1. Field of the Invention
The present invention relates to a tire uniformity measuring apparatus for simply measuring a variation in the load exerted radially on a tire being measured.
2. Description of the Prior Art
As the network of expressways spreads and automobiles are required to be driven continuously at higher speeds for longer periods of time, many efforts have been made to improve safety, drivability and riding comfort of automobiles.
There has been a strong need for high-performance automotive tires which have a primary function to hold automobiles on road, and hence research and development of such tires find themselves active nowadays.
Noises, vibrations, and impaired drivability occasioned while a car is driven at high speeds tend to give the driver and passengers a rough ride, accelerate their fatigue, and moreover invite the risk of causing a traffic accident. One of factors which cause these undesirable phenomena is considered to be non-uniformity of tires that includes untrue or out-of-round tire shapes and irregularities in tire rigidity due to uneven thickness and hardness around the circumference of a tire. These physical irregularities arise out of the fact that tires are made of various laminated materials such as rubber, synthetic fibers, steel cords, bead wires and others.
There has been established a standard for measuring tire uniformity based on which tire manufacturers inspect all of their tires. Tires which have been found nonuniform are ground to correct radial force variations (called "R.F.V."). Uniformity of tires has also been demanded by a proposed reduction in the overall weight of cars and hence the weight of members under spring means under the current program for saving resources and energy.
Conventional tire uniformity measuring apparatus include a rotatable cylindrical drum against which a tire being measured is held at a fixed interaxial distance for measuring a variation in the radial force (R.F.V.) exerted to the shaft of the drum being revolved. With the fixed interaxial distance between the drum and the tire, the conventional apparatus are required to have an increased overall rigidity of the apparatus. The known apparatus are also disadvantageous in that the drum is driven to rotate at high speeds, say, several tens of revolutions per minute, a sophisticated electrical measurement circuit is required, and the apparatus are large in size, costly to construct, and take a prolonged period of time for measurement.