Positioning apparatus for inertial sensors

An inertial sensor of the type having an inertially responsive pendulum and a rigid support structure for operatively supporting the pendulum, includes an improved pendulum attitude adjustment assembly which allows precise adjustment of the verticality of the pendulum. The rigid support structure includes a base portion and a pendulum mount portion which is pivotally attached to the base portion. The base is secured at a fixed location and at a fixed attitude relative to the housing. The pendulum is attached at one end to the pendulum mount portion and another end of the pendulum is free to move in response to inertial forces. The attitude adjustment assembly includes an adjustment shaft which is operably coupled to the pendulum mount portion to achieve rotation of the pendulum mount portion with respect to the base portion through a first angle when the adjustment shaft is rotated through an angle greater than the first angle. The pendulum mount portion is preferably rotatable with respect to the base portion through an angle in excess of ninety degrees, and the adjustment shaft has a threaded coupling arrangement which preferably requires rotation of the shaft through a number of degrees in order to rotate the pendulum mount portion a single degree relative to the base portion, thereby providing a desirably high order of resolution while also achieving ease and convenience of operation.

BACKGROUND OF INVENTION 
This invention relates generally to inertial sensors and more particularly 
to inertial sensors or accelerometers which are used to automatically 
operate the brakes of a trailer or other towed vehicle. 
Inertial sensors or accelerometers are well known and at least certain 
types thereof are commonly used to detect deceleration of the towing 
vehicle and to automatically actuate and control brakes in a trailer or 
other towed vehicle in response to detected amounts of such deceleration. 
These accelerometers generally rely on a pendulum-type inertial member 
which swings or flexes in the direction of movement of the towing and 
towed vehicle upon deceleration thereof. Means are provided for detecting 
the magnitude of such pendulum movement and actuating the brakes of the 
towed vehicle in an appropriate manner. 
One of the most effective such type of inertial sensor or accelerometer 
application in use today is that generally shown in U.S. Pat. Nos. 
3,967,863 and 3,981,544, which are assigned to the Assignee of the present 
invention. Furthermore, U.S. Pat. No. 5,058,960, also assigned to the 
Assignee of the present invention, discloses additional refinements 
primarily relating to an improved method of suspending a multiple-layer, 
elastically deformable pendulum using an adhesive connection directly 
between a rigid support and one side of the multiple-layer pendulum, 
whereby damped but unrestricted floating movement of the different layers 
of the pendulum longitudinally with respect to one another during flexure 
of the pendulum is achieved to provide smoother and more controlled 
braking action. In addition, this patent discloses a rigid support 
structure having a flexible hinge which allows the position of a 
pendulum-mounting portion to be changed with respect to that of a base 
portion in order to correct for non-verticality of the pendulum when 
mounted in an actual operating environment. Verticality adjustment of the 
pendulum is achieved by rotating a knob which is essentially directly 
coupled to the pendulum-mounting portion through parallel shafts which are 
eccentrically and rigidly connected together. 
Accordingly, while providing a fundamental and important improvement in 
pendulum-type accelerometer mountings, U.S. Pat. No. 5,058,960 utilized a 
basically conventional structure to adjust the attitude of the pendulum 
(i.e., verticality) which was inherently difficult to precisely control 
because of the difficulty of manually rotating a knob with the desired 
degree of accuracy, especially when relatively tiny increments of motion 
are necessary, due to the one-to-one correspondence between the angular 
displacement of the knob and that of the pendulum. For example, with a 
direct coupling between the knob and the pendulum mount, wherein the 
angular displacement of the pendulum is equal to that of the knob, a one 
degree adjustment in the position of the pendulum requires that the knob 
be rotated by only one degree. Thus, even if the adjustment knob is 
relatively large, i.e., three-fourths inch in diameter, an adjustment of 
one degree equates to a knob rotation of only about six one-thousandths of 
an inch. Such precise movement of a manual knob is at best very difficult, 
if not impossible for many or even most people. Accordingly, there remains 
a need for an improved pendulum attitude-adjustment assembly, wherein 
precise adjustments of the pendulum can be easily achieved. 
SUMMARY OF THE INVENTION 
This invention provides a significantly improved inertial sensor mount 
having an attitude-adjustment assembly which provides precise 
adjustability of the verticality of the inertial member so that optimum 
performance of the inertial sensor can be achieved irrespective of the 
particular angle at which the inertial sensor is mounted to a dashboard or 
the like of a towing vehicle. In particular, the attitude-adjustment 
assembly of the invention allows easy and precise adjustment of the 
inertial member vertical attitude by providing a mechanism whereby 
rotation of an adjustment shaft causes the pendulum to rotate relative to 
the housing or framework of the inertial sensor through an angle which is 
significantly smaller than the angle through which the adjustment shaft is 
rotated. That is to say, the inertial member attitude-adjustment assembly 
of the invention provides a mechanical reduction mechanism wherein 
rotation of an input or adjustment shaft through a first angle effects 
rotation of the inertial member through a significantly reduced angle. The 
invention thereby overcomes the inherent difficulty in making small 
angular adjustments of the inertial member (e.g., pendulum) of known 
inertial sensors wherein the attitude-adjustment knob is directly coupled 
to the pendulum support structure. In other words, whereas known inertial 
sensors include an attitude-adjustment knob for adjusting the verticality 
of the inertial member wherein a one-to-one correspondence exists between 
the angular displacement of the adjustment knob and the angular 
displacement of the inertial member, the present invention provides an 
attitude-adjustment assembly wherein the ratio of the angular displacement 
of the attitude-adjustment knob to the angular displacement of the 
inertial member is significantly greater than one. Furthermore, the 
invention provides particularly novel and advantageous implementations of 
this concept, which enable the achievement of manufacturing, economy, 
simplicity, ease of operation and reliability. 
In accordance with a first aspect of the invention, the inertial sensor 
includes a housing, a primary support structure having a base portion 
mounted in fixed relationship to the housing, an inertial member support 
portion which is rotatable relative to the base portion, and an 
attitude-adjustment assembly which allows precise adjustment of the 
verticality of the inertial member by providing a mechanical arrangement 
wherein rotation of an input adjustment shaft through any particular angle 
effects rotation of the inertial member mount with respect to the base 
through an angle which is less than the angle through which the adjustment 
shaft is rotated. 
In accordance with a preferred embodiment of the invention, the 
attitude-adjustment assembly includes an operating or adjustment shaft 
which is rotatable about its longitudinal axis, and wherein rotation of 
this shaft through any particular angle effects translational movement of 
the shaft in a direction along its longitudinal axis through a 
proportional linear displacement. One end of the adjustment shaft is 
preferably directly coupled to an attitude-adjustment knob which extends 
outwardly from the housing of the inertial sensor device, and the other 
end of the adjustment shaft is coupled to an actuator arm which is 
pivotally connected to the inertial member mount portion of the overall 
support structure. More specifically, the rotational or longitudinal axis 
of the adjustment shaft is substantially perpendicular to the axis about 
which the inertial member mount rotates relative to the base portion of 
the support structure, and the pivot axis of the actuator arm relative to 
the inertial member mount portion of the support structure is 
substantially parallel to that spaced from the pivot axis of the mount 
portion relative to the base portion of the support structure. The 
actuator arm generally provides a linear extension between the end of the 
adjustment shaft and the pivot axis between the actuator arm and the mount 
portion of the support structure, while allowing free rotation of the 
adjustment shaft about its rotational axis relative to the actuator arm, 
which does not rotate with or about the longitudinal axis of the 
adjustment shaft. 
In order to achieve the desired translational movement of the adjustment 
shaft with respect to its longitudinal axis as it is rotated about its 
longitudinal axis, the adjustment shaft includes threads which engage an 
internally threaded member held in a substantially stationary position 
relative to the housing of the inertial sensor. When the adjustment shaft 
is rotated, the resulting translational movement of the adjustment shaft 
along its longitudinal axis is transferred to the actuator arm, which 
moves substantially linearly and in substantially the same direction as 
the adjustment shaft. This causes the pivot axis between the actuator arm 
and the pendulum mount portion of the rigid support structure to move 
relative to the pivot axis between the pendulum mount portion and the base 
portion of the rigid support structure, whereby rotation of the inertial 
member mount portion with respect to the base portion is achieved. In 
addition to allowing rotation of the adjustment shaft relative to the 
actuator arm, the connection between the adjustment shaft and the actuator 
arm must allow the actuator arm to pivot slightly relative to the 
adjustment shaft, because the movement of the pivot axis between the 
actuator arm and the mount portion of the support structure traverses an 
arcuate path about the stationary axis between the mount portion and the 
base portion of the rigid support structure. 
In accordance with another preferred mode of the invention, the inertial 
member mount portion and inertial member mounted thereon are rotatable 
with respect to the base portion of the support structure and housing 
through a relatively large angle to allow the inertial member to be 
vertically oriented by means of the attitude-adjustment assembly, thereby 
allowing the inertial sensor device to be mounted on a support surface, 
such as a dashboard of a vehicle, which is inclined at any of a variety of 
different angles. More specifically, with respect to the illustrated 
embodiment of the invention, the inertial sensor device can be mounted 
with its base or chassis substantially abuttingly adjoined to a support 
surface whose angle can vary from about -20 degrees to about +80 degrees 
with respect to a vertical plane while allowing the attitude of the 
inertial member to be appropriately adjusted in a vertical plane. The 
degree of vertical adjustability provided allows the inertial member to be 
appropriately oriented in a vertical plane when the inertial sensor device 
(i.e., brake controller) is mounted onto the dashboard of most vehicles. 
The invention provides the above-mentioned advantages relating to precision 
vertical adjustability of the inertial member by utilizing a relatively 
simple and inexpensive attitude-adjustment assembly which translates 
rotational movement of a control knob to rotation of the inertial member 
with respect to the housing of the inertial sensor device at a reduced 
rotational rate relative to the rate at which the knob is turned, so that 
minor adjustments in the inertial member attitude can be easily achieved 
as needed or desired.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred example of the inertial sensor or accelerometer of the 
invention is generally of the type described in U.S. Pat. Nos. 3,981,544 
and 5,058,960, which are hereby incorporated by reference herein. The 
electronic circuitry to be used in the most preferred embodiment is 
described in co-pending PCT application Ser. No. PCT/US96/13507, filed 
Aug. 20, 1996, which claims priority based on U.S. provisional application 
Ser. No. 60/002,540 filed Aug. 21, 1995. Although the particular inertial 
sensor used in practicing the invention can potentially be of practically 
any known type, the flexible pendulum type referred to above is shown and 
described for purposes of illustration, but it will be understood that 
this should be deemed representative of others, and the particular word 
"pendulum" used throughout thus understood to mean "inertial member" to 
the extent appropriate. In addition, relative to particular terms of 
orientation and the like, for purposes of describing the invention words 
which relate relative position of one element to another or portions of 
one element to other portions of that element, such as "upwardly," 
"downwardly" and the like, should be interpreted with respect to the 
relationships shown in FIG. 3 unless otherwise indicated, and not 
understood in any particular limiting manner. 
Whereas most controllers or actuators for controlling the brakes on 
trailers or other vehicles which are towed by a vehicle, such as an 
automobile, pickup truck or the like, are mounted under the dashboard of 
the towing vehicle, the controller 10 of the invention is specially 
adapted to be mounted on the front surface of a dashboard 12 generally in 
a position, shown in FIG. 1. The controller 10 includes a housing 14 
comprised of a base or chassis 16 which constitutes the rear of the device 
as mounted in FIG. 1 (or the top, if horizontally mounted under the 
dashboard), and a cover or housing member 18 which constitutes the sides, 
ends and front (or bottom, if horizontally mounted). 
The invention relates primarily to the mechanical elements of the inertial 
sensor apparatus used in the controller 10, and more specifically to 
refinements in the structural arrangement of the mechanical components 
which provide a compact, inexpensive pendulum support structure with an 
improved pendulum attitude-adjustment assembly which facilitates precise 
adjustment of the nominal or inertially neutral position of the pendulum. 
More specifically, with reference to FIGS. 2 and 3, the mechanical, as 
well as the electrical, components of the inertial sensor are mounted on a 
printed circuit board 20 which is disposed atop the chassis 16. The 
mechanical components of the inertial sensor include a support structure 
22 comprising a base portion 24 having a pair of upstanding, spaced-apart 
lower support arms 26, 27 and a pendulum mount portion 28 having a pair of 
spaced-apart upper support arms 29, 30 and a cross member 32 which bridges 
the upper support arms. The lower portion of each of the upper support 
arms 29, 30 is pivotally or hingedly connected to the upper portion of a 
respective one of the lower support arms 26, 27 so that pendulum mount 
portion 28 is pivotable with respect to the base portion 24. Although a 
variety of different means may be employed for pivotally connecting the 
pendulum mount portion to the base portion of the remainder of the support 
structure, the preferred such hinge or pivot connection is preferably 
provided by a thin flexible web or living hinge 34 which is preferably 
integrally formed with the pendulum mount portion and base portion of the 
support structure. In particular, the support structure is preferably a 
single molded plastic part and preferably formed of nylon, although 
various other materials can be suitably employed. 
A pendulum 36 is suspended at its upper end from cross member 32 with the 
bottom end of pendulum 36 being free to move in response to inertial 
forces. The bottom end of pendulum 36 supports a weight holder 38 which 
carries a weight 40. The side of weight holder 38 which faces the support 
structure 22 has a shutter 42 (FIG. 7) which blocks a light beam 
transmitted from a light source 44 when pendulum 36 is in its normal 
vertical, resting position. The controller 10 is normally mounted so that 
chassis 16 faces or abuts the front of the dashboard of a towing vehicle 
(FIG. 1) so that pendulum 36 will swing toward circuit board 20 upon 
deceleration of the towing vehicle when the towing vehicle is moving in 
the forward direction (FIG. 3). Accordingly, upon deceleration of a towing 
vehicle moving in the forward direction, shutter 42 will move toward the 
circuit board 20 along with pendulum 36 whereby light from light source 44 
will pass through slot 46 in shutter 42 and impinge upon a light detector 
48 (FIG. 7) to create a proportional electric signal which acts upon the 
related inertial sensor circuitry to actuate the brakes of a towed 
vehicle. The shutter, pendulum, light source, light detector and 
electrical circuitry are designed to provide a braking response which is 
appropriate to the rate of deceleration of the towing and towed vehicles. 
The pendulum 36 is preferably a flexing, multi-layer cantilever beam-type, 
as described in U.S. Pat. No. 5,058,960. Additionally, the manner in which 
the weight holder 38 and weight 40 are attached to pendulum 36, the manner 
in which pendulum 36 is attached to pendulum mount portion 28, and the 
light source 44 and light detector 48 can generally be as set forth in 
U.S. Pat. No. 5,058,962. Pendulum mount portion 28 also includes a 
blocking bar 50 (FIG. 3) which extends between upward support arms 29, 30. 
Blocking bar 50 is preferably located near the bottom end of pendulum 36 
to prevent undue excursion of the pendulum in a direction toward the 
circuit board 20. Additionally, pendulum mount portion 28 includes a pair 
of blocking arms 51, 52 which are located adjacent the lower portion of 
pendulum 36 so as to prevent undue excursion of the pendulum in a 
direction away from circuit board 20. Blocking bar 50, and especially 
blocking arms 51, 52 is primarily intended to prevent undue excursion of 
pendulum 36 during shipping and handling of the inertial sensor, whereby 
undesirable bending and permanent creasing of the pendulum is prevented. 
Pendulum mount portion 28 of support structure 22 also includes, at one 
side thereof, a mounting flange 54 (FIGS. 2 and 3) having a flange surface 
which is generally perpendicular to the axis through which pendulum mount 
portion 28 rotates with respect to base portion 24. Supported on mounting 
flange 54 and spaced outwardly therefrom is an actuator arm retainer 
flange 56, which is parallel to flange 54. Retainer flange 56 when viewed 
from the side is a generally circular-shaped plate having a large V-notch 
which extends past the center of circular retainer flange 56. Mounting 
flange 54 includes a circular aperture 58 into which is fitted a 
cylindrical stub axle 59 which projects laterally from an actuator arm 60 
that forms a bell-crank which connects or links an adjustment shaft 62 to 
pendulum mount portion 28. The axis of rotation defined by circular 
aperture 58 and cylindrical axle 59 is generally parallel and spaced away 
from the axis of rotation between pendulum mount portion 28 and base 
portion 24, so that forces imposed upon mounting flange 54 through 
aperture 58 by axle 59 will cause pendulum mount portion 28 to pivot with 
respect to base portion 24. 
Adjustment shaft 62 includes a head portion 64 (FIG. 2) which is received 
within a slot 67 in a connector block 66 secured to arm 60. Head portion 
64 is fixedly and preferably integrally attached to one end of adjustment 
shaft 62. Head-receiving slot 67 retains head portion 64 so that 
translational movement of adjustment shaft 62 along its longitudinal axis 
is transmitted to actuator arm 60 and to mounting flange 54 through axle 
59, which engages aperture 58. Head portion 64 is retained by the 
head-receiving slot 67 of connector block 66 so that head portion 64, 
along with adjustment shaft 62, can freely rotate about the longitudinal 
axis of adjustment shaft 62, but not shift longitudinally relative to 
connector block 66. Chassis 16 includes an upstanding post 68 upon which 
is mounted an anchor retainer 70 having a receiving slot 72 which receives 
and retains an internally threaded nut-like anchor member 74. Adjustment 
shaft 62 is externally threaded, with the threads thereof engaging the 
internal threads of the fixed anchor member 74, whereby rotation of 
adjustment shaft 62 causes translational movement of the adjustment shaft 
along its longitudinal axis. The resulting forces are transmitted through 
actuator arm 60 to pendulum mount portion 28 via the bell-crank formed by 
axle 59 and the offset journal aperture 58 on mounting flange 54 of 
pendulum mount portion 28. 
Anchor member 74 is retained in receiving slot 72 of anchor retainer 70 in 
a substantially stationary position, although anchor retainer 70 may be 
made of at least slightly resiliently deformable material which will allow 
a minor amount of tilting of anchor member 74 and shaft 62 with respect to 
anchor retainer 70 to ensure axial alignment and resulting free-running 
conditions between member 74 and shaft 62 during rotation of flanges 54 
and 56 caused by the action of the aforementioned bell crank, which will 
impart some resultant axial tilting to shaft 62 by carrying the head 64 up 
and down. The end of shaft 62 which is opposite the end thereof attached 
to actuator arm 60 is connected to a pendulum attitude-adjustment knob 76 
which projects outwardly from housing 18 and is freely rotatable with 
respect thereto. 
The preferred apparatus used to implement the invention is preferably 
constructed from inexpensive standard, commercially available hardware 
whenever possible. For example, adjustment shaft 62 and head portion 64 
preferably comprise a standard panhead screw, desirably a left-hand 
threaded screw. Internally threaded anchor member 74 is most preferably a 
standard hexagonal nut. The externally accessible adjustment knob 76 is 
most preferably connected to adjustment shaft 62 by means of a hexagonal 
nut 78 which is fixedly secured (as for example by a strong adhesive such 
as cyanoxylate) to the end of adjustment shaft 62 opposite the end 
attached to actuator arm 60. Knob 76 preferably includes a hexagonally 
shaped recess 77 having a length at least equal to the length of travel of 
adjustment shaft 62 and its attached hexnut 78 along the longitudinal axis 
of adjustment shaft 62. The hexagonal shaped recess 77 of knob 76 slidably 
but nonrotatably receive the hexagonal nut 78, so that knob 76 and hexnut 
78 rotate together and nut 78 slides axially within recess 77 as shaft 62 
is axially translated. Knob 76, anchor retainer 70 and actuator 60 are all 
preferably made of nylon or other suitable materials. 
As shown in FIGS. 5, 6 and 7, the inertial sensor of the invention can be 
mounted in a variety of different positions while allowing the pendulum to 
readily and easily be adjusted to a vertical orientation. For example, 
FIG. 5 shows the device as mounted on a vehicle dashboard or other such 
surface which slopes upwardly and away from the driver at an angle of 
about twenty degrees beyond vertical, FIG. 6 shows it as mounted to a 
surface which slopes downwardly and away from the driver at a relatively 
steep angle, and FIG. 7 shows the device as mounted beneath and generally 
parallel to an essentially horizontal surface. The illustrated device can 
thus be mounted at essentially any angle between those shown in FIGS. 5 
and 7, with the pendulum being readily adjustable to a vertical position, 
i.e., the attitude-adjustability afforded for the pendulum is over ninety 
degrees, and preferably at least about one-hundred degrees. 
Support structure 22 and the components comprising the inertial member 
attitude-adjustment assembly include a number of features which prevent or 
at least impede over-rotation of the adjustment shaft beyond its intended 
limits. More specifically, a sleeve 80 (FIGS. 2, 3, 5 and 6) is disposed 
on the adjustment shaft 62 between hexnut 78 and hexnut 74 to prevent or 
at least restrict over-rotation of left-hand threaded adjustment shaft 62 
in a counter-clockwise direction, so that rotation of the upper portion of 
pendulum 36 away from the printed circuit board 20 is limited to the 
position generally indicated in FIG. 6. Likewise, the extent to which 
adjustment shaft 62 can be rotated in the clockwise direction is limited, 
as shown in FIG. 6, by a pair of spaced, parallel walls 82, 83 (see FIG. 
2) which project laterally from anchor retainer 70 and are engaged in 
flush abutting relation by the head-receiving connector member 66 of 
actuator arm 60 to prevent or at least restrict further movement of 
actuator arm 60 in a direction toward knob 76. 
As shown in FIG. 4, base portion 24 of support structure 22 preferably 
includes a plurality of integral, resilient mounting clips 25 which 
project through circuit board 20 to retain support structure 22 on circuit 
board 20 preferably by means of a snap-in type engagement. 
As a specific example of components used in the illustrated embodiment of 
the invention, a 6-32 panhead machine screw having left-handed threads and 
a length of 1.25 inches is utilized to achieve a 32:1 reduction in the 
amount of angular displacement or rotation of shaft 62 relative to the 
amount of angular displacement or rotation of pendulum mount portion 28 
with respect to base portion 24. This means that about eight complete 
revolutions of knob 76 are required to cause the pendulum mount portion 28 
to rotate ninety degrees with respect to the base portion 24 and, in turn, 
that knob 76 must be rotated a full thirty-two degrees to bring about one 
degree of adjustment in the attitude of the pendulum. Accordingly, very 
convenient operation is provided by which extremely fine adjustments in 
the pendulum attitude can be easily achieved. 
With respect to the basic operation of the inertial sensor apparatus, after 
the controller 10 is properly mounted and electrically connected to the 
towing vehicle, the pendulum attitude is adjusted with respect to 
verticality. This is done by rotating knob 76 until a light-emitting diode 
84 lights up to signal that the pendulum 36 is vertically oriented, as 
particularly discussed in the aforementioned copending U.S. Provisional 
patent application Ser. No. 60/002,540. In this regard, users of such 
controllers often prefer to orient the pendulum 36 or other such inertial 
sensor element in a position which is at least slightly off the true 
vertical in order to select a desired inertial response. That is, one may 
use such settings to select a relative lag between the onset of towed 
vehicle braking following initial braking of the tow vehicle, thereby 
providing a particular mode of system response which is preferred by 
certain individuals. The controller 10 also includes a bank of light 
emitting diodes (LEDs) 85, 86, 87 and 88 which light up to indicate the 
amount of braking current being applied to actuate the brakes of the towed 
vehicle, i.e., the number of LEDs 85-88 which are lighted is proportional 
to the amount of deceleration and the amount of braking required. 
A further aspect of the apparatus disclosed herein is an integrally molded 
light-dam/LED-locator board 90 (FIGS. 2 and 3) which is provided to 
properly position the above-mentioned LEDs 84-88 on printed circuit board 
20 and to shield light detector 48 from any stray light transmitted from 
or through the LEDs, which is of considerable importance to the proper 
functioning of the electro-optical part of the device, and thus the basic 
operation of the controller 10. Furthermore, the presence of this 
structure greatly facilitates ease and accuracy of assembly during 
manufacture, and thus helps ensure high quality at lower expense. In 
addition, the invention provides an effective and advantageous way to 
mount the Field Effect Transistors (FETs) 100, 102, which comprise the 
preferred output current control switch components. As best shown in FIG. 
2, these are preferably mounted upon an embossment 104 on metal chassis 
16, at slots or cut-outs 105, 106 in circuit board 20, in order to more 
effectively conduct heat away from the FETs than if they were mounted to 
the circuit board itself. A FET which handles as much current as 
brake-actuators typically may draw (i.e., at least on the order of 
twenty-five to thirty amps), if mounted directly to a circuit board in a 
small electrical device having a substantially complete enclosure without 
any forced-air circulation, would tend to generate more heat than can be 
effectively dissipated, which results in overheating of the FET. Such 
overheating causes the FET and the electrical device in which it is 
utilized to function erratically or to fail to perform properly. The 
inventor has discovered that this problem can be overcome by mounting the 
FETs in essentially direct contact with metal chassis 16, i.e., with the 
body of the FET in thermal contact, or at least in very close proximity to 
the embossment. In this manner, the chassis 16 serves as an effective heat 
sink which quickly conducts heat away from the FETs where it can be more 
effectively transferred to the surroundings by conduction from the base to 
the structure on which it is supported and by free convection to the 
surrounding air. In the most preferred embodiment, a thin layer or sheet 
103 of silicone or the like is interposed between the FET body and 
embossment 104 to provide electrical isolation while maintaining good 
heat-transfer therebetween. 
The above description is considered that of the preferred embodiments only. 
Modification of the invention will occur to those skilled in the art and 
to those who make and use the invention. Therefore, it is understood that 
the embodiments shown in the drawings and described above are merely for 
illustrative purposes and are not intended to limit the scope of the 
invention, which is defined by the following claims.