·Table of Contents
·Methods and Instrumentation
Evaluation of tyre temperature distribution using fast scanning pyrometerH. Madura, Z. Sikorski, H. Polakowski, M. Dabrowski
Institute of Optoelectronics, Military University of Technology,
2 Kaliskiego St. 00-908 Warsaw, Poland, fax. (+48 22) 6668950,
e-mail: hmadura @wat.waw.pl
The paper presents a fast scanning pyrometer with photon detector (PV) operating within the 8-12 mm spectral range used for rotating-tire-temperature-distribution evaluation in an automatic test-bed. The pyrometer ensures remote temperature recording of objects moving with velocity up to 250 km/h. Mapping of measurement data of the one-dimensional scanning pyrometer onto the tire surface
is done through computer processing using look-up calibration tables.
With motorization development the construction of car tyres has changed, too . Tyres of a new type must be tested under the conditions, as much as possibly, similar to the real ones. One of the factors allowing evaluation both technical state of tyre and its quality is temperature distribution on a tyre surface [2-4].
IR cameras were mostly used for this purpose. However, measurement with IR camera needs to stop the wheels what disturbs thermal conditions on a tyre surface. The results of such a measurement include significant errors.
Due to wheel symmetry, information on temperature distribution on a tyre surface can be achieved using the temperature distribution of one tyre's section only. For dynamic measurements of rotating tyres the fast scanning pyrometers with a photon detector operating within the range of 8-12 mm were used.
The fast IR pyrometer consists of measuring head, positioning and electronic system, and computer controller (Fig.1).
The measuring head (1) is used for conversion of IR radiation, emitted by a tyre surface, into corresponding to it voltage value proportional to an object temperature. The measuring head incorporates a radiometric system (an objective with a germanium lens, thermoelectrically cooled photon IR detector with a preamplifier), laser indicators of a measured area and positioning system (regulation in a vertical position by the angle of ± 45o).
|Fig 1: Fast scanning pyrometer for temperature measurements of car wheels; 1 - measuring head, 2 - positioning and electronic system, 3 - computer controller.||Fig 2: Diagnostic stand used for car wheels testing (Stand I).|
The positioning and electronic system (2) enables movement of the measuring head in a horizontal direction at the distance up to 400 mm with the resolution of 0.1 mm. In addition, the system includes electronic components (power supplies, controllers of a stepping motor, synchronisation units).
The computer controller (3) consists of IBM PC computer equipped with analogue-digital converter and interface card with an operating system of the pyrometer. Special software for the pyrometer, in addition to temperature registration, enables also measurement of tyre rotation velocity and automatically chooses a sampling rate.
A picture of the fast pyrometer on a diagnostic stand (Stand I) is shown in Fig.2.
The pyrometer ensures remote control recording of a surface temperature of an object moving with the velocity up to 250 km/h. Dimensions of a measuring area, at the distance of 1 m, are 5x5 mm and the distances between the consecutive measurement areas are 3 mm. One measuring cycle comprises 1000 measurements and automatically chosen sampling period depends on the object's speed. Measuring range of the pyrometer is 20-300 oC with the resolution of 0.50 oC and its operating temperature is 5-30 oC. The measuring area is illuminated with a laser diode working at the wavelength of 670 nm and the cycle's start is marked by an optoelectronic sensor.
|Fig 3: Principle of assignation of pyrometer indications to adequate measuring points. Exemplary profile of registered temperatures for the tyre of 145R13 size.|
The applied design of the fast IR pyrometer enables measurements of temperature distribution on a tyre surface at two measuring stands. At Stand I (Fig2) a tyre is rolled along internal surface of a cylinder of 8 m diameter and there is a possibility to change a tyre static load. The examined tyre surface can be seen periodically in the pyrometer field of view. Synchronisation of temperature measurements with the rotation of the examined tyre ensures an optoelectronic non-contact proximity detector.
The principle of assignation of pyrometer indications to adequate measuring points is presented in Fig. 3. This figure shows also exemplary profile of the registered temperature. Letter A denotes start of the registration process and B its end.
At Stand II (Fig.5) a tyre (1) rotation is forced by a drum rotation (5) while a vehicle (car) is immovable. Measurement of tyre temperature can be performed from a side of a tyre tread (as shown in Fig.5) or from a tyre side. Between the successive temperature measurements the pyrometer head is automatically shifted by means of a positioning system (according to the given programme).
|Fig 4: Temperature distribution vs. tyre velocity (Stand I).||Fig 5: Diagram of diagnostic stand for car wheels testing (Stand II): 1- measuring head, 2- positioning and electronic system, 3- computer controller, 4-tyre under testing, 5- rotating drum.|
The described fast IR pyrometer determines temperature of a tyre surface on the basis of the value of electrical signal from radiometric head with simultaneous consideration of an ambient temperature. Relation between these values has been experimentally determined using the standard sources of infrared radiation.
For pyrometer calibration within the measuring range of 20-70 oC the Differential infrared Reference Source DCN 100 of the HGH Systems Infrarouges Massy was used and within the range 70-300 oC the M 360 source of the Mikron Instrument Company, Inc. was applied.
Relation between the registered voltage (U) from a radiometric head and the temperature of the investigated object (T) and the ambient temperature (T0) is described by the following relationship:
T = T0 + U(a1 + U(a2 + U(a3 + a4U)))
where a1, a2, a3, a4 coefficients are the numbers determined experimentally.
Temperature distribution on a surface of a tyre rolled for 20 minutes with the velocity of 40, 60 and 80 km/h and with constant static tyre load is illustrated in Fig.4 (Stand I). The measurements carried out for various velocities and various times of tyre rolling enable determination of temperature changes as a function of tyre velocity for the measuring point of the tyre surface.
A dynamic method of temperature measurement of external surface of tyres using fast IR pyrometer is characterised by many advantages in comparison with thermovision methods. Temperature registration is carried out during a tyre motion, so measurement results are significantly much more reliable than the results obtained with IR camera for stopped (immovable) objects. On the basis of temperature distributions one can estimate adequate exploitation parameters of a tyre such as nominal static load and pressure inside a tyre.
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