Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2000-01-24
2002-09-03
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209260, C152S904000
Reexamination Certificate
active
06443199
ABSTRACT:
TECHNICAL FIELD
This invention relates to automobile and light truck tire combinations designed specifically for either the front wheel position or rear wheel position of front engine four wheeled mounted vehicles.
BACKGROUND ART
Automobile and light truck vehicles that have front engines and front steering suspensions have a vehicle weight distribution that is heavily loaded on the front position tires and lightly loaded on the rear position tires.
Light truck tires are routinely driven with no weight in the bed of the vehicle causing the rear tire position to typically operate at 50% of the tires rated load. When the truck is carrying weight the load can be increased up to 100% of the tires rated load on the rear tires.
Mini-vans and sport utility vehicles in addition to being weight distribution sensitive have higher centers of gravity than automobiles.
These multi purpose vehicles (MPV) put greater demands on tires due to their higher center of gravity and non-uniform weight distribution. This combination causes the vehicle to undergo greater amounts of vehicle roll putting higher loads on the outside shoulders of the front tires with nesulting increases in wear rates. Goodyear developed the Wrangler GS-A and Wrangler Aquatred to meet these demands by engineering a tread design with distinct tread zones for specific performance demands. The outside shoulder was solidified to resist the tendency for fast front tire shoulder wear while providing traction through tread blocks in the other zones of the tread. This design approach provided an inproved level of tread-wear and traction for MPV's in all wheel positions.
Tires for the front wheel positions of MPV's are subjected to special demands because of the higher center of gravity of the vehicle and the greater tendency for the vehicle to roll onto the outside shoulders of the tire. Looldng at the footprint patch of the prior art tire in the front right wheel position (as depicted in
FIG. 1
) one notes the higher outside contact area of the shoulder
2
. The tire geometry has been designed by increasing the trad mass distribution in this portion of the tread to rest the higher pressure and abrasion. The remainder of the tread area is optimized for traction and hydroplaning resistance. This state of the art design approach is embodied in the Wrangler GS-A and Wrangler Aquatred tires and represents the present state of the art in tread designs for MPV's.
The rear wheel position of MPV's creates special demands on the tires because of the lighter and variable loading of the tire. The footprint of
FIG. 2
depicts the same prior art tire of
FIG. 1
when placed on the rear position at 50% load. At this position the centerline pressure of the footprint is highest and needs to resist abrasion. Larger tread elements are needed at the centerline to resist this higher abrasion tendency while still providing traction and hydroplaning restance by providing open shoulders a design that is in direct conflict with the needs of the front position tire.
The requirements for an all wheel position tire require a balance of design characteristics to meet the performance needs of both front and rear tire applications. Inevitably, certain design tradeoffs or balances must be made in order to achieve performance levels for both positions. This results in a balanced design that cannot be fully optimized for either position. The Wrangler GS-A and Wrangler Aquateed represents the state of the art approach in balanced performance while still meeting the special needs of the front tire positions on MPV's.
To push tire performance to the next level, new approaches to design and materials must be discovered. One attempt to push design towards the next level of tire performance for MPV's light trucks and automobiles focuses on optimizing the functional design based on wheel position requirements. The front tire requirements have been addressed by the prior art but were not fully exploited because of all wheel position demands. The demands of the rear position have been studied and understood but until recently have not been fully optimized due to the requirements for all wheel position capability. This invention focuses on optimizing both front and rear positions by designing a combination of tires having a unique tire for each position front and rear. The front tires can be more fully optimized to resist fast outside shoulder wear while providing outstanding wet traction and handling. The rear position can be more fully optimized to resist the fast centerline wear associated with rear wheel drive and light loads while providing high levels of driving traction.
To optimize the front tire position, the invention employs multiple tread radii contouring the tread to achieve improved tread pressure distribution. Additionally, tread pattern mass is adjusted to enhance anti-hydroplaning performance while still providing resistance to outside shoulder wear. Since front ties encounter water on the road first, they must be more capable of anti-hydroplaning performance than the rear ties that run in their trough or wake.
To optimize the rear ties position, the invention also employs multiple tread radii contouring the tread to achieve full contact of the tire footprint from shoulder to shoulder. This allows for more even tread-wear across the tread with secondary benefits of function improvement through full tread pattern contact. This has been previously difficult to achieve because of the light loading of the rear position and the use of all wheel position design balances resulting in high centerline pressure and wear. Additionally, the tread mass distribution can now be optimized to rest fast centerline abrasion with tread design pattern details specifically suited for rear wheel drive traction.
Optimizing both front and rear designs based on functional requirements can result in tires that require no rotation and perform to higher levels of performance than tires that are designed for all wheel position use.
While it has been known in the art that specific tires for a particular wheel position can improve performance by the selection of certain distinct tread patterns that are wheel specific as is taught in German patent DE 3901624A1. These concepts have been limited to exotic racing type vehicles or high performance vehicles which may even employee different sized tires.
The invention disclosed below employs not only a distinct tread mass distribution but also teaches a specific footprint shape factor at normal pressure for variable vehicle loading conditions which can be achieved by unique tread arc curvatures for the front position tires and the rear position tires.
DESCRIPTION OF THE INVENTION
SUMMARY OF THE INVENTION
A pneumatic radial tire combination for four-wheeled automobile or light truck vehicles has a pair of front steer position tires and a pair of rear position tires. Each front steer position tire or rear position tire has a footprint, each footprint has an axial width W, as measured at the lateral extremes of the footprint, a centerplane CP midway between the lateral extremes of the footprint.
The tire combination has a pair of front steer position tires and a pair of rear position tires. The front steer position tire has a footprint when the tire is normally inflated for normal load that has a footprint shape factor of greater than 1.00 at a 50% load, and about 1.00 at both 85% load and 100% load. The footprint shape factor is defined as the maximum circumferential extent of the tire's footprint at the centerplane of the tire's footprint width divided by the average of the circumferential extent of the tire's footprint width as measured at 40% of the footprint from both sides of the central plane of the footprint.
The rear position fire footprint, when the tire is normally inflated for normal load, has a footprint shape factor of about 1.00 at 50% load, and 1.00 or less than 1.00 at 85% load and 100% load when measured similar to the method described for the front position tires.
The footprints of
Gilliam Donald Woodrow
Kolowski Michael Alois
Miller Frederick William
Scarpitti Anthony John
Trares Keith Carl
King David L.
Maki Steven D.
The Goodyear Tire & Rubber Company
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