ELECTRONICALLY CONTROLLED LOCKING DIFFERENTIAL
HAVING UNDER-DASH CONTROL SYSTEM
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates, in general, to electronically controlled locking
differentials and, in particular, to an electronically controlled locking differential having an
under-dash system adapted to control operation of the differential.
2. Description of the Related Art
[0002] In automotive applications, an electronically controlled locking differential of
the related art may be actuated either manually and is designed expressly for a four-wheel-
drive (4WD) vehicle to allow the differential to be locked or unlocked when it is so desired.
The driver can lock the front and/or rear wheels by manually activating a switch or button
mounted to a dashboard or console of the vehicle. This type of torque-controlling device is
well-known in the aftermarket. More specifically, an aftermarket system including the
differential can be installed using a large push-button switch, which is adapted to be mounted
to the dashboard, wire harness, relay, and routing wires.
[0003] However, installation of this type of differential into the 4WD vehicle
typically requires drilling or boring a hole through the dashboard to mount the relay, route
wires, and install the switch that activates and deactivates the differential. Several
disadvantages are associated with this installation. In particular, this installation is time-
consuming and complicated by requiring modification of the dashboard and complicated
wiring. In addition, improper drilling or boring can damage the dashboard, negatively affect
the aesthetics of the vehicle interior, and increase cost and time of the installation.
[0004] Thus, there is a need in the related art for an electronically actuated locking
differential that provides control, power, traction, and off-road performance to a 4WD

vehicle. There is also a need in the related art for such a differential where installation does
not require drilling or boring a hole into and through a dashboard of the 4 WD vehicle. There
is also a need in the related art for such a differential where installation of the controls is not
time-consuming, complicated, and costly and does not damage the dashboard. There is also a
need in the related art for such a differential that prevents actuation when 4WD functionality
is not necessary. There is also a need in the related art for such a differential that helps
provide longer life to the battery of the vehicle. In particular, there is a need in the related art
for an aftermarket electronically actuated locking differential system that incorporates these
features.
SUMMARY OF THE INVENTION
[0005] The present invention overcomes the disadvantages in the related art in an
electronically controlled locking differential that includes an electromagnetic coil and a
control system adapted to control operation of the differential. The control system has a
module adapted to be mounted under a dashboard of a vehicle and a circuit electrically
interfacing with the module. The circuit has a latching switch that is electrically connected to
first and/or second sources of power and adapted to provide latching power of the
differential. A latching component is electrically connected to the latching switch and
adapted to provide latching power of the differential. The circuit is disabled when power to
the control system is turned off and in "standby" mode when power to the control system is
turned on. Upon the latching switch being activated, current flows through the circuit to
activate the latching component, and the differential is actuated.
[0006] The electronically controlled locking differential of the present invention
provides control, power, traction, and off-road performance to a 4WD vehicle. Installation of
the control system does not require drilling or boring a hole through a dashboard of the 4WD

vehicle; is not time-consuming, complicated, or costly; and does not damage the dashboard.
The control system also integrates various controls into an efficient package and provides
more safety and better control and feedback of status of the differential relative to such
systems of the related art. Furthermore, momentary "on/off' latching and drop-out power of
the differential is controlled. In addition, actuation of the differential is prevented when 4 WD
functionality of the vehicle is not desired. In this way, premature wear of the differential and
related parts and an axle and corresponding tires of the 4WD vehicle is avoided. Moreover,
since the differential resets when power to the 4WD vehicle is turned off, the differential
helps provide longer life to a battery of the vehicle. The control system can be a part of an
aftermarket electronically actuated locking differential system and employed with OEM
applications as well.
[0007] Other objects, features, and advantages of the present invention are readily
appreciated as the same becomes better understood while reading the subsequent description
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF EACH FIGURE OF THE DRAWINGS
[0008] FIG. 1 is an axial cross-sectional view of an electronically controlled locking
differential of the present invention showing the differential in its actuated, locked mode.
[0009] FIG. 2 is an enlarged fragmentary axial cross-sectional view of the differential
illustrated in FIG. 1 showing the differential in its non-actuated, unlocked mode.
[0010] FIG. 3 is a perspective partial view of a module of a control system of the
present invention that controls the electronically controlled locking differential illustrated in
FIGS. 1 and 2.
[0011] FIG. 4 is a schematic view of a circuit of the control system of the
electronically controlled locking differential illustrated in FIGS. 1 and 2.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0012] Referring now to the figures, where like numerals are used to designate like
structure, one embodiment of an electronically controlled locking differential having an
under-dash control system of the present invention is generally indicated at 10. It should be
appreciated by those having ordinary skill in the related art that the differential 10 can be
employed in 4WD vehicles, in particular, and any suitable vehicles, in general. It should also
be appreciated that the control system of the present invention can be employed with any
suitable electronically controlled locking differential. The one described below and shown in
FIGS. 1 and 2 is only exemplary, and the control system can be employed with an
electronically controlled locking differential that is structurally and functionally different than
this one. It should also be appreciated that the control system can be employed by an OEM
or in the aftermarket. In the latter case, the control system is adapted to be mounted under the
dashboard of a 4WD vehicle and is only part of an installation kit that can include a wire
harness, relay, and routing wires and is commonly known in the related art. Those having
ordinary skill in the related art should be able to install the differential to the 4WD vehicle
using just the kit and necessary tools.
[0013] As shown in FIGS. 1 and 2, the differential 10 includes a gear case, generally
indicated at 12, and an end cap, generally indicated at 14, which may be fastened to the gear
case 12 by any suitable fastener, such as by a plurality of bolts (not shown). The gear case 12
and end cap 14 cooperate with each other to define a gear chamber, generally indicated at 16.
Torque input to the differential 10 is typically by an input ring gear (not shown), which may
be attached to a flange 18 as is commonly known in the related art. A gear set is supported
within the gear chamber 16 and has at least a pair of input pinion gears 20 (only one of which
is shown). The pinion gears 20 are mounted rotatably about a pinion shaft 22 that is secured
relative to the gear case 12 by any suitable means. The pinion gears 20 are input gears of the

gear set and disposed in meshing engagement with a respective pair of left and right side
gears, generally indicated at 24, 26. The side gears 24, 26 define respective sets of internal,
straight splines 28, 30 that are adapted to be in splined engagement with mating external
splines on a respective pair of left and right axle shafts (not shown). The gear case 12 defines
annular hub portions 32, 34 on which may be mounted a respective pair of bearing sets that
are used to provide rotational support for the rotating differential 10 relative to an outer
housing or carrier as is commonly known in the related art.
[0014] A rotation-prevention mechanism, generally indicated at 36, has a generally
annular collar member 38 and is disposed entirely within the gear case 12 and operably
associated with side gear 24 (the first output gear). An actuator, generally indicated at 40, is
disposed primarily external to the gear case 12. More specifically, the actuator 40 is disposed
at the end of and about the gear case 12 adjacent side gear 26 (the second output gear) and
has a single ramp plate, generally indicated at 42, that defines a plurality of ramp surfaces 44.
The gear case 12 defines a plurality of cylindrical openings 46 within each of which is
slidably disposed an elongated, generally cylindrical actuation member 48. There is one
ramp surface 44 for each actuation member 48. A locking mechanism of the differential 10
includes the collar member 38 and actuation members 48. The actuator 40 also has an
electromagnetic coil, generally indicated at 50, that exerts a required retarding torque on the
ramp plate 42, thus initiating ramp-up of the actuation members 48. The collar member 38 is
biased toward the non-actuated, "unlocked" mode by a wave spring 52. The electromagnetic
coil 50 is energized by a pair of electrical leads 54.
[0015] During normal, straight-ahead operation of a vehicle, no differentiation occurs
between the left and right axle shafts or side gears 24, 26. Therefore, the pinion gears 20 do
not rotate relative to the pinion shaft 22. As a result, the gear case 12, pinion gears 20, and

side gears 24, 26 all rotate about an axis of rotation "A" as if the gear case 12, pinion gears
20, and side gears 24, 26 are a solid unit.
[0016] The differential 10 may be controlled manually, wherein a driver of the
vehicle manually selects "locked" mode (rather than "unlocked" mode) to operate the
differential 10. For example, when, say, the vehicle is at rest, the driver simply manually
activates a switch or button, such as a simple momentary-type "on/off toggle or rocker
switch or push button, mounted to the dashboard or a console of the vehicle. In this way, an
electric circuit (which is described below) is closed, thereby providing current in the circuit
and a lamp located in or near the toggle switch or push button to indicate to the driver that the
differential is actuated. Current flows in the circuit and ultimately to the electromagnetic coil
50 of the differential 10. The differential 10 then operates in the "locked" mode when, for
example, the vehicle is in first gear or reverse. In tiris way, the first output gear 24 is locked
relative to the gear case 12, preventing any further differentiation between the first output
gear 24 and gear case 12. FIG. 1 shows the differential 10 in its actuated, "locked" mode,
and FIG. 2 shows the differential 10 in its non-actuated, "unlocked" mode.
[0017] FIG. 3 shows a part of a control system, generally indicated at 56, that is
adapted to control operation of the differential 10. More specifically, the figure shows one
embodiment of a module, generally indicated at 58, that is adapted to be mounted under the
dashboard. In particular, the module 58 includes a front panel, generally indicated at 60, and
a rear panel, generally indicated at 62. Upon installation of the module 58, the front panel 60
faces a passenger compartment of the 4WD vehicle. The driver and/or another passenger of a
front seat of the vehicle have/has a view of the front panel 60 and manual access to both the
front and rear panels 60, 62. In an embodiment of the module 58, rugged aluminum encloses
the module 58.

[0018] The front panel 60 includes a soft-touch "on/off' or latching switch 64 that is
adapted to be manually pushed to activate ("ON")/de-activate ("OFF") the differential 10
momentarily so as to provide latching power of the differential 10. The front panel 60 further
includes a plurality of LEDs, generally indicated at 66, that are adapted to indicate when,
respectively, a sensor detects that the differential 10 is locked ("Lock"), the sensor does not
detect that the differential 10 is locked ("Unlock"), and the control system 56 detects an
external fault (described below) or loss of continuity of the electromagnetic coil 50 of the
differential 10 ("Fault"). In each case, the corresponding LED 66 is illuminated. The front
panel 60 further includes a pair of multi-segmented bar-graph displays 68, 70 that indicate,
respectively, amount of travel of the lock mechanism (the collar member 38 and actuation
members 48) of the differential 10 and amount of variable voltage being applied to the
electromagnetic coil 50. In the embodiment of the module 58 shown, bar-graph display 68
includes of five segments and is scaled at one volt per segment. Bar-graph display 70
includes of seven segments and is scaled at two volts per segment.
[0019] The rear panel 62 includes a potentiometer 72 that is adapted to hold a
particular level of voltage for the differential 10 and be adjusted to various levels of potential.
In the embodiment shown, the potentiometer is in the form of a dial 72. The rear panel 62
further includes a multi-pin connector, generally indicated at 74, that is adapted to act as an
interface between the control system 56 and 4WD vehicle. In this way, excessive wiring of
the vehicle is eliminated. In one embodiment of the module 58, the connector 74 can be a
"Molex type" connector. In the embodiment of the module 58 shown, the connector 74
consists of nine pins each or a plurality of which is/are designed to sense a particular activity.
For example, pins labeled "1," "2," and "3" can serve collectively as the sensor that detects
the differential 10 being locked or unlocked ("Lock'VUnlock"), pins labeled "4" and "5" can
serve collectively as the sensor that detects the electromagnetic coil 50, pin labeled "6" can

serve as the sensor that detects positive charge of a battery of the 4WD vehicle, pin labeled
"7" can serve as the sensor that detects power of a switched ignition of the 4WD vehicle
(described below), pin labeled "8" can serve as the sensor that detects negative charge of the
battery, and pin labeled "9" can serve as the sensor that detects the external fault or loss of
continuity of the electromagnetic coil 50 ("Fault"). The sensor in the differential 10 required
to detect locking of the differential 10 can be a "Hall effect" sensor or simple dry-contact
switch. The rear panel 62 further includes a fuse 76 that allows internal protection of wiring
of the control system 56 in case of electrical shorts in a circuit of the control system 56 as
will be described in greater detail below. In one embodiment, the fuse is a spade-style fuse
76.
[0020] Referring more specifically to detection of the external fault or loss of
continuity of the electromagnetic coil 50, fault input is controlled by the dial 72 and can be of
any suitable direct-current source—like a speed signal, pressure transducer, switch of a
transmission of the vehicle, or digital output from an electronic control unit (ECU) of the
vehicle. When a fault is detected, the module 58 switches to "standby" mode, and the "Fault"
LED 66 is illuminated. By way of example, zero to five volts of direct current may be pre-set
to equate to a speed of the 4 WD vehicle of zero to fifty miles per hour, and the differential 10
may be pre-set to disengage when the speed of the vehicle exceeds twenty miles per hour.
Therefore, if the differential 10 is activated and the speed of the vehicle exceeds the pre-set
speed, the module 58 automatically shuts off and is not automatically reactivated until the
speed of the vehicle returns to twenty miles per hour or slower. In this way, an external-fault
input of, say, up to about five volts of direct current is used to remotely turn off the
differential 10 using an external sensor. Also, if, for instance, the fault input is a signal from
a computer of the vehicle and the ECU has detected a reason that the differential 10 should
not be activated, then the "Fault" LED 66 remains illuminated and the control system 56 does

not allow activation of the differential 10. Those having ordinary skill in the related art
should appreciate that the fault input is optional and operation of the module 58 would be
unaffected if the fault input were missing.
[0021] It should be appreciated by those having ordinary skill in the related art that
the module 58 can be installed at any suitable location under the dashboard, in particular, and
any suitable location of the passenger compartment, in general, and be enclosed by any
suitable material. It should also be appreciated that the front panel 60 can include any
suitable type of mechanism that is adapted to activate/de-activate the differential 10 and any
suitable kind and number of indicators and/or displays. It should also be appreciated that
each of the bar-graph displays 68, 70 can consist of any suitable number of segments and
define any suitable scale. It should also be appreciated that the indicators 66 and/or displays
68, 70 can have any suitable structural relationship with each other and the front panel 60. It
should also be appreciated that the rear panel 62 can include any suitable mechanisms that are
adapted to, respectively, hold a particular level of voltage for the differential 10 and be
adjusted to various levels of potential and act as an interface between the control system 56
and 4WD vehicle. It should also be appreciated that the connector 74 can be any suitable
type of connector and consist of any suitable number of pins each or a plurality of which
is/are designed to sense any particular suitable activity. It should also be appreciated that the
fuse 76 can be any suitable type of fuse. It should also be appreciated that the dial 72,
connector 74, and fuse of the rear panel 62 can have any suitable structural relationship with
each other and the rear panel 62.
[0022] FIG. 4 depicts a circuit, generally represented at 78, of the control system 56
that electrically interfaces with the module 58. More specifically, the circuit 78 depicts the
connector 74, in general, and electromagnetic coil 50 of the differential 10 as a "unit under
test" switch line, in particular. In this way, the differential 10 is electrically connected to the

control system 56. The circuit 78 also depicts a direct twelve-volt battery line, generally
indicated at 79, of the 4WD vehicle and a twelve-volt switched-ignition line, generally
indicated at 80, from a switched ignition of the vehicle as power sources. The circuit 78 also
depicts a ground line, generally indicated at 81, a "unit under test" ground line, generally
indicated at 82, and a fault line, generally indicated at 83. The circuit 78 delivers pulse-
width-modulation (PWM) output. The high side of the circuit 78 controls damping and
switching for activation while the low side of the circuit 78 controls driving and switching for
faults. The figure shows different patterns for the respective lines of the circuit 78, and each
line is described in detail immediately below.
[0023] The "unit under test" switch line 50 is electrically connected to a latching
component, generally indicated at 84, in the form of a double-pole, double-throw control
relay 84. More specifically, the "unit under test" switch line 50 is electrically connected to a
first switch, generally indicated at 86, of the relay 84 that includes a set of contacts 87 for
high current. The "unit under test" switch line 50 is also electrically connected to a self-test
coil indicator/"off' switch, generally indicated at 88, and a resistor 90. The self-test coil
indicator/"off' switch 88 ensures that the electromagnetic coil 50 is present, and the control
system 56 can perform a periodic test to ensure that the electromagnetic coil 50 is present.
The "unit under test" switch line 50 leads ultimately to engagement of the "Lock" LED 66.
[0024] The battery line 79 is electrically connected to the fuse 76 and a resistor 92.
The switched-ignition line 80 is electrically connected to a transistor 94 and the relay 84.
More specifically, the switched-ignition line 80 is electrically connected to a second switch,
generally indicated at 96, of the relay 84 that includes a set of contacts 97 for low current.
The switched-ignition line 80 is also electrically connected to a resistor 98 and an "on"
switch 100.

[0025] Ground line 81 is electrically connected to "unit under test" ground line 82,
which is electrically connected to an in-line diode 102, the "unit under test" switch line 50,
and a further ground line, generally indicated at 104. Diode 102 is adapted to conduct current
to the relay 84 and dampen a reverse-bias-voltage spike, and ground line 104 is electrically
connected to a capacitor 106.
[0026] The fault line 83 is electrically connected to ground line 104 and a further
ground line, generally indicated at 108, which is electrically connected to a resistor 110 that
serves to adjust filter. The fault line 83 is also electrically connected to a resistor 112,
transistor 94, another transistor 114, and another resistor 116. Transistor 114 is electrically
connected to a ground line, generally indicated at 118. A ground line 120 is electrically
connected to a transistor 122, ground line 118, resistor 98, and another resistor 124, which is
electrically connected to transistor 94. Transistor 94 is adapted to transfer a current that is
flowing through the circuit across resistor 124, toggle the "Fault" LED 66, and invert a
signal. Transistor 114 transfers the current across resistor 112 to ground when the transistor
114 is switched, and transistor 122 transfers the current across resistor 98.
[0027] Ground line 120 is also electrically connected to an in-line diode 128 and a
"latching" coil 130, which is a part of the relay 84 and adapted to introduce a counter-EMF
into the circuit 78 when current changes. Diode 128 is adapted to conduct current to the relay
84 and dampen a reverse-bias-voltage spike. Ground line 120 is also electrically connected
to the second switch 96 of the relay 84, the "on" switch 100, the self-test coil indicator/"off'
switch 88, a test diode 132 (which is electrically connected to resistor 92), another resistor
134, and a standby diode 136, which is electrically connected to the switched-ignition line 80.
Resistors 90, 92, 134 are adapted to drop the amount of flow of current in the circuit 78 and
protect the respective LEDs 66. A ground line 138 is electrically connected to a fault diode
140, which is electrically connected to the fault line 83, and an engage diode 142, which is

electrically connected to resistor 90. Diodes 132,136,140,142 are adapted to be electrically
connected to the corresponding LEDs 66.
[0028] In the embodiment of the circuit 78 shown, each of resistors 90, 92, 134 may
be a 1.2 kilo-ohm resistor, each of resistors 98, 110 may be a 1.0 kilo-ohm resistor, and each
of resistors 112, 116, 124 may be a 470-ohm resistor. Each of diodes 102, 128 may be a
"1N4004" diode. Transistor 94 may be a "NTE123A" transistor, transistor 114 may be a
"2N3904" transistor, and transistor 122 may be a "2SD669A" transistor. The capacitor 106
may have a capacitance of 0.01 microfarads, and the relay 84 may be a "W92S7012-12"
relay.
[0029] It should be appreciated by those having ordinary skill in the related art that
the circuit 78 can be electrically connected to each of the differential 10, battery, and
switched ignition by any suitable means. It should also be appreciated that the first and
second switches 86, 96 can have any suitable relationship with each other. It should also be
appreciated that each of resistors 90, 92, 98, 110, 112,116,124, 134 can be any suitable type
of resistor and provide any suitable amount of resistance; each of diodes 102, 128 can be any
suitable type of diode; each of transistors 94, 114, 122 can be any suitable type of transistor;
the capacitor 106 can define any suitable amount of capacitance; and the relay 84 can be any
suitable type of relay. It should also be appreciated that a path of flow of current through the
circuit 78 can start at any suitable point of the circuit 78.
[0030] In operation, when ignition or key-switch power is off, all functions of the
control system 56 are disabled, except for testing of the electromagnetic coil 50 of the
differential 10. To test the electromagnetic coil 50, switch 64 is pushed to de-activate the
differential 10. As a result, a loop is closed at, say, about ten milliamps of current to verify
that the electromagnetic coil 50 is present. In turn, at least one of the bar-graph displays 68,
70 is illuminated, or a separate test lamp can be illuminated to show such presence. When

ignition or key-switch power is on, the module 58 is in "standby" mode. A backlit button can
be illuminated in a particular color to show that the module 58 is in this mode.
[0031] To turn on or provide latching power to the differential 10 when the module
58 is in the "standby" mode, switch 64 of the front panel 60 is pushed. As a result, full
voltage is applied to the control system 56 by the battery of the 4WD vehicle, and the module
58 is in "engage" mode. In turn, the "Lock" LED 66 is illuminated (or the backlit button can
be illuminated in a particular different color to show that the module 58 is in this mode).
Bar-graph display 68 shows the amount of travel of the lock mechanism of the differential 10,
and bar-graph display 70 shows the amount of "full" voltage being applied to the
electromagnetic coil 50. Upon the connector 74 detecting that the differential 10 is locked,
the voltage drops back to the particular level of voltage for the differential 10 held by the dial
72, which can be adjusted to various levels of potential. This level of voltage should vary
depending upon the particular differential with which the control system 56 is employed and
can be, for example, about one-third of the full voltage applied to the control system 56 by
the battery, or, about four volts of direct current. Alternatively, the particular level of voltage
for the differential 10 held by the dial 72 can be pre-programmed. Either way, current draw
from the battery is reduced. In turn, bar-graph display 70 shows the amount of reduced
"hold" voltage being applied to the electromagnetic coil 50. As the module 58 toggles from
the "standby" to "engage" modes, applying voltage to the electromagnetic coil 50 and
engaging and latching the differential 10, the "Unlock" and "Lock" LEDs 66 toggle with
respect to each other.
[0032] To turn off the differential 10, switch 64 is pushed again. As a result, the
switched-ignition line 80 places the module 58 in standby mode, thereby preventing
activation of the differential 10 and drain of the battery when the 4WD vehicle is not in use.
In turn, the "Unlock" LED 66 is illuminated, and bar-graph displays 68, 70 show that there is

neither travel of the lock mechanism nor voltage being applied to the electromagnetic coil 50.
If pin labeled "9" detects an external fault or loss of continuity of the electromagnetic coil 50,
then the "Fault" LED 66 is illuminated such that activation of the differential 10 is not
allowed unless and until the fault or loss is cleared. If ignition power is cycled, e.g., the
vehicle is turned off and then turned back on later, the module 58 drops out power to the
differential 10 when the vehicle is turned off, and the differential 10 is not powered again
unless and until the differential 10 is reactivated. The control system 56 contains a high-side
drop-out circuit 78. In this way, any in-line switch can be an external safety mechanism by
which any interruption in the ignition power automatically shuts off the module 58. For
example only and not by way of limitation, a limit switch of the transmission can serve as
such mechanism such that it automatically shuts off the module 58 when it detects that the
vehicle is operating in first gear or reverse.
[0033] Since the module 58 of the control system 56 is mounted under the dashboard
of the 4WD vehicle and, thus, holes need not be drilled through the face of the dashboard of
the vehicle, it should be appreciated by those having ordinary skill in the "vehicle design and
manufacturing" art that the control system 56 overcomes the aforementioned disadvantages
of such systems of the related art. The control system 56 also controls the differential 10
while providing safety features and updates of the status of the differential 10. Operation of
the control system 56 is based upon an electronic momentary-switch-latching-relay system
with feedback to detect locking of the differential 10 and then control of power consumption.
The control system 56 also incorporates a PWM signal to activate and hold on the differential
10 and a high- and low-side drop-out circuit 78. The control system 56 also prevents
accidental operation of the differential 10 and provides external safety inputs on the
switched-ignition line 80. The control system 56 also features twelve-volt thirty-amp max
switching (twelve-volt ten-amp max PWM switching), switched-ignition high-side-fault

drop-out, variable direct-current-fault input (less than about a ten-milliamp draw), and
variable direct-current lock-hold level.
[0034] The differential 10 provides control, power, traction, and off-road performance
to a 4WD vehicle. Also, installation of the control system 56 does not require drilling or
boring a hole through a dashboard of the 4WD vehicle; is not time-consuming, complicated,
or costly; and does not damage the dashboard. The control system 56 integrates various
controls into an efficient package and provides more safety and better control and feedback of
status of the differential 10 relative to such systems of the related art. Furthermore,
momentary "on/off latching and drop-out power of the differential 10 is controlled. In
addition, actuation of the differential 10 is prevented when 4WD functionality of the vehicle
is not desired. In this way, premature wear of the differential 10 and related parts and an axle
and corresponding tires of the 4WD vehicle is avoided. Moreover, since the differential 10
resets when power to the 4WD vehicle is turned off, the differential 10 helps provide longer
life to a battery of the vehicle. The control system 56 can be a part of an aftermarket
electronically-actuated-locking-differential system and employed with OEM applications as
well.
[0035] The present invention has been described in an illustrative manner. It is to be
understood that the terminology that has been used is intended to be in the nature of words of
description rather than of limitation. Many modifications and variations of the present
invention are possible in light of the above teachings. Therefore, within the scope of the
appended claims, the present invention may be practiced other than as specifically described.

WE CLAIM
1. An electronically controlled locking differential (10) comprising:
an electromagnetic coil (50); and
a control system (56) adapted to control operation of said differential (10) and
including:
a module (58) adapted to be mounted under a dashboard of a vehicle; and
a circuit (78) electrically interfacing with said module (58) and having:
a latching switch (64) that is electrically connected to at least
one of first and second sources of power and adapted to provide
latching power of said differential (10); and
a latching component (84) that is electrically connected to said
latching switch (64) and adapted to provide latching power of said
differential (10);
wherein said circuit (78) is disabled when power to said control
system (52) is turned off and in "standby" mode when power to said
control system (56) is turned on and, upon said latching switch (64)
being activated, current flows through said circuit (78) to activate said
latching component (84) and said differential (10) is actuated.
2. An electronically controlled locking differential (10) as set forth in claim 1,
wherein said module (58) includes a front panel (60) and a rear panel (62) that face a
passenger compartment of the vehicle when said module (58) is mounted under the
dashboard.

3. An electronically controlled locking differential (10) as set forth in claim 2,
wherein said front panel (60) of said module (58) includes an "on/off switch (64) that is
adapted to be manually pushed to activate/de-activate said differential (10) momentarily so as
to provide latching power of said differential (10); a plurality of LEDs (66) that are adapted
to indicate at least when a sensor detects that said differential (10) is locked, said sensor does
not detect that said differential (10) is locked, and said control system (56) detects an external
fault or loss of continuity of said electromagnetic coil (50) of said differential (10); and a
plurality of displays (68, 70) that indicate at least amount of travel of said differential (10)
and amount of variable voltage being applied to said electromagnetic coil (50).
4. An electronically controlled locking differential (10) as set forth in claim 2,
wherein said rear panel (62) of said module (58) includes a potentiometer (72) that is adapted
to hold a particular level of voltage for said differential (10) and be adjusted to various levels
of potential and a connector (74) that is adapted to act as an interface between said control
system (56) and the vehicle and has a plurality of pins each of which is designed to sense a
particular electrical activity of the vehicle.
5. An electronically controlled locking differential (10) as set forth in claim 1,
wherein said latching component (84) includes a double-pole, double-throw control relay (84)
mat includes a first switch (86), a second switch (96), and a coil (130) and, upon said latching
switch (64) being activated, current flows through said circuit (78) to activate said relay (84),
said second switch (96) closes, and said differential (10) is actuated.
6. An electronically controlled locking differential (10) as set forth in claim 5,
wherein said first switch (86) includes a set of contacts (87) for high current, said second

switch (96) includes a set of contacts (97) for low current, and said coil (130) is adapted to
introduce a counter-EMF into said circuit (78) when current changes.
7. An electronically controlled locking differential (10) as set forth in claim 6,
wherein said latching switch (64) includes an "on" switch (100) and an "off switch (88),
wherein upon said "on" switch (100) being activated, current flows through said circuit (78)
to activate said relay (84), said second switch (96) closes, and said differential (10) is
actuated.
8. An electronically controlled locking differential (10) as set forth in claim 1,
wherein said control system (56) further includes at least one in-line diode (128) that is
adapted to conduct current to said relay (84) and dampen a reverse-bias-voltage spike.
9. An electronically controlled locking differential (10) as set forth in claim 1,
wherein said control system (56) further includes at least one resistor (90, 92, 98, 110, 112,
116,124,134) that is adapted to drop the amount of flow of current in said circuit (78).
10. An electronically controlled locking differential (10) as set forth in claim 9,
wherein said control system (56) further includes at least one transistor (94, 114, 122) that is
adapted to transfer the current across at least one of said resistors (90, 92, 98, 110, 112, 116,
124,134).
11. A control system (56) adapted to control operation of an electronically
controlled locking differential, said control system (56) comprising:
a module (58) adapted to be mounted under a dashboard of a vehicle; and

a circuit (78) electrically interfacing with said module (58) and having:
a latching switch (64) that is electrically connected to at least one of
first and second sources of power and adapted to provide latching power of the
differential; and
a latching component (84) that is electrically connected to said latching
switch (64) and adapted to provide latching power of the differential;
wherein said circuit (78) is disabled when power to said control system
(56) is turned off and in "standby" mode when power to said control system
(56) is turned on and, upon said latching switch (64) being activated, current
flows through said circuit (78) to activate said latching component (84) and
the differential is actuated.
12. A control system (56) as set forth in claim 11, wherein said module (58)
includes a front panel (60) and a rear panel (62) that face a passenger compartment of the
vehicle when said module (58) is mounted under the dashboard.
13. A control system (56) as set forth in claim 12, wherein said front panel (60) of
said module (58) includes an "on/off' switch (64) that is adapted to be manually pushed to
activate/de-activate the differential momentarily so as to provide latching power of the
differential; a plurality of LEDs (66) that are adapted to indicate at least when a sensor
detects that the differential is locked, said sensor does not detect that the differential is
locked, and said control system (56) detects an external fault or loss of continuity of the
differential; and a plurality of displays (68, 70) that indicate at least amount of travel of the
differential and amount of variable voltage being applied to the differential.

14. A control system (56) as set forth in claim 12, wherein said rear panel (62) of
said module (58) includes a potentiometer (72) that is adapted to hold a particular level of
voltage for the differential and be adjusted to various levels of potential and a connector (74)
that is adapted to act as an interface between said control system (56) and the vehicle and has
a plurality of pins each of which is designed to sense a particular electrical activity of the
vehicle.
15. A control system (56) as set forth in claim 11, wherein said latching
component (84) includes a double-pole, double-throw control relay (84) that includes a first
switch (86), a second switch (96), and a coil (130) and, upon said latching switch (64) being
activated, current flows through said circuit (78) to activate said relay (84), said second
switch (96) closes, and the differential is actuated.
16. A control system (56) as set forth in claim 15, wherein said first switch (86)
includes a set of contacts (87) for high current, said second switch (96) includes a set of
contacts (97) for low current, and said coil (130) is adapted to introduce a counter-EMF into
said circuit (78) when current changes.
17. A control system (56) as set forth in claim 16, wherein said latching switch
(64) includes an "on" switch (100) and an "off switch (88), wherein upon said "on" switch
(100) being activated, current flows through said circuit (78) to activate said relay (84), said
second switch (96) closes, and the differential is actuated.

18. A control system (56) as set forth in claim 11, wherein said control system
(56) further includes at least one in-line diode (128) that is adapted to conduct current to said
relay (84) and dampen a reverse-bias-voltage spike.
19. A control system (56) as set forth in claim 11, wherein said control system
(56) further includes at least one resistor (90, 92, 98, 110, 112, 116, 124, 134) that is adapted
to drop the amount of flow of current in said circuit (78).
20. A control system (56) as set forth in claim 19, wherein said control system
(56) further includes at least one transistor (94, 114, 122) that is adapted to transfer the
current across at least one of said resistors (90,92,98,110,112,116,124,134).

An electronically controlled locking differential (10) includes an
electromagnetic coil (50) and a control system (56) adapted to control
operation of the differential (10). The control system (56) has a module (58)
adapted to be mounted under a dashboard of a vehicle and a circuit (78)
electrically interfacing with the module (58). The circuit (78) has a latching
switch (64) that is electrically connected to first and/or second sources of
power and adapted to provide latching power of the differential (10). A
latching component (84) is electrically connected to the latching switch (64)
and adapted to provide latching power of the differential (10). The circuit
(78) is disabled when power to the control system (56) is turned off and in
"standby" mode when power to the control system (56) is turned on. Upon
the latching switch (64) being activated, current flows through the circuit
(78) to activate the latching component (84), and the differential (10) is
actuated.