invention. In the drawing, “d” is
EMBODIMENTS a thickness of the disc 4, “S” is an end Surface area of the
60 core 1 through which the magnetic flux passes to the disc 4,
FIG. 1 is a perspective view of an eddy current brake of “R” is a distance between the centers of the disc 4 and the
this invention, showing the operational theory of the brake. end Surface area of the core 1, “r” is a radius of the disc 4,
AS shown in the drawing, the brake of this invention “a” and “b' are width and length of the end surface of the
comprises a core 1, which is wound with a coil 2 at a middle core 1, respectively. In Such a case, the total magnetic flux
portion and is bent with both ends of the core 1 facing each 65 d, flowing in the magnetic circuit comprising the core 1
other while being Spaced out at an interval. The core 1 thus provided with a gap, is represented by the following expres
forms an electric magnet. A brake disc 4, concentrically Sion (1).
 US 6,286,637 B1

(1) NY’, (8)

In the expression (1), F and R are magnetomotive force When compensating for the expression (8) using the
and magnetic reluctance, respectively, which are represented compensation factors C. and C while considering the leakage
by the following expressions (2) and (3). flux, the nonuniform flux and the configuration of the core
1, the expression (8) is represented by the following expres
F-N (2) sion (9).
l (3) T-Tié (9)
In the expression (9), T, is C.CoRSd (uN/l), and
15 compensation factors C. and C are respectively represented
In the expressions (2) and (3), N is the number of turns of by the expressions (10) and (11).
the coil 2 wound on the core 1, 1 is a length of the gap, uo
a == 11 -- 3. lacta?), a i? fl-girl,
(10)
is a permeability of the core 1 in the air. When the perme aretan b2 T , 2
ability to of the core 1 in the air is infinite, the magnetic
reluctance R in the core 1 is Zero. In Such a case, the (11)
magnetic reluctance in the air only affects the total magnetic C = 0.51 -
ab
reluctance of the magnetic circuit. From the expressions (1) R2
to (3), the density B of magnetic flux is represented by the ill -- ..) (r-R)?
following expression (4).
25
1 (4) The braking torque of the contactleSS eddy current brake
S of this inventon is calculated from he above expres
Sions (1) to (11).
In order to experimentally show both the practically and
AS shown in the expression (4), neither the permeability the operational effect of the eddy current brake of this
at of the core 1 nor the size and configuration of the end invention used as an anti-Slip brake System for cars, a
Surface area of the core 1, through which the magnetic flux miniature Simulation model was manufactured. Prior to
3 passes, affects the density B of the magnetic flux. manufacturing Such a miniature Simulation model, it was
However, when considering the Saturation of density of necessary to consider the size, configuration, material and
magnetic flux in a Strong magnetic material, the density of 35 production Style of the core, the material of the brake disc,
magnetic flux ranges from about 0.4T to about 2.1 T, so that and the distance to the position of the core. In an effort to
the input current for the coil 2 is limited. The current J, prevent any eddy current loSS and allow a Smooth flow of
induced in the conductive disc 4 due to the relative action magnetic flux, it was preferable to use a Silicon Steel plate as
between the density of magnetic flux and the rotary con the material of the core. It was more preferable to use a
ductor 4, is represented by the following expression (5). 40 Silicon Steel plate, having a high knee point in the hysteresis
loop, as the material of the core. However, in the Simulation
J=o(uxB) (5) model, the core was made of SM45C. For ease of
manufacture, the core was formed by layering a plurality of
In the expression (5), O and u are conductivity and linear Steel plates, individually having a U-shaped profile and 0.5
Velocity, respectively, with the linear Velocity u being mea 45 mm thickness, in a way Such that the resulting core had a
Sured at a point through which the magnetic flux passes. rectangular cross-section. When the Steel plates were
When the electric power Pd, consumed in the conductor, is layered, it was originally necessary to insulate the junctions
completely converted into a braking torque Tb by the eddy between the Steel plates in order to prevent a generation of
current, the braking torque Tb is represented by the follow eddy current due to a variation of the magnetic flux in the
ing expression (6). 50 core. However, Such an insulation was preferably neglected
during the manufacture of the Simulation model Since the
T, = P. (6)
variation of the magnetic flux in the core is not remarkable.
8 In addition, it was preferable to use a copper alloy, having
a high conductivity, as the material of the brake disc.
55 Practically, the brace disc of the simulation model was made
In the expression (6), 6 is a rotating Speed of the disc 4. of chrome having a conductivity of 3.57x101/S2m). In
From the expression (5), the total power consumption Pd is order to calculate the distance R between the centers of the
represented by the following expression (7). disc and the core, it was necessary to calculate the distance
R capable of maximizing T. in the expression (9). The design
P = p. x Volume (7) 60 parameters of the Simulation model are given in Table 1.
= c-Risdo B? TABLE 1.
Design Parameters of Simulation Model
In the expression (7), p is the resistivity. The braking 65 Weight of Model 4 kg
torque Tb of the expression (6) is thus also represented by Moment of Inertia of Wheel 9.58 x 10 kg.m2
the following expression (8).
 US 6,286,637 B1
7 8
In a detailed description, each core 1, which is formed by
TABLE 1-continued layering a plurality of insulated Silicon Steel plates, is
positioned on the edge of the copper disc 4 in a way Such that
Design Parameters of Simulation Model the edge of the disc 4 is positioned in the gap between both
Radius of wheel 50 mm ends of the core 1. The core 1 is wound with a coil 2. The
Number of Turns of Coil 970 turn above core 1 is fixed, So that each end of the core 1 is spaced
Gap between Disc and Core 1rnm apart from the disc 4 by a gap without being brought into
Radius of Disc 50 mm
Thickness of Disc 3 mm contact with the disc 4. Therefore, there does not exist any
Width of end surface of Core 40 mm contact braking torque between the core 1 and the disc 4. In
Height of end surface of Core 20 mm the embodiment of FIG. 4, two stators, individually com
Distance between the Centers of Disc and Core 32.9 mm prising the core 1 and the coil 2, are arranged on the edge of
the disc 4 while being Spaced apart from each other at an
When the braking torque is reduced, the braking distance angle of 90°. Each of the stators is fixedly held on a knuckle
is increased. In addition, when the braking torque is exceed by a mounting plate (nor shown). The coil 2, wound on each
ingly high, the brake causes a car to slip on the ground 15 of the cores 1, is connected to the current amplifier 8.
Surface. Therefore, it is necessary to maintain an appropriate When a brake pedal 9 is operated by a driver while driving
braking torque in order to reduce the braking distance. When a car, the current amplifier8 Supplies a variable current to
designing a sliding mode controller capable of effectively the coils 2 of the Stators in accordance with a pedaling force
enduring the uncertainty of both the load torque of the brake acting on the pedal 9. In Such a case, a magnetic field is
and the friction factor between the wheels and the ground formed in both the core 1 and the gap between the two ends
Surface while assuming that the controller only has infor of Said core 1. Since the disc 4 is positioned in the gap
mation of a known characteristic equation of the friction between the ends of the core 1, an eddy current is formed in
factor between the wheels and the ground Surface relative to the brake disc 4 due to the magnetic field. Therefore, a
the Slip ratio, but does not practically measure the relation braking torque is generated due to a relative action between
between the friction factor and the slip ratio, it is possible to 25 the eddy current and the magnetic field. In Such a case, an
calculate the input control current value (u) represented by appropriate input control current value is applied to the coils
the following expression (12). 2 of the cores from the control unit 7, thus accomplishing an
1 (12)
appropriate slip ratio.
Particularly, when the brake is operated with a car running
at a high Speed, the magnetic field, formed in the brake disc
int, - i) + (r. + 1 + A got t)} as?o -- 4, is somewhat effectively variable only by the rotating
action of the disc 4. In Such a case, the current amplifier8
Supplies a DC current to the coils 2 SO as no generate a
braking torque, with the DC current being variable in
35 accordance with the pedaling force acting on the brake pedal
9. On the other hand, when the brake is operated with the car
The invention will be more clearly understood from the running at a low speed or being Stopped on a slope, the
following detailed description taken in conjunction with the current amplifier8 Supplies an AC current with different
preferred embodiment. phases (90) to the coils 2 So as to generate a braking force,
FIG. 4 is a perspective view of an Eddy current brake for 40 the AC current being variable in the frequency in accordance
cars in accordance with the primary embodiment of this with the pedaling force. Such an AC current allows the
invention. AS shown in the drawing, the brake of this magnetic field in the disc 4 to be effectively variable, so that
invention comprises a copper brake disc 4. The brake also the brake generates a desired braking torque.
has a Stator which comprises a core 1 wound with a coil 2. In order to compare the operational performance of the
The above core 1 or an electric magnet is fixedly held on a 45 eddy current brake of this invention with that of a typical
knuckle by a mounting plate (not shown). The brake further hydraulic brake, the operational performances of both
comprises a current amplifier 8 which is used as a power brakes were experimentally measured using Simulation
Source for the coil 2. In the above brake, the current models, and the Simulation results are shown in the graphs
amplifier8 Supplies the input control current value from the of FIGS. 6a to 7d.
control unit 7 to the coils 2, thus allowing a car to be stopped 50 FIGS. 6a and 6b are graphs, showing the simulation
with a shortest braking distance during a Sudden Stop of the results of an anti-lock brake System (ABS) having a typical
car. The above current amplifier8 is designed to selectively hydraulic brake, with the Simulation results being measured
apply a DC current to the coils 2 when a car runs at a high using a 1+e,fra 4+ee miniature simulation model. FIGS. 7a
Speed, or to apply an AC current with different phases to the to 7d are graphs, showing the Simulation results of an ABS
coils 2 when the car runs at a low speed or is stopped on a 55 having an eddy current brake of this invention, with the
Slope, thus providing a variable braking torque for the Simulation results being measured using a /4 miniature
wheels in accordance with conditions of the car. In Such a Simulation model.
case, the DC current is variable in accordance with a From the simulation results shown in the graphs of FIGS.
pedaling force acting on a brake pedal 9, while the AC 6a to 7d, it is noted that the eddy current brake of this
current being variable in the frequency in accordance with 60 invention effectively maintainings an appropriate slip ratio,
the pedaling force. When the current amplifier8 is provided thus accomplishing a short braking distance in comparison
with a battery, corresponding to +Vs, it is not necessary to with a typical hydraulic brake even when a driver does not
give a transformer to the amplifier8. When using two stators have any information about conditions of a road.
in the brake as shown in FIG. 4, the two Stators are arranged AS described above, the present invention provides a
while being spaced apart from each other at an angle of 90. 65 contactless eddy current brake for cars. The brake of this
Such an arrangement of the Stators allows the brake to invention generates a desired contactleSS braking torque
generate a desired high braking torque. using electric power, thus effectively preventing a frictional
 US 6,286,637 B1
10
abrasion of brake pads different from typical hydraulic or a speed Sensor positioned around Said axle, thus Sensing
pneumatic brakes. The brake also Selectively Supplies dif revolutions of said wheel;
ferent currents: AC or DC current, to the coil of a stator in a control unit calculating a DC or AC control current in
accordance with the running Speed of a car, thus generating response to a speed signal output from Said Sensor, thus
a desired braking torque when the brake is operated while outputting an appropriate control current value to the
driving a car at a high or low speed. The eddy current brake coil of each of Said cores, and
of this invention thus effectively brakes a car with an
improved operational reliability and Safety. a current amplifier Supplying the control current value
Although the preferred embodiments of the present inven from the control unit or a current value from a brake
tion have been disclosed for illustrative purposes, those 1O pedal to the coils of the cores, wherein Said current
skilled in the art will appreciate that various modifications, amplifier allows a DC current to be supplied to the coils
additions and Substitutions are possible, without departing when the car runs at a high Speed or allows an AC
from the Scope and Spirit of the invention as disclosed in the current with different phases to be supplied to the coils
accompanying claims. when the car runs at a low Speed or is stopped on a
What is claimed is: 15 slope, with the DC current being variable in accordance
1. A contactleSS eddy current brake for cars, comprising: with a pedaling force acting on Said brake pedal and the
a brake disc concentrically integrated with an axle of a car AC current being variable in a frequency in accordance
and provided inside a wheel of Said car; with Said pedaling force.
two cores arranged around an edge of Said disc while 2. The contactleSS eddy current brake according to claim
being spaced apart from each other at an angle of 90, ° 1, wherein said brake disc is made of copper.
each of Said cores being wound with a coil, thus
forming an electric magnet;