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Aircraft Wheel Speed Sensor/Transducer (WSS or WST)

Aircraft Wheel Speed Sensor/Transducer (WSS or WST). Jeremy Goldin Mechatronics: ECE 5320 Sensor/Actuator Literature Survey Assignment #1 Dept. of Electrical and Computer Engineering Utah State University E: jeremy.goldin@aggiemail.usu.edu; F: (435)797-3054 (ECE Dept.). February 23, 2010.

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Aircraft Wheel Speed Sensor/Transducer (WSS or WST)

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  1. Aircraft Wheel Speed Sensor/Transducer(WSS or WST) Jeremy Goldin Mechatronics: ECE 5320 Sensor/Actuator Literature Survey Assignment #1 Dept. of Electrical and Computer Engineering Utah State University E: jeremy.goldin@aggiemail.usu.edu; F: (435)797-3054 (ECE Dept.) February 23, 2010

  2. Outline • Reference list • To probe further • Detailed References and Handbooks • Introduction • Major Applications • History • Basic Operating Principle • Major Specifications • Limitations • Benefits ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  3. Reference list • Crane Aerospace (2010). • [1] Hydro-Aire Brake Control Systems Wheel Speed Measurement Technical Document, August 2001. From: http://www.craneae.com/Products/Landing/downloads/WheelSpeedSensorTransducer.pdf • [2] Antiskid Tutorial Technical Document, June 2000. From: http://www.craneae.com/Products/Landing/downloads/AntiskidTutorial.pdf ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  4. Reference List • NASA Glenn Research Center (2010). • [3] Beginner’s Guide to Aerodynamics, Last Updated: Mar 04 2010. From: • http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html • Hybernetics Ltd. • [4] Wheel Speed Transducers Product Information, Retrieved Mar 7 2010. From: • http://www.hyperneticsltd.com/products/wheel_speed_transducers/wheel_speed_transducers.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  5. To explore further • http://en.wikipedia.org/wiki/Anti-lock_braking_system • MIL-B-8075D-1 Brake Control Systems, Antiskid, - Aircraft Wheels - General Specification for • SAE Aerospace Recommended Practice ARP 1070 – Design and Testing of Antiskid Brake Control Systems for Total Aircraft Compatibility • SAE Aerospace – AIR 1739 – Information on Antiskid Systems ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  6. Introduction • When an aircraft is implementing a landing, its obvious primary goal is to come to a stop. At some point this stopping involves the application of wheel brakes, typically once the aircraft has completely settled a majority of its weight upon the ground. • A major concern upon applying wheel brakes for a fast moving, high load object, is the possibility of skidding the tires and thus losing control of the stop. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  7. Introduction • One solution to preventing the tires from skidding is by introducing a sensor inside the wheel axle that can measure the speed of the wheel, and then through a separate controller that determines the speed of the aircraft, the rate of wheel deceleration versus the rate of aircraft deceleration or the comparative speeds, can be controlled so that enough friction is applied to the tire-runway surface to prevent loss of control or blowing of tires. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  8. Major Applications • The main application of wheel speed sensing devices is as part of an antiskid or brake control system that controls the speed of the wheel to obtain maximum braking and prevent loss of control or blown tires. Figure 1: Antiskid Control Loop [2] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  9. Major Applications • Some aircraft systems also use the wheel speed output for spoiler control or other landing systems that depend on weight transition to the wheels and thus wheel spin-up. Figure 2: Aircraft Aerodynamics Components [3] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  10. History • Aircraft Wheel Speed Sensing Devices were first introduced as part of an antiskid control system • 1929 - The first system was introduced by Gabriel Voisin – utilized a drum and flywheel attached to a valve – low wheel speeds caused the drum to spin slower than the flywheel, which caused the valve to open and pressure to bypass the brake Figure 3: Typical Modern Wheel Speed Transducer [1] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  11. History • 1946 – Hydro-aire Hytrol System implemented on the B-47. Utilized a simple AC generator used to compare paired wheels – if the averaged voltage of one was too slow, a relay would close, activating a bypass on the brake valve • 1960’s – Hydro-aire Mark II System available – utilized purely electromagnetic wheel speed sensors ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  12. Basic Operating Principle • There are 4 main types of wheel speed sensing devices used on aircraft: • Electromagnetic Wheel Speed Transducers • Electromagnetic Wheel Speed Sensor Two-part Assembly • DC Wheel Speed Sensor • Fiber Optic Wheel Speed Transducer ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  13. Electromagnetic Wheel Speed Transducers • This type of sensor is in-axle, couples with a hubcap attached to the wheel, and operates as a variable reluctance device using a magnet or bias current to provide the magnetic field. The output is a signal of a frequency proportional to the wheel speed. Figure 4: Typical WST Cross-Section [1] ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  14. Electromagnetic Wheel Speed Sensor Two-part Assembly This type of sensor operates under the same principle as the single assembly transducer, except the magnetic/coil sensor portion is separate from the field affecting material that is attached to the wheel. Figure 5 – Wheel Speed Sensor Assembly Cross-section [1] This allows device installation outside of the axle, when such space is needed for something else. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  15. DC Wheel Speed Sensor • This type of sensor is functionally equivalent to a DC generator. This causes the output voltage level to be proportional to the speed of the rotor. • This type of sensor is placed inside the axle and coupled with the wheel through a hubcap. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  16. Fiber Optic Wheel Speed Transducer • This type of sensor uses an optical emitter and sensing device to send pulses corresponding to the speed of the wheel. This is also an in-axle type sensor. It must be powered to achieve signal modulation. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  17. Major Specifications • Due to aircraft specific operations, the wheel speed sensor typically has the following as the critical requirements: • Extreme Operating Temperatures: Typically 150-250 deg F Operating, and over 400 deg non-operating, due to in-axle brake temperatures; and -65 deg F non-operating for high altitude flight • Robustness/Reliability: Typically must last 10,000-20,000 cycles before failure • Output Strength: 1-2V peak-to-peak output at taxi speeds for optimal control. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  18. Limitations • Electromagnetic WST • Requires shielded wire for signal transmission – EMI susceptible – grounding for noise removal can be difficult to implement • Electromagnetic WSS Assembly • Highly susceptible to vibration for most applications. Air Gap is difficult to maintain for consistent signal output. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  19. Limitations • The DC Wheel Speed Sensor • Brushed contacts are highly susceptible to wear and heat damage, leading to early failure • Poor method of failure – as coils degrade, signal output strength is reduced, but this implies a lower speed. Calibration becomes difficult • Fiber Optic WST • Reliability reduced due to extreme conditions in the axle for the sensitive internal components • Requires separate power source ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  20. Benefits • Electromagnetic WST • Very reliable • Relatively low cost • Consistent signal outputs throughout its life • Electromagnetic WSS Assembly • Mounting provisions outside of axle for restricted conditions • Very simple components ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  21. Benefits • The DC Wheel Speed Sensor • Signal output is a direct voltage level, removing most of the analog to digital conversion circuitry • Robust signal against EMI or noise (high frequencies can be filtered out completely) • Fiber Optic WST • Signal output is direct TTL type, removing conversion circuitry • Robust signal against EMI or noise ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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