Extendable vehicle running board

A running board for an overland vehicle including first and second bell cranks with swing arms which move relative to the vehicle in opposing arcuate displacements. An elongated central running board member is flexibly connected to the swing arms to form a linkage which is extended and retracted. An extension compensator is included to compensate for changes in the overall length of the linkage. A motor-powered drive pivots the swing arms and preferably provides a control mechanism which coordinates the swing arm motions to keep the running board level. The drive can be automatically controlled by a door switch or other sensor.

TECHNICAL FIELD 
The present invention relates to an improved running board for an overland 
vehicle, and more specifically to a moveable running board which includes 
an apparatus for controllably extending and retracting the running board 
from a first, stored position, to a second, deployed position. 
BACKGROUND OF THE INVENTION 
The prior art includes a number of fixed running boards and extendible and 
retractable steps of various designs which may be employed on overland 
vehicles. Extendible assemblies normally include a step or footrest 
surface which may be moved between a retracted position and an extended 
operational position in which to assist passengers entering or exiting 
from the vehicle. 
While the prior art devices have operated with varying degrees of success, 
they have several shortcomings which have detracted from their usefulness. 
For example, many of the commercially available running boards which are 
installed as standard equipment on vehicles are normally fixed at a 
predetermined height and orientation relative to the vehicle. Although 
they can provide an intermediate step which facilitates the entry and exit 
of passengers from the vehicle, these devices are still placed high above 
the ground. This requires individuals who are entering or exiting the 
vehicle to lift up or reach down with their feet a substantial distance in 
order to place them onto the running board or the surface of the earth, as 
the case may be. If the surface of the earth is uneven, the distance may 
be even greater, thereby making the entrance or exit from the vehicle, for 
some individuals, quite difficult or even hazardous. Such may be 
particularly problematic in the case of people who have various physical 
handicaps or limitations. 
The prior art apparatus also in general do not satisfactorily address the 
needs of vans, crew cab pickup, or other four-door vehicles which have a 
need to assist persons by providing more convenient footrests over an 
extended length along the side of the vehicle. 
Moreover, most prior art apparatus have further been unattractive in view 
of their complexity of design, and their associated costs of 
manufacturing. Thus there is a need for an improved extendible and 
retractable running board. 
SUMMARY OF THE INVENTION 
The vehicle running board apparatus of the present invention includes first 
and second end members mounted to the vehicle, a longitudinal running 
board member pivotably connected to the end members, an extension linkage 
subassembly, a drive assembly for rotating the end members, and a control 
system for automatically initiating extension and retraction of the 
running board apparatus. 
In accordance with aspects of the invention, the first and second end 
members are preferably bell cranks, each bell crank having a rotatable 
collar or sleeve portion, a swing arm, and a control arm. The bell cranks 
are attached to the vehicle in an orientation such that the collar portion 
extends horizontally outward from the vehicle while the control and swing 
arms are oriented in a plane generally transverse to the collar portion. 
In accordance with other aspects of the invention, the bell cranks are 
supported on the vehicle by first and second supports having a support 
base and a support shaft, the support base being rigidly attached to the 
vehicle chassis or frame and the support shaft being rigidly attached to, 
or integrally formed with, the base and extending outward from the vehicle 
in a generally horizontal plane. The bell crank collars are mounted to the 
support shafts and rotate thereabout them. 
In accordance with further aspects of the invention, the longitudinal 
member is preferably connected at each end to an end member swing arm to 
allow relative angular displacement between the longitudinal member and 
each swing arm. Facia pieces may optionally be attached to the 
longitudinal member, the end member swings arms, or some combination 
thereof. 
In accordance with still further aspects of the invention, the extension 
linkage subassembly includes a retractable and extendable portion for 
permitting movement of the vehicle running board apparatus between 
retracted and extended positions. The retracted vehicle running board 
position includes the longitudinal member lying at a first height, while 
the extended vehicle running board position includes the longitudinal 
member lying at a second height that is vertically lower than the first 
height. 
In accordance with yet other aspects of the invention, the extension 
linkage subassembly is preferably formed by the combination of the 
longitudinal member and the first and second end member swing arms. The 
second end member swing arm includes first and second portions in a 
telescopic or sliding relation. The preferred vehicle running board 
apparatus further includes a biasing member for urging the first and 
second portions toward each other. An optimal biasing member being a 
compression spring. 
In accordance with yet further aspects of the invention, the drive assembly 
preferably includes a drive motor having a drive shaft upon which an 
output bar having opposed ends is attached. A first connecting rod is 
rotatably attached at a proximal end to an end of the output bar. A second 
connecting rod is rotatably attached at a proximal end to the opposed 
output bar end. Distal connecting rod ends are rotatably attached to the 
first and second end members, and in particular, to the control arms. 
Angular rotation of the drive shaft causes angular displacement of the 
connecting rods and their respective end member control arms, further 
causing extension or retraction of the extension linkage subassembly and 
its corresponding lowering or raising of the longitudinal member. 
In accordance with still yet other aspects of the invention, the control 
system includes a sensor such as a door activated switch for sensing the 
position of the vehicle door. A controller receives an input signal from 
the sensor. The controller is connected to the drive motor and outputs a 
signal to the drive motor in order to effectuate the appropriate vehicle 
running board apparatus response.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
This disclosure of the invention is submitted in furtherance of the 
constitutional purposes of the U.S. Patent Laws "to promote the progress 
of science and useful arts" (Article 1, Section 8). 
A preferred vehicle running board apparatus according to the present 
invention is generally shown by the numeral 10 in FIG. 1. The running 
board 10 is mounted on an overland vehicle 11. The vehicle is shown upon 
the surface of the earth or other supporting ground 12. The overland 
vehicle has earth-engaging tires 13, which position the overland vehicle, 
and more specifically a chassis or frame 14, above the surface of the 
earth. 
FIGS. 2 and 3 show that running board apparatus 10 includes a pair of 
support members 20. Support members 20 are constructed for mounting upon 
the vehicle underbody, such as along the rocker panels, upon a frame 
addition or extension, or to a unibody bottom vehicle panel. The preferred 
support members 20 are individually designated as first bell crank support 
21 and second bell crank support 22, respectively. The first and second 
supports 21 and 22 mount to the vehicle to provide support for a first end 
member 30 and a second end member 50, respectively. The supports and end 
members are preferably constructed and engaged in a manner which allows 
the end members to pivot or otherwise swing upon or rotate about their 
respective supports. 
As shown, each support 21 and 22 includes a support base portion 23. Base 
23 is mounted to the vehicle, preferably at a fixed position utilizing 
conventional fastening techniques, such as by welding or bolting. Supports 
21 and 22 each advantageously includes a support shaft 24 which extends 
outwardly and provides a journal section upon which the end members 30 and 
50 pivot. The shafts are advantageously made integral with the base 
portion. 
The pair of support members 20 are mounted to the vehicle at positions 
which are along or adjacent to the sides of the vehicle. As shown in FIG. 
1, the first support 21 is mounted aft of the second support 22, both 
being at positions spaced approximately the same distance from the 
longitudinal centerline or axis of vehicle 11. The pivot axes of end 
members 30 and 50 are defined by the journal sections of the shafts 24. 
These pivot axes are transverse to the longitudinal axis of the vehicle. 
Further, each of the shafts 24 is oriented in a substantially parallel, 
spaced relationship upon the vehicle. Each of the cylindrically shaped 
shafts 24 has an extreme distal end 25 which is positioned outboard on the 
vehicle. 
The first end member 30 is preferably in the form of a bell crank. The 
first bell crank 30 includes a central portion, or collar portion 31 (also 
called a sleeve or sleeve portion). Collar 31 is in the form of a tubular 
sleeve which has a bore or channel 32. The bore has a diametral dimension 
that is just slightly greater than the outside diametral dimension of the 
cylindrically shaped journal of shaft 24. Therefore, the central portion 
31 of the first bell crank is operable to receive one of the cylindrically 
shaped shafts 24. This renders the first bell crank pivotal about a first 
pivot axis defined by the shaft. 
The first bell crank 30 also includes a pair of arms. The pair of arms 
include a first or control arm 34. The control arm has a proximal end 35 
which is secured to the collar or sleeve portion 31, such as by welding or 
the like. The control arm also has an opposite distal end 36. 
The first bell crank 30 also includes a second or swing arm 40. Swing arm 
40 has a proximal end 41 which is secured to the tubular collar or sleeve 
31, such as by welding or the like. The swing arm 40 has an opposite 
distal end 42. 
FIGS. 3 and 4 best show the second end member 50. Second end member 50 is 
preferably in the form of a second bell crank. The second bell crank 50 
has a central portion or collar 51 (also called a sleeve or sleeve 
portion) which is advantageously in the form of a tubular sleeve. Collar 
51 includes a bore or channel 52 which receives the support shaft 24. The 
channel has a predetermined diametral dimension which is slightly greater 
than the journal portion of the cylindrically shaped shaft 24 which is 
received therein. As shown, the second bell crank 50 is pivotal relative 
to the support shaft 24. 
Second bell crank 50 also includes a pair of second bell crank arms. The 
pair includes a first or control arm 54. Control arm 54 has a proximal end 
55 which is affixed or secured, such as by welding or the like, to the 
collar or sleeve 51. The control arm also has an opposite distal end 56. 
Second bell crank 50 also includes a second or swing arm 60. Swing arm 60 
has a distal end 58 and a proximate end 59. The proximal end is connected 
to the sleeve 51. As shown, second bell crank swing arm 60 includes a 
first portion 61, and a second portion 62 which cooperate to allow 
longitudinal extension and contraction. Details of the function and 
relationship provided by first and second portions 61 and 62 is explained 
below in connection with the extension compensator description of which 
they form a part. 
The first and second arms of the bell cranks 30 and 50 are preferably 
connected to their respective sleeves 31 and 51 at different axial 
positions along the sleeves. This displaced positioning of the bell crank 
arms along the axis of the sleeve is desirable for several reasons as is 
indicated below. The control arms 34 and 54 of the two bell cranks are 
substantially aligned at complementary inboard locations. Control arms 34 
and 54 are preferably positioned at or near the inboard ends of the 
sleeves 31 and 51. The swing arms 40 and 60 are similarly in substantially 
aligned positions near the outboard ends of the sleeves 31 and 51. 
The preferred running board assembly also includes a third or central 
longitudinal member 120. Longitudinal member 120 is supported by the swing 
arms 40 and 60 of the respective first and second bell cranks 30 and 50. 
The longitudinal member 120 has a forward end 122 and an opposing or 
rearward end 123. The longitudinal member is flexibly connected to the 
swing arms 40 and 60 so as to allow relative angular displacement between 
the longitudinal member and each swing arm. This is advantageously 
accomplished by providing a pivotal connection between the longitudinal 
member and the swing arms. As best illustrated by FIGS. 3 and 4, a pair of 
hinges 124 movably and pivotally mounts the longitudinal member 120 to the 
respective swing arms 40 and 60. In the preferred construction shown, the 
longitudinal member 120 is a hollow or tubular piece which defines a 
longitudinal member channel 125 therein. See FIG. 4. 
Longitudinal member 120 can be used directly as a footrest upon which a 
person steps, or can otherwise function directly as a running board. FIG. 
1 shows a preferred alterative wherein longitudinal member 120 is covered 
with an exposed central running board facia piece 127. Central running 
board facia 127 covers the longitudinal member 120 and provides a wider 
footrest. Similarly, FIG. 1 also shows a rearward facia piece 131 and 
forward facia piece 132 which are connected to the first and second swing 
arms 40 and 60. The facia pieces can be made in a variety or styles and 
shapes as desired. Metals, fiberglass or other materials are appropriate. 
The first and second swing arms 40 and 60 form with the longitudinal member 
120 an extension linkage subassembly. The extension linkage is in the 
retracted position shown in FIG. 2 arranged such that the swing arms 40, 
60 and longitudinal member are approximately aligned between the support 
shafts 24. In the extended deployed position shown in FIG. 3, the 
extension linkage subassembly is moved into an arrangement or 
configuration wherein the swing arms 40 and 60 have each pivoted in 
opposite angular directions. The distal ends of the swing arms are moved 
downwardly. The configuration shown in FIG. 3 has a longer linkage path 
length between shafts 24, than the path length shown in FIG. 2. The swing 
arms preferably are displaced angular amounts which move the longitudinal 
member the same amount at each end. This downwardly or combined downwardly 
and outwardly motion places the central longitudinal member is a more 
accessible position for use by a person entering or exiting the vehicle. 
The extended position of the linkage subassembly also places the swing 
arms in opposed angled relationship pointing downward to stabilize the 
ends of the longitudinal member. 
Running board assembly 10 is advantageously provided with an extension 
compensator 81. See FIG. 2. Extension compensator 81 is preferably 
included as part of at least one of the extension linkage members. As 
shown, extension compensator is formed as part of the second swing arm 60. 
Second swing arm 60 is adapted to include an extension compensator first 
portion 61 which slides relative to a second portion 62. The first portion 
61 includes a main body piece 63. Body piece 63 has a distal or first end 
64, and an opposing second or proximal end 65. As best seen in FIG. 4, a 
substantially semicircular seat 70 is formed in the proximal end 65 and 
provides a means for guiding the second portion. Seat 70 further limits 
relative motion between the first and second portions when contracted 
since seat 70 may abut against collar 51 when the board is in its 
retracted position. 
The main body piece 63 further includes a channel 71 which has 
predetermined cross-sectional dimensions. FIG. 4 shows that the first and 
second portions 61 and 62 are slidably connected in a telescoping 
relationship. The second portion 62 is received within the first portion 
61, and has a second portion main body 72 which has a proximal or first 
end 74 and an opposite, second or distal end 73. Proximal end 74 is fixed, 
as by welding or the like, to the central portion or collar 51. 
The extension compensator also preferably includes a compensator biasing 
spring 76. Spring 76 is connected to urge the two complementary parts 61 
and 62 of the compensator into a retracted position. Spring 76 also more 
generally biases the hinge 124 connecting longitudinal member 120 with the 
second bell crank swing arm 60. As shown, a spring connection feature 75 
is provided in a predetermined position internally of the second portion 
62. Spring 76 has one end 77 connected to first spring connection 75. 
Shown in FIG. 4, spring connection 75 is a pin positioned transversely 
within the second portion 62 upon which the one end 77 of spring 76 is 
hooked. The spring has an opposite end 78 which is similarly held by a 
second spring connection 126 which is mounted in channel 125 of the 
longitudinal member. The rigid connection at hinge 124 transfers the force 
of spring 76 to the first portion 61. The operation of the spring will be 
discussed hereinafter. 
Extension compensator 81 also includes a movement limiting member or 
extension stop 79. Stop 79 is fastened on the distal end 73 of the second 
portion 62 and engages a shoulder 69 formed within the proximal end 65 of 
the first portion 61. Stop 79 limits the movement of the second portion 62 
relative to the first portion 61 to an extended position. 
The first and second portions are movable in a relative manner along a 
substantially reciprocal linear path of travel, shown in FIG. 4 by arrow 
80. This slidable reciprocal motion extends between a first or contracted 
position 81 (FIG. 2) wherein the second swing arm 60 has the shortest 
length dimension, to a second or extended position 82 (FIG. 3) where the 
second swing arm 60 has the longest length dimension. As will be 
recognized, the second bell crank 50 is also movable along a swing arc 83 
from a first arc position 84 corresponding to the retracted position to a 
second arc position 85 corresponding to the extended position (see FIG. 
4). 
The running board assembly also preferably includes a drive assembly which 
is generally designated by the numeral 90. As shown, drive 90 is 
advantageously powered. The preferred drive 90 includes both an operator 
and a swing arm pivot control mechanism which are integrated. The swing 
arm pivot control mechanism is fully described below. 
The operator includes a drive motor 91. Motor 91 can be mounted or 
otherwise borne by the overland vehicle 11. Alternatively, the motor can 
be otherwise mounted to apply force to operate the extension linkage 
between the extended and retracted positions. Motor 91 is operable to 
rotate in both a clockwise and counterclockwise direction so as to provide 
both powered extension and powered retraction of the running board 
assembly. An energizing control system is provided for controlling the 
motor as described below. 
The motor 91 includes a drive shaft 92 which controllably transmits torque 
to a motor output bar 93 which is preferably mounted upon the shaft. 
Output bar 93 is preferably symmetrical about the motor shaft axis and 
provides opposing drive ends 95. A first drive end is connected to a first 
drive arm connecting rod 101, and a second drive end is connected to a 
second drive arm connecting rod 102. Each drive arm has a proximal end 103 
which is mounted on one end of the output bar 93, and an opposite distal 
end 104. The near and remote ends 103 and 104 of both drive connecting 
rods 101 and 102 are pivotally mounted by means of pins or fasteners 94 to 
the output bar 93 and the control arms 34 and 54, respectively. Further, 
the first connecting rod 101 has a plurality of apertures 106 formed 
therein and which provides a convenient means to adjust the travel of the 
apparatus 10. It should be understood that energizing the motor imparts 
substantially simultaneous and corresponding rotational movement to the 
drive output bar 93. This rotational motion, in turn, imparts force to the 
respective connecting rods. As force is imparted or transmitted, the first 
and second bell cranks 30 and 50 are caused to pivot in substantially 
opposite directions, and along their given, arcuately shaped paths of 
travel 43 and 83 (FIG. 3), respectively. 
The drive also includes features and is constructed so as to form a swing 
arm control mechanism. The swing arm control is provided by the connecting 
rods 101 and 102 which are coupled to a coordinating link in the form of 
the drive output bar 93. The coordinating drive link output bar 93 pivots 
as supported by the bearing (not shown) of motor 91. The distances between 
the motor pivot axis and the connecting pins 94 at the drive ends 95 are 
appropriately sized so as to provide substantially equal angular 
displacement of the pin connections which is ultimately transferred to 
both swing arms 40 and 60. The angular displacement of the swing arms is 
also affected by the lengths of the control arms 34 and 54 and the lengths 
of the swing arms 40 and 60. The desired net effect is to provide 
extension of the longitudinal member in a coordinated fashion with each 
end of the longitudinal member being moved an approximately equal 
distance. This provides a running board surface which maintains the same 
orientation relative to the vehicle. 
The running board apparatus 10 also preferably is provided with a control 
system 180 which is effective at automatically controlling the running 
board to extend and retract. FIG. 5 shows the control system 180. The 
control system preferably includes a sensor 181. Sensor 181 is preferably 
in the form of a door activated switch (FIG. 1) which senses the condition 
of the vehicle to determine whether the door is opened or closed. The 
sensor signal is detected by controller 188 which can be a variety of 
electrical devices, including a relay. The controller is connected to 
motor 91 so as to operate the motor into an extension mode when the 
vehicle door is opened. Alternatively, the controller controls to operate 
the motor into a retraction mode when the door switch senses the vehicle 
door is closed. This allows automatic extension and retraction of the 
running board. The controller output connections will depend on the 
specific motor used, a variety of which are acceptable. 
The operation of running board 10 has been described hereinabove in whole 
or in part. However, a summarizing explanation is now provided. The 
running board 10 for an overland vehicle 11 is best seen by a study of 
FIGS. 3 and 4. As shown therein, the support bases of the pair of support 
members are attached directly to the vehicle frame. Also shown in FIGS. 3 
and 4, first and second bell crank support members 21 and 22 are borne by 
the overland vehicle 11, and are positioned in predetermined, fixed-spaced 
relation, one-to-the-other. The support bases are preferably placed so 
that the semicircular seat 70 of the second end member swing arm first 
portion 61 is adjacent the second end member collar 51 when the running 
board is in its inoperative position. First and second bell cranks 30 and 
50, respectively, are individually pivoted or otherwise swung supported by 
the first and second bell crank support members. The swing arms thereof 
are movable along individual, substantially arcuately shaped paths of 
travel 43, and 83 respectively. The motor output bar opposing drive ends 
are attached to the first and second drive connecting rods via the 
fasteners 94. If it is desired to make the assembly automatic, then the 
control system 180 is installed. Facie pieces are also added if desired. 
The drive assembly 90 is operated in force transmitting relation relative 
to the first and second bell cranks. Finally, the longitudinal member 120 
at its opposite ends 122 and 123, is supported upon the first and second 
bell crank swing arms, respectively. The longitudinal member is movable 
along a given path of travel 140 between a first or fully retracted 
position 141 and a second or extended position 142 when the drive assembly 
is energized and controlled to extend. 
More specifically, the vehicular running board 10 includes a first bell 
crank 30, which is mounted for pivotable movement on the overland vehicle 
11, and wherein the first bell crank includes first and second arms 34, 
and 40 which have predetermined, fixed length dimensions. In addition, the 
second bell crank 50 is also mounted for pivotal movement on the overland 
vehicle 11, and is movable along a predetermined path of travel 83 which 
is substantially in the same plane as the path of travel 43 of the first 
bell crank. Further, the second bell crank has a first arm 54, which has a 
fixed length dimension, and a second arm 60, which has an adjustable 
length dimension. In particular, the second portion 62 telescopes within 
the first portion 61. The second portion is movable along a given path of 
travel 80 from a first, or contracted position 81, to a second, or 
extended position 82, when the drive assembly is energized for driving the 
running board 120 from the first, stored position 141 to the second, 
deployed position 142. As should be recognized, this extension or 
lengthening of the second arm, compensates for the movement of the running 
board as it is urged along its respective path of travel 140. 
The drive assembly central drive link output bar 93 is disposed in force 
receiving relation relative to the motor 91. Further, first and second 
connecting rods 101 and 102 are mounted in force transmitting relation 
with the output bar. The first and second connecting rods 101 and 102 are 
respectively connected in force transmitting relation relative to the 
individual first arms 34, and 54 of each of the first and second bell 
cranks 30 and 50. As best illustrated by reference to FIG. 3, when the 
motor 91 is energized, the force imparted by the motor has the effect of 
causing the individual bell cranks 30 and 50 to rotate in opposite 
directions and along their respective, arcuately shaped paths of travel 43 
and 83. Still further, the force of the motor has the effect of driving 
the running board 120 along its respective path of travel 140 between the 
first, stored position 141, and the second, deployed position 142. As the 
running board moves along its respective path of travel, it is maintained 
in a substantially horizontal orientation. 
Use of the running board assembly not having a control system is 
accomplished by placing a person's weight upon the upper surface of the 
longitudinal member 120. Since a person's weight is a generally greater 
force on the longitudinal member than the tensive force of the compensator 
biasing spring 75, the first and second portions 61, 62 of the second end 
member bell crank swing arm 60 will telescopically extend, and 
longitudinal member 120 will move downward. These movements will continue 
until the second portion stop sleeve 79 meets the first portion shoulder 
69, at which time the assembly stabilizes. The member 120 is preferably 
kept substantially horizontal regardless of where the person places his or 
her weight. This may be accomplished by using the drive assembly to rotate 
the first and second end member bell cranks 30, 50 in unison the same 
angular amount, although, in opposite angular directions. Once the person 
has removed his or her weight from the longitudinal member, the tensive 
force of the compensator biasing spring 75 urges the first and second 
portions 61, 62 to telescopically retract, which further causes the 
longitudinal member 120 to move upward and the first and second end member 
bell cranks 30, 50 to rotate counterclockwise and clockwise, respectively. 
The running board is thus moved back to its inoperative position. 
Use of the running board assembly including a control system is 
accomplished by opening and closing of the vehicle door. Opening of the 
door is sensed by sensor 181 which inputs the signal to the controller 
188. The controller outputs a command signal to the drive assembly drive 
motor 91 to cause the rotation of the motor output bar 93 via the drive 
shaft 92. Rotation of the motor output bar 93 causes like angular 
movements of the first and second end member bell cranks 30 and 50, 
although, in opposite angular directions. The torque of the drive motor is 
large enough to overcome the tensive force of the compensator biasing 
spring that is urging the linkage subassembly toward its retracted 
position. Therefore, the linkage subassembly is forced to its extended 
position, ready to be used by a person entering or exiting the vehicle. 
Closing the vehicle door causes the opposite response, wherein the control 
assembly commands the drive assembly to retract the linkage subassembly. 
Therefore, the running board 10 of the subject invention can be utilized 
for operation on a wide variety of different overland vehicles 11 without 
substantial modifications thereto. In addition, the present invention may 
be used in all manner of other commercial environments where an 
extendible, and retractable, sideboard, or intermediate step may find 
usefulness. Further, the running board 10 can be easily installed, is 
simple to maintain, and further can be manufactured at a nominal price 
from steel, fiberglass, plastic or other suitable materials. 
In compliance with the statute, the invention has been described in 
language more or less specific as to structural and methodical features. 
It is to be understood, however, that the invention is not limited to the 
specific features shown and described, since the means herein disclosed 
comprise preferred forms of putting the invention into effect. The 
invention is, therefore, claimed in any of its forms or modifications 
within the proper scope of the appended claims appropriately interpreted 
in accordance with the doctrine of equivalents.