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By
Joe Evert -
Gale Banks Engineering
Banks’ electronic products offer customers exclusive ActiveSafety™ redundant design. ActiveSafety is an easier way of saying what Banks engineers refer to as Failure Modes Effects Analysis, or FMEA for short. This paper explains
what FMEA is, how it makes
our products different and what benefit it provides to our customers. I’ll
warn you up front though, it gets a little deep, but if you’re interested,
it is worth the read.
FMEA
is an acronym for Failure Modes Effect Analysis. This is
really a design process and standard that Banks applies to
its electronic
products. In order
to understand this, it’s important to understand how late model vehicles
are designed from an electronics standpoint. The
Modern Vehicle
As you probably already know, newer vehicles are a marriage
between highly sophisticated electronics and mechanical
devices. The heart of the electronic
system is an
on-board computer system that rivals the power of your desktop PC, but built
rugged enough to withstand the harsh automotive environment. The on-board
computer, usually called a Powertrain Control Module (PCM),
literally controls the operation
of the engine and transmission. To do this the PCM is connected to numerous
sensors on the engine and transmission that monitor such parameters as engine
speed,
temperature, gear position, throttle position, manifold pressure and a whole
host of other items. These are referred to as inputs to the PCM. In order
for the PCM to control anything it must have some type
of output actuator that
performs the actual control. For instance, the PCM controls the fuel injectors
to precisely
control the amount of fuel delivered to the engine. Every item the PCM is
responsible for controlling must have some type of output
actuator. On a newer vehicle
it’s
not uncommon to have over 15 input sensors and 20 output actuators. (See
Figure to Left)
Hardware & Software
Just like your home PC, the vehicle computer has software
that controls how it operates. Without this software
the computer would just be a bunch of
electronic parts inside a box, without function and unable to perform any
tasks. The software
on your vehicle is very sophisticated and contains thousands of lines of
code. This code is flashed or burned into the microprocessor in the PCM.
It’s
this code that controls how much fuel is delivered, when and at what speed
the transmission shifts, etc. In many respects it has to be much more reliable
than
the software on your PC. You wouldn’t exactly appreciate your PCM
locking up on you as you were merging on the freeway. Because of this,
manufacturers
spend millions of dollars testing and debugging software before it is released
for production. Even then it is sometimes necessary to update the software
after the vehicle is in the field to correct or improve vehicle operation.
This is
commonly referred to as a "reflash."
On-Board
Diagnostics
Events happen very quickly in the world of automotive electronics.
The computer system must execute several thousand lines
of code in a fraction
of a second.
A fuel injector may only need to be held open for a few milliseconds
to deliver the proper amount of fuel. If a sensor or actuator
fails it can
wreak havoc
on the system and possibly render the vehicle disabled. Because of this,
one of
the most important functions of the PCM is to perform diagnostics on
the vehicle. This occurs continuously as soon as the vehicle
is turned on.
It’s here
where you really begin to appreciate what goes into one of these vehicles.
The basis for these diagnostics is a control loop that uses a sense and
control strategy.
The computer senses a parameter and then controls something based on
that parameter. But what happens if the sensor goes bad, or just becomes
unplugged? How can the
PCM discern the difference between a defective sensor and actual output
value? Two strategies are employed to accomplish this: Design Strategy
and Comparative
Analysis.
Design
Strategy deals with the actual design and output characteristics
of sensors used on your vehicle. For this discussion we’ll talk
about a boost sensor. Most analog sensors on the vehicle are capable
of output voltages from 0-5 volts.
However, the design strategy ensures the actual sensor range is usually
between .5-4.5 volts. The voltages below .5 volt and above 4.5 volts
are considered reserved
and are considered failures by the PCM. The PCM knows that if these
values are seen, the sensor could be unplugged, shorted or may have
completely
failed. In
this case the PCM would ignore this input and may use the last known
good value or try to calculate an estimated value based on inputs from
other sensors.
Comparative
Analysis is a software feature that compares sensor values
to each other to determine if the system is functioning
properly. In
the example
above,
the Design Strategy wouldn’t detect that the sensor is out
of range if its output was within the .5-4.5 volt operating range.
Let’s
assume that the boost sensor is designed to provide 3.25 volts at
15 pounds of boost but
the actual output is 2.00 volts because there is a leaking hose near
the sensor. The 2.00 volts is within range but still not correct
for the actual boost present.
The PCM could detect this by comparing the measured boost value to
a calculated value which is determined by analyzing and comparing
to other engine parameters.
For instance, if the PCM measures that the engine is operating at
2,500 RPM and is at wide-open throttle, it could calculate an "expected"
boost value. It would then compare the measured value to determine
if it
is in range. In this example the PCM may calculate the expected boost
value to be between
3.00-3.5 volts. If the measured value is 2.0 volts the PCM would
consider this out of range and use the calculated value instead.
In
either case, if the PCM determines that the output of the boost
sensor is incorrect, it will set a Diagnostic Trouble Code
and illuminate
the
Check Engine
Light to indicate a failure to the driver. There are hundreds of
diagnostic codes that help the technician diagnose the vehicle.
Each code represents
a specific
type of failure. The codes are stored in the PCM’s memory
and can be retrieved by the technician using a diagnostic scan
tool.
As
you can see, the manufacturer has gone through a lot of trouble
to ensure that your vehicle is as reliable as possible.
It contains
sophisticated
diagnostics and is designed to constantly monitor itself to detect
any anomalies or failures.
Aftermarket
Products & FMEA
There are numerous aftermarket products out there for your
vehicle. At first glance they all may look like the same
type of electronic
control
module
even though they may have been engineered in a completely different
way. First,
we need to understand what these products do and how they affect
the operation of
the vehicle. Typically, these modules install in-between the PCM
and its sensors and actuators. If the product was not designed
properly, it becomes
the weak
link in the system and literally undoes everything the manufacturer
has done to make the vehicle reliable. This is where FMEA comes
to life.
FMEA is Banks’ design
requirement to maintain the integrity of the vehicle’s electronic
control system.
As
a result of this design requirement, it is necessary to implement
numerous safety mechanisms divided into two layers — a hardware
layer and software
layer.
Hardware
Layer of FMEA
The engineering department at Banks analyzes the vehicle
and designs its hardware to integrate seamlessly with the
vehicle’s existing electronics. Our design
process ensures that our electronics do not adversely affect
the vehicle in any way. The hardware is also designed to
monitor itself and provide an automatic
bypass which restores the vehicle to factory condition should
something malfunction. This function is accomplished by
incorporating many watchdog circuits to continually
watch the operation of the control module. If the module loses
power or in the unlikely event of a component failure,
this watchdog will place the module into
a mechanical bypass. This functionality is critical when installing
any type of aftermarket electronic module since the module
will be required to regenerate
the vehicle’s sensor signals to the vehicle’s PCM.
It only makes sense that the aftermarket product be as reliable
or more reliable than the vehicle’s
existing electronics.
A
good example of this design is presented in the control module
offered for the Chevrolet Duramax engine.
This module controls
injection timing,
fuel injector
pulse width and fuel rail pressure. Our module contains two
microprocessors for this application. Each microprocessor
is responsible for
separate tasks; however,
both processors must continually communicate with one another
and report normal functionality. In this case the processors
watch
each other.
If either processor
goes off-line, the other processor will instantly restore
the vehicle to stock form. In addition to this, a separate
circuit
continually
monitors both processors’ activity,
and if it detects any abnormal operation it can automatically
restore the vehicle to stock, as well. It is this redundant
level of design that sets the Banks product
line apart from the competition.
Banks
also uses the most sophisticated components, manufacturing
process and testing
procedures to ensure product quality.
Products are fully
tested prior
to shipment using the latest test equipment. In fact, Banks
uses LabView, the same testing and simulation software
that is used
by NASA, JPL
and other prestigious
organizations. This significant investment in hardware
and software is another advantage provided by Banks products.
Software
Layer of FMEA
Just like the factory computer systems, Banks control modules
include advanced diagnostic features. Our software is designed
to continually monitor and diagnose
itself. In the event of a malfunction, a diagnostic code is set which can
help you pinpoint the problem. Diagnostic codes can be
read by viewing the number
of LED flashes on the side of the module. This feature is something you won’t
find on competitors’ products.
Our
software also monitors vehicle parameters. Our Duramax product
monitors automatic transmission parameters and if it
detects slippage, it will automatically
derate power to compensate, thereby preventing transmission damage. If
you install the optional Speed-Loader with the thermocouple,
our module will
automatically derate power if exhaust gas temperatures become too high.
Our software also
detects when the Torque Converter Clutch is locking up and derates power
for a fraction of a second to reduce transmission wear.
The
Banks Difference
Modern vehicles are a complex synergy of electronics and
mechanics. The aftermarket products you choose should not
compromise this and should be
engineered to
the same or higher standard. Although a competitor’s electronic
box may work, it may not be engineered to the same standard as a Banks
product.
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