Power heterogeneity of the tire

The circumference of the tire can be considered as a set of very small elastic elements, whose stiffness varies depending on production conditions. These elastic elements are compressed when interacting with the road surface and return to their original position. The oscillation in the stiffness of the spring in both directions - radial and transverse - causes a spread in the forces of compression and recovery during rotation of the tire. On an ideal tire that runs along a perfectly smooth path, the force distributed between the machine and the tire will be constant. However, a standardly assembled tire running along a perfectly flat road will exert a variable force on the vehicle, which will repeat each rotation of the tire. This wobble is a source of various driving damage. Manufacturers of both tires and cars seek to reduce the amount of such damage in order to improve the dynamic performance of the vehicle.

Measurement axes

Axis of oscillation of force. Tire forces are divided along three axes: radial, transverse, and tangent (or longitudinal). The radial axis extends from the center of the tire to the tread, or is it the vertical axis from the roadway through the center of the tire to the vehicle. This axis supports the weight of the car. The transverse axis moves away from the tread in different directions. It runs parallel to the axis on which the tire is mounted. The tangent axis is the one in the direction the tire goes.

Fluctuation of Radial Strength

Since the radial force acts upward and supports the vehicle, the oscillation of the radial force describes a change in this force as the tire rotates along the road. While the tire rotates, and elastic elements with different spring stiffnesses touch and come off the surface, the force will change. Imagine a tire holds a load of 1,000 pounds (≈454 kg) and follows a perfectly flat path. That is, up and down variation from this value will be typical for strength. Fluctuation between 995 and 1003 pounds will be characterized as a fluctuation in radial force (RFV) of 8 pounds. RFV can be expressed as a double amplitude value, maximum value minus minimum, or any harmonic value described below.

Harmonic Analysis

An analysis of the Raman harmonic waveform, as well as other measurements of force fluctuations, can be represented as a complex waveform. This form can be expressed in accordance with its harmonic using the Fourier Transform (PF). PF allows you to parameterize various aspects of the dynamic properties of the tire. The first harmonic, expressed as RF1H (first harmonic of radial force), describes the amplitude of the force fluctuation, which sends a pulse to the vehicle once every rotation. RF2H expresses the amplitude of the radial force that causes a pulse twice per revolution, etc. Often these harmonics have known causes, and can be used to diagnose production problems. For example, a tire mold secured with 8 bolts can thermally deform and cause an eighth harmonic, so having a high RF8H can indicate a mold fixing problem. RF1H is the main cause of movement disorders, followed by RF2H. Large harmonics are less problematic, because the tire rotation speed at the trunk speeds measures the time of the harmonic value, creating damage at such high frequencies that they are absorbed or overcome by other dynamic conditions of the vehicle.

Fluctuation of shear force

Since the lateral force acts side to side along the axis on which the tire is mounted, the fluctuation of the lateral force characterizes the change in the given force as the tire rotates under load. While the tire rotates, and elastic elements with different spring stiffnesses touch and come off the surface, the lateral force will change. During rotation, the tire can exert a lateral pressure of approximately 25 pounds (≈11.3 kg), causing the rudder to pull in one direction. Fluctuation between 22 and 26 pounds can be described as shear force fluctuation or LFV. LFV can be expressed as a double amplitude value, maximum value minus minimum, or any harmonic value described below. The transverse force is significant, for example, fixed on a car, the transverse force can be positive by moving the car to the left, or negative - by moving it to the right.

Oscillation of tangential force

Since the lateral force acts in the direction of motion, the oscillation of the tangential force characterizes a change in a given force as the tire rotates under load. As the tire rotates, and the elastic elements with different spring stiffnesses touch and come off the surface, the tangential force will change. During rotation, the tire exerts high traction to accelerate the vehicle and maintain its speed at a constant speed. In steady state, up and down variation from this value may be typical for strength. This variation can be characterized as TFV. Under test conditions at the same speeds, the TFV can detect itself through a slight speed instability, occurring at each revolution, due to a change in the rolling radius of the wheel. TFV is not measured during production tests.

Taper

Taper is a parameter based on shear force behavior. This is a characteristic describing the tendency of a tire to spin like a cone. This tendency affects the steering performance of the vehicle. In order to determine the taper, the transverse force is measured in two directions - clockwise (LFCW) and counterclockwise (LFCCW) clockwise. The taper is calculated as half the difference between these two values, taking into account the fact that the values ​​clockwise and counterclockwise have opposite signs. Tapering is an important parameter for production testing. In many high-class cars, tires with equal taper are mounted on the left and right sides of the car, taking into account the fact that these taper indicators neutralize each other and provide smoother driving performance with a small rotation effect. It is for this purpose that tire manufacturers measure taper and sort into groups depending on the results.

Side Angle (Wheel)

Side angle is a parameter based on the behavior of the lateral force. This characteristic is usually described as the tendency of the tire to "crawl like a crab", or move from side to side, while maintaining a straight line. This trend affects the steering characteristics of the car. in order to determine PlayStyre, it is necessary to measure the lateral force in both directions - clockwise (LFCW) and counterclockwise (LFCCW) clockwise. The angle of lateral withdrawal is calculated as half the sum of these values, taking into account that the values ​​have opposite signs clockwise and counterclockwise. In production tests, this angle is not calculated.

Radial runout

Radial runout (RRO) describes the deviation of the roundness of the tire from the ideal circle. RRO can be expressed as a double amplitude value, as well as harmonic values. The RRO reports the movement to the vehicle, which is somewhat similar to the fluctuation of the radial force. RRO is often measured closer to the center line of the tire, while some tire manufacturers are able to measure RRO from three positions: left shoulder, center, right shoulder.

Crossbeat

Side Runout (LRO) describes the deviation of a sidewall of a tire from an ideal plane. LRO can be expressed as a double amplitude value, or as a harmonic value. The LRO reports the movement to the vehicle, which is somewhat similar to the fluctuation in lateral force. LRO is often measured at the top of the sidewall, closer to the tread shoulder.

Bulge and recess along the sidewall

Given that a tire is a complex of numerous components vulcanized in a mold, there are many changes in process parameters by which tires can be classified as defective. The bulges and valleys along the sidewall are such defects. A bulge is an underpressure on the sidewall that increases with inflation. A depression is a repressing that does not expand equally with the adjacent zone. Both cases are considered visual defects. In production, tires are measured in order to identify tires with excessive visual defects. Bulges can also indicate improper assembly conditions, for example, the lack of cord, which carries the risk of injury. Therefore, tire manufacturers set strict tire inspection standards for bulges. The bulge and depression along the sidewall are also called thickening, pothole and tuberous sidewall.

Power heterogeneity machines are specialized equipment that automatically examines tires for tire uniformity parameters described above. They consist of several subsystems, including transporting the tire, seating it on the cartridge, measuring rims, lubricating the bead, pumping with air, loading drum, spindle drive, measuring force and geometry.

First, the tire is centered, then its beads are lubricated for a softer fit on the measuring rims. The tire is indexed on the test assembly and mounted on the lower cartridge. The upper cartridge lowers until it touches the upper side. The tire inflates to the set pressure value. The loading drum extends all the way to the tire and exerts a loading force. The spindle drive accelerates the tire to test speed. As soon as speed, force and pressure are stabilized, load cells measure the force exerted by the tire on the load drum. The force signal is processed in analog circuits, then analyzed and provides measurement parameters. Depending on various standards, tires are marked with the following marks: the angle of the upper deviation of the radial force, the side of the positive taper and the value of the taper.

Other types of machines

There are numerous varieties and innovations among several manufacturers of power tire heterogeneity machines. The standard test speed supplied by the standard loading drum for such machines is 60 rpm, which is approximately 5 mph (8.05 km / h). High-speed machines are used in the research field, where speeds can reach 260 km / h and higher. Such machines were also introduced into production tests. Along with this, machines are used that combine the measurement of force fluctuations and dynamic equilibrium.

The oscillation of the radial and transverse forces can be reduced on the machine tool of the power of heterogeneity through roughening. At the center of the grinding cycle, the grinder is brought to the center of the tread and removes the rubber on the RFV protrusions. Above and below the tread shoulder, grinders are used to reduce the size of the contact surface or contour and the resulting fluctuation in force. Upper and lower grinders can be changed independently of each other in order to reduce taper values. Grinders are also used to correct excessive radial runout.

On a tire force heterogeneity machine, radial and lateral runout, taper and convexity can also be measured. For this, several generations of measurement technologies are used. They include: contact needle, capacitive sensors, fixed-point laser sensors, laser wide-grip systems.

Contact needle

Contact needle technology uses a touch sensor to move across the surface of the tire while it is spinning. Analog measuring equipment reads the movement of the probe and records the shape of the beat oscillation. When measuring radial runout, the needle is fixed on a wide-reach blade that can measure voids in the tread pattern. When measuring lateral runout on the sidewall, the needle goes along a very narrow smooth path. The contact needle method is one of the earliest technologies that requires considerable effort to maintain its mechanical efficiency. A small grip on the sidewall limits the effectiveness of detecting hernias and depressions in the rest of the sidewall.

Capacitive Sensors

Capacitive sensors create a dielectric field between the bus and the sensor. As the distance between the sensor and the bus changes, the properties of the voltage and / or current of the dielectric field change. Analog circuits are used to measure changes in the field and record the shape of the beat. Compared to contact needles, the grip area of ​​capacitive sensors is approximately 10 mm wider. The capacitive sensor method is one of the earliest technologies that has worked well; however, the sensor must be positioned very close to the surface of the tire, so that collisions between the tire and the sensor can lead to long-term repair work. In addition, some sensors are very sensitive to humidity, which leads to incorrectly read data. A 10 mm surface grip also means that the bulge measurement is limited to a small tire area. Capacitive sensors use void filtering to avoid the effect of cavities between the tread blocks on radial runout measurement, and character filtering to avoid the influence of protruding letters and a pattern on the sidewall.

Fixed-Point Laser Sensors

Fixed-point laser sensors have been developed as an alternative to the two previous methods. Lasers combine a narrow capture path with a long distance to the tire. In order to cover a wider area, mechanical positioning systems were introduced, allowing the reading of various zones on the sidewall. Fixed-point laser sensors use void filtering to avoid the effects of cavities between the tread blocks on radial runout measurements, and character filtering to avoid the effect of protruding letters and a pattern on the sidewall.

Wide Capture Laser Systems

Wide-capture laser systems were introduced in 2003 and have established themselves as the most susceptible and reliable methods for measuring runout, bulge, and trough. These sensors project a spectral line instead of a point, thereby covering a larger area. Датчики по боковине могут свободно измерить весь участок от борта до плеча протектора и исследовать всю боковину на дефекты грыжи или впадин. Широкие радиальные датчики могут замерить от 300 и более мм, покрывая всю ширину протектора. Это позволяет охарактеризовать RRO на нескольких дорожках. Датчики широкого захвата функционируют на достаточно большом расстоянии, чтоб избежать столкновения с шиной. Применяемые двухмерная фильтрация полостей протектора и фильтрация букв на боковине позволяют исключить эти характеристики из измерений биения.