Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02809692 2013-03-15
VEHICLE DIFFERENTIAL LOCK DISENGAGEMENT BYPASS
Field of the Invention
The present invention relates to differential locking systems on vehicles, and
specifically to such
systems where incorporating an automatic lock disengagement mechanism.
Background of the Invention
It is well known in the art of motor vehicle design to provide a differential
to enable wheels at
opposed ends of an axle to rotate at different speeds, for example to avoid
undue tire wear, It is
also well known to provide certain vehicles with a locking differential which
selectively forces
the wheels to rotate at the same speed no matter what the difference in
traction, thereby
providing a tractive advantage in some circumstances.
Also, inter-axle differentials have been developed for use on vehicles with
multiple axles,
whereby the differential can be locked and power is transmitted equally to all
axles. The locking
differential system locks the wheels on an axle, while the inter-axle system
locks the multiple
axles together thereby forcing the drivetrain to transmit power to all axles
equally for maximum
traction. In the case of certain vehicles designed for pulling heavy loads,
such as a road/rail
power unit when in rail operation mode, it is important that the differential
and inter-axle locks
remain engaged during operation.
Despite the advantages of the selective locking system, it has been determined
that in certain
circumstances it may be desirable to disengage the locks and later re-engage
them, and such
disengagement means have become a factory standard addition. For example, in
some trucks the
inter-axle lock may be designed to automatically disengage in response to a
condition such as a
low-traction event in which the anti-lock braking system (ABS) initiates,
which allows for more
effective braking. The lock then re-engages automatically after cessation of
the low-traction
event.
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However, the automatic nature of the lock disengagement is problematic in
other contexts. The
locks are designed primarily to maximize traction, and an operator hauling a
heavy load may
therefore wish to have the locks engaged at all times during hauling even when
faced with
intermittent low-traction events. In the case of snow plows ascending an
icy slope,
S disengagement of the inter-axle lock can reduce adhesion and terminate
the ascent, and similar
situations have been noted with logging trucks pulling heavy loads on
washboard road surfaces.
As a further example, it is critical in a road/rail vehicle in rail transport
operation mode that
traction not be lost when pulling railcars, but it is common to experience
traction loss or slippage
on a rail that could result in ABS initiation and lock disengagement, and.
subsequent automatic
re-engagement under load can damage the differentials and axles.
What is needed, therefore, is a system and method for selectively bypassing
the factory
differential lock disengagement means.
Summary of the Invention
The present invention therefore seeks to provide a method and system for
selectively bypassing
the differential lock disengagement means.
According to a first aspect of the present invention, then, there is provided
a method for
selectively bypassing a disengagement system for differential locking means in
a vehicle having
a selectively lockable differential, the differential locking means
disengageable by means of a
control valve in communication with the differential locking means, the method
comprising the
steps of:
a. providing a bypass valve moveable between first and second positions;
b. positioning the bypass valve between the control valve and the
differential locking
means;
c. setting the bypass valve in the first position, thereby allowing
unimpeded communication
between the control valve and the differential locking means; and
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d.
selectively actuating the bypass valve to move the bypass valve to the second
position,
thereby blocking communication between the control valve and the differential
locking
means and preventing disengagement of the differential locking means.
In exemplary embodiments of the first aspect, the disengagement system
disengages the
differential locking means in response to a low-traction event. The
differential locking means
are preferably fluid-powered and the control valve is a solenoid valve capable
of controlling fluid
feed to the differential locking means. The vehicle is most preferably
provided with a pneumatic
system capable of use with the differential locking means. The communication
between the
control valve and the differential locking means is preferably fluid
communication, with the
bypass valve a pneumatic valve configured to control passage therethrough of a
working gas.
The step of setting the bypass valve in the first position is preferably
achieved by biasing the
bypass valve in the first position. The step of selectively actuating the
bypass valve to move the
bypass valve to the second position is preferably achieved by introduction of
working gas
pressure to an actuator of the bypass valve, which introduction of working gas
pressure
preferably occurs in response to a vehicle condition change; where the vehicle
is a road/rail
vehicle, the vehicle condition change is preferably inflation of air bags
during conversion to a
rail mode of vehicle operation.
According to a second aspect of the present invention, there is provided a
bypass system for use
with a disengagement system for differential locking means in a vehicle having
a selectively
lockable differential, the differential locking means powered by a power fluid
selectively
allowed by disengagement control means, the bypass system comprising:
valve means for receiving a power fluid alternatively from the disengagement
control
means in a first position and a power fluid source in a second position;
biasing means for biasing the valve means in the first position;
actuation means for switching the valve means from the first position to the
second
position; and
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power fluid transfer means for supplying the disengagement control means and
the valve
means;
such that in the first position, the valve means allows unimpeded power fluid
flow
between the disengagement control means and the differential locking means;
and
in the second position, the valve means blocks power fluid flow between the
disengagement control means and the differential locking means and thereby
prevents
disengagement of the differential locking means by the disengagement control
means
while allowing power fluid flow directly from the power fluid source to the
differential
locking means.
In exemplary embodiments of the second aspect, the disengagement system
disengages the
differential locking means in response to a low-traction event, the
disengagement control means
comprise a solenoid valve capable of controlling power fluid feed to the
differential locking
means, and the power fluid is a pressurized gas. The actuation means
preferably move the valve
means to the second position by introduction of power fluid to an actuator of
the valve means,
which introduction of power fluid occurs in response to a vehicle condition
change; where the
vehicle is a road/rail vehicle the vehicle condition change is inflation of
air bags during
conversion to a rail mode of vehicle operation.
A detailed description of an exemplary embodiment of the present invention is
given in the
following. It is to be understood, however, that the invention is not to be
construed as being
limited to this embodiment.
Brief Description of the Drawings
hi the accompanying drawings, which illustrate an exemplary embodiment of the
present
invention:
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Figure 1 is a simplified schematic view of a bypass system in accordance with
the present
invention in the un-actuated position; and
Figure 2 is a simplified schematic view of the bypass system of Figure 1 in
the actuated
position.
An exemplary embodiment of the method and system of the present invention will
now be
described with reference to the accompanying drawings.
Detailed Description of Exemplary Embodiment
A pneumatic control system is described in the following, but it will he clear
to those skilled in
the art that the bypass method and system of the present invention could be
applied with any
other suitable system including a hydraulic control system. Only those parts
or components of
the vehicle systems that are necessary for an understanding of the present
invention will be
described herein, as those skilled in the art will fully understand the
broader mechanical and
operational context of the bypass system of the present invention and its
application in particular
situations.
In prior art systems, a solenoid valve is inserted in the air feed line
between the air source and the
differential lock and inter-axle lock (the differential lock and inter-axle
lock collectively referred
to herein as the "differential lock" or "lock"). The solenoid therefore acts
as a gate to
alternatively allow or restrict air flow to the lock depending on the solenoid
design. As
explained above, such solenoids are designed to respond to ABS initiation (low-
traction events)
to block air flow to the locks, thereby disengaging the locks, and then
subsequently allow air
flow back to the locks once the trigger event has ceased.
Turning now to Figures 1 and 2, a bypass system 10 in accordance with the
present invention is
illustrated. The method and system of the present invention will be described
with reference to
these Figures.
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In the bypass system 10, the factory standard control valve 12 (a solenoid) is
in place between
the air source 16 and the output line 44 to the differential locks. The
control valve 12 is fed by a
feed line 18 from the air source 16 and comprises an inlet 20 and an outlet
22, the outlet 22
feeding air to an output line 28. This portion of the illustrated embodiment
is similar to the prior
art design, arid the control valve 12 is wired to receive signals from the ABS
in a conventional
manner that will not he described further herein. The bypass system 10 also
comprises a bypass
valve 14, which in the illustrated embodiment is an air piloted three-port air
valve. The bypass
valve 14 is operated remotely by pneumatic signals provided by pressurized
gas, as will be
explained below.
3.0
The bypass valve 14 comprises upper and lower blocks 24, 26. The upper block
24 comprises a
closed port 34 and an open port 36, while the lower block 26 comprises a
closed port 30 and an
open port 32. The bypass valve 14 further comprises an actuator 38 that is
controlled by means
of an air bag air pressure source 40 and pressurized air supply line 42, the
actuator 38 of
conventional design.
The bypass valve 14 is biased by means of a spring 46 into a first position,
which is illustrated in
Figure 1, and there is no counteracting pressure 40 through supply line 42 to
signal the actuator
38 to switch the bypass valve 14 to the second position. In this first
position, pressurized air is
supplied to the differential locks through the control valve 12. Pressurized
air is provided by the
air source 16 and is forced through the feed line 18. As the lower port 30 of
the lower block 26
is closed, the pressurized air must flow to the control valve 12 through the
inlet 20. At this point,
the control valve 12 will either allow the pressurized air to flow through the
outlet 22, output line
28 and open port 32 of the lower block 26 to the output line 44 to the locks
(in which case the
differential is locked) or will block the flow of pressurized air to the locks
(in which case the
differential is unlocked). In the exemplary embodiment, the control valve 12
is configured to
receive a signal from the vehicle ABS, such that the control valve 12 blocks
air flow in response
to initiation of an ABS event and subsequently allows air flow in response to
a signal indicating
cessation of the ABS event. In the first position, then, the control valve 12
determines on an
automatic basis whether the locks will be engaged or disengaged.
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In a road/rail vehicle, this first position would normally be preferred when
the vehicle is in the
road transport mode of operation. In the rail transport mode of operation,
however, this would
be problematic, as described above. The bypass valve 1.4 is accordingly
capable of shifting to a
second position as described below.
The bypass valve 14 can be shifted into the second position, as illustrated in
Figure 2. When it is
desired to operate a road/rail vehicle in a rail transport mode of operation,
for example, air bags
are inflated to lower the rail gear relative to the vehicle, body and push the
vehicle body
upwardly, such that the rubber tires are elevated and the rail wheels can
engage the rails.
Inflating the air bags 40 sends pressurized air through the supply line 42 to
the actuator 38 of the
bypass valve 14, thereby countering the force of the spring 46 and switching
the bypass valve 14
to the second position. For other vehicles, other means of signalling the
actuator 38 would be
appropriate and within the knowledge of those skilled in the art.
In the second position, the upper block 24 is now engaged. Pressurized air is
provided by the air
source 16 and is forced through the feed line 18, but the lower port 36 is
open and pressurized air
can therefore flow directly through the bypass valve 14 to the output line 44
for the differential
locks. The upper port 34 is closed, with the result that pressurized air fed
through the feed line
18 and inlet 20 to the control valve 12 can pass through the outlet 22 into
the output line 28 but is
blocked from passing through the bypass valve 14. Therefore, in the second
position, the effect
of the control valve 12 is negated such that it does not impact pressurized
air supply to the locks,
while a direct open supply of pressurized air to the locks is supplied through
the open port 36.
Pressurized air is accordingly constantly supplied to the locks during this
bypass phase, such that
the locks remain engaged even in the event of a low-traction event triggering
the control valve 12
flow restriction.
When the bypass valve 14 is switched back to the first position, the control
valve 12 once again
can automatically allow or restrict pressurized air supply to the locks, as
shown in Figure 1. In.
the case of a road/rail vehicle, for example, this would occur when the
vehicle was converted
from a rail transport mode of operation to a road transport mode of operation
by deflation of the
air bags and release of the pressure on the actuator 38.
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The foregoing is considered as illustrative only of the principles of the
invention. The scope of
the claims should not be limited by the exemplary embodiment set forth in the
foregoing, but
should be given the broadest interpretation consistent with the specification
as a whole.
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