U.S. patent application number 10/988472 was filed with the patent office on 2005-04-28 for steer-by-wire handwheel actuator.
This patent application is currently assigned to DELPHI TECHNOLOGIES, INC.. Invention is credited to Augustine, Michael J., Cole, Michael J., Magnus, Brian J..
Application Number | 20050087384 10/988472 |
Document ID | / |
Family ID | 23154371 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050087384 |
Kind Code |
A1 |
Magnus, Brian J. ; et
al. |
April 28, 2005 |
Steer-by-wire handwheel actuator
Abstract
A steer-by-wire handwheel actuator in a vehicle is presented.
The handwheel actuator comprises a driver input shaft; a gear train
connected to the driver input shaft; a motor responsive to control
signals from a controller and variably geared to the gear train; a
electro-mechanical brake responsive to the control signals from the
controller and geared to one of the driver input shaft and the gear
train; and a stop mechanism attached to a housing and coupled to
one of the electro-mechanical brake and the gear train.
Inventors: |
Magnus, Brian J.;
(Frankenmuth, MI) ; Augustine, Michael J.;
(Mayville, MI) ; Cole, Michael J.; (Saginaw,
MI) |
Correspondence
Address: |
Michael D. Smith
DELPHI TECHNOLOGIES, INC.
Legal Staff, Mail Code: 480-410-202
P.O. Box 5052
Troy
MI
48007-5052
US
|
Assignee: |
DELPHI TECHNOLOGIES, INC.
|
Family ID: |
23154371 |
Appl. No.: |
10/988472 |
Filed: |
November 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10988472 |
Nov 12, 2004 |
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10163927 |
Jun 6, 2002 |
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6817437 |
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60299342 |
Jun 19, 2001 |
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Current U.S.
Class: |
180/402 |
Current CPC
Class: |
B62D 5/006 20130101 |
Class at
Publication: |
180/402 |
International
Class: |
B62D 005/00 |
Claims
1. A steer-by-wire handwheel actuator utilizing a controller
operative to accept as input thereto data from the steer-by-wire
system and generate therefrom control signals in a vehicle
comprising: a driver input shaft; a gear train connected to the
driver input shaft; a motor responsive to the control signals from
the controller and variably geared to the gear train, the motor
including a motor shaft driven therefrom and a motor pulley
connected to the motor shaft and having cogs circumferentially
arranged; an electro-mechanical brake responsive to the control
signals from the controller and geared to one of the driver input
shaft and the gear train; and a stop mechanism attached to a
housing and coupled to one of the electro-mechanical brake and the
gear train, wherein the gear train is a pulley and gear train
assembly, said gear train assembly including: a driver feedback
pulley connected to the driver input shaft; a speed reducer pulley
having cogs circumferentially arranged for positive engagement with
the motor pulley cogs and being connected to the driver input
shaft; and a spur gear connected to the driver input shaft.
2-3. (canceled)
4. The steer-by-wire handwheel actuated as set forth in claim 1
wherein the speed reducer pulley and the motor pulley are
positively engages via a cogged belt.
5. The steer-by-wire handwheel actuator as set forth in claim 1
further comprising: a modular unit having a biasing member to
provide mechanical resistance to one of the driver input shaft and
the gear train.
6. The steer-by-wire handwheel actuator as set forth in claim 5
wherein the modular unit includes a ball nut assembly operably
connected to said driver input shaft.
7. The steer-by-wire handwheel actuator as set forth in claim 6
wherein said ball nut assembly is biased in a predetermined
position corresponding to an on center steering position.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. provisional
application No. 60/299,342, filed Jun. 19, 2001 the contents of
which are incorporated by reference herein in their entirety.
TECHNICAL FIELD
[0002] This invention relates to a steer-by-wire system, and more
particularly to a steer-by-wire handwheel actuator.
BACKGROUND
[0003] It is known in the art to have a steering system with
mechanical linkage from the steering wheel to the steerable road
wheels. Even with power assist, the driver of a mechanically linked
vehicle can feel the forces of the road against the steerable
wheels through the steering wheel. Indeed, this is a desired
feature of direct linkage and is sought out by purchasers of high
performance vehicles in the form of so-called "rack-and-pinion"
steering. The road forces felt in the steering wheel give the
driver feedback he can use to anticipate and control the vehicle,
or at least create the comfortable feeling that he is in control of
the vehicle. Remove this feedback, such as in the case of "mushy"
power steering, and the driver will have the uncomfortable feeling
of being separated from the road wheels, not quite in control, and
will tend to oversteer his vehicle, particularly in demanding
situations such as sharp or sudden turns.
[0004] By definition, a steer-by-wire system has no mechanical link
connecting the steering wheel from the road wheels. In effect, the
steering wheel is little more than a joystick, albeit an extremely
sophisticated joystick. Exemplary of such known steer-by-wire
systems is commonly-assigned U.S. Pat. No. 6,176,341, issued Jan.
23, 2001 to Ansari, which is wholly incorporated herein by
reference. What is needed is to provide the steer-by-wire driver
with the same "road feel" that a driver receives with a direct
mechanical link. Furthermore, it is desirable to have a device that
provides a mechanical back up "road feel" in the event of multiple
electronic failures in the steer-by-wire system. In addition, a
device that provides positive on-center feel and accurate torque
variation as the handwheel is rotated is also desirable. Existing
steer-by-wire devices produce excessive lash, excessive noise and
insufficient over-load torque capability as the handwheel is
rotated to its end of travel in either direction.
BRIEF SUMMARY
[0005] A steer-by-wire steering system is defined as a steering
system with no mechanical connection between a steering wheel and a
set of steering gears or actuators. Such systems are advantageous
because they permit auto and other vehicle designers great latitude
in use of space that would normally be taken up by mechanical
linkages, among other reasons.
[0006] In an exemplary embodiment of the invention, a steer-by-wire
handwheel actuator is described, which provides feedback of road
forces to the operator of a steer-by-wire vehicle. A handwheel
actuator comprises a driver input shaft; a gear train connected to
the driver input shaft; a motor responsive to control signals from
a controller and connected to the gear train; an electro-mechanical
brake responsive to the control signals from the controller and
connected to one of the driver input shaft and the gear train; and
a stop mechanism attached to a housing and coupled to one of the
electro-mechanical brake and the gear train.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a perspective view of a prior art hard contact
driving system;
[0008] FIG. 2 is a schematic representation of the steer-by-wire
handwheel actuator in signal communication with a steer-by-wire
steering system;
[0009] FIG. 3 is a perspective view of an exemplary embodiment of a
steer-by-wire handwheel actuator;
[0010] FIG. 4 is a rear/plan view of a an exemplary embodiment of a
steer-by-wire handwheel actuator of FIG. 3;
[0011] FIG. 5 is a front /plan view of a an exemplary embodiment of
a steer-by-wire handwheel actuator shown in FIG. 4 detailing cross
sectional divisions that follow;
[0012] FIG. 6 is a cross section view of an exemplary embodiment of
a steer-by-wire handwheel actuator depicted in FIG. 5, Section
6-6;
[0013] FIG. 7 is a cross section view of an exemplary embodiment of
a steer-by-wire handwheel actuator depicted in FIG. 5, Section
7-7;
[0014] FIG. 8 is a cross section view of an exemplary embodiment of
a steer-by-wire handwheel actuator depicted in FIG. 5, Section
8-8;
[0015] FIG. 9 is a cross section view of a modular unit attached to
a steering shaft to provide auxiliary steering resistance;
[0016] FIG. 10 is a cross section view of an alternative embodiment
of the steer-by-wire handwheel actuator of FIG. 3 with a
combination worm gear and direct drive power transmission; and
[0017] FIG. 11 is another cross section view of the alternative
embodiment of the steer-by-wire handwheel actuator of FIG. 10 with
worm gear power transmission taken perpendicular to the view of
FIG. 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] Referring to FIG. 1, a typical prior art steering system is
depicted. A steering wheel 10 is connected to a steering column 11
which in turn is connected to a steering intermediate shaft 12 via
universal joint 14. Another universal joint 16 couples intermediate
steering shaft 12 to an electric power steering assist assembly
(rack assist) 18. It is evident that mechanical direct connection
exists throughout the prior art driving system.
[0019] FIG. 2 is a schematic representation of a steer-by-wire
steering system 600 as it is comprises a controller 400, a first
electro-mechanical actuator 202 and a second electro-mechanical
actuator 302, each actuator 202, 302 in signal communication 400a,
400b with the controller 400. In one embodiment, the first and
second electro-mechanical actuators 202, 302 comprising a motor,
crank arm, steering arm and tie rod, are in turn connected
respectively to a first wheel 200 and a second wheel 300 and are
operative thereby to steer the wheels 200, 300 under the command of
the controller 400. In another embodiment, it will be appreciated
by one skilled in the pertinent art that one actuator is optionally
linked to both road wheels 200, 300 to operably steer wheels 200,
300 using one motor to actuate the sole actuator.
[0020] Still referring to FIG. 2, a handwheel actuator 100 of the
present disclosure is in signal communication 100a, 100b with the
controller 400 of the steer-by-wire steering system 600. Handwheel
actuator 100 is in further communication with an external motive
source 500, such as a driver from whom the handwheel actuator 100
receives steering commands by way of a driver input shaft 102. The
controller 400 is also operative to receive as input thereto a
signal 700 indicative of vehicle velocity, as well as a signal 500a
indicative of the position of the driver input shaft 102 and a
signal 500b indicative of the torque on the driver input shaft 102.
Signals 500a and 500b are generated from sensors disposed in
handwheel actuator 100 proximate shaft 102.
[0021] With reference to FIG. 3, therein depicted is a
representation of the handwheel actuator 100 of a preferred
embodiment. The handwheel actuator 100 includes a housing 130, a
driver input shaft 102 and a gear train 104 coupled to the driver
input shaft 102. In the interest of clarity, the gear train 104
comprises a driver feedback pulley 106, a speed reducer pulley 108,
and a spur gear 110 (See also FIG. 7, as gear train 104 is shaded
completely). The driver input shaft 102 is rotatably positioned
between an upper bearing 54 and a lower bearing 56, and position
sensors 20 and torque sensor 22 operably connected to driver input
shaft 102. Position sensors 20 electronically detect the angular
position of the driver input shaft 102, while the torque sensor 22
electronically detects and evaluates the torsional force acting on
the driver input shaft 102. The angular displacement of the hand
steering wheel 10 is detected by sensors 20, 22, processed, and
applied to a servo motor (not shown) to move steerable wheels (not
shown). The handwheel actuator 100 of FIGS. 3 and 6 includes an
electric motor 114 having a motor shaft 116 rotatively driven by
the motor 114. Attached or optionally formed into the motor shaft
116 is a motor pulley 118. Attached to the motor pulley 118 is a
belt 128 positively driving pulley 108 of the gear train 104.
Continuing in FIG. 3 in conjunction with FIG. 7, the handwheel
actuator 100 further includes an electro-mechanical brake 120
having an electro-mechanical brake shaft 122 rotatively controlled
by the electro-mechanical brake 120. Attached or optionally formed
into the electro-mechanical brake shaft 122 is a pulley 124 driving
a belt 136 operably connected to the gear train 104. More
specifically, the belt 136 is connected to the driver feedback
pulley 106 in an exemplary embodiment.
[0022] It should be noted that a preferred embodiment of the
handwheel actuator utilizes an electric sine commutated brushless
motor 114 for its primary power transmission because the sine wave
commutation provides for a low torque ripple. Furthermore, it is
preferred that the belt 128 used to transmit the power from the
motor 114 is a small-cogged belt to provide positive drive, high
efficiency, low noise, and nearly zero lash. In using a cogged
belt, it has been found to yield approximately 98% efficiency. In
addition, a preferred embodiment uses a magnetic particle brake for
the electro-mechanical brake 120, however alternative embodiments
also include electro-rheological fluid devices.
[0023] Magnetorheological fluids suitable for use in the handwheel
actuator 100 are disclosed in U.S. Pat. No. 5,896,965, issued 27
Apr. 1999, to Gopalswamy et al. for a Magnetorheological Fluid Fan
Clutch; U.S. Pat. No. 5,848,678, issued 15 Dec. 1998, to Johnston
et al. for a Passive Magnetorheological Clutch; U.S. Pat. No.
5,845,752, issued 8 Dec. 1998, to Gopalswamy et al. for a
Magnetorheological Fluid Clutch with Minimized Resistance; U.S.
Pat. No. 5,823,309, issued 20 Oct. 1998, to Gopalswamy et al. for a
Magnetorheological Transmission Clutch; and U.S. Pat. No.
5,667,715, issued 16 Sep. 1997, to Foister, R. T. for
Magnetorheological Fluids; the disclosures of all of which are
incorporated herein by reference in their entirety. An alternative
embodiment utilizing an electro-rheological fluid device having
magnetorheological fluid for obtaining a variable resistance to the
driver input shaft is disclosed in Patent Application number
DP-300272, entitled "Variable Road Feedback Device For
Steer-By-Wire System."
[0024] It is to be noted that utilizing a magnetic particle brake
or a magnetorheological fluid device provides virtually no
resistance to a driver input shaft when there is no magnetic force
induced by a control module. However, when it becomes desirable to
give the vehicle operator a feel of the road, a control module
energizes a magnetic field in the magnetic particle brake or the
magnetorheological fluid device causing the magnetic particle brake
or the magnetorheological fluid device in turn to provide variable
passive resistance. The variable passive resistance along with
active resistance provided by the electric motor gives the vehicle
operator a feel of the road by transferring the resistance upon the
steering wheel. Thus, causing the vehicle operator to "feel" or
sense the road.
[0025] Returning to FIG. 3 and incorporating FIG. 8, the handwheel
actuator 100 illustrates generally a stop mechanism 126 enclosed by
housing 130 and comprising the spur gear 110 of the gear train 104
geared to a reducing spur gear 132. Reducing gear 132 further
comprises interior arcuate stop guides 126a, 126b, one on either
side of the gear 132 having a first stop pin 126c disposed within
said stop guide 126a and having a having a second stop pin 126d
disposed within stop guide 126b, such that as spur gear 110
rotates, reducing gear 132, and thus spur gear 110, is mechanically
restrained as the first stop pin and second stop pin make
simultaneous contact with one pair of two ends 126e, 126f of one
end of the interior arcuate stop guides 126a, 126b (See FIG. 8).
The other end of the internal arcuate stop guides 126a, 126b is not
shown. The first stop pin and second stop pin are attached to the
housing 130. In an exemplary embodiment, the stop pins 126c, 126d
are rubber coated and provide over 100 Nm of overload torque
capability.
[0026] Still referring to FIG. 3, a modular unit 140 is attached to
the shaft 102 that acts as a mechanical back-up device to provide
auxiliary steering resistance in the steer-by-wire system 600.
Modular unit 140 allows full lock-to-lock travel of the steering
handwheel 10 while providing torsional resistance to handwheel
rotation up to a specified saturation torque.
[0027] Referring to FIG. 9, modular unit 140 is shown in more
detail and described below. Modular unit 140 provides an adjustable
on-center feel and return-to-center mechanism for the steer-by-wire
handwheel actuator 100 to provide a passive steering system feel
similar to current production hydraulic assisted rack and pinion
systems. Modular unit 140 provides the driver with force feedback
throughout the range of travel of the handwheel 10. Modular unit
140 comprises a ball screw assembly 142 including a hollow sleeve
144 that slip fits over the ball screw assembly 142 and is
rotationally fixed using an anti-rotation pin assembly 148 and a
key 149 opposite thereto. Rotation pin assembly 148 includes a pin
150 slidably engaged against an exterior sleeve 144. Anti-rotation
pin assembly 148 further includes a pin retainer 152 and screw 154
that is disposed in an aperture 156 of retainer 152 and received in
a threaded aperture 158 of housing 162 defining modular unit 140.
Pin 150 is configured with a slot 163 positioned thereon to allow a
portion of retainer 152 to be received therein while maintaining
pin 150 slidably disposed in an aperture formed in housing 162 to
engage an outside surface of a sleeve 144 when screw 154 is fixed
against retainer 152 by tightening screw 154 in threaded aperture
158. Sleeve 144 has a channel 164 configured on a periphery thereof
to allow axial translation of sleeve 144 while limiting rotation
thereof. Sleeve 144 engages a threaded portion 166 of shaft 102 via
a ball nut 168 disposed in sleeve 144. Ball nut 168 is retained in
sleeve 144 with a ball nut retainer nut 169. Ball nut 168 has
complementary threads to engage threaded portion 166. Screw shaft
102 is supported in a ball bearing assembly 170 that is disposed at
one end in housing 162.
[0028] Bearing assembly 170 is retained in housing 162 with a
bearing cap 172 that is mechanically fastened to housing 162 with
mechanical fasteners 174. A bearing nut 176 is engageable with
another threaded portion of shaft 102 to fix shaft 102 relative to
bearing assembly 170 which is fixed relative to housing 162. At an
opposite end 178 of housing 162 an end cap 180 encloses a cavity
formed in housing 162. At the same end 178 a retaining nut 182 is
threaded onto the end of sleeve 144 and an external spring return
nut 196 is threaded into housing 162. Disposed against retaining
nut 196 and retaining nut 182 is a first spring retaining washer
188 having an aperture allowing ball screw 144 to slide
therethrough. A second spring retaining washer 190 is disposed
against a shoulder 192 of sleeve 144 and shoulder 198 of housing
162. Like washer 188, washer 190 includes an aperture that allows
sleeve 144 to slide therethrough. A plurality of biasing members
194 is disposed intermediate washers 188, 190. Each biasing member
is preferably a disc spring or Belleville washer. The plurality of
biasing members 194 is more preferably a stack of disc springs
circumferentially disposed about sleeve 144 while allowing
translation of sleeve 144 therethrough. The stack of disc springs
are preferably formed by alternating the orientation of contiguous
disc springs to provide a compression type biasing member 194. The
spring pack or plurality of biasing members 194 is stacked in
series to provide desired spring load and maximum travel. The
springs are designed and preferably preloaded to a stack height
that gives a non-linear spring rate with a very gradual slope.
[0029] Spring retaining nut 182 is preferably configured as an
adjustment preload nut that is threaded onto the sleeve 144 and
tightened to a specified position to set the appropriate spring
preload on the biasing members 194. An external spring return nut
196 has exterior threads threadably engaged with complementary
threads in housing 162 at end 178 for engaging washer 188 when
sleeve 144 translates toward end 178 pushing washer 192 to compress
biasing members 194 which push against washer 188 which is
prevented from translating toward end 178 by fixed nut 196. When
sleeve 144 translates away from end 178, nut 182 pushes against
washer 188 to compress biasing members 194 against washer 192 that
is prevented from translating away from end 178 by a shoulder 198
formed in housing 162. The preload on the biasing members 194 is
configured to provide an identical bias when shaft 102 is rotated
in either direction since the spring pack or plurality of biasing
members 194 is configured in a parallel arrangement to bias the
shaft indicative of a return-to-center position. It will be
recognized that although the plurality of biasing members has been
described as a single series stack of disc washers, multiple stacks
are also contemplated. More specifically, it is contemplated that a
first stack may be disposed on one side of ball nut 168 while a
second stack is disposed on the other side of ball nut 168. In this
manner, when shaft is rotated in one direction, the first stack is
compressed and when shaft 102 is rotated in an opposite direction,
the second stack is compressed.
[0030] In operation, as the hand wheel 10 is rotated from the
center position, the steering shaft 102 rotates at the same speed.
As the steering shaft 102 rotates, the ball nut 168 and hence
sleeve 144 translates left or right in an axial direction relative
to shaft 102 shown in FIG. 9 depending on direction of rotation.
When the sleeve 144 translates it compresses the spring stack
giving a gradual load increase on the ball nut 168. The axial load
increase reflects through the ball nut 168 giving an increasing
torque feed back to the driver as the hand wheel 10 is turned
further from center. The mechanism will not run out of travel since
the hand wheel actuator will reach its end of travel stop before
maximum travel of the ball nut 168 is reached. When the driver
releases the hand wheel 10 the ball nut 168 will backdrive on the
screw due to the axial load imbalance until it reaches the
equilibrium load at the center position.
[0031] Turning to FIG. 4, a preferred embodiment depicted in FIG. 3
is shown from the rear, and FIG. 5 illustrates the front/plan view
of FIG. 4. FIG. 5 also illustrates three cross sections taken for
the Figures referenced above that follow. FIGS. 4 and 5 illustrate
the housing 130 coupled to a bracket 160 for attaching a handwheel
actuator to a vehicle mounting interface.
[0032] In FIG. 2, in conjunction with FIGS. 6 and 7, the handwheel
actuator 100 is operative to accept as input thereto, firstly,
steering commands by way of the driver input shaft 102 from an
outside motive source such as a driver 500, secondly, the first
control signal 100a from the controller 400 to the motor 114 and
thirdly, a second control signal 100b from the controller 400 to
the electro-mechanical brake 120. The steering commands are
typically the clockwise or counterclockwise rotation of the driver
input shaft 102. The first control signal 100a originating from the
controller 400 controls the input to the speed reducer pulley 124
by the motor 114. The second control signal 100b controls a
feedback torque directed to the driver input shaft 102 by the
electro-mechanical brake 120.
[0033] In FIGS. 6 and 7, the clockwise or counterclockwise rotation
of the driver input shaft 102 instigates the action of the speed
reducer pulley 124. By way of pulley 108 the motor shaft 116 is
positively driven by belt 128. Such engagement results in a gear
ratio, R.sub.1, of the speed reducer pulley 124. As vehicular
operating conditions change, e.g., a change in vehicular speed or a
change in the position of the driver input shaft 102, plus the
application of road forces acting upon the steer-by-wire system 600
(See FIG. 2), the first control signal 100a, based upon the
changing operating conditions, activates the motor 114 so as to
control speed reducer pulley 124, namely resisting or assisting to
the motion of reducing pulley 108 and allowing controlled rotation
thereof. Based upon the aforesaid changing operating conditions,
the second control signal 100b from the controller 400 activates
the electro-mechanical brake 120 so as to provide a resistive
torque to the speed reducer 104 by way of the engagement of the
electro-mechanical brake 120 to the driver input shaft 102 through
the electro-mechanical brake shaft 122, the pulley 124, belt 136,
and the driver feedback pulley 106. The resistive torque results in
a feedback torque that provides the driver 500 with additional
tactile response to steering commands.
[0034] Referring now to FIGS. 10 and 11, an alternative embodiment
for eliminating pulleys 118, 108 and 124, 106 and corresponding
belts 128 and 136, respectively, are illustrated. Motor 114 is in
direct drive relationship with motor shaft 116 operably connected
to shaft 102 absent a connection via a speed reducer. Motor 114
includes a motor stator 206 surrounding a motor rotor 208 operably
connected to shaft 116 for rotation thereof when rotor 206 is
energized. Motor shaft 116 is connected to driver input shaft 102
via a sleeve assembly 212 having a torsion bar 214 disposed therein
for torque sensing by torque sensor 22. Sleeve assembly 212 is
connected to a worm gear 216 that is engaged to a worm 218. Worm
218 is rotatably supported between two bearings 222 and is operably
connected to brake 120 via shaft 122 at one end thereof. In an
exemplary embodiment, brake 120 provides up to about 6 Nm of torque
feedback by braking that is transmitted to worm 218, worm gear 216,
to sleeve assembly 212, and then to driver input shaft 102, while
motor 114 provides up to about 4 Nm of torque feedback in
conjunction with the 6 Nm from brake 120 to driver input shaft for
a total of up to about 10 Nm. Motor 114 generates the torque
through shaft 116, to sleeve assembly 212, and then to the driver
input shaft 102. Using the worm and worm gear drive with the direct
drive motor connection, zero lash and comparable noise are
experienced compared with the belt drive previously described
above.
[0035] It will be understood that a person skilled in the art may
make modifications to the preferred embodiment shown herein within
the scope and intent of the claims. While the present invention has
been described as carried out in a specific embodiment thereof, it
is not intended to be limited thereby but intended to cover the
invention broadly within the scope and spirit of the claims.
* * * * *