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Combined environmental testing for equipment used on automobiles
-Overview and test approach- |
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Jyuro Izumi*
Automobiles face societal demands such as conserving
energy, promoting recycling, and preventing pollution,
while at the same time they must respond to purchaser
desires for improved safety and greater comfort
and convenience. The complex control systems employed
to meet these demands can only be discussed in terms
of car electronics. The continued development of
vehicle electronic equipment has led to an age requiring
diagnostic systems, serial data transmission control,
and information displays as well as data transmission
to navigational and other equipment inside and outside
the vehicle. This burgeoning use of vehicle-mounted
electronic equipment has led to a diversity of mounting
environments, so that sometimes even when the environmental
endurance of an individual part is well understood,
the results could change when the equipment is actually
mounted on the vehicle. Some mounting sites are
within the relatively benign environment of the
passenger cabin, but the majority of parts are used
in harsher environments, such as outside in low
temperatures, or subjected to the high heat and
humidity and the mechanical vibration of the engine
compartment. To maintain the rated safety and performance
for the long term in the environments where the
parts are actually used, combined environmental
testing is carried out on electronic equipment mounted
on many types of vehicles, as well as for the machinery
built into the electronic equipment. In this article,
I would like to present some examples of the approach
of combined environmental testing in which temperature,
humidity, and vibration are combined to create the
environments in which the parts are presumed to
be used in the vehicle. |
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There
is a strong trend toward incorporating electronic
control to attain the high performance and
high functionality of today's automobiles.
The greatest efforts in technological development
are being poured into this field, and the
functions of every type of control system
are growing increasingly complex. Within this
situation, we can note that:
(1) Customers are demanding more safety and
comfort features, and safety and comfort equipment
such as four-wheel drive, braking control,
and traction control are becoming standard
on many cars.
(2) Fuel consumption and exhaust gas regulations
are becoming stricter, while at the same time
the customer is seeking improvements in both
driveability and general driving features,
all of which requires higher level control.
With vehicle control systems relying
on ever-more-sophisticated electronics, the
reliability of the electronic control equipment
has a major impact on the overall reliability
of the vehicle.
In general, the usage environment
affects the durability and operating characteristics
of electronic devices and units. Therefore,
when studying the developmental design and
application of the equipment built into these
devices and units, the crucial problems have
become how environmental test items should
be set with regard to actual usage conditions,
and how to maintain practicality and requisite
performance while keeping costs reasonable.
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| 2. The usage environments
of equipment mounted on vehicles |
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| The vehicle usage
environment includes such factors as temperature,
humidity, vibration, rainwater, weatherability,
voltage fluctuation, and surge voltage. When considering
temperature, we find that the vehicle itself is
a source of heat production, and the temperature
in the engine compartment gets up to around 100°C,
it goes over 65°C in the trunk, and can hit 100°C
at sites such as the instrument panel in the vehicle
interior. With humidity, we find it is not limited
to high humidity caused by rainwater. Sudden changes
in temperature cause dew condensation, which reaches
a maximum of 95 percent humidity in the trunk at
38°C. Next, turning to vibration, we find that the
body shake vibration occurring while driving receives
2.2 to 4.4 G's of acceleration, and the engine vibration
generates 20 to 40 G's of acceleration that affects
the engine compartment. |
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| 3. The affects of temperature
and humidity environments on vehicle-mounted
equipment |
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3-1 Vehicle
heat sources
(engine compartment temperature conditions)
The major sources of heat in the
vehicle are engine heat and friction heat
from the braking and automatic transmission
systems. Temperature conditions in the engine
compartment are particularly severe in hot
weather when driving in traffic jams or going
uphill. Newer model vehicles have smaller
ventilation openings to reduce air drag while
at the same time having to cope with greater
heat output due to equipment such as DOHC
and turbochargers. The increased heat combined
with the reduced ventilation means that temperatures
of 80 to 120°C must be handled. Table 1 gives
maximum temperatures for different areas of
the engine compartment.
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Table
1 Maximum temperatures at different
areas of the engine compartment
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Location
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Maximum temperature
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| Engine
coolant |
120°C
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| Engine
oil |
120°C
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| Transmission
oil |
150°C
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| Intake
manifold |
120°C
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| Exhaust
manifold |
650°C
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| Alternator
air intake |
130°C
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| Quoted from "Vehicle
electronics and reliability" |
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3-2 Cabin
temperature while car is parked
When the car is parked under a
blazing sun and the passenger cabin is shut
tight, the car becomes like a sun room. The
temperature climbs to around 110 to 120°C in
the vicinity of the front and rear panels,
which are exposed to direct sunlight. The
temperature of the headlining and the area
of the front and rear seats reaches 65 to
85°C. Table 2 gives maximum temperatures for
different areas inside the passenger cabin.
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Table 2 Maximum temperatures at different
areas of the passenger cabin Location
Maximum temperature
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Location
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Maximum temperature
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| Top
of the front instrument
panel |
120°C
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| Bottom
of the front instrument
panel |
71°C
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| Passenger
cabin floor |
105°C
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| Rear deck |
117°C
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| Headlining |
83°C
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| Quoted from "Vehicle
electronics and reliability" |
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3-3
Vehicle humidity environment
Most cars today come equipped
with air conditioning, and when the doors
are opened and closed, high humidity outside
air flows in and tends to cause dew condensation
to form on air-conditioned equipment. To take
vehicle-installed audio equipment as an example,
when a car has been parked in a cold area
such as at a ski resort, the car is started
up and the heater is turned on, blasting hot
air from the engine compartment onto the audio
equipment installed on the exterior of the
front panel. The sudden change in temperature
creates a gap between the panel temperature
and the temperature inside the passenger cabin.
Table 3 shows maximum humidity for different
areas inside the passenger cabin. |
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Table
3 Maximum humidity at different areas
of the vehicle
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Location
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Maximum humidity
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Engine
compartment (around engine)
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38°C,
95%RH
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Engine
compartment (dashboard)
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66°C,
80%RH
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Passenger
seats
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66°C,
80%RH
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Around
both side doors
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38°C,
95%RH
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Around
front dash panel
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38°C,
95%RH
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Floor
sheet
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66°C,
80%RH
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Rear
deck
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38°C,
95%RH
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Trunk
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38°C,
95%RH
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| Quoted from "Vehicle
electronics and reliability" |
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3-4 Examples
of demands on electronic equipment by temperature
environments
Temperature
environments require that vehicle-mounted electronic
equipment meet the following conditions.
| (1) |
Operate normally at high
and low temperatures. |
| (2) |
Operate normally during
severe temperature increase or drop within
a short period. The ability to meet these
conditions becomes crucial in environments
that include such factors as severe temperature
fluctuations and vibrations from starting
up or stopping. |
Example
1:
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Starting up after having
been parked under a blazing summer sun requires
the ability to operate safely at 80 to 120°C.
After driving 10 minutes, the air condi-tioner
lowers the temperature to 15 to 20°C,
and then the car is parked again and returns
to the high tem-perature. |
| Example
2: |
Starting the engine in the
early morning in the dead of winter in a northern
climate (about -30°C)
requires the ability for all functions simultaneously
to operate normally. After driving for 10
minutes, the engine compartment reaches 80
to 120°C,
and the heater warms the passenger cabin to
20 to 25°C,
then the engine is turned off and the temperature
returns to minus 30°C. |
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3-5 Environments that
vehicle electronic sensors must endure
Electronics sensors in vehicles are subjected
to severe usage environment conditions in regard to such
factors as temperature, humidity, vibration, high voltage
surges, and power fluctuations. Malfunctions could lead
to highway accidents, and so the equipment must have high
ratings in safety and reliability.
Requirements for electronic sensors for vehicles
include the following.
| (1) |
Precision requirements are not
particularly severe compared to other fields. |
| (2) |
Reliability and environmental
endurance requirements are much more severe than
in other fields. |
Table 4 shows specifications and environmental
endurance requirements for sensors with various applications.
The newest applications for sensors include measurements
by two axis acceleration sensors to control the chassis,
and measurements by three axis acceleration sensors to
operate air bags. |
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Table 4 Specifications
and environmental endurance requirements for sensors
with various applications
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Home use
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Measurement
use
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Airplane
use
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Vehicle
use
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Precision
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Several
%
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0.1 to
1%
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0.1 to
1%
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1 to several
%
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Environmental
endurance
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Operating
temperature |
-10 to
50°C
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0 to 40°C
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-55 to
70°C
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-40 to
120°C
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| Vibration |
~
5G
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1G
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0.5 ~
10G
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2 ~
25G
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| Source
voltage fluctuation |
±10%
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±10%
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±10%
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±50%
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| Electromagnetic
environment |
Good
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Good
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Good to
Worst
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Bad
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| Saltwater |
No
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No
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Yes
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Yes
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| Water |
Yes
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No
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Yes
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Yes
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| Muddy
water |
No
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No
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No
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Yes
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| Gases |
No
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No
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No
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Yes
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| Reliability
(failure rate) |
-
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-
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(Max.
10-9)
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106km(10-9)
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