PDC Sensor Outdoor - UV-Stabilized Housings and Thermal Cycling Resistance for Exposed Automotive Ultrasonic Sensors
This technical article explores the UV-stabilized housings and thermal cycling resistance of outdoor PDC sensors, covering the UV stabilization mechanisms, the thermal cycling testing for temperature extremes, the combination of UV and thermal exposure, the verification of the mechanical integrity, and the integration with the vehicle bumper for the exposed mounting.
The UV-stabilized housings for outdoor PDC sensors use the UV absorbers and the HALS to prevent the photodegradation of the polymer. The UV absorbers (e.g., benzotriazoles) absorb the UV radiation and convert it to the heat, preventing the polymer chain scission. The HALS (hindered amine light stabilizers) scavenge the free radicals generated by the UV exposure, preventing the oxidation. The UV stabilization is typically added to the polymer resin during the compounding, with the concentration optimized for the outdoor exposure. The UV stability is verified through the accelerated weathering tests, such as the Xenon arc or the QUV tests, with the sensor's color, the gloss, and the mechanical properties measured. The UV stability ensures that the sensor maintains the structural integrity and the acoustic performance over the service life.
PDC Sensor
The thermal cycling resistance of outdoor PDC sensors is critical for the operation in the extreme temperature variations, such as the daily thermal cycling from the night cold to the day heat. The thermal cycling test cycles the sensor between the low temperature (-40°C) and the high temperature (+85°C) with the specified dwell times and the ramp rates, typically for 500-1000 cycles. The test verifies the sensor's resistance to the thermal stress, which can cause the cracking of the housing, the delamination of the potting, the loosening of the connectors, and the shifts in the transducer's resonance. After the thermal cycling, the sensor's acoustic performance, the sealing integrity, and the electrical insulation are verified. The thermal cycling test ensures that the sensor withstands the temperature variations without the degradation.
The combination of the UV exposure and the thermal cycling is also tested to simulate the real-world exposure, where the sensor is exposed to the sunlight (UV) and the temperature variations simultaneously. The combined test uses the weathering chambers with the UV lamps and the temperature control to cycle the temperature while exposing the sensor to the UV radiation. The combined test provides the more realistic assessment of the sensor's durability, as the UV exposure can accelerate the thermal degradation. The combined test verifies that the sensor maintains the performance and the integrity after the simultaneous exposure.
The verification of the mechanical integrity of outdoor PDC sensors includes the impact testing, the vibration testing, and the abrasion testing. The impact testing verifies the sensor's resistance to the stone chips and the debris, with the sensor subjected to the impacts from the projected stones. The vibration testing verifies the sensor's resistance to the road vibration, with the sensor subjected to the random vibration up to 10 g. The abrasion testing verifies the sensor's resistance to the scratches from the cleaning and the debris, with the sensor face rubbed with the abrasive material. The mechanical integrity ensures that the sensor remains functional and the sealed after the physical stresses.
The integration of outdoor PDC sensors with the vehicle bumper requires the consideration of the drainage and the protection. The sensor must be mounted in the orientation that allows the water to drain away from the sensor face, preventing the water accumulation that could affect the acoustic transmission. The bumper design should provide the protection from the direct stone impacts, with the sensor recessed or shielded. The wiring harness must be routed to avoid the chafing and the water ingress. The integration is verified through the field testing, with the sensors tested on the vehicles in the real-world conditions. The outdoor sensors provide the reliable performance in the exposed conditions, ensuring the driver's safety. Understanding the outdoor design and the verification helps in the proper sensor selection and the integration for the all-weather parking assistance.
