Cookies on the CLAVIS website
The CLAVIS Fourier Measurement System monitors the tension of the drive belt using an optical sensor head. It has two forms, one for Electric Power Assisted Steering (EPAS) belts and the other for Front End Auxiliary Drive (FEAD) belts.
Electric power assisted steering (EPS/EPAS) or motor-driven power steering (MDPS) uses an electric motor to assist the driver of a vehicle. Sensors detect the position and torque of the steering column, and a computer module applies assistive torque via the motor, which connects to either the steering gear or steering column. This allows varying amounts of assistance to be applied depending on driving conditions.CLAVIS sets the belt tension on all EPAS units produced by the four volume manufacturers, TRW, Nexteer (Delphi), SKF and Hitachi.
Front-End Auxiliary Drive (FEAD) or accessory drive systems in motor vehicles are used to drive auxiliary equipment, such as alternator, coolant pump, power steering pump or A/C compressor.Accessories are driven by a poly V-belt or Serpentine belt, the tension of which is precisely adjusted to the required loads using a mechanical or hydraulic tensioning system. Guide pullies are used to create the required wrap angle around the front-end accessories. Poly V-belts are designed to perform at high loads transmitting the engine torque – up to 350 Nm is not unusual in modern cars, without slip from the crankshaft to all its accessories.
The CLAVIS system monitors the tension of the drive belt using the gauge. The gauge unit contains the optical sensor which recovers the belt vibration signal and the hammer assembly which forces the belt into vibration.The gauge contains a solenoid activated hammer which is used to vibrate the belt. An infra red optical sensor is employed to convert the belt vibration into an electrical signal which is processed by the control cabinet. The gauge unit is connected to the control cabinet via a 2m cable. A PC may be connected to the control cabinet to initiate measurements and record the subsequent belt vibration frequency. The resulting belt frequency is shown on a LED display. This may be particularly useful when first setting up the system.
The tension of the drive belt is determined by tapping the belt with an electro-mechanical hammer and monitoring the subsequent vibration using an infra-red optical sensor and associated electronics.The hammer is pushed against the belt by a small solenoid within the gauge sensor head which is excited by a 10 ms 48V pulse generated within the control cabinet under microprocessor control.The gauge sensor head contains a photo diode and a LED which are used to monitor the belt vibration. The LED is driven with a 20 KHz square wave producing around 25 mW of modulated infra red light. The light is reflected by the belt and detected by the photo diode. The signal from the photo diode is electronically processed in the control cabinet by a technique known as synchronous demodulation which reduces unwanted environmental noise and recovers the signal modulation.As the belt vibrates the amplitude of the modulated light entering the photo diode changes producing a subsequent change in the recovered signal. The signal is then amplified and filtered. The signal is fed into a Schmidt trigger to produce a square wave which is then fed into a microprocessor. The microprocessor determines the frequency of oscillation of the belt by observing several vibration cycles. In addition prior to the Schmidt trigger the analogue signal is sampled at a rate of 1.024 kHz in order to calculate the Fourier transform of the sample to determine the frequency spectrum.
The CLAVIS system analyses the belt signal in two different ways. An
Belts vibrating at multiple frequencies have been noted as a particular problem for EPAS units that have a composite pulley as opposed to a metal pulley. This combination of multiple sinusoids can result in a waveform that is problematic for interval-based analysis to determine the belt frequency and thus the tension. In a situation when a pure frequency cannot be achieved through good positioning of the gauge, the Fast Fourier Transform (FFT) can be used to determine alternative belt tension setting criteria.In a situation when a pure frequency cannot be achieved through good positioning of the gauge the FFT can be used to determine alternative belt tension setting criteria.
The sensor unit contains a high power infra red LED and a spectrally matched photo diode.The unit should be kept clean and free from grease or oil. If the unit becomes damaged it may be replaced by removing the sensor head top cover. The sensor wires should be unsoldered from the sensor PCB. The unit may then be removed. The new unit may then be fitted taking care to solder the wires correctly to the sensor PCB.An air feed connector is present on the sensor head to prevent belt dust from gathering inside the sensor head. Dry air should be fed to the sensor at 5 – 10 PSI.