Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02847791 2014-07-09
7`1111,
FIELD OF THE INVENTION
The invention relates to Automatic Brake Applicator systems (ABA) required on
mining
equipment in Ontario according to the Occupational Health and Safety Act
R.R.O. 1900
Reg. 854, Part V and similar statutes in many other countries and
jurisdictions. ABA
systems are in use in various different forms on mobile equipment.
BACKGROUND OF THE INVENTION
An A.B.A. system is a fail-safe emergency brake system usually consisting of
hydraulic
and electrical components arranged in such a way that they will automatically
apply a
spring applied ¨ hydraulically released brake (SAHR), in the event of specific
system
failures. System triggers include failure in main electrical power, automatic
transmission
pressure failure, accumulator pressure failure, (SAHR brake pressure failure),
and
engine oil pressure failure. The systems that are integral to maintaining
control on the
moving vehicle should be checked regularly so that they ensure that an
operator can
maintain control, and also to ensure that they function as an automatic
application in
the case of emergency.
As with all safety systems, the A.B.A. system needs to be tested and confirmed
that it is
functioning correctly. Given the differences in manufacturers and complexity
of some
vehicles, and the need to ensure that the pressure switch may be set to the
right
pressures, that it has become more difficult for technicians to understand
each unique
A.B.A. and independently test each safety feature.
Also, an ABA Relay is used if you lose transmission or accumulator pressure or
engine
oil pressure. This will lose power to the ABA relay and result in dropping
latch on the
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relay and also lose power to the solenoid and thus applying brakes.
Fail safe SAHR emergency brake systems typically have springs which apply the
brakes and utilize stored hydraulic energy, via a pressure accumulator type
device, to
hold the mechanical friction components of a vehicle brakes in a released
position.
Conventionally, the operator would apply the brake through a service brake
pedal, or
the application of the emergency brake button. This would open an electrical
circuit
that is maintaining power to a hydraulic solenoid or relay, that is providing
a path
between the accumulator and the SAHR brake. With the power to the solenoid
removed, the brake pedal and the SAHR brake hydraulics maintaining the SAHR
brake
in the released position are removed, therefore allowing the springs to cause
the
mechanical friction components to engage and stop the vehicle. The core system
that
maintains and controls the SAHR brake is called the "Charge Circuit". The
charge
circuit maintains the pressure for the whole brake circuit. Release pressure
is usually
regulated through the service brake pedal.
While the various above features are described in relation to a hydraulic
pressure
operated system, it will be appreciated that there are other ABA systems
incorporating
other forms of fluid medium, such as pressurized nitrogen in some cases, and
in other
cases provide a reduced pressure functioning in the same way as the pressure
of the
hydraulic or nitrogen system. The accumulator stores more energy for more
brake
applications. For the purpose of this discussion, the word pressure is deemed
to relate
to both positive pressure such as in the hydraulic or nitrogen systems.
A.B.A. ¨ Pressure Monitoring and Testing
The charge circuit of an emergency brake system is monitored for pressure in
three
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locations with three different pressure sensors, namely;
Impending Brake Pressure Sensor (Impending Brake), indicates when the brakes
will
be coming on.
Accumulator Pressure Sensor (Accumulator Sensor). This puts the brakes on at a
certain pressure.
Secondary Brake Pressure Sensor (Brake Pressure Sensor). This controls the
brake
light, and turns the brake button light out.
The impending brake sensor and accumulator sensor are on the charge circuit
main
line and the brake pressure sensor. The brake pressure switch is in the same
line as
the Accumulator.
The accumulator and impending pressure sensors (typically pre-set switches)
monitor
the charge circuit, ensuring enough stored hydraulic is available to maintain
a fully
released SAHR brake. The roles of these sensors are to both indicate to the
operator
the state of the pressure and to automatically apply the brakes in the event
the
pressure becomes too low. In the event of a total pressure loss the fail-safe
will fully
engage and stop the vehicle automatically.
However, if the pressure loss is gradual, the SAHR brake may become semi-
engaged,
generating enough friction to potentially over-heat and destroy the brake. The
brakes
are wet disc brakes and they have cooling oil in them. The friction required
to generate
heat is minimal and may not impair vehicle performance, and therefore will go
unnoticed by the operator. During a gradual pressure loss, the impending
switch will
indicate to the operator a warning that the pressure is becoming low and an
automatic
brake application is impending. Further loss in pressure will result in the
accumulator
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pressure sensor triggering the A.B.A system. They will not destroy them with a
fast
brake application.
The third sensor, brake pressure sensor, monitors the pressure at the brake
and
visually indicates to the operator its position, released or applied. If the
brake fails to
release when a request by the operator is made, the light will indicate the
brake as
applied.
A.B.A. ¨ Engine Monitoring and Testing
Some manufacturers have chosen to monitor the engine oil with regards to the
A.B.A.
system. If the engine dies, a drop in engine oil pressure will activate the
A.B.A. and put
the brakes on. To test the engine oil pressure switch, you would interrupt
power to the
ECU to simulate an engine failure, which can be done using a relay as noted
below.
A.B.A. ¨ Transmission Monitoring and Testing
The transmission, specifically automatic/semi-automatic, is an integral
component in
the control of a vehicle speed as it relates to safety. Transmissions that
utilize pressure
applied clutches for gear selection can fail-unsafe. Disconnection of drive
between the
engine and the drive wheels can result in a "free-wheel" or neutral condition
that
removes the dynamic engine braking effect. In a downhill scenario this can
result in
unexpected acceleration of the vehicle.
Monitoring the pressure that maintains the transmission clutches and therefore
the
drive/engine connection, and controlling the A.B.A. system has been an
industry
standard when utilizing such transmissions with unsafe fail modes_ Another way
to test
the transmission ABA would be to add a relay to interrupt power to the ECU to
kill the
engine.
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BRIEF SUMMARY OF THE INVENTION
To test these sensors it is necessary to simulate a gradual loss in pressure.
The A.B.A.
testing device (Pendant) of the invention will energize an installed "test
solenoid and
fixed orifice" to bleed down the charge circuit in a controlled descent. The
technician will
note the pressure on installed gauges as the test progresses and the pressure
loss
simulation occurs. The pressures at which the warnings and final brake
application
occur should correlate with manufacturer's specifications for that vehicle.
Any
difference between the pressures noted during the test and the manufacturers
specifications, will indicate a requirement for servicing, and may indicate an
actual fault
in the system.
To test the A.B.A. the testing Pendant includes a means of simulating an
engine failure
and transmission failure. The automatic application of the emergency SAHR
brake
would be the expected result. All indicators should confirm this.
Testing the transmission ¨ A.B.A. control similarly requires the installation
of a solenoid
and orifice to gradually "bleed" down transmission pressure to point where the
sensor
indicates a warning and automatic emergency brake application occurs. The
coincident
pressure on the system gauge would be recorded and compared to the
manufacturer's
specifications. Another option would be to use a relay to interrupt power to
the ECU,
simulating an engine failure.
70 These connections within the vehicle are connected to a connector plug
which will be
mounted typically in the cab of the vehicle. A technician testing that vehicle
can simply
carry the pendant into that vehicle, plug it in to the connection plug and
carry out the
necessary tests.
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The various features of novelty which characterize the invention are pointed
out
with more particularity in the claims annexed to and forming a part of this
disclosure.
For a better understanding of the invention, its operating advantages and
specific
objects attained by its use, reference should be made to the accompanying
drawings
and descriptive matter in which there are illustrated and described preferred
embodiments of the invention.
IN THE DRAWINGS
Figure 1 is a schematic circuit diagram showing both the main pressure circuit
controlling the brakes and also showing the additional bleed circuits, and the
pendant;
DESCRIPTION OF A SPECIFIC EMBODIMENT
Referring to Figure 1, it will be seen that this illustrates in part braking
equipment
already installed in most heavy machinery especially in the mining industry.
EXISTING EQUIPMENT.
This will comprise the braking system and hydraulic pressure operating system
(SAHR),
typical on many pieces of heavy earth moving and mining equipment.
The brake operating cylinders are shown generally as (10a), (10b) .
These cylinders contain typically a piston , and a spring (not shown) on one
side of the
piston. The opposite side of the piston is operated, typically, by hydraulic
pressure
fluid. So long as the pressure is maintained it will hold the piston to
compress the
spring. In this condition, the brakes are disengaged and the vehicle can be
operated
normally. A drop in the pressure will release of the spring and will cause
operation of
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the brakes in known manner.
Hydraulic pressure is supplied from a pressure source (12), typically a pump
supplying
an accumulator and charge circuit. The hydraulic fluid. is connected to the
brakes via
the main pressure charge line (14) . The charge line (14) line is connected to
a brake
solenoid (16) which is controlled by an emergency button (18) typically
mounted in a
control panel (20) on the dash board of the vehicle.
In the cab there would also be the usual brake pedal (not shown) for normal
operation
of the brakes which would also connect with the brake solenoid (16).
Typically these will be electrical controls,
The brake solenoid (16) will typically be connected to a hydraulic tank (24).
These components are already present in the vehicle and are typical of SAHR
systems
in general. Obviously, in the case of a gas operated system the receptacle
would be an
accumulator tank.
When braking is required, for example by the driver, or in an emergency
situation, then
the hydraulic pressure will drop, the pistons will be moved by the springs,
and these will
then operate the brakes. This is what is known as the typical spring activated
hydraulic
release (SAHR) system. Other systems may incorporate compressed gas such as
nitrogen (not shown). In each case however, the result is generally the same.
So long
as the pressure is maintained, the brakes are disengaged and the vehicle can
operate.
If the pressure is reduced, some braking action will be applied, and if the
pressure is
discontinued altogether, the vehicle should be brought to a stop.
The vehicle will also have an engine (25) and transmission (26).
However in any system it is possible for some leaks to develop, which have the
effect of
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slowly bleeding off the pressure. When this happens, the springs in the brake
cylinders
, will begin to take over and will cause slight contact between the brakes and
the friction
elements of the brakes. This may not be noticeable to the operator since it
will not
interfere with the operation of the vehicle. However, continued operation of
the vehicle
with the brakes rubbing, will cause the brakes to burn out. For these reasons,
testing of
the brake systems is mandatory in many jurisdictions. In the past, testing of
the A.B.A.
systems has required skilled technicians and hours of down time with each
machine.
The present invention is directed to providing a more efficient testing system
and a
system which can be applied to each vehicle on a regular basis, with a minimum
of
vehicle down time. This will greatly increase the safety of the operation of a
fleet of
vehicles and at the same time, will also maximize the useful operating time of
each
vehicle thereby increasing production.
EQUIPMENT TO BE INSTALLED
Referring first of all to the hydraulic system (BAHR), illustrated in the
first embodiment
in Figure 1, the system according to the invention, will require the
installation of a brake
bleed line solenoid (40 ), connecting with the main charge line (14) at
junction (42).
The bleed solenoid (40) is connected by a bleed line (44) to a controlled
bleed orifice
(46), and from the orifice ( 46) to the hydraulic tank ( 24,) which is already
part of the
vehicle brake system.
The bleed solenoid (40 ) is connected by an electric cable (48 ), to the
vehicle control;
panel.
The electrical cable (48) and the bleed solenoid (40) , and the bleed line and
the bleed
orifice (46) will all require installation on a permanent basis in each
vehicle, together
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with the control panel.
In order to simulate a brake or a transmission failure the charge line is
connected to an
accumulator pressure switch (50), and to an impending brake warning switch
(52) .
These two switches are in turn connected via wires (54) and (56) to the
vehicle panel
(20). Charge valve (57) is connected to pipe (14).
In order to simulate a transmission failure a transmission pressure switch (60
) is
connected to the transmission via pipe (62). This switch is also connected to
the vehicle
panel via wire (64).
The transmission is further connected to a transmission solenoid (66) via
outlet pipe
(68) and return pipe (70). This solenoid is connected via wire (72) to the
vehicle panel.
All these components will require permanent installation in the vehicle. The
vehicle
panel (20) will require a brake accumulator pressure lamp (74), a transmission
pressure
warning lamp (76), an impending brake warning lamp (78), and an engine power
lamp
(80). Engine (25) will require an oil pressure switch (82) and an engine test
relay (84)
both being connected to wire (48). Also, relay (84) could test transmission
and interrupt
power to the ECU to simulate engine failure.
THE TEST PENDANT
The system is completed by means of the test pendant (90). The test pendant
incorporates a plurality of separate switches (92, 94, 96). A cable (98) with
a
plug (100) permits the pendant to be plugged into the connecting receptacle
(102) on
the vehicle control panel (20 ) in the cab of the vehicle.
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Once the pendant is plugged in to the receptacle the tests may proceed. By
depressing
the appropriate button, the technician may signal a slow leak in the brake
system itself.
In this test, he will watch the gauges in the cab of the vehicle and see when
the brakes
are applied, and note down the pressures at which they are applied. If there
is any
difference between the manufacturers specified pressures and the pressure
noted
when the impending light comes on, then it indicates a requirement for
service.
The technician can also simulate an engine failure, and note the pressures at
which the
engine oil pressure switch is working, and the brakes are applied in that
case.
A technician can also simulate a transmission failure and note the pressures
at which
the brakes are applied in that case. ABA Relay (86) will apply the brakes if
you lose
power from any of the three pressure switches.
The foregoing is a description of a preferred embodiment of the invention
which
is given here by way of example only. The invention is not to be taken as
limited to any
of the specific features as described, but comprehends all such variations
thereof as
come within the scope of the appended claims.
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