SAE J1455 Recommended Environmental Practices for Electronic Equipment Design in Heavy-Duty Vehicle Applications
The scope of SAE J1455 testing encompasses the range of environments that influence the performance and reliability of the electronic equipment designed for heavy-duty on and off-road vehicles, as well as any appropriate stationary applications which also use these vehicle-derived components. A few examples of such vehicles are on and off-highway trucks, trailers, buses, construction equipment, and agricultural equipment including implements.
SAE J1455 testing is intended to aid the designer of commercial vehicle electronic systems and components by providing guidelines that may be used to develop environmental design goals. Specific test requirements are to be agreed upon by the customer and supplier.
SAE J1455 Environmental Test Types
Thermal factors are one of the most typical environmental hazards to vehicle electronic components.
Sources for temperature extremes and variations include:
- The vehicle’s climatic environment. ex: the diurnal and seasonal cycles
- Heat sources and sinks generated by the vehicle’s operation
- Self-heating of the equipment due to its internal dissipation
- Vehicle operational mode and actual mounting location
The damaging effects of thermal cycling include:
- Cracking of printed circuit board or ceramic substrates
- Fatigue failures of solder joints
- Delamination of printed circuit boards and other interconnect system substrates
- Seal failures
- Failure of circuit components
Both a primary and secondary source of humidity exists within vehicles. In addition to the primary source of externally applied ambient humidity, the cyclic thermal-mechanical stresses caused by operational heat sources introduce a variable vapor pressure on the seals. Temperature gradients set up by these cycles can cause the resulting moisture to be drawn into the enclosure.
Actual relative humidity in vehicles depends on factors such as:
- Operational heat sources
- Trapped vapors
- Cool-down effects
The most common way to determine the effect of humidity on electronic components is to over-test and examine any failures. Generally, 8-hour active humidity cycling under accelerated conditions is recommended. However, a second test can consist of an 8 to 24-hour exposure at 103 kPa gauge pressure. Modes of failure may include the following:
- Corrosion of metal parts
- Changes in electrical properties
- Surface bridging corrosion and condensation between circuits
- Decomposition of organic matter
Salt Spray Atmosphere
Salt spray environments generally affect vehicle electronic components mounted on the chassis, exterior, and under-hood area. In coastal regions, salt is derived from sea breezes. In colder climates, salt is derived from road salt. Although the salt spray is unlikely to be in the interior of the vehicle, it is recommended to evaluate the floor area for potential effects of saline solutions. These solutions may be transferred from the outside environment by vehicle operators, passengers, and transported equipment.
Effects on performance due to salt spray are generally the same as those associated with water and water vapor. However, it must be noted that corrosion effects and alteration of conductivity are accelerated by the presence of saline solutions and conflicting changes in pH.
Exposure to Chemicals and Oils
Electronic components mounted on or in vehicles are exposed to varying amounts of chemicals and oil. This may include the following:
- Engine oils and additives
- Transmission oil
- Rear axle oil
- Brake fluid
- Axle grease
- Fuel additives
- Soap and detergents
- Spray paint
Loss of integrity of the enclosure can result in corrosion or contamination of vulnerable internal components. This will cause reduced performance or possible loss of function.
Immersion or splash tests are generally performed following other environmental tests. This test sequence is done so because it tends to aggravate incipient defects in enclosure materials, seals, seams, and bushings that might otherwise escape notice. A brush application may be used for hazardous materials and light to moderate exposure.
Steam Cleaning and Pressure Washing
The intense heat from cleaning and the caustic nature of chemical agents used in washing solutions create a severe environment for devices and associated wiring and connectors mounted in the engine, chassis, and exterior areas. Intrusion into connector areas and exterior packaging can cause degradation or loss of function and performance. Exposure to high heat, extreme water pressure, and caustic detergents can cause the following:
- A degradation of insulation and seals
- Cracking of vinyl connectors and component packaging
Fungus testing is used to determine the resistance of the vehicle electronic component to fungi. This test also determines if the equipment is adversely affected by fungi under conditions favorable for their development. These conditions include high humidity, a warm atmosphere, and inorganic salts.
Effects on performance are as follows:
- Microorganisms digest organic materials. Thus, degrading the substrate, reducing the surface tension, and increasing moisture penetration.
- Products of cellular metabolism diffuse out of the cells. This causes physical and chemical changes to the material.
- Microorganisms produce bridges across components. This may result in electrical failure.
- Resistance to biological attack can be determined by chemical analysis of the nutritive value of materials and material decomposition products used in the equipment.
A common way to determine the effect of fungal growth is to isolate the test item with a fungal pore solution. Next, incubate the inoculated component to permit fungal growth. Lastly, examine and test the item. Incubation normally takes place under cyclic temperature and humidity conditions. These must approximate environmental conditions and assure suitable fungal growth.
Any fungal growth that occurs is examined and a determination is made as to long-term effects. There are two criteria for fungal growth to be permitted. First, if a clear certain determination is made that no degradation of performance will occur over the life of the product. Second, the fungal growth will not detract from the appearance of visible portions of the product.
Dust and Sand
Dust creates a harsh environment for chassis, under-hood, and exterior-mounted devices. Dust can also be a long-term problem in interior locations. This includes the dash and seats. Sand, primarily windblown, is an important environmental consideration for components mounted in the chassis, exterior, and under-hood areas. Exposure to fine dust causes the following:
- Problems with moving parts
- Forms of conductive bridges
- Acts as an absorbent material for the collection of water vapor
Sand and dust tests are recommended to be at room temperature. The same does not need to be operating. However, functional tests are conducted before and after testing.
Gravel bombardment affects areas such as the chassis, lower engine, and exterior mounted electronic components. Gravel from unimproved roads and highway salt dispersing equipment are just a couple of sources of gravel damage.
Some superficial or cosmetic damage may be acceptable. However, gravel damage can cause the following:
- Immediate loss of function of the components
- Loss of connector or enclosure integrity
With the exception of air shipment of unenergized controls, operation in a vehicle should follow the anticipated operating limits. Completed controls are expected to be stressed over limits of absolute pressure. With increased altitude, effects can arise as follows:
- Reduction in convection heat transfer efficiency
- Change in mechanical stress on packages that have internal cavities
- A noticeable reduction in the high voltage breakdown characteristics of systems with electrically stressed insulators, conductors, or air surfaces.
Mechanical vibration is another key factor in vehicle component design. Vibration levels may vary during vehicle operation. From low severity to high severity when traversing rough roads at high speeds. The vibration characteristics may vary with the mounting location, in addition to the vehicle mode of operation. Several electronic component failure modes or performance degradations are possible. This can consist of the following:
- Loss of wiring harness electrical connection due to improper connector design or assembly.
- Metal fatigue failure at stress concertation points due to resonant excitation of tuned mass structures in the electronic component.
- Mount structure failures due to acceleration forces.
- Seal leakage due to mechanical flexing at the seal or other interface areas.
- Temporary aberration of equipment performance due to acceleration forces.
Automotive mechanical shock is divided into four categories:
Shipping and handling shocks – These are similar to those encountered in non-vehicle applications as a result of the shipping and handling processes.
Installation harness shock – It is common production line practice to lift and carry components by their harness. Therefore, it is recommended that the
harness design incorporates secure fastening and suitable strain relief.
Operational shock – The shocks encountered during the life of the vehicle that are caused by curbs, potholes, etc., can be very severe. These
vary widely in amplitude, duration, number, and test conditions.
Crash shock – This is included as an operating environment for safety systems. The operational requirements for these systems are
limited to longitudinal shock at the present time.
Combined Environmental Testing
The vehicle environment consists of many natural and induced factors. Combinations of these factors are more serious than the effect of exposing samples to each environmental factor in a series. A careful study is made during design analysis to determine the possibility of design susceptibility to a combination of environmental factors. If this susceptibility exists, a combined environmental test should be considered.
The damaging effects from combined environmental testing are greater than those noted in the individual elements above. Additional effects can include the cracking of material and leakage paths
General Heavy-Duty Truck Electrical Environment
Factors unique to truck/tractor that make the vehicular environment more severe include:
- Interaction with other vehicular electronic/electrical systems on the truck
- Voltage variations
- Customer added equipment
- Lack of maintenance
Discussion of the electrical environment falls into three categories:
- Electrical, Steady-State – Including variations in applied vehicle DC voltages with a characteristic frequency at or
- Electrical Transient, and Noise- Including all noise and high voltage transients with characteristic frequencies above
- Electromagnetic Compatibility and Electromagnetic Interference.
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