U.S. patent application number 11/533180 was filed with the patent office on 2007-06-07 for electronic aircraft braking system with brake wear measurement, running clearance adjustment and plural electric motor- actuator ram assemblies.
This patent application is currently assigned to GOODRICH CORPORATION. Invention is credited to Franklin C. Christ, Mihai Ralea.
Application Number | 20070125607 11/533180 |
Document ID | / |
Family ID | 25316236 |
Filed Date | 2007-06-07 |
United States Patent
Application |
20070125607 |
Kind Code |
A1 |
Ralea; Mihai ; et
al. |
June 7, 2007 |
ELECTRONIC AIRCRAFT BRAKING SYSTEM WITH BRAKE WEAR MEASUREMENT,
RUNNING CLEARANCE ADJUSTMENT AND PLURAL ELECTRIC MOTOR- ACTUATOR
RAM ASSEMBLIES
Abstract
An electrically actuated aircraft brake system and method which
provides for brake wear measurement, brake running clearance
adjustment, ram position-based control and improved construction
and operation. Brake wear and running clearance measurement are
obtained by analyzing the output of position sensing circuitry. The
position sensing circuitry, preferably including a LVDT position
sensor, is also used to determine braking load, a brake controller
including circuitry for effecting displacement of one or more
reciprocating rams to load a brake disk stack by a predetermined
amount based on a present displacement value of the position signal
obtained from the position sensor. The position sensor preferably
includes a LVDT transducer connected between the reciprocating ram
and a brake housing, and the motive device preferably includes a
servo motor. Also provided is an actuator housing including a
guideway for each ram, the guideway and ram having the same
polygonal cross-section, whereby the ram nut is guided and
restrained from rotation by the guideway as it is translated by a
ball screw in threaded engagement with the ram nut for selective
movement into and out of forceful engagement with the brake disk
stack for applying and releasing braking force on a rotatable
wheel. An electric motor is drivingly connected to each ball screw
by a first gear integral with the ball screw, a second gear in mesh
with the first gear, and a pinion on a rotating drive shaft of the
electric motor.
Inventors: |
Ralea; Mihai; (Boonton
Township, NJ) ; Christ; Franklin C.; (Pompton Plains,
NJ) |
Correspondence
Address: |
DON W. BULSON (GOODRICH);RENNER, OTTO, BOISSELLE & SKLAR, LLP
1621 EUCLID AVENUE
19TH FLOOR
CLEVELAND
OH
44115
US
|
Assignee: |
GOODRICH CORPORATION
Four Coliseum Centre 2730 West Tyvola Road
Charlotte
NC
|
Family ID: |
25316236 |
Appl. No.: |
11/533180 |
Filed: |
September 19, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10796776 |
Mar 9, 2004 |
7108107 |
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|
11533180 |
Sep 19, 2006 |
|
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|
10268409 |
Oct 10, 2002 |
6702069 |
|
|
11533180 |
Sep 19, 2006 |
|
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|
09486687 |
Mar 1, 2000 |
6471015 |
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11533180 |
Sep 19, 2006 |
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08853513 |
May 9, 1997 |
6003640 |
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11533180 |
Sep 19, 2006 |
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Current U.S.
Class: |
188/72.1 ;
188/1.11W; 188/71.5 |
Current CPC
Class: |
B60T 8/325 20130101;
F16D 2055/0058 20130101; F16D 2121/24 20130101; F16D 2065/386
20130101; F16D 2066/005 20130101; F16D 66/00 20130101; F16D 66/02
20130101; F16D 66/021 20130101; F16D 2125/48 20130101; B60T 13/74
20130101; B60T 8/1703 20130101; F16D 2127/06 20130101; B64C 25/44
20130101; F16D 2125/52 20130101; F16D 2055/0091 20130101; B60T
8/885 20130101; F16D 65/56 20130101; F16D 65/18 20130101; F16D
2066/003 20130101; F16D 2125/40 20130101; F16D 55/36 20130101 |
Class at
Publication: |
188/072.1 ;
188/001.11W; 188/071.5 |
International
Class: |
F16D 55/08 20060101
F16D055/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 1998 |
US |
PCT/US98/02764 |
Claims
1. A brake system comprising: a brake disk stack; a reciprocating
ram; a motive device operatively connected to the reciprocating ram
for selectively moving the reciprocating ram into and out of
forceful engagement with the brake disk stack for applying and
releasing braking force on a rotatable wheel; a controller for
controlling the motive device for selective control of the
reciprocating ram and regulation of the force applied by the
reciprocating ram against the brake disk stack, and a position
sensor which supplies a position signal representative of the
position of the reciprocating ram; and wherein the controller
includes means for effecting displacement of the reciprocating ram
to load the brake disk stack by a predetermined amount based on a
present displacement value of the position signal obtained from the
position sensor.
2. A brake system as set forth in claim 1, wherein the position
sensor includes a LVDT transducer.
3. A brake system as set forth in claim 2, comprising a brake
housing to which said motive device is mounted, and said LVDT
transducer is connected between said reciprocating ram and brake
housing.
4. A brake system as set forth in claim 1, wherein the motive
device is a servo motor.
5. A brake system as set forth in claim 1, in combination with an
aircraft wheel assembly.
6. A method for controlling operation of a brake system, the brake
system including a motive device operatively connected to a
reciprocating ram for selectively moving the reciprocating ram into
and out of forceful engagement with the brake disk stack for
applying and releasing braking force on a rotatable member, and a
controller for controlling the motive device for selective control
of the reciprocating ram and regulation of the force applied by the
reciprocating ram against the brake disk stack, said method
comprising the steps of: using a position sensor to supply a
position signal representative of the position of the reciprocating
ram; effecting displacement of the reciprocating ram to load the
brake disk stack by a predetermined amount based on a present
displacement value of the position signal obtained from the
position sensor.
7. A method as set forth in claim 6, wherein the step of using a
position sensor includes using a LVDT transducer.
8. A method as set forth in claim 6, wherein a torque motor is used
as the motive device for selectively moving the reciprocating ram
into and out of forceful engagement with the brake disk stack.
Description
RELATED APPLICATION DATA
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/796,776 filed Mar. 9, 2004, which is a
continuation of U.S. patent application Ser. No. 10/268,409 filed
Oct. 10, 2002, which is a continuation of U.S. patent application
Ser. No. 09/486,687, filed Mar. 1, 2000, which is a
continuation-in-part of U.S. patent application Ser. No.
08/853,513, filed May 9, 1997. The aforesaid applications are
hereby incorporated herein by reference in their entireties.
FIELD OF THE INVENTION
[0002] The invention herein described relates generally to brake
control systems, more particularly to electronic braking systems,
and still more particularly to aircraft braking systems.
BACKGROUND OF THE INVENTION
[0003] Known in the prior art are aircraft wheel and brake
assemblies including a non-rotatable wheel support, a wheel mounted
to the wheel support for rotation, and a brake disk stack having
front and rear axial ends and alternating rotor and stator disks
mounted with respect to the wheel support and wheel for relative
axial movement. Each rotor disk is coupled to the wheel for
rotation therewith and each stator disk is coupled to the wheel
support against rotation. A back plate is located at the rear end
of the disk pack and a brake head is located at the front end. The
brake head houses a plurality of actuator rams that extend to
compress the brake disk stack against the back plate. Torque is
taken out by the stator disks through a static torque tube or the
like.
[0004] As the brake disks wear, the running clearance of the
actuator rams correspondingly increases. To maintain an acceptable
running clearance, mechanical adjustor devices have been employed.
While functional, these devices add weight and complexity to the
braking system, and need to be overhauled usually each time the
brake disk stack is replaced. For at least these reasons, it would
be desirable to provide for running clearance adjustment without
the need for these mechanical adjustor devices.
[0005] Present day aircraft brake systems also have employed wear
pin indicators to measure overall wear of the brake disk stack.
Brake wear is indicated by the length of the pin relative to a
reference plate. This arrangement requires a visual inspection of
the pin to determine wear and is inherently imprecise. It would be
desirable to provide for brake wear measurement without the need
for a visual inspection and with greater precision.
[0006] Moreover, it would be desirable to provide for brake
actuator running clearance and brake wear indication utilizing
means that may be interfaced into an electro-mechanical brake
system. Electro-mechanical braking systems eliminate drawbacks
associated with hydraulic braking systems such as fluid leaks, high
maintenance requirements, fire hazard and higher overall
weight.
[0007] Electrically actuated aircraft brakes of various
configurations are known, as exemplified by U.S. Pat. Nos.
4,381,049, 4,432,440, 4,542,809 and 4,567,967. The brake assemblies
shown in these patents include electric motors which respond to an
electrical control signal to effect rotation of a ring gear member
which interacts through a plurality of balls to drive a linearly
movable ram member into contacting engagement with a brake disk
stack to effect compression thereof and braking of a wheel.
[0008] In U.S. Pat. No. 4,596,316, another configuration of an
electrically actuated brake uses a roller screw drive wherein a
ring gear member interacts through a plurality of roller screws to
drive a ram member into engagement with the brake pressure plate to
effect compression of the brake disk stack for braking action. A
plurality of electric motors and their associated pinions drive a
ring gear into rotation and the plurality of roller screws effect
linear axial movement of the ram member.
[0009] In U.S. Pat. No. 4,865,162, a further electrically actuated
aircraft brake employs a roller screw drive mechanism driven by an
electric torque motor through a gear drive associated with either
the screw or the nut of the roller screw drive mechanism. Rotation
of the gear drive by the torque motor moves the other one of the
screw or nut into axial engagement with a brake disk stack to
compress the stack for braking. A plurality of the roller screw
drive mechanisms and respective gear drives and torque motors are
mounted in a balanced arrangement about the axis of the wheel to
apply and release a brake pressure force on the brake disk stack in
response to an electrical control signal to the torque motors.
[0010] In U.S. Pat. No. 4,995,483, there is described a motor
position feedback control system for an electrically actuated
aircraft brake. The system controller provides brake clamping and
declamping in response to a position feedback controlled brake
actuator in which an electric torque motor drives a rotating member
of a reciprocating drive mechanism to axially move another member
into and out of engagement with a brake pressure plate of a
multi-disk brake assembly. The position feedback is obtained using
a rotor position resolver which provides relative position
information to the controller. Such a system requires a
re-calibration of the position sensor after a power interruption
which may result in loss of braking capability, long recovery time
and possible uncommanded brake clamp force application.
[0011] Among other things, it would be desirable to have an
electrically actuated aircraft brake that has greater durability
than the prior art brakes that use roller screw drive mechanisms,
thereby to minimize deterioration of components that may lead to
increased friction in the mating screw components and the
associated loss of efficiency and response of the brake. Also, it
would be desirable to have an electrically actuated brake wherein
equal force can be applied by multiple ram actuators and which
optimizes brake clamping force dynamic response.
SUMMARY OF THE INVENTION
[0012] The present invention provides a brake system and method,
particularly an electrically actuated aircraft brake system and
method, which provides various advantages over known brake systems
and methods.
[0013] According to one aspect of the invention, a brake system and
method are provided to enable brake wear measurement while
eliminating the need for previously used brake wear indicator pins.
More particularly, brake wear measurement is obtained by analyzing
the output of position sensing circuitry. In a preferred
embodiment, present brake disk stack height is measured using an
actuator position sensor or sensors, and the output of the sensor
or sensors is compared to a reference brake disk stack height to
provide an indication of the amount of brake wear. The reference
brake disk stack height preferably is obtained by loading the brake
disk stack by a predetermined amount and using the actuator
position sensor or sensors to measure the displacement of the
actuator ram or rams to the brake disk stack. In brake systems
employing multiple actuator rams, the outputs of respective
position sensors are averaged to provide an actuator displacement
measurement for the associated brake disk stack. The actuator
position sensor preferably is an absolute position encoder that
outputs a signal representative of the actual position of the
actuator ram relative to the brake housing.
[0014] Accordingly, a preferred embodiment of the invention
provides a brake system and method characterized by a brake disk
stack, at least one reciprocating ram, a motive device operatively
connected to the reciprocating ram for selectively moving the
reciprocating ram into and out of forceful engagement with the
brake disk stack for applying and releasing braking torque on a
rotatable member (e.g., a wheel), and a controller that controls
the motive device for selective control of the reciprocating ram
and regulation of the force applied by the reciprocating ram
against the brake disk stack. In accordance with the invention, a
position sensor supplies a position signal representative of the
position of the reciprocating ram, and the controller includes
means for effecting displacement of the reciprocating ram to load
the brake disk stack by a predetermined amount to obtain from the
position sensor a present displacement value of the position
signal, and for comparing the present displacement value to a
reference displacement value to provide a measurement of wear of
the brake disk stack.
[0015] A preferred embodiment of the invention is further
characterized by the use of a position sensor directly linked to
the actuator ram, and preferably one that is robust. A preferred
position sensor is a LVDT transducer, although other types of
transducers may be used, for example a potentiometer, an optical
encoder, a RVDT transducer with a rotary input provided by suitable
gearing, etc. As is preferred, the LVDT transducer is connected
between the reciprocating ram and a brake housing to which the
motive device is mounted. The motive device preferably is an
electric servo motor, and the controller preferably includes a
processor for controlling actuator position and application force.
The processor preferably is programmed to perform the aforesaid
brake wear measurement, and also a new brake disk stack measurement
routine for obtaining a brake wear reference value for the new
brake disk stack. The new brake disk stack measurement routine
includes the steps of effecting displacement of the reciprocating
ram to load the new brake disk stack by a predetermined amount to
obtain from the position transducer a new brake disk stack
displacement value of the position signal and then storing,
preferably in non-volatile memory, the new brake disk stack
displacement value as the reference displacement value against
which subsequently obtained present displacement values are
compared to provide a measurement of wear of the brake disk
stack.
[0016] The present invention also provides a brake system and
method, particularly an electrically actuated aircraft brake system
and method, which provides for running clearance adjustment while
eliminating the need for previously used mechanical adjustor
devices. Running clearance adjustment is obtained by performing a
running clearance adjustment routine which analyzes the output of
the position sensing circuitry. In a preferred embodiment, the
brake controller is operable to effect movement of the
reciprocating ram for loading the brake disk stack by a
predetermined amount to obtain from the position transducer a
present displacement value of the position signal, and then to use
the present displacement value to determine a running clearance
position of the reciprocating ram. More particularly, provision is
made for subtracting the predetermined clearance value from the
present displacement value to obtain a new running clearance value,
storing the new running clearance value in memory, and then using
the new running clearance value in determining the running
clearance position of the reciprocating ram.
[0017] As will be appreciated, an improved brake system arises from
the use of either one or both of the above summarized wear
measurement and running clearance features. In addition, these
features are particularly useful in aircraft brake systems and
particularly an electrically actuated aircraft brake system which
does not need hydraulic components which are subject to various
drawbacks including fluid leaks, high maintenance requirements,
fire hazard, higher overall weight, etc.
[0018] According to another aspect of the invention, there is
provided an electro-mechanical brake assembly comprising a brake
disk stack; a housing including a guideway; a ram nut guided by the
guideway for movement toward and away from the brake disk stack; a
lead (preferably a ball) screw in threaded engagement with the ram
nut whereupon rotation of the lead screw effects linear movement of
the nut for selective movement into and out of forceful engagement
with the brake disk stack for applying and releasing braking force
on a rotatable wheel; and an electric motor drivingly connected to
the lead screw gear for rotating the lead screw to effect movement
of the ram nut toward and away from the brake disk stack. In
contrast to prior art ram assemblies using, for example, a key or
spline to prevent rotation of the ram as it moves linearly, the
guideway and ram nut of the present invention respectively have
polygonal cross-sections defined by plural outer side surfaces
which rotationally interfere with one another to restrain rotation
of the ram nut relative to the housing. This arrangement provides
for maximum alignment and resistance to cocking and binding of the
ram, while minimizing sliding friction.
[0019] In a preferred embodiment, the electric motor is drivingly
connected to the lead screw by a first gear integral with the lead
screw, a second gear in mesh with the first gear, and a pinion on a
rotating drive shaft of the electric motor. Also in a preferred
embodiment, the outer side surfaces of the guideway and ram nut are
planar, and the outer side surfaces of each one of the guideway and
ram together define a regular polyhedron.
[0020] According to another broad aspect of the invention, there is
provided a brake system wherein a position sensor is used to
determine braking load. In a preferred embodiment, the brake system
comprises a brake disk stack; a reciprocating ram; a motive device
operatively connected to the reciprocating ram for selectively
moving the reciprocating ram into and out of forceful engagement
with the brake disk stack for applying and releasing braking force
on a rotatable wheel; a controller for controlling the motive
device for selective control of the reciprocating ram and
regulation of the force applied by the reciprocating ram against
the brake disk stack; and a position sensor which supplies a
position signal representative of the position of the reciprocating
ram; and characterized by the controller including circuitry for
effecting displacement of the reciprocating ram to load the brake
disk stack by a predetermined amount based on a present
displacement value of the position signal obtained from the
position sensor. This arrangement provides for optimum brake
clamping force dynamic response, eliminates or minimizes hysteresis
associated with other means of control, and enables the system to
apply equal force on all actuators. The position sensor preferably
includes a LVDT transducer connected between the reciprocating ram
and a brake housing, and the motive device preferably includes a
servo motor.
[0021] The foregoing and other features of the invention are
hereinafter fully described and particularly pointed out in the
claims, the following description and the annexed drawings setting
forth in detail one or more illustrative embodiments of the
invention, such being indicative, however, of but one or a few of
the various ways in which the principles of the invention may be
employed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a diagrammatic illustration of an exemplary
multi-actuator computer controlled brake actuation system.
[0023] FIG. 2 is a diagrammatic illustration of a brake actuator
and associated servo amplifier employed in the system of FIG.
1.
[0024] FIG. 3 is a perspective view of an exemplary brake housing
and actuator assembly useful in the system of FIG. 1.
[0025] FIG. 4 is a schematic view showing a brake actuator assembly
in relation to a new brake disk stack.
[0026] FIG. 5 is a schematic view showing the brake actuator in
relation to a worn brake disk stack.
[0027] FIG. 6 is a flowchart illustrating a method for measuring
brake disk stack wear.
[0028] FIG. 7 is a flowchart illustrating a method for obtaining a
new brake disk stack reference value.
[0029] FIG. 8 is a flowchart illustrating a method for measuring
brake actuator displacement.
[0030] FIG. 9 is a flowchart illustrating a method for effecting
running clearance adjustment.
[0031] FIG. 10 is a schematic view showing the running clearance in
relation to actuator ram displacement.
[0032] FIG. 11 is an end elevational view of another brake actuator
assembly useful in the system of FIG. 1.
[0033] FIG. 12 is a part elevational, part sectional view of the
brake actuator assembly of FIG. 11, taken along the line 12-12 of
FIG. 11.
[0034] FIG. 13 is a partial sectional view of the brake actuator
assembly of FIG. 11, taken along the line 13-13 of FIG. 11.
[0035] FIG. 14 is a partial sectional view of the brake actuator
assembly of FIG. 11, taken along the line 14-14 of FIG. 11.
[0036] FIG. 15 is a partial sectional view of the brake actuator
assembly of FIG. 11, taken along the line 15-15 of FIG. 14.
[0037] FIG. 16 is a partial sectional view of the brake actuator
assembly of FIG. 11, taken along the line 16-16 of FIG. 13.
[0038] FIG. 17 is an elevational view of the brake actuator
assembly of FIG. 11, with a torque take-out bracket assembled
thereon.
[0039] FIG. 18 is a edge view of the brake actuator assembly and
torque take-out bracket, looking from the line 18-18 of FIG.
17.
[0040] FIG. 19 is a edge view of the brake actuator assembly and
torque take-out bracket, looking from the line 19-19 of FIG.
17.
DETAILED DESCRIPTION OF THE INVENTION
[0041] Referring now in detail to the drawings, FIG. 1
diagrammatically illustrates an exemplary multi-actuator computer
controlled brake actuation system 20 to which the principles of the
invention may be applied. The major functions of the system 20 are
performed by a controller 21 and a brake actuator assembly 22. The
brake actuator assembly 22 may be mounted in a conventional manner
on a wheel and brake assembly 23 to apply and release braking force
on a rotatable wheel 24 of such wheel and brake assembly. The
present invention is particularly suited for use in aircraft
braking systems, as will be appreciated by those skilled in the
art.
[0042] Because the invention was conceived and developed for use in
an aircraft braking system and particularly in association with the
system 20, it will be herein described chiefly in this context.
However, the principles of the invention in their broader aspects
can be adapted to other types of systems including, for example,
hydraulic systems wherein hydraulic actuators are used and
controlled either hydraulically or electrically. Moreover, the
following discussion of an exemplary multi-actuator computer
controlled brake actuation system is given for the sake of
illustration and not by way of limitation, except as defined in the
claims included at the end of this specification. Accordingly, only
general operational details and features of such system will be
described so as not to obscure the teachings of the present
invention with details that may vary from one particular
application to another.
[0043] In the illustrated exemplary system 20, the brake actuator
assembly 22 includes at least one and preferably a plurality of
electro-mechanical actuators 27. The controller 21 includes a
corresponding number of independent servo amplifiers 28, a
micro-processor 29 with associated peripherals, and a data
input/output (I/O) circuitry 30. As depicted, plural (for example,
four) independent, linear electro-mechanical servo loops operate in
a position mode, i.e., the linear position of each actuator is a
function of an analog input voltage (or digital equivalent for a
digital signal processor) applied to a position command input.
[0044] In FIG. 2, a representative electro-mechanical brake
actuator 27 and associated servo amplifier 28 are illustrated in
greater detail. The brake actuator 27 includes an electric servo
motor 33, gear train 34, and a reciprocating output ram 35. The
brake actuator has associated therewith an output ram position
sensor 36 which provides for actuator position feedback as
depicted. Although not shown, the brake actuator 27 also has
associated therewith a motor tachometer to provide for velocity
feedback.
[0045] The servo amplifier 28 includes servo loop compensation
networks and amplifiers 39, and a DC motor driver 40 with
associated control logic and current control circuitry. More
particularly, the position servo amplifier 28 may include an inner
motor current control servo loop 42, an intermediate motor velocity
servo loop 43, and a ram position servo loop 44. Each loop may be
compensated to obtain desired performance in terms of bandwidth,
and to provide for uniform dynamic response of all brake actuators
27. In addition, the servo amplifier 28 includes means for
controlling motor current and therefore the output force of the
brake actuator in response to a force control input. The force
control input may be an analog input signal that controls motor
current level while the aforesaid position command input controls
actuator displacement. As will be appreciated, the analog input
signals may be replaced by digital input signals if a digital
signal processor is used in the servo amplifier for actuator
control.
[0046] As indicated, the displacement of each actuator 27 is
controlled by the electronic controller 21 (FIG. 1). The
micro-processor 29 of the controller provides brake control
algorithm processing, temporary data storage, in RAM, program
memory storage, non-volatile data storage, and control of the servo
amplifiers 28 via the input/output circuitry 30. The input/output
circuitry 30 provides for digital-to-analog data conversion,
generating the analog position commands and the analog motor
current control commands to the four actuators, analog-to-digital
data conversion to monitor the actuator position sense and motor
current feedback signals, and signal discretes for auxiliary
functions such as motor brake control. The micro-processor may also
be interfaced via a serial communication link with other control
components as needed, such as, for example, a anti-skid brake
control unit. Although a micro-processor is utilized in the
illustrated preferred embodiment, processing alternatively could be
done analog as opposed to digital, or intermixed with digital
processing as may be desired.
[0047] In the illustrated system, the four servo amplifiers 28
(FIG. 2) are independent and functionally identical, each amplifier
being controlled by the micro-processor 29, responding to the
position commands and motor current control signals from the
processor, and feeding back the actuator position and motor current
sense signals to the processor via the I/O circuitry 30.
[0048] The controller may use two separate power sources: for
example, a 28 VDC supply to power the low level electronic
circuitry and 28 to 270 VDC supply to power the four actuator
motors through the motor driver power stage. The 28 VDC actuator
power may be utilized in emergency situations when 270 VDC is not
available to power system fault.
[0049] Further details of an exemplary brake actuator assembly 22
are shown in FIGS. 3-5. The brake actuator assembly includes a
housing 47 that provides for the mounting of an electro-mechanical
actuator 27, it being understood that typically multiple actuators
will be mounted to the housing, such as four functionally identical
actuators located at respective quadrants of the housing. The
illustrated housing has a bolt circle 48 for mounting to the
overall wheel and brake assembly 23 (FIG. 1). Each actuator 27 may
include a DC brushless servo motor 50 and suitable reduction
gearing 52 that translates rotary motor motion to linear motion of
the ram 35 (the rams are hidden from view in FIG. 3). The brushless
DC servo motor 50 may have integrated or otherwise associated
therewith a friction type, fail-safe (power-off engaged) brake (not
separately shown), and a resolver (not separately shown) for motor
rotor commutation and angular velocity sensing. The resolver
provides motor position feedback and velocity information. In
particular, the resolver provides an electrical signal that is
proportional to motor shaft position.
[0050] The ram 35 of each actuator is mechanically connected to an
LVDT position sensor 74, such as by bracket 75. The LVDT armature
76 may be adjustably attached to the bracket (or the sensor body to
the brake housing) by suitable means that provides for LVDT setting
and position calibration. A cover (not shown), or the like, may be
provided to protect for the LVDT mounting mechanism. Although an
LVDT sensor is preferred, other types of position
sensors/transducers may be used as desired for a particular
application.
[0051] The purpose of the brake actuator(s) 27 is to impress a
clamping force on the stack 80 of brake disk elements. The
electro-mechanical (EM) actuator(s) operate simultaneously to
produce a clamping force between a brake reaction plate 78 and the
actuator output rams 35. An exemplary system utilizes four
actuators, operating simultaneously, to provide the total brake
clamping force required. However, the size and number of actuators
may be varied to provide the total brake clamping force required.
The actuators may be operated in a controlled displacement mode
such that the clamping force is proportional to the deflection of
the reaction plate. Although each actuator can operate
independently, the actuators may be commanded in pairs (or
otherwise), the actuators of each pair being located physically on
diametrically opposite sides on the brake housing.
[0052] The brake disk stack 80 includes alternating rotor disks 81
and stator disks 82 mounted with respect to a torque tube 83 or
similar member and the wheel (not shown) for relative axial
movement. Each rotor disk 81 is coupled to the wheel for rotation
therewith and each stator disk 82 is coupled to the torque tube 83
against rotation. A back plate 85 is located at the rear end of the
brake disk stack and functions as a force reaction member via the
reaction plate 78. The brake actuator 27 is mounted to brake
housing 47 fixed with respect to the torque tube. The ram 35 of the
actuator extends to compress the brake disk stack 80 against the
back plate 85, and torque is taken out by the stator disks 82
through the static torque tube 83 (or the like).
[0053] As the brake disks wear, the collective axial thickness
thereof will decrease. In accordance with the invention, the
controller 21 (FIG. 1) is suitably programmed to carry out a wear
measurement routine which is illustrated by the flow chart shown in
FIG. 6 and a running clearance adjustment routine which is
illustrated by the flow chart shown in FIG. 9. The wear measurement
routine preferably uses a reference value corresponding to zero
wear, such value corresponding to the thickness of a new brake disk
stack. The new brake stack reference value is determined by the
controller in accordance with a routine illustrated by the flow
chart shown in FIG. 7. Both the wear measurement routine and the
new brake disk stack reference measurement routine preferably use a
further routine for measuring actuator displacement, this routine
being illustrated by the flow chart shown in FIG. 8.
[0054] In FIG. 8, actuator displacement measurement begins at step
88 where the actuator rams (or ram in a single actuator system) are
extended by the controller to load the brake disk stack by a
predetermined amount. The amount of loading need only be enough to
ensure that the individual disks of the brake disk stack are held
against one another to remove any slack in the stack. For this
purpose, the actuator rams preferably apply about 10% of maximum
braking force to the brake disk stack. At step 89, the displacement
(travel) X of each actuator ram is measured using the respective
position sensor 74 (FIGS. 4 and 5). Then, preferably, an average
actuator ram displacement is calculated at step 90, and at step 91
the average actuator ram displacement Xave is used to establish the
actuator displacement value Xd. More particularly, in the
illustrated preferred embodiment where the controller operates the
actuators in pairs (each pair including diametrically opposite
actuators), the actuator ram displacement of the actuators of each
pair is measured and used to calculate an average actuator
displacement value for that pair of actuators. Thus average
actuator displacements are calculated for each set of paired
actuators. This is done because positions of the rams may vary for
the same input, as when one actuator pushes harder than the other
actuator with which it is paired.
[0055] In FIG. 7, the new brake disk stack reference measurement
routine begins at step 93 where the actuator displacement
measurement routine of FIG. 8 is used to return an actuator ram
displacement measurement Xd for a new brake disk stack. At step 94,
the new brake disk stack reference measurement value Xref (see FIG.
4) is then set by the controller to the measured clearance Xd. At
step 95, the new brake disk stack reference value is then stored,
preferably in non-volatile memory, for use by the brake wear
measurement routine.
[0056] Returning now to FIG. 6, brake wear measurement begins at
step 97 where the actuator displacement measurement routine of FIG.
8 is used to return an actuator ram displacement measurement Xd for
the brake disk stack which has undergone wear as depicted in FIG.
5. Then, at step 98, brake disk stack wear Xw is calculated by
subtracting the brake disk stack reference measurement value Xref
from the measured ram displacement Xd. The brake disk stack wear Xw
then may be stored at step 99 in memory. The brake disk stack wear
Xw may also be used by the controller to provide a warning signal
if the brake disk stack wear satisfies a predetermined criteria.
For example, if the brake disk stack has worn to a predetermined
percentage of its original thickness, then a signal may be given to
indicate that the brake disk stack requires replacement.
[0057] Referring now to FIG. 9, the running clearance adjustment
routine begins upon the system being powered up initially at step
102. After initialization, operation proceeds to a background loop
at step 103. The background loop includes as one of its procedures
(other procedures may include, for example, health monitoring
procedures and command confirmation procedures) a step 104 where
the controller checks to see if a running clearance adjustment
should be made. In the illustrated system, this is determined by
the brake control system which may send an enable command at an
appropriate time for running clearance adjustment, as when the
landing gear is extended before landing, or when the plane is on
the ground. If the prescribed criteria is not satisfied, the
controller returns to the background loop 103. If the prescribed
criteria is satisfied, the controller proceeds to step 105 at which
all actuators are positioned at the then active running clearance
position. Then, at step 106, the actuator rams (or ram in a single
actuator system) are extended to load the brake disk stack by a
predetermined amount. As before, the amount of loading need only be
enough to ensure that the individual disks of the brake disk stack
are held against one another, again to remove any slack from the
stack. For this purpose, the actuator rams preferably apply 10% of
maximum braking force to the brake disk stack. At step 107, the
displacement Xd (travel) of each actuator ram (or average
displacement of paired actuators) is measured using the respective
position sensor 74 (FIGS. 4 and 5). Then, at step 108, a new
running clearance PRCLN is calculated for each actuator (or
actuator pair) by subtracting a fixed displacement Xrclr from the
measured ram displacement Xd (or average displacement). At step
109, the new running clearance value PRCLN is set as the active
running clearance PRCL which is stored, preferably in non-volatile
memory. Finally, at step 110, the controller positions each
actuator at the active running clearance position, after which the
controller returns to the background loop.
[0058] It is noted that although the position sensor is used to
provide information on the position of the ram, the resolver could
be used to provide the running clearance adjustment. That is, the
controller can use the output of the resolver to determine the
running clearance position of the rams. However, preferably an
absolute position encoder is used. The absolute position sensor
(e.g. LVDT 74) is insensitive to a power loss, whereas use of a
resolver, or other relative position based system, may lose track
of the ram position (the resolver could change position with no
corresponding output being registered by the controller).
[0059] Referring now to FIGS. 11 and 12, another exemplary brake
actuator assembly is generally indicated by reference numeral 122.
The brake actuator assembly 122 includes a housing 147 that
provides for the mounting of multiple electro-mechanical actuators,
such as the illustrated four functionally identical actuators 127
located at respective quadrants of the housing. The illustrated
housing has a bolt circle 148 for mounting in a wheel and brake
assembly, such as in a known manner to a torque tube included in
such an assembly. Each actuator 127 preferably includes a DC
brushless servo motor 150, an intermediate cluster gear member 151,
and a ball screw assembly 152. The brushless DC servo motor 150 may
have integrated or otherwise associated therewith a friction type,
electrically actuated brake (not separately shown), and a resolver
(not separately shown) for motor rotor commutation and angular
velocity sensing. The resolver provides motor position feedback and
velocity information. In particular, the resolver can provide an
electrical signal that is proportional to motor shaft position
under normal operating conditions. The motor brake may be a
power-on type or a power-off type, as desired for a particular
application. The motor brake is useful for parking the aircraft. To
this end, the actuator rams can all be extended to engage the
brakes and then the motor brakes may be engaged to hold the
actuator rams in their extended/engaged positions. Once the motor
brakes are engaged, power to the motor components of the servo
motor 150 (the ram drive motor components) can be shut off. The
specific motor selection will be dependent on the requirements for
a given braking application. In the illustrated embodiment, the
servo motor components, friction brake and resolver are all
integrated into a common motor housing and collectively may be
referred to as a servo motor.
[0060] As shown in FIGS. 12-15, the intermediate cluster gear
member 151 provides for two stages of reduction gearing and
includes a first stage gear 155 and a second stage gear 156. The
first stage gear, which provides the first stage of gear reduction,
is a bevel gear that meshes with a bevel gear 157 integral with the
drive shaft 158 of the motor. The second stage gear 156 is a
straight spur gear that mates with a ball screw gear 159 formed
integrally with a ball screw 162. The intermediate cluster gear
member is supported by ball bearings 160 and 161 at its ends.
Although reference herein is made to certain structures as being
integral as is preferred, it should be understood such structures
alternatively may be composed of discrete components joined
together to form a functionally equivalent structure.
[0061] The ball screw assembly 152 is comprised of the ball screw
162 with the integral gear 159, a hexagonal ball nut 163 that
translates rotary motion to linear motion of the ball nut, and a
pad 164 that attaches to the end of the ball nut and provides the
interface to the brake disk pressure plate. The ball screw and ball
nut, which provide a third stage of reduction, may be of a known
configuration and thus the respective spiral grooves thereof and
associated balls have not been illustrated as the same would be
immediately evident to one skilled in the art. The ball nut (also
herein referred to as a ram or ram nut) is free to translate along
the axis of the ball screw upon rotation of the ball screw, but not
to rotate, as the ball nut is guided by a hexagonal bore 165 in the
housing 147.
[0062] As best seen in FIG. 16, the hexagonal bore or guideway 165
and the ball nut 163 respectively have, in the illustrated
preferred embodiment, corresponding polygonal cross-sections
defined by plural inner/outer side surfaces (commonly indicated by
reference numeral 166) which rotationally interfere with one
another to restrain rotation of the ram nut 163 relative to the
housing 147. As is preferred and illustrated, one or more of the
side surfaces, most preferably all of the side surfaces, are planar
and form regular polyhedrons providing a close sliding fit between
the ball nut and guideway. It will be appreciated, however, that
other configurations may be used although less preferred. For
example, the number of sides may be varied from the illustrated
six-sided polygons (hexagons), as may be desired for a particular
application. The six-sided polyhedral configuration provides
desired sliding and anti-rotational characteristics.
[0063] Preferably, a lubricant, particularly a suitable grease, is
used to lubricate that relatively sliding surfaces 166 of the ball
nut 163 and guideway 165. It has been found that the grease and
close clearance between the ball nut and guideway prevent entry of
any appreciable amount of dirt or other foreign material at the
sliding surfaces interface so as to prevent any significant
degradation of performance. However, if desired, a suitable seal,
such as a wiper seal or a rolling diaphragm seal, could be employed
to seal against passage of dirt or other undesirable materials
between the sliding surfaces. An exemplary grease for the ball
screw and ram nut assembly is MIL-G-81322 and an exemplary grease
for the gear train is MIL-G-81827.
[0064] The driving torque is applied to the mechanism through the
integral gear that drives the ball screw 162 causing the ball nut
163 to translate thus converting input torque to linear output
force. The translating ball nut contacts the front of the stack of
brake disks through the interface pad 164 and functions as an
actuator ram 135. The ball screw is supported by three bearings, a
radial bearing 167 and a thrust roller bearing 168 at the outboard
end of the ball screw and a radial ball bearing 169 at a location
intermediate the nut-engaging threaded portion of the ball screw
and the integral gear 158. A bearing plate 170 is used to support
the ball bearing 169 in the housing. An actuator cover 171 locates
the radial and thrust bearings and provides mechanical thrust
support for the ball screw. The cover is attached to the actuator
housing by suitable means such as screws 172 (FIG. 11).
[0065] Each ball nut 163 (actuator ram 135) is mechanically
connected to an LVDT position sensor 174, such as by bracket 175.
The LVDT armature 176 may be adjustably attached to the bracket (or
the sensor body to the brake housing) by suitable means that
provides for LVDT setting and position calibration. A cover 177 may
be provided to protect the LVDT mounting mechanism. Although an
LVDT sensor is preferred, other types of position
sensors/transducers may be used as desired for a particular
application.
[0066] Like the brake actuators 27 (FIGS. 4 and 5), the purpose of
the brake actuator(s) 127 is to impress a clamping force on a stack
of brake disk elements. The electro-mechanical (EM) actuator(s)
operate simultaneously to produce a clamping force between a brake
reaction plate and the actuator output rams 135. Again, the size
and number of actuators may be varied to provide the total brake
clamping force required. The position of the rams, as opposed to
motor current, preferably is used to obtain desired braking load.
It is noted however that the above described running calibration
technique is carried out in a current mode, although with use of
the position transducer.
[0067] The use of position sensing and position servo for
controlling brake force application provides advantages over other
control methodologies. One advantage is the elimination or
reduction of hysteresis associated with other means of control,
such as force control where the clamping force application is
controlled via motor current application. Another advantage is that
position mode control provides for optimum brake clamping force
dynamic response. By sensing the position at the actuator ram and
using absolute position sensing, as compared to relative position
sensing (see, for example, U.S. Pat. No. 4,995,483), enhances
performance aspects of the system. The system will recover
immediately from disturbances such as power outages during braking
without the possibility of uncommanded brake application. As above
mentioned, the relative position sensing technique used in the
prior art (see, for example, U.S. Pat. No. 4,995,483) requires a
re-calibration of the position sensor after a power interruption
which may result in loss of braking capability, long recovery time
and possible uncommanded brake clamp force application.
[0068] As will be evident to the skilled person, brake clamp
application relies on the spring constant of the brake torque tube
since brake clamp force is a function of the actuator ram
displacement and the torque tube spring constant. When applying a
clamping force, the brake controller calculates the required
position for given clamping force using the torque tube spring
constant as the proportional constant. The value for the torque
tube constant can be the theoretical value or can be directly
measured by the system using a calibration routine running as an
extension of the running clearance calibration routine. That is,
the spring constant calibration routine can measure the ram
displacement, .DELTA.X, for each ram, for a full force command,
.DELTA.Force, and calculate the spring constant, given by
.DELTA.X/.DELTA.Force.
[0069] Another advantage provided by the present invention is the
capability of equalizing, by way of the aforesaid calibration, the
brake clamping force between the four (plural) rams without the
need for sensing the force on each actuator ram.
[0070] Although each actuator 127 can operate independently, the
actuators may be commanded in pairs (or otherwise) using two
controllers, the actuators of each pair being located physically on
diametrically opposite sides on the brake housing. If one
controller were to fail, the remaining controller would still be
functioning. The controllers may also be programmed to compensate
for failure of one or more of the position sensors 174, as by then
using current and torque feedback to control the position of the
corresponding actuator ram or rams. That is, the controller may be
programmed to operate in a position mode (the preferred normal mode
of operation) and a current mode (back-up mode in event of position
sensor failure).
[0071] In a power failure mode, it will be appreciated that any
resultant retraction of an engaged actuator ram 135 may be quite
rapid (as arises from the high efficiency and reversibility of the
ball screw and ball nut, and the other gearing, and from the high
spring force that may be stored in the torque tube under braking
conditions). The rapid retraction of the ram may cause significant
shock to the system as the ram bottoms out at the end of its
permitted degree of travel, which in the illustrated embodiment is
determined by engagement against the annular shoulder surface of
the housing 178 at the outboard end of the ram guideway.
Preferably, the ram's return motion is stopped slowly to provide a
"soft stop." This may be accomplished mechanically by the
interpositioning of springs between the back (outboard) end of the
ram and the shoulder surface. This however adds weight and size to
the actuator assembly. A more preferred approach according to the
present invention is to provide an electronic soft stop for each
ram. This is accomplished by coupling the motor to a damping
circuit (preferably provided in the controller) in a power failure
mode so that the retarded motion of the motor slows the ram down to
provide a soft landing. The damping circuit dissipates the energy
stored in the motor inertia, plus the load spring induced loads,
such that the actual ram speed is reduced to a safe level as the
actuator ram reaches the back feed retract stop (i.e., whatever
structure is used to limit the maximum retraction of the ram). The
soft stop circuit includes a resistive element for energy
dissipation, solid state switches and power monitoring and control
logic circuitry to couple the motor to the resistive element under
the appropriate operating conditions. More particularly, when the
power monitoring logic detects a power failure, the motor is
coupled by the solid switching (or other suitable means) to the
resistive components for reducing the motor speed to a safe
level.
[0072] During normal operation, the position of the ram is known by
reason of the position transducer, and thus the controller can
function to prevent any hard landing of the ram.
[0073] Referring now to FIGS. 17-19, a torque take-out bracket 185
is shown assembled on the brake actuator assembly 122. The torque
take-out bracket 185 extends diametrically across the housing 147
and functions as an interface between the brake actuator assembly
and a landing gear axle structure (not shown). The landing gear
structure, as is well known in the art, may include a wheel axle,
steering linkage and, in particular, a torque reaction arm. The
torque reaction arm and torque take-out bracket 185 have
interengaging devices which provide for transfer of torque from the
torque take-out bracket to the torque reaction arm when braking
force is being applied to the disk brake stack by the brake
actuator assembly. In the illustrated embodiment, the take-out
bracket 185 has on the outboard side thereof an axially opening
recess (socket) 187 for receiving a torque reaction lug on the
torque reaction arm. The recess 187 is located adjacent the
radially outer peripheral portion 189 of the housing which has a
recess 190 (FIG. 11) in an outboard side face 191 (FIG. 12) thereof
in which the adjacent end of the take-out bracket is captured. In
this manner the torque reaction arm and torque take-out bracket are
rotationally interlocked.
[0074] The recess 190 is formed in the radially outer peripheral
portion 189 of the housing 147 which is circumferentially
continuous and circumscribes housing compartments containing the
motors 150 and the guideways 165 containing the actuator ram nuts
163 as best seen in FIGS. 1 and 17. At the side of the housing
diametrically opposite the recess, there is provided another recess
193 for a load cell 194. As is preferred, the housing is formed
slightly oblong at its end adjacent the load cell recess 193 so
that additional housing structure protrudes radially outwardly of
the circular peripheral portion thereof to provide a radially
enlarged receptacle for the load cell. It is noted that this
arrangement is enabled by the use of the above described
intermediate cluster gear member 151. In addition to providing two
stages of gear reduction, the intermediate cluster gear member 151
allows the motors to be positioned radially inwardly of the outer
peripheral ring portion of the housing and thus provides radial
clearance with the load sensor and the torque lug.
[0075] The load cell 194 is mounted to the torque take-out bracket
at the end thereof diametrically opposite the end thereof including
the torque reaction recess 187. Accordingly, the load cell
functions as a secondary lug for torque take-out and thus the
output of the load cell will be indicative of brake torque.
[0076] As though skilled in the art will appreciate, other types of
screw drives may be used in place of the preferred ball screw
drive. Accordingly, the reference herein to lead screw is intended
to be a generic reference to screw drive devices and the like.
[0077] Although the invention has been shown and described with
respect to a certain preferred embodiment or embodiments, it is
obvious that equivalent alterations and modifications will occur to
others skilled in the art upon the reading and understanding of
this specification and the annexed drawings. In particular regard
to the various functions performed by the above described integers
(components, assemblies, devices, compositions, etc.), the terms
(including a reference to a "means") used to describe such integers
are intended to correspond, unless otherwise indicated, to any
integer which performs the specified function of the described
integer (i.e., that is functionally equivalent), even though not
structurally equivalent to the disclosed structure which performs
the function in the herein illustrated exemplary embodiment or
embodiments of the invention. In addition, while a particular
feature of the invention may have been described above with respect
to only one of several illustrated embodiments, such feature may be
combined with one or more other features of the other embodiments,
as may be desired and advantageous for any given or particular
application.
[0078] In addition, the invention is considered to reside in all
workable combinations of features herein disclosed, whether
initially claimed in combination or not and whether or not
disclosed in the same embodiment.
* * * * *