Patent Application
20140319901
The present teachings generally include a wheel assembly with a tire.
Tires play an important role in vehicle fuel economy. The tire consumes energy as it rolls along the road surface, deflecting under the various forces generated between the road surface and the vehicle. The repeated cycles of deformation and recovery consume energy, referred to as hysteretic losses. The energy is ultimately provided by the fuel. Due to the hysteric losses within the structure of the tire, a certain amount of energy is consumed within the tire structure and then rejected into the surrounding environment as heat energy. Tires in general become more efficient, rejecting less energy to the environment, as the temperature of the tire increases. There are multiple heat energy rejection paths from the tire to the environment and some of those paths convey more energy than others.
A tire and wheel assembly includes a wheel that has a rim. The wheel has a first thermal conductivity. A tire is attached to the wheel to define an annular tire cavity enclosed by the tire and the rim. An insulating member is on the rim within the tire cavity. The insulating member has a second thermal conductivity lower than the first thermal conductivity and is configured to absorb heat from the cavity when a temperature of the cavity is above a first predetermined temperature. The insulating member is also configured to release the absorbed heat back to the cavity when the temperature of the cavity is below a second predetermined temperature lower than the first predetermined temperature. The insulating member can be a fibrous blanket. In another embodiment, the insulating member is a bladder filled with a liquid or gel. The tire and wheel assembly assists in retaining the warmth of the warm air generated during driving.
The insulating member can be a passive heat sinking material that stores heat energy generated during vehicle operation to be returned to the vehicle cavity while the vehicle is parked or at the beginning of vehicle operation, elevating the temperature of the tire for improved efficiency during the “cold” vehicle operation while the tire is stabilizing to its normal (fully warmed-up) operating temperature. The insulating member reduces energy loss from the tire and wheel assembly in the form of heat and should increase the fuel efficiency of the tire for short duration drive cycles where the tire does not typically have time to reach a fully warmed-up operating temperature.
The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,
Each tire and wheel assembly 12 includes a wheel 16 and a tire 18 mounted on the wheel 16. The tire 18 is made at least in part of a rubber compound. The entire structure of the tire 18 is constantly changing shape as the tire 18 rotates while the vehicle 10 is moving with respect to the road 20, causing hysteretic losses. Due to the viscoelastic nature of the tire 16, the hysteretic losses of the tire 16 decrease as a temperature of the tire 16 reaches a predetermined tire temperature. For example, as a tread portion 17 of the the tire 16 interfaces with the road 20, shown in
Referring to
The wheel 16, including the rim 28, is a metallic material such as steel. The wheel 16 has a first thermal conductivity that is greater than a thermal conductivity of the tire 18. For example, if the wheel 16 is an aluminum alloy, it may have a thermal conductivity of about 215 Watts/meter/Kelvin (W/m/K). If the wheel 16 is steel, it may have a thermal conductivity of about 33 W/m/K. Accordingly, in known tire and wheel assemblies, the majority of heat loss from the tire cavity is through the rim of the wheel, leading to longer periods before the temperature of the tire cavity reaches a predetermined operating temperature and greater hysteretic losses. The present tire and wheel assembly 12 solves this problem by providing an insulating member 40 that contacts and covers an entire outer annular surface 42 of the rim 28 between the tire beads 29, 30 that would otherwise be exposed to the tire cavity 36. That is, the insulating member 40 covers an annular surface 44 of the rim 28 between the tire beads 29, 30 at a circumference 45 of the wheel 16 so that the entire cavity 36 is surrounded by the tire 18 and the insulating member 40. In other words, no portion of the wheel 16 is exposed to the tire cavity 36.
The insulating member 40 has a second thermal conductivity lower than the first thermal conductivity of the wheel 16. In other words, the insulating member 40 is a relatively better heat insulator than the wheel 16. For example, the insulating member 40 can be a foam material with a thermal conductivity of 0.03 W/m/K. The material of the insulating member 40 is selected so that the first thermal conductivity will significantly shield heat loss from the cavity 36 at least until the contained air within the cavity 36 reaches a first predetermined temperature corresponding with a desired predetermined operating temperature of the tire 18 and operating efficiency of the tire 18. In one example, the first predetermined operating temperature is about 30 degrees Celsius (° C.) above the ambient temperature in the environment surrounding the tire. If the ambient temperature is 20° C., then the first predetermined operating temperature is 50° C. The rate of heat absorption by the insulating member 40 allows the cavity 36 to reach the first predetermined operating temperature more rapidly than if the surface 44 of the rim 28 was in contact with the cavity 36. The insulating member 40 absorbs heat from the cavity 36 when a temperature of the cavity 36 is above the first predetermined temperature. That is, the rate of heat absorption by the insulating member 40 allows the temperature of the cavity 36 to rise at least to the predetermined operating temperature. The insulating member 40 thus acts as a passive heat sink that stores energy generated during vehicle operation to be returned to the cavity 36 when the vehicle 10 is parked or restarted, elevating the temperature of the tire 18 for improved efficiency during “cold” vehicle operation. Decreasing the heat transfer rate through the wheel 16 may allow the tire 18 to reach a more advantageous temperature level from an energy efficiency point more rapidly, decreasing the energy consumption of the tire 18 and thereby increasing fuel efficiency of the vehicle 10. In other words, the insulating member 40 reduces energy loss from the tire and wheel assembly 12 in the form of heat and increases the fuel efficiency of the tire 18 for short duration drive cycles where the tire 18 does not typically have the time to reach the first predetermined operating temperature.
At least some of the heat absorbed by the insulating member 40 will be released to the ambient surroundings 47 (i.e., outside of the vehicle 10, as indicated in
Furthermore, the material of the insulating member 40 is chosen so that when the temperature of the cavity 36 subsequently falls below a second predetermined temperature due to slowing of the vehicle, or a temporary stop of the vehicle, such as during traffic or for a relatively short period on which the vehicle 10 is completely off, a temperature difference between the insulating member 40 and the cavity 36 is such that at least some of the absorbed heat is released from the insulating member 40 into the cavity 36. The second predetermined temperature is lower than the first predetermined temperature. In one example, the second predetermined temperature is lower than the first predetermined temperature by 10° C. So, if the ambient temperature is 20° C., then the second predetermined temperature is 40° C. In other examples, the second predetermined temperature could be any temperature in the range of 5° C. to 20° C. lower than the first predetermined temperature. The release of heat to the cavity 36 aids in raising the tire temperature to at least the predetermined tire temperature more quickly than if the wheel rim 18 was not covered by the insulating member 40.
In the embodiment of
In one embodiment, the bladder 150 is a tubular polymer material that has a thermal conductivity lower than that of the wheel 16. The liquid or gel substance 152 has a relatively high heat capacity that is greater than the heat capacity of air. That is, the substance 152 has a second heat capacity greater than a first heat capacity of air. If the substance 152 is a liquid, it can be a silicon-based material, or any other material that can either remain a liquid or at least partially solidify as it absorbs heat. As the substance 152 releases heat, it returns to liquid form. If the substance 152 is a gel, it can be a similar material as the liquid, in gel form, and can include a phase-change agent that allows the substance 152 to improve the heat absorption or rejection of the blanket 150. Known phase-change agents cause the material to change from a gel to a liquid or from a gel to a solid over a predetermined temperature range. In changing phase from a gel to a liquid or from a solid to a liquid, such materials absorb and store latent heat, and in changing phase from a liquid to a gel or a solid, such materials release heat. Despite the phase change, however, the material with the phase change agent maintains a relatively constant temperature.
While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims.
