Note: Descriptions are shown in the official language in which they were submitted.
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ANTILOCK BRAKE SYSTEM
Field of Invention
The present invention relates to the field of brake systems. In particular, to
an antilock
brake system.
Background
An antilock braking system (commonly known as ABS) is a system used on a
wheeled
vehicle which prevents the wheels from locking when brakes acting on each of
the
wheels are applied. A typical ABS comprises a control module, wheel speed
sensors and
one or more brake hydraulic modulators. A wheel speed sensor is typically
associated
with each wheel (alternatively, a pair of wheels on a common axle can share a
wheel
speed sensor). The wheel speed sensor provides a speed signal to the control
module
from which the control module can derive the speed of the wheel as well as
acceleration
and deceleration of the wheel. Based on the speed signals received from the
wheel speed
sensors and the application of one or more control algorithms, the control
module can
determine when one of the wheels is approaching lock-up. When a wheel is
approaching
lock-up the control module sends a control signal to the hydraulic modulator
to modulate
the brake acting on the wheel. The hydraulic modulator modulates the brake by
alternately relieving and reapplying the brake pressure applied by a brake
master cylinder
to the brake at the wheel.
The hydraulic modulator typically comprises solenoid operated valves connected
to a
brake circuit associated with each wheel. The valves permit hydraulic pressure
applied to
the brake by the master cylinder to be interrupted and the pressure relieved
and reapplied.
In some implementations the hydraulic modulator can also comprise a high-
pressure
hydraulic pump and a pressure accumulator. The pump and accumulator can be
used to
reapply pressure to the brake as the hydraulic modulator cycles between
relieving and
reapplying pressure to the brake. The hydraulic modulator is typically a
complex and
expensive-to-manufacture component that increases the cost of producing and
operating a
vehicle equipped with a conventional antilock brake system.
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Summary of Invention
The present invention is directed to an antilock brake system for use with a
self
energizing brake system in a wheeled vehicle. The self energizing brake system
can have
hydraulic actuators that act on a rotor and a brake exciter that provides for
disengagement
of the actuators from the rotor. The antilock brake system has wheel speed
sensors, each
associated with one the vehicle wheels, that provide a speed signal to a
control module.
The control modules determines when a wheel is in a state of immanent brake
lock-up
and generates a control signal. Responsive to the control signal a brake
disengagement
module provides for regulation of the brake force generated by the brake
system
connected to the wheel by alternately causing the exciter to operate the
actuators to
disengage and to re-engage the rotor.
In accordance with one aspect of the present invention, an antilock brake
system for use
in a wheeled vehicle having associated with each of a plurality of wheels a
self
energizing brake system having hydraulically interconnected actuators that act
on an
eccentric rotor to generate a brake force and a brake exciter that provides
for operating
the actuators between a first position not in engagement with the eccentric
rotor and a
second position in engagement with the eccentric rotor, the antilock brake
system
comprising: a plurality of wheel speed sensors, each one connected to one of
the plurality
of wheels such that it can sense rotation of the wheel and generate a speed
signal
representative of the speed of rotation of the wheel; a control module that
can receive
said speed signal from each of said plurality of wheel speed sensors, can
apply pre-
determined algorithms to said speed signals to determine when any of the
wheels is in a
state of immanent brake lock-up and can generate a control signal for a wheel
that is in a
state of immanent brake lock-up; and a plurality of brake disengagement
modules, each
one associated with a self energizing brake system, that can, responsive to
said control
signal received from said control module, cause the exciter to operate the
actuators into
the first position not in engagement with the eccentric rotor; wherein cyclic
generation of
said control signal by said control module provides for regulation of braking
forces
generated by the self energizing brake system.
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Other aspects and features of the present invention will become apparent to
those
ordinarily skilled in the art to which it pertains upon review of the
following description
of specific embodiments of the invention in conjunction with the accompanying
figures.
Brief Description of Drawing-ss
The present invention will be described in conjunction with the drawings in
which:
Figures 1 A and B are a front and side view, respectively, of a schematic
representation
of a brake system with which the present invention can be used.
Figure 2 is a side view of a schematic representation of another exemplary
embodiment
of a brake system which the present invention can be used.
Figures 3 A and B are a front and side partial cross-sectional views,
respectively, of a
brake effecter module which the present invention can be used.
Figures 3 C - E are front partial cross-sectional views of a brake effecter
module which
the present invention can be used showing the brake controller valve and the
brake
exciter in a variety of operating positions.
Figure 4 is a schematic representation of an exemplary embodiment of the
antilock brake
system according to the present invention together with an example environment
in
which the antilock brake system can be used.
Detailed Description
Figure 4 is a schematic representation of an exemplary embodiment of an
antilock brake
system 400 according to the present invention together with an example brake
system
100 with which the antilock brake system 400 can be used. The antilock brake
system
400 comprises a control module 410, a plurality of wheel speed sensors 420 and
a
plurality of brake disengagement modules 430. Note that for illustrative
purposes only
one wheel speed sensor 420 and one braking disengagement module 430 is
represented in
Figure 4. Each of the plurality of wheel speed sensors 420 is a sensor that is
connected to
the wheel (not illustrated) so that it can sense rotation of the wheel and
send a speed
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signal that represents the rotational speed of the wheel to the control module
410. In the
embodiment illustrated in Figure 4 the wheel speed sensor 420 is connected to
the brake
system 100 via a shaft 440; the brake system 100 is connected to the wheel
(not
illustrated). In an alternative embodiment the wheel speed sensor 420 can be
connected
directly to the wheel so that it can sense rotation of the wheel. From the
speed signals
received from each of the wheel speed sensors 420, the control module 410 can
derive the
speed, acceleration and deceleration of each of the wheels. The control module
410 can
use one or more control algorithms that take into account the speed of each
wheel, the
relative speeds of the wheels, the rates of acceleration and deceleration of
each wheel,
and other similar parameters to determine when each wheel is in a state of
immanent
brake lock-up. Each of the plurality of brake disengagement modules 430 is
operably
connected to the control module 410 and to the brake system 100 connected to
one of the
wheels.
Figures 1 A and B are a front and side view, respectively, of schematic
representations of
a brake system 100 with which the present invention can be used in, for
example, a
wheeled vehicle. The brake system 100 is comprised of a rotor 110 and a brake
effecter
module 120. The rotor 110 can be connected to a vehicle wheel (not shown) so
as to
rotate when the wheel rotates. The rotor has two eccentric (cam) surfaces 112.
The
brake effecter module 120 has a pair of hydraulically interconnected actuators
122, a
brake control valve 124 and a brake exciter 126. Each of the pair of actuators
122 can
engage a different one of the two eccentric surfaces 112 of the rotor. The
brake control
valve 124 effects braking by restricting the flow of a working fluid that is
pumped out by
each of the actuators 122 as it engages the rotating rotor. The degree of
restriction to the
flow of the working fluid can be varied to adjust the amount of braking force
applied.
The working fluid can be, for example, brake fluid, automatic transmission
fluid (ATF)
or other similar non-compressible fluids. The brake system 100 can be
considered self
energizing in that it is not reliant on a substantial external source of
energy to effect
braking. The energy required to pump the working fluid is derived from the
rotation of
the rotor 110. The brake exciter 126 provides for disengagement of the
actuators 122
from the rotor when braking force is not being applied.
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The rotor 110 is substantially disc-shaped with two eccentric surfaces 112
disposed for
peripheral engagement by the actuators 122 (see Fig. 1 B). The two eccentric
surfaces
112 have corresponding cam profiles in terms of a number of undulations on
each surface
and the amplitude of the undulations. The two eccentric surfaces 112 can be
arranged
such that there is a radial angle displacement between corresponding points on
the
eccentric surfaces 112 (i.e. that one eccentric surface 112 is rotated
relative to the other).
When installed on a vehicle, the rotor 110 is so arranged that it is rotatably
connected to a
wheel (not illustrated) of the vehicle. Rotation of the wheel causes the rotor
110 to rotate
and braking force applied to the rotor 110 causes braking (deceleration) of
the wheel.
The brake system 100 can also be used to prevent acceleration of the wheel
such as, for
example, to hold the vehicle stationary.
The rotor 110 of Figures 1 A and B has four lobes on each of the two eccentric
surfaces
112. In an alternative embodiment of the brake system 100, each eccentric
surface 112
can have one, two, three or more lobes while remaining within the scope and
spirit of the
present invention. In a further alternative embodiment, the rotor 110 can be
formed from
two disc elements (in immediate contact or spaced apart) each having an
eccentric
surface 112. Figure 2 is a side view of a schematic representation of another
exemplary
embodiment of a brake system 100 in which the two eccentric surfaces 112 can
be
arranged on the interior periphery of the rotor 110 for engagement by a brake
effecter
module 120 having actuators 122 extending radially outward relative to the
axis of
rotation of the rotor 110. In yet another alternative embodiment the two
eccentric
surfaces 112 can be arranged on the sides of the rotor 110 for engagement by
the brake
effecter module 120 having actuators 122 extending laterally toward the sides
of the rotor
110.
Figures 3 A and B are a front and side partial cross-sectional views,
respectively, of the
brake effecter module 120 with which the present invention can be used. The
pair of
actuators 122 engages the rotor 110 (not shown in Figures 3 A and B, see
Figures 1 A
and B) in order to generate braking forces. Each actuator 122 is comprised of
a cam
follower 130 and a hydraulic cylinder 132. The hydraulic cylinder 132 contains
a piston
134 which can reciprocate in the hydraulic cylinder 132. The cam follower 130
is
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connected to the piston 134 and moves in and out of the hydraulic cylinder
132, through
an aperture, in conjunction with movement of the piston 134. A low-friction
interface
136 is disposed at one end of the cam follower 130. The low-friction interface
136 can
engage (i.e. come in contact with) one of the eccentric surfaces 112 of the
rotor. The
low-friction interface 136 preferably generates little frictional resistance
to rotational
motion of the rotor relative to the actuator 122. The low-friction interface
136 can, for
example, be comprised of a ball bearing, a roller bearing or other similar low-
friction
bearing mechanisms including sliding mechanisms.
When the brake system 100 is applying braking force, the actuator 122 is
engaged with
the rotor 110. Each cam follower 130 moves back and forth (i.e. reciprocates)
in
response to the undulations on the eccentric surface 112 of the rotating rotor
110. The
back and forth movement of the cam follower 130 results in similar movement of
the
piston 134 and therefore expansion and contraction of the volume of working
fluid in the
hydraulic cylinder 132.
The actuators 122 are arranged to engage different points along the respective
cam
profiles (i.e. undulations) of the eccentric surfaces 112 such that one
actuator 122 is
engaged with a rising portion of one eccentric surface 112 while the other
actuator 122 is
engaged with a falling portion of the other eccentric surface 112 at a given
position of the
rotor 110. At any point in the rotation of the rotor 110 one of the actuators
122 has its
cam follower 130 extending out to the rotor 110 while the other actuator 122
has its cam
follower 130 being retracted in by the rotor 110. In an alternative embodiment
the rotor
110 can have a single eccentric surface 112 and the brake effecter module 120
be so
arranged that each of the two actuators 122 engages the single eccentric
surface 112 such
that one actuator 122 is engaged with a rising portion of the eccentric
surface 112 while
the other actuator 122 is engaged with a falling portion of the eccentric
surface 112 at a
given position of the rotor 110.
As the actuators 122 extend and retract in response to the rotation of the
rotor 110 each in
turn alternately pumps working fluid out and pumps working fluid in.
Restriction of the
working fluid flow by the brake control valve 124 results in restricted
displacement of
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working fluid from one hydraulic cylinder 132 to the other hydraulic cylinder
132. In
turn the extension and the retraction of the actuators 122 is resisted by the
restricted
working fluid flow out of each actuator 122 thereby applying a braking force
to the rotor
110.
The interconnection between the two actuators 122 can have substantially the
same cross-
sectional area as the bores of the hydraulic cylinders 132 in the actuators
122 thereby
providing for substantially unrestricted fluid communications when the brake
control
valve 124 is in an open position (see Figure 3A and B). The brake control
valve 124 is
operable from the open position to a closed position (see Figure 3D) while
providing
progressively restricted flow at positions in between (see Figure 3C). The
brake control
valve 124 can, for example, be a spool valve, a ball valve, port valve or
other similar
proportionate flow-restricting mechanism. The brake control valve 124 provides
for
substantially unrestricted fluid flow through when in the open position. The
brake
control valve 124 can provide one or more passages 138 through which the
working fluid
can flow.
The braking force applied to the rotor 110 is proportional to a brake force
control signal
received by the brake system 100. The brake force control signal is
proportionate to a
desired braking input provided by a vehicle operator at an operator interface
such as, for
example, a brake pedal (not shown). The brake force control signal can take
the form of
an electrical signal, a hydraulic pressure signal, a pneumatic signal or other
similar
signaling mechanisms (not shown) that provide for the propagation of a
proportionate
(i.e. variable) control signal. Correspondingly, the brake control valve 124
can be
operated by an electric motor, an electric solenoid, a hydraulic actuator, a
pneumatic
actuator or other similar mechanism (not shown). In the case of a hydraulic
pressure
signal, the pressure required for the hydraulic pressure signal can be
substantially less
than the operating pressure of the working fluid in the brake system 100.
Referring again to Figure 3B, the brake control valve 124 is operated by an
electric motor
(not shown) through a worm gear arrangement 140. The worm gear arrangement 140
provides for the electric motor to operate the brake control valve 124 to any
position from
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the open position to the closed position. In addition, since the worm gear
arrangement
140 is non-reversible, it prevents any other forces acting on the brake
control valve 124
(such as internal forces resulting from restricted working fluid flow) from
operating the
brake control valve 124 to a different position.
The brake exciter 126 provides for expansion of the hydraulic volume of the
interconnection between the actuators 122. The brake exciter 126 is operable
between an
engage position (see Figures 3 A, C and D) and a disengage position (see
Figure 3 E). In
the engage position, the actuators 122 are in engagement with the rotor and
therefore
braking force can be applied. In the disengage position, the actuators 122 are
withdrawn
out of engagement with the rotor thereby eliminating resistance on the rotor
when
braking force is not being applied. Disengagement of the actuators 122 is
effected by the
exciter increasing the hydraulic volume of the interconnection between the
actuators 122
when in the disengaged position thereby causing the actuators 122 to be drawn
into their
respective hydraulic cylinder 132s.
1 S The brake exciter 126 can be operated by an electric motor (not shown)
through a worm
gear arrangement 142. The worm gear arrangement 142 provides for the electric
motor
to operate the brake exciter 126 from the engage position to the disengage
position. In
addition, since the worm gear arrangement 142 is non-reversible, it prevents
any other
forces acting on the brake exciter 126 (such as operating pressure of the
working fluid)
from operating the brake exciter 126 toward the disengage position. In an
alternative
embodiment the brake exciter 126 can be operated by an electric stepper motor,
an
electric solenoid, a hydraulic actuator, a pneumatic actuator or other similar
mechanisms.
In an alternative embodiment of the brake system 100, a plurality of brake
effecter
modules 120 can engage a rotor 110.
Referring again to Figure 4, each brake disengagement module 430 is arranged
to allow
normal operation of the exciter 126 of the brake system 100 to which it is
operably
connected and to provide for overriding of the normal operation of the exciter
126. The
control module 410 can send a control signal to the brake disengagement module
430 to
cause it to override the normal operation of the exciter 126 when the control
module 410
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has determined that the wheel with which the brake disengagement module 430 is
associated is in a state of immanent brake lock-up. When the brake system 100
is
applying braking force the exciter 126 is normally in the engage position (see
Figure 3C).
The brake disengagement module 430 overrides the normal operation of the
exciter 126
by operating the exciter 126 into the disengage position thereby mitigating
the braking
action of the brake system 100 (see Figure 3F). Operation of the exciter 126
into the
disengage position causes the actuators 122 to retract out of engagement with
the rotor
110. The control signal from the control module 410 can cause the brake
disengagement
module 430 to cycle between overriding the normal operation of the exciter 126
and
allowing normal operation. When normal operation of the exciter 126 is
restored, the
actuators reengage the rotor 110 and provide for braking action by the brake
system 100.
The control module 410 can control the cycle frequency and duration of
intervention (i.e.
overriding of normal exciter 126 operation) of the brake disengagement module
430 in
order to regulate the braking action of the brake system 100.
The control module 410 can control each of the brake disengagement modules 430
separately to provide for individual regulation of the brake system 100 at
each of the
wheels.
The antilock brake system 400 of the present invention does not directly
affect the brake
control signal being provided to the brake system 100. Regulation of the brake
force is
accomplished by disengaging the actuators from the rotor while not requiring
that
operation of the brake control valve 124 be affected.
It will be apparent to one skilled in the art that numerous modifications and
departures
from the specific embodiments described herein may be made without departing
from the
spirit and scope of the present invention.
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